Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
CONTROL APPARATUS AND CONTROL METHOD FOR AUTOMATIC TRANSMISSION
Document Type and Number:
WIPO Patent Application WO/2008/132591
Kind Code:
A3
Abstract:
A control apparatus includes: a gear-shift prediction unit (31) that predicts whether a power-on downshift using a clutch-to-clutch shift operation needs to be performed as a next gear-shift; and a standby pressure supply control unit (32) that supplies a pressure for placing a first friction engaging element, which contributes to the next gear-shift, in the standby state, which is achieved immediately before engagement of the first friction engaging element is started, to the first friction engaging element, when the gear shift prediction unit (31) predicts that the power-on downshift using the clutch-to-clutch shift operation needs to be performed as the next gear-shift. When it is determined that a condition for performing the next gear-shift is satisfied based on the accelerator operation and the vehicle drive state, a shift command signal (Ia to Ie) is output to bring the first friction engaging element out of the standby state and engage the first friction engaging element

Inventors:
KONDO, Tomohiro (1 Toyota-cho,Toyota-shi, Aichi-ken, 471-8571, JP)
KONDO, Masami (1 Toyota-cho,Toyota-shi, Aichi-ken, 471-8571, JP)
SATO, Toshimitsu (1 Toyota-cho,Toyota-shi, Aichi-ken, 471-8571, JP)
Application Number:
IB2008/001035
Publication Date:
December 24, 2008
Filing Date:
April 25, 2008
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
TOYOTA JIDOSHA KABUSHIKI KAISHA (1 Toyota-cho, Toyota-shi, Aichi-ken, 471-8571, JP)
KONDO, Tomohiro (1 Toyota-cho,Toyota-shi, Aichi-ken, 471-8571, JP)
KONDO, Masami (1 Toyota-cho,Toyota-shi, Aichi-ken, 471-8571, JP)
SATO, Toshimitsu (1 Toyota-cho,Toyota-shi, Aichi-ken, 471-8571, JP)
International Classes:
F16H61/06; F16H59/18; F16H59/66
Foreign References:
US20060247084A12006-11-02
JP2001173771A2001-06-26
JP2005265063A2005-09-29
Download PDF:
Claims:
CLAIMS:

1. A control apparatus for an automatic transmission, which executes a shift control by outputting a shift command signal for selectively engaging and disengaging multiple friction engaging elements of the automatic transmission based on an accelerator operation and a drive state of a vehicle, comprising: a gear shift prediction unit that predicts whether a power-on downshift using a clutch-to-clutch shift operation for engaging a first friction engaging element among the multiple friction engaging element and disengaging a second friction engaging element among the multiple friction engaging element needs to be performed as a next gear shift; a standby pressure supply device that supplies a pressure for placing the first friction engaging element, which contributes to the next gear shift, in a standby state, which is achieved immediately before engagement of the first friction engaging element is started, to the first friction engaging element, when the gear shift prediction unit predicts that the power-on downshift using the clutch-to-clutch shift operation needs to be performed as the next gear shift; and an engagement pressure control unit that outputs the shift command signal to bring the first friction engaging element out of the standby state and engage the first friction engaging element, when it is determined that a condition for performing the next gear shift is satisfied based on the accelerator operation and the drive state of the vehicle.

2. The control apparatus according to claim 1, further comprising: a prediction maintenance determination unit that determines whether a prediction on the next gear shift made by the gear shift prediction unit is maintained at predetermined time intervals, when the pressure for placing the first friction engaging element in the standby state is supplied to the first friction engaging element by the standby pressure supply device, wherein: the engagement pressure control unit brings the first friction engaging element out of

the standby state and engages the first friction engaging element, when the prediction maintenance determination unit determines that the prediction on the next gear shift is maintained and it is determined that the condition for performing the next gear shift is satisfied based on the accelerator operation and the drive state of the vehicle; and the engagement pressure control unit drains the pressure, which has been supplied to the first friction engaging element to place the first friction engaging element in the standby state, when the prediction maintenance determination unit determines that the prediction on the next gear shift is no longer maintained.

3. The control apparatus according to claim 1 or 2, wherein the gear shift prediction unit predicts whether the power-on downshift using the clutch-to-clutch shift operation needs to be performed as the next gear shift based on at least one of a first time in which an accelerator operation amount continues to be increased by the accelerator operation and a second time in which a point indicating the drive state of the vehicle is approaching a downshift line in a shift diagram for the automatic transmission,

4. The control apparatus according to any one of claims 1 to 3, further comprising a prediction standby time calculation unit that calculates a prediction standby time until an output of the shift command signal for the next gear shift, when the gear shift prediction unit predicts that the power-on downshift using the clutch-to-clutch shift operation needs to be performed as the next gear shift, while a current gear shift is being performed based on the accelerator operation and the drive state of the vehicle, wherein the standby pressure supply device supplies the pressure for placing the first friction engaging element, which contributes to the next gear shift, in the standby state, to the first friction engaging element, when the prediction standby time becomes shorter than a pressure boosting time, which is required to place the first friction engaging element in the standby state that is achieved immediately before engagement of the first friction engaging element is started, by a predetermined time.

5. The control apparatus according to claim 4, wherein the prediction standby time calculation unit calculates the prediction standby time based on a deceleration of the vehicle and a difference between a current vehicle speed in a shift diagram for the automatic transmission and a vehicle speed when a point indicating the drive state of the vehicle reaches a downshift line that is passed when the vehicle speed is reduced from the current vehicle speed.

6. The control apparatus according to claim 4 or 5, wherein the prediction standby time calculation unit calculates the prediction standby time based on a difference between a current accelerator operation amount in a shift diagram for the automatic transmission and an accelerator operation amount when a point indicating the drive state of the vehicle reaches at least one downshift line that is passed when the accelerator operation amount is increased from the current accelerator operation amount and an amount of change in the accelerator operation amount per unit time.

7. The control apparatus according to any one of claims 4 to 6, wherein: the gear shift prediction unit predicts whether the power-on downshift to a gear that is lower than a current gear by at least two stages needs to be performed as the next gear shift and a gear shift after next based on the accelerator operation and the drive state of the vehicle; the prediction standby time calculation unit calculates each of a first prediction standby time until the output of the shift command signal for the next gear shift and a second prediction standby time until an output of the shift command signal for the gear shift after next; and the pressure for placing the first friction engaging element, which contributes to the gear shift after next, in the standby state is supplied to the first friction engaging element, when the second prediction standby time becomes shorter than the pressure boosting time for the gear shift after next by a predetermined time.

8. The control apparatus according to any one of claims 1 to 7, wherein the pressure for placing the first friction engaging element in the standby state is lower than a pressure at which the first friction engaging element is engaged.

9. A control method for an automatic transmission, comprising: predicting whether a power-on downshift using a clutch-to-clutch shift operation for engaging a first friction engaging element and disengaging a second friction engaging element needs to be performed as a next gear shift, the first friction engaging element and the second friction engaging element being included in multiple friction engaging element that are selectively engaged in the automatic transmission based on an accelerator operation and a drive state of a vehicle; placing the first friction engaging element, which contributes to the next gear shift, in a standby state in which a pressure lower than a pressure required to engage the first friction engaging element is supplied to the first friction engaging element, when it is predicted thai the power-on downshift using the clutch-to-clutch shift operation needs to be performed as the next gear shift; and outputting a shift command signal to bring the first friction engaging element out of the standby state and engage the first friction engaging element, when it is determined that a condition for performing the next gear shut is satisfied based on the accelerator operation and the drive state of the vehicle.

Description:

CONTROL APPARATUS AND CONTROL METHOD

FOR AUTOMATIC TRANSMISSION

FIELD OF THE INVENTION [0001] The invention relates generally to a control apparatus and control method for an automatic transmission. More specifically, the invention relates to a control apparatus and control method for an automatic transmission, which reduces torque shock while also ensuring quick response to abrupt demands for acceleration.

BACKGROUND OF THE INVENTION

[0002] A determination as to whether gears of an automatic transmission for a vehicle should be shifted is made based on the vehicle drive state such as a vehicle speed and as accelerator pedal operation amount and the running condition. If the accelerator pedal operation amount is abruptly increased or if the vehicle enters a steep uphill slope, the automatic transmission sometimes needs to be shifted to a gear that is lover than the current gear by at least two steps. In such a case, shift shock is likely to occur in the automatic transmission. Such shift shock may be reduced by first downshifting the automatic transmission to a gear that lies midway between the current gear and the target gear and then downshifting it to the target gear. However, downshifting the automatic transmission to the target gear in this way increases the time required to complete the gear shift

[0003] There is a multi-speed automatic transmission for a vehicle, which has a relatively simple structure formed by combining a main shift unit having a small number of gears with an auxiliary shift unit having a high gear and a low gear. In this case as well, if simultaneous gear shift is performed, that is, if one of the main shift unit and the auxiliary shift unit is shifted to a higher gear and the other shift unit is shifted to a lower gear shift shock is likely to occur. Such shift shock may be reduced by first shifting one of the shift units to a lower gear and then shifting the other shift unit to a lower gear.

However, downshifting the automatic transmission in this way increases the time required to complete the gear shut

[0004] Therefore, a control apparatus for an automatic transmission, which reduces torque shock while also ensuring quick response to abrupt demands for acceleration has been suggested

[0005] An example of this type of control apparatus for an automatic transmission is described in Japanese Patent Application Publication No. JP-05-99310 (JP-A-05-99310).

This control apparatus determines whether a speed of change in an engine load is equal to or higher than a predetermined value, when a first shift determination is made, that is, when it is determined that one of a main shift unit and an auxiliary shift unit should be shifted to a higher gear and the otheτ shift unit should be shifted to a lower gear. If the speed of change in the engine load is equal to or higher than the predetermined value, the control apparatus predicts that a second shift determination, which differs from the first shift determination, will be made and waits until the second shift determination is made without executing a control for performing first gear shift. After the second shift determination is made, the control apparatus performs second gear shift. In this way, the time required to complete the gear shift is reduced.

[0006] An air-discharge control is sometimes executed over a hydraulic pressure control circuit of an automatic transmission of which the gears may be shifted by performing a clutch-to-clutch shift operation, that is, by disengaging a first clutch and engaging a second clutch. In this case, if a friction engaging element under the air-discharge control is required to be engaged, the hydraulic pressure for engaging the friction engaging element becomes higher than usual, which may cause shift shock. In order to avoid occurrence of such a situation, it is predicted whether a determination that the gears should be shifted will be made based on the vehicle drive state, and the air-discharge control is not executed when the gears are being shifted. Foτ example, Japanese Patent Application Publication No. 2003-148603 (JP- A-2OG3- 148603) describes a control apparatus for an automatic transmission, which executes this control. [0007] In an automatic transmission that includes t main shift unit and an auxiliary

shift unit, in some cases, hydraulic pressure needs to be supplied to friction engaging elements of the main shift unit and the auxiliary shift unit and the auxiliary shift unit is shifted to a lower gear in the next gear shift In such a case, greater shift shock may be caused. Tb avoid occurrence of such a situation, a predetermined holding pressure is supplied in advance to a hydraulic clutch of the auxiliary shift unit, which will be engaged in the next gear shift For example, Japanese Patent Application Publication No. 2001-173771 (JP-A-2001-173771) describes a control apparatus for an automatic transmission, which executes this control.

[0008] In order to reduce a delay in engagement of a friction engaging element while also suppressing unnecessary drag torque (torque which is generated due to friction between clutch discs (friction engaging element) when the friction engaging element is not fully engaged) of the friction engaging element, the likelihood of engagement in the next gear shift is determined for each individual friction engaging, element and the positions of pistons of the friction engaging elements are controlled based on the determination results. For example, Japanese Patent Application Publication No.

2005-265063 (JP-A-2005-265063) describes a control apparatus for an automatic transmission, which executes this control.

[0009] For example, when the vehicle enters a steep uphill slope and is therefore suddenly decelerated or when an accelerator pedal is continuously operated, the automatic transmission needs to be shifted to a gear that is lower than the current gear by at least two steps and a power-on downshift (downshift that is performed in a power-on state in which drive power is transmitted from the engine to drive wheels) is performed using a clutch-to-clutch shift operation. In this case, if a driver depresses the accelerator pedal slowly or the amount by which the driver additionally depresses the accelerator pedal (the amount of increase in the accelerator pedal operation amount) is not sufficient, the control apparatuses for an automatic transmission described above do not make a determination, at one time, that the automatic transmission needs to be shifted to a target gear that is lower than the current gear by at least two steps. Therefore, the automatic transmission is shifted in sequence, for example, first shifted from fourth gear to third

gear and then shifted from third gear to second gear.

[0010] Namely, in the case where the power-on downshift is performed using the clutch-to-clutch shift operation instead of using a one-way clutch that provides a synchronizing timing for downshift, if, during first gear shift, the next gear shift is started, a time that is required for the friction engaging element, which will be engaged in the next gear shift, to achieve a predetermined engagement torque (torque capacity) is not ensured. Therefore, the next gear shift is performed before the timing, at which the turbine speed reaches a value corresponding to the gear that will be selected by the next gear shift, is reached. As a result, a significant shift shock is caused. Therefore, even if the timing, at which the point indicating the vehicle drive state crosses the downshift line for the next gear shift in the shift diagram, is reached during the first power-on downshift, it is necessary to delay a supply of engagement pressure to the friction engaging element that will be engaged in the next gear shift until first gear shift is completed. [0011] Therefore, even if the driver thinks that he or she performs an appropriate accelerator pedal operation in response to a change in the vehicle drive state, the drive power does not respond to the accelerator pedal operation sufficiently quickly and the driver does not feel a good acceleration feel. It is particularly difficult to meet demands for drivability in recent automatic transmissions having an increased number of gears.

SUMMARY OF THE INVENTION

[0012] The invention provides a control apparatus for an automatic transmission, which makes it possible to perform a downshift to a gear that is lower than a current gear by at least two steps quickly while also minimizing shift shock even when a power-on downshift is performed using a clutch-to-clutch shift operation instead of using a one-way clutch, thereby improving response of drive power to an accelerator operation.

[0013] A first aspect of the invention relates to a control apparatus for an automatic transmission. The control apparatus for an automatic transmission executes a shift control by outputting a shift command signal for selectively engaging and disengaging

multiple friction engaging elements of the automatic transmission based on an accelerator operation and the drive state of a vehicle. The control apparatus according to the first aspect of the invention includes: a gear shift prediction unit that predicts whether a power-on downshift using a ciutch-to-clutch shift operation for engaging a first friction engaging element among the multiple friction engaging element and disengaging a second friction engaging element among the multiple friction engaging element needs to be performed as a next gear shift; a standby pressure supply device that supplies a pressure for placing the first friction engaging element, which contributes to the next gear shift, in a standby state, which is achieved immediately before engagement of the first friction engaging element is started, to the first friction engaging element, when the gear shift prediction unit predicts that the pσweτ-on downshift using the clutch-to-clutch shift operation needs to be performed as the next gear shift; and an engagement pressure control unit that outputs the shift command signal to bring the first friction engaging element out of the standby state and engage the first friction engaging element, when it is determined that a condition for performing the next gear shift is satisfied based on the accelerator operation and the drive state of the vehicle,

[0014] According to the first aspect of the invention, when it is predicted that the power-on downshift using the clutch-to-clutch shift operation needs to be performed as the next gear shift, the pressure for placing the first friction engaging element, which is engaged in the next gear shift, in the standby state (slippage state in which effective friction engaging torque is not transmitted between friction discs even if a hydraulic piston has reached the engagement-side stroke end), which is achieved immediately before engagement of the first friction engaging element is started, is supplied in advance to the first friction engaging element. Therefore, even if the time until the next gear shift is short, by reducing the pressure boosting time that is required to achieve the standby pressure, the friction engaging element, which is engaged in the next gear shift, is immediately brought out of the standby state and engaged when the condition for performing the next gear shift is satisfied and a shift command signal is output Therefore, it is not necessary to delay an output of the shift command signal. As a result,

it is possible to minimize a delay in startiog the next gear shift, and improve the response of the drive power to the operation performed by a driver.

[0015] The control apparatus for an automatic transmission according to the first aspect of the invention may further include a prediction maintenance determination unit that determines whether a prediction on the next gear shift made by the gear shift prediction unit is maintained at predetermined time intervals, when the pressure for placing the first friction engaging element in the standby state is supplied to the first friction engaging element by the standby pressure supply device. The engagement pressure control unit may bring the first friction engaging element out of the standby state and engage the first friction engaging element, when the prediction maintenance determination unit determines that the prediction on the next gear shift is maintained and it is determined that the condition for performing the next gear shift is satisfied based on the accelerator operation and the drive state of the vehicle. The engagement pressure control unit may drain the pressure, which has been supplied to the first friction engaging element to place the first friction engaging element in the standby state, when the prediction maintenance determination unit determines that the prediction on the next gear shift is no longer maintained.

[0016] In the case where the pressure for placing the first friction engaging element is supplied to the first friction engaging element, when the prediction on the next gear shift is maintained and the condition for performing the next gear shift is satisfied, the first friction engaging element is brought out of the standby state and engaged. On the other hand, when the prediction on the next gear shift is no longer maintained, the pressure, which has been supplied to the first friction engaging element to place the first friction engaging element in the standby state, is drained. Therefore, it is possible to avoid occurrence of dragging of the friction engaging element due to unnecessary standby pressure. As a result, it is possible to minimize an increase in the oil temperature and deterioration of a friction member.

[0017] In the control apparatus for an automatic transmission according to the first aspect of the invention, the gear shift prediction unit may predict whether the power-on

downshift using the clutch-to-clutch shift operation needs to be performed as the next gear shift based on at least one of a first time in which an accelerator operation amount continues to be increased by the accelerator operation and a second time in which a point indicating the drive state of the vehicle is approaching a downshift line in a shift diagram for the automatic transmission.

[0018] With this configuration, it is possible to accurately detect the state in which a prediction on the next gear shift is made,

[0019] The control apparatus for an automatic transmission according to the first aspect of the invention may further include a prediction standby time calculation unit that calculates a prediction standby time until an output of the shift command signal for the next gear shift, when the gear shift prediction unit predicts that the power-on downshift using the clutch-to-clutch shift operation needs to be performed as the next gear shift, while a current gear shift is being performed based on the accelerator operation and the drive state of the vehicle. The standby pressure supply device may supply the pressure for placing the first friction engaging element, which contributes to the next gear shift, in the standby state, to the first friction engaging element, when the prediction standby time becomes shorter than a pressure boosting time, which is required to place the first friction engaging element in the standby state that is achieved immediately before engagement of the first friction engaging element is started, by a predetermined time. [0020] Thus, it is possible to place the first friction engaging element in the standby state that is achieved immediately before engagement of the first friction engaging element is stated, when the shift command signal for the next gear shift is output In addition, it is possible to avoid occurrence of dragging of the friction engaging element due to unnecessary standby pressure, and minimize an increase in the temperature of the hydraulic fluid that transmits the pressure and deterioration of the friction member. The predetermined time may be a time that is required to place the second friction engaging element, which is disengaged in the next gear shift, in the standby state, which is achieved immediately before engagement of the second friction engaging element is started, or in a stale in which the second friction engaging element is disengaged by a

slightly larger amount than in the standby state (to decrease the hydraulic pressure to the standby pressure or a hydraulic pressure that is slightly lower than the standby pressure).

[0021] In the control apparatus for an automatic transmission according to the first aspect of the invention, the prediction standby time calculation unit may calculate the prediction standby time based on a deceleration of the vehicle and a difference between a current vehicle speed in the shift diagram for the automatic transmission and a vehicle speed when the point indicating the drive state of the vehicle reaches a downshift line that is passed when the vehicle speed is reduced from the current vehicle speed.

[0022] With this configuration, the prediction standby time is accurately calculated. [0023] In the control apparatus for an automatic transmission according to the first aspect of the invention, the prediction standby time calculation unit may calculate the prediction standby time based on a difference between a current accelerator operation amount in the shift diagram for the automatic transmission and an accelerator operation amount when the point indicating the drive state of the vehicle reaches at least one downshift line that is passed when the accelerator operation amount is increased from the current accelerator operation amount and an amount of change in the accelerator operation amount per unit time.

[0024] With this configuration as well, the prediction standby time is accurately calculated. [0025] In the control apparatus for an automatic transmission according to the first aspect of the invention, the gear shift prediction unit may predict whether the power-on downshift to a gear that is lower than a current gear by at least two stages needs to be performed as the next gear shift and a gear shift after next based on the accelerator operation and the drive state of the vehicle; the prediction standby time calculation unit may calculate each of a first prediction standby lime until the output of the shift command signal for the next gear shift and a second prediction standby time until an output of the shift command signal for the gear shift after next; and the pressure for placing the first friction engaging element, which contributes to the gear shift after next, in the standby state may be supplied to the first friction engaging element, when the

second prediction standby lime becomes shorter than the pressure boosting time for the gear shift after next by a predetermined time.

[0026] In this case, when the automatic transmission is shifted to a gear that is lower than the current gear by at least two stages, it is possible to set the timing, ai which engagement of the friction engaging element which will be engaged in the gear shift after next is started, to a more appropriate timing, in consideration of, for example, the timing at which the friction engaging element that is disengaged in the gear shift after next is disengaged, and a change in the vehicle drive state after the prediction on the gear shift is made. In addition, if the determination as to whether the prediction on the gear shift after next is maintained is made earlier, the accuracy of prediction on the gear shift after next is enhanced.

[0027] Io the control apparatus for an automatic transmission according to the first aspect of the invention, the pressure for placing the first friction engaging element in the standby state may be lower than a pressure at which the first friction engaging element is engaged.

[0028] A second aspect of the invention relates to a control method for an automatic transmission. According to the control method, it is predicted whether a power-on downshift using a clutch-to-clutch shift operation for engaging a first friction engaging element and disengaging a second friction engaging element needs to be performed as a next gear shift The first friction engaging element and the second friction engaging element are included in multiple friction engaging element that are selectively engaged and disengaged in the automatic transmission based on an accelerator operation and the drive stale of a vehicle, When it is predicted that the power-on downshift using the clutch-to-clutch shift operation needs to be performed as the next gear shift, the first friction engaging element, which contributes to the next gear shift, is placed in a standby state in which a pressure lower than a pressure required to engage the first friction engaging element is supplied to the first friction engaging element. When it is determined that a condition for performing the next gear shift is satisfied based on the accelerator operation and the drive state of the vehicle, a shift command signal is output

to bring the first friction engaging element out of the standby state and engage the first friction engaging element.

[0029] According to the first aspect and the second aspect of the invention, when it is predicted that the power-on downshift using the clutch-to-clutch shift operation needs to be performed as the next gear shift, the pressure for placing the first friction engaging clement, which is engaged in the next gear shift, in the standby state, which is achieved immediately before engagement of the first friction engaging element is started, is supplied in advance to the first friction engaging element. Therefore, even if the time until the next gear shift is short, by reducing the pressure boosting time that is required to achieve the standby pressure, the friction engaging element which is engaged in the next gear shift is immediately brought out of the standby state and engaged when the condition for performing the next gear shift is satisfied and a shift command signal is output Therefore, it is not necessary to delay an output of the shift command signal, unlike the related art. It is possible to perform a downshift to a gear that is lower than a current gear by at least two steps quickly while also minimizing shift shock. Thus, it is possible to provide the control apparatus for an automatic transmission with which the response of the drive power to the accelerator operation is improved.

BRIEF DESCRIPTION OF THE DRAWINGS [0030] The foregoing and further features and advantages of the invention will become apparent from the following description of an example embodiment with reference to the accompanying drawings wherein the same or corresponding portions will be denoted by the same reference numerals and wherein:

FIG 1 is a block diagram showing the entirety of a control apparatus for an automatic transmission according to an embodiment of the invention;

FIG 2 is a view schematically showing the automatic transmission and the control apparatus for the automatic transmission according to the embodiment of the invention;

FIG 3 is an operation chart showing the relationship between the gears and engagement states of friction engaging elements of the automatic transmission according

to the embodiment of the invention;

FIG 4 is a shift diagram for the automatic transmission, which is shown in the form of a constant map, according to the embodiment of the invention;

FIG 5 is a cross-sectional view schematically showing the friction engaging element according to the embodiment of the invention;

FIG 6 is a flowchart showing a control routine executed by the control apparatus for an automatic transmission according to the embodiment of the invention; and

FIG 7 is a timing chart showing a change in the speed of rotation that is input in a gear shift mechanism and changes in the engagement pressures for engaging the friction engaging elements that are engaged at the respective gears, the changes being caused when the automatic transmission according to the embodiment of the invention is shifted to a gear that is lower than the current gear by two steps, that is, first shifted from fourth gear to third gear and then shifted from third gear to second gear.

DETAILED DESCRIPTION OF THE EMBODIMENT

[0031] Hereafter, an example embodiment of the invention will be described with reference to the accompanying drawings.

[0032] FIG 1 is a block diagram showing the entirety of a control apparatus for an automatic transmission according to an embodiment of the invention. FIG 2 is a view schematically showing the automatic transmission and the control apparatus for the automatic transmission. FIG 3 is an operation chart showing the relationship between the gears and engagement states of friction engaging elements of the automatic transmission according to the embodiment of the invention. FIG 4 is a shift diagram for the automatic transmission, which is shown in the form of a constant map, according to the embodiment of the invention.

[0033] As shown in FIG 1, a vehicle (automobile of which the entirety is not shown in the figures) in the embodiment of the invention includes an engine 11 thai is a power engine, and an automatic transmission 12 that transmits the drive power from the engine 11 to wheels (drive power output portions) (not shown). The automatic transmission 12

includes a torque converter 14, a gear shift mechanism 15 and a hydraulic pressure control unit 16.

[0034] Although not shown in detail in FiG 1, as in known multi-cylinder internal combustion engines, combustion chambers, which are defined by pistons, are formed within respective cylinders of the engine 11. Each cylinder is provided with an intake valve and an exhaust valve that open and close at predetermined timing, and a spark plug thai extends in the combustion chamber, A throttle valve is provided on the upstream side in an intake passage that is formed by an intake manifold, and an injector (fuel injection device) that injects fuel is provided at a position within a region from the intake passage to the combustion chamber of each cylinder.

[0035] As shown in FlG 2, the torque converter 14 includes: a pump impeller 14a (input-side member) that is connected to an output shaft 11a of the engine 11 via a shell cover 14s; a turbine runner 14b (output-side member) that faces the pump impeller 14a and that is connected to a transmission input shaft Min of the gear shift mechanism 15; a stator 14c that is positioned between the pump impeller 14a and the turbine runner 14b; and hydraulic fluid (not shown) stored in the shell cover 14s. When a flow of the hydraulic fluid is caused due to the rotation of the pump impeller 14a, which is the input-side member of the torque converter 14 and which is driven by the output shaft lla of the engine 11, the turbine runner 14b receives an inertia force of the flow and rotates the transmission input shaft Min of the gear shift mechanism 15. In addition, the flow of the hydraulic Quid that returns from the turbine runner 14b to the pump impeller 14a is adjusted by the stator 14c, whereby a torque amplification effect is caused by a reaction force from the stator 14c In addition, the torque converter 14 is provided with a lock-up clutch 14d that selectively locks the pump impeller 14a and the shell cover 14s, which are the input-side members of the torque converter 14, to the turbine runner 14b, which is the output-side member of the torque converter 14. The torque transmission efficiency is enhanced by using such mechanical clutch in combination with the torque converter 14. In addition, the stator 14c is supported by the gear shift mechanism 15 via a one-way clutch 14e, and the reaction force is received by the one-way clutch 14e.

[0036] The gear shift mechanism 15 is formed of a planetary gear train of which the upper half portion is shown in FIG 2. The gear shift mechanism 15 includes: the transmission input shaft Min that receives the rotation from the turbine runner 14b; a cylindrical first rotating shaft M1 that is selectively connected to the transmission input shaft Min by a clutch C1 (clutch that is engaged at reverse gear) and that is selectively connected to a transmission case 15h by a brake B1 (brake that is engaged at second and fourth gears); a cylindrical second rotating shaft M2 that is provided between the transmission input shaft Min and the first rotating shaft Ml and that is selectively connected to the transmission input shaft Min by a clutch C0 (clutch that is engaged at high gears); and a first planetary gear unit 17 and a second planetary gear unit 18 that are adjacent to each other in the axial direction thereof.

[0037] The first planetary gear unit 17 includes: a sun gear S1 that is fixed to the first rotating shaft M1; a ring gear R1 that is connected to a carrier Cr2 of the second planetary gear unit 18; pinions P1 that are in mesh with the sun gear S1 and the ring gear R1; and a carrier Cr1 that is connected to the second rotating shaft M2, that supports (he pinions P1 in such a manner that the pinions P1 are allowed to rotate about their axes and turn around the sun gear S1 and that is selectively locked to the transmission case 15h via a low one-way clutch F1.

[0038] The second planetary gear unit 18 includes: a sun gear S2 that is fixed to the transmission input shaft Min; a ring gear R2 that is selectively connected to the carrier Cr1 of the first planetary gear unit 17 via a clutch C2 (clutch that is engaged at low gears); pinions P2 that are in tnesb with the sun gear S2 and the ring gear R2; and the carrier Cr2 that supports the pinions P2 in such a manner that the pinions P2 are allowed to rotate about their axes and turn around the sun gear S2, and that is fixed to the ring gear R1 of the first planetary gear unit 17. The carrier Cr2 is connected to a transmission output shaft Mout, and rotates together with the transmission output shaft Mout. The rotation of the transmission output shaft Mout of the gear shift mechanism 15 is transmitted toward the wheels via a differential gear unit (not shown). [0039] Although the detailed hydraulic circuit configuration of the hydraulic

pressure control unit 16 is not shown in the figures, the hydraulic pressure control unit 16 includes electromagnetically-driven units 61a, 61b, 61c, 61d and 61c that correspond to the clutches C0, C1, and C2, and brakes B1 and B2, respectively; control valve units 62a,

62b, 62c, 62d and 62c that control the hydraulic pressures that are supplied to the clutches C0, C1 and C2, and the brakes B1 and B2 based on at least control forces from the electromagnetically-driven units 61a, 61b, 61c, 61d and 6Ie, respectively; a modulator valve 63 that regulates the line pressure from an oil pump 19 provided in the automatic transmission 12 to a predetermined pressure and then supplies the regulated pressure Io the control valve unit 62a to 62e; and a manual valve 64 that selects an oil passage, to which the line pressure from the oil pump 19 is supplied, in response to an operation performed by the driver, that is, supplies the line pressure from the oil pump 19 to a D-range oil passage L1 when Drive-range is selected and supplies the line pressure from the oil pump 19 to a R-range oil passage L2 when Reverse-range is selected. The control valve units 62a to 62e control the hydraulic pressures that are supplied to the clutches C0, C1 and C2 and the brakes B1 and B2 based on at least the control forces from the electromagnetkally-driven units 61a to 61e from among the control forces from the electromagnetically-driven units 61a to 61c, the modulator pressure from the modulator valve 63, and the control pressure from the manual valve 64.

[0040] The electromagnetically-driven units 61a to 61e are driven in a predetermined combination that corresponds to a target gear. The clutches C0 to C2 and the brakes B1 and B2 in the gear shift mechanism 15 are controlled based on the command currents Ia,

Ib, Ic, Id and Ie (shift control signals) supplied to the electromagnetically-driven units

61a to 61e from an ECU 30, which will be described later in detail, so that the optimum gear is selected according to a predetermined shift pattern. The clutches C0, C1 and C2 and the brakes B1 and B2 are the friction engaging elements that are engaged/disengaged by the hydraulic pressure control unit 16 based on the gear that should be selected by the gear shift mechanism 15. As shown in FIG 3, the clutches C0, C1 and C2 and the brakes B1 and B2 are engaged/disengaged in a predetermined combination that corresponds to a target geat

[0041] FIG 4 is a shift diagram that defines the basic condition for the shift control executed over the automatic transmission 12. As shown in FIG 4, the gear of the automatic transmission 12 is determined by the ECU 30 based on a data map in the shift diagram that uses the vehicle speed and the accelerator pedal operation amount (or the throttle valve opening amount) as parameters. The automatic transmission 12 is shifted to a higher gear when the point indicating the relationship between the vehicle speed and the accelerator pedal operation amount (vehicle drive state) crosses an upshift line indicated by a solid line in FIG 4, and shifted to a lower gear when the point crosses a downshift line indicated by a dashed line in FIG 4. [0042] Meanwhile, as shown in FlG 1, the engine 11 is provided with an accelerator pedal operation amount sensor 21 that detects a depression amount of an accelerator pedal (not shown), a throttle valve opening amount sensor 22 that detects an opening amount of a throttle valve (not shown), a coolant temperature sensor 23 that detects a temperature of a coolant in the engine 11, an intake air amount sensor 24, for example, an airflow meter, and an engine speed sensor 25 that is a crank angle sensor which detects a predetermined amount of rotation of a crankshaft, which is achieved each time the crankshaft is rotated by a predetermined angle.

[0043] On the side of a vehicle body (not shown), there are provided a brake pedal sensor 26 that detects a depression amount of a brake pedal or a depression force applied to the brake pedal, and a shift position sensor 27 that delects a position to which a shift lever provided in a vehicle compartment has been operated

(0044) A turbine speed sensor 28 that detects a rotational speed Nt which corresponds to the rotational speed of the turbine runner 14b is provided on the output side of the torque converter 14. A vehicle speed sensor 29 that detects a rotational speed of the transmission output shaft Mout is provided on the output side of the gear shift mechanism 15.

[0045] In addition, the vehicle in the embodiment of the invention is provided with an inclination sensor 41 that detects an inclination of the vehicle body in its longitudinal direction with respect to its horizontal attitude, and a G sensor 42 that detects an

acceleration and a deceleration of the vehicle.

[0046] The information delected by each of the season 21 to 29, 41 and 42 is transmitted to the ECU (electronic control unit) 30, which is a transmission computer that is formed integrally with an engine control computer. [0047] Although the detailed hardware configuration of the ECU 30 is not shown in the figures, the ECU 30 includes a CPU, a ROM, a RAM, a B-RAM (backup RAM that uses a battery as a backup power supply), an A/D converter, a constant voltage power source, a communication IC, etc The ECU 30 is able to receive, for example, signals from a control computer of another electronic control system (not shown). The ECU 30 controls the electromagnetically-driven units 61a to 61e in the hydraulic pressure control unit 16 to execute, for example, a shift point control for the gear shift mechanism 15 and a lock-up control for the torque converter 14 based oo the shift position, the vehicle speed, the accelerator pedal operation amount and the vehicle running condition, and to execute a line pressure control for the automatic transmission 12 so that the optimum line pressure is achieved based on the torque generated by the engine.

[0048] The ECU 30 includes a gear shift prediction unit 31, a standby pressure supply control unit 32, and an engagement pressure control unit 33. The gear shift prediction unit 31 predicts whether a power-on downshift using a clutch-to-clutch shift operation needs to be performed as the next gear shift. If the next gear shift is a downshift, for example, from fourth gear to third gear (4 th to 3 rd in FlG 3) or from third gear to second gear (3 rd to 2 nd in FIG 3), the gear shift prediction unit 31 predicts that the power-on downshift using the clutch-to-clutch shift operation needs to be performed as the next gear shift When the gear shift prediction unit 31 predicts that the power-on downshift using the clutch-to-clutch shift operation needs to be performed as the next gear shift, the standby pressure supply control unit 32 executes a control to supply a hydraulic pressure that is used to place one of the friction engaging elements, which will contribute to the next gear shift, in a standby state that is achieved immediately before the effective friction engagement is started (hereinafter, referred to as "standby pressure''). The friction engaging element to which the standby pressure is supplied is, for example,

the clutch C2 that is engaged in a downshift from fourth gear to third gear or the brake B1 that is engaged in a downshift from third gear to second gear, In this specification, the standby pressure means a hydraulic pressure used to place friction discs 52 and 56 in a slippage state in which effective friction engaging torque (transmission torque) is not transmitted between the friction discs 52 and 56 even if a piston 57 shown in FIG 5 has reached the engagement-side stroke end That is, the standby pressure is lower than a hydraulic pressure at which the effective friction engagement torque (transmission torque) is transmitted between the friction discs 52 and 56. At the standby pressure, the transmission torque is not transmitted between the friction discs 52 and 56. The standby pressure supply control unit 32 may be regarded as a standby pressure supply device according to the invention. When it is determined that the condition for performing the next gear shift is satisfied based on the accelerator pedal operation and the vehicle drive state, the engagement pressure control unit 33 selectively outputs shift command signals

Ia to Ie to shift the one friction engaging element from the standby state to the friction engagement state in which a predetermined capacity of torque is transmitted.

[0049) In this specification, the clutch-to-clutch shift operation means a gear shift operation performed by engaging the first friction engaging element and disengaging the second friction engaging element, that is, a gear shift operation performed by changing the engagement states of the first and second friction engaging elements. The first and the second friction engaging elements are the friction engaging elements that contribute to a gear shift More specifically, the clutch-to-clutch shift operation means a gear shift operation performed by changing the engagement states of the clutch C2 and (he brake B1, thai is, an operation for a gear shift from fourth gear to third gear in FlG 3, or a gear shift operation performed by changing the engagement slates of the clutch C0 and the brake B1, thai is, an operation for a gear shift from third gear to second gear. The power-on downshift means a gear shift to a lower gear that is performed while the drive power is transmitted from the engine 11 to the wheels via the gear shift mechanism 15 of the automatic transmission 12. [0050] The gear shift prediction unit 31 calculates a first time and a second time

based on the information detected by, for example, the accelerator pedal operation amount sensor 21, the throttle valve opening amount sensor 22 and the vehicle speed sensor 29. During the first time, the accelerator pedal operation amount is continuously increased by additionally depressing the accelerator pedal (not shown). During the second time, the point indicating the vehicle drive stale is approaching the downshift line

D21, D32 or D43 in the shift diagram for the automatic transmission 12. Then, it is predicted whether the power-on downshift using the clutch- to-clutch shift operation needs to be performed as the next gear shift based on at least one of the first time and the second time. Then, when predicting that the power-on downshift using the clutch-to-clutch shift operation needs to be performed as the next gear shift, the gear shift prediction unit 31 rums on (= 1) a next gear shift prediction flag, which will be described later in detail In other cases, the gear shift prediction unit 31 rums off (= 0) the next gear shift prediction flag.

[0051] The ECU 30 further includes a prediction maintenance determination unit 34 that determines whether the prediction on the next gear shift made by the gear shift prediction unit 31 is maintained at predetermined time intervals, when the standby pressure is supplied to the first friction engaging element by the standby pressure supply control unit 32. When the prediction maintenance determination unit 34 determines that the prediction on the next gear shift is maintained and it is determined that the condition for performing the next gear shift is satisfied based on the accelerator pedal operation and the vehicle drive state, the first friction engaging element, that is, the dutch C2 or the brake B1 is immediately brought out of the standby state and is effectively engaged When the prediction maintenance determination unit 34 determines that the prediction on the next gear shift is not maintained, the standby pressure supply control unit 32 drains the standby pressure that has been supplied to the first friction engaging element, that is, the clutch C2 or the brake B1.

[0052] The standby pressure supply control unit 32 constitutes a standby pressure supply device together with the clutches C0 to C2 and the brakes B1 and B2. The standby pressure is supplied by the standby pressure supply device using, for example,

the following configuration.

[0053] FIG 5 is a cross-sectional view schematically showing the friction engaging element according to the embodiment of the invention. The clutches C0 to C2 and the brakes B1 and B2, which are the hydraulic multiple-disc friction engaging elements (hereinafter, hydraulic multiple-disc friction engaging elements in a broad sense will be referred to as "hydraulic multiple-disc clutches" where appropriate), are engaged and disengaged in the same manner as that in which a hydraulic multiple-disc clutch 50 shown in FIG 5 is engaged and disengaged. In the hydraulic multiple-disc clutch 50, the piston 57 moves against a biasing force of a return spring 58 within a predetermined stroke rangt based on a supplied hydraulic pressure Pc. Then, the multiple friction discs 52, which are supported in a splined manner by a one element 51 that is in a rotatable state or in a locked state, and the multiple frictioo discs 56, which are supported in a splined manner by another element 55 that is in a rotatable state or in a locked state, are pressed to each other between the piston 57 and a stopper 53 that is fitted to the one element 51. Thus, the hydraulic multiple-disc clutch 50 is engaged. When the piston 57 of the hydraulic multiple-disc clutch 50 is pushed back by the biasing force of the return spring 58 due to a decrease in the supplied pressure or cancellation of supply of the hydraulic pressure, the multiple friction discs 52 that are supported by the one element 51 and the multiple friction engaging elements 56 that are supported by the other element 55 are no longer pressed to each other. As a result, the hydraulic multiple-disc clutch 50 is disengaged,

[0054] With the hydraulic pressure control unit 16 of the automatic transmission 12, for example, an electromagnetic proportional solenoid valve is used to adjust the pressure of the hydraulic fluid thai is supplied to the clutch or the brake, which is formed of the hydraulic multiple-disc clutch 50. Thus, a half-engaged state may be formed between a fully-disengaged state and a fully engaged state. In the fully-disengaged state, a clearance, which is equal to or larger than a predetermined amount at which the friction discs 52 and 56 are slidabte with each other, is formed between the friction discs 52 and 56. In the fully-engaged state, there is no clearance between the friction discs 52 and 56

and slippage (relative rotation) is not caused between the one element 51 and the other element 55. In the half-engaged state, the clearance between the friction discs 52 and 56 is smaller than the predetermined amount and sufficiently smooth slippage (relative rotation) may be caused between the one element 51 and the other element 55. The half-engaged state corresponds to the standby state that is achieved immediately before effective engagement of the hydraulic multiple-disc clutch 50 is started. The hydraulic pressure (standby pressure) that is supplied to the pision57 of the hydraulic multiple-disc clutch 50 to place the hydraulic multiple-disc clutch 50 in the standby state is approximately one-tenths (1/10) to one-thirds (1/3) of the hydraulic pressure that is supplied to the piston 57 to place the multiple-disc clutch 50 in the fully-engaged state

(hereinafter, referred to "engagement pressure")- To place the hydraulic multiple-disc clutch 50, which has been in the fully-disengaged state, in the standby state, the piston 57 is moved toward the position, at which the multiple-disc clutch 50 is engaged, against the biasing force of the return spring 58, and the clearance (and the oil film thickness) between the friction discs 52 and 56 is reduced to an amount within a range in which an effective engagement torque, which will contribute to a gear shift, is not generated.

[0055] The standby pressure supply control unit 32 of the ECU 30 selectively supplies a command current for generating the standby pressure, which is smaller than the command current for supplying the engagement pressure, to the electromagnetically-drivcn units 61a to 61e to place the friction engaging element, which will be engaged in the next gear shift, from among the clutches C0 to C2 and the brakes Bl and B2 in the standby state.

[0056] The ECU 30 further includes a prediction standby time calculation unit 35. In some cases, while the current gear shift is being performed based on the accelerator pedal operation and the vehicle drive state, the gear shift prediction unit 31 predicts that the power-on downshift using the clutch-to-cJutch shift operation needs to be performed as the next gear shift. In this case, the prediction standby time calculation unit 35 calculates a prediction standby time Tpr,(see FIG 7) until an output of a shift command signal for the next gear shift at predetermined time intervals.

[0057] When the prediction standby time Tpr that is calculated by the prediction standby time calculation unit 35 becomes shorter than a pressure boosting time Tc (Tc1 or Tc2 in FIG 7), which is required to place the friction engaging element that will be engaged in the next gear shift, for example, the clutch C2 which is engaged in a downshift from fourth gear to third gear, or the brake B1 which is engaged in a downshift from third gear to second gear, in the standby state that is achieved immediately before engagement of the friction engaging element is started, by a predetermined time, the standby pressure supply control unit 32 supplies a standby pressure to the friction engaging element that will be engaged in the next gear shift, for example, the clutch C2 that is engaged in a downshift from fourth gear to third gear, or the brake B1 that is engaged in a downshift from third gear to second gear. The predetermined time is a time that is required (o place the friction engaging element chat will be disengaged in the next gear shift, for example, the brake B1 which is disengaged in a downshift from fourth gear to third gear, or the clutch C0 which is disengaged in a downshift from third gear to second gear in the standby state, which is achieved immediately before engagement of the friction engaging element is started, or in a state in which the friction engaging element is disengaged by a slightly larger amount than in the standby state (to decrease the hydraulic pressure to the standby pressure for the friction engaging element that will be disengaged in the next gear shift or the hydraulic pressure that is slightly lower than the standby pressure). However, the predetermined time may be shorter than the time described above, if the engagement pressure supplied to the friction engaging element that will be engaged in the next gear shift does not rise as quickly as that when the shift condition is satisfied.

[0058] The standby time calculation unit 35 of the ECU 30 calculates the prediction standby time based on the deceleration of the vehicle and the difference between (he current vehicle speed (for example, point N in FIG 4) in the shift diagram for the automatic transmission 12 and the vehicle speed when the point indicating the vehicle drive state reaches the downshift line that will be passed when the vehicle speed is reduced from the current vehicle speed, for example, the vehicle speed when the point

indicating the vehicle drive stale reaches the downshift line D43.

[0059] The deceleration in this specification may be a value detected by the G sensor 42, a deceleration calculated based on a change in the value detected by a wheel speed sensor (not shown), a deceleration calculated based on a change in the value detected by the vehicle speed sensor 29 or the rotational speed of the output shaft of the transmission, or a deceleration calculated based on whether the pressure at an output port of a brake master cylinder (not shown) has increased, the information detected by the inclination sensor 41, etc, or a deceleration of the vehicle obtained by another method.

[0060] The prediction standby time calculation unit 35 may calculate the prediction standby time Tpr based on the difference between the current accelerator pedal operation amount in the shift diagram for automatic transmission 12, for example, the accelerator pedal operation amount indicated by the point N in FlG 4, and the accelerator pedal operation amount when the point indicating the vehicle drive state reaches at least one downshift line which will be passed when the accelerator pedal operation amount is increased from the current accelerator pedal operation amount, for example, the accelerator pedal operation amount when the point indicating the vehicle drive stale reaches D43, and an amount of change in the accelerator pedal operation amount per unit time.

[0061] The standby pressure supply control unit 32 of the ECU 30 starts supplying the standby pressure to the friction engaging element that will be engaged in the next gear shift immediately after the prediction standby time Tpr becomes shorter than, for example, the pressure boosting time Tc, which is required to place the friction engaging element that will be engaged in the next gear shift in the standby state by the predetermined time. When the shift condition is satisfied, the hydraulic pressure is increased to a value that exceeds the standby pressure to move the piston 57 to the engagement-side stroke end (the position in the standby state). However, unlike the case where the shift condition is satisfied, the piston 57 is moved to a position at which the friction engaging element that will be engaged in the next gear shift is placed in the standby state at the standby pressure. When the prediction standby time Tpr becomes shorter than the pressure boosting time Tc

that is required to place the friction engaging clement that will be engaged in the next gear shift in the standby state, the gear shift prediction unit 31 may predict that the power-on downshift using the clutch-to-clutch shift operation needs to be performed as the next gear shift In this case, the next gear shift prediction flag is turned on, when the prediction standby time Tpr becomes shorter than the pressure boosting time Tc that is required to place the friction engaging element which will be engaged in the next gear shift in the standby state.

[0062] Next, the effects will be described

[0063] FIG 6 is a flowchart showing a control routine executed over the automatic transmission according to the embodiment of the invention by the ECU 30 at predetermined time intervals while the vehicle is driven. FIG 7 is a timing chart showing a change in the speed of rotation that is input in the gear shift mechanism and changes in the engagement pressures for engaging the friction engaging elements that are engaged at the respective gears, the changes being caused when the automatic transmission according to the embodiment of the invention is shifted to a gear that is lower than the current gear by two steps, that is, first shifted from fourth gear to third gear and then shifted from third gear to second gear.

[0064] In the shift control shown in FIG 6, it is first determined whether the next gear shift prediction flag is on (step SH). [0065] The next gear shift prediction flag is turned on by the gear shift prediction unit 31 in the following manner. For example, the gear shift prediction unit 31 turns on the next gear shift prediction flag, when at least one of the following conditions 1) to 3) is satisfied: 1) the first time (duration of time), in which the accelerator pedal operation amount is continuously increased by further depressing the accelerator pedal, reaches a predetermined additional depression continuation time Tf (milliseconds), for example, several seconds (shorter than 10 seconds); 2) the second time, in which the point indicating the vehicle drive state is moving toward the downshift line D21, D32 or D43 in the shift diagram for the automatic transmission 12, for example, the vehicle keeps decelerating at a certain rate, reaches a predetermined time, for example, several seconds

(shorter than 10 seconds); and 3) the prediction standby time Tpr until the next gear shift becomes shorter than the pressure boosting time Tc that is required to place the friction engaging element that will be engaged in the next gear shift in the standby state. Alternatively, the gear shift prediction unit 31 may turn on the next gear shift prediction flag, when one or two conditions which are given higher priority are satisfied, Further alternatively, the gear shift prediction unit 31 may turn on the next gear shift prediction flag, when ail the conditions are satisfied.

[0066] The state in which the next gear shift prediction flag is on shows that it is predicted that the power-on downshift using the clutch-to-cluicb shift operation needs to be performed as the next gear shift, as described above,

[0067] When it is determined that the next gear shift prediction flag is not on, a determination as to whether the next gear shift prediction flag is on is made within a predetermined time (step S11). Namely, the determination step is periodically executed until the next gear shift prediction flag is turned on. [0068] When the next gear shift prediction flag is turned on by the gear shift prediction unit 31, an affirmative determination is made in step S11.

[0069] At this time, if, for example, a downshift from fourth gear to third gear is being executed as the current shift operation, the standby pressure supply control unit 32 of the ECU 30 supplies the standby pressure thai is lower than the piston stroke end pressure (hydraulic pressure required to move the piston 57 to the engagement-side piston end) to the friction engaging element which will be engaged in the next gear shift, for example, the brake B1 that is engaged in a downshift from third gear to second gear, before the next gear shift is started (step S 12).

[0070] Next, it is determined whether the next gear shift prediction flag is off (step S 13), Namely Jl is determined whether the prediction on the next gear shift is no longer maintained after the hydraulic pressure is supplied Io place the friction engaging element that will be engaged in the next gear shift in the standby state.

(0071) At this time, if the next gear shift prediction flag is not off and the next gear shift prediction flag is maintained a! on, it is then determined whether the condition foτ

performing the power-on downshift as the next gear shift has been satisfied in the shift diagram that is stored in the ROM of the ECU 30 in the form of a constant map (step S14). If the condition has not been satisfied, the immediately preceding step, that is, the step for determining whether the next gear shift prediction flag is off is executed again. [0072] If the gear shift prediction unit 31 turns off the next gear shift prediction flag (resets to zero) due to a change in the accelerator pedal operation performed by the driver or a change in the inclination of an uphill slope, the standby pressure supply control unit 32 drains the standby pressure for the clutch ("clutch" in this case means one of the friction engaging elements including the brakes) that will be engaged in the next gear shift (step S15).

[0073] On the othet hand, if the next gear shift prediction flag is kept on and the condition for performing the power-on downshift as the next gear shift is satisfied in the shift diagram, a shift control signal for performing the next gear shift is output. That is, the command currents that correspond to the electromagnetically-driven unit 61a to 61c are supplied in a predetermined combination shown in FIG 3 (step S 16).

[0074] With the control apparatus for an automatic transmission according to the embodiment of the invention, for example, as indicated by the solid line in FIG 7, even if the time for shifting the automatic transmission 12 from third gear, which is the current gear, to second gear, which is the next gear, is short, the brake B1 that will be engaged in the next gear shift is placed in advance in the standby state by the standby pressure (see the hydraulic pressure supplied to the friction engaging element that is engaged in second gear in FlG 7), Therefore, when a shift command signal indicating a downshift from third gear to second gear is output, the hydraulic pressure that is supplied to the brake B1, which is the friction engaging element that will be engaged in the next gear shift, has already been boosted to a level, at which the brake B1 is placed in the standby state, or a value close to the level When the hydraulic pressure that is supplied to the friction engaging element which will be disengaged in the downshift from third gear to second gear based on a shift command signal indicating a downshift from third gear to second gear, for example, the clutch C0, is decreased to the standby pressure or a pressure that is

slightly lower I ban the standby pressure (see a decrease in the hydraulic pressure supplied (o the friction engaging element that is engaged in thin) gear in FIG 7), the hydraulic pressure that is supplied to the brake B1, which is the friction engaging element that will be engaged in the next gear shift, has already been boosted to the standby pressure. Therefore, the hydraulic pressure that is supplied to the brake B1 increases from the standby pressure to the engagement pressure quickly and the brake B1 is engaged promptly.

[0075] In FIG 7, the dashed tine indicates the hydraulic pressure which is supplied to a friction engaging element that is engaged in second gear by an apparatus according to a related art The hydraulic pressure starts to be supplied to the friction engaging element, after a shift command signal for downshifting the automatic transmission from third gear to second gear is output Then, the hydraulic pressure is maintained at a value in the standby state after the piston stroke is started at a hydraulic pressure equal to or higher than the standby pressure, and then increased to the engagement pressure. Therefore, according to the related art, if the automatic transmission is shifted from fourth gear to second gear, the drive power is changed twice as shown by the dashed line near the synchronous rotational speed for third gear in FIG 7.

[0076] In contrast, according to the embodiment of the invention, the pressure boosting time thai is required to place the brake B1, which is the friction engaging element that will be engaged in the next gear shift, in the standby state is reduced Therefore, a shift command signal is output without delay when the condition for performing the next gear shift is satisfied. As a result, delay in starting the next gear shift is prevented, and the gear shift is approximated to the gear shift performed at one time from fourth gear to second gear indicated by the dashed-two dotted line near the synchronous rotational speed for third gear in FIG 7. Thus, a change in the drive power is caused substantially only once. As a result, the response of the drive power to the operation performed by the driver is improved

[0077] In the embodiment of the invention, when the prediction on the next gear shift is maintained and the condition for performing the next gear shift is satisfied the friction

engaging element thai will be engaged in the next gear shift, for example, the brake Bl, is brought out of the standby state and engaged. However, if the prediction on the next gear shift is no longer maintained after the standby pressure is supplied to the brake Bl, the standby pressure that has been supplied to the brake B1 is drained. Therefore, i( is possible to prevent occurrence of dragging of the brake B1 (generation of unnecessary torque in the brake B1) due to unnecessary standby pressure, an increase in the oil temperature, and deterioration of the friction member.

[0078] In addition, the gear shift prediction unit 31 predicts whether the power-on downshift using the clutch-to-clutch gear shift operation needs to be performed as (he next gear shift based on at least one of the first time in which the accelerator pedal operation amount continues to be increased by the accelerator pedal operation and the second time in which the point indicating the vehicle drive state is approaching the downshift line in the shift diagram. Therefore, rt is possible to accurately detect the state in which a prediction on the next gear shift is made. (0079] The ECU 30 includes the prediction standby time calculation unit 35 that calculates the prediction standby time Tpr until an output of a shift command signal for the next gear shift at predetermined time intervals, when the gear shift prediction unit 31 predicts that the poweτ-on downshift using the clutch-to-clutch gear shift operation needs to be performed as the next gear shift while the current gear shift is being performed. When the prediction standby time Tpr becomes shorter than the pressure boosting time, which is required to place the friction engaging element that will be engaged in the next gear shift in the standby state which is achieved immediately before engagement of the friction engaging element is started, by the predetermined time, the standby pressure supply control unit 32 supplies the standby pressure to the friction engaging element, which will be engaged in the next gear shift Therefore, the friction engaging element is in the standby state that is achieved immediately before start of the engagement, when a shift command signal for the next gear shift is output. In addition, it is possible to prevent occurrence of unnecessary dragging of the friction engaging element due to unnecessary standby pressure, an increase in the oil temperature and deterioration of the

friction member.

[0080] The standby time calculation unit 35 calculates the prediction standby time

Tpr based on the deceleration of the vehicle detected by the G sensor 42 and the difference between the current vehicle speed in the shift diagram and the vehicle speed when the point indicating the vehicle drive state reaches the downshift line that will be passed when the vehicle speed is reduced from the current vehicle speed. Alternatively, the prediction standby time calculation unit 35 calculates the prediction standby time Tpr based on the difference between the current accelerator pedal operation amount in the shift diagram and the accelerator pedal operation amount when the point indicating the vehicle drive state reaches at least one downshift line which will be passed when the accelerator pedal operation amount is increased from the current accelerator pedal operation amount, and an amount of change in the accelerator pedal operation amount per unit time. As a result, it is possible to accurately calculate the prediction standby time

Tpr. [0081] In the embodiment of the invention described above, the gear shift prediction unit 31 of the ECU 30 makes a prediction on the next gear shift from the current gear. Alternatively, the gear shift prediction unit 31 may make predictions on the next gear shift from the current gear and the gear shift after next (gear shift that will be performed after the next gear shift). [0082] Namely, the gear shift prediction unit 31 may predict whether the power-on downshift from the current gear, for example, fourth gear, to a gear lower than the current gear by two stages needs to be performed as the next gear shift and the gear shift after next based on the accelerator pedal operation and the vehicle drive state. In addition, the prediction standby time calculation unit 35 may calculate the first prediction standby time until an output of a sift command signal for the next gear shift, for example, the gear shift from fourth gear to third gear (Tpr1 in FIG 7), and the second prediction standby time until an output of a shift command signal for the gear shift after next (Tpr2 in FIG 7) at predetermined time intervals. When the second prediction standby time Tpr becomes shorter than the pressure boosting time Tc2 for the gear shift after next by a

predetermined time, the standby pressure may be supplied to the friction engaging element that will be engaged io the gear shin after next, for example, the brake B1.

[0083] In this case, when the automatic transmission is shifted to a gear that is lower than the current gear by at least two stages, it is possible to set the timing, at which engagement of the brake B1 that is the friction engaging element which will be engaged in the gear shift after next is started, to a more appropriate timing, in consideration of the tuning at which the friction engaging element that will be disengaged, for example, the clutch C0, is disengaged in the gear shift after next, and the gear shift and a change in the vehicle drive state after the prediction on the gear shift is made. In addition, it is possible to start the determination as to whether the prediction is maintained earlier to enhance the accuracy of prediction on the gear shift after next As a result, even if the rime for the gear shift is short, it is not necessary to delay an output of a shift command signal, unlike the related art Therefore, it is possible to shift the automatic transmission to a gear that is lower than the current gear by at least two stages, while also minimizing shift shock. As a result, it is possible to provide the control apparatus for an automatic transmission with which the response of the drive power to the accelerator pedal operation is improved

[0084] In addition, the prediction on the next gear shift and the prediction on the gear shift after next may be made, only when an operation for demanding sudden acceleration is performed, for example, when the rate of increase in the accelerator pedal operation amount per unit time is equal to or higher than a predetermined value, or when a kick down sensor (not shown) is turned on (the accelerator pedal operation amount is the maximum value). In addition, the standby pressure is shown as a constant pressure in

FIG 7, However, the standby pressure may be gradually increased until the friction engaging element is placed in the standby state or may be provided with a dither.

[0085) In the embodiment of the invention described above, the automatic transmission 12 does not include an auxiliary transmission. However, the invention may be applied to a case in which the automatic transmission is formed of a main shift unit and an auxiliary shift unit that is connected to the main shift unit at a position on the input

side or the output side of the main shift unit, and the power-on downshift using clutch-to-clutch shift operation is performed in the automatic transmission.

[0086] As described above, according to the invention, when it is predicted that the power-on downshift using the clutch-to-clutch shift operation needs to be performed as the next gear shift, the standby pressure is supplied in advance to the friction engaging element thai will be engaged in the next gear shift to place the friction engaging element in the standby slate that is achieved immediately before engagement thereof is started Even if the time until the next gear shift is short, by reducing the pressure boosting time that is required to achieve the standby pressure, the friction engaging element which will be engaged in the next gear shift is immediately brought out of the standby state and engaged when the condition for performing the next gear shift is satisfied and a shift command signal is output. Therefore, unlike the related art, it is not necessary to delay an output of the shift command signal As a result, it is possible to downshift the automatic transmission to a gear lower than the current gear by at least two stages quickly while also minimizing shift shock. Therefore, it is possible to provide the control apparatus for an automatic transmission with which the response of the drive power to the accelerator pedal operation is improved. The invention is effective for control apparatuses for an automatic transmission, especially, for control apparatuses for an automatic transmission, which reduce torque shock while also ensuring quick response to abrupt demands for acceleration.

(0087] While the invention has been described with reference to the example embodiment thereof, it is to be understood that the invention is not limited to the described embodiments oτ constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the described invention are shown in various example embodiment and configurations, other combinations and configuration, including more, less or only a single element, are also within the scope of the appended claims.