FIELD OF THE INVENTION

[0001] The present invention relates to control devices for vehicles that are equipped with an engine and a continuously variable transmission.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0002] As a transmission that transmits the torque and rotational speed generated by an engine (e.g. internal combustion engine) to a driving wheel in an appropriate manner corresponding with a traveling state of the vehicle that is equipped with the engine, an automatic transmission that automatically establishes an optimal transmission ratio between the engine and the driving wheel is known in the related art.

2. Description of the Related Art [0003] The automatic transmission of a vehicle may be a planetary gear type transmission that sets the transmission using a planetary gear system and a frictional engagement element such as a clutch and a brake, or a belt type continuously variable transmission (CVT) that changes the transmission ratio in a stepless manner.

[0004] Belt-type CVTs generally include: a primary pulley (input pulley) that is provided with a pulley groove (V groove); a secondary pulley (output pulley) that is provided with a pulley groove (V groove); and a belt that is wound around the primary pulley and the secondary pulley. As one of the pulleys increases the groove width, the other pulley reduces the pulley width. In this way, the belt radius (effective diameter) on the pulley changes relatively and continuously in order to obtain the appropriate transmission ratio steplessly. The torque transmitted by the belt-type CVT corresponds with the load that is applied in the direction that brings the belt and the pulley into mutual contact. In this way, the pulleys hold the belt while giving the tension on the belt.

[0005] The speed-change of the belt-type CVT is performed by increasing/reducing the groove width of the pulley groove as described above. Specifically, the primary pulley and the secondary pulley are each constituted with a fixed sheave and a movable sheave. In order to change the speed of the vehicle, the movable sheave is moved fore-and-aft in the axial direction by a hydraulic actuator disposed on the backside of the movable sheave. [0006] As described above, in the belt type CVT, the belt is pinched by the pulley in order to keep the belt tension, and the pinched state of the belt is changed in order to change the transmission ratio. In order to provide the necessary transmission torque, the hydraulic pressure that corresponds to the required torque, such as engine load is supplied to the hydraulic actuator on the secondary pulley side. The hydraulic actuator on the primary pulley side supplies the hydraulic pressure for changing the transmission ratio. In this way, the groove width of the primary pulley and the groove width of the secondary pulley are changed at the same time.

[0007] In the vehicle equipped with such a CVT, a target input rotational speed (basic primary sheave target rotational speed) is calculated using a map, with the parameters that represent a vehicle speed and an accelerator pedal operation amount (accelerator operation amount) that shows a required output amount. Then, the hydraulic actuator on the primary pulley side of the CVT is controlled so that the actual rotational speed of the input shaft matches the target input rotational speed. The transmission ratio is set automatically in this way. [0008] The map used to control the transmission ratio of the CVT is prepared so that optimal fuel-efficiency for a vehicle speed and the accelerator operation amount is achieved. Thus, the transmission ratio may always be set to provide optimal fuel-efficiency. However, if the transmission ratio of the CVT is always controlled in order to obtain high fuel efficiency, the CVT may not respond quickly to the driver's acceleration operation. Accordingly, the driver may not be able to feel a desired acceleration.

[0009] To solve this problem, a technique that allows the driver to feel the acceleration upon the acceleration operation is described in Japanese Patent Application Publication No. 2006-051842 (JP-A-2006-051842). [0010] As described in JP-A-2006-051842, when an acceleration request is made by the driver with the operation of the accelerator pedal (when the accelerator operation amount reaches a certain threshold or larger) a target input rotational speed for acceleration is calculated according to the map or the like. The target input rotational speed for acceleration is higher than a target input rotational speed for normal operation (target input rotational speed for automatic transmission) that is used for normal operation of the accelerator pedal and that increases with a certain inclination in proportion to the increase of the vehicle speed. Then, the input shaft rotational speed is feedback-controlled, so that the deviation between the calculated target input rotational speed for acceleration and the actual input shaft rotational speed of the CVT falls within a certain range. At the same time, the output torque of the engine is controlled. Accordingly, the driver is able to feel the acceleration upon the accelerating operation. The control that is performed at the acceleration is referred to as "linear shift control". Hereinafter, the target input rotational speed for acceleration used for the linear shift control is also referred to as "target input rotational speed for linear shift control".

[0011] In addition to an automatic shift mode, in which the transmission ratio of the CVT is changed automatically in accordance with the traveling state of the vehicle, some vehicles equipped with a CVT may feature a manual shift mode, in which the driver may change the transmission ratio of the CVT through a manually-operated switch. [0012] In the manual shift mode, the speed-change is performed in such a way that the transmission ratio of the CVT is changed stepwise within a range of transmission ratios (for example within 7 forward speeds) in accordance with the driver's operation of the manually-operated switch (up-down shift operation). In the manual shift mode, for example, the target input shaft rotational speed (hereinafter, referred to as "target input rotational speed for manual shifting") is calculated from the map, which is configured with a parameter that represents vehicle speed, based on the transmission ratio established by the operation on the manually-operated switch. The transmission ratio is automatically established by controlling the hydraulic actuator on the primary pulley side of the CVT so that the actual input shaft rotational speed reaches the target input rotational speed for manual shifting. A steering shift switch (paddle switch) that is disposed in the steering wheel may be employed as the manually-operated switch. In a vehicle equipped with such a steering shift switch, the driver may select the manual shift mode without releasing the driver's hands from the steering wheel. [0013] In a vehicle that allows a choice between the automatic shift mode and the manual shift mode, the manual shift mode is selected when the steering shift switch is operated while traveling in the automatic shift mode. When a downshift request is made with the depression of the accelerator pedal during the travel with the manual shift mode, the automatic shift mode (D range) is resumed. Specifically, as shown in FIG 13 for example, if the target input rotational speed for automatic shifting when the accelerator pedal is depressed is higher than the target input rotational speed for manual shifting (target input rotational speed in the transmission ratio after downshift operation (the next lower transmission ratio (at higher engine speed))), the return-determination condition is established and the transmission mode is returned from the manual shift mode to the automatic shift mode. Under such circumstances, the return control is hereinafter referred to as "related art control".

[0014] Now, the reason why the return determination uses the transmission ratio after downshift (the target input rotational speed in the transmission ratio that is one step lower than the current transmission ratio (at higher engine speed)) will be explained. In the vehicle that allows a choice between the automatic shift mode and the manual shift mode, normally, the automatic shift mode (D range) is resumed only when the driver depresses the accelerator pedal while the vehicle is in motion and the transmission is operating in the manual shift mode and when the driver exhibits the "clear intention for downshift". The determination criterion for the "clear intention for downshift" is defined as the time when the request for downshift to the transmission ratio from the current transmission ratio to the next lower transmission ratio is made. For this reason, when the automatic shift mode (D range) is resumed from the manual shift mode, establishment of the return-determination condition is determined when the target input rotational speed for automatic shifting reaches the target input rotational speed for manual shifting (synchronized rotational speed) in the transmission ratio that is one step lower than the current transmission ratio.

[0015] Japanese Patent Application Publication No. 11-141663

(JP-A-11-141663) describes a technique for returning the transmission mode from the manual shift mode to the automatic shift mode. In the technique described in

JP-A-11-141663, the automatic shift mode is resumed, for example when a large depression of the accelerator pedal operation is detected (at the beginning of overtaking or kickdown).

[0016] As described above, in the related art control, at the request for downshift made by depression of the accelerator pedal, the transmission mode returns from the manual shift mode to the automatic shift mode when the target input rotational speed for automatic shifting reaches or exceeds the target input rotational speed for manual shift mode. However, if the accelerator operation amount at the time of downshift request is larger than the determination threshold of the linear shift control, the target input rotational speed after return determination is switched to the target input rotational speed for linear shift control. As shown in FIG 13 for example, if the target input rotational speed for linear shift control at the return determination is lower than the target input rotational speed for manual shifting, the input shaft rotational speed of the CVT (engine speed) is reduced while the driver depresses the accelerator pedal in order to accelerate the vehicle. In this case, because sufficient driving force cannot be obtained for the acceleration request of the driver, the driver may feel uncomfortable.

[0017] In the technique that is described in JP-A-11-141663, when there is the linear shift control during the returning operation from the manual shift mode, the rotational speed decreases for the same reason as indicated above.

SUMMARY OF THE INVENTION

[0018] The present invention provides a control device for vehicle that prevents the input shaft rotational speed of a CVT from decreasing when the transmission mode is returned from the manual shift mode to the linear shift control.

[0019] A first aspect of the present invention relates to a control device for a vehicle that is provided with the engine and the CVT that allows a choice between the automatic shift mode and the manual shift mode. The control device includes a linear shift control section that that executes linear shift control, in which engine speed is increased in accordance with increases in the acceleration of the vehicle when an accelerator operation amount is a determination threshold or larger. In this control device, when a shift mode is returned from the manual shift mode to the automatic shift mode, which includes the linear shift control, the control device changes a condition of return determination based on the accelerator operation amount at the time of returning operation.

[0020] The linear shift control is one of the controls executed during the automatic shift mode. When the transmission mode is returned from the manual shift mode, the accelerator operation amount determines whether the shift mode returns to the normal automatic shift mode or the linear shift control.

[0021] According to the control device for vehicle described above, reduction in input shaft rotational speed of the CVT can be prevented when the shift mode is returned from the manual shift mode to the linear shift control.

[0022] The control device for a vehicle may include a linear shift control possibility determination section that performs the return determination based on a target input rotational speed for automatic shifting, a target input rotational speed for manual shifting, and a target input rotational speed for linear shift control that are calculated from a traveling state of the vehicle, and that determines possibility of the linear shift control based on the accelerator operation amount at the time of the returning operation, in which if the linear shift control possibility determination section determines that the linear shift control is impossible, the control device may determine that the condition of return determination is satisfied when the target input rotational speed for automatic shifting reaches the target input rotational speed for manual shifting or higher, and may return the shift mode to the automatic shift mode, and if the linear shift control is possible, the control device may determine that the condition of return determination is satisfied when the target input rotational speed for linear shift control reaches the target input rotational speed for manual shifting or higher, and may return the shift mode to the linear shift control. [0023] In the control device for a vehicle, the return determination may be executed when downshift is requested with depression of an accelerator pedal.

[0024] As described above, when the accelerator operation amount at the downshift request by depression of the accelerator pedal is the accelerator operation amount that leads the transmission mode to the linear shift control, the return determination is performed not with a target input rotational speed for automatic shifting but with a target input rotational speed for the control after returning-operation that is a target input rotational speed for linear shift control. As a result, the input shaft rotational speed of the

CVT (engine speed) is prevented from lowering at the returning-operation (see FIG 11). Accordingly, sufficient driving force can be obtained when the driver requests for acceleration, so that an uncomfortable feel of the driver can be reduced.

[0025] When a traveling state of the vehicle are the same the target input rotational speed for linear shift control may be set higher than the target input rotational speed for automatic shifting. [0026] As the traveling state of the vehicle, vehicle speed and accelerator operation amount may be used.

[0027] A second aspect of the present invention relates to a control method of the vehicle that is provided with the engine and the CVT that allows a choice between the automatic shift mode and the manual shift mode. The control method of the vehicle includes: executing a linear shift control that increases engine speed in accordance with an increase of acceleration of the vehicle if an accelerator operation amount is a determination threshold or larger; and a condition of return determination based on the accelerator operation amount at the time of returning operation when a shift mode is returned from the manual shift mode to the automatic shift mode that includes the linear shift control.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The foregoing and further features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG 1 is a schematic diagram of a vehicle according to an embodiment of the present invention;

FIG 2 is a circuit diagram of a hydraulic-control circuit that controls a hydraulic actuator of a primary pulley of a belt type CVT;

FIG 3 is a circuit diagram of the hydraulic-control circuit that controls the clamping force of a belt in a belt type CVT;

FIG 4 is a drawing that illustrates a steering wheel provided with an upshift switch and a downshift switch; FIG 5 is a block diagram of a configuration of a control system such as an ECU;

FIG 6 is a graph that illustrates a target input rotational speed map for the automatic shift mode;

FIG 7 is a graph that illustrates a target input rotational speed map for the manual shift mode; FIG 8 is a graph that illustrates a target input rotational speed map for linear shift control;

FIG 9 is a graph that illustrates a map that is used for controlling belt clamping force;

FIG 10 is a flowchart that illustrates return determination processes;

FIG 11 is a timing chart that illustrates an example of return determination process; FIG 12 is a timing chart that illustrates another example of return determination process; and

FIG 13 is a timing chart that illustrates an example of a conventional return determination process.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] FIG 1 is a schematic diagram of a vehicle according to an embodiment of the present invention.

[0030] The vehicle according to the present embodiment is a front-engine-front-wheel drive (FF) type vehicle and includes: an engine (internal combustion engine) 1 that is a power source for traveling; a torque converter 2 that is a hydraulic power transmission device; an forward-reverse drive switching device 3; a belt type continuously variable transmission (CVT) 4; a speed reduction gear unit 5; a differential gear unit 6, and an electronic control unit (ECU) 8. The control device for a vehicle is mainly constructed with: the ECU 8, a primary pulley rotational speed sensor 105; a secondary pulley rotational speed sensor 106; an accelerator operation amount sensor 107; and a hydraulic-control circuit 20 that are described later.

[0031] A crankshaft 11, which is an output shaft of the engine 1, is connected to the torque converter 2. The output of the engine 1 is transmitted from the torque converter 2 through the forward-reverse drive switching device 3, the belt type CVT 4, and the speed reduction gear unit 5 to the differential gear unit 6, and then distributed to the right and left driving wheels (not shown).

[0032] Next, the engine 1, the torque converter 2, the forward-reverse drive switching device 3, the belt type CVT 4, and the ECU 8 will be described. [0033] The engine 1 may be, for example, a multi-cylinder gasoline engine.

An amount of air drawn into the engine 1 is regulated by an electrically-controlled throttle valve 12. The throttle valve 12 may electrically be controlled independently of the driver's operation on the accelerator pedal. The throttle opening amount is detected by a throttle-opening sensor 102. The temperature of coolant in the engine 1 is detected by the coolant temperature sensor 103.

[0034] The throttle opening amount of the throttle valve 12 is controlled by the ECU 8. Specifically, the ECU 8 controls the throttle opening amount of the throttle valve 12 to obtain an optimal intake air amount (target intake air amount) corresponding to the engine operating state, such as the engine speed Ne detected by the engine speed sensor 101, and the depression amount of the accelerator pedal (accelerator operation amount ace). Specifically, the ECU 8 detects the actual throttle opening amount of the throttle valve 12 by using the throttle opening sensor 102, and controls a throttle motor 13 in a feedback manner so that the actual throttle opening matches the (target) throttle opening to obtain the target intake air amount. [0035] The torque converter 2 includes: a pump impeller 21 on the input shaft side; a turbine runner 22 on the output shaft side; a stator 23 that develops a torque increasing function; and a one way clutch 24. The torque converter 2 transmits power through a fluid between the pump impeller 21 and the turbine runner 22. [0036] The torque converter 2 is provided with a lockup clutch 25 that directly connects the input side and the output side of the torque converter 2. The lockup clutch 25 is a hydraulic friction clutch that is frictionally engaged with a front cover 2a by the differential pressure (lockup differential pressure) ΔP between the hydraulic pressure in an engaging-side hydraulic chamber 26 and the hydraulic pressure in a disengaging-side hydraulic chamber 27, where ΔP = hydraulic pressure in engaging-side hydraulic chamber 26 - hydraulic pressure in disengaging-side chamber 27. The lockup clutch 25 is fully engaged, half engaged (in slippage), or disengaged by the control of the differential pressure ΔP.

[0037] When the lockup clutch 25 is fully engaged, the pump impeller 21 and the turbine runner 22 rotate together. When the lockup clutch 25 is engaged in a certain slippage state (half engaged state), the turbine runner 22 rotates after the pump impeller 21 with a certain amount of slippage. On the other hand, when the lockup differential pressure ΔP is set to a negative value, the lockup clutch 25 is disengaged.

[0038] The torque converter 2 is provided with a mechanical oil pump (hydraulic pressure source) 7 that is connected to the pump impeller 21 and that is driven together with the pump impeller 21.

[0039] The forward-reverse drive switching device 3 includes a planetary gear mechanism 30 of a double pinion type, a forward clutch Cl, and a reverse brake Bl.

[0040] The sun gear 31 of the planetary gear mechanism 30 is integrally connected to a turbine shaft 28 of the torque converter 2. A carrier 33 of the planetary gear mechanism 30 is integrally connected to an input shaft 40 of the belt type CVT 4. The carrier 33 and the sun gear 31 are selectively connected through the forward clutch Cl. The ring gear 32 is selectively fixed to a housing through the reverse brake Bl.

[0041] The forward clutch Cl and the reverse clutch Bl are a hydraulic type frictional engagement element that is engaged or disengaged by a hydraulic-control circuit 20 that is described later. When the forward clutch Cl is engaged and the reverse brake Bl is disengaged, the forward-reverse drive switching device 3 is integrally rotated, and a forward power transmission path is established. In this state, the driving force for forward travel is transmitted to the belt type CVT 4.

[0042] On the other hand, when the reverse brake Bl is engaged and the forward clutch Cl is disengaged, a reverse power transmission path is established by the forward-reverse drive switching device 3. In this state, the input shaft 40 rotates in the opposite direction of the turbine shaft 28, and the driving force in the reverse direction is transmitted to the belt type CVT 4. When the forward clutch Cl and the reverse brake Bl are both disengaged, the forward-reverse drive switching device 3 becomes neutral (disengaged) to disengage the power transmission.

[0043] The belt type CVT 4 includes: an input side primary pulley 41, an output side secondary pulley 42; and a metal belt 43 that is wound around the primary pulley 41 and the secondary pulley 42.

[0044] The primary pulley 41 is a variable pulley that can vary its effective diameter, and includes: a fixed sheave 411 that is fixed to the input shaft 40; and a movable sheave 412 is provided on the input shaft 4Q and moves in the axial direction of the input shaft 40. The secondary pulley 42 is also a variable pulley that can vary its effective diameter, and includes: a fixed sheave 421 that is fixed to the output shaft 44; and a movable sheave 422 is provided on the output shaft 44 and moves in the axial direction of the output shaft 44.

[0045] A hydraulic actuator 413 that changes the V groove width between the fixed sheave 411 and the movable sheave 412 is arranged on the movable sheave 412 side of the primary pulley 41. A hydraulic actuator 423 that changes the V groove width between the fixed sheave 421 and the movable sheave 422 is arranged on the movable sheave 422 side of the secondary pulley 42.

[0046] In the belt type CVT 4 with above structure, when the hydraulic pressure of the hydraulic actuator 413 of the primary pulley 41 is controlled, the groove width of the primary pulley 41 and secondary pulley 42 is changed, and then the loop radius of the belt 43 (effective diameter) is changed. In this way, the transmission ratio γ (γ = rotational speed of the primary pulley (rotational speed of the input shaft) Nin / rotational speed of the secondary pulley (rotational speed of the output shaft) Nout) is changed in a continuous manner. The hydraulic pressure of the hydraulic actuator 423 of the secondary pulley 42 is controlled so as to clamp the belt 43 with the predetermined clamping force that does not allow the belt to slip. These controls are executed by the ECU 8 and the hydraulic-control circuit 20.

[0047] Among the hydraulic-control circuit 20, the hydraulic-control circuit of the hydraulic actuator 413 of the primary pulley 41, and the hydraulic-control circuit of the hydraulic actuator 423 of the secondary pulley 42 of the belt type CVT 4 will be described with reference to FIG. 2 and FIG 3.

[0048] First, as shown in FIG 3, the hydraulic pressure that is generated by an oil pump 7 is regulated by the primary regulator valve 203, and line pressure PL is established. The hydraulic control pressure that is output from the linear solenoid valve

(SLT) 201 is supplied through a clutch application control valve 204 to the primary regulator valve 203, and the hydraulic control pressure is used as pilot pressure.

[0049] There may be a case in which switching the clutch application control valve 204 causes the supply of the hydraulic control pressure from the linear solenoid valve (SLS) 202 to the primary regulator valve 203. The hydraulic control pressure is used as pilot pressure to regulate the line pressure PL. The hydraulic pressure regulated by a modulator valve 205, with the line pressure PL as original pressure, is supplied to the linear solenoid valve (SLT) 201 and the linear solenoid valve (SLS) 202.

[0050] The linear solenoid valve (SLT) 201 outputs the hydraulic control pressure in accordance with the electric current value determined by the duty signal (duty value) transmitted from the ECU 8. The linear solenoid valve (SLT) 201 is a normally-open valve.

[0051] The linear solenoid valve (SLS) 202 outputs the hydraulic control pressure in accordance with the electric current determined by the duty signal (duty value) transmitted from the ECU 8. Like the linear solenoid valve (SLT) 201, the linear solenoid valve (SLS) 202 is also a normally-open valve.

[0052] In the hydraulic-control circuit shown in FIG 2 and FIG 3, the modulator valve 206 regulates the hydraulic pressure that is output from the modulator valve 205 to a certain pressure, and supplies the regulated hydraulic pressure, for example, to a duty solenoid valve (DSl) 304, a duty solenoid valve (DS2) 305, and a belt clamping force control valve 303 that are described later.

[0053] Now, the hydraulic-control circuit of the hydraulic actuator 413 of the primary pulley 41 will be described. As shown in FIG 2, an upshift speed-change control valve 301 is connected to the hydraulic actuator 413 of the primary pulley 41.

[0054] A spool 311 is disposed in the upshift control valve 301 and is movable in the axial direction of the upshift control valve 301. A spring 312 is provided at one end (upper end side in FIG 2) of the spool 311. A first hydraulic port 315 is formed in the upshift control valve 301 on the opposite side of the spool 311 from the spring 312. A second hydraulic port 316 is formed on the side of the spool 311 at which the spring 312 is provided.

[0055] The first hydraulic port 315 is connected with a duty solenoid valve

(DSl) 304 that outputs the hydraulic control pressure in accordance with the electric current value that is determined by the duty signal (duty value) transmitted by the ECU 8. The hydraulic control pressure output by the duty solenoid valve (DSl) 304 is applied to the first hydraulic port 315. The second hydraulic port 316 is connected with a duty solenoid valve (DS2) 305 that outputs the hydraulic control pressure in accordance with the electric current value that is determined by the duty signal (duty value) transmitted by the ECU 8.

The hydraulic control pressure output by the duty solenoid valve (DS2) 305 is applied to the second hydraulic port 316.

[0056] The upshift speed-change control valve 301 is includes: an input port 313 to which the line pressure PL is supplied; input/output port 314 that is connected (communicated) to the hydraulic actuator 413 of the primary pulley 41; and an output port 317. When the spool is in the upshift position (lower side in FIG 2), the output port 317 is closed, and the line pressure PL is supplied from the input port 313 through the input/output port 314 to the hydraulic actuator 413 of the primary pulley 41. In contrast, when the spool 311 is in the closing position (upper side in FIG 2), the input port 313 is closed, and the hydraulic actuator 413 of the primary pulley 41 communicates with the output port 317 through the input/output port 314.

[0057] A spool 321 that is movable in the axial direction is disposed in the downshift speed-change control valve 302. One end of the spool 321 (lower side in FIG. 2) is provided with a spring 322 and a first hydraulic port 326. An opposite end portion of the spring 322 with respect to the spool 321 is provided with a second hydraulic port 327. The first hydraulic port 326 is connected to the duty solenoid valve (DSl) 304, and the hydraulic control pressure that is output by the duty solenoid valve (DSl) 304 is applied to the first hydraulic port 326. The second hydraulic port 327 is connected to the duty solenoid valve (DS2) 305, and the hydraulic control pressure that is output by the duty solenoid valve (DS2) 305 is applied to the second hydraulic port 327. [0058] The downshift speed-change control valve 302 is includes an input port

323, an input/output port 324, and a discharge port 325. The input port 323 is connected to a bypass control valve 306. The hydraulic pressure supplied to the input port 323 is the line pressure regulated by the bypass control valve 306. In the downshift speed-change control valve 302, when the spool 321 is in the downshift position (upper side in FIG 2), the input/output port 324 is communicated with the discharge port 325. However, when the spool 321 is in the closing position (lower side in FIG 2), the input/output port 324 is closed. The input/output port 324 of the downshift speed-change control valve 302 is connected to the output port 317 of the upshift speed-change-control valve 301.

[0059] In the hydraulic-control circuit shown in FIG 2, if the hydraulic control pressure output by the duty solenoid valve (DSl) 304 is supplied to the first hydraulic port 315 of the upshift speed-change control valve 301, the spool 311 moves to the upshift position (upper side in FIG 2) by the thrust of the hydraulic control pressure. Accordingly, when the spool 311 moves (to the upshifting side), the hydraulic oil (line pressure PL) is supplied, with a flow rate that corresponds to the hydraulic control pressure, from the input port 313 through the input/output port 314 to the hydraulic actuator 413 of the primary pulley 41. At the same time, the output port 317 is closed to prevent the hydraulic oil from flowing to the downshift speed-change control valve 302. Accordingly, the speed-change control pressure increases, and the V groove width of the primary pulley 41 is narrowed to reduce the transmission ratio γ (upshift).

[0060] When the hydraulic control pressure that is output by the duty solenoid valve (DSl) 304 is supplied to the first hydraulic port 326 of the downshift speed-change control valve 302, the spool 321 moves to the upper side in FIG 2 to close the input/output port 324. [0061] However, when the hydraulic control pressure output by the duty solenoid valve (DS2) 305 is supplied to the second hydraulic port 316 of the upshift speed-change control valve 301, the spool 311 is moved to the downshift position (lower side in FIG 2) by the thrust of the hydraulic control pressure. By shifting the spool 311 to the downshift side, the hydraulic oil in the hydraulic actuator 413 of the primary pulley 41, with a flow rate that corresponds to the hydraulic control pressure, flows into the input/output port 314 of the upshift speed-change control valve 301. The hydraulic oil that has flowed into the upshift speed-change control valve 301 is sent through the output port 317 and the input/output port 324 of the downshift speed-change control valve 302, and discharged from the discharge port 325. Accordingly, the speed-change control pressure is reduced and the V groove width of the input side movable pulley 42 is widened to increase the transmission ratio γ (downshift).

[0062] When the hydraulic control pressure output by the duty solenoid valve (DS2) 305 is supplied to the second hydraulic port 327 of the downshift speed-change control valve 302, the spool 321 moves to the lower side in FIG 2 to communicate the input/output port 324 with the discharge port 325.

[0063] When the hydraulic control pressure is output by the duty solenoid valve (DSl) 304, the hydraulic oil is supplied from the upshift speed-change control valve 301 to the hydraulic actuator 413 of the primary pulley 41 to upshift the speed-change control pressure continuously. When the hydraulic control pressure is output by the duty solenoid valve (DS2) 305, the hydraulic oil in the hydraulic actuator 413 of the primary pulley 41 is discharged from the discharge port 325 of the downshift speed-change control valve 302 to downshift the speed-change control pressure continuously.

[0064] In the present embodiment, a target input rotational speed Nint is calculated from the map, which is determined in advance based on the vehicle speed V and the accelerator operation amount ace. Then, in order to match an actual input shaft rotational speed Nin with the target input rotational speed Nint, the belt type CVT 4 controls the transmission ratio in correspondence with the deviation (Nint - Nin).

Specifically, the solenoid valve and the like that are disposed in the hydraulic-control circuit 20 in FIG 2 and FIG 3 are controlled in a feedback manner to control the supply and discharge of hydraulic oil to the hydraulic actuator 413 of the primary pulley 41.

[0065] In the present embodiment, the CVT allows a choice between the automatic shift mode (including the linear shift control) and the manual shift mode, as described later. Details of the speed-change control in the automatic shift mode and in the manual shift mode are described later.

[0066] Now, the hydraulic-control circuit of the hydraulic actuator 423 of the second pulley 42 will be described with reference to FIG 3.

[0067] As shown in FIG 3, the belt clamping force control valve 303 is connected to the hydraulic actuator 423 of the secondary pulley 42. [0068] The spool 331 that can move in the axial direction is disposed in the belt clamping force control valve 303. One end of the spool 331 (lower side in FIG 3) is provided with a spring 332 and a first hydraulic port 335. An opposite end portion of the spring 332 with respect to the spool 331 is provided with a second hydraulic port 336. The first hydraulic port 335 is connected to the linear solenoid valve (SLS) 202, and the hydraulic control pressure that is output by the linear solenoid valve (SLS) 202 is applied to the first hydraulic port 335. Hydraulic pressure from the modulator valve 206 is applied to the second hydraulic port 336.

[0069] The belt clamping force control valve 303 includes an input port 333, to which the line pressure PL is supplied, and an output port 334, which is connected (communicated) to the hydraulic actuator 423 of the secondary pulley 42.

[0070] In the hydraulic-control circuit in FIG 3, when the hydraulic control pressure output by the linear solenoid valve (SLS) 202 exceeds the hydraulic pressure that is supplied to the hydraulic actuator 423 of the secondary pulley 42, the spool 331 of the belt clamping force control valve 303 moves to the upper side in FIG. 3. In this case, the hydraulic pressure supplied to the hydraulic actuator 423 of the secondary pulley 42 is increased, thereby increasing the belt clamping force.

[0071] ' In contrast, when the hydraulic control pressure output by the linear solenoid valve (SLS) 202 falls below the hydraulic pressure that is supplied to the hydraulic actuator 423 of the secondary pulley 42, the spool 331 of the belt clamping force control valve 303 moves to the lower side in FIG 3. In this case, the hydraulic pressure supplied to the hydraulic cylinder of the secondary pulley 42 is reduced, thereby reducing the belt clamping force.

[0072] Accordingly, the hydraulic control pressure output by the linear solenoid valve (SLS) 202 is used as a pilot pressure to regulate the line pressure PL, and the regulated hydraulic pressure of the secondary pulley 42 is supplied to the hydraulic actuator 423 to increase or reduce the belt clamping force.

[0073] In the present embodiment, the belt clamping force of the belt type CVT

4, in other words the hydraulic pressure of the hydraulic actuator 423 of the secondary pulley 42 is controlled by the hydraulic control pressure output by the linear solenoid valve

(SLS) 202 based on the map of the predetermined necessary hydraulic pressure (belt clamping force), shown in FIG 9 for example. Here, the map is determined in order to prevent the belt from sliding, and based on the accelerator operation amount ace, which corresponds to the transmission torque, and the transmission ratio γ (γ = Nin/Nout). The map in FIG 9 is equivalent to the clamping force control condition and stored in a ROM 82

(see FIG 5) of the ECU 8.

[0074] In the present embodiment, as shown in FIG 4, the steering wheel 110 is provided with the upshift switch 111 and the downshift switch 112. A control signal from the upshift switch 111 and the downshift switch 112 is input to the ECU 8. [0075] The upshift switch 111 and the downshift switch 112 are, for example, a paddle switch (momentary switch or automatic return switch). By controlling the shift switches 111 and 112, the manual shift mode is established.

[0076] In the present embodiment, as shown by the map in FIG 7, there are 7 speeds from a first speed to a seventh speed. Each time the upshift switch 111 is operated, the transmission upshifts to the next higher speed (for example, 1st → 2nd — > 3rd — * — ►

7th). Likewise, each time the downshift switch 112 is operated, the transmission downshifts to the next lower speed (for example, 7th → 6th —» 5th → ^•• → 1st). The speed-change control of the belt type CVT 4 in the manual shift mode will be described later.

[0077] In the present embodiment, in addition to the shift switches 111 and 112, the vehicle is provided with a parking switch and a reverse switch that is operated for reverse travel. The parking switch and the reverse switch are disposed, for example, on an instrument panel or a console panel. In addition to these switches, a neutral switch that is operated for selecting a neutral transmission ratio may be disposed as necessary. Instead of disposing the neutral switch, it may be configured that the neutral transmission ratio is set when the upshift switch 111 and the downshift switch 112 are operated simultaneously.

[0078] As shown in FIG 5, the ECU 8 includes the CPU 81, the ROM 82, the RAM 83 and the backup RAM 84. [0079] The ROM 82 stores various control programs and maps that are used when executing the control programs. The CPU 81 performs computation based on the control programs and maps stored in the ROM 82. The RAM 83 is a memory that temporarily stores the computation result of the CPU 81 and the data inputted from various sensors. The backup RAM 84 is a nonvolatile memory that saves the necessary data and the like when the engine 1 stops.

[0080] The CPU 81, the ROM 82, the RAM 83 and the backup RAM 84 are connected to each other via a bus 87, and also connected to an input interface 85 and an output interface 86.

[0081] The input interface 85 of the ECU 8 is connected with: an engine speed sensor 101; a throttle opening sensor 102; a water temperature sensor 103; a turbine rotational speed sensor 104; a primary pulley rotational speed sensor 105; a secondary pulley rotational speed sensor 106; an accelerator operating amount sensor 107; a CVT oil temperature sensor 108; a brake pedal sensor 109; the upshift switch 111; and the downshift switch 112. An output signal from these sensors is sent to the ECU 8, such as a signal that indicates: rotational speed Ne of the engine 1 (engine speed Ne); throttle opening θth of the throttle valve 12; coolant temperature Tw of the engine 1; rotational speed Nt of the turbine shaft 28 (turbine speed Nt); primary pulley rotational speed (input shaft rotational speed) Nin; secondary pulley rotational speed (output shaft rotational speed) Nout; accelerator pedal operation amount (accelerator operation amount) ace; oil temperature of the hydraulic-control circuit 20 (CVT oil temperature The); operation amount of the brake pedal; and the of operation on the shift switches 111 and 112.

[0082] The output interface 86 is connected with a throttle motor 13, a fuel injection device 14, an ignition device 15, and a hydraulic pressure control circuit 20. [0083] Among the signals that are supplied to the ECU 8, the turbine speed Nt matches the primary pulley rotational speed (input shaft rotational speed) Nin during the forward travel in which the forward clutch Cl of the forward-reverse drive switching device 3 is engaged, and the secondary pulley rotational speed (output shaft rotational speed) Nout corresponds to the vehicle speed V. The accelerator operation amount ace represents the driver's requesting output amount. The vehicle speed V may be detected by a vehicle speed sensor.

[0084] The ECU 8 executes, for example, the output control of the engine 1 and engagement/disengagement control of the lockup clutch 25 based on the output signal of the various sensors described above. Output of the engine 1 is controlled by controlling the throttle motor 13, the fuel injection device 14, the ignition device 15, and the like.

[0085] Furthermore, the ECU 8 executes speed-change control in the automatic shift mode, speed-change control in the manual shift mode, linear shift control, and the return determination process. These controls are described below.

[0086] The speed-change control in the automatic shift mode is described next. In the present embodiment, the automatic shift mode (D range) is set during the normal operation (for example, when the shift switches 111 and 112 are not operated). In the automatic shift mode, the speed-change control is executed to change the transmission ratio γ of the belt type CVT 4 automatically and continuously according to the traveling state of the vehicle. For example, the ECU 8 calculates the vehicle speed V from the output signal of the secondary pulley rotational speed sensor 106, and calculates the accelerator pedal operation amount (accelerator operating amount ace) that represents the driver's requesting output amount from the output signal of the accelerator operation amount sensor 107, and then obtains the target input rotational speed for automatic shifting Nintaut based on the vehicle speed V and the accelerator operation amount ace.

[0087] Specifically, as shown in FIG 6, the target input rotational speed for automatic shifting Nintaut is calculated by using the map of the target input rotational speed for automatic shifting Nintaunt based on the vehicle speed V and the accelerator operation amount ace. If the CVT is currently operated in the automatic shift mode, the transmission ratio of the belt type CVT 4 is controlled according to the deviation between the target input rotational speed for automatic shifting Nintaut and the actual input shaft rotational speed Nin (calculated from the output signal of the primary pulley rotational speed sensor 105) in the way that Nintaut and Nin reach the same speed.

[0088] The map in FIG 6 is determined to produce optimal fuel efficiency in accordance with the vehicle speed V and the accelerator operation amount ace, so that the transmission ratio can always be set for optimal fuel efficiency by using this map. In the map of FIG 6, the target input rotational speed for automatic shifting Nintaut is set in the way that the transmission ratio γ is increased as the vehicle speed is slow and the accelerator operation amount ace is large. The target input rotational speed Nintaut, which is the target value of the primary pulley rotational speed (input shaft rotational speed) Nin, corresponds to the target transmission ratio that falls within the range of the minimum transmission ratio γmin to the maximum transmission ratio γmax of the belt type CVT 4. The target input rotational map for automatic shifting that is shown in FIG. 6 is stored in the ROM 82 of the ECU 8. [0089] The speed-change control in the manual shift mode is described. The ECU 8 calculates the vehicle speed V from the output signal of the secondary pulley rotational speed sensor 106, and obtains the target input rotational speed for manual shifting Nintman based on the vehicle speed V. [0090] Specifically, the ECU 8 calculates the target input rotational speed for manual shifting Nintman, with reference to the map in FIG 7, based on the transmission ratio that is determined by the vehicle speed V or the operation on the upshift switch 111 or the downshift switch 112 shown in FIG 4. The map in FIG. 7 is determined as the target input rotational speed for manual shifting Nintman for each transmission ratio of 1st, 2nd, 3rd, 4th, 5th, 6th, and 7th speeds with a parameter that represents the vehicle speed V. If the CVT is currently operated in the manual shift mode, the transmission ratio of the belt type CVT 4 is controlled according to the deviation between the target input rotational speed for manual shifting Nintman and the actual input shaft rotational speed Nin (Nintman-Nin) to equalize the rotational speeds Nintman and Nin. [0091] In the present embodiment, for example, if the downshift switch 112 is operated and the transmission mode switches from the automatic shift mode to the manual shift mode, the target input rotational speed for automatic shifting Nintaut is calculated from the vehicle speed V and the accelerator operation amount ace that are detected immediately before the mode switching operation. If the calculated target input rotational speed Nintaut is, for example, between the 5th and the 4th speed in the map of FIG 7, the fourth transmission ratio "4th" on the downshift side is selected, and then the target input rotational speed for manual shifting Nintman is obtained. If the downshift switch 112 is subsequently operated again, the third transmission ratio "3rd" is selected, and then the target input rotational speed for manual shifting Nintman is obtained. [0092] On the other hand, when the upshift switch 111 is operated and the transmission mode is switched from the automatic shift mode to the manual shift mode, the target input rotational speed for automatic shifting Nintaut is calculated from the map in FIG 6 based on the vehicle speed V and the accelerator operation amount ace that are detected immediately before the mode switching operation. If the calculated target input rotational speed Nintaut is, for example, between the 5th and the 4th speed in the map of FIG 7, the fifth transmission ratio "5th" on the upshift side is selected, and the target input rotational speed for manual shifting Nintman is obtained. If the upshift switch 111 is subsequently operated again, the sixth transmission ratio "6th" is selected, and then the target input rotational speed for manual shifting Nintman is obtained.

[0093] The map shown in FIG 7 is stored in the ROM 82 of the ECU 8. In the map shown in FIG 7, the target input rotational speed for manual shifting Nintman is highest in 1st speed if the vehicle speed V is the same, and decreases as the transmission ratio increases toward the 7th speed. For example, when the transmission ratio is downshifted from the "3rd" to the "2nd" speed, the input shaft rotational speed Nin (engine speed Ne) of the belt type CVT 4 increases. When the transmission ratio is upshifted from the "3rd" to the "4th" speed, the input shaft rotational speed Nin (engine speed Ne) decreases.

[0094] The manual shift mode returns to the automatic shift mode, for example, when the shift switches 111 and 112 have not been operated for predetermined time period or when the return determination condition is satisfied after the downshifting operation with accelerator pedal depression that is described later.

[0095] The linear shift control is a control that increases the engine speed Ne along with the increase of the vehicle acceleration when the acceleration is requested by the driver's accelerator pedal operation.

[0096] In the present embodiment, the target input rotational speed for linear shift control Nintlin is obtained by using the map in FIG 8 to control the speed-change of the belt type CVT 4. The map in FIG 8 is determined as the target input rotational speed for linear shift control Nintlin with the parameters that represent the vehicle speed V and the accelerator operation amount ace. The map in FIG. 8 is stored in the ROM 82 of the ECU 8. In the map of FIG. 8, the target input rotational speed for linear shift control Nintlin is set higher than the target input rotational speed for automatic shifting Nintaut in FIG 6 as long as the traveling states of the vehicle (vehicle speed V and accelerator operation amount ace) are in the same condition. The target input rotational speed for linear shift control Nintlin in FIG 8 increases with a certain inclination in proportion to the increase of the vehicle speed V.

[0097] The ECU 8 calculates the vehicle speed V from the output signal of the secondary pulley rotational speed sensor 106, and also calculates the accelerator operation amount ace from the output signal of the accelerator operation amount sensor 107. Then, the ECU 8 calculates the target input rotational speed for linear shift control Nintlin, with reference to the map in FIG 8, based on the calculated vehicle speed V and the calculated accelerator operation amount ace. When the accelerator operation amount ace obtained from the output signal of the accelerator operation amount sensor 107 reaches a linear shift control threshold Thacc (see FIG 11) or larger, the linear shift control is enabled, and the belt type CVT 4 is controlled under the linear shift control in accordance with the deviation between the target input rotational speed for linear shift control Nintlin and the actual input shaft rotational speed Nin (calculated from the output signal of the primary pulley rotational speed sensor 105) to equalize the rotational speeds Nintlin and Nin. [0098] The linear shift control is one of the controls that is executed during the automatic shift mode. If the transmission mode returns to the automatic shift mode from the manual shift mode, the transmission mode is returned to one of the normal automatic shift mode and the linear shift control depending on the accelerator operation amount.

[0099] The process (return determination process) that determines the return from the manual shift mode to the automatic shift mode (including the linear shift control) will be described, with reference to the flowchart in FIG 10 and the timing charts in FIG 11 and FIG 12. The operation in FIG 10 is executed by the ECU 8 at predetermined intervals (for example, several milliseconds to several tens of milliseconds).

[0100] As a precondition, in the present embodiment, when the vehicle is traveled or parked, the target input rotational speed for automatic shifting Nintaut, the target input rotational speed for manual shifting Nintman, and the target input rotational speed for linear shift control Nintlin are calculated by the ECU 8 sequentially (for example, every control cycle). The target input rotational speed calculated sequentially is used for the return determination process of step ST104 or ST106. Here, the target input rotational speed for manual shifting Nintman that is used for return determination process is supposed to be one step below the current manual transmission ratio (for example, if the current transmission ratio is 4th speed, then the target input rotational speed for manual shifting Nintman will be 3rd speed). [0101] Next, the reason why the target input rotational speed for manual shifting

Nintman, used for return determination process, is one step lower than the current transmission ratio (one lower speed range) will be explained. First, in the vehicle that allows a choice between the automatic shift mode and the manual shift mode, under normal conditions, if the driver depresses the accelerator pedal while the vehicle is moving and the transmission is operating in the manual shift mode, and only if the driver expresses the "clear intention for downshift", the transmission mode returns to the automatic shift mode (D range). Here, "clear intention for downshift" is defined as the time when there is a request for downshift from the current transmission ratio to the next lower speed range. For this reason, the return determination process uses a target input rotational speed for manual shifting Nintman that is the next lower speed than the current transmission ratio.

[0102] In step STlOl, the ECU determines whether the current transmission mode is the manual shift mode based on the operation information (presence/absence of operation) of the shift switches 111 and 112. If the result is affirmative, the process proceeds to step ST102. If the result of the step STlOl is negative, the return determination process ends.

[0103] In the step ST102, the ECU determines whether there is a downshift request with depression of the accelerator pedal based on the output signal from the accelerator operation amount sensor 107. If the result is affirmative, the process proceeds to a step ST103. If the result of the step ST102 is negative, the return determination process ends.

[0104] In the step ST103, the ECU determines whether the accelerator operation amount ace that is calculated from the output signal of the accelerator operation amount sensor 107 equals or exceeds the linear shift control determination threshold Thacc (see FIG 11 and FIG. 12). If the result of the step ST 103 is affirmative, the ECU determines that the execution condition is satisfied (linear shift control is possible), and the process proceeds to a step ST104.

[0105] In the related art control, as shown in FIG. 13, the transmission mode returns to the linear shift control when the target input rotational speed for automatic shifting is equal to or exceeds the target input rotational speed for manual shifting when the accelerator operation amount is equal to or exceeds the linear shift control determination threshold. It causes a problem in that the input shaft rotational speed of the belt type CVT 4 (engine speed) is reduced when the transmission mode is returned to the linear shift control. [0106] In contrast, in the control of the present embodiment, when the execution condition of the linear shift control is satisfied, the condition for the return determination changes. As shown in FIG 11, the return determination is not performed even when the target input rotational speed for automatic shifting Nintaut exceeds the target input rotational speed for manual shifting Nintman (target input rotational speed that is for one step lower than the current transmission ratio). The ECU 8 determines that the condition for the return determination is satisfied if the target input rotational speed for linear shift control Nintlin is equal to or exceeds the target input rotational speed for manual shifting Nintman (Nintlin = Nintman) (when the determination result of the step ST104 becomes true), and then the ECU 8 returns the transmission mode from the manual shift mode to the linear shift control (automatic shift mode) (step ST105).

[0107] In this way, if the accelerator operation amount ace at the downshift request with the depression of the accelerator pedal is equal to or exceeds the linear shift control determination threshold (ace = Thacc), the return determination is performed by using the target input rotational speed of the linear shift control Nintlin. Accordingly, as shown in FIG 11, the input shaft rotational speed Nin of the belt-type CVT 4 (engine speed Ne) is prevented from decreasing during the return process. Thus, sufficient driving force is provided when acceleration is requested.

[0108] If the determination result of step ST103 is negative, that is, if the accelerator operation amount ace at the downshift request with depression of the accelerator pedal is below the linear shift control determination threshold Thacc (ace < Thacc), the ECU 8 determines that execution of the linear shift control is impossible. In this case, as shown in FIG 12, the ECU 8 uses, for return determination, the target input rotational speed for automatic shifting Nintaut and the target input rotational speed for manual shifting Nintman (target input rotational speed that is for one step lower than the current transmission ratio). If the target input rotational speed for automatic shifting Nintaut is equal to at least the target input rotational speed for manual shifting Nintman (Nintaut = Nintman) (i.e., if the determination result of step ST106 is positive), the ECU 8 determines that the condition for the return determination is satisfied, and then returns the transmission mode to the normal automatic shift mode (step ST107).

[0109] The linear shift control determination threshold Thacc used in determination process of step ST103 in FIG 10 is the value used to determine whether the acceleration is operated more actively than the steady travel on flat road or regular travel.

The linear shift control determination threshold Thacc may be an empirical value obtained by experiment, calculation, etc.

[0110] In the present embodiment, the invention is applied to the control device for the vehicle equipped with a gasoline engine. However, the present invention may be applied to the control device for the vehicle equipped with other types of engine, such as a diesel engine. The power source of the vehicle may be, besides an engine (internal combustion engine), an electric motor or a hybrid type power source that is provided with both of an engine and an electric motor.

[0111] In the present embodiment, the present invention is applied to the control device for a vehicle equipped with the belt type CVT. However, the present invention may also be applied to a control device for a vehicle equipped with a different type of CVT, such as a toroidal CVT.

[0112] The present invention is not limited to a front-engine-front-wheel drive (FF) vehicle, but may be applied to a front-engine-rear-wheel drive (FR) vehicle or a four-wheel drive vehicle.

[0113] The present invention may be applied to the control device for a vehicle that is provided with an engine and a CVT. Particularly, the present invention may be applied to the control device for vehicle that allows a choice between the automatic shift mode and the manual shift mode.

[0114] While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various example combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the scope of the appended claims.