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Title:
HYDRAULIC CONTROL CIRCUIT FOR VEHICLE
Document Type and Number:
WIPO Patent Application WO/2016/016703
Kind Code:
A1
Abstract:
A hydraulic control circuit includes a torque converter, oil passages, a lockup relay valve and a pressure regulating valve. A first oil passage is connected with a first oil chamber of the torque converter, and a second oil passage is connected with a second oil chamber. The first oil chamber is configured to feed hydraulic pressure that makes the lockup clutch engaged. The pressure regulating valve is configured to regulate hydraulic pressure of the third oil passage connected with the first and the second oil passage. A feedback port of the pressure regulating valve is configured to receive hydraulic pressure for moving the pressure regulating valve to a valve opening side. The feedback port is connected with one of the first oil passage and the second oil passage. The pressure regulating valve is configured to discharge oil downstream when given hydraulic pressure is fed to the feedback port.

Inventors:
MIZUNO YOSHIHIRO (JP)
KUWABARA SHINYA (JP)
Application Number:
PCT/IB2015/001230
Publication Date:
February 04, 2016
Filing Date:
July 23, 2015
Export Citation:
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Assignee:
TOYOTA MOTOR CO LTD (JP)
International Classes:
F16H61/14
Foreign References:
US20040204290A12004-10-14
US5347885A1994-09-20
DE10124821A12002-01-31
US5627750A1997-05-06
US5991680A1999-11-23
JP2013170606A2013-09-02
Download PDF:
Claims:
CLAIMS:

1. A hydraulic control circuit for a vehicle, the hydraulic control circuit comprising: a torque converter including a lockup clutch, a first oil chamber, and a second oil chamber, the first oil chamber being configured to feed hydraulic pressure that makes the lockup clutch engaged, and the second oil chamber being configured to feed hydraulic pressure that makes the lockup clutch released;

oil passages including a first oil passage, a second oil passage, and a third oil passage, the third oil passage being connected with the first oil passage and the second oil passage, the first oil passage being connected with the first oil chamber, and the second oil passage being connected with the second oil chamber;

a lockup relay valve provided between the third oil passage and the first oil passage, the lockup relay valve being provided between the third oil passage and the second oil passage, the lockup relay valve being configured to switch a communication destination of the third oil passage to any one of the first oil passage and the second oil passage; and

a pressure regulating valve connected with the third oil passage, the pressure regulating valve being configured to regulate hydraulic pressure of the third oil passage, the pressure regulating valve including a feedback port, the feedback port being configured to receive hydraulic pressure for moving the pressure regulating valve to a valve opening side, the feedback port being connected with one of the first oil passage and the second oil passage, and the pressure regulating valve being configured to discharge oil downstream when given hydraulic pressure is fed to the feedback port.

2. The control circuit according to claim 1, wherein

the pressure regulating valve includes:

an input port connected with the third oil passage;

a discharge port configured to be communicated with the input port and discharge oil downstream, when the pressure regulating valve regulates pressure of the third oil passage;

an elastic body configured to bias the pressure regulating valve to a valve closing side; and

a receiving port connected with the third oil passage, the receiving port being configured to receive hydraulic pressure for moving the pressure regulating valve to the valve opening side.

Description:
HYDRAULIC CONTROL CIRCUIT FOR VEHICLE

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The invention relates to a hydraulic control circuit for a vehicle, and especially to filling of oil in a torque converter.

2. Description of Related Art

[0002] There is well known a vehicle having a torque converter, which functions as a fluid transmission device that amplifies torque of a drive source. The torque converter transmits power through fluid (oil), and the torque converter is filled with oil.

When a vehicle is left for a long period of time, oil in the torque converter leaks from a sealing part and so on. When the vehicle is started in this state, oil could not be filled in the torque converter in time for depression of an accelerator, which could cause delay in start of the vehicle. Also, the vehicle could start suddenly once the torque converter is filled with oil. In particular, when temperature is low, oil viscosity is high, and it tends to take longer to fill the torque converter with oil. To address this problem, in an oil pump control device according to Japanese Patent Application Publication No.

2013-170606 (JP 2013-170606 A), a technique is disclosed, in which a speed ratio E (= Nt / Ne) is calculated as required from engine rotation speed Ne and turbine rotation speed Nt of a torque converter, and a quantity of oil, which is set based on the calculated speed ratio E, is filled by using an electric oil pump.

[0003] However, the oil pump control device according to JP 2013-170606 A requires the electric oil pump for filling the torque converter with oil, a control device that controls the electric oil pump, and so on. There is thus a problem of a significant cost increase.

SUMMARY OF THE INVENTION

[0004] The invention provides a hydraulic control circuit in a vehicle having a torque converter, in which the hydraulic control circuit enables swift filling of oil even when oil has leaked from the torque converter, and is simply structured.

[0005] A hydraulic control circuit related to an aspect of the invention is for a vehicle. The hydraulic control circuit includes a torque converter, oil passages, a lockup relay valve and a pressure regulating valve. The torque converter includes a lockup clutch, a first oil chamber, and a second oil chamber. The first oil chamber is configured to feed hydraulic pressure that makes the lockup clutch engaged. The second oil chamber is configured to feed hydraulic pressure that makes the lockup clutch released. The oil passage includes a first oil passage, a second oil passage, and a third oil passage. The third oil passage is connected with the first oil passage and the second oil passage. The first oil passage is connected with the first oil chamber, and the second oil passage is connected with the second oil chamber. The lockup relay valve is provided between the third oil passage and the first oil passage and the lockup relay valve is provided between the third oil passage and the second oil passage. The lockup relay valve is configured to switch a communication destination of the third oil passage to any one of the first oil passage and the second oil passage. The pressure regulating valve is connected with the third oil passage. The pressure regulating valve is configured to regulate hydraulic pressure of the third oil passage. The pressure regulating valve includes a feedback port. The feedback port is configured to receive hydraulic pressure for moving the pressure regulating valve to a valve opening side. The feedback port is connected with one of the first oil passage and the second oil passage. The pressure regulating valve is configured to discharge oil downstream when given hydraulic pressure is fed to the feedback port.

[0006] In a pressure regulating valve having a conventional structure, pipeline resistance of an oil passage becomes large when temperature is low. Therefore, even in a state where oil in the torque converter has leaked, hydraulic pressure is generated in the pressure regulating valve due to the pipeline resistance, and the hydraulic pressure makes the pressure regulating valve open, thus allowing oil to be discharged downstream. In short, in the pressure regulating valve having the conventional structure, it takes time to fill the torque converter with oil. On the contrary, in the control circuit according to the invention, the pressure regulating valve is provided with the feedback port connected with a first oil passage and a second oil passage, and, unless given hydraulic pressure is fed from the feedback port, the pressure regulating valve does not discharge oil downstream. Therefore, even when temperature is low, oil is not discharged from the pressure regulating valve unless the torque converter is filled with oil. Thus, it is possible to improve filling speed of oil to be filled in the torque converter. Further, it is not necessary to provide an electric oil pump and so on for oil filling in order to improve filling speed of oil. In addition, it is only required to provide the feedback port of the pressure regulating valve, and the first oil passage or the second oil passage connected with the feedback port, thereby making the structure simple. [0007] The pressure regulating valve may include an input port, a discharge port, an elastic body and a receiving port. The input port is connected with the third oil passage. The discharge port is configured to be communicated with the input port and discharge oil downstream, when the pressure regulating valve regulates pressure of the third oil passage. The elastic body is configured to bias the pressure regulating valve to a valve closing side. The receiving port is connected with the third oil passage. The receiving port is configured to receive hydraulic pressure for moving the pressure regulating valve to the valve opening side. In the pressure regulating valve in the control circuit written above, the receiving port and the feedback port are provided. Therefore, compared to a control circuit without the feedback port, force applied in a direction for moving the pressure regulating valve to the regulating side becomes larger. The pressure regulating valve is structured so as not to discharge oil unless the given hydraulic pressure is fed to the feedback port. In the case where the pressure regulating valve is provided with the elastic body, biasing force of the elastic body for biasing the pressure regulating valve to the non-regulating side becomes large in order to resist the force in the direction for moving the pressure regulating valve to the regulating side. Therefore, even if oil temperature is low when a vehicle starts, the pressure regulating valve does not operate to the regulating side, and it is thus possible to improve filling speed of oil to be filled in the torque converter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG 1 is a skeleton view explaining a structure of a vehicle driving device to which the present invention is suitably applied; and

FIG. 2 is a view showing a hydraulic control circuit that controls the vehicle driving device in FIG. 1, especially a structure around the hydraulic control circuit that controls a lockup clutch of a torque converter.

DETAILED DESCRIPTION OF EMBODIMENTS

[0009] An example of the invention is explained below in detail with reference to the drawings. In the example below, the drawings are simplified or modified as appropriate, and a dimensional ratio, a shape and so on of each part are not always accurate. [0010] FIG. 1 is a skeleton view explaining a structure of a vehicle driving device 10 to which the invention is applied. The vehicle driving device 10 is a horizontal automatic transmission, is employed suitably for a FF (front engine/front drive) vehicle, and is provided with an engine 12 as a drive source for running. Output of the engine 12, which is structured by an internal combustion engine, is transmitted from a crankshaft of the engine 12 and a torque converter 14 serving as a fluid transmission device to a differential gear mechanism 22 through a steering reverser 16, a belt-type continuously variable transmission (CVT) 18, and a mechanical reduction gear 20, and then distributed to left and right driving wheels 24 L, 24R.

[0011] The torque converter 14 is provided in a power transmission route between the engine 12 and the driving wheels 24, includes a pump impeller 14p, a turbine impeller 14t, and a stator impeller 14s, and transmits power through fluid. The pump impeller 14p is connected with the crankshaft of the engine 12, and the turbine impeller 14t is connected with the steering reverser 16 through a turbine shaft 34 corresponding to an output side member of the torque converter 14. The stator impeller 14s is inserted between the pump impeller 14p and the turbine impeller 14t, and connected with a non-rotary member through a one-way clutch. A lockup clutch 26 is also provided between the pump impeller 14p and the turbine impeller 14t. The lockup clutch 26 is engaged (fastened) or released as hydraulic pressure feed for an engagement side oil chamber 29 and a release side oil chamber 30 is switched by a lockup relay valve 74 and so on inside a hydraulic control circuit 60 (FIG. 2). As the lockup clutch 26 is engaged completely, the pump impeller 14p and the turbine impeller 14t are rotated integrally. Thus, the lockup clutch 26 directly and selectively connects input and output of the torque converter 14 (the pump impeller 14p and the turbine impeller 14t) with each other. A mechanical oil pump 28 is connected with the pump impeller 14p. Driven and rotated by the engine 12, the oil pump 28 generates hydraulic pressure for controlling gear change of the continuously variable transmission 18, generating belt clamping force, controlling engagement and release of the lockup clutch 26, and feeding lubricant oil to each part. The pump impeller 14p is connected with the engine 12 through the crankshaft. Therefore, the oil pump 28 is driven with rotation of the engine 12.

[0012] The steering reverser 16 is structured mainly by a forward clutch CI, a reverse brake Bl, and a double pinion type planetary gear 16p. The turbine shaft 34 of the torque converter 14 is connected integrally with a sun gear 16s, and an input shaft 36 of the continuously variable transmission 18 is connected integrally with a carrier 16c. On the other hand, the carrier 16c and the sun gear 16s are connected with each other selectively through the forward clutch CI. A ring gear 16r is selectively fixed to a housing through the reverse brake Bl. The forward clutch CI and the reverse brake Bl correspond to intermittent devices, and are both hydraulic frictional engagement devices that are frictionally engaged by a hydraulic actuator.

[0013] Once the forward clutch CI is engaged and the reverse brake Bl is released, the steering reverser 16 rotates integrally. At this time, the turbine shaft 34 is connected directly with the input shaft 36. Thus, a forward power transmission route is established (achieved), and drive power in a forward direction is transmitted to the continuously variable transmission 18 side. When the reverse brake Bl is engaged and the forward clutch CI is released, the steering reverser 16 establishes (achieves) a backward power transmission route. At this time, the input shaft 36 is rotated in an opposite direction with respect to the turbine shaft 34, and drive power in a backward direction is transmitted to the continuously variable transmission 18 side. When both the forward clutch CI and the reverse brake Bl are released, the steering reverser 16 becomes a neutral state (a power transmission interrupted state) in which power transmission is interrupted.

[0014] The continuously variable transmission 18 is provided with a driving side pulley (a primary pulley) 42, which serves as an input side member provided in the input shaft 36 and has a variable effective diameter, a driven side pulley (a secondary pulley) 46, which serves as an output side member provided in an output shaft 44 and has a variable effective diameter, and a transmission belt 48 wound around the variable pulleys 42, 46. Power is transmitted through frictional force between the variable pulleys 42, 46 and the transmission belt 48.

[0015] The variable pulleys 42 and 46 are structured by including fixed variable rotors 42a and 46a, which are fixed to the input shaft 36 and the output shaft 44, respectively, movable rotors 42b and 46b, which are provided so as not to rotate about axes of the input shaft 36 and the output shaft 44 and so as to move along the axis direction, and a driving side hydraulic actuator (a primary pulley side hydraulic actuator) 42c and a driven side hydraulic actuator (a secondary pulley side hydraulic actuator) 46c, which serve as hydraulic actuators that give thrust to change widths of V-shaped grooves between the fixed variable rotors 42a and 46a, and the movable rotors 42b and 46b, respectively. As feeding and discharging flow rates of hydraulic oil for the driving side hydraulic actuator 42c are controlled by the hydraulic control circuit, the widths of the V-shaped grooves of the variable pulleys 42, 46 change, thereby changing a winding diameter (an effective diameter) of the transmission belt 48. Thus, a change gear ratio γ (= input shaft rotation speed Nin / output shaft rotation speed Nout) is changed continuously. Pressure regulation of belt clamping pressure Pd, which is hydraulic pressure of the driven side hydraulic actuator 46c, is controlled by the hydraulic control circuit. Thus, the transmission belt 48 is controlled so as not to slip.

[0016] FIG. 2 is a view of the hydraulic control circuit 60 that controls the vehicle driving device 10, especially showing the structure around the hydraulic control circuit 60, which controls the lockup clutch 26 of the torque converter 14.

[0017] The hydraulic control circuit 60 is structured by including the oil pump 28, a primary regulator valve 64, a secondary regulator valve 70, a lockup control valve 72, and the lockup relay valve 74. The oil pump 28 sucks up and discharges oil stored in an oil pan 62, and is driven by the engine 12. The primary regulator valve 64 (herein after, referred to as a primary valve 64) regulates pressure of oil discharged from the oil pump 28 to first line pressure PL, and is a relief valve. The secondary regulator valve 70 (herein after, referred to as a pressure regulating valve 70) regulates pressure of oil, which is discharged from the primary valve 64 for pressure regulation, to second line pressure Psec (herein after, referred to as secondary pressure Psec), and is a relief valve. The lockup control valve 72 (herein after, referred to as a control valve 72) controls engagement pressure of the torque converter 14. The lockup relay valve 74 (herein after, referred to as a relay valve 74) changes over between oil passages communicated with the engagement side oil chamber 29 and the release side oil chamber 30 of the torque converter 14. The oil passage, to which hydraulic pressure discharged from the primary valve 64 is supplied, is branched into an oil passage connected with the pressure regulating valve 70 and an oil passage connected with the torque converter 14. An oil passage 68 from the pressure regulating valve 70 to the relay valve 74 is an example of a third oil passage of this invention, and oil passages 112 and 84 connecting the relay valve and the torque converter 14 are examples of a first oil passage and a second oil passage, respectively.

[0018] The primary valve 64 is controlled by control pressure outputted form a linear solenoid valve (not shown), and regulates hydraulic pressure discharged from the oil pump 28 as source pressure so that the oil passage 68 has first line pressure PL in accordance with a running state of a vehicle. Similarly, the pressure regulating valve 70 regulates hydraulic pressure discharged from the primary valve 64 as source pressure so that the oil passage 68 has the secondary pressure Psec in accordance with a running state of the vehicle. [0019] The pressure regulating valve 70 is a relief type pressure regulating valve, which is provided so as to reduce hydraulic pressure of the oil passage 68 so that the hydraulic pressure in the oil passage 68 does not exceed a given value. The pressure regulating valve 70 is connected with an input port 81, which is connected with the oil passage 68, and with the lubricant oil passage 88. The pressure regulating valve 70 is structured by including a discharge port 82, a spool valve piece (not shown), a spring 80, a first port 83, and a second port 86. The discharge port 82 is communicated with the input port 81 as required when pressure is regulated. The spool valve piece switches a communicating state between the input port 81 and the discharge port 82. The spring 80 biases the spool valve piece to a non-regulating side (a valve closing side). The first port 83 is connected with the oil passage 68, and receives hydraulic pressure for moving (switching) the spool valve piece to a regulating side (a valve opening side). The second port 86 connects the relay valve 74 and the torque converter 14 with each other, is connected with the later-described engagement side oil passage 112 communicating with the engagement side oil chamber 29 of the torqiie converter 14, and receives hydraulic pressure for moving (switching) the spool valve piece to the regulating side (valve opening side). In the pressure regulating valve 70, when hydraulic pressure of the oil passage 68 is regulated, the input port 81 and the discharge port 82 are communicated with each other. In short, the pressure regulating valve 70 is opened. Operation of the pressure regulating valve 70 to the valve opening side is referred to as operation to the regulating side, and operation to the valve closing side is referred to as operation to the non-regulating side (non operating side). The spring 80 is an example of an elastic body of the invention, the first port 83 is an example of a receiving port of the invention, and the second port 86 is an example of a feedback port of the invention.

[0020] In the pressure regulating valve 70, biasing force of the spring 80 to bias the spool valve piece to the valve closing side is referred to as Fl. Pressing force of hydraulic pressure supplied from the first port 83 for switching (moving) the spool valve piece to the valve opening side is referred to as F2. Pressing force of hydraulic pressure supplied from the second port 86 for switching (moving) the spool valve piece to the valve opening side is referred to as F3. When Fl is larger than the sum of F2 and F3 (Fl > F2 + F3), the spool valve piece is moved to the valve closing side (the non-regulating side). When the spool valve piece closes the valve, communication between the input port 81 and the discharge port 82 is interrupted, and oil in the oil passage 68 is not discharged from the discharge port 82. [0021] Meanwhile, in the pressure regulating valve 70, when Fl is smaller than the sum of F2 and F3 (Fl < F2 + F3), the spool valve piece is moved to the valve opening side. When the spool valve piece opens the valve, the input port 81 and the discharge port 82 are communicated with each other, and oil in the oil passage 68 is thus discharged from the discharge port 82. Oil discharged from the discharge port 82 passes through the lubricant oil passage 88 and is fed to various lubricating parts 90 of the vehicle driving device 10.

[0022] The pressure regulating valve 70 is structured to be open when given hydraulic pressure, which is set in advance, is fed to the first port 83, with which the oil passage 68 is connected, and the second port 86, with which the release side oil passage 84 is connected. To be specific, rigidity of the spring 80, a pressure receiving area Al of an oil chamber (not shown) to which hydraulic pressure of the oil passage 68 is fed through the first port 83, a pressure receiving area A2 of an oil chamber (not shown) to which hydraulic pressure of the release side oil passage 84 is fed through the second port 86, and so on are designed to have necessary values.

[0023] The control valve 72 (a lockup control valve 72) regulates the secondary pressure Psec as source pressure to control pressure Pcont that is fed to the lockup clutch 26. The control valve 72 is structured by including an input port 92 connected with the oil passage 68, an output port 94, a spool valve piece (not shown), a spring 96, a control port 100, and a discharge port 102. The output port 94 is connected with the relay valve 74. The spool valve piece controls a communicating state between the input port 92 and the output port 94. The spring 96 biases the spool valve piece to a side on which the input port 92 and the output port 94 are communicated with each other. Signal pressure Pslu of a linear solenoid valve 98 is fed to the control port 100. The discharge port is connected with the oil pan 62.

[0024] In the control valve 72, the control pressure Pcont outputted from the output port 94 is controlled as appropriate by the signal pressure Pslu outputted from the linear solenoid valve 98. For example, in a case where the signal pressure Pslu is not outputted from the linear solenoid valve 98, the input port 92 and the output port 94 are communicated with each other, and the secondary pressure Psec is outputted from the output port 94 as the control pressure Pcont, When the signal pressure Pslu increases, communication between the input port 92 and the output port 94 is interrupted, and the output port 94 and the discharge port 102 are communicated with each other. At this time, the control pressure Pcont becomes zero. The control pressure Pcont decreases in proportion to the signal pressure Pslu of the linear solenoid valve 98. [0025] The relay valve 74 (the lockup relay valve 74) is provided in the oil passage 68 that connects the pressure regulating valve 70 and the torque converter 14 with each other, and functions as a changeover valve which changes a communication destination of the oil passage 68 to either the engagement side oil chamber 29 or the release side oil chamber 30. The relay valve 74 is structured by including a first input port 104, a second input port 106, a first output port 108, a second output port 110, a drain port 111, a spool valve piece (not shown), a spring 114, and a switching port 118. The control pressure Pcont outputted from the control valve 72 is inputted to the first input port 104. The secondary pressure Psec is fed to the second input port 106. The first output port 108 is connected with the release side oil passage 84 communicated with the release side oil chamber 30 of the lockup clutch 26. The second output port 110 is connected with the engagement side oil passage 112 communicated with the engagement side oil chamber 29 of the lockup clutch 26. The drain port 111 is connected with the oil pan 62. The spool valve piece switches a communicating state of the ports of the relay valve 74. The spring 114 biases the spool valve piece to the lockup clutch release side. Switching pressure Psl outputted from an on/off solenoid valve 116 is fed to the switching port 118, and the switching port 118 receives hydraulic pressure for switching the spool valve piece to a lockup clutch engagement side.

[0026] In the relay valve 74, in a case where the switching pressure Psl is not outputted from the on/off solenoid valve 116, the spool valve piece is moved to the lockup clutch release side (a side where lockup is off) by biasing force of the spring 114. In this case, as shown in FIG. 2, communication of the first input port 104 is interrupted, and the second input port 106 and the first output port 108 are communicated with each other. Further, the second output port 110 and the drain port 111 are communicated with each other.

[0027] Accordingly, the oil passage 68 is communicated with the release side oil chamber 30 through the relay valve 74 and the release side oil passage 84, and the secondary pressure Psec is fed to the release side oil chamber 30 of the lockup clutch 26. Further, since the second output port 110 and the drain port 111 are communicated with each other, the engagement side oil chamber 29 is connected with the drain port 111 through the engagement side oil passage 112. Thus, a pressure difference ΔΡ (= Pon - Poff) between hydraulic pressure Pon of the engagement side oil chamber 29 and hydraulic pressure Poff of the release side oil chamber 30, which corresponds to the engagement pressure of the lockup clutch 26, becomes a negative value, and the lockup clutch 26 becomes a release state. [0028] In this case, hydraulic pressure of the engagement side oil passage 112 becomes low. Therefore, in the pressure regulating valve 70, Fl becomes larger than the sum of F2 and F3 (Fl > F2 + F3), and the pressure regulating valve 70 is thus closed.

[0029] On the other hand, in the relay valve 74, when the switching pressure Psl is outputted from the on/off solenoid valve 116, and the switching pressure Psl is fed to the switching port 118, the spool valve piece (not shown) is moved to the lockup clutch engagement side (a side where lockup is on) against the biasing force of the spring 114. In this case, the first input port 104 and the first output port 108 are communicated with each other, and the second input port 106 and the second output port 110 are communicated with each other.

[0030] Accordingly, the oil passage 68 is communicated with the engagement side oil chamber 29 through the relay valve 74 and the engagement side oil passage 112, and the secondary pressure Psec is fed to the engagement side oil chamber 29 of the lockup clutch 26 through the relay valve 74 and the engagement side oil passage 112. Further, the control pressure Pcont, which is controlled by the control valve 72, is fed to the release side oil chamber 30 of the lockup clutch 26 through the relay valve 74 and the release side oil passage 84. Then, since the pressure difference ΔΡ (= Pon - Poff) of the lockup clutch 26 becomes a pressure difference (= Psec - Pcont) between the secondary pressure Psec and the control pressure Pcont, the engagement pressure of the lockup clutch 26 is controlled by the control pressure Pcont.

[0031] For example, in a case where the signal pressure Pslu is not outputted from the linear solenoid valve 98, the control pressure Pcont becomes the secondary pressure Psec. Thus, the engagement pressure (pressure difference ΔΡ) of the lockup clutch 26 becomes zero, making the lockup clutch 26 into a substantially release state. Since the control pressure Pcont is reduced as the signal pressure Pslu increases, the pressure difference ΔΡ (= Pon - Poff (Pcont)) becomes large. In other words, the lockup clutch 26 is slip engaged. Then, once the signal pressure Pslu exceeds a given value, the lockup clutch 26 is engaged completely.

[0032] When the relay valve 74 is switched to the side where the lockup is on, the secondary pressure Psec is fed to the engagement side oil passage 112. Thus, the secondary pressure Psec is also fed to the second port 86 of the pressure regulating valve 70. Therefore, Fl becomes smaller than the sum of F2 and F3 (Fl < F2 + F3), and the pressure regulating valve 70 is thus opened. In short, the input port 81 and the discharge port 82 are communicated with each other, and oil is discharged from the discharge port 82. [0033] Immediately after a vehicle is stopped, oil is filled in the torque converter. However, after leaving the vehicle for a long period of time, oil leaks from the sealing part and so on gradually, and could cause an insufficient amount of oil filled in the torque converter. When the vehicle is started in this state, time is required to fill the torque converter with oil. Therefore, when an accelerator pedal is depressed, there could be a delay in start of a vehicle. It is also possible that a vehicle could start suddenly once oil is filled. Therefore, at the time of start of a vehicle, it is necessary to fill the torque converter with oil swiftly.

[0034] Conventionally, there has been no second port 86 of the pressure regulating valve 70, which receives hydraulic pressure of the engagement side oil passage 112 communicated with the engagement side oil chamber 29 of the lockup clutch 26. Even in the case where the second port 86 is not provided, no hydraulic pressure of the oil passage 68 is generated normally unless oil is filled in the torque converter 14. Therefore, the pressure regulating valve 70 is not opened, and oil in the oil passage 68 is filled in the torque converter through the relay valve 74 and the release side oil passage 84. When a vehicle starts, the lockup clutch 26 is released. Therefore, the second input port 106 and the second output port 110 are communicated with each other, and oil in the oil passage 68 is fed into the torque converter through the relay valve 74 and the release side oil passage 84. However, when temperature of oil is low, oil viscosity becomes high and a pressure loss (pipeline resistance) inside the pipeline is increased. Therefore, even when the torque converter is not filled with oil, hydraulic pressure of the oil passage 68 is generated, and the pressure regulating valve 70 is opened, thereby causing a delay in filling of oil in the torque converter.

[0035] On the other hand, in this example, the pressure regulating valve 70 is further provided with the second port 86 that is connected with the engagement side oil passage 112 and receives hydraulic pressure of the engagement side oil passage 112, thereby preventing the pressure regulating valve 70 from operating when a vehicle starts. As stated above, in the pressure regulating valve 70, when the biasing force Fl of the spring 80, which biases the spool valve piece to the valve closing side, is smaller than the sum (F2 + F3) of the pressing force F2 by hydraulic pressure fed from the first port 83 for switching the spool valve piece to the valve opening side, and pressing force F3 by hydraulic pressure fed from the second port 86 for switching the spool valve piece to the valve opening side, the spool valve piece is moved to the valve opening side. In short, the pressure regulating valve 70 operates and oil in the oil passage 68 is discharged from the discharge port 82. [0036] When a vehicle starts, the oil passage 68 is connected with the engagement side oil passage 112 through the relay valve 74 and the torque converter 14. Therefore, strictly speaking, when hydraulic pressure fed to the first port 83 is hydraulic pressure PI, hydraulic pressure P2, which is lower than the hydraulic pressure PI, is fed to the second port 86. This is caused by a pipeline loss of the oil passage 68 and a loss due to throttle when oil passes through the relay valve 74. Therefore, in the pressure regulating valve 70, when a pressure receiving area of the oil chamber (not shown), to which hydraulic pressure is fed from the first port 83 of the pressure regulating valve 70, is regarded as an area Al, and a pressure receiving area of an oil chamber (not shown), to which hydraulic pressure is fed from the second port 86, is regarded as an area A2, total pressing force Ftotal, which moves the spool valve piece of the pressure regulating valve 70 to the valve opening side, is the sum (= PI x Al + P2 x A2) of the product (= PI x Al) of the hydraulic pressure PI and the pressure receiving area Al, and the product (= P2 x A2) of the hydraulic pressure P2 and the pressure receiving area A2. Once the total pressing force Ftotal becomes larger than the biasing force Fl of the spring 80, the pressure regulating valve 70 is opened. Thus, when the pressure regulating valve 70 is opened, the following formula (1) is established. The given hydraulic pressure PI (the given value) and the given hydraulic pressure P2 are set in advance to values that do not deteriorate durability of the hydraulic control circuit 60.

Fl = Pl x Al + P2 x A2 ... (1)

[0037] Conventionally, since the second port 86 is not provided, the following formula (2) is established. The given hydraulic pressure PI is set to the same value in the formula (1) and the formula (2). Therefore, the biasing force Fl in this example is larger than conventional biasing force Fl'. Therefore, the biasing force Fl of the spring 80 in the pressure regulating valve 70, in other words, rigidity of the spring 80, is set higher than the conventional case where the second port 86 is not provided.

Fl' = Pl x Al ... (2)

[0038] Hence, the biasing force Fl of the spring 80 is larger than the conventional biasing force Fl', and, when a vehicle starts with low oil temperature, the pressure regulating valve 70 is not opened until oil is filled in the torque converter 14 and hydraulic pressure fed to the second port 86 is increased to the given hydraulic pressure P2. Therefore, oil in the oil passage 68 is fed entirely to the torque converter 14. Thus, a filling speed of oil to be filled in the torque converter is improved. The given hydraulic pressure P2 corresponds to the given hydraulic pressure fed to the feedback port according to the invention. [0039] As stated above, in a pressure regulating valve having a conventional structure, pipeline resistance increases when temperature is low. Therefore, even in a state where oil in the torque converter has leaked, hydraulic pressure is generated in the pressure regulating valve due to pipeline resistance, and the pressure regulating valve is opened by the hydraulic pressure. Then, oil is discharged downstream from the pressure regulating valve, and filling of oil in the torque converter thus takes time. On the contrary, the second port 86, which is connected with the engagement side oil passage 112 communicated with the engagement side oil chamber 29, is added to the pressure regulating valve 70. Therefore, unless the given hydraulic pressure P2 is fed from the second port 86, oil is not discharged from the pressure regulating valve 70. Hence, even when temperature is low, oil is not discharged from the pressure regulating valve 70 unless the torque converter 14 is filled with oil, thereby improving filling speed of oil to be filled in the torque converter 14. Also, in improving the filling speed of oil, an electric oil pump and so on for oil filling are not needed, and, only the second port 86 of the pressure regulating valve 70 and the oil passage that is connected with the second port 86 are required. Therefore, the structure is simple.

[0040] According to the example, the pressure regulating valve 70 is provided with the first port 83 and the second port 86. Therefore, compared to a case without the second port 86, force that acts on the side for switching the pressure regulating valve 70 to the regulating side becomes larger. Since the pressure regulating valve 70 is structured so as not to discharge oil unless the given hydraulic pressure is fed to the second port 86, biasing force of the spring 80 for biasing the pressure regulating valve 70 to the non-regulating side also becomes larger so as to resist the force. Therefore, even if oil temperature is low when a vehicle starts, the pressure regulating valve 70 does not operate toward the regulating side, thereby improving filling speed of oil to be filled in the torque converter 14.

[0041] The example of the invention has been explained in detail based on the drawings. However, the invention is also applied in other forms.

[0042] For example, in the foregoing example, the second port 86 is connected with the engagement side oil passage 112. However, the invention is not limited to this, and the second port 86 may be connected with the release side oil passage 84. In the case where the second port 86 is communicated with the release side oil passage 84, the secondary pressure Psec is fed to the release side oil passage 84 in a state where the relay valve 74 is switched to the side where the lockup is off. Therefore, the biasing force Fl of the spring 80, which biases the spool valve piece to the valve closing side, becomes smaller than the sum (F2 + F3) of the pressing force F2 by hydraulic pressure fed from the first port 83 for switching the spool valve piece to the valve opening side, and the pressing force F3 by hydraulic pressure fed from the second port 86 (the engagement side oil passage 112) for switching the spool valve piece to the valve opening side (Fl < F2 + F3). Thus, the pressure regulating valve 70 is opened. In other words, the input port 81 ad the discharge port 82 are communicated with each other, allowing oil to be discharged from the discharge port 82.

[0043] In the foregoing example, secondary pressure Psec is fed to the oil passage 68. However, line pressure PL or hydraulic pressure regulated by other valve may be fed.

[0044] In the foregoing example, the hydraulic pressure of the oil passage 68 is fed to the second port 86 of the pressure regulating valve 70 through the relay valve 74. However, the invention is not limited to this. For example, in a case where the control valve 72 is arranged on the side closer to the torque converter 14 than the relay valve 74, the oil passage 68 may be connected with the second port 86 of the pressure regulating valve 70 through the control valve 72. In other words, the hydraulic control circuit that controls engagement pressure of the lockup clutch 26 is not limited to the example, and may have any structure as long as an oil passage, which fills oil in the torque converter 14 when a vehicle starts, is connected with the second port 86 of the pressure regulating valve 70.

[0045] In the foregoing example, the continuously variable transmission 18 is provided as the driving device 10. However, the invention may be applied to, for example, a driving device having a stepped automatic transmission. The invention may be applied as necessary to any vehicle provided with a torque converter.

[0046] The foregoing is one of embodiments only, and the invention may be carried out in forms to which various changes and improvements are added based on knowledge of a person skilled in the art.