Hydraulic control device for an automatic transmission

Abstract: A primary regulator valve has a cutback port which regulates a line pressure to increase, at the first speed of D range, a thro­ ttle pressure is applied to the cutback port through a cutback valve. The primary regulator valve sets the line pressure from a line pressure port higher. The cutback valve has a spool which is compressed in one direction. A first control chamber which is connected to a hydraulic servo (for example, a second brake hydraulic servo) which hydraulic pressure is applied at more than the second speed is formed against the pressing direction, a second control chamber which is connected to a hydraulic servo (for example, a second-coast brake hydraulic servo) to limit a coasting condition of the second speed is so formed as to follow the above pressing direction. At the second speed of second range, the cutback valve, as the first speed of D range, the throttle pressure is applied to the cutback port. Furthermore, the primary regulator valve has a control chamber which regulates the line pressure to decrease. A pressure control valve (for example, a linear solenoid valve to control a lock-up clutch) is connected to the control chamber to reduce the line pressure when a manual valve is selected from N range to D or R range.

Description: The present invention relates generally to a hydraulic control device for an automatic transmission, which may be mounted on an automobile, and relates more particularly to a line pressure control device and the structure of a primary regulator valve and a cutback valve. Conventionally, a hydraulic control device for an automatic transmission mounted on an automobile has a cutback valve. The cutback valve has a control chamber to which hydraulic pressure is applied at the or more than second speed, an input port to which a throttle pressure is applied, and an output port which applies the input pressure to a throttle valve as a cutback pressure. When operating at the first speed, because hydraulic pressure is not applied to the second brake hydraulic servo, the input port and the output port of the cutback valve are disconnected, so that the cutback valve applies no cutback pressure to the throttle valve. Under this condition, because no cutback pressure is applied to the throttle valve at the spool return side, the throttle valve makes the line pressure a comparatively high throttle pressure. This high throttle pressure is applied to the primary regulator valve, so that the line pressure is set comparatively high, and a high clutch engaging force is generated corresponding to a high load torque at starting. At the second speed, hydraulic pressure is applied to the second brake hydraulic servo, so that the input port and the output port of the cutback valve are switched to be connected, and the cutback pressure is applied to the throttle valve. Under this condition, the throttle valve is applied with the cutback pressure at the spool return side, so that a comparatively low throttle pressure is generated, and is applied to the primary regulator valve. As a result, the line pressure is set to be low, so that the engaging force of clutch and brake is low to prevent shift shock. With regard to the above line pressure control, as explained, the cutback pressure is applied to the throttle valve. Consequently, in the throttle valve at a top end of the spool, a spring from a downshift plug is applied, while at a bottom end of the spool, a return spring is applied. Furthermore, the throttle valve has three areas on the spool: an area to regulate the line pressure to the throttle pressure; a first step area where a feedback pressure caused by the throttle pressure is applied; and a second step area where the cutback pressure is applied. Due to this arrangement, the spool has a three-stage structure. Such a three-stage structure makes the throttle valve more complicated because the throttle valve normally has a downshift plug and a throttle cam having a power-to-assist mechanism. Thus, forming the valve is intricate and laborious, and the cross-section areas of the step areas may be small. Consequently, the hydraulic response is not sufficient, and furthermore, the structure is complicated and the average diameters of the spool may be small, so that valve sticking caused by foreign materials may easily occur. At the second range, the cutback valve is in the connected condition at the second speed, so that the line pressure is set to be comparatively low. Consequently, in the case that a vehicle tries to get out of a tyre rut or start on a snowy road, the line pressure is comparatively low even from second speed starting, so that the engaging force of the frictional engaging elements is insufficient, and efficient starting is not performed. Generally, with regard to an automobile having an automatic transmission, when a selection lever is operated from the neutral N to the drive D or the reverse R range, the line pressure is applied to a hydraulic servo of a certain frictional engaging element, the certain frictional engaging element (a forward clutch, a direct clutch and a first & reverse brake) is suddenly engaged, and a so-called selecting shock may occur. Aims of the present invention are: to apply a cutback pressure from a cutback valve to a primary regulator valve to enhance response of the line pressure control and reliability; to simplify the structure of the primary regulator valve to prevent valve sticking; to apply the cutback pressure at the second speed of the second range as well as the first speed to enable starting from the second speed condition; and to control the primary regulator valve to prevent selection shocks when shifting not only from the N to D range but also from the N to R range without adding any special devices. A hydraulic control device for an automatic transmission is known from EP-A-0209075 - in which a primary regulator valve has not only a throttle pressure port to modulate the line pressure according to the engine torque but also a port to increase the line pressure if the line pressure acts as a clutch. According to the present invention, however, a hydraulic control device for an automatic transmission comprises: hydraulic fluid servos for clutch and brake engagement and release of elements of a transmission gear mechanism; a hydraulic fluid circuit for supplying line pressure to said hydraulic fluid servos; a primary regulator valve connected to said hydraulic fluid circuit for regulating the line pressure supplied to the hydraulic fluid servos, and having a cutback pressure port for receiving a cutback pressure at a predetermined transmission speed and a throttle pressure port for receiving a throttle pressure; an output-responsive valve connected to said hydraulic fluid circuit for modulating the line pressure to a throttle pressure corresponding to the torque of an engine for driving the automatic transmission, said output-responsive valve having a throttle pressure outlet connected to said throttle pressure port of said primary regulator valve for supplying throttle pressure for regulating the line pressure in response to the engine torque; and a cutback valve connected between the throttle pressure outlet of said output-responsive valve and said cutback pressure port of said primary regulator valve and is operable in response to a predetermined transmission speed for supplying a cutback pressure to said primary regulator valve at the predetermined transmission speed to increase the line pressure, whereby the primary regulator valve regulates the line pressure so as to increase the line pressure at the predetermined transmission speed in response to both the throttle pressure and the cutback pressure. Preferably, said output-responsive valve is a throttle valve which operates in response to a throttle opening ratio, and said cutback valve is switched to disconnect its input and output ports by hydraulic pressure which is applied to a certain hydraulic servo at more than second speed of forward running. Said primary regulator valve may comprise: a main spool, a sub spool and a plug which contact each other, whereby said main spool regulates said line pressure and regulates a converter hydraulic pressure which is applied to a secondary regulator valve, and one of a line pressure applied at reverse running, a hydraulic pressure responding to engine output applied from said output-responsive valve, and a cutback pressure from said cutback valve is respectively applied to one of one end of said plug, one end of said sub spool and a step section of said sub spool to increase said line pressure. Said cutback valve may comprise: a spool which is pressed in one direction, a first control chamber constituted against said pressing direction, a second control chamber constituted along with said pressing direction, an input port which is applied with said hydraulic pressure in response to engine output, an output port which applies said hydraulic pressure in response to engine output to said primary regulator valve, and a drain port, whereby a certain hydraulic servo to which hydraulic pressure is applied at the or more than second speed is connected to said first control chamber, and a brake hydraulic servo which limits a coasting condition at said second speed is connected to said second control chamber so that said line pressure is set higher when coasting is limited at said second speed same as at said first speed. Preferably, said cutback valve further comprises a spring which is compressedly situated at one end of said spool, said first control chamber being constituted at another end of said spool, and said second control chamber being constituted at said one end of said spool and housing said spring. In a preferred embodiment, described in more detail hereinafter, there is a hydraulic control device for an automatic transmission having hydraulic servos for a clutch and a brake which engage and release certain elements of a transmission gear mechanism, a primary regulator valve which regulates the line pressure applied to the servos, an output-responsive valve (for example, a throttle valve), and a cutback valve which generates cutback pressure at a certain shifting stage. The primary regulator valve has a cutback port which regulates the line pressure to control its rise, and said port is connected to an output port of the cutback valve. At a certain shifting stage, an input port of the cutback valve and the output port are connected so that hydraulic pressure of the output-responsive valve is applied to the cutback port. Due to this operation, the primary regulator valve is regulated to raise the line pressure by a certain amount. The primary regulator valve also has a main spool, a sub spool and a plug. The main spool regulates the line pressure and connects to a secondary regulator valve to regulate a converter hydraulic pressure. To one end of the plug, to one end of the sub spool and to a step-section of the sub spool, are applied the line pressure for reverse running, an engine output-responsive pressure from the output-responsive valve and the cutback pressure from the cutback valve, respectively, to raise the line pressure. The cutback valve has a spool, one of whose ends is pressed by a spring, a first control chamber located at the end towards which the spool is pressed, a second control chamber located at the end from which the spool is pressed, an input port which is applied with the engine output-responsive pressure (for example, throttle pressure), an output port which applies the output-responsive pressure to the primary regulator valve, and a drain port. The first control chamber is connected to a certain hydraulic servo to which hydraulic pressure is applied at the or more than the second speed (for example, the second brake hydraulic servo) and the second control chamber is connected to a hydraulic servo to limit the coasting state of the second speed (the second-coast brake hydraulic servo). The line pressure is set to be rather high at the coast-limited state of the second speed as well as the first speed. The primary regulator valve has a control chamber which regulates the line pressure to reduce it, and said chamber receives a control pressure from the control valve. The pressure control valve is controlled by a signal from a sensor which detects a selected position of a manual valve, so that the control hydraulic pressure is applied to the chamber from the pressure control valve at the operation from the neutral range N to the drive range D, or the drive range D to the reverse range R. As one example, the pressure control valve is a linear solenoid valve which controls a lock-up clutch, and the control pressure from the valve is applied to the control chamber of the primary regulator valve through a solenoid relay valve. Furthermore, the solenoid relay valve is switched by the hydraulic pressure which is applied to a certain hydraulic servo (for example, the second brake hydraulic servo) at the or more than the second speed. Based on the above structure, at the first speed of the D range, for example, as no hydraulic pressure is applied to the second brake hydraulic servo, the cutback valve is at a left-half position due to the pressing force of the spring, and the input port and the output port are connected. At this stage, the output-responsive pressure from the output-responsive valve (throttle valve) is applied to the cutback pressure port of the primary regulator valve through the input port and the output port. Due to the application of pressure, in the primary regulator valve, the main spool and the sub spool are moved downward as a left-half position, so that the drain port is about to be closed to set the line pressure at the line pressure port rather high. At the second speed of the D range, however, as hydraulic pressure is applied to the second brake hydraulic servo, the pressure is applied to the first control chamber, and thus the cutback valve is switched to a right-half position, the output port and the input port are disconnected, and the output port is connected to the drain port. No hydraulic pressure is applied to the cutback pressure port, the primary regulator valve is kept under the right-half position, and the line pressure port and the drain port are connected so that the line pressure is caused to be rather low. With reference to the primary regulator valve, the output-responsive pressure (throttle pressure) is applied to a port, the main spool is pressed downward through the sub spool, while a feedback pressure separate from the line pressure is applied to a lower control chamber, thus these two hydraulic pressures are balanced to determine the line pressure. In addition to the balance of these pressures, due to the cutback pressure at the cutback port, the line pressure is made to be high. In the case that the manual valve is selected to the reverse range R, the line pressure is applied to a port of the manual valve, and the line pressure is applied to an inlet port of the primary regulator valve. Because of this, the main spool is pressed downward through the plug and the sub spool, so that the line pressure is set to be higher than in the case when the cutback pressure is being applied. When the manual valve is selected to the second range, at the second speed, the line pressure is applied to the second-coast brake hydraulic servo, and thus the line pressure is applied to the second control chamber of the cutback valve. In this state, although the line pressure is applied to the first control chamber, by the spring the cutback valve is in the left-half position, so the input port and the output port are connected. Then, the cutback pressure is applied to the primary regulator valve so that the line pressure is set to be high as at the first speed. Due to this condition, a strong engaging force acts on the frictional engaging elements, so that starting from the second speed is effectively performed. On the other hand, when a driver shifts the manual valve from the neutral range N to the drive range D or the reverse range R, a control unit generates a certain signal based on the sensor which senses the position of the manual valve. By the signal, the control valve (for example, the lock-up solenoid valve) operates, and a certain hydraulic pressure is applied to the control chamber of the primary regulator valve. The line pressure port is connected to the drain port at a certain flow-through ratio. Consequently, the hydraulic pressure to each hydraulic servo is reduced, so that selecting shock at the selecting operation is lightened. Incidentally, with regard to the control to reduce the line pressure based on the pressure control valve, one possible idea is that pressure is reduced simultaneously with the selecting operation of the manual valve (from N range to D range, or from N range to R range), and after that the pressure gradually rises so that the pressure comes to normal hydraulic pressure after a certain time by a timer-control to lighten only a selecting shock. Another possible idea is that the pressure reduced condition is kept until signals generated by the throttle sensor and the like at starting are sent to the control unit, and then the pressure reduced condition is released by the starting signal to prevent not only the selecting shock but also creeping which occurs during the selecting operation. In the drawings: FIG. 1 is a hydraulic circuit diagram of a line pressure control device according to the present invention; FIG. 2 is a cross-sectional view of an automatic transmission to which the present invention is applied; FIG. 3 is a schematic representation of the automatic transmission; FIG. 4 is a hydraulic circuit diagram of the automatic transmission; and FIG. 5 is a table of operation showing the operation of solenoid valves, clutches, brakes and one-way clutches at each shifting position. The present invention will now be explained along with the drawings. An automatic transmission 1, as shown in FIGS. 2 and 3, has a torque converter 2, a planetary transmission gear mechanism 3 and a hydraulic control device 5 which are housed in a converter housing 6, a transmission case 7, an extension housing 9, a valve body 10 and an oil pan 11. The torque converter 2 has a lock-up clutch 12, so that rotation of an input member 13 is transmitted to an input shaft 15 of the transmission gear mechanism 3 through hydraulic flow of the torque converter 2 or the lock-up clutch 12. The gear mechanism 3 comprises an over-drive planetary gear unit 17 and a main transmission unit 21 including a front planetary gear unit 19 and a rear planetary gear unit 20. The over-drive planetary gear unit 17 comprises a planetary pinion 22, a carrier 24 which is directly connected to the input shaft 15 and supports the pinion 22, a sun gear 23 which encloses the input shaft 15, and a ring gear 25 which is connected to an input shaft 26 of the main transmission mechanism 21. An over-drive direct clutch CO and a one-way clutch FO are situated between the carrier 24 and the sun gear 23, and an over-drive brake BO is situated between the sun gear 23 and the case 7. The front planetary gear unit 19 comprises a planetary pinion 28, a carrier 29 which is directly connected to an output shaft 27 and supports the pinion 28, a sun gear 30a which encloses the output shaft 27 and is constituted integrally with a sun gear 30b of the rear planetary gear unit 20, and a ring gear 31 which is connected to the input shaft 26 through a forward clutch C1. A direct clutch C2 is situated between the input shaft 26 and the sun gear 30, a second-coast brake B1 composed of a band brake is situated between the sun gear 30 and the case 7, and a one-way clutch F1 and a second brake B2 are radially situated between the sun gear 30 and the case 7. The rear planetary gear unit 20 comprises a planetary pinion 32, a carrier 33 which supports the pinion 32, the sun gear 30b, and a ring gear 35 which directly connects to the output shaft 27. A first & reverse brake B3 and a one-way clutch F2 are situated radially between the carrier 33 and the case 7. Incidentally, 36 in FIG. 2 is an oil pump. As shown in FIG. 2, with regard to the over-drive planetary gear unit 17, the one-way clutch FO is situated between a boss 23a of the sun gear 23 and a sleeve 24a of the carrier 24. A flange member 40 which constitutes a cylinder extends from the boss 23a. The flange member 40 encloses a piston member 41 to form a hydraulic actuator of the clutch CO, the over-drive direct clutch CO being situated between the sleeve 24a and an inner surface of the flange 40. The over-drive brake BO is situated between an outer surface of the flange 40 and the case 7. Furthermore, a brim 42 is fixed on a peripheral part of the flange 40. A non-contacting type sensor 45 such as one employing light or magnetism and the like is situated on the case 7 so that the sensor 45 faces plural through holes or slits which are formed in the brim 42. The sensor 45 is situated to detect the rotational speed of the input shaft 15, in other words, to detect the rotational speed of the brim 42 which rotates together with the input shaft 15 at the first, second and third speeds when the clutch CO is engaged. A speed sensor 46 which detects vehicle speed is situated in the extension case 9. Signals of the sensors 45 and 46 and other sensors are sent to a control unit C to control solenoid valves S1, S2, S3 and S4 which are explained later. A selection (gear) lever, an accelerator pedal, a brake pedal and so on are arranged at a driver's seat (not shown). The selection lever is connected to and operates on a manual valve 51 (see FIG. 4), which will be explained hereinafter, to shift to each range such as neutral N, drive D, reverse R, second 2, low L and parking P. Among shifting operations, the operations from N to D and R ranges are sensed by a position sensor 47 (see FIG. 1). The accelerator pedal is connected to a throttle and a throttle valve 53 (see FIG. 4) through wires. The opening ratio of the throttle is sensed by a throttle sensor 49. The throttle sensor 49 is a starting sensor which senses the starting operation of the driver. However, another sensor, for example, a sensor sensing the releasing operation of the brake pedal, is also usable as a starting sensor. Next, the hydraulic control device 5 is explained along with FIG. 4. CO, C1 and C2 are hydraulic servos for each clutch, and BO, B1, B2 and B3 are hydraulic servos for each brake. 2 is the torque converter, 12 is the lock-up clutch, and 36 is the oil pump. 51 is the manual valve where a line pressure port p is connected to ports a, b, c and d which correspond to ranges of R, P, N, D, 2 and L, as shown in FIG. 5. 52 is a primary regulator valve which relates to the present invention and regulates the line pressure to each hydraulic servo. The structure of the valve 52 will be explained later on. 53 is the throttle valve, 55 is a secondary regulator valve, 56 is a lock-up control valve, 57 is a lock-up relay valve, 58 is a solenoid relay valve, and 59 is a cutback valve. 60 is a 1-2 shift valve, 61 is a 2-3 shift valve, 62 is a 3-4 shift valve, 63 is a reverse inhibit valve, 65 is a low-coast modulator valve, and 66 is a second-coast modulator valve. 67 is an accumulator for the clutch CO, 70 is an accumulator for the clutch C2, and 71 is an accumulator for the brake B2. 72 is an accumulator control valve which regulates hydraulic pressure applied to back pressure chambers 69a, 70a and 71a of the accumulators 69, 70 and 71, respectively, and controls the low-coast modulator valve 65 and the second-coast modulator valve 66. S1 and S2 are solenoid valves to control the shift valves 60, 61 and 62. S3 is a linear solenoid which regulates hydraulic pressure from a solenoid regulator valve 73 and applies regulated pressure to the accumulator control valve 72. S4 is a linear solenoid valve which applies hydraulic pressure to the lock-up control valve 56 and the lock-up relay valve 57 and performs the line pressure control which will be explained later on. An explanation of the line pressure control will be given with respect to FIG. 1. The primary regulator valve 52 has three movable members: a main spool 52a, a sub spool 52b and a plug 52c which contact each other and move together. In the region of the main spool 52a are provided: a feedback port f applying hydraulic pressure to the bottom end of the main spool 52a, a control chamber port e applying hydraulic pressure to a step-like area of the main spool 52a, a line pressure port p2, a port h connected to the secondary regulator valve 55 and a drain port EX. Furthermore, in the region of the sub spool 52b are provided: a throttle pressure port i applying hydraulic pressure to the top of the sub spool 52b and a cutback pressure port j applying hydraulic pressure to a step-like area of the sub spool 52b. The plug 52c has an R range line pressure port d1 which applies hydraulic pressure at the top of the plug 52c. The line pressure port p2 is connected to an output side of the oil pump 36 to regulate the pump pressure to be a line pressure and can connect to each hydraulic servo CO, C1, C2, BO, B1, B2 and B3. This line pressure is applied to an input port p3 of the solenoid modulator valve 73, a line pressure port p4 of the throttle valve 53 and also to a pressure relief valve 75. The hydraulic pressure from the port h is first applied to the secondary regulator valve 55 where the pressure is regulated as a converter pressure, then applied to the torque converter 2 through the lock-up relay valve 57. When the manual valve 51 is positioned in the R range, the R range line pressure port d1 is connected to the port d of the manual valve 51 where the line pressure is applied (see FIG. 4). In the solenoid relay valve 58, a spool 58a is pressed downward by a spring 58b. The solenoid relay valve 58 has, at its bottom end, a control chamber o connected to the second brake hydraulic servo B2, an input port k, a first output port el, a drain port EX, and a second output port 1. The input port k is connected to both ports k1 and k2 of the lock-up solenoid valve S4, the first output port el to the control chamber port e of the primary regulator valve 52, and the second output port 1 to control chambers 11 and 12 of the lock-up control valve 56 and the lock-up relay valve 57 as shown in FIG. 4. The lock-up solenoid valve S4 is composed of a linear solenoid valve. The valve S4 has an input port m, the output port k1, the throttle port k2 and a drain port EX. Hydraulic pressure applied to the input port m is regulated by electric signals from the control unit C and the regulated pressure is taken out from the output port k1. A hydraulic pressure from the port m1 where the line pressure (p3) is reduced to a certain value by the solenoid modulator valve 73 is applied to the input port m of the valve S4. The throttle valve 53 is composed of two movable members: a downshift plug 53a and a spool 53b. A throttle cam 53c connected to the accelerator pedal by wires or the like is arranged on the top of the plug 53a, where the throttle pressure is applied from the port i2 to act as a power assist mechanism which reduces the pressing force of the throttle cam 53c. The line pressure port p4, a throttle pressure port i3, a drain port EX and a feedback port i4 formed at a step-like section are all provided in the region of the spool 53b. According to the rotation of the throttle cam 53c, a spring 53d is pressed through the plug 53a, and this pressing force moves the spool 53b to balance the pressing force of the spring 53d against the hydraulic pressure of the feedback port i4 and a lower end spring 53e. Namely, based on the movement of the spool 53b according to the rotation of the throttle cam (throttle pedal), the line pressure at the port p4 is regulated to be a throttle pressure, and the throttle pressure is taken out from the throttle pressure port i3. Incidentally, the lower end spring 53e can be adjusted by a screw 53f. With reference to the cutback valve 59, a spool 59a is pressed downward by a spring 59b. An upper control chamber s which is connected to the second-coast brake hydraulic servo B1 is formed at the top end of the spool 59a, while at the bottom end of the spool 59a, a lower control chamber o1 is formed. Furthermore, the cutback valve 59 has an input port q, an output port j1 and a drain port EX. The lower control chamber o1, as shown in FIG. 4, is connected to the second brake hydraulic servo B2 as well as the control chamber o of the solenoid relay valve 58. The operation of the embodiment will now be explained. The solenoid valves S1, S2 and S4; the clutches CO, C1 and C2; the brakes BO, B1, B2 and B3; the one-way clutches FO, F1 and F2; are operated at the positions of P, R, R (speed is more than 7 km/h), N, D, 2 and L ranges, as shown in FIG. 5. In other words, at the first speed of the D or 2 range; the solenoid valve S1 is ON, so that the over-drive direct clutch CO, the one-way clutches FO, F2 and the forward clutch C1 are engaged, other elements all being released. Accordingly, all elements of the over-drive planetary gear unit 17 rotate together through the clutch CO and the one-way clutch FO; thus rotation of the input shaft 15 is transmitted to the input shaft 26 of the main transmission unit 21 without reducing rotation speed. At the main transmission unit 21, rotation of the input shaft 26 is transmitted to the ring gear 31 of the front planetary gear unit 19, and transmitted to the carrier 29 and the output shaft 27 which is integrally connected with the carrier 29. At the same time, the rotation is transmitted to the carrier 33 of the rear planetary gear unit 20, and the carrier 33 is provided with torque in the left rotational direction. However, the carrier 33 is restrained by the one-way clutch F2; thus the planetary pinion 32 rotates, and this rotation is transmitted to the ring gear 35 which is integrally connected with the output shaft 27. When the manual valve 51 is moved from the N range to the D range, because of electric signals of the position sensor 47 certain electric signals are sent from the control unit C to the linear solenoid valve S4. The hydraulic pressure from the output port m1 of the solenoid modulator valve 73 is applied to the port m of the valve S4, regulated to a certain pressure, and taken out from the port k1, and furthermore the pressure is applied to the port k of the solenoid relay valve 58. At this moment, the relay valve 58 is in the left-half position because no hydraulic pressure is applied to the control chamber o because the second brake is released. Consequently, the pressure at the port k is applied to the control chamber e of the primary regulator valve 52 through the port e1. In this state, in the primary regulator valve 52, the throttle pressure applied from the throttle valve 53 is applied to the port i, and the throttle pressure is also applied to the port j through the port q and the port j1 of the cutback valve 59 which is in the left-half position based on the second-coast brake B1 and the second brake B2 being released. Accordingly, the spool 52a is pressed downward, so that the primary regulator valve 52 is in the condition that comparatively high line pressure for the first speed is generated. However, as the control pressure is applied to the control chamber e, the line pressure for the first speed is reduced by a certain amount. Because of these motions, when the manual valve 51 is changed from the N to the D range, the line pressure is reduced, and thus the pressure applied to the over-drive direct clutch hydraulic servo CO and the pressure applied to the forward clutch hydraulic servo C1 are reduced, so that the engagement of these clutches is smooth. Subsequently, the control pressure from the linear solenoid valve S4 is gradually reduced by the timer control so that the line pressure from the primary regulator valve 52 goes back to normal. Thus, the further engagement of these clutches is secured. In this state, as the cutback valve 59 is in the left-half position, the ports q and j1 are connected, and the throttle pressure from the throttle valve 53 is applied to the cutback pressure port j of the primary regulator valve 52 through the above ports q and j1. Accordingly, the main spool 52a is pressed downward through the sub spool 52b, so the line pressure is set rather high to generate a strong engaging force of the clutch against high load at starting. Incidentally, one possible idea is that the control unit C sends electric signals after receiving electric signals from a starting sensor such as the throttle sensor 49, if a driver shows no intention to start such as by pressing the accelerator pedal, and the line pressure is kept just under the engaging pressure of the clutches CO, C1 to prevent a creeping phenomenon which occurs when selecting from the N to the D range. At the second speed of the D range; the solenoid valve S2 is ON in addition to the solenoid valve S1. The over-drive direct clutch CO, the one-way clutch FO, the forward clutch C1, the one-way clutch Fl and the second brake B2 are engaged, other elements all being released. Accordingly, the over-drive planetary gear unit 17 is still kept under the direct operating condition, and the rotation of the input shaft 15 is transmitted to the input shaft 26 without reducing rotation speed. At the main transmission unit 21, rotation of the input shaft 26 is transmitted to the ring gear 31 through the forward clutch C1, and the sun gear 30 is provided with torque in the left rotational direction through the pinion 28. However, the sun gear 30 is restrained from rotating in the left rotational direction by the operation of the one-way clutch F1 because of engagement of the brake B2; consequently, the planetary pinion 28 rotates and the carrier 29 rotates. Then the rotation of the carrier 29 is directly transmitted to the output shaft 27, namely the rotation is transmitted only through the front gear unit 19 to the output shaft 27. In this state, because the line pressure is applied to the second brake hydraulic servo B2, the line pressure is applied to the control chamber o of the solenoid relay valve 58, and thus the valve 58 is in the right-half position. The input port k and the second output port l are connected, and the control pressure from the linear solenoid valve S2 is ready to be applied to the control chambers l1 and l2 of the lock-up control valve 56 and the lock-up relay valve 57. Due to these conditions, the lock-up solenoid valve S4 is controlled by electric signals from the control unit C based on electric signals from the speed sensor 46 and the throttle sensor 49 and the like, and subsequently the lock-up clutch 12 is controlled. Because the line pressure is applied to the second brake hydraulic servo B2, the cutback valve 59 is switched to the right-half position by application of the line pressure to the control chamber o1. In this state, the throttle port q is closed, the port j1 is connected to the drain port EX, and accordingly the port j of the primary regulator valve 52 is in a draining condition. In the primary regulator valve 52, the pressing force on the spool 52a is reduced, so that the line pressure is set rather low in accordance with the second speed or more. When the speed stage is in or more than the second speed, i.e. the second, third and fourth speeds, as the line pressure is applied to the second brake hydraulic servo B2, the line pressure is still kept under this low condition. At this moment, when friction plates of the second brake B2 start to contact by application of hydraulic pressure to the B2 hydraulic servo, the output torque varies, and as a result the rotational speed of the flange 40 which rotates together with the input shaft 15 also varies. The variation in rotation is detected by the sensor 45, and then the solenoid valve S3 is controlled by the electric signals of the control unit C based on the signals of the sensor 45. Consequently, hydraulic pressure applied from the solenoid modulator valve 73 is regulated in the solenoid valve S3 and such regulated pressure is taken as a certain control hydraulic pressure, and the certain control pressure is applied to the control port of the accumulator control valve 72. The control valve 72 is in the state that the line pressure is applied to the back pressure chamber 71a of the accumulator 71, and the state changes that in which the control pressure is applied to the back pressure chamber 71a. Thus, the accumulator back pressure is reduced by a certain amount, and after a certain time, based on the control pressure from the linear solenoid valve S3, the accumulator back pressure is gradually reduced, so that the output torque is smoothly varied. Thus, when shifting up from the first speed to the second speed, shift shock caused by engaging the second brake B2 is reduced, so that shift-up operation is conducted smoothly. In addition to shifting up from the first speed to the second speed, reduction of shift shock is obtained when shifting from the second speed to the third speed, from the third speed to the fourth speed, and also during down-shifting operations. At the third speed of the D or second range; the solenoid valve S1 is OFF, and the over-drive direct clutch CO, the one-way clutch FO, the forward clutch C1, the direct clutch C2 and the second brake B2 are engaged, other elements all being released. As a result, the over-drive planetary gear unit 17 is in the direct operating condition, and in the main transmission mechanism 21, the elements of the front planetary gear unit 19 rotate together because the clutches C1 and C2 are engaged; thus rotation of the input shaft 26 is transmitted to the output shaft 27 without reducing rotation speed. At the fourth speed of the D range, or the highest shift stage; the solenoid valve S2 is also OFF, and the forward clutch C1, the direct clutch C2, and the second brake B2 are engaged. The main transmission mechanism 21, as in the third speed, is under the direct operating condition, while at the over-drive planetary gear unit 17, the direct clutch CO is released and the over-drive brake BO is engaged. Accordingly, the sun gear 23 is locked by the brake BO, and the planetary pinion 22 rotates with the carrier 24 which also rotates. Rotation is transmitted to the ring gear 25 as an over-drive rotation, and the over-drive rotation is transmitted to the input shaft 26 of the main transmission mechanism 21, which is in the direct operating condition. When the manual valve 51 is shifted to the second range; the first and third speeds are the same as those of the D range. When shifted to the second speed, the second-coast brake B1 is engaged in addition to the forward clutch C1, the over-drive direct clutch C0 and the second brake B2, so that the sun gear 30 of the main transmission mechanism 21 is restrained to actuate the engine brake. In the table of operation of FIG. 5, a first speed is provided in the second range; however, it is preferable for the second range to start from the second speed. At this moment, because of the engagement of the second-coast brake B1, as the line pressure is applied to the upper control chamber s of the cutback valve 59, even if the line pressure is applied to the lower control chamber o1 due to the engagement of the second brake B2, the cutback valve 59 is kept in the left-half position by the pressing force of the spring 59b. Accordingly, the cutback pressure is applied through the ports q and j1 to the port j of the primary regulator valve 52, and thus the primary regulator valve 52 generates comparatively high line pressure as in the first speed of the D range. Each clutch and brake is provided with strong engaging forces. Such strong forces function effectively when a vehicle tries to get out from tyre ruts or when starting on snowy roads from the second speed by setting the manual valve 51 in the second range. When the engine brake is actuated, based on electric signals from the speed sensor 46, the control unit C sends electric signals to the linear solenoid valve S3, so that the solenoid valve S3 generates certain hydraulic pressure according to a vehicle speed. The certain pressure from the solenoid valve S3 is applied to the accumulator control valve 72. The valve 72 reduces the line pressure by a certain amount and sends this reduced pressure to the control port. The pressure at the control port is applied to the control chamber of the second-coast modulator valve 66, and hydraulic pressure from the output port of the valve 66 is regulated, and this regulated pressure is applied to the second-coast brake hydraulic servo Bl. Due to these motions, the modulator valve 66 reduces the hydraulic pressure to the servo B1 in accordance with the vehicle speed, so that the second-coast brake B1 reduces its torque capacity corresponding to the slowing down of the speed, and the engine brake is smoothly actuated. At the second speed of the L range; the operation is the same as the second speed of the second range. At the first speed; the first & reverse brake B3 is engaged in addition to the forward clutch C1 and the over-drive direct clutch CO, so that the carrier 33 of the rear planetary gear unit 20 is restrained, and thus the engine brake is actuated. At this moment, based on electric signals of the speed sensor, the regulated pressure from the output port of the modulator valve 65 is reduced proportional to the vehicle speed, and this reduced pressure is applied to the hydraulic servo B3. The first & reverse brake B3 actuates the engine brake with a large torque capacity when running fast, while at the time of a reduction of vehicle inertial force due to slowing down of the speed, the brake B3 adequately actuates the engine brake with reducing torque capacity. At the reverse range; the over-drive clutch CO, the one-way clutch FO, the direct clutch C2 and the first & reverse brake B3 are engaged, other elements all being released. Accordingly, the over-drive planetary gear unit 17 is in the direct operating condition, and in the main transmission mechanism 21, rotation of the input shaft 26 is directly transmitted to the sun gear 30 through the clutch C2, and as the carrier 33 is restrained by the brake B3, the rotation of the sun gear 30 is transmitted to the ring gear 35 as reverse rotation through the pinion 32 which rotates, and thus the output shaft 27 rotates reversely. When the manual valve 51 is shifted from the N to the R range, because of electric signals of the control unit C to which signals from the position sensor 47 are sent, the linear solenoid valve S4 generates a certain control hydraulic pressure. Also in the R range, the solenoid relay valve 58 is in the left-half position, so that the ports k and e1 are connected, the control pressure of the linear solenoid valve S4 is applied to the control chamber e of the primary regulator valve 52 through the ports k and e1, and thus the line pressure is reduced by a certain amount. Thus, shift shock when shifting from the N to the R range is prevented. At the R range; the line pressure is applied to the port d of the manual valve 51, and the line pressure at the port d is applied to the R range line pressure port d1 of the primary regulator valve 52. Even if the throttle pressure from the cutback valve 59 is not applied, the main spool 52a is pressed downward strongly through the plug 52c and the sub spool 52b so that the line pressure is set higher than for the first speed condition. Then, the over-drive direct clutch CO, the direct clutch C2 and the first & reverse brake B3 generate strong engaging forces corresponding to the gear ratio. When the manual valve 51 is shifted to the R range, if the vehicle speed is over a certain level, for example 7 km/h, the solenoid valve S2 is ON, so the direct clutch C2 is released, and as a result, no reverse running condition occurs. The technical advantages of the preferred embodiment will now be summarised. The primary regulator valve (52) has the cutback pressure port (j) which enables the line pressure to be regulated, the cutback pressure being applied from the cutback valve (59). Due to the above arrangement, high load torque can be accepted by increasing the line pressure for the first speed, and the line pressure at the second speed can be set rather lower to prevent shift shock. A simple two-stage spool (53a,53b) is employed in the output-responsive valve (throttle valve 53), so that the precision of regulation of hydraulic pressure against engine output is improved and valve sticking due to foreign materials is surely prevented. The line pressure is controlled by the cutback pressure which is directly applied to the primary regulator valve (52), so that hydraulic response is enhanced and improved. The primary regulator valve (52) has the main spool (52a), the sub spool (52b) and the plug (52c). One end of the plug is associated with a port (d1), one end of the sub spool is associated with a port (i) and a step-like section is associated with a port (j), such that one of the three operates to increase the line pressure at one relevant operation. So at the R range and the first speed, adequate line pressure control is conducted, while because three simple movable members are employed, the hydraulic pressure is applied to comparatively large areas, so that hydraulic precision is enhanced and valve sticking caused by foreign materials is surely prevented. With reference to the cutback valve (59), the second control chamber (s) is formed at the opposite end from the first control chamber (o1), and the chamber (s) is connected to the second-coast brake hydraulic servo (B1), so that at starting from the second speed of the 2 range, the increased line pressure provided by the cutback valve can be applied to the servo (B1). Strong engaging force is generated, so that escape from a tyre rut or starting on a snowy road are securely and precisely performed. The cutback valve (59) can generate the cutback pressure even though the spring (59b) is housed only in the second control chamber, so that the structure is not complicated to attain the above functions at a low production cost. Regarding the primary regulator valve (52), the control chamber port (e) is provided. The control pressure from the linear solenoid valve (S4) which is controlled by electric signals of the position sensor (47) is applied to the port (e) at the required moment, so that the line pressure which is released from the primary regulator valve (52) is controlled to prevent selection shock. The device can be constructed simply without adding extra valves, and furthermore, the selection shock when shifting from the N to the R range is prevented as well as that from the N to the D range. The regulating valve to control the lock-up clutch (12) is the solenoid valve (S4), and the control pressure from the solenoid valve (S4) is applied to the control chamber port (e) of the primary regulator valve (52) through the solenoid relay valve (58). Due to this arrangement, as the solenoid valve (S4) which operates at selecting from the N to the D range, can be utilized when shifting from the N to the R range, the structure of the device can be further simplified. In the case that the solenoid relay valve (58) is switched by the pressure applied to the second brake hydraulic servo (B2), the valve (58) is easily and securely switched. At selecting from N to D ranges, and N to R ranges, selecting shocks are surely prevented, and at more than the second speed, the lock-up clutch (12) is surely operated and controlled.

Claims: A hydraulic control device for an automatic transmission, comprising: hydraulic fluid servos for clutch and brake engagement and release of elements of a transmission gear mechanism; a hydraulic fluid circuit for supplying line pressure to said hydraulic fluid servos; a primary regulator valve (52) connected to said hydraulic fluid circuit for regulating the line pressure supplied to the hydraulic fluid servos, and having a cutback pressure port (j) for receiving a cutback pressure at a predetermined transmission speed and a throttle pressure port (i) for receiving a throttle pressure; an output-responsive valve (53) connected to said hydraulic fluid circuit for modulating the line pressure to a throttle pressure corresponding to the torque of an engine for driving the automatic transmission, said output-responsive valve having a throttle pressure outlet connected to said throttle pressure port of said primary regulator valve for supplying throttle pressure for regulating the line pressure in response to the engine torque; and a cutback valve (59) connected between the throttle pressure outlet of said output-responsive valve (53) and said cutback pressure port of said primary regulator valve (52) and operable in response to a predetermined transmission speed for supplying a cutback pressure to said primary regulator valve at the predetermined transmission speed to increase the line pressure, whereby the primary regulator valve regulates the line pressure so as to increase the line pressure at the predetermined transmission speed in response to both the throttle pressure and the cutback pressure. A hydraulic control device according to claim 1, characterised in that: said output-responsive valve (53) is a throttle valve which operates in response to a throttle opening ratio, and said cutback valve (59) is switched to disconnect its input and output ports by hydraulic pressure which is applied to a certain hydraulic servo at more than second speed of forward running. A hydraulic control device according to claim 1 or claim 2, characterised in that said primary regulator valve comprises: a main spool (52a), a sub spool (52b) and a plug (52c) which contact each other, whereby said main spool regulates said line pressure and regulates a converter hydraulic pressure which is applied to a secondary regulator valve, and one of a line pressure applied at reverse running, a hydraulic pressure responding to engine output applied from said output-responsive valve, and a cutback pressure from said cutback valve is respectively applied to one of one end of said plug, one end of said sub spool and a step section of said sub spool to increase said line pressure. A hydraulic control device according to any preceding claim, characterised in that said cutback valve comprises: a spool (59a) which is pressed in one direction, a first control chamber (o1) constituted against said pressing direction, a second control chamber (s) constituted along with said pressing direction, an input port (q) which is applied with said hydraulic pressure in response to engine output, an output port (j1) which applies said hydraulic pressure in response to engine output to said primary regulator valve, and a drain port (EX), whereby a certain hydraulic servo to which hydraulic pressure is applied at the or more than second speed is connected to said first control chamber, and a brake hydraulic servo which limits a coasting condition at said second speed is connected to said second control chamber so that said line pressure is set higher when coasting is limited at said second speed same as at said first speed. A hydraulic control device according to claim 4, characterised in that said cutback valve further comprises: a spring which is compressedly situated at one end of said spool, said first control chamber (o1) being constituted at another end of said spool, and said second control chamber (s) being constituted at said one end of said spool and housing said spring.

Inventors: ISHIKAWA KAZUNORI, IWATSUKI KUNIHIRO C O TOYOTA J, KASHIHARA YUJI C O TOYOTA JIDO, KONDO TADASHI C O TOYOTA JIDOS, TANIGUCHI HIROJI C O TOYOTA JI, TANIGUCHI TAKUJI, TOMOMATSU HIDEO, TSUKAMOTO KAZUMASA, ISHIKAWA, KAZUNORI, IWATSUKI, KUNIHIRO C/O TOYOTA JIDOSHA K.K., KASHIHARA, YUJI C/O TOYOTA JIDOSHA K.K., KONDO, TADASHI C/O TOYOTA JIDOSHA K.K., TANIGUCHI, HIROJI C/O TOYOTA JIDOSHI K.K., TANIGUCHI, TAKUJI, TOMOMATSU, HIDEO, TSUKAMOTO, KAZUMASA
Applicants: AISIN AW CO, TOYOTA MOTOR CO LTD, AISIN AW CO., LTD., TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1989
Main classification: F16H61
IPC codes: F16H61, F16H59, F16H63