Hydraulic control device for an automatic transmission

Abstract: An accumulator back pressure control device for an automatic transmission, the accumulator back pressure is regulated when a shift valve is switched. For example, when shifting up from the first to the second speed, when the second brake starts to engage by switching of the shift valve, rotation speed of the input side varies by the change of the output torque of a trans­ mission gear mechanism. By detecting the rotation change by a sensor, the pressure control valve (linear solenoid) is control­ led by signals from a control unit so that the control pressure from the pressure control valve is controlled at required moment. By this, for example, a control valve, by the change of hydraulic pressure at the control pressure port, regulates the pressure of oil source (line pressure port) and applies such regulated pressure to the back pressure chamber of the B2 accumulator to change the back pressure of the accumulator. When shifting from the second to the third speed, the back pressure of the C2 accumulator is controlled, and when shifting from the third to the fourth speed, the back pressure of the B0 accumulator is controlled. When down shifting, the operations are performed in same manner as the above.

Description: The present invention relates to a hydraulic control device for an automatic transmission, particularly one mounted on an automobile, and more especially relates to a device to control an accumulator back pressure. Conventionally, a hydraulic device for an automatic transmission has a hydraulic servo for a brake or clutch operatively hydraulically connected with an accumulator so that engaging pressure or releasing pressure is determined by a characteristic of the accumulator to reduce a shift shock. Control pressure works on a back pressure side of the accumulator so that the back pressure is lowered when a throttle opening ratio is small to further reduce shift shock. Furthermore, as shown in JP-A-61-130653, an accumulator control valve is controlled by a solenoid valve which is in turn controlled based on an opening ratio of a throttle to reduce shift shock. The above-mentioned device having an accumulator control valve applies constant accumulator back pressure to the back pressure side of the accumulator during shifting as shown in Fig. 6(d) and Fig. 7(d) by the dotted lines. Accordingly, hydraulic pressure applied to the clutch (or brake) rises, as shown at a point A of Fig. 6(c) by the dotted lines, based on a starting resistance of an 0-ring, and after that the hydraulic pressure rises per constant ratio B till the clutch plates are completely engaged. As a result, an output torque, as shown in Fig. 6(b) by the dotted lines, rises sharply to a point A' corresponding to the point A, and has a sharp peak B' caused by the change of coefficient of friction of the frictional member. Similarly, when the hydraulic pressure is released, as shown in Fig. 7(c) by the dotted lines, the clutch hydraulic pressure is lowered, so that the output torque rises sharply as shown in Fig. 7(b) by the dotted lines. It is thus difficult to reduce shift shocks at both up-shifting and down-shifting. It is known from EP-A-279606, relevant only for purposes of novelty, for there to be back pressure control for an accumulator of an automatic transmission wherein the back pressure depends firstly from a throttle pressure and secondly from a pressure controlled by a solenoid valve which is controlled by the turbine speed. It is also known from JP-A-61-149657, acknowledged in the pre-characterising portion of the present main claim, for there to be a hydraulic control device in an automatic transmission having a transmission gear mechanism including rotational elements driven at various respective rotational speeds in different speed stages of the transmission, and at least one frictional engaging element operatively connected to one of the rotational elements and engageable for restraining the rotation of said one of the rotational elements, comprising: a source of hydraulic fluid pressure; a hydraulic servo operatively connected to said at least one frictional engaging element for selectively engaging and disengaging said at least one frictional engaging element; a shift valve operatively hydraulically connected in the control device between said source of hydraulic fluid pressure and said hydraulic servo for selectively supplying hydraulic fluid from said source to said servo and draining hydraulic fluid from said servo during respective shifting operations in which said at least one frictional engaging element is being put into engagement or is being disengaged; and shift-shock inhibiting means for inhibiting shock created at said at least one frictional engaging element during a said shifting operation, said shift-shock inhibiting means including, an accumulator having a back pressure chamber in operative hydraulic communication with said hydraulic servo for regulating the pressure of hydraulic fluid issuing to said hydraulic servo, accumulator control means operatively hydraulically connected in the control device between said source of hydraulic pressure and the back pressure chamber of said accumulator for regulating the pressure of hydraulic fluid generated in said back pressure chamber during said shifting operation, sensor means for detecting the rotational speed of one of the rotational elements and for issuing signals indicative of the rotational speed, and an electronic control unit operatively connected to said sensor means and to said accumulator control means for receiving the signals issued by said sensor, and for controlling said accumulator control means based on said signals to regulate the pressure of hydraulic fluid generated in said back pressure chamber during said shifting operation to a pressure which causes said at least one frictional engaging element to restrain the rotation of said one of the rotational elements in a manner in which the rotational speed of said one of the rotational elements during the shifting operation corresponds to a predetermined rotational speed. The present invention is characterised in that said sensor means is for detecting the rotational speed of one of said rotational elements which stops at the highest gear ratio of said transmission gear mechanism. The transmission gear mechanism may include an input shaft, a main transmission unit, and an over-drive planetary gear unit, the over-drive planetary gear unit disposed between the input shaft of the transmission gear mechanism and the main transmission unit and including a carrier connected to the input shaft, a sun gear and a clutch disposed between the sun gear and the carrier, wherein said one of the rotational elements associated with said sensor means is the sun gear. A plurality of frictional engaging elements may be provided for restraining the rotation of respective ones of the rotational elements of the transmission gear mechanism, wherein a plurality of hydraulic servos are operatively connected to the frictional engaging elements, respectively, for selectively engaging and disengaging the frictional engaging elements, said shift-shock inhibiting means includes a plurality of accumulators having back pressure chambers in operative hydraulic communication with said hydraulic servos, respectively, for regulating the pressure of hydraulic fluid issuing to said hydraulic servos, and said accumulator control means is operatively hydraulically connected in the control device between said source of hydraulic pressure and the back pressure chamber of each of said accumulators. The accumulator control means may comprise a linear solenoid valve. The accumulator control means may comprise an accumulator control valve and a linear solenoid valve, said accumulator control valve being in operative hydraulic communication with the back pressure chamber of said accumulator, and said linear solenoid valve controlling the position of said accumulator control valve responsive to said electronic control unit. Finally, the accumulator control means may further include a throttle valve operatively hydraulically connected to said accumulator control valve for causing said accumulator control valve to regulate the pressure of hydraulic fluid generated in the back pressure chamber of said accumulator in response to throttle pressure generated by said throttle valve. In a preferred embodiment, described in more detail hereinafter, there is a hydraulic control device for an automatic transmission, comprising: hydraulic servos to control frictional engaging elements (for example, a second brake, a direct clutch and an over-drive brake) to engage or restrain certain elements (for example, a sun gear of a main transmission unit) of a transmission gear mechanism; accumulators situated in parallel with the hydraulic servos; shift valves to apply and drain hydraulic pressure to and from the hydraulic servos and the accumulators; and back pressure chambers to apply an accumulator back pressure formed at respective back sides of pistons of the accumulators. Hydraulic pressure regulated by a pressure control valve (for example, a linear solenoid valve) is applied to the chambers, and the pressure control valve is controlled by a sensor which detects a change in the rotational speed when shifting the shift valves. The sensor is a rotation speed detecting sensor for detecting a rotation of a member which rotates as a result of an engagement of a frictional engaging element, and has different rotating ratio of an output shaft at each shifting stage and stops at the highest shifting stage. As one example, hydraulic pressure from the pressure control valve is applied to a control port of an accumulator control valve, so that the hydraulic pressure of a certain oil source (for example, a line pressure) is regulated, and is applied to the accumulator back pressure chambers from a regulating port of the valve. Based on the above structure, when up-shifting from the first speed to the second speed, for example, the second brake starts to engage due to switching of the shift valve, and the rotational speed of the input varies because the output torque of the shift gear mechanism varies. By detecting the change of rotational speed through the sensor, the pressure control valve is controlled by the signals from the sensor at a required moment. Due to the above, the control valve regulates the hydraulic pressure from the oil source (the line pressure port) based on the hydraulic pressure applied to the port of the control valve, and the regulated pressure is applied to the back pressure chamber of the accumulator from the regulating port of the control valve, so that the accumulator back pressure is varied. Then, the starting resistance of the O-ring and the coefficient of friction of the friction member are averaged, so that the brake hydraulic pressure varies, and the output torque varies smoothly. When down-shifting, by changing the accumulator back pressure based on the pressure control valve, the clutch (or brake) hydraulic pressure and the output torque similarly vary. In the drawings: Fig. 1 is a schematic cross-sectional view of a main part of a hydraulic control device which relates to the present invention; Fig. 2 is a total 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; Fig. 5 is a table of operation of solenoid valves, clutches, brakes and one-way clutches at each shifting position; Fig. 6 is a graphical representation showing the up-shift time vs. the following items: Fig. 6(a) is a graphical representation of the up-shift time and rotating speeds of each element; Fig. 6(b) is a graphical representation of the up-shift time and the output torque; Fig. 6(c) is a graphical representation of the up-shift time and the clutch (brake) hydraulic pressure; Fig. 6(d) is a graphical representation of the up-shift time and the accumulator back pressure; Fig. 7 is a graphical representation showing the down-shift time vs. the following items: Fig. 7(a) is a graphical representation of the down-shift time and rotating speed of each element; Fig. 7(b) is a graphical representation of the down-shift time and the output torque; Fig. 7(c) is a graphical representation of the down-shift time and the clutch (brake) hydraulic pressure; Fig. 7(d) is a graphical representation of the down- shift time and the accumulator back pressure; Fig. 8 is a view of a partially modified embodiment; and Fig. 9 is a view of another partially modified embodiment. 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 C0 and a one-way clutch F0 are situated between the carrier 24 and the sun gear 23, and an over-drive brake B0 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, 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, 38 is an output shaft rotation sensor, and 39 is a rotation output gear for a speedometer. As shown in Fig. 2, with regard to the over-drive planetary gear unit 17, the one-way clutch F0 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 C0, the over-drive direct clutch C0 being situated between the sleeve 24a and an inner surface of the flange 40. The over-drive brake B0 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 on 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 C0 is engaged. Next, the hydraulic control device 5 is explained along with Fig. 4. C0, C1 and C2 are hydraulic servos for each clutch, and B0, B1, B2 and B3 are hydraulic servos for each brake. 2 is the torque converter, 36 is the oil pump, 45 is the speed sensor, and 51 is a 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, S and L, as shown in the table in Fig. 5. 52 is a primary regulator valve, 53 is a 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, 66 is a second-coast modulator valve, 67 is an accumulator for the clutch C0, 69 is an over-drive brake accumulator for the brake B0, 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. S1, S2 and S3 are solenoid valves to control the shift valves 60, 61 and 62. S4 is a linear solenoid valve which regulates hydraulic pressure from a solenoid regulator valve 73, and the regulated pressure is applied to the accumulator control valve 72. Next, an accumulator control device which is a main part of the present invention is explained along with Fig. 1. The accumulator control valve 72 has a line pressure port p1, a back-up port p2, a regulating port h connected to back pressure chambers 71a, 70a, 69a of accumulators 71, 70, 69, a feedback port i, a control port j to which hydraulic pressure from the linear solenoid valve S4 is applied, drain ports ex and a spring 72b which presses one end of a spool 72a. The linear solenoid valve S4 is controlled by a control unit C based on an electric signal from the sensor 45 which detects a C0 rotation, or the rotational speed of the sun gear 23 of the over-drive planetary gear unit 17. The solenoid valve S4 has ports j1, j2 which are connected to the port j of the accumulator control valve 72, and a port k1 which is connected to a regulating port k of a solenoid modulator valve 73, to a port p3 of which the line pressure is applied so that the line pressure is reduced as required to the port k1 of the solenoid valve S4. The B2 accumulator 71 has an accumulator chamber 71b, a back pressure chamber 71a having a small volume, and springs 71d, 71e having certain spring constants which are compressedly situated at both ends of a piston 71c. The back pressure chamber 71a is hydraulically connected to the port h of the control valve 72, while the accumulator chamber 71b is hydraulically connected to the second brake hydraulic servo B2 through an orifice 80 and check ball 81, the chamber 71b also being connected to the port m of the 1-2 shift valve 60. In the 1-2 shift valve 60, hydraulic pressure from the solenoid valve S2 works on a spool-top chamber p4 to switch a spool 60a. When the valve S2 is ON, the spool 60a is at the left-half position (the second, third and fourth speeds), then the line pressure port p5 and the port m are through or connected, while when the valve S2 is OFF, the spool 60a is at the right-half position (the first speed), the port p5 and the port m are disconnected, and the port m is connected to the drain port ex. In the same way, the over-drive brake accumulator 69 has an accumulator chamber 69b, a back pressure chamber 69a, and a spring 69d having a certain spring constant which is compressedly situated at the side of piston 69c opposite the accumulator chamber 69b. The back pressure chamber 69a is hydraulically connected to the port h of the accumulator control valve 72, and the accumulator chamber 69b is hydraulically connected to the over-drive brake hydraulic servo B0 through an orifice and a check ball, and is connected to a certain port of the 3-4 shift valve 62 (the port n to which the line pressure is applied at the left-half position of the valve 61 as shown in Fig. 4.) The accumulator 70 for the direct clutch C2 has an accumulator chamber 70b, a back pressure chamber 70a having a small volume, and springs 70d, 70e having certain spring constants which are compressedly situated at both ends of piston 70c. The back pressure chamber 70a is hydraulically connected to the port h, while the accumulator chamber 70b is hydraulically connected to the direct clutch hydraulic servo C2 through an orifice and a check ball, and is connected to a certain port of the 2-3 shift valve 61 (the port m to which the line pressure is applied at the left-half position of the valve 61 or port o (Fig. 4) of the reverse inhibit valve 63 through a mutual switching valve 75). Incidentally, the accumulators 71, 69 and 70 for the second brake hydraulic servo B2, the over-drive brake hydraulic servo B0 and the direct clutch hydraulic servo C2 are controlled by one accumulator control valve 72 and the solenoid valve S4 through each back pressure chamber 71a, 69a and 71a - however, these servos are not engaged at the same time. The operation of the embodiment will now be explained. The solenoid valves S1, S2 and S3; the clutches C0, C1 and C2; the brakes B0, B1, B2 and B3; the one-way clutches F0, 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 C0, the one-way clutches F0, 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 C0 and the one-way clutch F0; 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 the 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. 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 C0, the one-way clutch F0, the forward clutch C1, the one-way clutch F1 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. As shown in Fig. 6, a shifting signal is sent a certain time after a shifting judgement is made. 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 varied rotation is detected by the sensor 45 so that an actual rotation Nco can be arranged to be nearly equal to a target rotation Nco*. In other words, the solenoid valve S4 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 S4 and such regulated pressure is taken from the ports j1, j2 as a certain control hydraulic pressure, which is applied to the port j of the accumulator control valve 72. The control valve 72 is at the right-half position (Fig. 1) by hydraulic pressure being applied to the back-up port p2 through an orifice 80, and the line pressure applied from the port p1 is taken out from the port h and applied to the back pressure chamber 71a of the accumulator 71. In the above state of the control valve 72, the control pressure from the port h works on a bulged section of the spool, and the pressure, with the pressing force of the spring 72b, moves the spool against the line pressure of the back-up port p2. Consequently, the line pressure of the port p1 is reduced in accordance with the control pressure and taken out from the port h. The reduced pressure works from the feedback port i to a lower part of the spool 72a. At the same time, the reduced pressure is applied to the back pressure chamber 71b of the accumulator 71. Because of this, the accumulator back pressure D as shown in Fig. 6(d) is reduced by a certain amount so that an excessive rise of the output torque A' as shown in Fig. 6(b) does not occur. When a shifting operation begins, the accumulator back pressure, as shown in E of Fig. 6(d), is feedback controlled so that the rotation Nco of the flange 40 (hereinafter called C0 rotation) is controlled to be the target rotation Nco*. Furthermore, just before the engagement, the accumulator back pressure F as shown in Fig. 6(d), is reduced by a certain amount per time so that a sharp rise of torque B' as shown in Fig. 6(b) caused by a change in the coefficient of friction does not occur. Due to the above, when up-shifting from the first to the second speed, a shift shock caused by the engagement of the second brake B2 is reduced. Incidentally, Nout shown in Fig. 6(a) is the rotation of the output shaft detected by the output shaft rotation sensor 38. At the third speed of the D or second range; the solenoid valve S1 is OFF, and the 2-3 shift valve 61 is switched to the left-half position (Fig. 4). The over-drive direct clutch C0, the one-way clutch F0, 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 under 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. The 2-3 shift valve 61 is switched due to the solenoid valve S1 being OFF, and the line pressure from the port m' is applied to the direct clutch hydraulic servo C2. At this moment, the line pressure is also applied to the accumulator chamber 70b of the C2 accumulator 70. As in the B2 accumulator 71, certain hydraulic pressure is applied to the back pressure chamber 70a of the C2 accumulator 70, and the linear solenoid valve S4 is controlled based on the signals from the speed sensor 45 so that the accumulator back pressure is controlled as shown in Fig. 6(d). Thus, the hydraulic pressure of the hydraulic C2 hydraulic servo rises as shown in Fig. 6(c). Shift shock is reduced when shifting from the second to the third speed as when shifting from the first to the second speed. At the fourth speed of the D range, or the highest shift stage; the solenoid valve S2 is also OFF, and the 3-4 shift valve 62 is switched to the left-half position. 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 C0 is released and the over-drive brake B0 is engaged. Accordingly, the sun gear 23 is locked by the brake B0, and the planetary pinion 22 rotates with the carrier 24 which also rotates. Rotation is transmitted to the ring gear 24 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 under the direct operating condition. At this time, the line pressure from the port n of the 3-4 shift valve 62 is applied to the over-drive brake hydraulic servo B0 and the accumulator chamber 69b of the accumulator 69. However, because of the release of the direct clutch C0 and the engagement of the brake B0, rotation of the brim 42 which is integrally connected to the flange 40 connected to the sun gear 23 is restrained, and this state is detected by the sensor 45. Certain hydraulic pressure is applied to the back pressure chamber 69a of the B0 accumulator 69, and the linear solenoid valve S4 is controlled based on the signals of the speed sensor 45. As shown in Fig. 6, the hydraulic pressure for the brake B0 is controlled. On the other hand, in the direct clutch hydraulic servo C0, pressure rises comparatively quickly because the accumulator 67 is without back pressure control, so that the clutch C0 is released earlier than the brake B0. However, the carrier 24 is still under the control of the one-way clutch F0 regardless of the release of the clutch C0. As a result, shifting from the third speed to the fourth is performed by the engagement of the brake B0 and the release of the clutch C0, and shift shock is reduced by the control of the B0 accumulator 69. When down-shifting from the fourth to the third speed, the over-drive direct clutch C0 is engaged and the over-drive brake B0 is released. When down-shifting from the third to the second speed, the direct clutch C2 is released. Furthermore, when down-shifting from the second to the first speed, the second brake B2 is released. Under the above situation, the linear solenoid valve S4 is controlled by the electric signals from the control unit C based on the speed sensor 45. Thus, the accumulator back pressure working in the back pressure chambers 69a of the B0 accumulator 69, 70a of the C2 accumulator and 71a of the B2 accumulator 71 is reduced in a certain manner. Due to this, shift shock is reduced when down-shifting as well as when up-shifting, so that all shifting operations are performed smoothly. As shown in Fig. 7(c), conventionally, hydraulic pressure reduction shown by the dotted lines is not enough because back pressure is set based on an up-shifting, while in the present invention, the pressure reduction is performed in the full lines, so that as shown in Fig. 7(b), the sharp change of output torque shown by the dotted lines is improved to that shown by the full lines. Due to this smooth output torque, shift shock at the down-shifting is reduced as well as when up-shifting and, as a result, shifting operation is smoothly performed. At the second speed of the second and L ranges; the second coast brake B1 is engaged, and the sun gear 30 of the main transmission mechanism 21 is restrained, so that the engine brake is actuated. At the first speed of the L range; the first & reverse brake B3 is engaged, and the carrier 33 of the rear planetary gear unit 20 is restrained, so that the engine brake is actuated. At the reverse range; the over-drive clutch C0, the one-way clutch F0, 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 under 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. 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; thus the output shaft 27 rotates reversely. 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. Next, embodiments which are partial modifications of the above embodiment are explained along with Figs. 8 and 9. In the embodiment shown in Fig. 8, as a hydraulic pressure source to apply to the accumulator control valve 72, a throttle pressure P th of a throttle valve 53 is employed. As in the previous embodiment, when regulated pressure from the linear solenoid valve S4 works on the control port j of the control valve 72, the throttle pressure at the throttle application port t1 is reduced by a certain amount, and the reduced pressure is applied to the back pressure chamber of the accumulator. Incidentally, as in the previous embodiment, the B0 accumulator 69 and the C2 accumulator 70 are controlled in the same manner as the B2 accumulator 71. In the embodiment shown in Fig. 9, the regulated hydraulic pressure from the linear solenoid valve S4 is directly applied to a back pressure chamber 71a'. Normally, the control pressure ports j1, j2 apply certain hydraulic pressure to the accumulator back pressure chamber 71a', and when the speed sensor 45 detects a speed change, the linear solenoid valve S4 is controlled to reduce the amount of hydraulic pressure with a certain timing. In the above embodiments, explanation is stated to be about an automatic transmission having the over-drive planetary gear unit 17, or sub-transmission unit. In addition to this arrangement, the engine-brake control device is also applicable to an automatic transmission without the above sub-transmission unit. In the above embodiments, explanation is also stated to be about a Simpson type transmission unit, but is not limited to this type, because the engine-brake control device is also applicable to the Ravigneaux type transmission unit. The technical advantages of the preferred embodiment will now be summarised. As explained, the hydraulic pressure of the accumulator back pressure chamber (71a), (70a), (69a) is controlled by the sensor (45) which detects the rotational speed which varies when shifting the shift valve, so that engaging and releasing of the frictional engaging elements (B2), (C2), (B0) are adequately controlled to make the change of output torque smooth, and to reduce the shift shocks when shifting. It is possible for the control of the accumulator back pressure chamber to provide control for both up-shifting and down-shifting so that the shift shock at down-shifting is reduced as well as at up-shifting. In the case that a member whose rotational speed is detected by the sensor (45) is the member (40, 42) which rotates during engagement of the frictional engaging element (C0), varies its rotational speed at each shifting stage and stops at the highest shifting stage; because the member (40, 42) is located at the input side near the case, the rotating speed change of the member can be easily and precisely detected. Furthermore, as shifting comes to the higher stage, and the change of rotating speed becomes small, it might have been difficult to detect the timing of the highest shifting stage. However, because the member (40) stops rotating at the highest shifting stage based on the release of the frictional engaging element (C0), the present invention enables the timing of the highest shifting stage (4th speed) to be precisely and correctly detected due to a large rotational change (stopping). In the case that a plurality of accumulators (71), (70), (69) which are not engaged at the same time are to be controlled; the accumulators can be controlled through plural shifting stages by a simple structure utilising one regulating valve (S4). In particular, in the case that the accumulators are a second brake accumulator (71), a direct clutch accumulator (70) and an over-drive accumulator (69); over all shifting stages, or between the first and second speeds, the second and the third speeds, and the third and fourth speeds, accumulator control can be performed. When one frictional engaging element (B0) is engaged, at the same time another frictional engaging element (C0) can be released because of the one-way clutch (F0) whereby, although there are two frictional engaging elements which are subject to gear changes, it is enough to control the back pressure of the accumulator of only one of the frictional engaging elements.

Claims: A hydraulic control device in an automatic transmission having a transmission gear mechanism including rotational elements driven at various respective rotational speeds in different speed stages of the transmission, and at least one frictional engaging element operatively connected to one of the rotational elements and engageable for restraining the rotation of said one of the rotational elements comprising: a source of hydraulic fluid pressure; a hydraulic servo (B2, C2, B0) operatively connected to said at least one frictional engaging element for selectively engaging and disengaging said at least one frictional engaging element; a shift valve (60, 61, 62) operatively hydraulically connected in the control device between said source of hydraulic fluid pressure and said hydraulic servo for selectively supplying hydraulic fluid from said source to said servo and draining hydraulic fluid from said servo during respective shifting operations in which said at least one frictional engaging element is being put into engagement or is being disengaged; and shift-shock inhibiting means for inhibiting shock created at said at least one frictional engaging element during a said shifting operation, said shift-shock inhibiting means including, an accumulator (71, 70, 69) having a back pressure chamber in operative hydraulic communication with said hydraulic servo for regulating the pressure of hydraulic fluid issuing to said hydraulic servo, accumulator control means (72, S4) operatively hydraulically connected in the control device between said source of hydraulic pressure and the back pressure chamber of said accumulator for regulating the pressure of hydraulic fluid generated in said back pressure chamber during said shifting operation, sensor means (45) for detecting the rotational speed of one of the rotational elements and for issuing signals indicative of the rotational speed, and an electronic control unit (C) operatively connected to said sensor means and to said accumulator control means for receiving the signals issued by said sensor, and for controlling said accumulator control means based on said signals to regulate the pressure of hydraulic fluid generated in said back pressure chamber during said shifting operation to a pressure which causes said at least one frictional engaging element to restrain the rotation of said one of the rotational elements in a manner in which the rotational speed of said one of the rotational elements during the shifting operation corresponds to a predetermined rotational speed; characterised in that said sensor means (45) is for detecting the rotational speed of one of said rotational elements (42) which stops at the highest gear ratio of said transmission gear mechanism. A hydraulic control device in an automatic transmission as claimed in claim 1 in which transmission the transmission gear mechanism includes an input shaft, a main transmission unit, and an over-drive planetary gear unit, the over-drive planetary gear unit disposed between the input shaft of the transmission gear mechanism and the main transmission unit and including a carrier connected to the input shaft, a sun gear and a clutch disposed between the sun gear and the carrier, wherein said one of the rotational elements associated with said sensor means is the sun gear (23). A hydraulic control device in an automatic transmission as claimed in either preceding claim in which transmission a plurality of frictional engaging elements are provided for restraining the rotation of respective ones of the rotational elements of the transmission gear mechanism, wherein a plurality of hydraulic servos (B2, C2, B0) are operatively connected to the frictional engaging elements, respectively, for selectively engaging and disengaging the frictional engaging elements, said shift-shock inhibiting means includes a plurality of accumulators (71, 70, 69) having back pressure chambers in operative hydraulic communication with said hydraulic servos, respectively, for regulating the pressure of hydraulic fluid issuing to said hydraulic servos, and said accumulator control means is operatively hydraulically connected in the control device between said source of hydraulic pressure and the back pressure chamber of each of said accumulators. A hydraulic control device in an automatic transmission as claimed in any preceding claim in which said accumulator control means comprises a linear solenoid valve. A hydraulic control device in an automatic transmission as claimed in any preceding claim in which said accumulator control means comprises an accumulator control valve (72) and a linear solenoid valve (S4), said accumulator control valve being in operative hydraulic communication with the back pressure chamber of said accumulator, and said linear solenoid valve controlling the position of said accumulator control valve responsive to said electronic control unit. A hydraulic control device in an automatic transmission as claimed in claim 5 in which said accumulator control means further includes a throttle valve operatively hydraulically connected to said accumulator control valve for causing said accumulator control valve to regulate the pressure of hydraulic fluid generated in the back pressure chamber of said accumulator in response to throttle pressure generated by said throttle valve.

Inventors: ISHIKAWA KAZUNORI C O AISIN AW, IWATSUKI KUNIHIRO, TAGA YUTAKA, TANIGUCHI TAKUJI C O AISIN AW, TSUKAMOTO KAZUMASA C O AISIN A, ISHIKAWA, KAZUNORI C/O AISIN AW CO., LTD., IWATSUKI, KUNIHIRO, TAGA, YUTAKA, TANIGUCHI, TAKUJI C/O AISIN AW CO., LTD., TSUKAMOTO, KAZUMASA C/O AISIN AW CO., LTD.
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