Line pressure control system for automatic transmission

Abstract: A line pressure control system for an automatic transmission including a multiple shift stage transmission gear mechanism having a plurality of power transmitting paths of different speed ratios, line pressure control device for controlling a line pressure for frictional elements of the transmission gear mechanism associated with each other to establish a desirable shift gear stage, shift period detecting means for detecting a time period for a shift operation accomplished in terms of operation of the frictional element controlled by the line pressure, first compensating device for controlling the line pressure in terms of a learning control in a manner that the time period for the shift operation is controlled to a target value, abnormality detecting device for detecting an abrupt change such as turbine speed raising, depression or driving torque depression in operating condition of the transmission, and second compensating device for compensating the line pressure prior to compensation of the line pressure by the first compensating means when the abrupt change is detected. The torque shock can be effectively obviated during shift operation.

Description: This invention relates to a line pressure control system for an automatic transmission of a vehicle, more specifically to a control system for controlling a line pressure by controlling a pressure regulating valve through a solenoid thereof. Generally, an automatic transmission is provided with a torque converter and a multiple stage transmission gear mechanism with a planetary gear mechanism. The transmission gear mechanism is provided with a plurality of frictional elements such as brakes, clutches for switching a power transmitting path therein to establish desirable shift gear stages. The frictional elements are adapted to be controlled in terms of hydraulic control circuit to be engaged and disengaged to make a shift operation. Since the line pressure seriously affects engaging force and switching speed of the frictional elements or shift shock in shift operation, the line pressure is necessary to be deliberately controlled. There has been known a line pressure control system for electrically controlling the line pressure of the hydraulic control circuit of the transmission mechanism comprising a pressure regulating valve for controlling the line pressure of which pilot pressure is controlled by a duty solenoid valve. According to the conventional line pressure control system, the line pressure is controlled by a duty ratio signal for the duty solenoid valve so that a desirable frictional engaging force is obtained in accordance with the magnitude of engine torque. Alternatively, the line pressure is controlled to obviate the shift shock during the shift operation. In this case, it is necessary to properly control timing of switching operation and change of the engaging force of the frictional elements between the engaged and disengaged position. Otherwise, the torque shock is undesirably produced because of improper change in the turbine and the engine speeds. In view of these problems, it has been known that the line pressure is controlled in terms of a time period of the shift operation. For example, Japanese Patent Publication JP-B-63-3183 (& GB-A-2 051 979) discloses a learning control of the line pressure for controlling the frictional elements wherein the time period of the shift operation is measured for changing the line pressure in a manner that the time period of the shift operation is controlled to a target value. The line pressure control disclosed in the Japanese Patent Publication JP-B-63-3183 is intended to make the time period of the shift operation constant to prevent the shift shock and restrict undue slip in the frictional elements. It should however be noted that the above learning control of the line pressure is disadvantageous in the following points. In one condition of the shift operation, a frictional element is associated with a one way clutch to accomplish a shift operation. In the other condition, one frictional element is released or goes off and another frictional element is engaged or comes on to accomplish a shift operation. In the one condition of the shift operation, the shift operation can be made without serious torque shock since power transmitting path can be switched smoothly. However, in the other condition of the shift operation, releasing timing of the one frictional element is not accorded with engaging timing of the other frictional element so that a change rate of capacity for transmitting torque through the one frictional element does not correspond to that for the transmitting torque through the other frictional element. As a result, firstly, even when the torque capacity of the one frictional element is reduced, turbine speed may produce temporarily an abrupt increase where the torque capacity of the other frictional element is not increased sufficiently. Secondly, when the torque capacity of the other frictional element is increased sufficiently, the turbine speed is reduced quickly to produce a depression of the turbine speed. Thirdly, when the one frictional element keeps a large amount of capacity and the other frictional element increase the torque capacity thereof rapidly, both of the frictional elements are kept at substantially engaged condition so that the engine torque is abruptly reduced to produce a torque depression as well. Thus, the element will be deteriorated in durability and reliability even where the time period for the shift operation is precisely controlled. It is therefore a primary object of the invention to prevent unusual shift operation such as abrupt increase or depression of the engine and/or turbine speed. Another object of the invention is to provide a control system for an automatic transmission in which an increase in rotation speed of input member of the transmission can be accurately detected to provide a proper control of a line pressure for frictional elements of the transmission during shift operation. Still another object of the invention is to provide a line pressure control system for an automatic transmission in which a line pressure for frictional elements is controlled based on a turbine speed change to reduce the shift shock. Yet another object of the invention is to provide a line pressure control system of an automatic transmission in which a line pressure is controlled at an initial stage of a shift operation to accomplish a prompt control of the line pressure. EP-A-0327004 discloses a generic automatic transmission in which the variation of torque and number of revolutions during the gear-shifting period can be adjusted. According to the present invention, there is provided a line pressure control system for an automatic transmission comprising: a multiple shift stage transmission gear mechanism having a plurality of power transmitting paths of different speed ratios; line pressure control means for controlling a line pressure for frictional elements of the transmission gear mechanism associated with each other to establish a desirable shift gear stage; shift period detecting means for detecting a time period for a shift operation accomplished in terms of operation of the frictional element controlled by the line pressure; and, first compensating means for controlling the line pressure in terms of a learning control in a manner that the time period for the shift operation is controlled to a target value; characterised by: abnormality detecting means for detecting an abrupt change of a rotation speed of an input member during the shift operation of the transmission; and, second compensating means for compensating the line pressure prior to compensation of the line pressure by the first compensating means when the abrupt change is detected. Preferably, the abnormality detecting means detects an abrupt raising of the rotation speed of the input member during the shift operation. The abnormality detecting means may detect a depression in the rotation speed of the input member of the automatic transmission during the shift operation. The abnormality detecting means may detect a depression in a driving torque transmitted through frictional elements of the transmission gear mechanism during the shift operation. In a preferred embodiment, the line pressure control means comprises a duty solenoid valve for controlling a pilot pressure of a line pressure control valve so that the line pressure is controlled. The second compensating means may compensate the line pressure to be increased so as to increase the torque capacity of an on-coming frictional element of the transmission gear mechanism when the rotation speed of the input member of the transmission gear mechanism is abruptly increased during the shift operation. The second compensating means may compensate the line pressure to be decreased so as to reduce the torque capacity of an off-going frictional element of the transmission gear mechanism when the speed of a turbine of the transmission gear mechanism is abruptly decreased during the shift operation. The second compensating means may compensate the line pressure to be decreased so as to reduce the torque capacity of an off-going frictional element of the transmission gear mechanism when a torque depression is produced during the shift operation. The above and other features of the present invention will be apparent from the detailed description of the preferred embodiment of the present invention taking reference with the accompanying drawings. In the accompanying drawings: Figure 1 is a block chart of a control system for the automatic transmission in accordance with the present invention; Figure 2 is a schematic view of a control system for an automatic transmission; Figure 3 is a systematic view of a hydraulic control circuit for the automatic transmission; Figures 4 and 5 are flow charts of a line control in accordance with a preferred embodiment of the present invention; Figure 6(a) is a view showing a map stored in a control unit for executing the line pressure control; Figure 6(b) is a graphical representation of the line pressure of the hydraulic control circuit for the automatic transmission; Figure 7 is a view showing a map stored in the control unit for the line pressure control; Figure 8 is a graphical representation showing a compensating coefficient for the line pressure and a throttle opening change speed; Figure 9 is a view showing a flow chart of the line pressure control in accordance with the present invention; Figures 10 through 14 are graphical representations of various factors for compensating the line pressure; Figure 15 is a view showing a flow chart of the line pressure compasating control; Figure 16 is a graphical representation showing a turbine speed change; Figure 17 is a graphical representation showing a compensating coefficient for the line pressure; and, Figures 18 and 19 are graphical representations of turbine speed and torque capacity of the frictional elements involved in the shift operation. There will be described a preferred embodiment of the present invention. Referring to Figure 1, a line pressure control system for an automatic transmission in the illustrated embodiment comprises line pressure control device 77 for controlling a line pressure for frictional elements establishing a desirable shift gear stage among a plurality of shift gear stages in a multiple transmission gear mechanism, shift period detecting device 80 for detecting a time period for a shift operation accomplished in terms of operation of the frictional element controlled by the line pressure, first compensating device 81 for controlling the time period to a target value to compensate the line pressure by a learning method, abnormality detecting device 82 for detecting an abrupt change in operating condition of the transmission, and second compensating device 83 for compensating the line pressure prior to the first compensating device 81 when the abrupt change is detected. Referring to Figure 2, there is shown a structure of an automatic transmission to which the present invention can be applied. In Figure 2, an output shaft 1 of an engine is connected with a torque converter 2. A mulitple stage transmission gear mechanism 10 is disposed adjacent to an output member of the torque converter 10. The torque converter 2 is provided with a pump 3 fixed to the output shaft 1 of the engine, a turbine 4, and a stator 5 mounted on a shaft 7 through a one-way clutch 6. The gear mechanism 10 comprisses an oil pump drive shaft 12 connected with the engine output shaft 1 at base end and with an oil pump 31 at a tip end thereof, a hollow turbine shaft 13 connected with the turbine 4 at base end outside of the oil pump drive shaft 12 and Rvigneaux-type planetary gear mechanism 14 around the turbine shaft 13. Theplanetary gear mechanism 14 is provided with a small sungear 15 and a large sun gear 16 which are disposed side by side in a longitudinal direction of the transmission gear mechanism 10. The planetary gear mchanism 14 is also provided with a short pinion gear 18, a long pinion gear 17 meshed with the large sun gear 16 and the short pinion gear 18, and a ring gear 19 meshed with the long pinion gear 17. There are provided a forward clutch 20 and a coast clutch 21 side by side as frictional elements between the turbine shaft 13 and the small sun gear 15. The small sun gear 15 is connected with the forward clutch 20 located rearward of the large sun gear 16 and a first one-way clutch 22 connected with the forward clutch 22 for preventing a reverse rotation of the turbine shaft 13. The coast clutch 21 is also arranged between the turbine shaft 4 and the small sun gear 15 is in a row with the forward clutch 20 and the one-way clutch 16. Outside of the coast clutch 21, there is disposed a 2-4 brake 23 provided with a brake drum 23a connected with the large sun gear 16 and a brake band 23b adapted to be engaged with the brake drum 23a so that when the 2-4 brake is engaged, the large sun gear is fixed. A reverse clutch 24 is arranged rearward of the brake 23 for controlling a power transmission between the large sun gear 16 and the turbine shaft 13 through the brake drum 23a to thereby establish a reverse shift stage. There is provided a low & reverse brake 25 between a carrier 14 of the planetary gear mechanism 14 and a casing 10 of the transmission gear mchanism 10 for controlling the engagement and disengagement between the carrier 14a and the casing 10a. The long pinion 17 is connected with the low & reverse brake 25 for fixing the long pinion 17 and with a second one-way clutch 26 arranged in a row with brake 25 for allowing a rotation of the long pinion 17 in the same direction as the engine output shaft 1. A 3-4 clutch 27 is arranged in front of the planetary gear mechanism 14 for controlling the engagement and disengagement of between the carrier 14a and the turbine shaft 13. An output gear 28 disposed in front of the 3-4 clutch 27 is connected with the ring gear 19 through an output shaft 28a. Numeral 29 denotes a lock-up clutch for directly connecting the engine output shaft 1 with the turbine shaft 13. The multiple transmission gear mechanism 10 as illustrated is provided with four shift gear stages for forward movement and one shift gear stage for reverse movement. The clutches 20, 21, 24 and 27 and brakes 23 and 25 are controlled to establish a desirable shaft gear stage among the plurality of the shift gear stages. The table 1 shows operations of the respective clutches and brakes in the respective shift gear stages of the transmission. In the table 1, reference O means that the corresponding element is under operation for transmitting a torque but the corresponding element to reference (O) is effected to transmit the power only when it functions as a driving element. Hereinafter, the hydraulic circuit 30 will be explained in connection with operations of the above frictional elements taking reference to Figure 3. As shown in Figure 3, the oil pump 31 discharges a hydraulic fluid to the hydraulic passage L1. The hydraulic pressure of the fluid is introduced into the pressure regulating valve 32. The pressure regulating valve 32 is controlled by the duty solenoid valve 33 to adjust the line pressure of the hydraulic control circuit 30. In detail, the hydraulic pressure from the pump 31 is reduced in a reducing valve 34 to a predetermined value. Thereafter, the hydraulic pressure is adjusted by virtue of a duty control of the solenoid valve 33 by controlling an amount of drain and introduced into the pressure regulating valve 32 as a pilot pressure therefor. Thus, the line pressure control of the hydraulic control circuit 30 is established. The regulated line pressure is introduced into a port g of a manual shift valve 35. The manual shift valve 35 is provided with a spool 35a connected with a select lever and associated with the lever so that the spool 35a can be moved in accordance with a manual operation for the select lever by a driver to a range D in which the gear shift operation is automatically made among the four forward gear stages, a range 2 in which the gear shift operation is automatically made among the first through a third gear stages of the transmission, a range 1 in which the gear shift operation is automatically made between the first and second gear stages and a reverse range R, a parking range P and a neutral range N. The port g is communicated with ports a and e when set at the range 1, with ports a and c when set in the range 2 and D, and with a port f when set at the reverse range R. The port a of the manual shift valve 35 is connected with a 1-2 shift valve 36 through the hydraulic line L2. The 1-2 shift valve 36 is subjected to a pilot pressure which is adapted to be controlled by a 1-2 solenoid valve 37. When the shift stage is the first stage, the 1-2 solenoid valve 37 is turned off so that a spool 36a thereof is moved toward the left end to connect a hydraulic passage L3 communicated with an apply chamber 23c of the 2-4 brake 23 to a draining port. When the shift stage is the second to fourth stages, the 1-2 solenoid valve 37 is turned on so that the spool 36a is moved toward the right end in the drawing. As a result, the hydraulic pressure is introduced from the port a into the apply chamber 23c of the 2-4 brake 23. When the shift stage is the first stage in the range 1, the 1-2 shift valve introduces the hydraulic pressure supplied from the port e of the manual shift valve 35 through a low reducing valve 38 into the low & reverse brake 25. The hydraulic pressure from the port a of the manual shift valve 35 is introduced into the 2-3 shift valve 39 as a pilot pressure as well. The 2-3 shift valve 39 is connected with the port c of the manual valve 35 through a hydaulic passage L4. The pilot pressure therefor is controlled by a 2-3 solenoid valve 40. When in the first and second stages, the 2-3 solenoid valve 40 is turned on causing a spool 39a of the valve 40 to be moved rightward so that a hydraulic passage L5 communicated with the 3-4 clutch 27 is connected with a draining passage to release the 3-4 clutch 27. The hydraulic passage L5 is also connected with a 3-4 shift valve 41 subjected to a pilot pressure controlled by a 3-4 solenoid valve 42. When the shift stage is the first, second and fourth stages in the range D, and the first in the range 2, the 3-4 solenoid valve 42 is turned on causing a spool 41a of the valve 42 to be moved rightward so that a hydraulic passage L6 communicated with a release chamber 23d of the 2-4 brake 23 is connected with a draining passage. When the shift stage is the third stage in the range D, second and third stage in the range 2 and the first and second stages in the range 1, the 3-4 solenoid valve 42 is turned off causing the spool 42a to be moved leftward so that the hydraulic passage L6 is connected with the passage L5 connected with the 2-3 shift valve 39. As a result, the introduction of the hydraulic pressure is controlled in accordance with the operation of the 2-3 shift valve 39. The 3-4 shift valve 41 controls a communication between a hydraulic passage L7 connected with the port a of the manual shift valve 35 and a hydraulic passage L8 connected with the coast clutch 21 to thereby control the engagement and disengagement of the coast clutch 21. Thus, the operation of the 2-4 brake and 3-4 clutch 27 as frictional element can be accomplished through the control of solenoid valves 37, 40 and 42 as shown in Table 1. The control circuit 30 is provided with a 1-2 accumulator 43, a 2-3 accumulator 44, a 2-3 timing valve 45, a 3-2 timing valve 46 and bypass valve 47 between the shift valves 36, 39 and 41 and the 2-4 brake 23 and the 3-4 clutch 27 for reducing a torque shock caused by switching operations thereof. In addition, the control circuit 30 is provided with a N-D accumulator 48 connected with a hydraulic passage L9 which supplies the hydraulic pressure from the port a of the manual shift valve 35 so as to engage the forward clutch 20 in the first and second stages of the range D, a N-R accumulator connected with a hydraulic passage L10 which supplies the hydraulic pressure from the port f of the manual shift valve 35 so as to engage the reverse clutch 24 in the reverse range R, a lock-up control valve 50 for controlling the lock-up valve 29, a lock-up solenoid valve 51 for controlling the lock-up control valve 50 and a converter relief valve 52. Hereinafter, a line pressure control will be explained taking reference with Figure 4. In controlling the line pressure, a judgement is made as to whether or not the vehicle is in a shift operation (step S₁). If the judgment is No, or when the vehicle is not in a shift operation, the line pressure is controlled in accordance with a throttle opening and turbine speed. If the judgment is Yes, a routine of Figure 5 for controlling the line pressure during the shift operation is executed (step S₃), in which a judgment is made as to whether or not a vehicle is in a shift up operation (step S₄). If the jugdment is Yes, the line pressure is controlled based on a learning control for a shift operation time period by carrying out a routine shown in Figure 9 wherein the line pressure is controlled to such a target value that can provide a desirable shift operation time period. If the judgment in step S₄ is No or when the vehicle is in a down shift operation, the line pressure is compensated based on a turbine speed raising due to the shift operation or a difference between a target turbine speed at the end of the shift operation and an actual turbine speed detected. Referring to Figure 5, a judgment is made as to whether or not the vehicle is in the up-shift condition in step S A1 . When in the up-shift condition, the throttle opening is read and the line pressrure P1 is determined based on shift stages involved in the shift operation and the throttle opening. This control effects to obviate the torque shock due to the shift operation. Since the torque shock due to the shift operation is concerned with engine output in response to the throttle opening and the gear stages, when the line pressure is decided irrespective of the gear stages involved in the shift operation, a proper control cannot be accomplished for any gear stage involved although accumulators in the hydraulic circuit can be adjusted to obviate the torque shock. According to the illustrated embodiment, the line pressure under the up-shift condition is obtained in light of a map stored in a control unit as shown in Figure 6(a) wherein the line pressure is provided in accordance with the gear stages involved in the shift operation and the throttle opening. In a conventional control, the line pressure takes a relatively high value for all gear stages involved as shown by a double-dot-dash line in Figure 6(b) whereas the line pressure of the illusrated embodiment takes a relatively low value as shown by real lines in Figure 6(b) and the line pressure is provided for each shift operation involving different gear stages. If the judgment of step S A1 is No, or when the vehicle is in a down shift condition, the control unit judges whether or not the down shift occurs from the third stage to the second stage (step S A4 ). If the judgment is Yes, the line pressure is calculated through steps S A5 ∼ S A8 ). If the judgment is No, the line pressure control without shift operation is executed. When the down-shift operation is made from the third stage to the second stage, the 3-4 clutch 27 goes off and the 2-4 brake 23 comes on. In this case, an engaging timing of the frictional element is necessary to be controlled for obviating the torque shock. In the case of down-shift operations other than the third to second stages, the 3-4 clutch or the 2-4 brake 23 is released so that the engaging timing of the frictional element is not necessary in terms of the line control. In controlling the line pressure when the down-shift operation is made from the third stage to second stage, the turbine speed is read (step S A5 ), a base line pressure Pl₀ is determined in accordance with the turbine speed (step S A6 ). Generally, the 2-4 brake is engaged when the turbine speed is settled to a proper value after the 3-4 clutch 27 is released. It should however be noted that the proper engaging timing depends on the turbine speed. In view of this, the base line pressure Pl₀ is stored in a memory of the control unit in the form of a map as shown in Figure 7 in accordance with the turbine speed. The base line pressure Pl₀ is obtained through the map. In steps S A7 , S A8 , the line pressure is compensated based on the throttle opening change speed which is obtained from several values of the throttle opening detected. This is because the engine speed (turbine speed) is rapidly increased as the throttle opening change speed is increased. Threfore, it is necessary to advance the engaging timing of the frictional elements. For this purpose, compensating coefficient Ca is determined in accordance with the throttle opening change speed. The coefficient Ca is multiplied to the base line pressure Pl₀ to obtain a final line pressure Pl. Thereafter, a duty ratio is determined for a duty solenoid valve SOS in step S A9 , a frequency of signal for driving the valve SOL is set in step S A10 , On-time period for the valve SOL is decided in step S A11 , and the valve SOL is actuated in step S A12 . Referring to Figure 9, a line pressure compensation control will be explained. This routine is executed for compensating the line pressure by meeans of the learning control. This routine is directed to compensate the line pressure Pl obtained in the step S A3 of Figure 5. When the vehicle is in the up-shift condition, the turbine speed is gradually reduced as the frictional element is coming on or being engaged. In this case, the time period for the shift operation depends on the engaging speed of the frictional element. In view of this, the line pressure is compensated in accordance with the time period for the shift operation. For this purpose, the turbine speed is read in step S B1 . A change rate Δ N T of the turbine speed is calculated in step S B2 . In step S B3 , the change rate Δ N T is compared with a predetermined value A. When the change rate Δ N T is not less than the value A, the control unit judges a raising of the turbine speed. In this case, a compensating coefficient C N is obtained through a map as shown in Figure 10 in step S B4 . As the change rate Δ N T is increased, the value C N is increased so that the base line pressure Pl₀ is increased. On the other hand, when the change rate Δ N T is smaller than the value A in step S B3 , the control unit waits a predetermined time period t in order to find a turbine speed depression. When the time period t has passed, the change rate Δ N T of the turbine speed is compared with a negative value -B in step S B7. When the change rate Δ N T is not greater than the value -B, the control unit judges a turbine speed depression. In this case, a compensating coefficient C N1 is obtained through a map as shown in Figure 11. As the change rate Δ N T is decreased, the value C N1 takes a smaller value to reduce the base line pressure Pl₀. In step S B7 , when the change rate Δ N T is larger than the value -B, the control unit judges whether or not the change rate Δ N T is within a predetermined range (-C ≦ Δ N T ≦ D) in the vicinity of zero. If the judgment is Yes, the control unit judges a torque depression due to the shift operation. In this case, the compensating coefficient C N2 is decreased as the change rate Δ N T is increased within the range (-C ≦ Δ N T ≦ D) to reduce the base line pressure Pl₀ in step S B5 . If the judgment in step S B9 is No, or when there is no turbine depression and no torque depression, the learning control for the line pressure is executed so as to accomplish a target value of the time period for the shift operation from steps S B11 . In step S B11 , the target turbine speed after the shift operation is speculated based on the turbine speed before the shift operation. In step S B12 , the control unit compares the target turbine speed with an actual turbine speed detected. When a difference between the target turbine speed and the actual turbine speed is smaller than a predetermined value and the turbine speed change rate Δ N T is smaller than a predetermined value, the control unit judges that the shift operation is completed. When the shift operation is completed, the control unit calculates the time period for the shift operation. In step S B14 , the control unit calculates a difference Δ T between actual time period and target time period for the shift operation. In step S B15 , a compenating coefficient Ct is obtained through a map as shown in Figure 14 in accordance with the difference Δ T. When the difference Δ T is close to zero, the coefficient Ct is set at 1. When the actual time period of the shift operation as shown by T₁ is smaller than the target value or when the difference Δ T takes a negative value, the coefficient Ct is set at a value smaller than 1 so that the line pressure is decreased as shown in Figure 13. When the actual time period of the shift operation as show by T₂ is greater than the target value or when the difference Δ T takes a positive value, the coefficient Ct is set at a value larger than 1 so that the line pressure is increased as shown in Figure 13. In step S B16 , the line pressure Pl is compensated by virtue of the coefficient Ct ( Pl=Pl × Ct ). Hereinafter, a compensation for the line pressure in the case of a turbine speed raising in step S₄ of Figure 4 will be explained taking reference with Figure 15. In step S E1 , the turbine speed is read. In step S E2 , the control unit speculates a target turbine speed N o after the shift operation based on the turbine speed before the shift operation. In step S E3 , the turbine speed change rate is calculated. In step S E4 , the control unit judges whether or not the change rate is reduced below a predetermined value such as points x₀, x₁, x₂ in Figure 16. When the turbine speed change rate is reduced below the predetermined value, the control unit judges that the shift operation is near the end. In this condition, the control unit detects the turbine speed N S . In step S E9 , the control unit calculates the difference Δ N between the detected turbine speed N S and the target turbine speed N o as the turbine speed raising. Thereafter, the control unit calculates the compensating coefficient Cn in light of a map shown in Figure 17 based on the difference Δ N in step S E7 . As the difference Δ N takes a positive value and increases, the coefficient Cn is inceased and takes a value greater than 1. As the difference Δ N takes a negative value and decreases, the coefficient Cn is decreased and takes a value smaller than 1. In step S E8 , the base line pressure is compensated by multiplying the coefficient Cn. The compensated line pressure Pl is employed for suceeding cycles. According to the above control, the turbine speed raising and depression can be prevented when the down-shift operation occurs. The procedures in the steps S B12 and S B13 in Figure 9 constitute a shift time detecting device for detecting the time period for shift operation T or the time period from the start to the completion of the shift operation. The procedures in steps S B14 through S B16 constitute the first compensating means. The procedures in steps S B1 through S B3 , S B6 , S B7 and S B9 constitute abnormality detecting means. The procedures in steps S B4 , S B8 and S B10 constitutes the second compensating means. When the up-shift operation is executed between the second stage and the third stage, the 2-4 brake 24 is released or goes off and the 3-4 clutch is engaged or comes on to transmit the torque through the two frictional elements. As shown by a broken line in Figure 18, when the turbine speed raising occurs during the shift operation because the turbine speed change rate Δ N T is not smaller than the predetermined value A, the compensating coefficient C N is set at a value greater than 1 and the line pressure Pl is compensated by multiplying the coefficient C N so that the line pressure Pl is increased. As a result, the torque capacity of the on-coming frictional element or 3-4 clutch 27 is increased in Figure 19 to suppress the turbine speed raising in the succeeding shift operation. To the contrary, when the turbine speed change rate Δ N T is not greater than the negative value -B as shown by a dot-dash line in Figure 18 and the turbine speed depression occurs, the compensating coefficient C N1 is set at a value smaller than 1 so that the line pressure pl is decreased to suppress the turbine speed depression. As shown by a double-dot-dash line in Figure 18, when the turbine speed change rate Δ N T is within the range (-C ≦ Δ N T ≦ D) and the torque depression occurs, the compensating coefficient C N2 is set at a value smaller than 1 so that the line pressure Pl is reduced. As a result, 2-4 brake 23, which is the off-going frictional element, is quickly reduced in the torque capacity. Concurrently, the on-coming frictional element is slowly engaged. Thus, a locked condition can be avoided that both the off-going and on-coming frictional elements are strongly engaged during the shift operation. Consequently, the engine torque depression can be prevented during the shift operation.

Claims: A line pressure control system for an automatic transmission comprising: a multiple shift stage transmission gear mechanism (10) having a plurality of power transmitting paths of different speed ratios; line pressure control means (77) for controlling a line pressure for frictional elements of the transmission gear mechanism associated with each other to establish a desirable shift gear stage; shift period detecting means (80) for detecting a time period for a shift operation accomplished in terms of operation of the frictional element controlled by the line pressure; and, first compensating means (81) for controlling the line pressure in terms of a learning control in a manner that the time period for the shift operation is controlled to a target value; characterised by: abnormality detecting means (82) for detecting an abrupt change of a rotation speed of an input member during the shift operation of the transmission; and, second compensating means (83) for compensating the line pressure prior to compensation of the line pressure by the first compensating means when the abrupt change is detected. A system according to claim 1, wherein the abnormality detecting means detects an abrupt raising of the rotation speed of the input member during the shift operation of the transmission. A system according to claim 1, wherein the abnormality detecting means detects a depression in the rotation speed of the input member during the shift operation of the transmission. A system according to claim 1, wherein the abnormality detecting means detects a depression in a driving torque transmitted through frictional elements of the transmission gear mechanism during the shift operation. A system according to claim 1, wherein the line pressure control means comprises a duty solenoid valve for controlling a pilot pressure of a line pressure control valve so that the line pressure is controlled. A system according to claim 1, wherein the second compensating means compensates the line pressure to be increased so as to increase the torque capacity of an on-coming frictional element of the transmission gear mechanism when the rotation speed of the input member of the transmission gear mechanism is abruptly increased during the shift operation. A system according to claim 1, wherein the second compensating means compensates the line pressure to be decreased so as to reduce the torque capacity of an off-going frictional element of the transmission gear mechanism when the speed of a turbine of the transmission gear mechanism is abruptly decreased during the shift operation. A system according to claim 1, wherein the second compensating means compensates the line pressure to be decreased so as to reduce the torque capacity of an off-going frictional element of the transmission gear mechanism when a torque depression is produced during the shift operation.

Inventors: BABA FUMIAKI, FUJIWARA TAKUJI, ISHII KOZO, YOSHIMURA HIROSHI, BABA, FUMIAKI, FUJIWARA, TAKUJI, ISHII, KOZO, YOSHIMURA, HIROSHI
Applicants: MAZDA MOTOR, MAZDA MOTOR CORPORATION
Application year: 1990
Main classification: F16H61
IPC codes: F16H61, F16H59