JPH0512510Y2 - - Google Patents

Description

[Detailed explanation of the idea]

(Industrial Application Field) The present invention relates to a line pressure control device for an automatic transmission that controls the line pressure for operating the transmission elements of the automatic transmission. (Prior Art and its Problems) In an automatic transmission using a planetary gear set, when the components of the planetary gear are fixed using a band brake, the following problems occur. That is, the braking capacity of the band brake differs depending on the direction of the force acting on the member to be fixed, and the braking capacity is smaller in the engine braking state (driving from the wheel side) than in the normal case.
For this reason, conventionally, when the select lever is selected to a gear position that primarily uses engine braking, the hydraulic pressure is made higher than in other cases to increase the band brake capacity as necessary. For example, in the case of a conventional three-speed forward automatic transmission as disclosed in Japanese Patent Application Laid-Open No. 56-55749, even if the oil pressure is increased as described above, the shift shock is not affected. This is because the same clutch is always engaged when moving forward, and there is no need to engage the clutch when the select lever is in the engine braking gear position. This is because the shift shock did not become larger even as the vehicle grew older. However, for example, the ``Nitsun Automatic Transaxle Maintenance Instruction Manual (F02A Type)'' (1972)
In the case of a 4-speed forward automatic transmission with overdrive, separate clutches are used for the 4th gear that achieves the overdrive state and the 2nd gear that achieves the engine braking state, as shown in It may be necessary to conclude a contract. In this case, if a band brake is used as a brake that operates together with the clutch during the second gear to achieve this engine braking condition, the following problem will occur. In other words, when driving in 4th gear and select the select lever position (fixed to 2nd gear or position below 2nd gear), if the hydraulic pressure is increased to secure the band brake capacity as in the past. , second
The clutch, which is switched from the released state to the engaged state at high speeds, has an excessive capacity because it is engaged by the increased hydraulic pressure in order to secure the band brake capacity. In other words, among the band brake and clutch that are to be engaged together when the engine brake is applied, the band brake is secured to ensure the effectiveness of the engine brake when the engine brake is applied when the released band brake is engaged while the clutch is engaged, and the band brake is It has not been possible to achieve both the prevention of shift shock during engine braking when the clutch is engaged while it is already engaged. A conventional method to solve the above problem is to provide two clutches that operate in second gear, one of which is in D.
Some clutches are used during normal driving on a range, etc., with the other clutch operating only when the range is selected, and the capacity of the other clutch being smaller than that of one clutch. This ensures that the clutch capacity remains appropriate even when oil pressure increases in the range. However, using two clutches as described above has the following drawbacks. That is, the price increases because a clutch dedicated to engine braking is required, and the space required to arrange the clutch increases the size and capacity of the entire automatic transmission. (Means for solving the problem) The present invention was made with the purpose of solving the above-mentioned problems, and in order to achieve this purpose, the present invention has the following release means. And so. The solution of this invention. To explain with the conceptual diagram of the claim shown in Fig. 1, one clutch 01 and 1
In the first high speed stage, which is equipped with at least a band brake 02 and a direct coupling stage, the clutch 01
is engaged and the band brake 02 is released to achieve an overdrive gear. In the second high speed gear, the clutch 01 is released and the band brake 02 is engaged, and the first or second high gear is engaged. In an automatic transmission that operates the engine brake by engaging both the clutch 01 and the band brake 02 by forcibly shifting from a gear to a low gear with a large gear ratio, the line pressure P created by the regulator valve 03. The _line pressure control means 04 for controlling the pressure level of
When the engine brake is applied from the first high speed stage with the band brake 02 being released while the band brake 02 is still engaged, pressure increase control is performed on the line pressure P _L , and the band brake 02 is released while the band brake 02 is still engaged. When the clutch 01 is engaged and the engine brake is applied from the second high speed stage, the line pressure P _L is not increased. (Function) When the engine brake is activated by engaging the band brake 02 from the first high speed stage, the line pressure control means 04 that controls the pressure level of the line pressure P _L produced by the regulator valve 03 controls the line pressure P _L Pressure increase control is performed. Therefore, the effectiveness of the engine brake can be ensured by the backup action that increases the engagement capacity of the band brake 02. Incidentally, since the engagement capacity of the already engaged clutch 01 is also increased at the same time, the durability and reliability of the clutch is ensured by preventing slipping. When the clutch 01 is engaged from the second high speed stage to operate the engine brake, the line pressure control means 04 that controls the pressure level of the line pressure P _L produced by the regulator valve 03 performs pressure increase control on the line pressure P _L. is not carried out. Therefore, it is possible to prevent a shift shock due to an excessive clutch engagement capacity. (Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.
In describing this embodiment, an automatic transmission with four forward speeds and one reverse speed to which the embodiment device is applied will be taken as an example. First, the power transmission mechanism of the automatic transmission will be explained. As shown in Figure 2, the power transmission mechanism consists of an engine crankshaft E, a torque converter T/
C, lock-up clutch LU/C, input shaft I, front planetary gear G1, 1st
Connecting member M1, second connecting member M2, rear planetary gear G2, output shaft O, reverse clutch R/C, high clutch H/C, low clutch L/C, low & reverse brake L&R/B, band brake B/
B. Equipped with one-way clutch OWC. The front planetary gear G1 and the rear planetary gear G2 are single pinion type planetary gears, and the front planetary gear G1 includes a front sun gear S1, a front internal gear R1 that meshes with the front sun gear S1 and the front internal gear R1, and a front pinion gear.
P1 and a front planetary carrier PC1 that supports it, the rear planetary gear G2 includes a rear sun gear S2, a rear internal gear R2, a rear pinion gear P2 that meshes with the rear sun gear S2 and the rear internal gear R2,
It is composed of a rear planet carrier PC2 that supports this. The first connecting member M1 is a member that connects the front internal gear R1 and the rear planet carrier PC2, and the second connecting member M2 connects the front planet carrier through torque transmission by tightening the low clutch L/C. rear
This is a member that connects PC1 and rear internal gear R2. The reverse clutch R/C, high clutch H/C, low clutch L/C, low & reverse brake L&R/B, band brake B/B, and one-way clutch OWC are shift elements for obtaining each gear stage by combined operation, When activated, it exhibits the following functions. Reverse clutch R/C connects input shaft I and front sun gear S1. High clutch H/C is input shaft I
and front planet carrier PC1. The low clutch L/C connects the front planet carrier PC1 and the rear internal gear R2. The low & reverse brake L&R/B fixes the front planet carrier PC1 to the transmission case TMC. Band brake B/B is front sun gear
Secure S1 to the transmission case TMC. The one-way clutch OWC rotates the front planet carrier PC1 in the normal direction (engine rotation direction).
is allowed, but reversal is not allowed and rotation is fixed. The band brake B/B is engaged by applying control hydraulic pressure to the engagement side of the band servo 10 (described later), the one-way clutch OWC is operated mechanically, and the other clutches and brakes are multi-disc friction clutches. The structure is fastened using controlled hydraulic pressure. Next, the operation of the shift elements at each shift position is shown in Table 2 below.

【table】

[Table] The ○ mark indicates operation. However, in the case of the band servo 10, hydraulic pressure acts on both the servo apply pressure on the engagement side and the servo release pressure on the disengagement side.
At range 3 speed (drive range 3 speed), band brake B/B is not engaged due to the difference in pressure receiving area. Next, among the hydraulic control devices for controlling the power transmission mechanism, a line pressure control device will be explained with reference to FIGS. 3 and 4. The line pressure control device of the embodiment is shown in FIGS. 3 and 4.
As shown in the figure, oil pump O/P, pressure regulator valve 1, manual valve 2,
Throttle valve 3, Daytent & failsafe valve 4, Kickdown modulator valve 5, Pressure modifier valve 6, Cutback valve 7, Backup valve 8, 3-4
It is equipped with a shift valve 9 and a band servo 10. Each component will be explained below. The oil pump O/P uses a variable displacement vane pump, and the oil chamber C/C of the control cylinder is connected to the oil passage 701 (feedback pressure oil passage) from the pressure regulator valve 1. The position of the cam ring is controlled so that the pump discharge amount remains constant above a predetermined rotation speed, eliminating excess flow at high rotation speeds and reducing energy consumption. The pressure regulator valve 1 is a valve that has the function of adjusting the oil discharged from the oil pump O/P to an optimal pressure (line pressure) depending on the driving condition and gear shift position. Structurally, a valve hole 101 having ports 101a to 101g, a spool 201 having lands 201a to 201d corresponding to the valve holes 101 and movable in the axial direction, and ports 301a to 301c.
a sleeve 3 fixed in the valve hole 101
01, a plug 401 which has lands 401a to 401c corresponding to the inner diameter of the sleeve 301 and is movable in the axial direction, a spring seat 501 arranged at the upper part of the plug 401, and lands between the spring seat 501 and the spool 201. 201d. Lands 201b and 201c of the spool 201,
and 201d are equal in diameter, and the diameter of the land 201a is smaller than these land diameters.
Land 401a of No. 01 has a larger diameter than land 401b. Port 101a, port 101c, 101g,
301c is a drain port. port 101
b and 101e are line pressure oil passages 70 through which the pressure-regulated oil discharged from the oil pump O/P flows.
0, and an orifice 800 is provided at the entrance of the port 101b. Port 101d
is connected to a feedback pressure oil passage 701 communicating with the oil chamber C/C of the oil pump O/P.
Port 101f is torque converter pressure oil passage 702
It is connected to the. Port 301a is connected to cutback pressure oil passage 703. port 301
b is connected to the pressure modifier pressure oil passage 704. On the spool 201 of the pressure regulator valve 1, a force due to line pressure acts on the port 101b as a force pushing it downward in the drawing (pressure reducing direction), and a spring acts as a force pushing it upward in the drawing (pressure increasing direction). Spring force due to 601 and port 30
The force due to the cutback pressure on 1a and the port 30
A force due to the pressure modifier pressure is applied to 1b. The spool 201 is operated by the balance of these forces, and the port 10
When the oil pressure in port 1b gradually increases and becomes greater than the upward force, the oil in port 101e is discharged to port 101f toward the torque converter T/C, and the pressure in port 101e decreases until it balances with the upward force. This pressure drop in port 101e also reduces the pressure in port 101b, which is communicated with line pressure oil passage 700.
The downward force becomes smaller and the spool 201 is pushed back upward. In this way, the spool 201
By repeating the up and down operation, port 10
The oil pressure of 1b, that is, the oil pressure of the line pressure oil passage 700, is always regulated to balance the upward force, and so-called line pressure is obtained. Note that the line pressure will change depending on the upward force applied to the plug 401 via the spring 601. In addition, in this pressure regulator valve 1, when the flow rate from the oil pump O/P is excessive and the force pushing down the spool 201 is large, the port 1
01e and 101d communicate, oil pump O/
Oil pressure is applied to the oil chamber C/C of P via the oil passage 701, and the discharge flow rate of the oil pump O/P is regulated to a predetermined flow rate. The manual valve 2 is a valve that is operated by a select lever 11 provided in the driver's seat and has the function of selecting a line pressure delivery port according to each select position. Valve operation is performed by moving the spool 202 by operating the select lever, and the ports to which line pressure is supplied in the P range position, R range position, N range position, D range position, range position, and range position are shown below. It is shown in Table 3.

[Table] Note that line pressure is supplied to the ports marked with ○ in Table 3, and all other ports are connected to drain ports. Structurally, it includes a valve hole 102 having ports 102a to 102e, and a spool 202 that has lands 202a and 202b corresponding to the valve hole 102 and is movable in the axial direction. Port 102a is connected to range pressure oil passage 705, port 102b is connected to range pressure oil passage 706, and port 102c is connected to D range pressure oil passage 70.
7, and the port 102d is connected to the line pressure oil path 7.
00, and the port 102e is connected to the R range pressure oil passage 708. The throttle valve 3 is a valve that has a function of regulating line pressure to a pressure (throttle pressure) corresponding to the throttle opening degree. Structurally, it includes a valve hole 103 having ports 103a to 103f, a spool 203 that has lands 203a to 203c corresponding to the valve hole 103 and is movable in the axial direction, and a land 2 of the spool 203.
Spring 303 that urges 03a to the right in the drawing
It is equipped with Lands 203a and 203b of spool 203
has a larger diameter than the land 203c. Ports 103a, 103b, and 103f are drain ports. port 103c and port 10
3e is connected to a throttle pressure oil passage 709, and an orifice 801 is provided at the entrance of the port 103e. Port 103d is connected to kickdown modulator pressure oil passage 710. A spring force from a spring 303 acts on the spool 203 of the throttle valve 3 in the right direction in the drawing, and a force due to the throttle pressure to the port 103e acts on the spool 203 in the left direction in the drawing. Therefore, the oil at the kickdown modulator pressure flowing in from the port 103d is regulated so that the forces in the left and right directions are balanced and become the throttle pressure. Note that one end of the spring 303 is connected to a day tent &
Since it is in contact with the spool 504 of the fail-safe valve 4, the spring force increases or decreases as the spool 504 moves in response to the amount of depression of the accelerator pedal. The day tent & failsafe valve 4 is linked to the accelerator pedal 12 via an accelerator pedal linkage, etc., and causes changes in the throttle opening degree to act on the throttle valve 3 via a spring 303, as well as presetting the throttle pressure. This valve has a detent valve function that supplies the pressure to the shear modifier valve 6, and a fail-safe function that allows the line pressure to directly act on the pressure modifier valve 6 to maintain the highest line pressure when the accelerator linkage is broken. It is. Components include a valve hole 104 having ports 104a to 104d, a movable sleeve 204 having a port communication groove 204a and a stopper protrusion 204b and movable in the axial direction on the inner surface of the valve hole 104, and fixed to the inner surface of the valve hole 104. fixed sleeve 3
04, fixed sleeve 304 and movable sleeve 20
A spring 404 is provided between the land 50 and the land 50 and urges the movable sleeve 204 to the left in the drawing.
4a and is movable in the axial direction on the inner surfaces of the movable sleeve 204 and the fixed sleeve 304.
It is equipped with When the accelerator linkage is broken, the land 504a abuts against the stopper protrusion 204b due to the force of the linkage spring, and moves the movable sleeve 204 against the spring 404 until it abuts against the fixed sleeve 304. port 104
a and 104d are connected to a throttle pressure oil passage 709, a port 104b is connected to a line pressure oil passage 700, and a port 104c is connected to a throttle pressure & line pressure oil passage 711 in which a shuttle ball 900 is provided in the middle. . As described above, the spool 504 of the day tent and failsafe valve 4 moves left and right in conjunction with the accelerator pedal to change the spring force of the spring 303. Also, during normal operation, port 10
Throttle pressure oil is directly delivered from port 4a to the throttle pressure & line pressure oil passage 711 via the port communication groove 204a, and when the accelerator linkage is broken, it is transferred from the port 104b to the port communication groove 204a.
Line pressure oil is directly delivered to the throttle pressure & line pressure oil passage 711 via the line pressure oil passage 711. The kick-down modulator valve 5 is provided to create a kick-down modulator pressure (base pressure of the throttle pressure) that reduces the upper limit pressure of the line pressure to a set pressure, and to obtain the optimum kick-down shift point. It's a valve. The structure includes a valve hole 105 having ports 105a to 105e, lands 205a and 205b corresponding to the valve hole 105, a spool 205 that is axially movable, and a spring that urges the spool 205 to the left in the drawing. 305. Ports 105d and 105e are drain ports. Port 105b is connected to line pressure oil passage 700. Port 105a and port 10
5c is a kickdown modulator pressure oil passage 710
An orifice 802 is provided at the entrance of the port 105a. The spool 205 of this kick-down modulator valve 5 receives a force from the kick-down modulator pressure as a force pushing it in the right direction in the drawing.
The spring force of the spring 305 acts on the end face of a and pushes it toward the left in the drawing.
Therefore, until the set pressure is reached, the oil flows from ports 105b to 105c while pushing the spool 205 to the right in the drawing, and when the set pressure is reached, the oil flows through ports 105d, which is a drain port, to maintain the balance of the force in the left and right directions. Repeat opening and closing of the port to maintain the set pressure. The pressure modifier valve 6 is a signal auxiliary valve for the pressure regulator valve 1, and is used to control the signal pressure (pressure modifier pressure) to adjust the line pressure to the optimum pressure according to the operating conditions. ) is a valve that has the function of creating Structurally, it includes a valve hole 106 having ports 106a to 106e, a spool 206 that has lands 206a and 206b corresponding to the valve hole 106 and is movable in the axial direction, and a spring 306 that biases the spool 206 upward in the drawing. It is equipped with Ports 106d and 106e are drain ports. Port 106b is connected to throttle pressure & line pressure oil passage 711. Port 106a
and port 106c are connected to pressure modifier pressure oil passage 704. A force due to the pressure modifier pressure is applied to the land 206 on the spool 206 of the pressure modifier valve 6 as a force pushing it downward in the drawing.
The spring force of the spring 306 acts as a force that acts on a and pushes upward in the drawing. Therefore, until the set pressure is reached, oil flows from port 106b to port 106c while pushing the spool 206 downward in the drawing, and when the set pressure is reached, port 106c, which is a drain port, is closed to maintain the balance of the vertical force. Repeat opening and closing of the ports including the above, and maintain the set pressure from then on. Note that when the accelerator linkage is broken, line pressure is applied to the port 106b instead of the throttle pressure, and oil at a higher pressure level is delivered to the pressure modifier pressure oil passage 704 in the same manner as described above. be done. Furthermore, when the manual valve 2 is switched from the D range position to the range position (or range position) and the engine brake is activated, backup pressure is delivered from the backup valve 8 to 106b via oil passages 712 and 711. Increase the line pressure by pressure regulator valve 1,
Ensure band brake B/B is fastened. The cutback valve 7 is a signal auxiliary valve for the pressure regulator valve 1, and is for D range 1st speed.
This valve has the function of creating signal pressure (cutback pressure) to increase line pressure in range 1 speed, range 1 speed, R range, P range, and N range. Structurally, it includes a valve hole 107 having ports 107a to 107e, a spool 207 that has lands 207a and 207b corresponding to the valve hole 107 and is movable in the axial direction, and a spring 307 that urges the spool 207 downward in the drawing. and ports 407a and 407 fixed in the valve hole 107.
The plug 507 is provided with a sleeve 407 having a diameter b, and a plug 507 that is movable in the axial direction on the inner surface of the sleeve 407. The land diameter of the spool 207 is larger than the diameter of the plug 507. Port 107a, 1
07b and 107e are drain ports. Ports 107c and 407a are connected to cutback pressure oil passage 703. Port 207b is connected to line pressure oil passage 700. port 407
b is connected to the second to fourth speed pressure oil passages 713. The spool 207 of this cutback valve 7 has D range 1 speed, range 1 speed, range 1 speed
In the speed, R range, P range, and N range, the spring force by the spring 307 acts as a downward force in the drawing, and no upward force in the drawing acts,
Port 107d and port 107c communicate with each other, and the line pressure is directly delivered to cutback pressure oil passage 703 as signal pressure of pressure regulator valve 1. In addition, the spool 207 of the cutback valve 7
For D range 2nd speed, D range 3rd speed, D range 4th
speed, range 2 speed, and range 2 speed, the force due to line pressure is applied to port 10 as a force in the upward direction in the drawing.
7b acts on the plug 507, and the spring 30
7 and move the spool 207 upward in the drawing. Due to this upward movement of spool 207, port 107d is closed by land 207b, and hydraulic pressure delivery to cutback pressure oil passage 703 is cut off. Backup valve 8 increases the line pressure to increase the engagement force of band brake B/B to increase the engine braking effect when selecting from D range 3rd gear to range 2nd gear or range 2nd gear to operate the engine brake. This valve has the function of securing the backup function and canceling the backup function when the accelerator pedal is depressed while the engine brake is activated. Structurally, the valve hole 108 has ports 108a to 108f, and the hole 208 has lands 208a and 208b corresponding to the valve hole 108 and communicates with the port 108a or 108b.
The spool 208 is provided with a spool 208 having a diameter of 1.c and movable in the axial direction, and a spring 308 that biases the spool 208 toward the left in the drawing. Port 108c is a drain port. The port 108b is connected to the second and third speed pressure oil passages 714. Port 108a is connected to servo release pressure oil passage 715. Port 108d is connected to backup pressure oil passage 712. Port 108e is connected to range pressure oil passage 706. Port 108f is connected to throttle pressure oil passage 709. When the spool 208 of the backup valve 8 shifts from 2nd speed to 3rd speed, a force is applied to move the spool 208 to the right in the drawing against the spring 308 due to the servo release pressure from the port 108a. After the directional movement, the 2nd and 3rd speed pressure from the port 108b fixes it in the rightward movement position, and when the 4th speed is reached, it returns to the left. In addition, spool 2 during downshift
The rightward position fixed state of 08 is maintained as it is even when switching from 3rd speed to 2nd speed, and returns to the left direction when switching from 2nd speed to 1st speed. The 2nd and 3rd speed pressure oil passages 714 are the servo apply pressure oil passages 716 (2nd and 3rd speed) of the band servo 10.
Hydraulic pressure from the oil pressure output in 3rd and 4th gears is passed through the 3-4 shift valve 9, and both oil passages 714 and 716 communicate when the valve spool of the 3-4 shift valve 9 is in the 2nd and 3rd gear positions. state, and when the valve spool is in the 4th gear position, both oil passages 714 and 716
This is an oil passage provided so that it is in a blocked state. Here, the servo release pressure and the 2nd and 3rd speed pressures at hydraulic output (marked with ○) are shown in Table 4 below.

[Table] Next, the effects of the embodiment will be explained. (a) When the engine brake is activated from D range 3rd speed In D range 3rd speed, back up valve 8
The spool 208 is in a fixed position in the right direction,
There is a system in which line pressure can be supplied to the pressure modifier valve 6. Therefore, when selecting from D range 3 speed to range 2 speed or range 2 speed, line pressure is supplied to the pressure modifier valve 6, and the line pressure becomes the engagement pressure of band brake B/B. It is possible to increase the level of engine braking, eliminate band brake B/B slippage due to the driving force from the tire side, and ensure the effectiveness of engine braking. (b) When the engine brake is activated from D range 4th speed In D range 4th speed, back up valve 8
The spool has returned to the left direction, and line pressure cannot be supplied to the pressure modifier valve 6. Therefore, when selecting from D range 4 speed to range 2 speed or range 2 speed, there is no line pressure supplied to the pressure modifier valve 6, and the pressure level of the line pressure becomes the engagement pressure of the low clutch L/C. This prevents the shift shock from occurring due to excessive engagement pressure on the low clutch L/C. As described above, in the line pressure control device of the embodiment, when the engine brake is applied from the 3rd speed in the D range, the line pressure is increased by the backup action, and when the engine brake is applied from the 4th speed in the D range, Because the line pressure is controlled to keep the line pressure at normal pressure, it is possible to ensure the effectiveness of the engine brake when the engine brake is activated by engaging the band brake B/B, and to ensure the effectiveness of the engine brake when the engine brake is activated by engaging the low clutch L/C. Preventing shift shock due to excessive fastening capacity can be achieved at the same time. Although the embodiments of the present invention have been described above in detail with reference to the drawings, the specific configuration is not limited to these embodiments, and the present invention may be modified without departing from the gist of the present invention. included. For example, in the embodiment, an example of an automatic transmission with four forward speeds is shown, but the present invention can also be applied to automatic transmissions with three forward speeds, five forward speeds, or the like. (Effects of the invention) As explained above, in an automatic transmission that has a direct gear and an overdrive gear, and has a band brake and a clutch that are engaged together when the engine brake is activated due to a forced gear shift to a low gear, the line When the engine brake is applied from the first high speed stage, the pressure control means is applied to the band brake and the clutch, which are to be engaged together when the engine brake is applied, while the clutch is kept engaged and the released band brake is engaged. Means for controlling the line pressure to increase and not performing the line pressure increasing control when the engine brake is applied from the second high speed stage by engaging the released clutch while the band brake is still engaged. Therefore,
When the band brake and the clutch are to be engaged together when the engine brake is operating, the band brake is engaged while the released band brake is released and the band brake is engaged. It is possible to achieve the effect of simultaneously preventing gear shift shock when engine braking is applied when a released clutch is engaged from a released state while the brake is still engaged.

[Brief explanation of the drawing]

Fig. 1 is a conceptual claim diagram showing a line pressure control device for an automatic transmission of the present invention, Fig. 2 is a skeleton diagram showing a power train to which the embodiment device is applied, and Fig. 3 is a line pressure control circuit of the embodiment device. Schematic diagram of
FIG. 4 is a line pressure control circuit diagram of the embodiment device. 01...Oil pump, 02...Regulator valve, 03...Line pressure control means.

Claims (1)

[Claims for Utility Model Registration] At least one clutch and one band brake are provided, and in the first high speed gear where a direct gear is achieved, the clutch is engaged, the band brake is released, and an overdrive gear is established. In the second high speed gear, where the gear ratio is achieved, the clutch is released and the band brake is engaged. In an automatic transmission having an engine brake operation when both are engaged, a line pressure control means for controlling the pressure level of the line pressure produced by the regulator valve,
Of the band brake and clutch that are to be engaged together when the engine brake is applied, the line pressure is increased when the engine brake is applied from the first high speed stage by engaging the released band brake while keeping the clutch engaged. When the band brake is engaged and the released clutch is engaged to operate the engine brake from the second high speed stage, the pressure increase control of the line pressure is not performed. Automatic transmission line pressure control device.