JPS62155362A - Control device for automatic gear - Google Patents

Abstract

PURPOSE:To prevent a shock of speed change by disposing a relief means for controlling a line pressure corresponding to a signal pressure due to a boost pressure at the downstream of a throttle valve K. CONSTITUTION:A signal pressure generating means L for generating a signal pressure due to a boost pressure at the downstream of a throttle valve K in an intake passage C of an engine 1 and a line pressure generating means M for generating a line pressure due to a signal pressure generated by the signal pressure generating means L are disposed. The line pressure is supplied to an actuator I through a valve means J and a relief means N for preventing the signal pressure generated by the signal pressure generating means L from being increased over a fixed value is disposed. Thereby, the remarkable increase of the line pressure can be prevented at the time of the kick down operation and a shock of speed change is also reduced.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an automatic transmission that is installed in an automobile and automatically changes gears according to the operating conditions of the automobile and the engine;
In particular, the present invention relates to a control device for an automatic transmission used with an engine equipped with an exhaust turbocharger.

(Prior Art) Generally, an automatic transmission is configured to obtain a plurality of gears by combining a torque converter and a transmission gear mechanism and switching the power transmission path of the transmission gear mechanism. The switching means for switching the transmission path includes friction members such as clutches and brakes that switch the coupling relationship of each component of the transmission gear mechanism, a plurality of hydraulic actuators that actuate each of these friction members, and hydraulic actuators for these actuators. It consists of a valve means for controlling the supply and discharge of hydraulic pressure. The valve means is actuated according to the operating conditions of the vehicle and engine (for example, vehicle speed and engine load), and the friction member is selectively engaged via the hydraulic actuator, thereby transmitting the power of the transmission gear mechanism. The route, that is, the gear stage is changed.

Incidentally, in this type of automatic transmission, line pressure control is performed in which the oil pressure (line pressure) supplied to the hydraulic actuator via the valve means is adjusted in accordance with the engine load. This increases or decreases the eight torques of the friction member in response to changes in the torque transmitted through the friction member depending on the engine load, thereby increasing or decreasing the torque capacity of the friction member relative to the transmitted torque. 1 (line pressure)
Problems such as a shock at the time of fastening due to an excessive capacity and slippage of the friction member due to an excessively small capacity are prevented. In that case, the above-mentioned engine load is determined by the opening degree of the throttle valve in the intake passage of the engine, as shown in Japanese Patent Laid-Open No. 58-34258, and the case where the opening degree of the throttle valve downstream of the throttle valve in the intake passage is used. There are cases where boost pressure is used, and especially according to the latter, the boot pressure corresponds to the engine load with high precision, so adjusting the line pressure according to this boost pressure can effectively prevent problems such as shocks as described above. This will be prevented.

However, if the line pressure is adjusted according to the boost pressure, when a kickdown operation is performed when the engine is equipped with an exhaust turbo supercharger,
That is, when the accelerator pedal is depressed to the fully open position and the gear is forcibly downshifted, the following problem occurs. In other words, when a kickdown operation is performed, the gear stage is downshifted and the engine speed changes to the throttle valve fully open position rl! As well as rising rapidly under
Along with this, the supercharging effect of the exhaust turbo supercharger increases, and as a result, the boost pressure increases significantly.

Therefore, the line pressure that is adjusted according to this boost pressure also becomes extremely high, and when a shift is performed under such conditions, a large shift shock occurs.

(Object of the Invention) The present invention addresses the above-mentioned problems in an automatic transmission used with an engine equipped with an exhaust turbo supercharger. The purpose of this invention is to prevent a problem in which a large shift shock occurs due to a marked increase in line pressure during a kickdown operation when pressure control is performed.

(Structure of the Invention) In order to achieve the above object, the automatic transmission control device according to the present invention is characterized by having the following structure.

First, the schematic configuration of an engine and an automatic transmission to which the present invention is applied will be explained. As shown in FIG. 1, the engine Δ is driven by exhaust gas passing through the exhaust passage B.
An exhaust turbo supercharging ID for supercharging intake air from the intake passage C to the combustion air is provided, and the automatic transmission 11E includes a torque converter F connected to the output shaft A' of the engine A, and the torque converter. A speed change gear mechanism G disposed on the output side of the speed change gear mechanism G, a plurality of friction members H...I] that obtain a plurality of gears by switching the power transmission path of the speed change gear mechanism G,・Hydraulic actuators that actuate H respectively ■...I and these actuators I
. . . Valve means J for controlling the supply and discharge of hydraulic pressure (line pressure) to and from I is provided. In addition to such a configuration, there is also a signal pressure generating means for generating a signal pressure corresponding to the boost pressure downstream of the throttle valve in the intake path C of the engine A, and a signal generated by the generating means. A line pressure generating means M for generating line pressure according to the pressure is provided, and this line pressure is applied to each actuator via the valve means J! . . 1, and is further provided with relief means N for preventing the signal pressure generated by the signal pressure generating means from rising beyond a predetermined value.

According to such a configuration, even if the boost pressure downstream of the throttle valve in the intake passage C becomes significantly high due to the action of the exhaust turbocharging tmD during a kickdown operation, the signal pressure generating means is activated in accordance with this boost pressure. The signal pressure generated by the line pressure adjustment means M does not rise above a predetermined value due to the action of the relief means N.
This also prevents the line pressure, which is adjusted according to the signal pressure, from becoming excessively high.

(Effects of the Invention) As described above, according to the present invention, in an automatic transmission used with an engine equipped with an exhaust turbo supercharger, line pressure is prevented from increasing significantly during a kickdown operation. This reduces or prevents the shock that occurs when shifting gears in a kickdown state, and improves the driving performance and shift feel during kickdown, which is the case with this type of automatic gearshift.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 2 shows the mechanical V4 structure and hydraulic circuit of the automatic transmission 1, and the automatic transmission 1 includes a torque converter 1
0, a multi-stage gear mechanism 20, and an overdrive gear mechanism 40 disposed between the two.

The torque converter 10 includes a pump 13 directly connected to the output shaft 3 of the engine 2 via a drive plate 11 and a case 12, a turbine 14 disposed in the case 12 to face the pump 13, and the pump 13. The stator 15 is disposed between the turbine 14 and the turbine 14, and an output shaft 16 is coupled to the turbine 14. Further, a lock-up clutch 17 is provided between the output shaft 16 and the case 12. This lock-up clutch 17 is constantly pressed in the engagement direction by the pressure of the hydraulic oil circulating within the torque converter 10, and is released when release hydraulic pressure is supplied to the working chamber 18.

The multi-speed gear mechanism 20 has a front planetary gear mechanism 21 and a rear planetary gear mechanism 22, and sun gears 23, 24 of both mechanisms 21, 22 are connected by a connecting shaft 25. The input shaft 26 to this multi-speed gear mechanism 20 is
It is configured to be connected to the connecting shaft 25 through the front clutch 27 and to the ring gear 29 of the front planetary gear mechanism 21 through the rear clutch 28, and the connecting shaft 25, that is, the inner planetary gear mechanism 21. A second brake 31 is provided between the sun gear 23, 22 and the transmission case 30. The binion carrier 32 of the front planetary gear mechanism 21 and the rear planetary tooth*i
The ring gear 33 of the mechanism 22 is connected to an output shaft 34, and a low reverse brake 36 is connected between the planetary gear mechanism 22 and the transmission case 30.
A one-way clutch 37 and a one-way clutch 37 are respectively provided.

On the other hand, in the overdrive speed change gear n IN 40, the binion carrier 41 is connected to the output shaft 16 of the torque converter 10, and the sun gear A742 and the ring gear 43 are connected by a direct clutch 44. Further, an overdrive brake 45 is provided between the sun gear 42 and the transmission case 30, and the ring gear 43 is connected to the input shaft 26 to the multi-speed gear mechanism 20.

Then, the power transmission paths of the multi-stage gear mechanism 20 and the overdrive gear mechanism 40 are switched by selectively operating the clutches 27, 28, 44, the brakes 31°, 36, 45, and the one-way clutch 37, As a result, four forward speeds and one reverse speed are obtained between the input shaft (torque converter output shaft) 16 and the output shaft 34.

In addition, in each range selected by the manual shift valve of the hydraulic circuit described later, the relationship between the operation of each clutch and brake and the gear position is as shown in Table 1.

(Hereinafter, blank space) Next, the configuration of the hydraulic circuit in the automatic transmission 1111 will be described.

This hydraulic circuit is equipped with a wheel pump 50 that is constantly driven by the engine output shaft 3, and the hydraulic pressure of the hydraulic oil discharged from the pump 50 into the discharge line 51 is adjusted to a predetermined line pressure by a pressure regulating valve 52. At the same time, this line pressure is introduced to the manual shift valve 54 via the input line 53. This manual shift valve 5
4 is provided with ranges P, R, N, D, and 2.1, and each of these ranges is provided with five ports a to C selectively communicated with the input line 53. It is being That is, a boat a communicates with the input line 53 in each range D and 2.1, a boat b communicates with the input line 53 in each range D and 2, and a boat C communicates with the line 53 in the R range. ,P,R
, 2, and 1 are provided, and a boat e is provided that communicates with the line 53 in each of the ranges R and 1. These boats a to e are provided with first to fifth line pressure lines 56, respectively.
．． 57, 58, 59.60 are connected.

First to third control lines 61, 62, and 63 are branched from the first line pressure line 56, and the first control line 61 is connected to the first line 61, 62, and 63 through an orifice 61'.
At the right end of the 2-shift valve 66 in the drawing (hereinafter the same),
The second control line 62 is connected to 2-3 through an orifice 62'.
The third control line 63 is led to the right end of the shift valve 67 through an orifice 63' to the right end of a 3-4 shift valve 68, respectively. In addition, these control lines 61
．． 62.63 each orifice 61'.

Drain lines 61" and 62II are connected between the shift valves 62' and 63' and the shift valves 66, 67 and 68, respectively.
, 53 II are branched and these drain lines 61
First to third shift solenoid pulps 71, 72, and 73 for opening and closing ", 62", and 63", respectively, are provided.

These solenoid valves 71, 72, 73 are respectively
Drain line 61”, 62 corresponding to ON (excitation)
”, 63” and the corresponding control lines 61, 62, 6.
3 generates pressures t and II, thereby moving each of the shift valves 66, 67, and 68 from the OFF position shown in the figure to the ON position on the left side. Then, the combination of ON and OFF of these solenoid valves 71 to 73, that is, the ON position and OFF of the shift valves 66 to 68
Depending on the combination with the position, each gear stage can be obtained as shown in Table 2.

(Hereinafter, blank space) Table 2 Note that the third solenoid valve 73 is in the OFF position during 1st and 2nd speeds in the D range, but in the lunge and 2nd gears.
When in first and second gear in the range, the respective ON positions are shown in parentheses in Table 2 above. This turns on the third solenoid valve 73 in the lunge and 2 ranges.
This is to supply hydraulic pressure to the backup controller 1 to the roll valve 77, which will be described later, via a line 76 branched from the third control line 63.

And the first to third solenoid valves 71 to 71 as described above.
73 ON, OFF or associated shift valves 6
Through the operations 1 to 68, line pressure is supplied to each clutch and brake so that the gear positions shown in Table 2 above are obtained.

That is, when the 1-2 shift valve 66 is in the OFF position, the fifth line pressure line 60 connected to the boat e of the manual shift valve 54 is communicated with the low reverse brake line 78 via the shift valve 66. Ru. Therefore, in lunge and R ranges where the boat e is connected to the input line 53, line pressure is supplied to the actuator 36a of the low reverse brake 36, thereby engaging the low reverse brake 36. When the 1-2 shift valve 66 moves to the ON position, the fifth line pressure line 60 and the low reverse brake line 78 are cut off, and the D, 2. A line 80 is branched from the first line pressure line 56 connected to the input line 53 at the lunge via a line 79 and led to the left end of the 1-2 shift valve 66, and is connected to the second brake engagement line 81. Line pressure is introduced into the engagement side balls 1 to 31a' of the actuator 31a of the second brake 31 through the line 81 through the one-way orifice 82. As a result, D.2. The second brake 31 is engaged when J3 is at Lunge. Incidentally, an accumulator 85 whose back pressure is controlled by a reducing valve 83 via a line 84 is provided downstream of this second brake engagement line 81, and this reducing valve 83 has the above-mentioned A line 79 branched from the 15-inch pressure line 56 is further branched to a line 86.

Further, a rear clutch line 87 is branched from a line 79 branched from the first line pressure line 56, and line pressure is introduced into the actuator 28a of the rear clutch 28 through the line 87 via a one-way orifice 88. It has become. As a result, the rear clutch 28 is engaged. The rear clutch line 87 is also provided with an accumulator 90 whose back pressure is controlled by a line 89 branched from the line 79.

Next, to the 2-3 shift valve 67, a second line pressure line 57 is connected to the boat b of the manual valve 54 and introduces line pressure in the D and 2 ranges, and a second line pressure line 57 is connected to the boat C and is connected to the R range. When the valve 67 is moved to the ON position, the second line pressure line 57 is connected to the front clutch line 91 and the valve 67 is in the OFF position. Sometimes the third line pressure line 58 is the front clutch line 91
are selectively communicated with. This front clutch line 91 introduces line pressure to the actuator 27a of the front clutch 27 via a one-way orifice 91', and thereby, in the D range, the 2-3 shift valve 67
The front clutch 27 is engaged when the valve 67 moves to the ON position and when the valve 67 is in the OFF position in the R range. Further, from the front clutch line 91, the release side boat 3 of the second brake actuator 31a is connected via the one-way orifice 92.93.
The second brake release line 94 leading to the third
A reducing valve 95 and a one-way orifice 96 are arranged in parallel on the line pressure line 58.

Further, an accumulator 98 whose back pressure is controlled is connected to the front clutch line 91 via a one-way orifice 99 via a line 97 branched from the upstream portion of the line 91.

Furthermore, from the second brake release line 94, 3-
A line 101 leading to the second timing valve 100 is branched. The 3-2 timing valve 100 is moved to the right by control pressure supplied to its left end, and connects the second brake line 94 to the drain line 102 via the line 101. In that case, the line 103 supplying the control pressure is connected to the orifice 1 in a line 79 branched from the first line pressure line 56.
04, but this orifice 104
A drain line 105 is provided downstream of the drain line 105, and a timing adjustment solenoid valve 106 for opening and closing the drain line 105 is provided.

Further, a line pressure line 107 branched from the pump discharge line 51 is led to the 3-4 shift valve 68 . This line 107 connects to the 3-4 shift valve 68
One-way orifice 1 when is in the right OFF position
08 and an accumulator 109, and supplies line pressure to the actuator 44a of the direct clutch 44 and the release side boat 45a'' of the actuator 45a of the overdrive brake 45. Therefore, in this case, the direct clutch 44
is engaged, and the overdrive brake 45 is released. Then, the 3-4 shift valve 68 is turned ON on the left side.
When moved to the position, the direct coupling clutch actuator 44a and the overdrive brake actuator 4
The supply of hydraulic pressure to the release side boat 45a'' of the overdrive brake actuator 45a is cut off, but at this time, line pressure is constantly supplied from the pump discharge line 51 to the engagement side boat 458' of the overdrive brake actuator 45a. Therefore, the overdrive brake 45 is engaged.

Here, five fourth line pressure lines connected to the boat d of the manual valve 54 are led to the left end of the 3-4 shift valve 68, and the line pressure introduced from this line 59 in ranges other than the D range. This prevents the 3-4 shift valve 68 from moving to the ON position. Further, the direct coupling clutch line 110 is equipped with an oil pressure sensor 110'.

A pressure regulating line 111 branched from the discharge line 51 of the oil pump 50 and reaching a pressure regulating valve 52 is communicated with a torque converter line 112 via the pressure regulating valve 52, and this line 112 is led into the torque converter 10. It's dark. Further, a line 113 branched from this line 112 is led to a lock-up valve 114, and from the lock-up valve 114 is connected to an operating chamber 1 of a lock-up clutch 17 in the torque converter 10.
A lock-up release line 115 is led to introduce hydraulic pressure to the clutch 8 to release the clutch 17. A lock-up control line 116 branched from the pump discharge line 51 is led to the right end of the lock-up valve 114 via an orifice 117, and a drain line 118 provided on the downstream side of the orifice 117 A solenoid valve 119 for lock-up control is provided. When this solenoid valve 119 is turned on, it closes the drain line 118 and generates control pressure in the control line 116, thereby moving the lock-up valve 114 to the left, thereby draining the hydraulic pressure in the lock-up release line 115. locked up clutch 1
7 is concluded.

In addition to the above configuration, this hydraulic circuit includes a vacuum throttle valve 120 that adjusts line pressure, and a vacuum diaphragm 121 that operates the valve 120 in accordance with the boost pressure in the intake passage of the engine. This vacuum diaphragm 121
As shown in the figure, the engine has a pressure chamber 121a into which boost pressure is introduced from the downstream side of the throttle valve 5 in the intake passage 4 of the engine. (The larger the pressure is, the larger the pressing force is applied to the vacuum throttle valve 120 in the right direction via the diaphragm 121b and the rod 121C.) On the other hand, Figures 2 and 3
As shown in the figure, the vacuum throttle valve 120 is
Hydraulic pressure is introduced through an input line 122 branched from the pressure regulating line 111, and a modulator pressure is generated by regulating this hydraulic pressure in a modulator pressure line 123. This modulator pressure is applied to the vacuum diaphragm. The greater the pressing force from 121 to the right (the greater the boost pressure), the higher the pressure regulation value. This modulator pressure is introduced into the pressure increasing port 52a of the pressure regulating valve 52 through the line 124, so that the line pressure regulated by the pressure regulating valve 52 increases as the boost pressure increases. The pressure will be regulated. A backup line 125 branched from the fourth line pressure line 59 is led to the vacuum throttle valve 120 via a throttle backup valve 126 and the backup control valve 77 described above.

The throttle backup valve 126 controls the modulator pressure or line pressure by adjusting the hydraulic pressure generated in the fourth line pressure line 59 in the second range and lunge and guiding it to the vacuum throttle valve 120 via the backup control valve 77. It acts to further increase the This pressure increase effect is obtained when the control pressure generated in the third control line 63 is introduced into the backup control valve 77 via the line 76 and the valve 77 communicates with the backup line 125. It has become.

In addition, in order to generate control pressure in the third control line 63 in the 1.2 range, the third shift solenoid valve 73 is turned ON in these ranges as described above (see Table 2). ).

Further, the modulator pressure is the modulator pressure line 12.
A pressure reduction line 127 branched from the pressure reduction port 52 of the pressure regulating valve 52 via a cutback valve 128
It is set to be introduced in b. In that case, the cutback valve 128 is operated on the line 12 at the second or higher gear shift position where control pressure is generated on the first control line 61.
The control pressure introduced from 9 causes the pressure reduction line 127 to
Therefore, the pressure regulation value of the line pressure by the pressure regulating valve 52 is cut back (pressure reduced) at the second gear or higher shift position.

However, in this hydraulic circuit, the modulator pressure is prevented from increasing beyond a predetermined value. That is, as shown in FIGS. 2 and 3, the modulator pressure generated by the vacuum throttle valve 120 is passed through the line 124 to the pressure increase port 5 of the pressure regulating valve 52
A relief line 130 is branched from a modulator pressure line 123 introduced into 2a, and a relief valve 131 is provided to one end of which the modulator pressure is supplied by this line 130. This relief valve 131 moves to the right in the drawing against a spring 131a when the modulator pressure exceeds a predetermined value, and connects a branch line 130a provided in the relief line 130 to a drain line 131b. and
Therefore, the modulator pressure is prevented from increasing beyond the pressure corresponding to the spring force of the spring 131a.

In addition, the first to third speed change solenoid valves 71 to 73 and the timing adjustment solenoid valve 1 in the above hydraulic circuit
06 and the lock-up solenoid valve 119 are turned on and off by a control circuit 200 shown in FIG. The control circuit 200 is composed of, for example, a microcomputer, and includes an input/output section, a random access memory RAM, a read-only memory ROM, and a central processing unit CPU. Then, the control circuit 2
00 is a turbine rotation signal S1 from a turbine rotation sensor 201 that detects the turbine rotation speed of the torque converter 10 corresponding to the vehicle speed as a basic signal used for shift control and lockup control, and a throttle valve in the intake passage 4 of the engine. The throttle opening signal S2 from the throttle opening sensor 202 that detects the opening of 5 (see FIG. Turn on the third solenoid valves 71, 72, and 73.

OFF control performs speed change control, and ON/OFF control of the lock-up clutch 17 in torque converter 10 is performed by ON/OFF control of the fifth solenoid valve 119. Also, turn on the fourth solenoid valve 106.

By controlling OF F ft, II, the engagement timing of the second brake 31 during the 3-2 downshift is controlled. Further, a kickdown signal S3 from a kickdown switch 203 that operates when the accelerator pedal is depressed to the fully open position is input to this control circuit 200, and when the signal S3 is input,
The control circuit 200 turns on the first to third solenoid valves 71, 72, 73, etc. for shifting to downshift the gear stage, 0FFIIJt2! It is designed to do this.

On the other hand, the engine 2 used with this automatic transmission ti11 is equipped with an exhaust turbo supercharger 210 as shown in FIG. This supercharger 210 includes a turbine 211 disposed on the exhaust passage 6 of the engine 2, and a turbine 211 disposed on the exhaust passage 6 of the engine 2.
11 and a blower 212 disposed on the intake passage 4 of the engine 2. When the turbine 211 is rotationally driven by the energy of the exhaust gas, the blower 212 is connected to the throttle valve 5 by the intake passage 4. It acts to supercharge the intake air into the combustion chamber through.

According to the above configuration, each shift solenoid valve 7L, 72.73 is turned on or off by a signal from the control circuit 200.
Each friction member 27.28, such as a clutch or brake, is operated via a shift valve 66.67.68.
31, 36.44°45 actuator 27a, 2
8a, 31a.

Line pressure is supplied to 36a, 44a, and 45a, whereby each of the friction members is selectively fastened to obtain the gears as shown in Table 1.

In that case, the line pressure is controlled by the pressure regulating valve 5 shown in FIG.
2, the pressure is adjusted to a predetermined pressure by the vacuum throttle valve 120 and vacuum diaphragm 121, and the modulator pressure generated in accordance with the boost pressure in the intake passage 4 of the engine 2 is input to the pressure increase port 52a of the valve 52. The line pressure is adjusted according to the boost pressure, ie the engine load. This prevents shift shock caused by the line pressure supplied to each of the actuators being too large relative to the transmission torque of the friction member, and slippage of the friction member caused by the line pressure being too small.

However, the above boost pressure becomes a significantly large value when the supercharging effect of the exhaust turbo supercharger 210 increases during kickdown operation, and therefore the modulator pressure corresponding to this boost pressure also becomes significantly high. Modulator pressure line 12 in which modulator pressure is generated
3 is connected to the relief valve 1 via the relief line 130.
31, the modulator pressure will not rise above a predetermined value. Therefore, the line pressure, which is increased in accordance with the modulator pressure, is prevented from becoming excessively high during the kickdown operation. As a result, in an automatic transmission system used with an engine equipped with an exhaust turbo supercharger, problems such as line pressure becoming extremely high during a kickdown operation and a large transmission shock occurring can be prevented.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of the present invention. Figures 2 and 3 show an embodiment of the present invention. Figure 2 shows the structure and hydraulic circuit of an automatic transmission, and Figure 3 shows the main parts of the hydraulic circuit and the configuration around the engine. FIG. DESCRIPTION OF SYMBOLS 1... Self-8 transmission, 2... Engine, 4... Intake passage, 5... Throttle valve, 10... Torque converter, 20. 40-'f speed gear 1 structure 27° 28 ．．
31, 36, 44.45...Friction member, 27a, 2
8a, 31a, 36a, 44a. 45a...Hydraulic actuator, 52...Line pressure adjustment means (pressure regulating valve>, 66.67.68...Valve means (shift valve), 120°121...Signal pressure generation means (120...・Vacuum thrower 1~le valve, 121... vacuum diaphragm), 131...
・Relief means (relief valve>, 210...Exhaust turbo supercharging.

Claims (1)

[Claims] (1) A torque converter used with an engine equipped with an exhaust turbo supercharger and connected to the output shaft of the engine, a speed change gear mechanism disposed on the output side of the torque converter, and a speed change gear mechanism of the speed change gear mechanism. A control device for an automatic transmission comprising a plurality of friction members for switching power transmission paths, a plurality of hydraulic actuators for respectively operating these friction members, and a valve means for controlling supply and discharge of hydraulic pressure to these actuators. , a signal pressure generating means for generating a signal pressure corresponding to the boost pressure downstream of the throttle valve in the intake passage of the engine; and adjusting the line pressure supplied to the hydraulic actuator according to the signal pressure generated by the generating means. 1. A control device for an automatic transmission, comprising: a line pressure adjusting means for controlling the signal pressure; and a relief means for preventing the signal pressure from increasing beyond a predetermined value.