JPH0921463A - Oil pressure controller for automatic transmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent shift shock by preventing rapid pressure fluctuation from generated in an oil pressure chamber such as a clutch, when a solenoid valve or an electric system breaks down. SOLUTION: When a clutch is in a released state, an on/off solenoid valve 11 is in the closed state and a spool 19 is in a position toward the left side from a position illustrated in a figure so that a drain (D) and a communicating path 21 are in a communicated state. When the on/off solenoid valve 11 is switched to an open state, the spool 5 moves from the position illustrated in the figure to the right direction due to lowering of the pressure of a pressure chamber 7 and a pressure supply path 8 and input ports 12, 13 are communicated with each other so that a clutch pressure of an oil pressure chamber of a clutch 1 increases by enhancing its pressure gradient. Secondarily, the pressure of the communicating path 21 gradually increases, the spool 19 moves to the position illustrated in the figure and a flow path passing through notches 17, 18 is throttled so that the clutch pressure increases slowly. When the clutch pressure increases, the spool 19 moves further in the right direction, the input port 13 and the communication path 21 are communicated with each other, and a pressure increases gradient is enlarged again.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control device for an automatic transmission, which hydraulically controls a speed change mechanism of the automatic transmission.

[0002]

2. Description of the Related Art Conventionally, automatic transmissions, which are often used for vehicles and the like, switch a hydraulic pressure applied to each friction engagement device by a hydraulic valve in order to smoothly transmit a rotational driving force according to a load. Gearshift control. The shift control is performed by the occupant's manual operation with the select lever that selects forward, neutral, or reverse, and the engine engagement by the engine control computer from the engine throttle opening to engage the friction engagement device. This is performed by automatic shifting that determines the state.

As a clutch pressure control mechanism of such a conventional hydraulic control system for an automatic transmission, there are the following two methods.
(1) Accumulator back pressure control system (Japanese Patent Publication No. 5-757
9) and (2) a direct control method of a solenoid valve (European Patent No. 564017-A1 and Japanese Patent Application Laid-Open No. 5-65957).

[0004]

[Problems to be Solved by the Invention]

(1) In the case of adopting the accumulator back pressure control method, the back pressure of a plurality of accumulators is controlled by a single solenoid valve, and a large number of clutches can be controlled by a small number of solenoid valves. However, there is a problem that the physical structure of the accumulator requires a large space for arranging the accumulator, and it is difficult to speed up the operation of the accumulator, which makes it difficult to achieve quick gear shifting.

(2) In the case of using the solenoid valve direct control system, a system of directly controlling the clutch pressure with a solenoid valve is adopted.
There are two types, a direct acting type and a pilot type. Either of these two methods has the advantages that the gear shift response is high and the elements corresponding to the accumulator can be eliminated, so that the body size is reduced and the configuration is simplified. However, there is a problem that the gear shift shock increases due to a failure of the solenoid valve or the electric system, or the gear shift shock causes a failure of the automatic transmission to disable gear shifting.

An object of the present invention is to provide an automatic transmission hydraulic control device which eliminates the accumulator for controlling the clutch pressure and reduces the size of the hydraulic control device.
Another object of the present invention is to suppress an increase in shock caused by a malfunction of a solenoid valve or a malfunction of an electric system, and prevent a gear shift failure due to a malfunction of a solenoid valve or a malfunction of the electric system. To provide.

Still another object of the present invention is to provide a hydraulic control device for an automatic transmission, which has a small size and ensures high responsiveness.

[0008]

A hydraulic control device for an automatic transmission according to claim 1 of the present invention switches the hydraulic pressure applied to a plurality of friction engagement elements provided in the automatic transmission to change the hydraulic pressure. A hydraulic control device for an automatic transmission, which controls a plurality of shift stages by engaging or disengaging a coupling element respectively, wherein engagement or disengagement of the friction engagement element (1) is selected, A switching means (2) communicating with the hydraulic chamber of the engaging element (1) and switching the hydraulic pressure between high pressure and low pressure, and a communication passage (2) between the switching means (2) and the hydraulic chamber.
1), which has an opening area changing means (3) capable of changing the opening area of the communication passage (21),
(3) employs a technical means characterized in that the opening area is changed according to the pressure of the hydraulic chamber of the friction engagement element (1).

According to the hydraulic control device for an automatic transmission of the first aspect, the accumulator for controlling the clutch pressure can be eliminated and the physical size of the hydraulic control device can be reduced.
Further, since the opening area of the opening area changing means (3) is changed according to the pressure of the hydraulic chamber of the friction engagement element (1), the increase of shock caused by the failure of the solenoid valve or the failure of the electric system is suppressed. In addition, it is possible to prevent the shift failure due to the malfunction of the solenoid valve or the malfunction of the electric system. Further, by controlling the switching means, it is possible to secure high responsiveness although the body size is small.

A hydraulic control device for an automatic transmission according to a second aspect of the present invention is the electro-hydraulic control valve for controlling the hydraulic pressure according to a commanded signal in the technical means according to the first aspect.
(28), the opening area changing means (3), the opening according to both the pressure of the hydraulic chamber of the friction engagement element (1) and the output hydraulic pressure of the electro-hydraulic control valve (28) The feature is that the area can be changed.

According to another aspect of the hydraulic control device for an automatic transmission of the present invention, the electric hydraulic control valve (2
By controlling the hydraulic pressure in (8), precise clutch pressure control becomes possible, high responsiveness can be secured and shift shock can be reduced. The hydraulic control device for an automatic transmission according to claim 3 of the present invention is the technical means according to claim 1, wherein the hydraulic chamber of the friction engagement element (1) and the opening area changing means (3).
A branch passageway (30) branching from the communication passageway (21) between and, and an electrohydraulic control valve (34, 35) provided in the branch passageway (30) for controlling hydraulic pressure according to a commanded signal. And having.

According to another aspect of the hydraulic control system for an automatic transmission of the present invention, the electrohydraulic control valve (34,
By controlling the hydraulic pressure by 35), precise clutch pressure control becomes possible, high responsiveness can be secured and shift shock can be reduced. A hydraulic control device for an automatic transmission according to a fourth aspect of the present invention is the technical means according to the first aspect, in which hydraulic pressures applied to a plurality of friction engagement elements provided in the automatic transmission are switched, respectively. A hydraulic control device for an automatic transmission, which controls a plurality of shift stages by engaging or disengaging an engaging element respectively, selecting engagement or disengagement of the friction engagement element (1), A switching means (2) communicating with the hydraulic chamber of the friction engagement element (1) for switching the hydraulic chamber to a high pressure or a low pressure, and a communication passage (21) between the switching means (2) and the hydraulic chamber are provided. And an opening area changing means (3) capable of changing the opening area of the communication passage (21) and a line pressure control means (37) capable of changing the line pressure according to the throttle opening or the output torque. , The opening area changing means
(3) is characterized in that the opening area can be changed according to the hydraulic chamber pressure of the friction engagement element (1) and the value of the line pressure.

According to the hydraulic control system for an automatic transmission of the fourth aspect, the line pressure control means (37) can change the line pressure according to the throttle opening or the output torque.
Precise clutch pressure control is possible, high responsiveness can be secured, and shift shock can be reduced. Claim 5 of the present invention
The hydraulic control device for an automatic transmission described in the technical means according to claim 4, further comprising an electrohydraulic control valve (41) for controlling hydraulic pressure in accordance with a commanded signal, and the opening area changing means (41). 3) is characterized in that the opening area can be changed by the output hydraulic pressure of the electrohydraulic control valve (41).

According to the hydraulic control device for an automatic transmission of claim 5, the opening area changing means (3) can change the opening area by the output hydraulic pressure of the electrohydraulic control valve (41). The clutch pressure can be controlled, high responsiveness can be secured, and shift shock can be reduced.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The friction engagement element includes a clutch as well as a brake. The switching means for switching the hydraulic pressure in the hydraulic chamber of the friction engagement element to high pressure or low pressure uses, for example, a spool valve and an electromagnetic control valve, but other valve means instead of the spool valve can be used. The opening area changing means may be, for example, a spool valve having a notch formed in the land portion of the spool valve. The opening area of the communication passage by the opening area changing means can be variably controlled by hydraulic control such as a solenoid valve.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) A first embodiment of the present invention is shown in FIGS.
FIG. 2 shows a hydraulic circuit in which the present invention is applied to a clutch portion which is one friction engagement element of the hydraulic control device for an automatic transmission according to the present invention. In FIG. 2, the pump line pressure PL
Acts on the hydraulic chamber of the clutch 1 through the switching valve 2 and the opening area changing means 3.

In the switching valve 2, the spool 5 is biased to the right in FIG. 2 by the compression coil spring 6, and the pressure chamber 7 is provided on the side opposite to the compression coil spring 6. The pressure supply passage 8 and the pressure chamber 7 are connected by a pressure supply passage 9, and the throttle 1 is provided in the middle of the pressure supply passage 9.
0 is provided. The pressure chamber 7 is an on-off solenoid valve 1
1 allows communication with the drain. In the open state of the on / off solenoid valve 11, the spool 5 moves to the right from the state shown in FIG. 2, and the pressure supply passage 8 passes through the circumference of the spool and the input port 1 of the opening area changing means 3.
It is designed to communicate with 2 and 13. On the contrary, when the on / off solenoid valve 11 is switched to the closed state, the pressure supply passage 8 communicates with the pressure chamber 7 via the throttle 10 and is represented by the product of the pressure of the pressure chamber 7 and the pressure receiving area of the spool 5. When the spool 5 moves leftward to a position where the pressing force and the biasing force of the compression coil spring 6 are balanced, and the spool 5 moves leftward to the position shown in FIG. 2, the pressure supply passage 8 and the input port 12,
13 is cut off.

The opening area changing means 3 includes an input port 12,
The opening areas of 13, the communication passage 21, and the hydraulic chamber of the clutch 1 change according to the position of the spool valve 14. Spool valve 1
Reference numeral 4 denotes a spool 19 having a first land portion 15, a second land portion 16 and notches 17 and 18, and the spool 1
2 is a compression coil spring 20 for urging 9 to the left in FIG.
Consists of Compression coil spring 20 and spool 19
The pressure chamber 22 on the opposite side with respect to is connected by a communication passage 21 and a feedback passage 23. Spring room 2
4 communicates with the drain 25. When the pressure of the input ports 12 and 13 in the initial state is low, the spool 19 is located further leftward than the position shown in FIG. 2 due to the urging force of the compression coil spring 20.
And the communication passage 21 are in communication with each other. In the intermediate position state shown in FIG. 2, the input ports 12 and 13 are in communication with the communication passage 21 through the notches 17 and 18, and in this state, the opening area of the communication passage is narrowed by the notches 17 and 18. It is in communication with each other. The pressure in the communication passage 21 acts on the pressure chamber 22 via the feedback passage 23. When the pressure in the pressure chamber 22 increases, the spool 19 moves further to the right of the position shown in FIG. 2 against the compression coil spring 20. Then, input port 1
3 and the communication passage 21 communicate with each other with a large opening.

Next, the operation of the first embodiment will be described. The operating state when the clutch pressure shifts from the zero state to the clutch pressure PL will be described with reference to the graph shown in FIG. First, in the initial state, the spool 19 of the opening area changing means 3 is located on the left side of the position shown in FIG. 2, so that the input port 12 and the communication passage 21 are in communication with each other.
First, the clutch 1 is released. The clutch 1 is moved from the released state to the engaged state as follows. The on / off solenoid valve 11 is switched from the closed state to the open state. Then, the pressure in the pressure chamber 7 is discharged to the drain 25 via the on / off solenoid valve 11, and the decrease in the pressure in the pressure chamber 7 causes the spool 5 to move to the right of the position shown in FIG. 2 due to the urging force of the compression coil spring 6. The pressure supply passage 8 and the input ports 12 and 13 are in communication with each other. Then, this line pressure PL is transmitted from the input port 12 to the communication passage 21.
Is supplied to the hydraulic chamber of the clutch 1 via. As a result, the clutch pressure in the hydraulic chamber of the clutch 1 gradually increases from zero. This is the state from time 0 to t ₁ shown in FIG.

Then, when the pressure in the communication passage 21 gradually increases, the power represented by the product of the pressure in the pressure chamber 22 and the pressure receiving area of the end surface of the spool 19 showing a pressure value equivalent to this pressure is applied to the compression coil spring 20. Spool 1 against the bias of
9 to the right to move to the position of the spool 19 shown in FIG. Then, in this position state, the notch 1
Since the flow passages passing through Nos. 7 and 18 are throttled, the clutch pressure P is as shown in the period from t _{1 to} t ₂ shown in FIG.
As shown between c ₁ and clutch pressure Pc ₂ , the clutch pressure gradually increases.

When the clutch pressure further increases, the spool 19 further moves to the right, the input port 13 and the communication passage 21 communicate with each other, and the pressure increase gradient increases again. The clutch pressure at this time is between Pc _{2 and} PL. In this way, when the clutch 1 is switched from the disengaged state to the engaged state, the clutch pressure increases from the zero pressure in the initial zero state with a large pressure increase gradient, and the pressure increase gradient becomes gentle.
Next, the pressure increase gradient becomes large and reaches the clutch pressure PL. Therefore, to the response of the zero state of the clutch pressure to change the clutch pressure PL in good condition, as failure of the on-off solenoid valve 11 and electric system occurs, Pc ₁ ~ the clutch pressure is shown in FIG. 3 A gradual change in the clutch pressure occurs during the period Pc ₂ , and the change in the clutch pressure reduces the shock caused by switching between engagement and disengagement of the clutch. Further, since such a shock is small, it is possible to prevent the shift from being disabled.

(Second Embodiment) FIG. 4 shows a second embodiment of the present invention.
Shown in In the second embodiment shown in FIG. 4, in addition to the configuration of the first embodiment, the pressure in the spring chamber 24 is controlled by the duty control valve 28.
Can be controlled by. Since other configurations are similar to those shown in FIG. 2, the same components as those shown in FIG. 2 are designated by the same reference numerals.

According to the second embodiment, the duty control valve 28 is a three-way solenoid valve, and the duty control valve 28
Since the pressure in the spring chamber 24 can be controlled by controlling the pressure, the stepwise characteristic of the clutch pressure can be changed from the solid line to the dotted line as shown in FIG. 5, for example. For example, the clutch pressure is changed stepwise with a relatively large clutch pressure value as the opening degree of the throttle valve of the internal combustion engine increases. That is, as shown in FIG. 5, the clutch pressure characteristic is made variable from the solid line position to the broken line position as the throttle opening increases, thereby suppressing an increase in shift shock due to a failure of the solenoid valve or the electric system. it can. Furthermore, FIG. 6 shows an example of a shift hydraulic control device having four clutches to which the second embodiment is applied.

In this embodiment, four clutches A, B,
In clutch pressure control of C and D, the pressure of each spring chamber 24 is controlled by a single duty control valve 28. That is, the pressure of the spring chamber 24 in the opening area changing means 3 of the clutch 1 can be hydraulically controlled by the single duty control valve 28. In this embodiment, the single duty control valve 28 is used to control the clutches A, B, C, D without providing the individual duty control valves for the individual clutches A, B, C, D. be able to.

(Application example of the second embodiment) Next, the hydraulic control device for an automatic transmission according to the present invention is applied to an automatic transmission for a vehicle (hereinafter, referred to as
FIG. 1 shows a system configuration in which an "automatic transmission" is referred to as an AT. In FIG. 5, EV represents a solenoid valve. FIG. 6 shows an embodiment of a hydraulic control circuit in which the hydraulic circuit shown in FIG. 1 is incorporated in the automatic transmission hydraulic control device shown in FIG. FIG. 6 shows an overall configuration relating to shift control of an automatic transmission.

The automatic transmission transmits the torque generated in the engine to the speed change drive device through a fluid transmission device such as a torque converter, and outputs the speed changes by a plurality of planetary gear devices in the speed change drive device. As is well known, the operation of the vehicle AT is automatically or manually performed by the transmission 300.
The internal gear connection is switched, and the rotational force from the engine (not shown) connected to the torque converter 200 is transmitted to the rear wheels or front wheels of the vehicle. The automatic transmission means 90 and the entire peripheral device thereof are inside an oil pan (not shown) inside the AT under the transmission 300, and a hydraulic circuit drain is provided around the hydraulic control device 400 inside the oil pan.

In the transmission 300, a known hydraulic pump 56 that is directly connected to the rotary shaft of the engine and is driven to rotate is provided, and the drive oil discharged from each hydraulic device to an oil pan or the like is supplied from an intake port 57. It sucks and supplies pressure oil to each device through the line pressure control valve 64. The pressure oil from the hydraulic pump 56 is a variable high pump oil pressure and is a line pressure control valve 6 which is an electromagnetic control type pressure control valve.
It is controlled to a constant high line pressure by 4 and supplied to each hydraulic equipment.

The hydraulic control device 400 includes an engaging hydraulic control valve 6
5 are provided. The engagement hydraulic control valve 65 arbitrarily controls the line pressure of the pressure oil supplied from the line pressure control valve 64, and supplies the pressure oil having a predetermined control pressure to the pressure supply passage 8. Each friction engagement device is a transmission 300
The gears are connected to gears forming respective gear ratios such as a planetary gear (not shown) therein, and by engaging or disengaging these friction engagement devices, the gear ratios are switched to perform gear shift control of the vehicle.

In this embodiment, a hydraulic switching valve housed in the manual transmission means 80 and operated by a manual operation (not shown),
This is a hydraulic control device for an automatic transmission, in which a hydraulic switching valve including an on / off solenoid valve 11 for four stages of automatic transmission accommodated in an automatic transmission means 90 can be independently operated. Each element of the planetary gear device is selectively engaged or disengaged by various clutches C0, C1, C2 and brakes B0, B1, B2, B3 to obtain a predetermined gear ratio, and the clutches C0, C1. , C2, brakes B0, B1, B2, B3
A single duty control valve 28 controls the spring chamber of the opening area changing means that communicates with the hydraulic chamber.

(Third Embodiment) FIG. 7 shows a third embodiment of the present invention.
Shown in The third embodiment shown in FIG. 7 is the opening area changing means 3
The clutch pressure is controlled by controlling the branch passage 30 communicating with the communication passage 21 according to the pressure of the inlet ports 12 and 13 to switch to the discharge passage 33 or the filling passage 32 by switching the switching valve 31. The filling passage 32 is provided with a filling electromagnetic valve 34, and the discharging passage 33 is provided with a discharging electromagnetic valve 35. When the pressure in the inlet ports 12 and 13 is relatively high, the branch passage 30 and the discharge passage 33 are communicated with each other, and when the pressure in the inlet port 12 or 13 is relatively low, the switching valve 31 is switched to fill the branch passage 30. It communicates with the passage 32. The clutch pressure in the communication passage 21 is
It is controlled by the filling electromagnetic valve 34 or the discharging electromagnetic valve 35.

FIG. 8 shows an example of an overall view of a hydraulic control system to which the third embodiment is applied. Each of the filling electromagnetic valve 34 and the discharging electromagnetic valve 35 for controlling the clutches A, B, C, D shown in FIG. 8 is one, and four clutches A, B, C,
Control D. Therefore, according to this third embodiment,
A switching valve 31 is provided in a branch passage 30 for guiding the clutch pressure of a plurality of clutches A, B, C, D, and this switching valve 31 is controlled by a single charging solenoid valve 34 and a single discharging solenoid valve 35. it can. Therefore, the number of expensive solenoid valves can be reduced and the clutch pressure can be properly controlled.

(Fourth Embodiment) A fourth embodiment of the present invention is shown in FIG.
Shown in The fourth embodiment shown in FIG. 9 is the opening area changing means 3
A spool position changing mechanism 37 for controlling the position of the spool 19 is provided on one end side of the spool 19.
The spool position changing mechanism 37 corresponds to the line pressure control means described in the claims, and controls the rod 38 axially protruding from one end of the spool 19 by the pressure of the pressure chamber 39 that guides the line pressure PL. It has become. That is, as the line pressure PL increases, the pressure in the pressure chamber 39 increases and pushes the rod 38 to the left, that is, the spool 19 is pushed to the left side in FIG. 9, and the clutch pressure level changes, for example, as indicated by the broken line in FIG. Change pressure value Pc ₁
Change to'or Pc ₂ '. For example, line pressure P
L increases as the throttle opening increases, the torque increases accordingly, and the clutch pressure increases.

According to the fourth embodiment, the clutch pressure is changed according to the throttle opening of the internal combustion engine for an automobile equipped with the shift hydraulic control device, and the clutch pressure is increased when the throttle opening is increased, so that the proper clutch is obtained. Pressure control is possible. (Fifth Embodiment) FIG. 10 shows a fifth embodiment of the present invention.

In the fifth embodiment, the spring chamber of the fourth embodiment shown in FIG. 9 is duty-controlled by a three-way duty control valve 41. Since the other components are basically the same as the configuration shown in FIG. 9, the same reference numerals are given to the components substantially the same as the components shown in FIG. This fifth
According to the embodiment, the pressure in the spring chamber 24 can be controlled more precisely by the three-way duty control valve 41, so that the clutch pressure can be controlled more precisely.

(Sixth Embodiment) A sixth embodiment of the present invention is shown in FIG.
It is shown in FIG. The sixth embodiment shown in FIG. 11 corresponds to the third embodiment shown in FIG.
It has a configuration in which the embodiment and the fourth embodiment shown in FIG. 9 are combined. That is, the position of the spool 19 is variable according to the line pressure, and the pressure of the communication passage 21 can be increased or decreased by the switching valve 31 according to the pressure of the inlet ports 11 and 12.

According to the sixth embodiment, since the operation of both the third and fourth embodiments can be obtained at the same time, it is a line pressure sensitive type solenoid valve for filling 34 or solenoid valve for discharging. 35 enables precise clutch pressure control.

[Brief description of drawings]

FIG. 1 is a block diagram showing a system configuration of an automatic transmission according to a second embodiment of the present invention.

FIG. 2 is a hydraulic circuit diagram showing a main part of the hydraulic control system according to the first embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a clutch pressure characteristic of the first embodiment.

FIG. 4 is a hydraulic circuit diagram showing a main part of a hydraulic control system according to a second embodiment of the present invention.

FIG. 5 is a characteristic diagram showing a clutch pressure characteristic of the second embodiment of the present invention.

FIG. 6 is a hydraulic circuit diagram of the entire system to which a second embodiment of the present invention is applied.

FIG. 7 is a hydraulic circuit diagram showing a main part of a hydraulic control device according to a third embodiment of the present invention.

FIG. 8 is a hydraulic circuit diagram of the entire system to which a third embodiment of the present invention is applied.

FIG. 9 is a hydraulic circuit diagram showing a main part of a hydraulic control device according to a fourth embodiment of the present invention.

FIG. 10 is a hydraulic circuit diagram showing a main part of a hydraulic control system according to a fifth embodiment of the present invention.

FIG. 11 is a hydraulic circuit diagram showing a main part of a hydraulic control system according to a sixth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 clutch 2 switching valve 3 opening area changing means 5 spool 6 compression coil spring 7 pressure chamber 8, 9 pressure supply passage 10 throttle 11 on / off solenoid valve 12, 13 input port 14 spool valve 15 first land portion 16 second land portion 17 , 18 notch 19 spool 20 compression coil spring 21 communication passage 22 pressure chamber 23 feedback passage 24 spring chamber 28 duty control valve 30 branch passage 41 three-way duty control valve (electrohydraulic control valve)

Claims (5)

[Claims] 1. An automatic switching control for switching a plurality of shift speeds by switching hydraulic pressures applied to a plurality of friction engagement elements provided in an automatic transmission and engaging or disengaging the plurality of friction engagement elements, respectively. A hydraulic control device for a transmission, which selects engagement or disengagement of the friction engagement element (1), communicates with a hydraulic chamber of the friction engagement element (1), and switches the hydraulic pressure to high pressure or low pressure. The switching means (2) and the opening area changing means (3) provided in the communication passage (21) between the switching means (2) and the hydraulic chamber and capable of changing the opening area of the communication passage (21). A hydraulic control device for an automatic transmission, characterized in that the opening area changing means (3) changes the opening area according to the pressure of the hydraulic chamber of the friction engagement element (1). 2. An opening area changing means having an electrohydraulic control valve (28) for controlling hydraulic pressure according to a commanded signal.
(3) is characterized in that the opening area can be changed according to both the pressure of the hydraulic chamber of the friction engagement element (1) and the output hydraulic pressure of the electrohydraulic control valve (28). Item 2. A hydraulic control device for an automatic transmission according to item 1. 3. A branch passage (30) branched from a communication passage (21) between the hydraulic chamber of the friction engagement element (1) and the opening area changing means (3), and the branch passage (30). The hydraulic control device for an automatic transmission according to claim 1, further comprising an electrohydraulic control valve (34, 35) provided in the control unit for controlling hydraulic pressure according to a commanded signal. 4. An automatic switching control for a plurality of shift speeds by switching hydraulic pressures applied to a plurality of friction engagement elements provided in an automatic transmission and engaging or disengaging the plurality of friction engagement elements, respectively. A hydraulic control device for a transmission, which selects engagement or disengagement of the friction engagement element (1), communicates with the hydraulic chamber of the friction engagement element (1), and increases or decreases the pressure of the hydraulic chamber. Switching means (2) for switching, and opening area changing means (3) provided in a communication passageway (21) between the switching means (2) and the hydraulic chamber and capable of changing the opening area of the communication passageway (21). And a line pressure control means (37) capable of changing the line pressure according to the throttle opening or the output torque, and the opening area changing means (3) is a hydraulic chamber of the friction engagement element (1). The automatic changeover characterized in that the opening area can be changed according to the pressure and the line pressure. Hydraulic control device for a machine. 5. An opening area changing means having an electrohydraulic control valve (41) for controlling hydraulic pressure according to a commanded signal.
(3) The opening area can be changed by the output hydraulic pressure of the electrohydraulic control valve (41).
A hydraulic control device for the automatic transmission described.