JP3498414B2 - Lock-up clutch control device for automatic transmission - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic transmission for appropriately controlling an automatic transmission having a torque converter in a transmission system capable of establishing a lockup state in which input and output are directly connected by a lockup clutch during coasting. The present invention relates to a lockup clutch control device for a machine.

[0002]

2. Description of the Related Art In recent years, in a vehicle operating state in a lockup region where a torque increasing function, a torque fluctuation absorbing function and the like by a torque converter are unnecessary, the torque converter can be put into a lockup state in which input and output are directly connected. A lock-up type automatic transmission tends to be adopted, and such an automatic transmission improves transmission efficiency and improves fuel efficiency.

Conventionally, in controlling the lock-up clutch of this type of torque converter, the throttle opening is controlled, for example, as in the automatic transmission described in the "NISAN SAN RE4R01A type full range electronic control automatic transmission maintenance manual" by the applicant of the present application. TVO
It is determined which one of the lockup (L / U) region and the converter (C / U) region the vehicle is operating, which is defined from the (engine operating load) and the vehicle speed V, and the torque converter is determined according to the determination result. In the lock-up area, the lock-up clutch is engaged to establish a lock-up state in which the input and output are directly connected, and in the converter area, the lock-up clutch is opened to release the direct connection. It is normal.

It is becoming more and more common for the torque converter during coasting of the vehicle to be in a lockup state in which the input and output elements are directly connected. However, when the brake pedal is depressed to brake during traveling in such a state, Especially on low friction roads, the rotation of the wheels is suddenly stopped, and the response delay of the torque converter becomes relatively large, and the release of the lockup clutch cannot keep up with this, and the engine drive-coupled to the wheels stops. There is a risk.

In order to avoid such an engine stall on a low friction road, Japanese Utility Model Publication No. Sho 64-21848 discloses a lock for an automatic transmission that releases a lockup clutch when a driver depresses a brake pedal. An up clutch control device has been proposed. However, in such a lock-up clutch control device for an automatic transmission, the lock-up clutch is released even during the sudden braking that needs to avoid the engine stall, so that the fuel consumption deteriorates.

As a lock-up clutch control device for an automatic transmission that prevents such deterioration of fuel consumption and avoids engine stall, there is a lock-up clutch control device that releases the lock-up clutch when a sudden deceleration of the vehicle is detected. It is published in the official gazette. However, in such a lockup clutch control device for an automatic transmission, there is a delay until the rapid deceleration of the vehicle is detected, as compared with the case where the lockup clutch control is performed with the operation of the brake. Therefore, when detecting the sudden deceleration of the vehicle and releasing the lockup clutch, in order to compensate for this delay, the engagement capacity of the lockup clutch is controlled to the minimum pressure required for engagement, and the lockup clutch is released. A device that improves the release response and a device that increases the output torque of the engine and prevents the occurrence of engine stall are required.

[0007]

However, even if the above measures are taken in order to avoid the engine stall and improve the fuel economy, the occurrence of abnormality in the sensor, actuator, etc., the change over time of the hardware, the variation, etc. Such a measure may not be effective due to the fail mode caused by torque phase feedback for suppression, learning control, or the like.

An object of the present invention is to provide a lockup control device for an automatic transmission, which is capable of both avoiding an engine stall and improving fuel efficiency even when a fail mode occurs when performing lockup control during coasting. Is to provide.

[0009]

A lockup control device for an automatic transmission according to a first aspect of the present invention is a transmission system for a torque converter 101 capable of establishing a lockup state in which input and output are directly connected by a lockup clutch. In the lock-up clutch control device for the automatic transmission 102, the inertia traveling detection means 104 for detecting that the vehicle 103 is coasting, and the inertia traveling detection means 104.
When the vehicle 103 detects that the vehicle 103 is coasting based on the detection signal, the lock-up clutch engagement capacity control means 105 that sets the engagement capacity of the lock-up clutch to the minimum pressure required for engagement, The brake pedal depression detecting means 106 for detecting a person's brake pedal depression operation, the rapid deceleration detecting means 107 for detecting the rapid deceleration of the vehicle 103, and the detection signal of the brake depression detecting means 106 during the coasting of the vehicle 103. When it is detected that the brake pedal is stepped on the basis of this, or when the vehicle 103 is suddenly decelerated based on the detection signal of the sudden deceleration detecting means 107, the lockup clutch releasing means 108 for releasing the lockup clutch, Engine torque increase control means 1 for increasing the output torque of the engine 109 0, the lock-up clutch releasing means 108 or the engine torque up control part 110
When an abnormality is detected based on the detection signal of the abnormality determining means 110 and the detection signal of the abnormality determining means 110, the lockup clutch is released in response to the signal from the brake depression detecting means 106, Further, when the abnormality is not detected, the sudden deceleration detecting means 10
The lock-up clutch release control means 112 for releasing the lock-up clutch in response to a signal from the control unit 7 is provided.

In the lock-up control device for an automatic transmission according to a second aspect of the present invention, the abnormality determining means 110 has a first fail mode indicating that the environmental condition of the engine 109 or the automatic transmission 102 has changed, and the engine. 109 or the second fail mode indicating a change with time or a failure of the automatic transmission 102, and the abnormality is discriminated.

[0011]

With the above structure, in the lock-up clutch control device for an automatic transmission according to claim 1 of the present invention, the vehicle 10
When the abnormality is detected in response to the signal from the lock-up clutch releasing means 108 during inertial running or the engine torque-up control means 110, the brake depression detecting means 1
The lockup clutch is released in response to the signal from 06. On the other hand, when no failure is detected, the lockup clutch is released in response to the signal from the rapid deceleration detection means 107. By such control, it is possible to avoid the engine stall and improve the fuel consumption even if an abnormality occurs.

In the lock-up clutch control device for the automatic transmission according to the second aspect of the present invention, the abnormality is detected by the engine 10
9 or the change in the environmental condition of the automatic transmission 102 and the change over time of the engine 109 or the automatic transmission 102, the failure, etc. are discriminated to prevent the control state of the vehicle 103 from remaining in the failed state. To do.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a lockup clutch control device for an automatic transmission according to the present invention will be described in detail with reference to the drawings. FIG. 2 is a system diagram showing an embodiment of a lockup clutch control device for an automatic transmission according to the present invention. The power of the engine 3 is input to the automatic transmission 1 via the torque converter 2, the input rotation speed is changed at a gear ratio according to the selected gear, and the input rotation is transmitted to the output shaft 4.

Here, in the automatic transmission 1, the selected shift speed is determined by the combination of ON / OFF of the shift solenoids 6 and 7 in the control valve 5, and the torque converter 2 has the lockup clutch engagement capacity in the control valve 5. By the duty control of the lockup solenoid 8 as the control means, it is possible to set the converter state in which the input / output elements are not directly connected or the lockup state in which the input / output elements are directly connected by a lockup clutch (not shown). The lockup solenoid 8 puts the torque converter 3 into a converter state by releasing a lockup clutch (not shown) when the drive duty D is 0%, and locks the torque converter 3 when the drive duty D is 100%. A lockup state is assumed by fastening (not shown).

The transmission controller 6 has the functions of lock-up clutch release means, torque-up control means, lock-up clutch release control means, and failure determination means. Controlled by 9. An information signal indicating the operating state of the vehicle is input to the transmission controller 9 from various sensors and actuators described later.

The throttle opening sensor 10, the idle rotation sensor 11, and the abnormal combustion detection sensor 12, which are provided in the proximity of the engine 3 and serve as inertial running detection means, include a throttle opening TVO, an idle rotation speed Ni, and an abnormal engine 3. An abnormal combustion signal E indicating that combustion is being performed is detected.

An engine rotation sensor 13 and a turbine rotation sensor 14 provided near the torque converter 2.
Detects the engine speed Ne and the automatic transmission input speed, that is, the torque converter output speed Nt, respectively.

The transmission output shaft rotation sensor 15 (corresponding to a sudden deceleration detecting means) provided near the transmission output shaft 4 is
The transmission output shaft speed No. is detected. Also, engine 3
An electronically controlled throttle abnormality signal EC indicating that an abnormality has occurred in the electronically controlled throttle is input to the transmission controller 9 from the engine controller 16 that controls the.

Further, as a sensor and an actuator for detecting the second fail mode of the vehicle which indicates a change or failure of the automatic transmission 1 or the engine 3 with time, a brake switch 17, an idle switch 18, an ignition device 19 as a brake depression detecting means. , Accessory 20, anti-skid 2
1 and traction control system 22
In addition, an oil temperature sensor 23, an air flow meter 24, and a water temperature sensor 25 are provided as sensors and actuators that detect the first fail mode indicating that the environmental conditions of the automatic transmission 1 or the engine 3 have changed.

The brake switch 17 generates a brake braking signal B indicating that the ON state at the time of braking by depressing the brake pedal is detected. Idle switch 18
Generates an idle switch signal I indicating that the ON state of the idle switch has been detected. The ignition device 19 generates an ignition signal IG indicating an ignition state. The auxiliary machine 20 generates an auxiliary machine signal H indicating the state of the auxiliary machine. Anti skid 2
1 generates an antiskid signal ABS indicating the state of antiskid. The traction control system 22 generates a traction control signal TCS indicating the state of the traction control system.

The oil temperature sensor 23 measures the hydraulic oil temperature C of the transmission 1, the air flow meter 24 measures the intake air amount Q to detect the load state of the engine 3, and the water temperature sensor 2
5 measures the water temperature W of a radiator (not shown).

The transmission controller 9 performs the following shift control by well-known calculation (not shown) based on these input information. That is, during the shift control, the transmission controller 9
Is the throttle opening TVO and the transmission output shaft speed No.
Based on the vehicle speed V calculated from the above, the optimum shift speed for the current driving state is obtained by, for example, a look-up method from table data, and the shift solenoids 6 and 7 are turned on and off so that the optimum shift speed is selected. I do.

Further, when the vehicle shifts to coasting while the lock-up clutch is engaged, the lock-up clutch engagement capacity for coasting is searched based on the map for each gear position from the vehicle speed V, the hydraulic oil temperature C, and the like. Then, the drive duty for achieving this lock-up clutch engagement capacity is calculated, and the calculated value is set as the drive duty D of the lock-up solenoid 8. At this time, the lock-up clutch engagement capacity for coasting is the smallest lock-up clutch engagement capacity in the range where the lock-up clutch (not shown) of the torque converter 2 does not slip, and the vehicle speed V
And the two-dimensional table data of the hydraulic oil temperature C are obtained for each gear position by an experiment or the like.

The drive duty D for coasting thus obtained is output to the lock-up solenoid 8 and the lock-up clutch (not shown) of the torque converter 3 is engaged with the smallest lock-up clutch within a range that does not slip. It can be fastened by capacity.

The operation of the lockup clutch control device for an automatic transmission according to the present invention will be described. 3 is a first flowchart of a control routine of the lockup clutch control device for the automatic transmission according to the present invention. This routine is, for example, 1
It is executed by a scheduled interrupt such as 0 msec. This control routine is executed after it is determined that the vehicle is coasting based on the throttle opening TVO detected by the throttle opening sensor 10 (FIG. 2).

First, at step 31, the second fail mode flag FLAG of the transmission controller 9 (FIG. 2).
It is determined whether (which will be described later) is set to 1, that is, whether the current control state of the vehicle is the second fail mode due to the change over time of the hardware situation.

When it is determined that the vehicle is in the second fail mode, in step 32, in order to perform the lockup clutch release control in response to the brake braking signal B (FIG. 2) from the brake switch 17 (FIG. 2), the vehicle This routine is ended while waiting for the occurrence of the sudden braking of.

If it is determined in step 31 that the second fail mode is not in effect, then in step 33 the operating states of various sensors and actuators used to avoid engine stall are inspected, and the second fail mode is currently generated. Judge whether or not.

In this example, in step 33, the following is judged. (1) Lockup solenoid 8 during coasting (Fig. 2)
Whether the set value of the drive duty D (FIG. 2) of 1 exceeds the value indicating the responsiveness limit. (2) Whether or not an abnormality has occurred in the throttle opening sensor 10 (FIG. 2). (3) Idle speed Ni detected by the idle speed sensor 11 (FIG. 2) (whether or not the duty of the idle control valve (ISC) obtained from FIG. 2 is abnormal. (4) Abnormal combustion detection Whether the sensor 12 (Fig. 2) is abnormal (5) Whether the transmission output shaft rotation sensor 15 (Fig. 2) is abnormal (6) Engine controller 16 (Fig. 2) The electronically controlled throttle abnormality signal EC (Fig. 2) is transmitted from the transmission controller 9
Whether it was entered in (Fig. 2). (7) Whether the idle switch 17 (FIG. 2) is abnormal. (8) Ignition device 19 (FIG. 2) to ignition signal IG (FIG. 2)
Whether or not occurred. (9) Whether an abnormality has occurred in the auxiliary machine 20 (FIG. 2). (10) Whether an abnormality has occurred in the anti-skid 21 (Fig. 2). (11) Whether an abnormality has occurred in the traction control system 22 (Fig. 2).

If even one of these judgments is abnormal, it is judged that the second fail mode is currently occurring, and the second fail mode flag FLAG of the transmission controller 9 (FIG. 2) is set to 1 Set (Step 3
4) and then in step 32 the brake switch 1
In order to release the lockup clutch in response to the brake braking signal B from 7 (FIG. 2), this routine is ended while waiting for the sudden braking of the vehicle.

Note that once the second fail mode flag FLAG is set to 1 in step 34, the second fail mode is not released unless it is externally reset to 0 for repair or repair.

When it is determined in step 33 that the second fail mode is not currently occurring, it is determined in step 35 whether the first fail mode is currently occurring due to a condition for avoiding engine stall, that is, a change in environmental conditions. To determine.

In this example, in step 35, the following is judged. (1) Whether the power supply voltage of the transmission controller 9 (FIG. 2) is smaller than the value indicating the variation limit. (2) Whether the hydraulic oil temperature C (FIG. 2) of the transmission 1 (FIG. 2) measured by the oil temperature sensor 23 (FIG. 2) is smaller than a value indicating the responsiveness limit. (3) Whether the operating oil temperature C (FIG. 2) of the transmission 1 (FIG. 2) measured by the oil temperature sensor 23 (FIG. 2) is larger than the value indicating the variation limit. (4) Whether the intake air amount Q (FIG. 2) measured by the air flow meter 24 (FIG. 2) is smaller than the limit value for avoiding engine stall. (5) Whether the water temperature W (FIG. 2) of the engine 1 (FIG. 2) measured by the water temperature sensor 25 (FIG. 2) is smaller than a limit value for avoiding engine stall.

If any one of these judgments is abnormal, it is judged that the first fail mode is currently occurring, and the brake switch 1 is judged in step 32.
In order to release the lockup clutch in response to the brake braking signal B (FIG. 2) from 7 (FIG. 2), this routine is ended while waiting for the sudden braking of the vehicle.

If it is determined in step 35 that the first fail mode is not currently occurring, lockup occurs when a rapid deceleration of the vehicle is detected by the vehicle speed V calculated from the transmission output shaft speed No (FIG. 2). In order to release the clutch (step 36), this routine is terminated while waiting for the sudden braking of the vehicle.

FIG. 4 is a second flowchart of the control routine of the lockup clutch control device for an automatic transmission according to the present invention. In this routine, the set value of the drive duty D (FIG. 2) of the lockup solenoid 8 (FIG. 2) during coasting is set to a value indicating the responsiveness limit as a reference of whether or not the second fail mode has occurred. It is determined whether or not the time is over, and is executed by a regular interrupt such as 10 msec. This control routine is executed after it is determined that the vehicle is coasting by the throttle opening TVO detected by the throttle opening sensor 10 (FIG. 2).

First, at step 41, the second fail mode flag FLAG of the transmission controller 9 (FIG. 2).
Is set to 1, that is, whether the current control state of the vehicle is the second fail mode.

If it is determined that the second fail mode is set, in step 42, the idle rotation sensor 11
The duty of ISC obtained from the idle speed Ni (FIG. 2) detected from (FIG. 2) is increased more than that during control during normal coasting, and the prevention of engine stall is further improved. The recovery shock is aggravated, that is, the shock is controlled so that the driver can easily recognize the shock and the like so that the driver can recognize the abnormality of the drive system.

Then, in step 43, the brake braking signal B (FIG. 2) from the brake switch 17 (FIG. 2).
To release the lockup clutch in response to
This routine is finished while waiting for the sudden braking of the vehicle.

When it is determined in step 41 that the second fail mode is not set, in step 44, the lockup clutch is locked during coasting in order to cope with the slip occurrence of the lockup clutch due to manufacturing variations of the clutch and the hydraulic circuit and aging. As a result of learning control of the up-clutch engagement capacity, the lock-up solenoid 8 during coasting
It is determined whether or not the set value of the drive duty D (FIG. 2) of (FIG. 2) exceeds a value indicating the responsiveness limit, that is, whether or not the second fail mode is currently occurring.

Based on the increase amount of the lock-up clutch engagement capacity at this time, it is inspected whether or not the lock-up clutch engagement capacity of the lock-up clutch release responsiveness abnormality required at the time of rapid deceleration of the vehicle is reached.

At step 44, drive duty D
When it is determined that the set value of (Fig. 2) exceeds the value indicating the responsiveness limit, the set value for detecting the rapid deceleration of the vehicle is lowered below the normal value to allow some malfunction, and then Improves deceleration detection responsiveness and further improves prevention of engine stalls.

In view of the detection accuracy of the rapid deceleration of the vehicle, when there is almost no difference from the release of the lockup clutch by the brake switch 17 (FIG. 2), it is necessary to determine whether to set the second fail mode. . Therefore, after step 45, it is determined whether the set value for detecting the rapid deceleration of the vehicle is higher than the detection accuracy limit (step 4).
6).

If it is determined in step 46 that the set value for detecting the rapid deceleration of the vehicle is not higher than the detection accuracy limit, it is determined whether the environmental condition is in a region where there is a large variation in the engagement force of the lockup clutch. In order to judge, whether or not the power supply voltage of the transmission controller 9 (FIG. 2) is smaller than a value indicating the variation limit, and whether the oil temperature sensor 2
It is determined whether or not the hydraulic oil temperature C (FIG. 2) of the transmission 1 (FIG. 2) measured by 3 (FIG. 2) is smaller than the value indicating the variation limit (step 47).

When it is determined in step 47 that the environmental condition is in the region where the variation in the engagement force of the lockup clutch is large, the set value of the drive duty D (FIG. 2) is the response limit as a result of this learning. Even if the value exceeds the value indicating, it cannot necessarily be concluded that the second fail mode is set. Therefore, the second fail mode is not set while the environmental condition is in the region where the variation in the engagement force of the lockup clutch is large, that is, the transmission controller 9
The second fail mode flag FLAG (FIG. 2) is not set to 1 and the brake switch 17 is set in step 43.
In order to release the lockup clutch in response to the brake braking signal B (FIG. 2) from (FIG. 2), this routine is ended while waiting for the occurrence of sudden braking of the vehicle.

When it is determined in step 48 that the environmental condition is in the region where the variation in the engagement force of the lockup clutch is small, it is determined that the second fail mode is currently occurring, and the transmission controller 9 ( (Fig. 2)
The second fail mode flag FLAG of is set to 1 (step 48).

As in step 34 (FIG. 3), once the second fail mode flag FLAG is set to 1 in step 48, it is set to 0 from outside when repairing or repairing.
The second fail mode is not released unless it is reset to.

Next, at step 42, the idle speed Ni detected by the idle speed sensor 11 (FIG. 2) is detected.
(Fig. 2) The ISC duty obtained by (Fig. 2) is increased more than that during control during normal coasting, and the prevention of engine stall is further improved, and the recovery shock is exacerbated by the driver. Control with a bounce that is easy to recognize so that the driver can recognize the abnormality of the drive system.

Thereafter, in step 43, this routine is terminated while waiting for the occurrence of sudden braking of the vehicle in order to perform the lockup clutch release control in response to the brake braking signal B from the brake switch 17 (FIG. 2).

Driving duty D in step 44
When it is determined that the set value of (FIG. 2) does not exceed the value indicating the responsiveness limit, that is, the second fail mode is currently occurring in various sensors and actuators used to avoid engine stall. If not, in step 49, whether the hydraulic oil temperature C (FIG. 2) of the transmission 1 (FIG. 2) measured by the oil temperature sensor 23 (FIG. 2) is smaller than a value indicating the responsiveness limit, and Water temperature sensor 2
5 (FIG. 2), it is determined whether the water temperature W (FIG. 2) of the engine 1 (FIG. 2) is smaller than the limit value for avoiding engine stall, and the first fail mode is currently generated. Judge whether or not.

When it is determined that the first fail mode has occurred, in step 43, in order to perform the lockup clutch release control in response to the brake braking signal B from the brake switch 17 (FIG. 2), the vehicle This routine is ended while waiting for the occurrence of the sudden braking of.

If it is determined in step 49 that the first fail mode is not currently occurring, lockup occurs when a sudden deceleration of the vehicle is detected by the vehicle speed V calculated from the transmission output shaft speed No (FIG. 2). In order to release the clutch (step 50), this routine is terminated while waiting for the sudden braking of the vehicle.

[0053]

As described above, according to the lockup clutch control device for an automatic transmission of the first aspect of the present invention, when an abnormality is detected, the braking of the brake is detected to detect the lockup clutch. When the abnormality is released and the abnormality is not detected, the sudden deceleration of the vehicle 103 is detected and the lockup clutch is controlled to prevent the engine from stall and improve the fuel consumption even if the abnormality occurs. be able to.

According to the lock-up clutch control device for an automatic transmission of the second aspect of the present invention, the control state of the vehicle 103 is broken by distinguishing the abnormality between the first fail mode and the second fail mode. It is possible to prevent the state from being left.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a lockup clutch control device for an automatic transmission according to the present invention.

FIG. 2 is a system diagram showing an embodiment of a lockup clutch control device for an automatic transmission according to the present invention.

FIG. 3 is a first flowchart of a control routine of a lockup clutch control device for an automatic transmission according to the present invention.

FIG. 4 is a second flowchart of a control routine of a lockup clutch control device for an automatic transmission according to the present invention.

[Explanation of symbols]

1 automatic transmission 2 Torque converter 3 engine 4 output shafts 5 control valves 6,7 shift solenoid 8 Lock-up solenoid 9 Transmission controller 10 Throttle opening sensor 11 Idle rotation sensor 12 Abnormal combustion detection sensor 13 Engine rotation sensor 14 Turbine rotation sensor 15 Transmission output shaft rotation sensor 16 engine controller 17 Brake switch 18 Idle switch 19 Ignition device 20 Auxiliary equipment 21 Antiskid 22 Traction control system 23 Oil temperature sensor 24 Air Flow Meter 25 Water temperature sensor ABS anti-skid signal B Brake switch signal C hydraulic oil temperature D drive duty E Abnormal combustion signal EC electric throttle error signal H auxiliary signal I Idle switch signal IG ignition signal Ne engine speed Ni idle speed No Transmission output speed Nt turbine speed Q Intake air volume TCS traction control signal TVO throttle opening W water temperature

Continuation of the front page (56) Reference JP-A-5-79557 (JP, A) JP-A-5-141525 (JP, A) JP-A-6-81692 (JP, A) JP-A-7-42827 (JP , A) Japanese Unexamined Patent Publication No. 4-370465 (JP, A) Actual Kaihei 7-14262 (JP, U) Actual Kaihei 5-21142 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) F16H 61/14

Claims (2)

(57) [Claims] 1. A lockup clutch control device for an automatic transmission having a torque converter in a transmission system capable of establishing a lockup state in which input and output are directly connected by a lockup clutch, wherein the vehicle is coasting. When detecting that the vehicle is coasting based on the coasting detection means for detecting and the detection signal of the coasting detection means, the engagement capacity of the lock-up clutch is set to be the minimum pressure required for engagement. Lock-up clutch engagement capacity control means, brake depression detection means for detecting the driver's brake pedal depression operation, sudden deceleration detection means for detecting sudden deceleration of the vehicle, and brake depression while the vehicle is coasting. Detecting that the brake pedal has been depressed based on the detection signal of the detecting means, or the sudden deceleration detecting hand. When it is detected that the vehicle has suddenly decelerated based on the detection signal of, the lockup clutch releasing means for releasing the lockup clutch, the engine torque up control means for increasing the output torque of the engine, and the lockup clutch releasing means or When an abnormality is detected based on an abnormality determining unit that determines an abnormality of the engine torque increase control unit and a detection signal of the abnormality determining unit, the lockup clutch is released in response to the signal from the brake depression detecting unit. When the abnormality is not detected, lockup clutch release control means for releasing the lockup clutch in response to the signal from the sudden deceleration detection means is provided. Lockup clutch control device. 2. The abnormality determining means is divided into a first fail mode indicating that an environmental condition of the engine or the automatic transmission has changed and a second fail mode indicating a temporal change or a failure of the engine or the automatic transmission. The lockup clutch control device for an automatic transmission according to claim 1, wherein an abnormality is separately determined.