Lock-up clutch control device

Abstract

To provide a lock-up control device capable of preventing occurrence of shocks in the middle of fastening a lock-up clutch (during transition).SOLUTION: While a lock-up clutch 24 is being fastened, a TCU 50 sets a lower limit value for an engine torque based on the deviation between an engine speed and a turbine speed of a torque converter 20, and the deviation between the engine torque and a fastening torque of the lock-up clutch 24, and requests an ECU 40 to control an engine 10 so that the engine torque does not fall below the lower limit value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a control device for a lock-up clutch that can directly connect an engine and an automatic transmission without a torque converter interposed between the engine and the automatic transmission. [Background technology]

[0002] Torque converters that use fluid (oil) to amplify engine torque (engine driving force) have been widely used in combination with vehicles equipped with stepped automatic transmissions (step ATs) or continuously variable transmissions (CVTs). Torque converters transmit engine torque via oil and have a torque amplification function, enabling smooth vehicle starts. Torque converters also have the function of absorbing vibrations generated by the engine. However, because torque converters transmit engine torque via oil, transmission loss occurs due to slippage (i.e., transmission efficiency decreases).

[0003] To suppress such a decrease in transmission efficiency due to the torque converter and improve fuel consumption (fuel economy), a lockup mechanism (lockup clutch) that directly connects the input (engine crankshaft) and the output (transmission input shaft) at a predetermined vehicle speed or higher is widely adopted. That is, when starting, the lockup clutch is disengaged so that amplified engine torque is input to the transmission input shaft via the torque converter, while when, for example, the vehicle is running steadily, the lockup clutch is engaged so that engine torque is input directly from the engine crankshaft to the transmission input shaft.

[0004] Inside the torque converter, a release chamber is defined on the front cover side, with a lockup piston provided with a lockup clutch in between, and an apply chamber is defined on the pump impeller side (opposite the release chamber). When engaging the lockup clutch, oil is allowed to flow from the apply chamber to the release chamber, generating a pressure difference between the apply chamber and the release chamber, and this pressure difference engages the lockup clutch. When releasing the lockup clutch, oil is allowed to flow from the release chamber to the apply chamber, which releases the lockup clutch (see, for example, Patent Document 1).

[0005] The lockup clutch is engaged and disengaged by adjusting the oil pressure (lockup apply pressure) supplied to the lockup clutch (the apply chamber). More specifically, the oil pressure of the oil supplied to the lockup clutch is adjusted (regulated) by, for example, a control unit (electronic control device) varying the duty ratio of the voltage applied to a solenoid valve installed in an oil passage connecting the apply chamber and the oil pump. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 9-112685 Summary of the Invention [Problem to be solved by the invention]

[0007] Incidentally, if the engine torque decreases while the lockup clutch is being engaged (i.e., while the engagement torque is gradually increasing (transitional period)), for example, by releasing the accelerator pedal, and the engine torque becomes less than the engagement torque of the lockup clutch, the lockup clutch may suddenly engage, causing a shock. If the engagement torque of the lockup clutch is reduced at this time, there is a risk of engine revving up, shock, or sudden acceleration occurring as the lockup clutch is released.

[0008] The present invention has been made to solve the above problems, and aims to provide a lock-up clutch control device that can prevent shocks from occurring during engagement (transition) of the lock-up clutch. [Means for solving the problem]

[0009] A lock-up clutch control device according to one aspect of the present invention comprises a lock-up clutch that can directly connect an engine and an automatic transmission without a torque converter interposed between the engine and the automatic transmission, and a control unit that controls the engagement and release of the lock-up clutch, wherein the control unit sets a lower limit value for engine torque based on the engagement torque of the lock-up clutch while the lock-up clutch is in the process of engagement, and controls the engine so that the engine torque does not fall below the lower limit value.

[0010] According to a lock-up clutch control device according to one aspect of the present invention, while the lock-up clutch is in the process of being engaged, a lower limit value for engine torque is set based on the engagement torque of the lock-up clutch, and the engine is controlled so that the engine torque does not fall below the lower limit value, thereby preventing sudden engagement of the lock-up clutch. [Effects of the Invention]

[0011] According to the present invention, it is possible to prevent shock from occurring during engagement (transition) of the lockup clutch. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a block diagram showing the configuration of a lock-up clutch control device according to an embodiment, and a power unit to which the lock-up clutch control device is applied; [Figure 2] FIG. 10 is a diagram showing an example of a map (engine torque reduction amount limit value map) that defines the relationship between the absolute value of the deviation between the engine speed and the turbine speed of the torque converter, the absolute value of the deviation between the engine torque and the target engagement torque of the lock-up clutch, and the engine torque reduction amount limit value. [Figure 3] 4 is a timing chart showing an example of changes in engine speed, turbine speed, engine torque, and lockup clutch engagement torque while the lockup clutch is being engaged. [Figure 4] 4 is a flowchart showing the procedure of lock-up clutch engagement processing (engine torque lower limit limiting processing) performed by the lock-up clutch control device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts will be designated by the same reference numerals. In addition, the same elements will be designated by the same reference numerals in each drawing, and redundant explanations will be omitted.

[0014] First, the configuration of a lock-up clutch control device 1 according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a block diagram showing the configuration of the lock-up clutch control device 1 and a power unit to which the lock-up clutch control device 1 is applied.

[0015] The engine 10 may be of any type, but may be, for example, a horizontally opposed, direct-injection, four-cylinder gasoline engine. In the engine 10, air drawn in through an air cleaner (not shown) is throttled by an electronically controlled throttle valve (hereinafter simply referred to as a "throttle valve") 13 provided in an intake pipe, passes through an intake manifold, and is drawn into each cylinder of the engine 10. The amount of air drawn in through the air cleaner is detected by an air flow meter 15. The throttle valve 13 is further provided with a throttle sensor 14 that detects the opening of the throttle valve 13. Each cylinder is equipped with an injector that injects fuel. Each cylinder is also equipped with a spark plug that ignites the air-fuel mixture and a built-in igniter coil that applies high voltage to the spark plug. In each cylinder of the engine 10, the mixture of the drawn air and the fuel injected by the injector is ignited by the spark plug and combusted. The resulting exhaust gas is discharged through an exhaust pipe.

[0016] In addition to the air flow meter 15 and throttle sensor 14 described above, a cam angle sensor 12 for identifying the cylinders of the engine 10 is attached near the camshaft of the engine 10. A crank angle sensor 11 for detecting the position of the crankshaft 10a is attached near the crankshaft 10a of the engine 10. The crank angle sensor 11 may be, for example, an electromagnetic pickup type. These sensors are connected to an engine control unit (hereinafter referred to as "ECU") 40, which will be described later. The ECU 40 is also connected to various sensors, such as an accelerator pedal sensor 16 for detecting the amount of depression of the accelerator pedal, i.e., the accelerator pedal opening, and a water temperature sensor for detecting the temperature of the coolant for the engine 10.

[0017] An automatic transmission 30 that converts and outputs driving force from the engine 10 is connected to a crankshaft 10a of the engine 10 via a torque converter 20 that has a clutch function and a torque amplification function.

[0018] The torque converter 20 is mainly composed of a pump impeller 21, a turbine liner 22, and a stator 23. The pump impeller 21 connected to the crankshaft 10a of the engine 10 generates a flow of oil, and the turbine liner 22, disposed opposite the pump impeller 21, receives power from the engine 10 via the oil and drives the output shaft. The stator 23, located between the two, rectifies the discharge flow (return) from the turbine liner 22 and returns it to the pump impeller 21, thereby generating torque amplification.

[0019] Torque converter 20 also has a lock-up clutch 24 that directly couples the input and output. When lock-up clutch 24 is not engaged (in a non-lock-up state), torque converter 20 amplifies the driving force of engine 10 and transmits it to automatic transmission 30, and when lock-up clutch 24 is engaged (in a lock-up state), torque converter 20 directly transmits the driving force of engine 10 to automatic transmission 30. In other words, lock-up clutch 24 can directly couple engine 10 and automatic transmission 30 without going through torque converter 20 that is interposed between engine 10 and automatic transmission 30.

[0020] The engagement and disengagement of lock-up clutch 24 is achieved by adjusting the oil pressure (lock-up apply pressure) supplied to lock-up clutch 24 (apply chamber). This lock-up apply pressure is controlled by a transmission control unit (hereinafter referred to as "TCU") 50. More specifically, TCU 50 adjusts (regulates) the oil pressure of the oil supplied to lock-up clutch 24, for example, by varying the duty ratio of a voltage applied to a solenoid valve disposed in an oil passage connecting the apply chamber and the oil pump.

[0021] The automatic transmission 30 is a stepped automatic transmission (step AT) that includes a transmission section including a transmission gear train and a hydraulic mechanism and is configured to be able to automatically change gears using the hydraulic mechanism. Note that the automatic transmission 30 may also be, for example, a continuously variable transmission (CVT) or a dual clutch transmission (DCT).

[0022] An output shaft rotation sensor 51 for detecting the rotation speed of the output shaft is attached near the output shaft of the automatic transmission 30. In addition, a range switch 52 is attached to the automatic transmission 30 and is connected to move in conjunction with a shift lever (selector lever) 55 to detect the selected position of the shift lever 55. The output shaft rotation sensor 51, range switch 52, etc. are connected to the TCU 50.

[0023] An oil temperature sensor 53 is attached to the automatic transmission 30 to detect the temperature of the hydraulic oil (ATF) (hereinafter simply referred to as "oil temperature") of the automatic transmission 30. A thermistor, for example, is used as the oil temperature sensor 53. The oil temperature sensor 53 is also connected to the TCU 50.

[0024] The shift control of the automatic transmission 30 is executed by the TCU 50. As described above, the TCU 50 also controls the engagement and disengagement of the lock-up clutch 24.

[0025] The TCU 50 is connected to an ECU 40 that comprehensively controls the engine 10 and the like via a CAN (Controller Area Network) 100 so as to be able to communicate with each other.

[0026] The ECU 40 is configured to include a microprocessor that performs calculations, an EEPROM that stores programs and the like for causing the microprocessor to execute various processes, a RAM that stores various data such as calculation results, a backup RAM in which the stored contents are maintained by a battery or the like, and an input / output I / F, etc. The ECU 40 is connected to various sensors such as the crank angle sensor 11, cam angle sensor 12, throttle sensor 14, air flow meter 15, accelerator pedal sensor 16, etc.

[0027] The ECU 40 identifies the cylinder from the output of the cam angle sensor 12, and determines the engine speed from changes in the rotational position of the crankshaft 10a detected by the output of the crank angle sensor 11. The ECU 40 also acquires various information, such as the intake air amount, accelerator pedal opening, air-fuel ratio of the air-fuel mixture, and water temperature, based on detection signals input from the various sensors described above. The ECU 40 then comprehensively controls the engine 10 by controlling the fuel injection amount, ignition timing, and various devices, such as the throttle valve 13, based on the acquired information. The ECU 40 also acquires engine torque from, for example, the intake air amount and engine speed.

[0028] The ECU 40 transmits information such as engine water temperature (coolant temperature), engine torque, engine speed, and accelerator pedal position to the TCU 50 and the like via the CAN 100. The ECU 40 also receives an engine torque lower limit value (lower limit request) and the like from the TCU 50 via the CAN 100. When the ECU 40 receives the engine torque lower limit value (lower limit request), the ECU 40 controls the engine torque so that it does not fall below the lower limit value, for example, by limiting the drive of the throttle valve 13 to the closing side (limiting the decrease in the intake air amount) (this will be described in detail later).

[0029] On the other hand, as described above, the output shaft rotation sensor 51, the range switch 52, the oil temperature sensor 53, etc. are connected to the TCU 50. In addition, the TCU 50 is also connected to a turbine rotation speed sensor 54 that detects the turbine rotation speed of the torque converter 20, etc.

[0030] Furthermore, the TCU 50 receives the engine speed, engine torque, accelerator pedal opening degree, etc. transmitted from the ECU 40 via the CAN 100. The TCU 50 performs shift control of the automatic transmission 30 and engages and disengages the lock-up clutch 24 based on various information such as the acquired engine speed, engine torque, accelerator pedal opening degree, output shaft speed (vehicle speed), and shift position of the shift lever 55 (state of the range switch 52).

[0031] In particular, the TCU 50 and the ECU 40 cooperate to prevent shocks from occurring when the lock-up clutch 24 is in the process of being engaged (during a transitional period).

[0032] The TCU 50 is configured to include a microprocessor that performs calculations, an EEPROM that stores programs and the like for causing the microprocessor to execute various processes, a RAM that stores various data such as calculation results, a backup RAM that maintains the stored contents using a battery, an input / output I / F, etc. The TCU 50 realizes the above functions by having the microprocessor execute programs stored in the EEPROM, etc.

[0033] When a predetermined lockup clutch engagement condition (for example, whether the speed is equal to or greater than a predetermined speed) is satisfied, the TCU 50 starts to engage the lockup clutch 24. At that time, the TCU 50 sets a target engagement torque (control target value of the engagement torque) for the lockup clutch 24 based on, for example, the engine torque, the engine speed, and the turbine speed of the torque converter 20, and gradually increases the engagement torque (hydraulic pressure) according to the target engagement torque.

[0034] Furthermore, while lockup clutch 24 is being engaged (i.e., while engagement torque is being gradually increased (transient)), TCU 50 sets a lower limit value of engine torque based on the target engagement torque (which may be actual engagement torque or hydraulic pressure) of lockup clutch 24. More specifically, TCU 50 sets a lower limit value of engine torque based on the absolute value (|Ne-Nt|) of the deviation between engine speed Ne and turbine speed Nt of torque converter 20, and the absolute value (|Te-Tl|) of the deviation between engine torque Te and target engagement torque Tl of lockup clutch 24.

[0035] Here, the TCU 50 sets a higher lower limit value for the engine torque as the absolute value (|Ne-Nt|) of the deviation between the engine speed and the turbine speed increases, and sets a higher lower limit value for the engine torque as the absolute value (|Te-Tl|) of the deviation between the engine torque and the target engagement torque of the lock-up clutch 24 increases.

[0036] That is, the smaller the absolute value of the deviation between the engine speed and the turbine speed (|Ne-Nt|), the lower the engine torque lower limit value is set by the TCU 50, and the smaller the absolute value of the deviation between the engine torque and the target engagement torque of the lock-up clutch 24 (|Te-Tl|), the lower the engine torque lower limit value is set by the TCU 50.

[0037] At this time, the TCU 50 first sets the engine torque decrease amount limit value (allowable change amount) to a smaller value as the absolute value (|Ne-Nt|) of the deviation between the engine speed and the turbine speed becomes smaller, and sets the engine torque decrease amount limit value to a smaller value as the absolute value (|Te-Tl|) of the deviation between the engine torque and the target engagement torque of the lock-up clutch 24 becomes smaller, thereby suppressing changes in engine torque. Next, the TCU 50 sets the engine torque lower limit value by subtracting the engine torque decrease amount limit value from the real-time engine torque (i.e., when the decrease amount limit value is set).

[0038] Here, a method for setting the engine torque reduction amount limit value will be described. For example, the EEPROM of the TCU 50 stores a map (engine torque reduction amount limit value map) that defines the relationship between the absolute value of the deviation between the engine rotation speed and the turbine rotation speed, the absolute value of the deviation between the engine torque and the target engagement torque of the lock-up clutch 24, and the engine torque reduction amount limit value. The engine torque reduction amount limit value is determined by searching this engine torque reduction amount limit value map based on the absolute value of the deviation between the engine rotation speed and the turbine rotation speed and the absolute value of the deviation between the engine torque and the target engagement torque of the lock-up clutch 24.

[0039] An example of the engine torque reduction amount limit value map is shown in Fig. 2. In Fig. 2, the horizontal axis represents the absolute value (Nm) of the deviation between the engine torque and the target engagement torque of the lock-up clutch 24, and the vertical axis represents the absolute value (rpm) of the deviation between the engine speed and the turbine speed. In the engine torque reduction amount limit value map, an engine torque reduction amount limit value is assigned for each combination (grid point) of the absolute value of the deviation between the engine speed and the turbine speed and the absolute value of the deviation between the engine torque and the target engagement torque of the lock-up clutch 24. In the engine torque reduction amount limit value map, the engine torque reduction amount limit value is set to decrease as the absolute value of the deviation between the engine speed and the turbine speed decreases. In addition, the engine torque reduction amount limit value is set to decrease as the absolute value of the deviation between the engine torque and the target engagement torque of the lock-up clutch 24 decreases.

[0040] Then, the TCU 50 requests the ECU 40 to control the engine 10 (engine torque) so that the engine torque does not fall below the set lower limit value. That is, the TCU 50 transmits the engine torque lower limit value (lower limit request) to the ECU 40 via the CAN 100.

[0041] On the other hand, as described above, when the ECU 40 receives an engine torque lower limit value (lower limit request) from the TCU 50 via the CAN 100, it controls the engine torque so that it does not fall below the lower limit value, for example, by limiting the drive of the throttle valve 13 to the closing side (limiting the decrease in the intake air amount).

[0042] Next, the operation of the lock-up clutch control device 1 will be described with reference to Fig. 4. Fig. 4 is a flowchart showing the procedure for lock-up clutch engagement processing (engine torque lower limit limiting processing) performed by the lock-up clutch control device 1. This processing is repeatedly executed at predetermined timings by the TCU 50 and the ECU 40.

[0043] First, in step S100, a determination is made as to whether a predetermined lockup clutch engagement condition is satisfied (for example, whether the vehicle is at or above a predetermined speed). If the predetermined lockup clutch engagement condition is not satisfied, the process temporarily exits. On the other hand, if the predetermined lockup clutch engagement condition is satisfied, the process proceeds to step S102.

[0044] In step S102, a target engagement torque (control target value of engagement torque) for lock-up clutch 24 is set based on the engine torque, engine rotation speed, and turbine rotation speed.

[0045] Subsequently, in step S104, the actual engagement torque (hydraulic pressure) of the lock-up clutch 24 is gradually increased according to the set target engagement torque.

[0046] Next, in step S106, a lower limit value of the engine torque is set based on the absolute value (|Ne-Nt|) of the deviation between the engine speed Ne and the turbine speed Nt, and the absolute value (|Te-Tl|) of the deviation between the engine torque Te and the target engagement torque Tl of the lock-up clutch 24. Note that the method for setting the lower limit value of the engine torque is as described above, and therefore a detailed description thereof will be omitted here.

[0047] In the following step S108, an engine torque lower limit value (lower limit request) is transmitted to the ECU 40 via the CAN 100. That is, a request is made to the ECU 40 to control the engine 10 so that the engine torque does not fall below the lower limit value. Thereafter, the process proceeds to step S110.

[0048] When an engine torque lower limit value (lower limit request) is received from the TCU 50 via the CAN 100, the ECU 40, for example, restricts the drive of the throttle valve 13 to the closing side (restricts the decrease in the intake air amount) and performs control so that the engine torque does not fall below the lower limit value (step S200).

[0049] Meanwhile, in step S110, a determination is made as to whether or not engagement of the lockup clutch 24 has been completed. If engagement of the lockup clutch 24 has not been completed, the process proceeds to step S102, and the processes from step S102 onwards are repeatedly executed. On the other hand, if engagement of the lockup clutch 24 has been completed, the process temporarily exits.

[0050] FIG. 3 shows an example of changes in engine speed (Ne), turbine speed (Nt), engine torque (Te), and lock-up clutch engagement torque (Tl) during engagement (transient) of lock-up clutch 24. The horizontal axis of FIG. 3 represents time (sec), and the vertical axis (upper row) represents engine speed (Ne) and turbine speed (Nt). The vertical axis (lower row) represents engine torque (Te) and engagement torque (Tl) of lock-up clutch 24. In FIG. 3, the solid line represents changes according to this embodiment, and the dashed line represents changes according to a comparative example (when there is no lower limit on engine torque). Additionally, the dashed line represents changes when there is no decrease in engine torque during engagement.

[0051] First, if there is no decrease in engine torque while the lock-up clutch 24 is being engaged, as shown by the dashed dotted line, after the lock-up clutch 24 begins to engage, the engagement torque (oil pressure) gradually increases, the engine speed gradually decreases, the differential rotation speed with the turbine speed gradually decreases (eventually becomes zero), and the lock-up clutch 24 is gradually (smoothly) engaged.

[0052] Next, in a comparative example (where there is no lower limit on engine torque), as shown by the dashed line, after the lock-up clutch 24 begins to engage, if the engine torque decreases at the timing when the engagement torque of the lock-up clutch 24 is increasing, the engine 10 and the automatic transmission 30 are suddenly engaged, causing a shock due to the inertia.

[0053] On the other hand, in this embodiment, as shown by the solid line, even if the engine torque decreases after the start of (during) engagement of the lock-up clutch 24, the lower limit of the engine torque is limited, that is, the engine 10 (engine torque) is controlled so that it does not fall below the lower limit, thereby suppressing the decrease in engine torque (engine speed) so as not to lead to sudden engagement of the lock-up clutch 24. As a result, sudden engagement (shock) of the lock-up clutch 24 is avoided.

[0054] As described above in detail, according to this embodiment, while the lock-up clutch 24 is in the process of engaging, a lower limit value for engine torque is set based on the target engagement torque of the lock-up clutch 24, and the engine 10 is controlled so that the engine torque does not fall below this lower limit value. This makes it possible to avoid sudden engagement of the lock-up clutch 24. As a result, it becomes possible to prevent shocks from occurring while the lock-up clutch 24 is in the process of engaging (during transition).

[0055] In particular, according to this embodiment, the lower limit value of the engine torque is set based on the deviation between the engine speed and the turbine speed, and the deviation between the engine torque and the engagement torque of the lock-up clutch 24. Therefore, it is possible to more appropriately set the lower limit value of the engine torque by taking into account the change in inertia (i.e., the degree of shock) that accompanies the engagement of the lock-up clutch 24.

[0056] More specifically, according to this embodiment, the smaller the deviation between the engine speed and the turbine speed, the smaller the engine torque reduction limit value is set, and the smaller the deviation between the engine torque and the engagement torque of the lock-up clutch 24, the smaller the engine torque reduction limit value is set, and the lower limit value of the engine torque is set by subtracting the engine torque reduction limit value from the real-time engine torque.

[0057] Therefore, according to this embodiment, the lower limit value of the engine torque is set higher as the deviation between the engine speed and the turbine speed increases, and the lower limit value of the engine torque is set higher as the deviation between the engine torque and the engagement torque of the lock-up clutch 24 increases. Therefore, the engine torque decrease amount limit value (relative value) is set so that the change in inertia (i.e., the degree of shock) caused by the engagement of the lock-up clutch 24 is kept below a predetermined value, and the lower limit value of the engine torque (absolute value) can be set from the engine torque decrease amount limit value.

[0058] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications are possible. For example, although the above embodiment has been described using an example in which the present invention is applied to an engine vehicle, the present invention can also be applied to any vehicle equipped with a torque converter, such as a hybrid vehicle (HEV).

[0059] In addition, in the above embodiment, a stepped automatic transmission (step AT) is used as the automatic transmission 30, but the automatic transmission 30 may also be, for example, a continuously variable transmission (CVT) or a DCT (Dual Clutch Transmission).

[0060] Furthermore, the configuration and functional division of the control system are not limited to those in the above-described embodiment, and for example, the ECU 40 and the TCU 50 may be integrated. [Explanation of symbols]

[0061] 1. Lock-up clutch control device 10 Engine 10a crankshaft 11 Crank angle sensor 12 Cam angle sensor 13 Throttle valve 14 Throttle sensor 15 Air flow meter 16 Accelerator pedal sensor 20 Torque converter 21 Pump impeller 22 Turbine liner 23 Stator 24 Lock-up clutch 30 Automatic transmission 40 ECU 50 TCU 51 Output shaft rotation sensor 52 Range switch 53 Oil temperature sensor 54 Turbine speed sensor 55 Shift lever 100 CAN

Claims

1. a lock-up clutch that can directly connect the engine and the automatic transmission without a torque converter interposed between the engine and the automatic transmission; a control unit that controls engagement and release of the lock-up clutch, a control unit for controlling the engine so that the engine torque does not fall below the lower limit value, the control unit setting a lower limit value for engine torque based on the engagement torque of the lock-up clutch while the lock-up clutch is in the process of engagement;

2. 2. The lock-up clutch control device according to claim 1, wherein the control unit sets a lower limit value for engine torque based on a deviation between an engine speed and a turbine speed of the torque converter, and a deviation between engine torque and an engagement torque of the lock-up clutch.

3. The control unit The larger the deviation between the engine speed and the turbine speed, the higher the lower limit value of the engine torque is set. The larger the deviation between the engine torque and the engagement torque of the lock-up clutch, the higher the lower limit value of the engine torque is set.

3. The lock-up clutch control device according to claim 2.

4. The control unit The smaller the deviation between the engine rotation speed and the turbine rotation speed, the smaller the engine torque decrease limit value is set, The smaller the deviation between the engine torque and the engagement torque of the lock-up clutch, the smaller the engine torque reduction limit value is set, 4. The lock-up clutch control device according to claim 3, wherein the lower limit value of the engine torque is set by subtracting the engine torque decrease limit value from the real-time engine torque.

5. 5. The lock-up clutch control device according to claim 4, wherein the control unit sets a control target value for the engagement torque of the lock-up clutch based on engine torque, engine speed, and turbine speed.

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