Drive unit for vehicle

Abstract

To elimination a judder of a friction clutch.SOLUTION: A drive unit for vehicle has a friction clutch having a piston for fastening a plurality of friction plates to each other, a valve unit for controlling working hydraulic pressure supplied to a piston oil chamber which is defined by the piston, and a control system for controlling the valve unit. The control system determines whether or not a judder is generated at the friction clutch in a state that a steering angle of a front wheel exceeds a threshold. When it is determined that the judder is generated at the friction clutch, the control system varies the working hydraulic pressure supplied to the piston oil chamber up and down in a state that the steering angle of the front wheel goes below the threshold.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present disclosure relates to a vehicle drive device. [Background technology]

[0002] Vehicles that drive front and rear wheels have a transfer clutch that distributes torque between the front and rear wheels. The transfer clutch is a friction clutch that transmits torque by bringing multiple friction plates into contact with each other. For this reason, depending on the condition of the friction surfaces formed on the friction plates, there is a risk of judder occurring in the friction clutch (see Patent Documents 1-3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-196810 A [Patent Document 2] JP 2001-336622 A [Patent Document 3] JP 2008-32232 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the occurrence of judder in a friction clutch such as a transfer clutch leads to vibration of the vehicle body, causing passengers to feel uncomfortable, and therefore there is a demand to eliminate judder in friction clutches. [Means for solving the problem]

[0005] According to the present disclosure, a vehicle drive device is provided in a power transmission path connecting front and rear wheels, and has a friction clutch including a plurality of friction plates lubricated with oil and a piston that fastens the plurality of friction plates together. The vehicle drive device has a valve unit connected to a piston oil chamber partitioned by the piston and controls a hydraulic oil pressure supplied to the piston oil chamber. The vehicle drive device has a control system including a processor and a memory communicably connected to each other, and controls the valve unit. The control system determines whether or not judder is occurring in the friction clutch when the steering angle of the front wheels is above a threshold value. When the control system determines that judder is occurring in the friction clutch, the control system executes hydraulic fluctuation control to fluctuate the hydraulic oil pressure supplied to the piston oil chamber up and down when the steering angle of the front wheels is below the threshold value. Effect of the Invention

[0006] According to the present disclosure, it is possible to eliminate judder in a friction clutch. [Brief description of the drawings]

[0007] [Figure 1] 1 is a diagram illustrating an example of a vehicle including a vehicle drive device according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a diagram illustrating an example of a power unit and a control system. [Diagram 3] FIG. 2 is a diagram illustrating an example of a basic structure of a control unit. [Figure 4] 10 is a flowchart showing an example of a procedure for executing judder determination control. [Diagram 5] 4 is a flowchart showing an example of a procedure for executing judder elimination control. [Figure 6] FIG. 11 is a diagram illustrating an example of execution time. [Figure 7] 4 is a timing chart showing an example of an execution state of judder elimination control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following description, the same or substantially the same configurations and elements will be denoted by the same reference numerals and repeated description will be omitted.

[0009] <Power unit> Fig. 1 is a diagram showing an example of a vehicle 11 equipped with a vehicle drive device 10 according to an embodiment of the present disclosure. As shown in Fig. 1, the vehicle 11 has a power unit 14 consisting of an engine 12 and a transmission 13. A rear wheel output shaft 15 of the power unit 14 is connected to rear wheels 18 via a propeller shaft 16 and a rear differential mechanism 17. The power unit 14 also has a front differential mechanism 20, which is connected to front wheels 21.

[0010] FIG. 2 is a diagram showing an example of the power unit 14 and a control system 60. As shown in FIG. 2, the transmission 13 of the power unit 14 has a torque converter 22, a speed change mechanism 23, and a transfer clutch 24. A speed change input shaft 25 of the speed change mechanism 23 is connected to the engine 12 via the torque converter 22. Also, as shown in FIG. 1 and FIG. 2, a speed change output shaft 26 of the speed change mechanism 23 is connected to the front wheels 21 via a gear train 27, a front wheel output shaft 28, and a front differential mechanism 20. Furthermore, the speed change output shaft 26 of the speed change mechanism 23 is connected to the rear wheels 18 via a transfer clutch 24, a rear wheel output shaft 15, a propeller shaft 16, and a rear differential mechanism 17.

[0011] In this way, the front wheels 21 and the rear wheels 18 are connected to each other via a power transmission path 29 that includes the front wheel output shaft 28 and the rear wheel output shaft 15, etc. In the example shown in Figures 1 and 2, the power transmission path 29 includes the transmission output shaft 26, the gear train 27, the front wheel output shaft 28, the front differential mechanism 20, the transfer clutch 24, the rear wheel output shaft 15, the propeller shaft 16, the rear differential mechanism 17, etc.

[0012] <Transfer clutch> As shown in FIG. 2, a transfer clutch (friction clutch) 24 is provided between the transmission output shaft 26 and the rear wheel output shaft 15 which constitute the power transmission path 29. The transfer clutch 24 has a clutch hub 30 connected to the transmission output shaft 26 and a clutch drum 40 connected to the rear wheel output shaft 15. The transfer clutch 24 also has a plurality of friction plates 31 attached to the clutch hub 30 and a plurality of friction plates 41 attached to the clutch drum 40. The transfer clutch 24 also has a piston 42 housed in the clutch drum 40 and a return spring 43 which biases the piston 42 towards a release position. The clutch drum 40 also has a piston oil chamber 44 defined by the piston 42, and the clutch hub 30 has a lubricating oil chamber 33 having a plurality of through holes 32.

[0013] In order to supply hydraulic oil to the piston oil chamber 44 and the lubricating oil chamber 33, the transmission 13 is provided with an oil pump 50 and a valve body 51. The valve body (valve unit) 51, in which a plurality of electromagnetic valves are incorporated, is connected to the piston oil chamber 44 via an oil passage 52, and is also connected to the lubricating oil chamber 33 via an oil passage 53. The valve body 51 has a function of controlling the flow rate and pressure of the hydraulic oil discharged from the oil pump 50, and also controls the supply destination of the hydraulic oil. In other words, the valve body 51 has a function of controlling the hydraulic oil pressure supplied to the piston oil chamber 44 and the lubricating oil chamber 33. The valve body 51 is not only connected to the transfer clutch 24 via the oil passages 52 and 53, but also connected to the torque converter 22 and the speed change mechanism 23 via other oil passages.

[0014] When the hydraulic pressure supplied to the piston oil chamber 44 is increased by controlling the valve body 51, the piston 42 is pushed toward the engaged position. This allows the friction plates 31, 41 to be pressed against each other, and the transfer clutch 24 can be controlled to be in the engaged state. On the other hand, when the hydraulic pressure supplied to the piston oil chamber 44 is reduced by controlling the valve body 51, the piston 42 is pushed back toward the released position by the spring force of the return spring 43. This allows the friction plates 31, 41 to be released from the pressed state, and the transfer clutch 24 can be controlled to be in the released state. Furthermore, by adjusting the hydraulic pressure supplied to the piston oil chamber 44 from the valve body 51, the friction plates 31, 41 can be brought into contact with each other while sliding against each other, and the transfer clutch 24 can be controlled to be in the slip state.

[0015] In addition, hydraulic oil is supplied to the lubricating oil chamber 33 of the clutch hub 30 from the valve body 51, and the friction plates 31, 41 of the transfer clutch 24 can be lubricated by the hydraulic oil. That is, the hydraulic oil supplied to the lubricating oil chamber 33 of the clutch hub 30 is discharged toward the friction plates 31, 41 from the through hole 32 of the clutch hub 30. This allows the friction surfaces of the friction plates 31, 41 to be lubricated, allowing the transfer clutch 24 to function properly. In this way, the transfer clutch 24, which is a wet friction clutch, has multiple friction plates 31, 41 that are lubricated with oil.

[0016] By controlling the transfer clutch 24 to an engaged state, the rotational speeds of the front wheels 21 and the rear wheels 18 can be made to match with each other, and the torque distribution ratio between the front wheels 21 and the rear wheels 18 can be controlled to "50:50". By controlling the transfer clutch 24 to a released state, the torque transmission to the rear wheels 18 can be cut off, and the torque distribution ratio between the front wheels 21 and the rear wheels 18 can be controlled to "100:0". Furthermore, by controlling the transfer clutch 24 to a slip state, it is also possible to arbitrarily adjust the torque distribution ratio between the front wheels 21 and the rear wheels 18 within a predetermined range.

[0017] <Control system> The vehicle drive device 10 has a control system 60 consisting of a plurality of electronic control units to control the power unit 14 and the like. The electronic control units constituting the control system 60 include a transmission control unit 61, an engine control unit 62, a brake control unit 63, and a driving assistance control unit 64. The transmission control unit 61 is an electronic control unit that outputs a control signal to the valve body 51 described above. The engine control unit 62 is an electronic control unit that outputs control signals to a throttle valve 65, an injector 66, and an ignition device 67.

[0018] The brake control unit 63 is an electronic control unit that outputs a control signal to a brake actuator 70 for controlling brake fluid pressure. The vehicle 11 is provided with a brake system 71 that brakes the front wheels 21 and the rear wheels 18. The brake system 71 has a master cylinder 73 that outputs brake fluid pressure in conjunction with a brake pedal 72, a caliper (brake mechanism) 75 that brakes a disc rotor 74 of the front wheel 21, and a caliper (brake mechanism) 77 that brakes a disc rotor 76 of the rear wheel 18. The master cylinder 73 and the calipers 75 and 77 are connected via a brake actuator 70 that controls the brake fluid pressure supplied to each of the calipers 75 and 77.

[0019] The driving assistance control unit 64 is an electronic control unit that calculates the distance between the preceding vehicle and the vehicle 11 in order to execute cruise control to follow the preceding vehicle. A front camera 80 that captures an image in front of the vehicle and a front radar 81 that detects an obstacle in front of the vehicle are connected to the driving assistance control unit 64. The driving assistance control unit 64 calculates the presence or absence of a preceding vehicle and the distance between the preceding vehicle based on image data and distance data from the front camera 80 and the front radar 81. The driving assistance control unit 64 also transmits preceding vehicle data such as the distance between the vehicles to a vehicle control unit 82 to be described later. When the driver operates a switch to execute cruise control, the vehicle control unit 82 controls the power unit 14 and the brake system 71 so as to maintain the set distance between the vehicles within a range not exceeding the set vehicle speed. The cruise control to follow the preceding vehicle is called adaptive cruise control.

[0020] Further, as an electronic control unit constituting the control system 60, there is a vehicle control unit 82 that outputs control signals to the above-mentioned control units 61 to 64. These control units 61 to 64, 82 are connected to each other so as to be able to communicate with each other via an in-vehicle network 83 such as a CAN (Controller Area Network). The vehicle control unit 82 sets operation targets of the power unit 14 and the brake system 71 based on input information from various control units and various sensors described later. Furthermore, the vehicle control unit 82 generates control signals according to the operation targets of the power unit 14 and the brake system 71, and outputs these control signals to the engine control unit 62, the transmission control unit 61, the brake control unit 63, etc.

[0021] Sensors connected to the vehicle control unit 82 include an accelerator sensor 90 that detects the operation state of the accelerator pedal, and a brake sensor 91 that detects the operation state of the brake pedal 72. Sensors connected to the vehicle control unit 82 include a vehicle speed sensor 92 that detects the vehicle speed, which is the traveling speed of the vehicle 11, an acceleration sensor 93 that detects the front-rear and left-right accelerations acting on the vehicle 11, and a steering angle sensor 94 that detects the steering angle of the steering wheel. Sensors connected to the vehicle control unit 82 include a rotation speed sensor 95 that detects the rotation speed of the transmission output shaft 26, and a rotation speed sensor 96 that detects the rotation speed of the rear wheel output shaft 15. A cruise switch 97 that is operated when the cruise control is performed and when it is stopped, and a start switch 98 that is operated when the control system 60 is started and stopped are also connected to the vehicle control unit 82.

[0022] Fig. 3 is a diagram showing an example of the basic structure of the control units 61-64, 82. As shown in Fig. 3, the control units 61-64, 82, which are electronic control units, have a microcontroller 102 incorporating a processor 100 and a main memory (memory) 101, etc. A predetermined program is stored in the main memory 101, and the program is executed by the processor 100. The processor 100 and the main memory 101 are connected to each other so as to be able to communicate with each other. Note that a plurality of processors 100 may be incorporated in the microcontroller 102, and a plurality of main memories 101 may be incorporated in the microcontroller 102.

[0023] Moreover, the control units 61 to 64, 82 each have an input circuit 103, a drive circuit 104, a communication circuit 105, an external memory 106, and a power supply circuit 107. The input circuit 103 converts signals input from various sensors into signals that can be input to the microcontroller 102. The drive circuit 104 generates drive signals for various devices such as the valve body 51 described above based on signals output from the microcontroller 102. The communication circuit 105 converts signals output from the microcontroller 102 into communication signals directed to other control units. Furthermore, the communication circuit 105 converts communication signals received from other control units into signals that can be input to the microcontroller 102. Furthermore, the power supply circuit 107 supplies a stable power supply voltage to the microcontroller 102, the input circuit 103, the drive circuit 104, the communication circuit 105, the external memory 106, and the like. Furthermore, the external memory 106, which is a non-volatile memory or the like, stores programs and various data.

[0024] <Judder Judgment Control> Next, a description will be given of the judder determination control for determining whether or not vibration, i.e., judder, is occurring in the transfer clutch 24. Fig. 4 is a flowchart showing an example of the execution procedure of the judder determination control. Each step of the judder determination control shown in Fig. 4 is executed by the processor 100 constituting the control system 60. The judder determination control shown in Fig. 4 is executed by the control system 60 at predetermined intervals after the control system 60 is started by operating the start switch.

[0025] As shown in Fig. 4, the control system 60 proceeds to step S10 and determines whether or not a judder flag FL1, which will be described later, has been reset, i.e., whether or not "FL1 = 0". The judder flag FL1 is a control flag that is set to "FL1 = 1" when judder is occurring in the transfer clutch 24. If the control system 60 determines in step S10 that "FL1 = 0", that is, when the occurrence of judder is not confirmed, it proceeds to step S11 and determines whether or not the steering angle of the front wheels 21 exceeds a predetermined threshold value A1.

[0026] When the control system 60 determines in step S11 that the steering angle of the front wheels 21 exceeds the threshold value A1, that is, when the control system 60 determines that the vehicle is in a turning state in which judder may occur, the control system 60 proceeds to step S12 to determine whether or not judder is occurring in the transfer clutch 24. Here, the situation in which the steering angle of the front wheels 21 exceeds the threshold value A1 is a situation in which the difference in rotation speed between the front wheels 21 and the rear wheels 18 exceeds a predetermined value due to turning, and this is a situation in which judder may occur in the transfer clutch 24. In addition, the steering angle, which is the turning angle of the front wheels 21, can be calculated based on the detection signal of the steering angle sensor 94. Note that the steering angles of the left and right front wheels 21 are different from each other, but the turning state may be determined using the larger steering angle, the smaller steering angle, or the average steering angle of the left and right wheels. In addition, since the steering angle of the front wheels 21 and the steering angle of the steering wheel are linked to each other, it goes without saying that the steering angle may be compared with a predetermined threshold value in step S11.

[0027] The control system 60 proceeds to step S12 and determines whether or not the vehicle body vibration value generated due to the judder exceeds a predetermined threshold value V1. Here, the vehicle body vibration value is a vibration value calculated based on the detection signal of the acceleration sensor 93, and is an amplitude value of the acceleration acting in the front, rear, left and right directions of the vehicle 11. If the control system 60 determines in step S12 that the vehicle body vibration value exceeds the threshold value V1, the control system 60 proceeds to step S13 and determines whether or not the clutch vibration value exceeds a predetermined threshold value V2. Here, the clutch vibration value is a vibration value calculated based on the detection signals of the rotation speed sensors 95, 96, and is an amplitude value of the rotation speed of the transfer clutch 24. Note that, as the clutch vibration value, the amplitude value of the rotation speed of the transmission output shaft 26 provided on the clutch input side may be used, or the amplitude value of the rotation speed of the rear wheel output shaft 15 provided on the clutch output side may be used.

[0028] Then, when the control system 60 determines in step S13 that the clutch vibration value exceeds the threshold value V2, that is, when the vehicle 11 is turning and the vehicle body vibration value exceeds the threshold value V1 and the clutch vibration value exceeds the threshold value V2, judder is occurring in the transfer clutch 24, so the process proceeds to step S14 and the judder flag FL1 is set (FL1=1). In this way, the presence or absence of judder occurring in the transfer clutch 24 is determined based on both the vehicle body vibration value and the clutch vibration value, so that the presence or absence of judder occurring can be determined with high accuracy.

[0029] In the above description, the presence or absence of judder is determined using both the vehicle body vibration value and the clutch vibration value, but the present invention is not limited to this. For example, when the vehicle body vibration value exceeds a threshold value V1 while the vehicle 11 is turning, it may be determined that judder is occurring in the transfer clutch 24. Also, when the clutch vibration value exceeds a threshold value V2 while the vehicle 11 is turning, it may be determined that judder is occurring in the transfer clutch 24.

[0030] <Judder elimination control> Hereinafter, a description will be given of the judder elimination control for eliminating the judder of the transfer clutch 24. Fig. 5 is a flow chart showing an example of the execution procedure of the judder elimination control. Each step of the judder elimination control shown in Fig. 5 is executed by the processor 100 constituting the control system 60. The judder elimination control shown in Fig. 5 is executed by the control system 60 at predetermined intervals after the control system 60 is started by operating the start switch.

[0031] As shown in FIG. 5, the control system 60 proceeds to step S20 and determines whether or not the judder flag FL1 is set, i.e., whether or not "FL1=1". When the control system 60 determines in step S20 that "FL1=1", that is, when judder is occurring in the transfer clutch 24, the control system 60 proceeds to step S21 and determines whether or not the steering angle of the front wheels 21 is below a predetermined threshold value A2. Note that in step S21, the control system 60 determines whether or not the vehicle 11 is traveling in a predetermined straight line. For this reason, the threshold value A2 may be the same value as the above-mentioned threshold value A1, or the threshold value A2 may be a value smaller than the threshold value A1.

[0032] When the control system 60 determines in step S21 that the steering angle is below the threshold A2, the process proceeds to step S22, where it determines whether the brake system 71 is operating, that is, whether the calipers 75, 77 of the front and rear wheels 21, 18 are operating. When the control system 60 determines in step S22 that the brakes are operating, the process proceeds to step S23, where it executes hydraulic pressure fluctuation control to fluctuate up and down the hydraulic pressure (hereinafter, referred to as clutch pressure) supplied to the piston oil chamber 44 of the transfer clutch 24. In this way, by executing the hydraulic pressure fluctuation control, it is possible to fluctuate the pressing force of the friction plates 31, 41. This makes it possible to actively replace the hydraulic oil adhering to the friction surfaces of the friction plates 31, 41, and to eliminate the judder of the transfer clutch 24.

[0033] On the other hand, when the control system 60 determines in step S22 that the brake system 71 is not operating, the process proceeds to step S24, where it is determined whether or not cruise control is being performed. When the control system 60 determines in step S24 that cruise control is being performed, the process proceeds to step S23, where it executes hydraulic pressure fluctuation control of the transfer clutch 24. That is, the control system 60 executes hydraulic pressure fluctuation control of the transfer clutch 24 while the cruise control is being performed, that is, while the vehicle is traveling at a constant speed where both the vehicle acceleration and the vehicle deceleration are below predetermined threshold values. This makes it possible to actively replace the hydraulic oil adhering to the friction surfaces of the friction plates 31, 41, as described above, and to eliminate judder in the transfer clutch 24.

[0034] Here, factors that may cause judder in the transfer clutch 24 include deterioration of the hydraulic oil adhering to the friction surfaces of the friction plates 31, 41, and adhesion of contaminants to the friction surfaces of the friction plates 31, 41. For this reason, by increasing or decreasing the pressing force of the friction plates 31, 41 to provide a small clearance between the friction plates 31, 41, the hydraulic oil adhering to the friction surfaces of the friction plates 31, 41 can be actively replaced. In other words, the friction surfaces of the friction plates 31, 41 can be washed with the hydraulic oil, which is considered to eliminate the judder of the transfer clutch 24. The hydraulic pressure fluctuation control of the transfer clutch 24 is executed under a condition in which the vehicle 11 is traveling in a predetermined straight line. As a result, even when the fastening force of the transfer clutch 24 is changed by the hydraulic pressure fluctuation control, that is, when the torque distribution ratio of the front and rear wheels 21, 18 is changed, the vehicle behavior during traveling can be stabilized.

[0035] Moreover, the hydraulic pressure fluctuation control of the transfer clutch 24 is executed with the brake system 71 in operation. This allows the hydraulic pressure fluctuation control to be executed while applying braking torque to the front and rear wheels 21, 18, and allows the hydraulic pressure fluctuation control to be executed with a change in the torque distribution ratio of the front and rear wheels 21, 18 without giving the driver any discomfort. Moreover, the hydraulic pressure fluctuation control of the transfer clutch 24 is executed with cruise control being executed. This allows the hydraulic pressure fluctuation control to be executed with the drive torque of the front and rear wheels 21, 18 in a stable state, and allows the hydraulic pressure fluctuation control to be executed with a change in the torque distribution ratio of the front and rear wheels 21, 18 without giving the driver any discomfort.

[0036] Then, when the control system 60 executes the hydraulic pressure fluctuation control of the transfer clutch 24 in step S23, the process proceeds to step S25, where it determines whether or not a predetermined execution time Ta has elapsed since the start of the hydraulic pressure fluctuation control. When it determines in step S25 that the execution time Ta has elapsed, the control system 60 proceeds to step S26, where it stops the hydraulic pressure fluctuation control, and resets the judder flag FL1 (FL1=0). Then, when the control system 60 resets the judder flag FL1 in step S26, the process proceeds to step S27, where it executes normal control of the transfer clutch 24. Note that, when executing normal control of the transfer clutch 24, the control system 60 sets a target operating hydraulic pressure based on the torque distribution ratio of the front and rear wheels 21, 18 and the input torque of the transfer clutch 24, and controls the clutch pressure based on this target operating hydraulic pressure.

[0037] Here, FIG. 6 is a diagram showing an example of the execution time Ta. As described above, the hydraulic oil for lubricating the friction plates 31, 41 is discharged from the through hole 32 of the clutch hub 30. In other words, the higher the rotation speed of the transfer clutch 24, the more the amount of hydraulic oil discharged from the clutch hub 30 increases, so it is considered that cleaning of the friction plates 31, 41 can be completed even with a short execution time Ta. For this reason, as shown in FIG. 6, the execution time Ta is set shorter as the rotation speed of the transfer clutch 24 increases. Note that, as the rotation speed of the transfer clutch 24, the rotation speed of the transmission output shaft 26, which is the input rotation speed of the transfer clutch 24, may be used, or the rotation speed of the rear wheel output shaft 15, which is the output rotation speed of the transfer clutch 24, may be used.

[0038] <Judder elimination control: timing chart> Fig. 7 is a timing chart showing an example of the execution status of the judder elimination control. In Fig. 7, "ON" of the brake system 71 means that the brake system 71 is operating, and "OFF" of the brake system 71 means that the brake system 71 is not operating. Also, "ON" of the cruise control means that the cruise control is being executed, and "OFF" of the cruise control means that the cruise control is stopped.

[0039] As shown at time t1 in FIG. 7, even if the brake system 71 is operating (symbol a1), when the judder flag FL1 is released (symbol b1), the transfer clutch 24 is controlled based on the target operating oil pressure Pa of the normal control (symbol c1). Then, as shown at times t2 and t3, when the judder flag FL1 is set (symbol b2) and cruise control is started (symbol d1), the hydraulic pressure fluctuation control of the transfer clutch 24 is started (symbol c2). In the hydraulic pressure fluctuation control of the transfer clutch 24, the clutch pressure is increased toward the first target hydraulic pressure P1 (symbol c3), and the clutch pressure is decreased toward the second target hydraulic pressure P2 (symbol c4). Then, as shown at time t4, when the hydraulic pressure fluctuation control is executed for a predetermined execution time Ta, the judder flag FL1 is released (symbol b3), and the transfer clutch 24 is switched from the hydraulic pressure fluctuation control to the normal control (symbol c5).

[0040] In this way, in the hydraulic pressure fluctuation control, the first target hydraulic pressure P1 and the second target hydraulic pressure P2 are alternately switched to fluctuate the clutch pressure of the transfer clutch 24 up and down. Here, the first target hydraulic pressure P1 is a hydraulic pressure higher than the target hydraulic pressure Pa immediately before the hydraulic pressure fluctuation control is started, and the second target hydraulic pressure P2 is a hydraulic pressure lower than the target hydraulic pressure Pa immediately before the hydraulic pressure fluctuation control is started. The second target hydraulic pressure P2, which is lower than the target hydraulic pressure Pa, is set to a hydraulic pressure for providing a minute clearance between the friction plates 31, 41. In addition, the holding time of the first target hydraulic pressure P1 and the holding time of the second target hydraulic pressure P2 are set in consideration of the response delay of the hydraulic control by the valve body 51 so that the clutch pressure reaches the first target hydraulic pressure P1 and the second target hydraulic pressure P2. In this way, by alternately switching the target hydraulic pressures P1 and P2 to execute the hydraulic pressure fluctuation control, contamination, deteriorated hydraulic oil, etc. can be removed from the friction surfaces of the friction plates 31, 41, and the judder of the transfer clutch 24 can be eliminated.

[0041] <Other embodiments> The present disclosure is not limited to the above-described embodiment, and may be modified in various ways without departing from the spirit of the present disclosure. In the above description, the control system 60 is configured by five control units 61-64, 82, but the present disclosure is not limited to this, and the control system 60 may be configured by one control unit, or may be configured by multiple control units. In the above description, the torque is distributed to the rear wheels 18 using the transfer clutch 24, but the present disclosure is not limited to this, and the torque may be distributed to the front wheels 21 using the transfer clutch 24.

[0042] In the above description, the hydraulic pressure fluctuation control of the transfer clutch 24 is executed under a state in which the cruise control is executed, but the present invention is not limited to this. In other words, as long as the vehicle is in a constant speed running state in which both the vehicle acceleration and the vehicle deceleration are below a predetermined threshold, the hydraulic pressure fluctuation control may be executed without being limited to the execution of the cruise control. In the above description, the hydraulic pressure fluctuation control of the transfer clutch 24 is executed under a state in which the calipers 75, 77 of the front and rear wheels 21, 18 are in operation, but the present invention is not limited to this, and it is sufficient that at least one of the calipers 75, 77 is in operation. In other words, the hydraulic pressure fluctuation control may be executed under a state in which the caliper 75 of the front wheel 21 is in operation, or the hydraulic pressure fluctuation control may be executed under a state in which the caliper 77 of the rear wheel 18 is in operation. In the illustrated example, the technology of the present disclosure is applied to the vehicle 11 equipped with the engine 12 as a power source, but the present invention is not limited to this, and the technology of the present disclosure may be applied to a hybrid vehicle equipped with the engine 12 and an electric motor as power sources. In addition, in the illustrated example, the oil pump 50 is driven by the engine 12, but this is not limiting, and an oil pump driven by an electric motor may also be used. [Explanation of symbols]

[0043] 10...vehicle drive device, 18...rear wheel, 21...front wheel, 24...transfer clutch (friction clutch), 29...power transmission path, 31, 41...friction plate, 42...piston, 44...piston oil chamber, 51...valve body (valve unit), 60...control system, 75, 77...caliper (brake mechanism), 100...processor, 101...main memory (memory), A1, A2...threshold value, Pa...target operating pressure, P1...first target pressure, P2...second target pressure, Ta...execution time

Claims

1. A vehicle drive device that drives front and rear wheels, a friction clutch provided in a power transmission path connecting the front wheels and the rear wheels, the friction clutch including a plurality of friction plates lubricated with oil and a piston for fastening the plurality of friction plates to each other; a valve unit connected to a piston oil chamber defined by the piston, the valve unit controlling a hydraulic pressure supplied to the piston oil chamber; A control system including a processor and a memory communicatively connected to each other, the control system controlling the valve unit; having The control system includes: determining whether or not judder is occurring in the friction clutch when the steering angle of the front wheels exceeds a threshold value; when it is determined that judder is occurring in the friction clutch, a hydraulic pressure fluctuation control is executed to fluctuate an operating hydraulic pressure supplied to the piston oil chamber up and down under a state in which the steering angle of the front wheels is below the threshold value. A drive unit for a vehicle.

2. 2. The vehicle drive device according to claim 1, The control system includes: when it is determined that judder is occurring in the friction clutch, the hydraulic pressure fluctuation control is executed under a state in which the steering angle of the front wheels is below the threshold value and a brake mechanism of at least one of the front wheels and the rear wheels is operating. A drive unit for a vehicle.

3. 2. The vehicle drive device according to claim 1, The control system includes: when it is determined that judder is occurring in the friction clutch, the hydraulic pressure fluctuation control is executed under a state in which the steering angle of the front wheels is below the threshold value and both the vehicle acceleration and the vehicle deceleration are below the threshold value. A drive unit for a vehicle.

4. 2. The vehicle drive device according to claim 1, The control system executes the hydraulic pressure fluctuation control by alternately switching between a first target hydraulic pressure and a second target hydraulic pressure, The first target hydraulic pressure is a hydraulic pressure higher than a target operating hydraulic pressure immediately before the hydraulic pressure fluctuation control is started, The second target hydraulic pressure is a hydraulic pressure lower than the target hydraulic pressure immediately before starting the hydraulic pressure fluctuation control. A drive unit for a vehicle.

5. 2. The vehicle drive device according to claim 1, The control system sets an execution time of the hydraulic pressure fluctuation control to be shorter as the rotational speed of the friction clutch becomes higher. A drive unit for a vehicle.

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