Driving force transmission device and control method for driving force transmission device

Abstract

A driving force transmission device and a control method for a driving force transmission device, the driving force transmission device comprising: an input rotating member (20) and an output rotating member (23); a multi-plate clutch (3); a pressing mechanism (6); and a control device (7), the control device (7) including a current supply circuit. The control device (7) is configured to calculate a torque command value based on the state of the vehicle, the torque command value being the driving force that needs to be transmitted through the multi-plate clutch (3), to calculate a current command value, correct the current command value, and control the current supply circuit so that a current depending on the current command value is supplied to the pressing mechanism (6). The control device (7) is configured to perform correction so as to increase or decrease the current command value by a correction amount depending on the rate of change of the torque command value.

Description

Technical Field

[0001] The present invention relates to a driving force transmission device that transmits a driving force through a multi-plate clutch, in which frictional sliding between clutch discs is lubricated by a lubricant, and also relates to a control method for the driving force transmission device. Background Art

[0002] Generally, a driving force transmission device that transmits a driving force through a multi-plate clutch is used to transmit a driving force to an auxiliary drive wheel of a four-wheel drive vehicle, in which frictional sliding between clutch discs is lubricated by a lubricant. As such a driving force transmission device, the applicant has proposed the driving force transmission devices described in Japanese Patent Application Laid-Open No. 2007-064251 (JP 2007-064251 A) and Japanese Patent Application Laid-Open No. 2009-014134 (JP 2009-014134 A).

[0003] In JP 2007-064251A, based on the results of an operation test after assembling a driving force transmission device that transmits an output torque corresponding to an input current from the driving source side of the vehicle to the auxiliary drive wheel side, an I-T characteristic as a characteristic of the input current and the output torque is stored in a storage unit, and the current is controlled based on the I-T characteristic stored in the storage unit. Thereby, the deviation of the characteristics of each driving force transmission device is reduced, and the accuracy of the output torque is improved.

[0004] In JP 2009-014134A, when the command current value calculated based on the command torque changes from being equal to or lower than a first predetermined current value to being higher than the first predetermined current value that releases the frictional engagement of the clutch discs, the start time is determined. When the command current value at the start time is equal to or less than a second predetermined current value, inrush current supply control for adding a correction value to the command current value is performed so that the command current value becomes the second predetermined current value. The second predetermined current value is a current value that allows the clutch discs to frictionally engage at a response speed equal to or higher than a predetermined response speed (a speed at which no response lag problem occurs during use). Summary of the Invention

[0005] In a driving force transmission device including the following multi-plate clutch and pressing mechanism, in which frictional sliding between clutch discs in the multi-plate clutch is lubricated by a lubricant, and the pressing mechanism presses the multi-plate clutch with a pressing force depending on the supplied current, a deviation between the command torque and the actually output torque (driving force) sometimes increases during an increase in the command torque. The inventors have seriously studied the cause of the deviation increase and countermeasures, and completed the present invention.

[0006] That is, the present invention can reduce the difference between the commanded torque and the torque actually output when the commanded torque increases, and can enhance the accuracy of the torque transmission of the multi-plate clutch.

[0007] A first aspect of the present invention is a driving force transmission device. The driving force transmission device includes: an input rotating member and an output rotating member, the input rotating member and the output rotating member being configured to rotate relative to each other coaxially; a multi-plate clutch including a plurality of clutch discs, the frictional sliding between the plurality of clutch discs being lubricated by a lubricant; a pressing mechanism configured to press the multi-plate clutch with a pressing force depending on the supplied current; and a control device including a current supply circuit configured to supply the current to the pressing mechanism. The output rotating member is configured such that the driving force of the vehicle is transmitted from the input rotating member to the output rotating member by the multi-plate clutch; the control device is configured to calculate a torque command value based on the state of the vehicle, the torque command value being the driving force that needs to be transmitted by the multi-plate clutch; the control device is configured to calculate a current command value corresponding to the torque command value; is configured to correct the current command value; and is configured to control the current supply circuit such that a current depending on the current command value corrected by the control device is supplied to the pressing mechanism. The control device is configured to correct the current command value so as to increase or decrease the current command value torque by an amount depending on the change rate of the torque command value.

[0008] With the above configuration, the difference between the commanded torque and the torque actually output when the commanded torque increases can be reduced, and the accuracy of the torque transmission of the multi-plate clutch can be enhanced.

[0009] The second aspect of the present invention relates to a control method for a driving force transmission device. The driving force transmission device includes: an input rotating member and an output rotating member, the input rotating member and the output rotating member being configured to rotate relative to each other coaxially; a multi-plate clutch including a plurality of clutch discs, the frictional sliding between the plurality of clutch discs being lubricated by a lubricant; a pressing mechanism configured to press the multi-plate clutch with a pressing force depending on a supplied current; and a control device. The driving force transmission device is configured such that the driving force of the vehicle is transmitted from the input rotating member to the output rotating member by the multi-plate clutch, and the control method includes: the control device calculating a torque command value based on the state of the vehicle, the torque command value being the driving force that needs to be transmitted by the multi-plate clutch; the control device calculating a current command value corresponding to the torque command value; the control device correcting the current command value so as to increase or decrease the current command value torque by an amount depending on the rate of change of the torque command value; and the control device supplying the current depending on the corrected current command value to the pressing mechanism.

[0010] With the above configuration, the difference between the commanded torque and the torque actually output when the commanded torque increases can be reduced, and the accuracy of the torque transmission of the multi-plate clutch can be enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals denote like elements, and in which:

[0012] Figure 1 is a schematic configuration diagram showing a schematic configuration example of a four-wheel drive vehicle equipped with a control device for a driving force transmission device according to an embodiment of the present invention;

[0013] Figure 2 is a cross-sectional view showing a configuration example of a torque coupler;

[0014] Figure 3 is a control block diagram showing an example of a control configuration of a control device;

[0015] Figure 4 is a graph showing an example of an I-T characteristic map;

[0016] Figure 5 is a graph showing the change in the transmission torque of a main clutch when the current supplied to an electromagnetic coil changes at a constant rate of change;

[0017] Figure 6Ais a graph showing the changes in the actual current value and the transmission torque of the main clutch when the current command value increases stepwise from zero;

[0018] Figure 6B is a graph showing Figure 6A an enlarged view of a part of the graph;

[0019] Figure 7 is a flowchart showing an example of a program of a process executed by a control unit;

[0020] Figure 8 includes a left graph, a center graph, and a right graph, which are graphs showing examples of the time changes in the transmission torque of the main clutch and the current command value when the torque command value becomes constant after rising at different change rates;

[0021] Figure 9 is a graph showing an example of a first correction value map;

[0022] Figure 10 is a graph showing an example of a second correction value map;

[0023] Figure 11A is a graph showing an example of the time changes in the transmission torque of the main clutch and the current command value during the rise of the torque command value, and shows a case where no correction is performed; and

[0024] Figure 11B is a graph showing an example of the time changes in the transmission torque of the main clutch and the current command value during the rise of the torque command value, and shows a case where correction is performed. Detailed Description of the Invention

[0025] Embodiment

[0026] Reference will be made to Figures 1 to 11B to describe embodiments of the present invention. The embodiments described below are shown as preferred specific examples for carrying out the present invention. Various technically preferred technical matters are specifically illustrated, but the technical scope of the present invention is not limited to such specific modes.

[0027] Figure 1 is a schematic configuration diagram showing a schematic configuration example of a four-wheel drive vehicle equipped with a control device for a driving force transmission device according to an embodiment of the present invention.

[0028] As Figure 1As shown in the figure, the four-wheel drive vehicle 100 includes: an engine 11 as a driving source; a transmission 12 that shifts the output of the engine 11; a left front wheel 181 and a right front wheel 182 as main driving wheels, and the driving force of the engine 11 shifted by the transmission 12 is constantly transmitted to the main driving wheels; and a left rear wheel 191 and a right rear wheel 192 as auxiliary driving wheels, and the driving force of the engine 11 is transmitted to the auxiliary driving wheels depending on the vehicle state of the four-wheel drive vehicle 100. When the driving force of the engine 11 is transmitted to the left front wheel 181, the right front wheel 182, the left rear wheel 191, and the right rear wheel 192, the four-wheel drive vehicle 100 becomes a four-wheel drive state, and when the driving force of the engine 11 is only transmitted to the left front wheel 181 and the right front wheel 182, the four-wheel drive vehicle 100 becomes a two-wheel drive state. Instead of the engine, an electric motor can be used as the driving source, and a so-called hybrid system in which the engine and the electric motor are combined can be used as the driving source.

[0029] The four-wheel drive vehicle 100 includes: a front differential 13; a propeller shaft 14; a rear differential 15; a pinion shaft 150 that transmits the driving force to the rear differential 15; a left drive shaft 161 and a right drive shaft 162 on the front wheel side; a left drive shaft 171 and a right drive shaft 172 on the rear wheel side; and a driving force transmission device 1 that transmits the driving force from the propeller shaft 14 to the pinion shaft 150.

[0030] The four-wheel drive vehicle 100 is equipped with: wheel speed sensors 101 to 104 that detect the rotational speeds of the left front wheel 181, the right front wheel 182, the left rear wheel 191, and the right rear wheel 192; an accelerator pedal sensor 105 that detects the depression amount of the accelerator pedal 111; and a steering angle sensor 106 that detects the steering angle of the steering wheel 112. The detection values of the sensors 101 to 106 are examples of the vehicle state of the four-wheel drive vehicle 100 for controlling the driving force transmission device 1.

[0031] The driving force transmission device 1 includes: a torque coupler 2 that is provided between the propeller shaft 14 and the pinion shaft 150; and a control device 7 that controls the torque coupler 2 and transmits the driving force from the propeller shaft 14 to the pinion shaft 150 depending on the vehicle state. The control device 7 can obtain the detection values of the wheel speed sensors 101 to 104, the accelerator pedal sensor 105, and the steering angle sensor 106, and control the torque coupler 2 by increasing or decreasing the current supplied to the torque coupler 2.

[0032] The driving force of the engine 11 is transmitted to the left front wheel 181 and the right front wheel 182 through the transmission 12, the front differential 13, and the left drive shaft 161 and the right drive shaft 162 on the front wheel side. The front differential 13 includes: a pair of side gears 131 that are respectively connected to the left drive shaft 161 and the right drive shaft 162 on the front wheel side so as not to be able to perform relative rotation; a pair of pinions 132 that engage the side gears 131 such that the gear axis of the pinion 132 is orthogonal to the gear axis of the side gear 131; a pinion shaft 133 that supports the pinions 132; and a front differential case 134 that houses the side gears 131, the pinions 132, and the pinion shaft 133.

[0033] The ring gear 135 is fixed to the front differential case 134, and the ring gear 135 engages with the pinion 141 provided at the vehicle front end portion of the propeller shaft 14. The vehicle rear end portion of the propeller shaft 14 is connected to the housing 20 of the torque coupler 2. The torque coupler 2 includes: an inner shaft 23 that is arranged so as to be able to perform relative rotation through the housing 20; and a pinion shaft 150 that is connected to the inner shaft 23 so as not to be able to perform relative rotation. Details of the torque coupler 2 will be described later.

[0034] The rear differential 15 includes: a pair of side gears 151 that are respectively connected to the left drive shaft 171 and the right drive shaft 172 on the rear wheel side so as not to be able to perform relative rotation; a pair of pinions 152 that engage the side gears 151 such that the gear axis of the pinion 152 is orthogonal to the gear axis of the side gear 151; a pinion shaft 153 that supports the pinions 152; a rear differential case 154 that houses the side gears 151, the pinions 152, and the pinion shaft 153; and a ring gear that is fixed to the rear differential case 154 and engages with the pinion shaft 150. The rear differential 15 distributes the driving force input from the pinion shaft 150 to the left rear wheel 191 and the right rear wheel 192 through the drive shafts 171, 172.

[0035] Structure of the driving force transmission device

[0036] Figure 2 is a cross-sectional view showing a structural example of the torque coupler 2. In Figure 2 the actuated state (torque transmission state) of the torque coupler 2 is shown on the upper side of the rotation axis O, and the non-actuated state (torque non-transmission state) of the torque coupler 2 is shown on the lower side. Hereinafter, the direction parallel to the rotation axis O will be referred to as the axial direction.

[0037] The torque coupler 2 is configured to include: a housing 20, which includes a front housing 21 and a rear housing 22 and serves as an input rotating member; an inner shaft 23, which is supported so as to be able to rotate relative to the housing 20 coaxially and serves as an output rotating member; a main clutch 3, which is disposed between the housing 20 and the inner shaft 23 and serves as a multi-plate clutch; a cam mechanism 4, which generates a driving force for pressing the main clutch 3; and an electromagnetic clutch mechanism 5, which receives a current supply from a control device 7 and actuates the cam mechanism 4. The cam mechanism 4 and the electromagnetic clutch mechanism 5 constitute a pressing mechanism 6, which presses the main clutch 3 with a pressing force depending on the current supplied from the control device 7.

[0038] The housing 20 encloses a lubricant, which lubricates the main clutch 3 and other components inside the housing 20. The main clutch 3 is a wet multi-plate clutch including a plurality of clutch discs, and the frictional sliding between the clutch discs is lubricated by the lubricant.

[0039] The front housing 21 integrally includes a cylindrical portion 21a having a cylindrical shape and a bottom portion 21b, and has a bottomed cylindrical shape. A concave thread 21c is formed on the inner surface of the open end of the cylindrical portion 21a. The drive shaft 14 (see Figure 1 ) is connected to the bottom portion 21b of the front housing 21, for example, by means of a universal joint. In addition, the front housing 21 has a plurality of outer spline protrusions 211 extending in the axial direction on the inner peripheral surface of the cylindrical portion 21a.

[0040] The rear housing 22 includes: a first annular member 221, which is made of a magnetic material (such as iron); a second annular member 222, which is made of a non-magnetic material (such as austenitic stainless steel) and is integrally connected to the inner peripheral side of the first annular member 221 by welding or the like; and a third annular member 223, which is made of a magnetic material (such as iron) and is integrally connected to the inner peripheral side of the second annular member 221 by welding or the like. An annular accommodation space 22a for accommodating the electromagnetic coil 53 is formed between the first annular member 221 and the third annular member 223. In addition, a convex thread 221a is formed on the outer peripheral surface of the first annular member 221, and the convex thread 221a is screwed into the concave thread 21c of the front housing 21.

[0041] The inner shaft 23 is formed in a cylindrical shape and is supported on the inner periphery of the housing 20 by a ball bearing 24 and a needle bearing 25. The inner shaft 23 includes a plurality of inner spline protrusions 231 extending in the axial direction on the outer peripheral surface of the inner shaft 23. In addition, a spline fitting portion 232 is formed on the inner peripheral surface of one end of the inner shaft 23, and one end of the pinion shaft 150 (seeFigure 1 ) so that relative rotation cannot be performed.

[0042] The main clutch 3 includes a plurality of main outer clutch disks 31 and a plurality of main inner clutch disks 32. The main outer clutch disks 31 and the main inner clutch disks 32 are alternately arranged in the axial direction. The frictional sliding between the main outer clutch disks 31 and the main inner clutch disks 32 is lubricated by a lubricant. The main outer clutch disks 31 rotate together with the front housing 21, while the main inner clutch disks 32 rotate together with the inner shaft 23. The main outer clutch disks 31 are made of metal and include a plurality of engaging protrusions 311 at the end of the outer periphery of the main outer clutch disks 31, and the plurality of engaging protrusions 311 engage with the outer spline protrusions 211 of the front housing 21. When the engaging protrusions 311 engage with the outer spline protrusions 211, the relative rotation of the main outer clutch disks 31 with respect to the front housing 21 is restricted, and the main outer clutch disks 31 can move in the axial direction with respect to the front housing 21.

[0043] The main inner clutch disks 32 include a plurality of engaging protrusions 321 at the end of the inner periphery of the main inner clutch disks 32, and the plurality of engaging protrusions 321 engage with the inner spline protrusions 231 of the inner shaft 23. When the engaging protrusions 321 engage with the inner spline protrusions 231, the relative rotation of the main inner clutch disks 32 with respect to the inner shaft 23 is restricted, and the main inner clutch disks 32 can move in the axial direction with respect to the inner shaft 23. Each of the main inner clutch disks 32 includes a disk-shaped base material 331 made of metal, and porous friction materials 332 bonded to both side surfaces of the base material 331. In the base material 331, a plurality of oil holes 333 through which the lubricant flows are formed on the inner side of the portion where the friction materials 332 are bonded. In each main inner clutch disk 32, oil grooves (not shown) through which the lubricant flows are formed on the surface in contact with the friction materials 332.

[0044] The cam mechanism 4 is configured to include: a pilot cam 41 that receives the rotational force of the housing 20 through the electromagnetic clutch mechanism 5; a main cam 42 that serves as a pressing member for pressing the main clutch 3 in the axial direction; and a plurality of spherical cam rollers 43 that are disposed between the pilot cam 41 and the main cam 42.

[0045] The main cam 42 integrally includes: an annular plate-shaped pressing portion 421 that contacts the main inner clutch disc 32 at one end of the main clutch 3 and presses the main clutch 3; and a cam portion 422 that is disposed closer to the inner circumference of the main cam 42 than the pressing portion 421. An oil hole 420 through which lubricant flows is formed to pass axially through the pressing portion 421. A spline engaging portion 421a formed at the end of the inner circumference of the pressing portion 421 engages with the inner spline protrusion 231 of the inner shaft 23, thereby restricting relative rotation between the main cam 42 and the inner shaft 23. Further, the main cam 42 is biased by a disc spring 44 disposed between the main cam 42 and a stepped surface 23a formed on the inner shaft 23, such that the main cam 42 is axially away from the main clutch 3.

[0046] The pilot cam 41 includes a spline protrusion 411 at the end of the outer circumference of the pilot cam 41, and the spline protrusion 411 receives a rotational force for rotating relative to the main cam 42 from the electromagnetic clutch mechanism 5. A thrust needle bearing 45 is disposed between the guide cam 41 and the third annular member 223 of the rear housing 22. A plurality of circumferential cam grooves 41a having different axial depths and a plurality of circumferential cam grooves 442a having different axial depths are formed on the facing surfaces of the cam portion 422 of the pilot cam 41 and the main cam 42. A cam roller 43 is disposed between the cam groove 41a of the pilot cam 41 and the cam groove 422a of the main cam 42.

[0047] By the rotation of the pilot cam 41 relative to the main cam 42, the cam mechanism 4 generates a pressing force for pressing the main clutch 3. In the main clutch 3, the pressing force from the cam mechanism 4 causes frictional contact between the main outer clutch disc 31 and the main inner clutch disc 32, and the driving force is transmitted from the housing 20 to the inner shaft 23 through the frictional force between the two clutch discs.

[0048] The electromagnetic clutch mechanism 5 is configured to include: an armature 50; a plurality of pilot outer clutch discs 51; a plurality of pilot inner clutch discs 52; an electromagnetic coil 53; and an annular yoke 54 made of a magnetic material and holding the electromagnetic coil 53. The electromagnetic coil 53 is accommodated in the accommodation space 22a of the rear housing 22 while being held by the yoke 54. The yoke 54 is supported by the third annular member 223 of the rear housing 22 through a ball bearing 26.

[0049] A current from the control device 7 is supplied as an exciting current to the electromagnetic coil 53 through a cable 531. By energizing the electromagnetic coil 53, a magnetic flux having a magnetic flux density depending on the magnitude of the exciting current is generated in a magnetic path G that includes the yoke 54, the first annular member 221 and the third annular member 223 of the rear housing 22, the pilot outer clutch disc 51, the pilot inner clutch disc 52, and the armature 50.

[0050] The pilot outer clutch disk 51 and the pilot inner clutch disk 52, which are respectively disk members made of a magnetic material (such as iron), are alternately arranged between the armature 50 and the rear housing 22 in the axial direction. A plurality of arc-shaped slits for preventing magnetic flux short-circuit are formed on the pilot outer clutch disk 51 and the pilot inner clutch disk 52, and the plurality of arc-shaped slits are located at positions where the plurality of arc-shaped slits and the second annular member 222 of the rear housing 22 are arranged in the axial direction.

[0051] The pilot outer clutch disk 51 includes a plurality of engaging protrusions 511 at the end of the outer periphery of the pilot outer clutch disk 51, and the plurality of engaging protrusions 511 engage with the outer spline protrusions 211 of the front housing 21. The pilot inner clutch disk 52 includes a plurality of engaging protrusions 521 at the end of the inner periphery of the pilot inner clutch disk 52, and the plurality of engaging protrusions 521 engage with the spline protrusions 411 of the pilot cam 41. Similar to the main clutch 3, the frictional sliding between the pilot outer clutch disk 51 and the pilot inner clutch disk 52 is lubricated by a lubricant.

[0052] The armature 50 is an annular member made of a magnetic material (such as iron), and a plurality of engaging protrusions 501 that engage with the outer spline protrusions 211 of the front housing 21 are formed on the outer periphery of the armature 50. Thus, the armature 50 can move relative to the front housing 21 in the axial direction, and the rotation of the armature 50 relative to the front housing 21 is restricted.

[0053] The electromagnetic clutch mechanism 5 attracts the armature 50 to the yoke 54 side by the magnetic force generated by the energization of the electromagnetic coil 53, and the movement of the armature 50 generates a frictional force between the pilot outer clutch disk 51 and the pilot inner clutch disk 52. The pilot outer clutch disk 51 and the pilot inner clutch disk 52 are in frictional contact while being pushed to the rear housing 22 side by the armature 50.

[0054] In the torque coupler 2, by the actuation of the electromagnetic clutch mechanism 5, the rotational force depending on the current supplied to the electromagnetic coil 53 is transmitted to the pilot cam 41. The pilot cam 41 rotates relative to the main cam 42, and the cam roller 43 rolls on the cam grooves 41a, 422a. Then, the rolling of the cam roller 43 generates a driving force for pressing the main clutch 3 against the main cam 42, and a frictional force is generated between the main outer clutch disk 31 and the main inner clutch disk 32.

[0055] Configuration of the control device

[0056] As Figure 1As shown in the figure, the control device 7 includes: a control unit 70 which includes a CPU (arithmetic processing unit); a storage unit 8 which stores programs and the like to be executed by the CPU of the control unit 70; and a current supply circuit 9 which supplies current to the electromagnetic coil 53 of the torque coupler 2 by switching the voltage of a DC power supply (such as a battery). The current supply circuit 9 includes a switching element (such as a transistor) and generates the current to be supplied to the electromagnetic coil 53 by switching the DC voltage based on a pulse width modulation (PWM) signal output from the control unit 70.

[0057] By executing the program stored in the storage unit 8 by the CPU, the control unit 70 functions as: a torque command value calculation unit 71 which calculates a torque command value, which is the driving force that needs to be transmitted by the main clutch 3, based on the vehicle state; a current command value calculation unit 72 which calculates a current command value corresponding to the torque command value; a current correction unit 73 which corrects the current command value; and a current control unit 74 which controls the current supply circuit 9 so that a current depending on the current command value corrected by the current correction unit 73 is supplied to the squeezing mechanism 6. Some or all of the functions of the torque command value calculation unit 71, the current command value calculation unit 72, the current correction unit 73, and the current control unit 74 can be implemented by hardware such as an ASIC and an FPGA.

[0058] Figure 3 is a control block diagram showing an example of the control structure of the control device 7. In addition to the program 81 executed by the CPU of the control unit 70, the storage unit 8 also stores a torque command value map 82, an I-T characteristic map 83, a first correction value map 84, and a second correction value map 85 in a non-volatile memory.

[0059] The torque command value calculation unit 71 refers to the torque command value map 82 based on the vehicle state and calculates the torque command value T*. For example, the torque command value map 82 defines: the relationship between the differential rotational speeds of the front and rear wheels, which is the difference between the average rotational speeds of the left front wheel 181 and the right front wheel 182 and the average rotational speeds of the left rear wheel 191 and the right rear wheel 192 and the first command torque component; the relationship between the depression amount of the accelerator pedal, the vehicle speed, and the second command torque component; and the relationship between the steering angle, the vehicle speed, and the third command torque component. The torque command value calculation unit 71 calculates the total value of the first to third torque components as the torque command value T*.

[0060] The current command value calculation unit 72 refers to the I-T characteristic map 83 and calculates the current command value I* corresponding to the torque command value T*. In the I-T characteristic map 83, the results of the operation test performed after assembling the torque coupler 2 during the production of the power transmission device 1 are stored. In this operation test, the driving force (torque) transmitted from the housing 20 to the inner shaft 23 is measured while the current to be supplied to the electromagnetic coil 53 is changed from zero to the maximum at a constant rate of change over time (the amount of current change per unit time). Hereinafter, the time during which the current to be supplied to the electromagnetic coil 53 changes from zero to the maximum during this operation test is referred to as the I-T characteristic measurement time. For example, the I-T characteristic measurement time is 5 seconds. In addition, hereinafter, the rate of change refers to the amount of change per unit time, and the current rate of change during the operation test is referred to as the reference rate of change.

[0061] Figure 4 is a graph showing an example of the I-T characteristic map 83. During the production of the power transmission device 1, the I-T characteristic map 83 is stored in the storage unit 8. In the I-T characteristic map 83, Figure 4 the multiple coordinate points shown in Figure 4 are recorded in a two-dimensional coordinate system. The current command value calculation unit 72 performs linear interpolation between the multiple coordinate points and calculates the current command value I* corresponding to the torque command value T*. Imax on the horizontal axis represents the maximum value of the current of the electromagnetic coil 53 in the operation test. For example, in the case where the torque command value T* is

[0062] The current correction unit 73 includes: a determination unit 731 that determines whether the current command value I* is to be corrected and how to correct it based on the time change in the torque command value T*; a first correction value calculation unit 732 that calculates a first correction value C1 based on the first correction value map 84; a second correction value calculation unit 733 that calculates a second correction value C2 based on the second correction value map 85; and an adder 734 that calculates the corrected current command value I** by adding the first correction value C1 and the second correction value C2 to the current command value I*. The details of the processing of the current correction unit 73 will be described below.

[0063] The current control unit 74 includes a subtracter 741, an F / B (feedback) control unit 742, and a PWM signal output unit 743. A corrected current command value I** is input to the subtracter 741, and an actual current value I detected by a current sensor 75 is input. The current sensor 75 detects the current supplied to the electromagnetic coil 53. The subtracter 741 calculates a current difference ΔI between the corrected current command value I** and the actual current value I, and outputs the calculated current difference ΔI to the F / B control unit 742.

[0064] The F / B control unit 742 calculates a feedback control amount based on the input current difference ΔI, and outputs the feedback control amount to the PWM signal output unit 743. The F / B control unit 742 calculates the total value of the following two values as the feedback control amount, that is, the value obtained by multiplying the current difference ΔI by a predetermined proportional gain, and the value obtained by multiplying the integral value of the current difference ΔI by a predetermined integral gain. The PWM signal output unit 743 performs PWM calculation depending on the feedback control amount, and outputs a PWM signal having a duty ratio depending on the feedback control amount to the current supply circuit 9.

[0065] In a non-powered state where the current from the current supply circuit 9 is not supplied to the electromagnetic coil 53, the main cam 42 of the cam mechanism 4 is away from the main clutch 3 by the biasing force of the disc spring 44, and a lubricant is interposed between the main outer clutch disc 31 and the main inner clutch disc 32. When the electromagnetic coil 53 is powered on in this state, the main clutch 3 is pressed toward the main cam 42. Then, the lubricant between the main outer clutch disc 31 and the main inner clutch disc 32 is gradually discharged, and the main outer clutch disc 31 and the main inner clutch disc 32 come into contact with each other to generate frictional force.

[0066] The current command value calculation unit 72 calculates a current command value I* by referring to an I-T characteristic map 83 set based on the result when the current supplied to the electromagnetic coil 53 is changed from zero to maximum during the I-T characteristic measurement time. Therefore, in a case where the rate of change of the current when the current supplied to the electromagnetic coil 53 is increased is higher than a reference rate of change, a larger amount of lubricant remains between the main outer clutch disc 31 and the main inner clutch disc 32 compared to each current value during the operation test, so that the torque to be transmitted by the main clutch 3 tends to be lower than that during the operation test. Conversely, in a case where the rate of change of the current when the current supplied to the electromagnetic coil 53 is increased is lower than the reference rate of change, a smaller amount of lubricant remains between the main outer clutch disc 31 and the main inner clutch disc 32 compared to each current value during the operation test, so that the torque to be transmitted by the main clutch 3 tends to be higher than that during the operation test.

[0067] Further, in a case where a rate of change of current when the current supplied to the electromagnetic coil 53 is decreased is higher than a reference rate of change, lubricant is less likely to flow into a gap between the main outer clutch disk 31 and the main inner clutch disk 32 as compared with each current value during the operation test, so that the torque to be transmitted by the main clutch 3 tends to be higher than that during the operation test. Conversely, in a case where a rate of change of current when the current supplied to the electromagnetic coil 53 is decreased is lower than the reference rate of change, a larger amount of lubricant flows into the gap between the main outer clutch disk 31 and the main inner clutch disk 32 as compared with each current value during the operation test, so that the torque to be transmitted by the main clutch 3 tends to be lower than that during the operation test.

[0068] Figure 5 is a graph showing changes in the transmission torque (actual torque) of the main clutch 3 when the current supplied to the electromagnetic coil 53 is changed from zero to maximum at a constant rate of change. This graph shows the relationship between the exciting current of the electromagnetic coil 53 and the transmission torque of the main clutch 3 when the time (scan time) during which the current supplied to the electromagnetic coil 53 is changed from zero to maximum is 1 second, 3 seconds, and 30 seconds. For example, in a case where the scan time is 1 second, the current supplied to the electromagnetic coil 53 is changed from zero to maximum at a constant rate of change for 1 second.

[0069] As Figure 5 shown in the graph, when the current increases, the shorter the scan time, the later the lubricant is discharged from the main clutch 3, and the lower the actually transmitted torque. In this way, when the scan time is shorter than the I-T characteristic measurement time, that is, when the current supplied to the electromagnetic coil 53 is higher than the reference rate of change, the transmission torque of the main clutch 3 is lower than the characteristic shown in the I-T characteristic map 83 when the current increases, and the transmission torque of the main clutch 3 is higher than the characteristic shown in the I-T characteristic map 83 when the current decreases. Further, when the scan time is longer than the I-T characteristic measurement time, that is, when the current supplied to the electromagnetic coil 53 is lower than the reference rate of change, the transmission torque of the main clutch 3 is higher than the characteristic shown in the I-T characteristic map 83 when the current increases, and the transmission torque of the main clutch 3 is lower than the characteristic shown in the I-T characteristic map 83 when the current decreases.

[0070] The inventors have found that the transmission torque of the main clutch 3 changes smoothly after the torque command value T* becomes constant even when the current supplied to the electromagnetic coil 53 is constant. Specifically, for example, when the torque command value T* gradually increases from zero and becomes a constant value, the transmission torque of the main clutch 3 gradually increases even when the current supplied to the electromagnetic coil 53 is constant. Further, when the torque command value T* gradually decreases and becomes a constant value, the transmission torque of the main clutch 3 gradually decreases even when the current supplied to the electromagnetic coil 53 is constant.

[0071] Figure 6A is a graph showing changes in the actual current value and the transmission torque of the main clutch 3 when the current command value I* increases stepwise from zero. Figure 6B is a graph showing Figure 6A an enlarged view of a part of the graph.

[0072] As Figure 6A and Figure 6B show, when the current command value I* increases stepwise from zero, the transmission torque of the main clutch 3 rapidly rises in the early stage, and then, when the lubricant between the main outer clutch disc 31 and the main inner clutch disc 32 is discharged, the transmission torque of the main clutch 3 rises smoothly for several seconds.

[0073] As Figure 5 shown in the graph in, the phenomenon in which the deviation amount between the transmission torque when the current increases and the transmission torque when the current decreases varies depending on the current change rate; and as Figure 6A and Figure 6B show, the phenomenon in which the transmission torque of the main clutch 3 changes smoothly with the change in the amount of lubricant between the main outer clutch disc 31 and the main inner clutch disc 32, can cause an error in the actual transmission torque with respect to the torque command value T*, and this is not desirable. In this embodiment, the occurrence of transmission torque errors caused by the above two phenomena is restricted by the following control method.

[0074] Figure 7 is a flowchart showing an example of a program of the process performed by the control unit 70 that calculates the corrected current command value I**. The control unit 70 executes each process in the flowchart in a predetermined calculation cycle (for example, 5 ms).

[0075] In Figure 7In the process of the flowchart shown, the control unit 70 maps based on the vehicle state reference torque command value 82 and calculates the torque command value T* (step S1). Then, the control unit 70 refers to the I-T characteristic map 83 and calculates the current command value I* corresponding to the torque command value T* (step S2). The process of step S1 is the process executed by the torque command value calculation unit 71, and the process of step S2 is the process executed by the current command value calculation unit 72.

[0076] Then, the control unit 70 calculates the change amount ΔT of the torque command value, where the change amount ΔT of the torque command value is the difference between the last value of the torque command value T* in the previous calculation cycle and the current value of the torque command value T* in the current calculation cycle (step S3). Then, the control unit 70 determines whether the absolute value of the change amount ΔT of the torque command value is less than a predetermined threshold A (step S4). The threshold A is a decimal value such that when the torque command value T* is substantially constant, the determination result in step S4 is affirmative (yes). Hereinafter, the state where the determination result in step S4 is affirmative (yes), that is, the state where the change rate of the torque command value T* is within a predetermined range, is referred to as a constant torque state.

[0077] In the case where the determination result in step S4 is affirmative (yes), the control unit 70 calculates the counter threshold B used in step S7 below based on the change rate of the torque command value T* before the determination result in step S4 becomes affirmative (yes) (step S5). Then, the control unit 70 counts the counter C for measuring time (step S6). In the case where the determination result in step S4 continues to be affirmative (yes), the process of step S5 can be performed only in the first calculation cycle and can be skipped in subsequent calculation cycles.

[0078] Then, the control unit 70 determines whether the counter C counted in step S6 is equal to or greater than the counter threshold B calculated in step S5 (step S7). In the case where the determination result is that the counter C is equal to or greater than the counter threshold B (S7: yes), the control unit 70 calculates the first correction value C1 by referring to the first correction value map 84 based on the detection time T evaluated from the counter C (step S8). The detection time T corresponds to the duration of the constant torque state and can be evaluated by multiplying the counter value of the counter C by the calculation cycle length. In addition, the control unit 70 calculates the corrected current command value I** by adding the first correction value C1 to the current command value I* (step S9).

[0079] In this way, in the constant torque state after the torque command value T* changes, the current correction unit 73 corrects the current command value I* by the first correction value C1 depending on the duration of the constant torque state. When the determination result in step S7 is negative (No), the control unit 70 terminates the process in this calculation cycle and does not perform the processes of steps S8 and S9.

[0080] On the other hand, in the case where the determination result in step S4 is negative (No), the control unit 70 resets the counter C to 0 (step S10). In addition, the control unit 70 calculates the change rate of the torque command value T* in the past predetermined time as the average value of the torque command value change amounts ΔT in the past plurality of calculation cycles (step S11). For example, when the predetermined time is 20 ms and the calculation cycle length is 5 ms, the change rate of the torque command value T* calculated in step S11 is the average value of the torque command value change amounts ΔT in the current calculation cycle and the past three calculation cycles.

[0081] Then, the control unit 70 calculates the second correction value C2 by referring to the second correction value map 85 based on the change rate of the torque command value T* calculated in step S11 (step S12). Then, the control unit 70 calculates the corrected current command value I** by adding the second correction value C2 to the current command value I* (step S13).

[0082] The processes of steps S4 to S7 and the process of step S10 are processes executed by the determination unit 731 of the current correction unit 73. The process of step S8 is a process executed by the first correction value calculation unit 732 of the current correction unit 73. The process of step S12 is a process executed by the second correction value calculation unit 733 of the current correction unit 73. The processes of steps S9 and S13 are processes executed by the adder 734 of the current correction unit 73.

[0083] A method for calculating the counter threshold B in step S5 will be described in detail here. The control unit 70 calculates the counter threshold B based on the change rate of the torque command value T* in the past predetermined time. The predetermined time should preferably be longer than the predetermined time in step S11, for example, 1 second or longer. As the change rate of the torque command value T* in the past predetermined time is higher, that is, as the change amount (absolute value) of the torque command value T* in the past predetermined time is larger, the control unit 70 sets the counter threshold B to a larger value.

[0084] This is because when the torque command value T* rapidly increases therein, the discharge of the lubricant from the gap between the main outer clutch disk 31 and the main inner clutch disk 32 is not completed, and the discharge of the lubricant from the gap between the main outer clutch disk 31 and the main inner clutch disk 32 continues until the torque command value T* becomes constant when the torque command value T* increases steadily. In addition, when the torque command value T* decreases, as the change rate of the torque command value T* is higher, the influence of the drag torque caused by the viscosity of the lubricant between the main outer clutch disk 31 and the main inner clutch disk 32 lasts for a longer time. Therefore, it is necessary to set the counter threshold B to a larger value.

[0085] It is desirable to set the counter threshold B such that the correction effect of the first correction value C1 appears when the transmission torque of the main clutch 3 substantially conforms to the torque command value T*. For example, it is desirable to derive the relationship between the change rate of the torque command value T* and the ideal counter threshold B from the results of tests conducted when the change rate of the torque command value T* changes.

[0086] In this way, the current correction unit 73 sets the counter threshold B depending on the change rate of the torque command value T* before the constant torque state, and starts to correct the current command value I* with the second correction value C2 after a predetermined time depending on the counter threshold B has elapsed since the start of the constant torque state.

[0087] For example, the counter threshold B can be changed depending on the estimated temperature of the lubricant or the rotational speed difference between the housing 20 and the inner shaft 23. The estimated temperature of the lubricant can be estimated, for example, based on the external temperature and the load state of the torque coupler 2, and the rotational speed difference between the housing 20 and the inner shaft 23 can be evaluated from the rotational speed difference between the front and rear wheels. The lower the temperature of the lubricant, the higher the viscosity of the lubricant. Therefore, as the estimated temperature of the lubricant is higher, it is desirable to lower the counter threshold B. In addition, the lower the rotational speed difference between the housing 20 and the inner shaft 23, the more smoothly the lubricant tends to be discharged. Therefore, as the rotational speed difference between the housing 20 and the inner shaft 23 is lower, it is desirable to lower the counter threshold B.

[0088] Figure 8 The left, center, and right diagrams in [diagram name] are graphs showing examples of the time changes of the transmission torque of the main clutch 3 and the current command value I* when the torque command value T* becomes constant after rising at different change rates. Figure 8 The left diagram in [diagram name] is a graph when the change rate of the torque command value T* is low. Figure 8 The center diagram in [diagram name] is a graph when the change rate of the torque command value T* is at a medium level, while Figure 8 the right diagram in [diagram name] is a graph when the torque command value T* rises in a stepwise manner. In Figure 8In the curve graph of the central figure, approximately 1.5 seconds before the torque command value T* becomes constant, the rate of change of the current command value I* is equivalent to the rate of change of the current supplied to the electromagnetic coil 53 during the operation test after the assembly torque coupler 2 is assembled.

[0089] As Figure 8 Shown in the left figure in, when the rate of change of the torque command value T* is low, the transmitted torque of the main clutch 3 is higher than the torque command value T*, while the torque command value T* is increasing, and even when the torque command value T* becomes constant, the transmitted torque of the main clutch 3 is higher than the torque command value T*. In this case, it is desirable to immediately start the correction process in steps S8 and S9.

[0090] As Figure 8 Shown in the right figure in, when the rate of change of the torque command value T* is high, the transmitted torque of the main clutch 3 cannot keep up with the increase of the torque command value T*, and even when the torque command value T* becomes constant, the transmitted torque of the main clutch 3 is lower than the torque command value T*. In this case, it is desirable to delay the start of the correction process in steps S8 and S9.

[0091] Figure 9 is a curve graph showing an example of the first correction value map 84. Figure 9 Shows the map information referred to by the control unit 70 in the constant torque state after the torque command value T* rises. As Figure 9 Shown in, the following characteristics are stored in the first correction value map 84, where the correction amount (absolute value) gradually increases until the detection time T becomes t1, and the correction amount becomes constant after the detection time T becomes t1. As Figure 9 Shown in, after the torque command value T* rises, the first correction value C1 in the constant torque state is negative, so the corrected current command value I** becomes smaller than the current command value I*, because the first correction value C1 is added to the current command value I* in step S9.

[0092] Regarding the map information of the first correction value map 84 referred to by the control unit 70 in the constant torque state after the torque command value T* drops, for example, it is the following map information, where Figure 9 the signs of the correction values in the map information shown in are opposite. The absolute value of the correction amount may be changed, and the time when the correction amount becomes constant ( Figure 9 t1 in) may be changed. The first correction value C1 in this case is positive, so the corrected current command value I** becomes larger than the current command value I*, because the first correction value C1 is added to the current command value I* in step S9.

[0093] In this way, in the constant torque state after the torque command value T* has increased, the current correction unit 73 performs correction so as to gradually decrease the current command value I* with a first correction value C1 that depends on the duration of the constant torque state. Further, in the constant torque state after the torque command value T* has decreased, the current correction unit 73 performs correction so as to gradually increase the current command value I* with the first correction value C1 that depends on the duration of the constant torque state.

[0094] Figure 10 is a graph showing an example of the second correction value map 85. The second correction value map 85 is an example of relationship information indicating the relationship between the rate of change of the torque command value T* and the second correction value C2. In the second correction value map 85, for each magnitude of the torque command value T* (0 Nm, and T1 to T5 (0 < T1 < T2 < T3 < T4 < T5)), the relationship between the rate of change of the torque command value T* calculated in step S11 and the second correction value C2 is defined. As the rate of change of the torque command value T* used as the horizontal axis of the graph, the average value of the changes ΔT of the torque command value in a plurality of past calculation cycles can be used, or the change ΔT of the torque command value, which is the difference between the torque command value T* in the previous calculation cycle and the torque command value T* in the current calculation cycle, can be used.

[0095] In Figure 10 the R1 on the horizontal axis represents the reference rate of change. The second correction value C2 represented by the vertical axis is positive when the rate of change of the torque command value T* represented by the horizontal axis is higher than the reference rate of change, and negative when the rate of change of the torque command value T* is lower than the reference rate of change. In this way, when the rate of change of the torque command value T* is higher than the reference rate of change when the torque command value T* is rising, the current correction unit 73 adds the second correction value C2 to the current command value I*, thereby setting the corrected current command value I** to a value greater than the current command value I*. That is, the current correction unit 73 performs correction so as to increase the current command value. Further, when the rate of change of the torque command value T* is lower than the reference rate of change when the torque command value T* is rising, the current correction unit 73 adds the second correction value C2 with a negative value to the current command value I*, thereby setting the corrected current value I** to a value smaller than the current command value I*. That is, the current correction unit 73 performs correction so as to decrease the current command value.

[0096] As Figure 10 shown in, the greater the deviation (difference) between the rate of change of the torque command value T* and the reference rate of change, the greater the magnitude (absolute value) of the second correction value C2. Further, when the rate of change of the torque command value T* is lower than the reference rate of change, Figure 10The slope of the curve shown in [reference] is greater than when the rate of change of the torque command value T* is higher than the reference rate of change. That is, the amount of change in the absolute value of the second correction value C2 is greater with respect to the amount of change in the magnitude of the torque command value T*.

[0097] In addition, when the torque command value T* decreases, the current correction unit 73 uses the value generated by inverting the sign of the second correction value C2 on the vertical axis shown in [reference] to correct the current command value I*. That is, the second correction value C2 when the torque command value T* increases and the second correction value C2 when the torque command value T* decreases shown in the second correction value map 85 are values that differ only in sign. Figure 10 In this way, when the amount of change in the torque command value T* is greater than the threshold A when the torque command value T* increases, the current correction unit 73 performs correction so as to increase the current command value I* by an amount of correction depending on the rate of change of the torque command value T*. In addition, when the amount of change in the torque command value T* is greater than the threshold A when the torque command value T* decreases, the current correction unit 73 performs correction so as to decrease the current command value I* by an amount of correction depending on the rate of change of the torque command value T*. In addition, the current correction unit 73 refers to the second correction value map 85 and increases the amount of correction of the current command value I* as the rate of change of the torque command value T* increases.

[0098]

[0099] Figure 11A Figure 11B and Figure 11A Each is a curve graph showing an example of the transmitted torque of the main clutch 3 and the time change of the current command value I* during the rise of the torque command value T*. Figure 11B shows the case where correction is not performed with the second correction value C2, Figure 11A shows the case where correction is performed with the second correction value C2. As shown in [reference], when the rate of change of the torque command value T* is low, the transmitted torque of the main clutch 3 is higher than the torque command value T*, but as shown in [reference], the difference between the transmitted torque of the main clutch 3 and the torque command value T* is reduced by the correction of the second correction value C2. Figure 11B

[0100] As the first correction value C1 shown in the first correction value map 84 and the second correction value C2 shown in the second correction value map 85, the first correction value C1 and the second correction value C2 previously set and stored in the storage unit 8 can be used without change, or can be changed, for example, based on the magnitude of the torque command value T*, the rotational speed difference between the outer housing 20 and the inner shaft 23, or the estimated temperature of the lubricant. In this case, it is desirable to increase the magnitudes (absolute values) of the first correction value C1 and the second correction value C2 as the torque command value T* is larger, as the rotational speed difference between the outer housing 20 and the inner shaft 23 is larger, or as the estimated temperature of the lubricant is lower.​​​

[0101] Effect of the embodiment

[0102] According to the embodiment of the present invention described above, the difference between the torque command value T* during rising and falling and the transmitted torque of the main clutch 3 can be reduced, and the accuracy of the transmitted torque of the main clutch 3 can be enhanced.

[0103] Supplementary description

[0104] The present invention has been described based on the embodiments. The embodiments do not limit the present invention according to the claims. It should be noted that all combinations of the features described in the embodiments are not necessarily means for solving the problems of the present invention.

[0105] The present invention can be appropriately modified without departing from the spirit of the present invention. For example, the configuration of the four-wheel drive vehicle 100 is not limited to Figure 1 the configuration illustrated therein, and the present invention can be applied to four-wheel drive vehicles and other vehicles having various configurations.

Claims

1. A driving force transmission device (1), characterized in that it includes: an input rotating member (20) and an output rotating member (23), the input rotating member (20) and the output rotating member (23) being configured to rotate relative to each other coaxially; a multi-plate clutch (3), the multi-plate clutch including a plurality of clutch discs, the frictional sliding between the plurality of clutch discs being lubricated by a lubricant; a pressing mechanism (6), the pressing mechanism being configured to press the multi-plate clutch (3) with a pressing force depending on the supplied current; and a control device (7), the control device including a current supply circuit, the current supply circuit being configured to supply the current to the pressing mechanism (6), wherein the output rotating member (23) is configured such that the driving force of the vehicle is transmitted from the input rotating member (20) to the output rotating member (23) by the multi-plate clutch (3); the control device (7) is configured to calculate a torque command value based on the state of the vehicle, the torque command value being the driving force that needs to be transmitted by the multi-plate clutch (3); the control device (7) is configured to calculate a current command value corresponding to the torque command value; configured to correct the current command value; and configured to control the current supply circuit such that the current depending on the current command value corrected by the control device (7) is supplied to the pressing mechanism (6), and the control device (7) is configured to correct the current command value so as to increase or decrease the current command value by a correction amount depending on the change rate of the torque command value.

2. The driving force transmission device (1) according to claim 1, characterized in that: the control device (7) is configured to increase the current command value when the change rate of the torque command value is higher than a reference change rate when the torque command value rises, and the control device (7) is configured to decrease the current command value when the change rate of the torque command value is lower than the reference change rate when the torque command value rises.

3. The driving force transmission device (1) according to claim 1, characterized in that: the control device (7) is configured to decrease the current command value when the change rate of the torque command value is higher than a reference change rate when the torque command value falls; and the control device (7) is configured to increase the current command value when the change rate of the torque command value is lower than the reference change rate when the torque command value falls.

4. The driving force transmission device (1) according to claim 2 or 3, characterized in that, the control device (7) is configured to increase the correction amount as the deviation between the change rate of the torque command value and the reference change rate becomes larger.

5. The driving force transmission device (1) according to any one of claims 1 to 3, characterized in that: the control device (7) is configured to correct the current command value by referring to relationship information indicating the relationship between the change rate of the torque command value and the correction amount; and The correction amount when the torque command value shown in the relationship information rises and the correction amount when the torque command value shown in the relationship information falls are values that differ only in sign.

6. A control method for a driving force transmission device (1), the driving force transmission device (1) comprising: an input rotating member (20) and an output rotating member (23), the input rotating member (20) and the output rotating member (23) being configured to rotate relative to each other coaxially; a multi-plate clutch (3) including a plurality of clutch discs, the frictional sliding between the plurality of clutch discs being lubricated by a lubricant; a pressing mechanism (6) configured to press the multi-plate clutch (3) with a pressing force depending on a supplied current; and a control device (7), the driving force transmission device (1) being configured to transmit a driving force of a vehicle from the input rotating member (20) to the output rotating member (23) through the multi-plate clutch (3), the control method being characterized by comprising: the control device (7) calculating a torque command value based on a state of the vehicle, the torque command value being a driving force that needs to be transmitted by the multi-plate clutch (3); the control device (7) calculating a current command value corresponding to the torque command value; the control device (7) correcting the current command value so as to increase or decrease the current command value by a correction amount depending on a change rate of the torque command value; and the control device (7) supplying the current depending on the corrected current command value to the pressing mechanism (6).

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