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

Abstract

Provided are a driving force transmission device and a control method for the driving force transmission device, the driving force transmission device (1) comprising: an input rotating member (20); an output rotating member (23); a multi-plate clutch (3); a squeezing mechanism (6); and a control device (7), the control device (7) comprising a current supply circuit (9). The control device (7) is configured to calculate a torque command value, calculate a current command value, correct the current command value, and control the current supply circuit (9) so that a current depending on the current command value is supplied to the squeezing mechanism (6). The control device (7) is configured to correct the current command value by a correction amount in a constant torque state after the torque command value changes, the constant torque state being a state in which a rate of change of the torque command value is within a predetermined range, the correction amount depending on the duration of the constant torque state.

Description

Technical Field

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

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

[0003] In JP 2007-064251A, based on the results of operational tests after assembling a driving force transmission device that transmits output torque corresponding to input current from a vehicle's drive source to auxiliary drive wheels, an IT characteristic, representing the characteristics of input current and output torque, is stored in a storage unit. Current is then controlled based on the IT characteristic stored in the storage unit. This reduces variations in the characteristics of the individual driving force transmission devices and improves the accuracy of output torque.

[0004] In JP 2009-014134A, the start-up time is determined when a command current value calculated based on command torque changes from a value equal to or lower than a first predetermined current value to a value higher than the first predetermined current value that releases frictional engagement of the clutch plates. If the command current value at the start-up time is equal to or lower than a second predetermined current value, inrush current supply control is performed, adding a correction value to the command current value so that the command current value reaches the second predetermined current value. This second predetermined current value is a current value that allows frictional engagement of the clutch plates at a predetermined response speed or higher (a speed that does not cause response lag during use). Summary of the Invention

[0005] For example, in a driving force transmission device including a multi-plate clutch in which frictional sliding between clutch plates is lubricated by lubricant and a pressing mechanism that presses the multi-plate clutch with a pressing force that depends on the supplied current, when the command torque becomes constant after increasing from zero to a predetermined value, the actual output torque (driving force) sometimes increases over time, even when the pressing force of the pressing mechanism is constant. The inventors have diligently studied the causes of and countermeasures for this torque increase and have completed the present invention.

[0006] That is, the present invention makes it possible to improve the accuracy of the transmission torque of the multi-plate clutch when the torque command value becomes constant after being varied.

[0007] The 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, both of which can rotate coaxially relative to each other; a multi-plate clutch, which includes a plurality of clutch plates, and the frictional sliding between the plurality of clutch plates is lubricated by a lubricant; a pressing mechanism, which is configured to press the multi-plate clutch with a pressing force depending on the current supplied; and a control device, which includes a current supply circuit configured to supply current to the pressing mechanism. The output rotating member is configured so that the driving force of the vehicle is transmitted from the input rotating member to the output rotating member through the multi-plate clutch. The control device is configured to calculate a torque command value based on the vehicle state, the torque command value being the driving force to be transmitted by the multi-plate clutch; 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 so 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 by a correction amount depending on a duration of the constant torque state in a constant torque state in which a rate of change of the torque command value is within a predetermined range after the torque command value changes.

[0008] With the above configuration, it is possible to improve the accuracy with which the multi-plate clutch transmits torque when the torque command value becomes constant after being varied.

[0009] A 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, both of which can coaxially rotate relative to each other; a multi-plate clutch, which includes a plurality of clutch plates, and the frictional sliding between the plurality of clutch plates is lubricated by a lubricant; a pressing mechanism, which presses the multi-plate clutch with a pressing force that depends on the current supplied; and a control device. The driving force transmission device transmits the driving force of the vehicle from the input rotating member to the output rotating member through the multi-plate clutch. The control method includes: the control device calculates a torque command value based on the vehicle state, the torque command value being the driving force to be transmitted by the multi-plate clutch; the control device calculates a current command value corresponding to the torque command value; the control device corrects the current command value by a correction amount in a constant torque state after the torque command value changes, the constant torque state being a state in which the rate of change of the torque command value is within a predetermined range, the correction amount depending on the duration of the constant torque state; and the control device supplies a current depending on the corrected current command value to the pressing mechanism.

[0010] With the above configuration, it is possible to improve the accuracy with which the multi-plate clutch transmits torque when the torque command value becomes constant after being varied. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Features, advantages, and technical and industrial significance of illustrative embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent 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 drive 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 coupling;

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

[0015] Figure 4 is a diagram showing an example of IT characteristic mapping;

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

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

[0018] Figure 6B It shows Figure 6A an enlarged view of a portion of a diagram;

[0019] Figure 7 is a flowchart showing a procedure example of processing executed by the control unit;

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

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

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

[0023] Figure 11Ais a diagram showing an example of temporal changes in the transmission torque and the current command value of the main clutch during a period when the torque command value rises, and shows a case where no correction is performed; and

[0024] Figure 11B is a diagram showing an example of temporal changes in the transmission torque and the current command value of the main clutch during the period when the torque command value rises, and shows a case in which correction is performed. DETAILED DESCRIPTION

[0025] Example

[0026] Will refer to Figures 1 to 11B The embodiments of the present invention are described below. The embodiments described below are shown as preferred specific examples for carrying out the present invention. Various technical matters that are technically preferred are specifically exemplified, but the technical scope of the present invention is not limited to this specific mode.

[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] like Figure 1 As shown in FIG, a four-wheel drive vehicle 100 includes an engine 11 as a driving source, a transmission 12 that changes the speed of the output of the engine 11, a left front wheel 181 and a right front wheel 182 as main drive wheels, to which the driving force of the engine 11, which has been changed in speed by the transmission 12, is constantly transmitted, and a left rear wheel 191 and a right rear wheel 192 as auxiliary drive wheels, to which the driving force of the engine 11 is transmitted according to 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 and the right front wheel 182 and 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 transmitted only 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 may be used as a driving source, and a so-called hybrid system in which an engine and an electric motor are combined may be used as a driving source.

[0029] The four-wheel drive vehicle 100 includes: a front differential 13; a propulsion shaft 14; a rear differential 15; a pinion shaft 150, which transmits 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, which transmits driving force from the propulsion shaft 14 to the pinion shaft 150.

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

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

[0032] The driving force of the engine 11 is transmitted to the left front wheel 181 and the right front wheel 182 via the transmission 12, the front differential 13, and the left and right drive shafts 161 and 162 on the front wheel side. The front differential 13 includes: a pair of side gears 131 respectively coupled to the left and right drive shafts 161 and 162 on the front wheel side so as to be non-rotatable relative to each other; a pair of pinion gears 132 engaged with the side gears 131 so that the gear axes of the pinion gears 132 are orthogonal to the gear axes of the side gears 131; a pinion shaft 133 supporting the pinion gears 132; and a front differential case 134 accommodating the side gears 131, the pinion gears 132, and the pinion shaft 133.

[0033] A ring gear 135 is fixed to a front differential case 134 and engages with a pinion gear 141 provided at the vehicle-front end portion of the propeller shaft 14. The vehicle-rear end portion of the propeller shaft 14 is coupled to the housing 20 of the torque coupling 2. The torque coupling 2 includes an inner shaft 23 arranged to be relatively rotatable through the housing 20, and a pinion shaft 150 coupled to the inner shaft 23 to prevent relative rotation. Details of the torque coupling 2 will be described later.

[0034] The rear differential 15 includes a pair of side gears 151, which are respectively coupled to a left drive shaft 171 and a right drive shaft 172 on the rear wheel side so as not to rotate relative to each other; a pair of pinion gears 152, which engage with the side gears 151 so that the gear axes of the pinion gears 152 are orthogonal to the gear axes of the side gears 151; a pinion shaft 153, which supports the pinion gears 152; a rear differential case 154, which houses the side gears 151, the pinion gears 152, and the pinion shaft 153; and a ring gear fixed to the rear differential case 154 and engaged 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 via the drive shafts 171 and 172.

[0035] Structure of the driving force transmission device

[0036] Figure 2 : is a cross-sectional view showing a configuration example of the torque coupling 2. Figure 2 , the upper side of the rotation axis O shows the actuated state (torque transmitting state) of the torque coupling 2, and the lower side shows the non-actuated state (torque non-transmitting state) of the torque coupling 2. Hereinafter, the direction parallel to the rotation axis O is referred to as the axial direction.

[0037] The torque coupling 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 coaxially relatively rotatable by the housing 20 and serves as an output rotating member; a main clutch 3, which is arranged between the housing 20 and the inner shaft 23 and serves as a multi-plate clutch; a cam mechanism 4, which generates a thrust for pressing the main clutch 3; and an electromagnetic clutch mechanism 5, which receives a supply of current 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 that depends on the current supplied from the control device 7.

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

[0039] The front housing 21 integrally includes a cylindrical portion 21a and a bottom portion 21b having a cylindrical shape, and has a bottomed cylindrical shape. Female threads 21c are formed on the inner surface of the open end portion of the cylindrical portion 21a. The propulsion shaft 14 (see Figure 1 ) is coupled to the bottom portion 21b of the front housing 21, for example, through a cross joint. In addition, the front housing 21 has a plurality of external 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 made of a magnetic material such as iron; a second annular member 222 made of a non-magnetic material such as austenitic stainless steel and integrally connected to the inner circumference of the first annular member 221 by welding or the like; and a third annular member 223 made of a magnetic material such as iron and integrally connected to the inner circumference of the second annular member 222 by welding or the like. An annular accommodating space 22a for accommodating the electromagnetic coil 53 is formed between the first annular member 221 and the third annular member 223. Furthermore, a male thread 221a is formed on the outer circumferential surface of the first annular member 221, which is screwed into the female thread 21c of the front housing 21.

[0041] The inner shaft 23 is formed into a cylindrical shape and is supported on the inner periphery of the housing 20 through a ball bearing 24 and a needle bearing 25. The inner shaft 23 includes a plurality of internal 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 portion of the inner shaft 23, in which one end portion of the pinion shaft 150 (see Figure 1 ) are fitted so that relative rotation is not possible.

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

[0043] The main inner clutch plates 32 include a plurality of engagement protrusions 321 at the end portions of their inner circumferences. These engagement protrusions 321 engage with the internal spline protrusions 231 of the inner shaft 23. When the engagement protrusions 321 engage with the internal spline protrusions 231, relative rotation between the main inner clutch plates 32 and the inner shaft 23 is restricted, while the main inner clutch plates 32 are able to move axially relative to the inner shaft 23. Each of the main inner clutch plates 32 includes a disc-shaped base material 331 composed of metal and a porous friction material 332 bonded to both side surfaces of the base material 331. A plurality of oil holes 333 are formed on the inner side of the portion of the base material 331 where the friction material 332 is bonded, through which lubricant flows. In each of the main inner clutch plates 3, an oil groove (not shown) is formed on the surface that contacts the friction material 332, through which lubricant flows.

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

[0045] The main cam 42 integrally comprises an annular plate-shaped pressing portion 421, which contacts the main inner clutch plate 32 at one end of the main clutch 3 and presses the main clutch 3; and a cam portion 422, which is located 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 axially through the pressing portion 421. A splined engagement portion 421a formed at the end portion of the inner circumference of the pressing portion 421 engages with the internal splined protrusion 231 of the inner shaft 23, restricting relative rotation of the main cam 42 and the inner shaft 23. Furthermore, the main cam 42 is biased axially away from the main clutch 3 by a disc spring 44 disposed between the main cam 42 and the stepped surface 23a formed on the inner shaft 23.

[0046] The leading cam 41 includes a splined protrusion 411 at the end portion of its outer periphery. This splined protrusion 411 receives rotational force from the electromagnetic clutch mechanism 5 relative to the main cam 42. A thrust needle roller bearing 45 is arranged between the leading 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 leading cam 41 and the cam portion 422 of the main cam 42. The cam roller 43 is arranged between the cam groove 41a of the leading cam 41 and the cam groove 422a of the main cam 42.

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

[0048] The electromagnetic clutch mechanism 5 is constructed to include: an armature 50; a plurality of leading outer clutch plates 51; a plurality of leading inner clutch plates 52; an electromagnetic coil 53; and an annular yoke 54, which is made of a magnetic material and holds the electromagnetic coil 53. The electromagnetic coil 53 is housed in the housing 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 via the ball bearing 26.

[0049] The electric current from the control device 7 is supplied as an excitation current to the electromagnetic coil 53 through the cable 531. By energizing the electromagnetic coil 53, a magnetic flux having a magnetic flux density depending on the magnitude of the excitation current is generated in a magnetic path G including the yoke 54, the first and third annular members 221 and 223 of the rear housing 22, the leading outer clutch plate 51, the leading inner clutch plate 52, and the armature 50.

[0050] Leading outer clutch plates 51 and leading inner clutch plates 52 are alternately arranged in the axial direction between the armature 50 and the rear housing 22. Each of the leading outer clutch plates 51 and leading inner clutch plates 52 is a disc member composed of a magnetic material such as iron. A plurality of arcuate slits are formed in the leading outer clutch plates 51 and leading inner clutch plates 52 at positions that allow the arcuate slits to be aligned with the second annular member 222 of the rear housing 22 in the axial direction, thereby preventing short-circuiting of magnetic flux.

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

[0052] The armature 50 is an annular member made of a magnetic material such as iron, and has a plurality of engaging protrusions 501 formed on its outer periphery. The engaging protrusions 501 engage with the external spline protrusions 211 of the front housing 21. Thus, the armature 50 can move in the axial direction relative to the front housing 21, while being restricted from rotating relative to the front housing 21.

[0053] The electromagnetic clutch mechanism 5 uses the magnetic force generated by energizing the electromagnetic coil 53 to attract the armature 50 to the yoke 54 side, and the movement of the armature 50 generates friction between the leading outer clutch plate 51 and the leading inner clutch plate 52. The leading outer clutch plate 51 and the leading inner clutch plate 52 are in frictional contact while being pushed to the rear housing 22 side by the armature 50.

[0054] In the torque coupling 2, the electromagnetic clutch mechanism 5 is actuated, and a rotational force dependent on the current supplied to the electromagnetic coil 53 is transmitted to the leading cam 41, causing the leading cam 41 to rotate relative to the main cam 42, and the cam roller 43 to roll on the cam grooves 41a and 422a. The rolling of the cam roller 43 then generates a thrust for pressing the main clutch 3 toward the main cam 42, and generates friction between the main outer clutch plates 31 and the main inner clutch plates 32.

[0055] Control device structure

[0056] like Figure 1 As shown in FIG, the control device 7 includes: a control unit 70 including a CPU (arithmetic processing unit); a storage unit 8 storing programs to be executed by the CPU of the control unit 70, and a current supply circuit 9 that supplies current to the electromagnetic coil 53 of the torque coupling 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 that calculates a torque command value as the driving force required to be transmitted by the main clutch 3 based on the vehicle state; a current command value calculation unit 72 that calculates a current command value corresponding to the torque command value; a current correction unit 73 that corrects the current command value; and a current control unit 74 that 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 pressing 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 may 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 configuration of the control device 7. In addition to the program 81 executed by the CPU of the control unit 70, the storage unit 8 stores a torque command value map 82, an IT characteristic map 83, a first correction value map 84, and a second correction value map 85 in a nonvolatile 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 front and rear wheel differential speeds (the difference between the average speed of the left front wheel 181 and the right front wheel 182 and the average speed of the left rear wheel 191 and the right rear wheel 192) and the first command torque component; the relationship between the accelerator pedal depression amount, 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 IT characteristic map 83 and calculates the current command value I* corresponding to the torque command value T*. In the IT characteristic map 83, the results of the operation test performed after assembling the torque coupling 2 when producing the driving force 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, and the current to be supplied to the electromagnetic coil 53 is changed from zero to maximum at a constant time change rate (current change amount per unit time). In the following, the time for the current to be supplied to the electromagnetic coil 53 to change from zero to maximum during the operation test is referred to as the IT characteristic measurement time. For example, the IT characteristic measurement time is 5 seconds. In addition, in the following, the change rate refers to the change amount per unit time, and the current change rate during the operation test is referred to as the reference change rate.

[0061] Figure 4 is a diagram showing an example of the IT characteristic map 83. When the driving force transmission device 1 is produced, the IT characteristic map 83 is stored in the storage unit 8. In the IT characteristic map 83, the Figure 4 The current command value calculation unit 72 performs linear interpolation between the coordinate points and calculates the current command value I* corresponding to the torque command value T*. max Indicates the maximum value of the current of the electromagnetic coil 53 during the operation test. For example, when the torque command value T* is Figure 4 When T1 is on the vertical axis of the graph, the current command value calculation unit 72 calculates I1 as the current command value I*, and I1 is a value corresponding to T1 on the horizontal axis.

[0062] The current correction unit 73 includes a determination unit 731 that determines whether and how the current command value I* should be corrected based on the temporal 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 a corrected current command value I** by adding the first correction value C1 and the second correction value C2 to the current command value I*. Details of the processing performed by the current correction unit 73 will be described below.

[0063] The current control unit 74 includes a subtractor 741, an F / B (feedback) control unit 742, and a PWM signal output unit 743. The subtractor 741 receives inputs of the corrected current command value I** and the actual current value I detected by the current sensor 75. The current sensor 75 detects the current supplied to the electromagnetic coil 53. The subtractor 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] F / B control unit 742 calculates a feedback control variable based on the input current difference ΔI and outputs it to PWM signal output unit 743. F / B control unit 742 calculates the total of two values as the feedback control variable: 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. PWM signal output unit 743 performs PWM calculations based on the feedback control variable and outputs a PWM signal having a duty ratio based on the feedback control variable to current supply circuit 9.

[0065] In the de-energized state, where no current is supplied to the electromagnetic coil 53 from the current supply circuit 9, the main cam 42 of the cam mechanism 4 is biased away from the main clutch 3 by the biasing force of the disc spring 44, and lubricant is interposed between the main outer clutch plates 31 and the main inner clutch plates 32. When the electromagnetic coil 53 is energized in this state, the main clutch 3 is pressed toward the main cam 42. The lubricant between the main outer clutch plates 31 and the main inner clutch plates 32 is then gradually discharged, and the main outer clutch plates 31 and the main inner clutch plates 32 come into contact with each other, generating friction.

[0066] The current command value calculation unit 72 calculates the current command value I* by referencing the IT characteristic map 83, which is set based on the results when the current supplied to the electromagnetic coil 53 changes from zero to maximum during the IT characteristic measurement period. Therefore, when the rate of change of the current when the current supplied to the electromagnetic coil 53 increases is higher than a reference rate of change, a larger amount of lubricant remains between the main outer clutch plates 31 and the main inner clutch plates 32 than at each current value during the operational test, causing the torque to be transmitted by the main clutch 3 to be lower than the torque during the operational test. Conversely, when the rate of change of the current when the current supplied to the electromagnetic coil 53 increases is lower than the reference rate of change, a smaller amount of lubricant remains between the main outer clutch plates 31 and the main inner clutch plates 32 than at each current value during the operational test, causing the torque to be transmitted by the main clutch 3 to be higher than the torque during the operational test.

[0067] Furthermore, when the rate of change of the current when the current to be supplied to the electromagnetic coil 53 is reduced is higher than the reference rate of change, lubricant is less likely to flow into the gap between the main outer clutch plates 31 and the main inner clutch plates 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 the torque during the operation test. Conversely, when the rate of change of the current when the current to be supplied to the electromagnetic coil 53 is reduced is lower than the reference rate of change, a larger amount of lubricant flows into the gap between the main outer clutch plates 31 and the main inner clutch plates 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 the torque during the operation test.

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

[0069] like Figure 5As shown in the graph, the shorter the sweep time, the later the lubricant is discharged from the main clutch 3 when the current increases, and the lower the actual transmitted torque. In this manner, when the sweep time is shorter than the IT characteristic measurement time, that is, when the current to be supplied to the electromagnetic coil 53 is higher than the reference change rate, the transmitted torque of the main clutch 3 is lower than the characteristic shown in the IT characteristic map 83 when the current increases, and the transmitted torque of the main clutch 3 is higher than the characteristic shown in the IT characteristic map 83 when the current decreases. Furthermore, when the sweep time is longer than the IT characteristic measurement time, that is, when the current to be supplied to the electromagnetic coil 53 is lower than the reference change rate, the transmitted torque of the main clutch 3 is higher than the characteristic shown in the IT characteristic map 83 when the current increases, and the transmitted torque of the main clutch 3 is lower than the characteristic shown in the IT characteristic map 83 when the current decreases.

[0070] The inventors have discovered that, after the torque command value T* becomes constant, the transfer torque of the main clutch 3 changes smoothly when the torque command value T* becomes constant after the change, even when the current to be 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 transfer torque of the main clutch 3 gradually increases even when the current to be supplied to the electromagnetic coil 53 is constant. Furthermore, when the torque command value T* gradually decreases and becomes a constant value, the transfer torque of the main clutch 3 gradually decreases even when the current to be 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 from zero in a stepwise manner. Figure 6B It shows Figure 6A An enlarged view of a portion of FIG.

[0072] like Figure 6A and Figure 6B As shown in , when the current command value T* increases from zero in a step-by-step manner, the transmission torque of the main clutch 3 rises rapidly in the early state, and then, when the lubricant between the main outer clutch plate 31 and the main inner clutch plate 32 is discharged, the transmission torque of the main clutch 3 rises steadily for a few seconds.

[0073] The deviation between the torque when the current increases and the torque when the current decreases varies depending on the rate of change of the current (e.g. Figure 5The phenomenon that the transmission torque of the main clutch 3 smoothly changes with the amount of lubricant interposed between the main outer clutch plates 31 and the main inner clutch plates 32 (as shown in FIG. 6 ) causes an error in the actual transmission torque relative to the torque command value T* and is therefore undesirable. In this embodiment, the occurrence of transmission torque errors caused by this phenomenon is limited by the following control method.

[0074] Figure 7 1 is a flowchart showing a procedure example of processing performed by the control unit 70 for calculating the correction current command value I**. The control unit 70 executes each process in the flowchart in a predetermined calculation cycle (for example, 5 ms).

[0075] exist Figure 7 In the process shown in the flowchart, the control unit 70 refers to the torque command value map 82 based on the vehicle state and calculates the torque command value T* (step S1). Then, the control unit 70 refers to the IT 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 performed by the torque command value calculation unit 71, and the process of step S2 is performed by the current command value calculation unit 72.

[0076] Next, the control unit 70 calculates the torque command value change ΔT, which 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). Next, the control unit 70 determines whether the absolute value of the torque command value change ΔT is less than a predetermined threshold value A (step S4). The threshold value A is such a small value that when the torque command value T* is substantially constant, the determination result in step S4 is affirmative (yes). Hereinafter, the state in which the determination result in step S4 is affirmative (yes), that is, the state in which the rate of change of the torque command value T* is within a predetermined range, is referred to as a constant torque state.

[0077] If the determination result in step S4 is affirmative (yes), the control unit 70 calculates the counter threshold value B used in step S7 described below based on the rate of change of the torque command value T* before the determination result in step S4 becomes affirmative (yes) (step S5). Next, the control unit 70 counts the counter C used to measure time (step S6). If the determination result in step S4 is continuously affirmative (yes), the processing of step S5 may be performed only in the first calculation cycle and may be skipped in subsequent calculation cycles.

[0078] Next, 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). If the counter C is equal to or greater than the counter threshold B as a result of the determination (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 estimated from the counter C (step S8). The detection time T corresponds to the duration of the constant torque state and can be estimated by multiplying the counter value of the counter C by the calculation cycle length. Furthermore, 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 manner, in the constant torque state after the torque command value T* is changed, 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 processing in this calculation cycle without performing the processing of steps S8 and S9.

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

[0081] Next, the control unit 70 calculates a second correction value C2 by referring to the second correction value map 85 based on the rate of change of the torque command value T* calculated in step S11 (step S12). The control unit 70 then calculates a 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 step S10 are performed by the determination unit 731 of the current correction unit 73. The process of step S8 is performed by the first correction value calculation unit 732 of the current correction unit 73. The process of step S12 is performed by the second correction value calculation unit 733 of the current correction unit 73. The processes of steps S9 and S13 are performed by the adder 734 of the current correction unit 73.

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

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

[0085] Ideally, counter threshold B is set so that the correction effect of first correction value C1 begins to appear when the transmission torque of main clutch 3 substantially matches torque command value T*. For example, it is desirable to derive the relationship between the rate of change of torque command value T* and ideal counter threshold B from the results of experiments conducted while varying the rate of change of torque command value T*.

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

[0087] For example, the counter threshold value B can be varied depending on the estimated lubricant temperature or the rotational speed difference between the housing 20 and the inner shaft 23. The estimated lubricant temperature can be estimated based on, for example, the external temperature and the load state of the torque coupling 2, and the rotational speed difference between the housing 20 and the inner shaft 23 can be evaluated based on the rotational speed difference between the front and rear wheels. The lower the lubricant temperature, the higher the lubricant viscosity. Therefore, the higher the estimated lubricant temperature, the more desirably the counter threshold value B is reduced. Furthermore, the lower the rotational speed difference between the housing 20 and the inner shaft 23, the smoother the lubricant tends to be discharged. Therefore, the lower the rotational speed difference between the housing 20 and the inner shaft 23, the more desirably the counter threshold value B is reduced.

[0088] Figure 8The left, center, and right graphs in are graphs showing examples of temporal changes in the transmission torque and the current command value I* of the main clutch 3 when the torque command value T* becomes constant after the torque command value T* increases at different change rates. Figure 8 The left graph is when the rate of change of the torque command value T* is low. Figure 8 The center graph in FIG is a graph when the rate of change of the torque command value T* is at a medium level. Figure 8 The right graph in is a graph when the torque command value T* is increased in a step-by-step manner. Figure 8 In the center graph in FIG, the rate of change of the current command value I* about 1.5 seconds before the torque command value T* becomes constant is equivalent to the rate of change of the current supplied to the electromagnetic coil 53 during the operation test after assembling the torque coupling 2.

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

[0090] like Figure 8 As shown in the right graph in FIG, when the rate of change of the torque command value T* is high, the transmission torque of the main clutch 3 cannot keep up with the increase in the torque command value T*, and when the torque command value T* becomes constant, the transmission 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 diagram showing an example of the first correction value map 84 . Figure 9 : shows the mapping information that the control unit 70 refers to in the constant torque state after the torque command value T* is increased. Figure 9 As shown in , the following characteristics are stored in the first correction value map 84: the correction amount (absolute value) gradually increases until the detection time T becomes t1, and the correction amount is constant after the detection time T becomes t1. Figure 9 As shown in , the first correction value C1 in the constant torque state after the torque command value T* increases is a negative value, and therefore, 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] The mapping information referred to by the control unit 70 in the constant torque state after the torque command value T* is reduced is, for example, the following mapping information: Figure 9The signs of the correction values in the mapping information shown in Figure 9 are opposite. The absolute value of the correction amount may be changed, and the time (t1 in

[0093] when the correction amount becomes constant) may be changed. The first correction value C1 in this case is a positive value, and thus, the corrected current command value I** becomes greater than the current command value I* because the first correction value C1 is added to the current command value I* in step S9.

[0094] Figure 10 is a diagram 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 change amount ΔT of the torque command value in a plurality of past calculation cycles may be used, or the change amount ΔT of the torque command value may be used, where ΔT 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.

[0095] In Figure 10 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* increases, the current correction unit 73 adds the second correction value C2 to the current command value I*, and thereby sets 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 to increase the current command value. In addition, 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* increases, the current correction unit 73 adds the second correction value C2 with a negative value to the current command value I*, and thereby sets the corrected current value I** to a value less than the current command value I*. That is, the current correction unit 73 performs correction to decrease the current command value.

[0096] like Figure 10 As 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. In addition, when the rate of change of the torque command value T* is lower than the reference rate of change, the greater the deviation (difference) between the rate of change of the torque command value T* and the reference rate of change is, the greater the magnitude (absolute value) of the second correction value C2. Figure 10 That is, the amount of change in the absolute value of the second correction value C2 is greater relative to the amount of change in the magnitude of the torque command value T*.

[0097] Furthermore, when the torque command value T* decreases, the current correction unit 73 uses Figure 10 The current command value I* is corrected by reversing the sign of the second correction value C2 on the vertical axis shown in FIG. 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.

[0098] In this manner, when the amount of change in torque command value T* exceeds threshold value A, which is used when torque command value T* increases, current correction unit 73 performs correction to increase current command value I* by a correction amount that depends on the rate of change of torque command value T*. Furthermore, when the amount of change in torque command value T* exceeds threshold value A, which is used when torque command value T* decreases, current correction unit 73 performs correction to decrease current command value I* by a correction amount that depends on the rate of change of torque command value T*. Furthermore, current correction unit 73 refers to second correction value map 85 and increases the correction amount of current command value I* as the rate of change of torque command value T* increases.

[0099] Figure 11A and Figure 11B Each of them is a graph showing an example of temporal changes in the transmission torque of the main clutch 3 and the current command value I* during the period when the torque command value T* rises. Figure 11A shows the case where no correction is performed with the second correction value C2, and Figure 11B FIG. 4 shows a case where correction is performed using the second correction value C2. Figure 11A As shown in FIG, when the rate of change of the torque command value T* is low, the transmission torque of the main clutch 3 is higher than the torque command value T*, but as shown in FIG. Figure 11B As shown in FIG, the difference between the transmission torque of the main clutch 3 and the torque command value T* is reduced by the correction of the second correction value C2.

[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 may be used without being changed, or may be changed based on, for example, the magnitude of the torque command value T*, the rotational speed difference between the housing 20 and the inner shaft 23, or the estimated temperature of the lubricant. In this case, the greater the torque command value T*, the greater the rotational speed difference between the housing 20 and the inner shaft 23, or the lower the estimated temperature of the lubricant, the more it is desirable to increase the magnitude (absolute value) of the first correction value C1 and the second correction value C2.

[0101] Effects of the embodiment

[0102] According to the embodiment of the present invention described above, it is possible to improve the accuracy of the torque transmitted by the main clutch 3 when the torque command value T* becomes constant after changing.

[0103] Supplementary Notes

[0104] The present invention has been described above based on the embodiment. The embodiment does not limit the present invention according to the claims. It should be noted that all combinations of characteristics described in the embodiment are not essential for the means of solving the problem of the present invention.

[0105] Without departing from the spirit of the present invention, the present invention can be implemented while being appropriately modified. For example, the structure of the four-wheel drive vehicle 100 is not limited to Figure 1 The present invention is based on the configuration illustrated in FIG, and 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 include: An input rotating member (20) and an output rotating member (23), wherein the input rotating member (20) and the output rotating member (23) are capable of coaxially rotating relative to each other; A multi-plate clutch (3), the multi-plate clutch (3) comprising a plurality of clutch plates, frictionally sliding between the clutch plates and 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; as well as A control device (7), comprising a current supply circuit (9), the current supply circuit (9) being configured to supply the current to the squeezing 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) through the multi-plate clutch (3); The control device (7) is configured to calculate a torque command value based on a vehicle state, the torque command value being a driving force to be transmitted by the multi-plate clutch (3); to calculate a current command value corresponding to the torque command value; to correct the current command value; and to control the current supply circuit (9) so that the current depending on the current command value corrected by the control device (7) is supplied to the squeezing mechanism (6); and The control device (7) is configured to correct the current command value by a correction amount in a constant torque state after the torque command value changes, wherein the constant torque state is a state in which the rate of change of the torque command value is within a predetermined range, and the correction amount depends on the duration of the constant torque state.

2. The driving force transmission device (1) according to claim 1, characterized in that The control device (7) is configured to correct the current command value in the constant torque state after the torque command value increases so as to gradually reduce the current command value by the correction amount depending on the duration of the constant torque state.

3. The driving force transmission device (1) according to claim 1 or 2, characterized in that: The control device (7) is configured to correct the current command value in the constant torque state after the torque command value is reduced so as to gradually increase the current command value by the correction amount depending on the duration of the constant torque state.

4. The driving force transmission device (1) according to claim 1 or 2, characterized in that: The control device (7) is configured to start correction of the current command value after a predetermined time has elapsed from the start of the constant torque state.

5. The driving force transmission device (1) according to claim 4, characterized in that The control device (7) is configured to set the predetermined time depending on a rate of change of the torque command value before the constant torque state.

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 coaxially rotatable relative to each other; a multi-plate clutch (3), the multi-plate clutch (3) including a plurality of clutch plates, frictionally sliding between the clutch plates being lubricated by a lubricant; a pressing mechanism (6), the pressing mechanism (6) pressing 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) transmitting the driving force of the vehicle from the input rotating member (20) to the output rotating member (23) via the multi-plate clutch (3), The control method is characterized by comprising: The control device (7) calculates a torque command value based on a vehicle state, wherein the torque command value is a driving force to be transmitted by the multi-plate clutch (3); The control device (7) calculates a current command value corresponding to the torque command value; The control device (7) corrects the current command value by a correction amount in a constant torque state after the torque command value changes, the constant torque state being a state in which the rate of change of the torque command value is within a predetermined range, the correction amount depending on the duration of the constant torque state; and The control device (7) supplies the current depending on the corrected current command value to the pressing mechanism (6).

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