Power transmission control device

Abstract

To provide a driving force transmission control device capable of improving accuracy of transmission torque.SOLUTION: A driving force transmission control device 2 includes: a driving force transmission device 2A for transmitting driving force of torque according to electric current supplied to an electromagnetic coil 63; and a control device 2B for controlling the driving force transmission device 2A by the electric current supplied to the electromagnetic coil 63. The control device 2B includes: a storage portion 8 for storing related information 82 indicating a relation between transmission torque and magnitude of electric current in keeping the electric current supplied to the electromagnetic coil 63 constant; torque command value calculation means 71 for calculating a torque comment value; and electric current command value calculation means 72 for calculating a value of the electric current to be supplied to the electromagnetic coil 63 according to the torque command value as an electric current command value. The electric current command value calculation means 72 makes the electric current command value gradually approach a value obtained by referring to the related information 82, in shifting from a fluctuation state in which variation per time of the torque command value is a prescribed value or more to a stationary state of less than the prescribed value.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a driving force transmission control device.

Background Art

[0002] Conventionally, in a four-wheel drive vehicle equipped with a main drive wheel and an auxiliary drive wheel and capable of switching between a two-wheel drive state in which the driving force of a drive source is transmitted only to the main drive wheel and a four-wheel drive state in which the driving force of the drive source is transmitted to the main drive wheel and the auxiliary drive wheel, a driving force transmission device capable of adjusting the driving force transmitted to the auxiliary drive wheel is mounted. The applicant of the present application has proposed the one described in Patent Document 1 as a driving force transmission device of this kind.

[0003] The driving force transmission device described in Patent Document 1 includes a main clutch having a plurality of clutch plates lubricated by lubricating oil for frictional sliding, a cam mechanism for generating a thrust force for pressing the main clutch, an electromagnetic clutch mechanism for operating the cam mechanism, and a control device. The electromagnetic clutch mechanism has an electromagnetic coil, an armature, a plurality of pilot outer clutch plates and pilot inner clutch plates, and a yoke for holding the electromagnetic coil. The control device has a torque command value calculation unit that calculates a torque command value, which is the driving force to be transmitted by the main clutch, based on the vehicle state, a current command value calculation unit that calculates a current command value corresponding to the torque command value, a current correction unit that corrects the current command value, and a current control unit that controls a current supply circuit so that a current corresponding to the current command value corrected by the current correction unit is supplied to the electromagnetic coil.

[0004] When the torque command value becomes a constant torque state after increasing, the current correction unit performs correction to gradually decrease the current command value by a correction amount corresponding to the duration of the constant torque state. Further, when the torque command value becomes a constant torque state after decreasing, the current correction unit performs correction to gradually increase the current command value by a correction amount corresponding to the duration of the constant torque state.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-85489 [Overview of the project] [Problems that the invention aims to solve]

[0006] In a four-wheel drive vehicle configured as described above, the torque command value may frequently switch between increasing and decreasing states depending on the driving conditions. In such cases, the current command value correction in the current correction unit may not be sufficient, leaving room for improvement.

[0007] Therefore, the present invention aims to provide a drive force transmission control device that can further improve the accuracy of transmitted torque. [Means for solving the problem]

[0008] To achieve the above objective, the present invention comprises a drive force transmission device that transmits a torque driving force corresponding to a current supplied to an electromagnetic coil between an input-side rotating member and an output-side rotating member, and a control device that controls the driving force transmitted between the input-side rotating member and the output-side rotating member by the current supplied to the electromagnetic coil, wherein the control device includes a storage unit that stores relational information showing the relationship between the torque transmitted between the input-side rotating member and the output-side rotating member and the magnitude of the current when the current supplied to the electromagnetic coil is kept constant, a torque command value calculation means that calculates the magnitude of the driving force to be transmitted from the input-side rotating member to the output-side rotating member as a torque command value, a current command value calculation means that calculates the value of the current to be supplied to the electromagnetic coil according to the torque command value as a current command value, and a current control means that supplies a current corresponding to the current command value to the electromagnetic coil. The aforementioned relationship information stores the relationship between the torque transmitted between the input-side rotating member and the output-side rotating member and the magnitude of the current when the current supplied to the electromagnetic coil is kept constant, corresponding to a plurality of torque command values ​​ranging from 0 to the rated torque. The current command value calculation means, when transitioning from a fluctuating state where the amount of change per unit time of the torque command value is greater than or equal to a predetermined value to a steady state where it is less than the predetermined value, calculates the current command value. According to the torque command value Obtained by referring to the aforementioned related information Related information reference value To provide a drive force transmission control device that gradually approaches [a certain value]. [Effects of the Invention]

[0009] According to the power transmission control device of the present invention, it is possible to achieve high precision in transmitted torque. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing a general configuration example of a four-wheel drive vehicle equipped with a drive force transmission control device according to an embodiment of the present invention. [Figure 2] This is a cross-sectional view showing an example of the configuration of a power transmission device. [Figure 3] This is a block diagram showing an example of the functional configuration of a control device. [Figure 4] This graph shows an example of the relationship between current and transmitted torque when the current supplied to the electromagnetic coil is changed. [Figure 5] This graph shows enlarged views of the first torque characteristic curve, the second torque characteristic curve, and a portion of the third torque characteristic curve. [Figure 6] (a) and (b) are graphs showing examples of the temporal changes in the current supplied to the electromagnetic coil and the transmitted torque. [Figure 7] (a) and (b) are graphs showing examples of the temporal changes in the current supplied to the electromagnetic coil and the transmitted torque. [Figure 8] (a) is a graph showing an example of the first map information. (b) is a graph showing an example of the second map information. [Figure 9] This flowchart shows an example of the processing that the control unit performs at each control cycle. [Modes for carrying out the invention]

[0011] [Embodiment] Embodiments of the present invention will be described with reference to the drawings. The embodiments described below are shown as preferred specific examples for carrying out the present invention, and some parts specifically illustrate various technically preferable technical matters, but the technical scope of the present invention is not limited to these specific embodiments.

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

[0013] As shown in Figure 1, the four-wheel drive vehicle 1 includes an engine 11 as a drive source that generates driving force according to the amount of operation (pressure) of the accelerator pedal 110, a transmission 12 that changes the output of the engine 11, left and right front wheels 181, 182 as main drive wheels to which the driving force of the engine 11, which has been shifted by the transmission 12, is always transmitted, and left and right rear wheels 191, 192 as auxiliary drive wheels to which the driving force of the engine 11 is transmitted according to the driving state of the four-wheel drive vehicle 1. Wheel speed sensors 101 to 104 are respectively positioned on the left and right front wheels 181, 182 and the left and right rear wheels 191, 192.

[0014] Furthermore, the four-wheel drive vehicle 1 is equipped with a front differential 13, a propeller shaft 14, a rear differential 15, a pinion gear shaft 150 that transmits driving force to the rear differential 15, left and right front drive shafts 161 and 162, left and right rear drive shafts 171 and 172, a power transmission device 2A positioned between the propeller shaft 14 and the pinion gear shaft 150, and a control device 2B that controls the power transmission device 2A. The power transmission device 2A and the control device 2B constitute the power transmission control device 2.

[0015] The driving force transmission device 2A transmits the driving force corresponding to the current supplied from the control device 2B from the propeller shaft 14 to the pinion gear shaft 150. The driving force of the engine 11 is transmitted to the left and right rear wheels 191, 192 via the driving force transmission device 2A. The control device 2B can acquire the wheel speed signals indicating the rotational speeds of the left and right front wheels 181, 182 and the left and right rear wheels 191, 192 detected by the wheel speed sensors 101 to 104, and the accelerator opening signal indicating the operation amount of the accelerator pedal 110 detected by the accelerator pedal sensor 105, and controls the driving force transmission device 2A by supplying current to the driving force transmission device 2A.

[0016] The driving force of the engine 11 is transmitted to the left and right front wheels 181, 182 via the transmission 12, the front differential 13, and the left and right drive shafts 161, 162 on the front wheel side. The front differential 13 has a pair of side gears 131, 131 respectively non-rotatably connected to the left and right drive shafts 161, 162 on the front wheel side, a pair of pinion gears 132, 132 meshing with the pair of side gears 131, 131 with their gear shafts orthogonal, a pinion gear shaft 133 supporting the pair of pinion gears 132, 132, and a front diff case 134 housing these.

[0017] A ring gear 135 is fixed to the front diff case 134, and this ring gear 135 meshes with a pinion gear 141 provided at the front end of the vehicle of the propeller shaft 14. The rear end of the vehicle of the propeller shaft 14 is connected to the housing 20 of the driving force transmission device 2A. The driving force transmission device 2A has an inner shaft 3 arranged to be relatively rotatable with respect to the housing 20, and a pinion gear shaft 150 is non-rotatably connected to the inner shaft 3. Details of the driving force transmission device 2A will be described later.

[0018] The rear differential 15 includes a pair of side gears 151, 151 connected to the left and right rear drive shafts 171, 172 so as not to rotate relative to each other, a pair of pinion gears 152, 152 that mesh with the pair of side gears 151, 151 with their gear shafts perpendicular to each other, a pinion gear shaft 153 that supports the pair of pinion gears 152, 152, a rear differential case 154 that houses these components, and a ring gear 155 fixed to the rear differential case 154 and meshing with the pinion gear shaft 150.

[0019] (Configuration of the power transmission system) Figure 2 is a cross-sectional view showing an example of the configuration of the drive force transmission device 2A. In Figure 2, the area above the rotation axis O shows the operating state of the drive force transmission device 2A, and the area below the rotation axis O shows the non-operating state of the drive force transmission device 2A. Hereinafter, the direction parallel to the rotation axis O will be referred to as the axial direction.

[0020] The drive force transmission device 2A comprises a housing 20 consisting of a front housing 21 and a rear housing 22, a cylindrical inner shaft 3 supported to be rotatable relative to the housing 20 on the same axis, a main clutch 4 positioned between the housing 20 and the inner shaft 3, a cam mechanism 5 that generates a thrust force to press the main clutch 4, and an electromagnetic clutch mechanism 6 that operates the cam mechanism 5 by receiving current from the control device 2B. The housing 20 is an example of the input-side rotating member of the present invention, and the inner shaft 3 is an example of the output-side rotating member of the present invention. The inside of the housing 20 is sealed with lubricating oil (not shown).

[0021] The front housing 21 is a bottomed cylindrical shape, having a cylindrical tubular portion 21a and a bottom portion 21b integrally. A female threaded portion 21c is formed on the inner surface of the open end of the tubular portion 21a. The propeller shaft 14 (see Figure 1) is connected to the bottom portion 21b of the front housing 21 via a cross joint. The front housing 21 also has a plurality of axially extending outer spline projections 211 on the inner circumferential surface of the tubular portion 21a.

[0022] The rear housing 22 is composed of 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 which is integrally bonded 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 which is integrally bonded to the inner circumference of the second annular member 222 by welding or the like. An annular housing space 22a for housing the electromagnetic coil 63 is formed between the first annular member 221 and the third annular member 223. In addition, a male threaded portion 221a is formed on the outer circumferential surface of the first annular member 221 which screws into the female threaded portion 21c of the front housing 21.

[0023] The inner shaft 3 has a plurality of inner spline projections 31 extending in the axial direction on its outer circumferential surface and is supported on the inner circumference side of the housing 20 by ball bearings 24 and needle roller bearings 25. A spline fitting portion 32 is formed on the inner surface of one end of the inner shaft 3 into which one end of the pinion gear shaft 150 (see Figure 1) is fitted so as not to rotate relative to it.

[0024] The main clutch 4 consists of a plurality of main outer clutch plates 41 and a plurality of main inner clutch plates 42 arranged alternately along the axial direction. The main outer clutch plates 41 rotate with the front housing 21, and the main inner clutch plates 42 rotate with the inner shaft 3. The main outer clutch plates 41 have a plurality of engaging projections 411 on their outer peripheral ends that engage with the outer spline projections 211 of the front housing 21. The main outer clutch plates 41 are restricted from relative rotation with the front housing 21 by the engagement of the engaging projections 411 with the outer spline projections 211, and are movable axially relative to the front housing 21.

[0025] The main inner clutch plate 42 has a plurality of engaging protrusions 421 on its inner circumference end that engage with the inner spline projections 31 of the inner shaft 3. The main inner clutch plate 42 is restricted from relative rotation with respect to the inner shaft 3 by the engagement of the engaging protrusions 421 with the inner spline projections 331, and is movable in the axial direction relative to the inner shaft 3. The main inner clutch plate 42 also has a disc-shaped base material 431 made of metal and friction material 432 attached to both sides of the base material 431. The base material 431 has a plurality of oil holes 433 formed inside the portion to which the friction material 432 is attached, for the flow of lubricating oil. The main outer clutch plate 41 has oil grooves (not shown) formed on the contact surface with the friction material 432 for the flow of lubricating oil.

[0026] The cam mechanism 5 is configured to include a pilot cam 51 that receives rotational force from the housing 20 via an electromagnetic clutch mechanism 6, a main cam 52 as a pressing member that presses the main clutch 4 in the axial direction, and a plurality of spherical cam balls 53 positioned between the pilot cam 51 and the main cam 52.

[0027] The main cam 52 integrally comprises a ring-shaped pressing portion 521 that contacts the main inner clutch plate 42 at one end of the main clutch 4 and presses the main clutch 4, and a cam portion 522 provided on the inner circumference side of the main cam 52 relative to the pressing portion 521. The main cam 52 has a spline engaging portion 521a formed at the inner circumference end of the pressing portion 521 that engages with the inner spline projection 331 of the inner shaft 3, thereby restricting relative rotation with the inner shaft 3. Furthermore, the main cam 52 is biased to move axially away from the main clutch 4 by a disc spring 54 positioned between it and a stepped surface 3a formed on the inner shaft 3.

[0028] The pilot cam 51 has a spline projection 511 on its outer circumference that receives a rotational force from the electromagnetic clutch mechanism 6 that rotates relative to the main cam 52. A thrust needle roller bearing 55 is positioned between the pilot cam 51 and the third annular member 223 of the rear housing 22. Multiple cam grooves 51a and 522a are formed on the opposing surfaces of the pilot cam 51 and the cam portion 522 of the main cam 52, respectively, with axial depths that vary along the circumferential direction. The cam ball 53 is positioned between the cam groove 51a of the pilot cam 51 and the cam groove 522a of the main cam 52.

[0029] The cam mechanism 5 generates a pressing force that presses the main clutch 4 against it as the pilot cam 51 rotates relative to the main cam 52. The main clutch 4 receives the pressing force from the cam mechanism 5, causing frictional contact between the main outer clutch plate 41 and the main inner clutch plate 42, and the driving force is transmitted by the frictional force generated between the main outer clutch plate 41 and the main inner clutch plate 42.

[0030] The electromagnetic clutch mechanism 6 comprises an armature 60, a plurality of pilot outer clutch plates 61, a plurality of pilot inner clutch plates 62, an electromagnetic coil 63, and an annular yoke 64 made of magnetic material that holds the electromagnetic coil 63. The electromagnetic coil 63 is held by the yoke 64 and housed in the housing space 22a of the rear housing 22. The yoke 64 is supported by a ball bearing 26 on the third annular member 223 of the rear housing 22, and its outer circumferential surface faces the inner circumferential surface of the first annular member 221. The inner circumferential surface of the yoke 64 also faces the outer circumferential surface of the third annular member 223.

[0031] The electromagnetic coil 63 is supplied with an excitation current from the control device 2B via the electric wire 631. When the electromagnetic coil 63 is energized, a magnetic flux is generated in the magnetic path G shown in Figure 2. The yoke 64, the first annular member 221 and the third annular member 223 of the rear housing 22, the multiple pilot outer clutch plates 61 and pilot inner clutch plates 62, and the armature 60, which form the path of this magnetic flux, are magnetic path forming members that form the magnetic path G. These magnetic path forming members have coercivity inherent to their respective materials and exhibit magnetic hysteresis, where the magnetic susceptibility is influenced not only by the strength of the magnetic field at that moment but also by past magnetization processes.

[0032] Multiple pilot outer clutch plates 61 and multiple pilot inner clutch plates 62 are disc-shaped members made of a magnetic material such as iron, and are arranged alternately along the axial direction between the armature 60 and the rear housing 22. Multiple arc-shaped slits are formed in the pilot outer clutch plates 61 and pilot inner clutch plates 62 at positions aligned axially with the second annular member 222 of the rear housing 22 to prevent short circuits of magnetic flux.

[0033] The pilot outer clutch plate 61 has a plurality of engaging projections 611 on its outer circumference that engage with the outer spline projections 211 of the front housing 21. The pilot inner clutch plate 62 has a plurality of engaging projections 621 on its inner circumference that engage with the spline projections 511 of the pilot cam 51. The frictional sliding between the pilot outer clutch plate 61 and the pilot inner clutch plate 62 is lubricated by lubricating oil, similar to the main clutch 4.

[0034] The armature 60 is an annular member made of a magnetic material such as iron, and has a plurality of engaging protrusions 601 formed on its outer circumference that engage with the outer spline protrusions 211 of the front housing 21. As a result, the armature 60 is movable in the axial direction relative to the front housing 21, and its relative rotation with respect to the front housing 21 is restricted.

[0035] The electromagnetic clutch mechanism 6 attracts the armature 60 towards the yoke 64 by the magnetic force generated when the electromagnetic coil 63 is energized, and this movement of the armature 60 generates a frictional force between the pilot outer clutch plate 61 and the pilot inner clutch plate 62. The pilot outer clutch plate 61 and the pilot inner clutch plate 62 are pressed against the rear housing 22 by the armature 60 and come into frictional contact.

[0036] In the drive force transmission device 2A, the operation of the electromagnetic clutch mechanism 6 transmits a rotational force corresponding to the current supplied to the electromagnetic coil 63 to the pilot cam 51, causing the pilot cam 51 to rotate relative to the main cam 52, and the cam ball 53 to roll in the cam grooves 51a, 522a. This rolling of the cam ball 53 generates a thrust force that presses the main clutch 4 against the main cam 52, and frictional force is generated between the multiple main outer clutch plates 41 and the multiple main inner clutch plates 42. In other words, the drive force transmission device 2A transmits a torque drive force corresponding to the current supplied to the electromagnetic coil 63 between the housing 20 and the inner shaft 3. The control device 2B controls the drive force transmitted between the housing 20 and the inner shaft 3 by the current supplied to the electromagnetic coil 63. Hereinafter, the magnitude of the drive force transmitted between the housing 20 and the inner shaft 3 will be referred to as the transmitted torque.

[0037] (Control device configuration) Figure 3 is a block diagram showing an example of the functional configuration of the control device 2B. The control device 2B includes a control unit 7 having a CPU (processing unit), a storage unit 8 having non-volatile memory such as EEPROM or flash memory, and a switching power supply unit 9 that switches the voltage of a DC power supply such as a battery to supply current to the electromagnetic coil 63 of the drive force transmission device 2A. The switching power supply unit 9 has switching elements such as transistors and generates current by switching the DC voltage based on the PWM (Pulse Width Modulation) signal output from the control unit 7.

[0038] The control unit 7 functions as a torque command value calculation means 71, a current command value calculation means 72, and a current control means 73 when the CPU executes a program 81 stored in the memory unit 8. The processing operations of the torque command value calculation means 71, the current command value calculation means 72, and the current control means 73 are performed at predetermined control cycles (e.g., 5ms).

[0039] The torque command value calculation means 71 calculates the magnitude of the driving force to be transmitted from the housing 20 to the inner shaft 3 as the torque command value. The torque command value is set to a larger value the greater the difference in front-to-rear wheel rotational speeds, which is the difference between the average rotational speed of the left and right front wheels 181, 182 and the average rotational speed of the left and right rear wheels 191, 192, and the larger the amount of operation of the accelerator pedal 110. For example, if the accelerator pedal 110 is operated to a predetermined amount and then the amount of operation becomes constant, the torque command value will change accordingly. The torque command value may also be increased or decreased according to the yaw rate, acceleration in the longitudinal direction and lateral direction of the vehicle, etc. Hereinafter, the state in which the torque command value is substantially constant will be called the steady state of the torque command value, and the state in which the torque command value fluctuates over time will be called the fluctuating state of the torque command value. More specifically, the steady state means that the amount of change in the torque command value per control cycle is less than a predetermined value (for example, 0.01% of the rated torque of the drive force transmission device 2A), and the fluctuating state means that the amount of change in the torque command value per control cycle is greater than or equal to this predetermined value.

[0040] The current command value calculation means 72 calculates the value of the current to be supplied to the electromagnetic coil 63 as the current command value, according to the torque command value calculated by the torque command value calculation means 71. The current control means 73 supplies the electromagnetic coil 63 with a current corresponding to the current command value calculated by the current command value calculation means 72. Specifically, it adjusts the duty cycle of the PWM signal that turns the switching elements of the switching power supply unit 9 on and off, and performs feedback control so that the current corresponding to the current command value is supplied to the electromagnetic coil 63.

[0041] In addition to the program 81, the memory unit 8 stores relational information 82, first torque characteristic information 83, second torque characteristic information 84, first map information 85, and second map information 86 as information used in the processing of the control unit 7.

[0042] The relational information 82 is information that shows the relationship between the torque transmitted between the housing 20 and the inner shaft 3 and the magnitude of the current when the current supplied to the electromagnetic coil 63 is kept constant. The first torque characteristic information 83 is information that shows the first torque characteristic, which is the characteristic of the change in transmitted torque when the current supplied to the electromagnetic coil 63 is gradually increased. The second torque characteristic information 84 is information that shows the second torque characteristic, which is the characteristic of the change in transmitted torque when the current supplied to the electromagnetic coil 63 is gradually decreased. The first map information 85 is map information that the current command value calculation means 72 refers to when the torque command value transitions from a fluctuating state in which it is gradually increasing to a steady state. The second map information 86 is map information that the current command value calculation means 72 refers to when the torque command value transitions from a fluctuating state in which it is gradually decreasing to a steady state.

[0043] The first torque characteristic information 83 and the second torque characteristic information 84 are based on the results of measuring the transmission torque when the current supplied to the electromagnetic coil 63 is increased and decreased at a predetermined rate of change after the assembly of each individual drive force transmission device 2A on the production line of the drive force transmission device 2A. The storage unit 8 of the control device 2B stores the first torque characteristic information 83 and the second torque characteristic information 84 of the drive force transmission device 2A that is combined in the four-wheel drive vehicle 1 when the control device 2B is mounted on the four-wheel drive vehicle 1. The second torque characteristic information 84 may be the difference in transmission torque when the current supplied to the electromagnetic coil 63 is gradually increased and when the current supplied to the electromagnetic coil 63 is gradually decreased. That is, in the following description, control based on the second torque characteristic can be control based on the first torque characteristic and the above difference.

[0044] The related information 82 is set, for example, based on experimental results or computer simulation results using multiple drive force transmission devices 2A. When the related information 82 is set based on experimental results using multiple drive force transmission devices 2A, the related information 82 is set based on the measurement results of the current supplied to the electromagnetic coil 63 and the transmitted torque when the transmitted torque is constant, without any increase or decrease in the magnetic flux density in magnetic path forming members such as the yoke 64, or an increase or decrease in the amount of lubricating oil interposed between the multiple main outer clutch plates 41 and the main inner clutch plate 42, and between the multiple pilot outer clutch plates 61 and the pilot inner clutch plate 62.

[0045] In the drive force transmission device 2A, as the current supplied to the electromagnetic coil 63 increases, the magnetic path forming members such as the yoke 64 are not sufficiently magnetized for this current, resulting in a decrease in the value of the transmitted torque relative to the current supplied to the electromagnetic coil 63. On the other hand, as the current supplied to the electromagnetic coil 63 decreases, the residual magnetism of the magnetic path forming members such as the yoke 64 increases the magnetic flux density in the magnetic path forming members, resulting in a increase in the value of the transmitted torque relative to the current supplied to the electromagnetic coil 63. Furthermore, changes in the amount of lubricating oil interposed between the multiple main outer clutch plates 41 and the main inner clutch plate 42, and between the multiple pilot outer clutch plates 61 and the pilot inner clutch plate 62, also contribute to fluctuations in the transmitted torque.

[0046] Figure 4 is a graph showing an example of the relationship between current and transmitted torque when the current supplied to the electromagnetic coil 63 is gradually increased from 0 to the rated current, and then gradually decreased from the rated current to 0. This graph shows a first torque characteristic line L1 that shows the transmitted torque when the current supplied to the electromagnetic coil 63 is gradually increased, and a second torque characteristic line L2 that shows the transmitted torque when the current supplied to the electromagnetic coil 63 is gradually decreased. As shown in Figure 4, when the current supplied to the electromagnetic coil 63 is gradually increased, the transmitted torque between the housing 20 and the inner shaft 3 becomes smaller compared to when the current is gradually decreased.

[0047] When a torque T, shown on the vertical axis of Figure 4, is transmitted from the housing 20 to the inner shaft 3, the current value at coordinate point P1 on the first torque characteristic line L1 corresponding to this torque T is I1, and the current value at coordinate point P2 on the second torque characteristic line L2 corresponding to this torque T is I2. In other words, the current value that needs to be supplied to the electromagnetic coil 63 to obtain the transmitted torque T is I1 when the current increases and I2 when the current decreases.

[0048] Here, the difference in the current value required to transmit a predetermined amount of driving force between the housing 20 and the inner shaft 3, when the current supplied to the electromagnetic coil 63 is gradually increased and when it is gradually decreased, is defined as the hysteresis amount. In the example shown in Figure 4, ΔI (=I1-I2), which is the difference between I1 and I2, is the hysteresis amount corresponding to the torque T. The hysteresis amount varies depending on the magnitude of the torque.

[0049] Furthermore, in Figure 4, the third torque characteristic line L3, which represents the relationship information 82, is shown as a dashed line. The third torque characteristic line L3 lies between the first torque characteristic line L1 and the second torque characteristic line L2, and is shifted towards the second torque characteristic line L2 side rather than the center position of the first and second torque characteristic lines L1 and L2. As shown in Figure 4, when the current value at coordinate point P3 on the third torque characteristic line L3 corresponding to torque T is I3, the current difference coefficient, which is the difference between current value I1 and current value I3 divided by the hysteresis amount ΔI, can be calculated using the formula (I1-I3) / ΔI. The relationship information 82 stores current difference coefficients corresponding to multiple torque command values ​​from 0 to rated torque. Note that the current difference coefficient may be a value that changes depending on the relative rotational speed and temperature of the left and right front wheels 181,182 and left and right rear wheels 191,192.

[0050] As described above, the third torque characteristic curve L3 is skewed towards the second torque characteristic curve L2, so the current difference coefficient is greater than 0.5 for all torque command values. The reason for this is that the main cam 52 of the cam mechanism 5 is biased to move away from the main clutch 4 by a disc spring 54 positioned between it and the stepped surface 3a formed on the inner shaft 3, and as the current supplied to the electromagnetic coil 63 decreases, the biasing force of the disc spring 54 quickly reduces the frictional force between the multiple main outer clutch plates 41 and the main inner clutch plate 42 of the main clutch 4.

[0051] The current command value calculation means 72 calculates the current command value by referring to the first torque characteristic stored as the first torque characteristic information 83 when the torque command value increases, and calculates the current command value by referring to the second torque characteristic stored as the second torque characteristic information 84 when the torque command value decreases. Furthermore, when the current command value calculation means 72 transitions from a state in which the torque command value is increasing or decreasing to a steady state in which the rate of change of the torque command value per unit time is less than a predetermined value, it gradually approaches the current command value from a value obtained by referring to the first or second torque characteristic to a value obtained by referring to the third torque characteristic stored as relational information 82. At this time, the current command value calculation means 72 gradually approaches the current command value from the first torque characteristic side or from the second torque characteristic side to a value obtained by referring to the third torque characteristic, depending on the control state before the steady state is reached.

[0052] In other words, when the current command value calculation means 72 transitions from a fluctuating state where the rate of change of the torque command value per unit time is greater than or equal to a predetermined value to a steady state where the rate of change of the torque command value per unit time is less than this predetermined value, it gradually adjusts the current command value to a value obtained by referring to the related information 82. This suppresses fluctuations in the transmitted torque caused by magnetic hysteresis of magnetic path forming members such as the yoke 64 and the influence of lubricating oil interposed between the multiple main outer clutch plates 41 and the main inner clutch plate 42, as well as between the multiple pilot outer clutch plates 61 and the pilot inner clutch plate 62, thereby improving the accuracy of the transmitted torque.

[0053] Furthermore, when the current command value calculation means 72 transitions from a fluctuating state in which the torque command value increases to a steady state, it corrects the current command value to decrease based on a first current correction amount obtained by referring to the first map information 85 according to the elapsed time since transitioning to the steady state. When the transition occurs from a fluctuating state in which the torque command value decreases to a steady state, it corrects the current command value to increase based on a second current correction amount obtained by referring to the second map information 86 according to the elapsed time since transitioning to the steady state. The current command value calculation means 72 switches the direction of this correction, that is, whether to correct the current command value to decrease or increase it, depending on whether the control state before reaching the steady state is on the right side (high current side) or the left side (low current side) of the third torque characteristic in the graph of Figure 4.

[0054] Next, with reference to Figures 5 and 6(a) and 6(b), specific examples of the operation of the drive force transmission control device before and after transitioning from a state of torque command value fluctuation to a steady state will be described.

[0055] Figure 5 is a graph showing enlarged portions of the first torque characteristic line L1, the second torque characteristic line L2, and the third torque characteristic line L3. Figures 6(a), (b) and 7(a), (b) are graphs showing examples of the temporal changes in the current supplied to the electromagnetic coil 63 and the transmitted torque. In Figures 6(a), (b) and 7(a), (b), the change in the current supplied to the electromagnetic coil 63 is shown by a solid line, and the change in the transmitted torque is shown by a dashed line.

[0056] In Figure 5, arrow A1 shows the change in the relationship between current and transmitted torque when the current supplied to the electromagnetic coil 63 is kept constant at I1, after a fluctuating state in which the current supplied to the electromagnetic coil 63 is increased from 0 to I1 at a constant rate of change over time. Figure 6(a) shows the temporal changes in transmitted torque and current at this time. The timing of the transition from the fluctuating state of the torque command value to the steady state is time t1 shown on the horizontal axis (time axis) of Figure 6(a).

[0057] When the current supplied to the electromagnetic coil 63 is changed in this way, the transmitted torque increases after time t1, even though the current is kept constant. This is because, after time t1, the magnetic flux density of the magnetic path forming members such as the yoke 64 gradually increases due to magnetic hysteresis of the magnetic path forming members, and the amount of lubricating oil interposed between the multiple main outer clutch plates 41 and the main inner clutch plate 42, and between the multiple pilot outer clutch plates 61 and the pilot inner clutch plate 62 decreases.

[0058] In this embodiment, when the torque command value transitions from a state of gradually increasing to a steady state, the current command value is corrected to decrease based on a first current correction amount obtained by referring to the first map information 85 according to the elapsed time since the transition to the steady state. In Figure 5, the change in the relationship between current and transmitted torque in this case is shown by arrow A2. In Figure 6(b), the temporal changes in transmitted torque and current at this time are shown. As shown by arrow A2 in Figure 5, by gradually decreasing the current value of the current supplied to the electromagnetic coil 63 from I1 after time t1, fluctuations in transmitted torque after time t1 are suppressed.

[0059] Furthermore, in Figure 5, arrow B1 shows the change in the relationship between current and transmitted torque when the current supplied to the electromagnetic coil 63 is kept constant at I2, after a fluctuating state in which the current supplied to the electromagnetic coil 63 is reduced from the rated current to I2 at a constant rate of change over time. Figure 7(a) shows the temporal changes in transmitted torque and current at this time. The timing of the transition from the fluctuating state of the torque command value to the steady state is time t2, shown on the horizontal axis (time axis) of Figure 7(a).

[0060] When the current supplied to the electromagnetic coil 63 is changed in this way, the transmitted torque decreases after time t2, even though the current is kept constant. This is because the magnetic flux density of the magnetic path forming members, such as the yoke 64, decreases after time t2 due to magnetic hysteresis of the magnetic path forming members, and the amount of lubricating oil interposed between the multiple main outer clutch plates 41 and the main inner clutch plate 42, and between the multiple pilot outer clutch plates 61 and the pilot inner clutch plate 62, increases.

[0061] In this embodiment, when the torque command value transitions from a state in which it is gradually decreasing to a steady state, the current command value is corrected to increase based on a second current correction amount obtained by referring to the second map information 86 according to the elapsed time since the transition to the steady state. In Figure 5, the change in the relationship between current and transmitted torque in this case is shown by arrow B2. In Figure 7(b), the temporal changes in transmitted torque and current at this time are shown. As shown by arrow B2 in Figure 5, by gradually increasing the current value of the current supplied to the electromagnetic coil 63 from I2 after time t2, fluctuations in transmitted torque after time t2 are suppressed.

[0062] Figure 8(a) is a graph showing an example of the first map information 85. The first map information 85 stores a first current correction amount whose absolute value increases as the elapsed time since transitioning to a steady state increases. Although the first current correction amount is a negative value, in Figure 8(a), the absolute value of the first current correction amount is shown on the vertical axis.

[0063] Figure 8(b) is a graph showing an example of the second map information 86. Similar to the first map information 85, the second map information 86 stores a second current correction amount, which is a positive value whose absolute value increases as the elapsed time since transitioning to a steady state increases. However, the second current correction amount is set to be smaller than the absolute value of the first current correction amount for all torque command values ​​and elapsed times. The scales of each axis in the graph shown in Figure 8(b) are the same as the scales of each axis in the graph shown in Figure 8(a).

[0064] Figure 9 is a flowchart showing an example of the processing performed by the control unit 7 in each control cycle. The control unit 7, as the torque command value calculation means 71, the current command value calculation means 72, and the current control means 73, repeatedly performs the processing shown in Figure 9 in each control cycle. Of the steps in the flowchart shown in Figure 9, step S1 is the processing performed by the torque command value calculation means 71, and step S16 is the processing performed by the current control means 73. The other steps are the processing performed by the current command value calculation means 72.

[0065] The torque command value calculation means 71 calculates a torque command value based on various vehicle conditions such as the difference in rotational speed between the front and rear wheels and the amount of operation of the accelerator pedal 110 (step S1). The current command value calculation means 72 calculates a current command value between the first torque characteristic information 83 and the second torque characteristic information 84, for example, in accordance with the torque command value calculated in step S1 (step S2).

[0066] Next, the current command value calculation means 72 determines whether the absolute value of the difference between the torque command value calculated in step S1 and the previous torque command value (which is the torque command value in the previous control cycle) is less than a predetermined value (step S3). If the result of the determination in step S3 is Yes, the count value is incremented (step S4). This count value indicates the elapsed time since the torque command value reached a steady state. On the other hand, if the result of the determination in step S3 is Yes, the count value is cleared to zero (step S5).

[0067] Next, the current command value calculation means 72 obtains a relational information reference value, which is a value obtained by referring to relational information 82 according to the torque command value calculated in step S1, and determines whether the current command value calculated in step S2 is greater than this relational information reference value (step S6). In the graph shown in Figure 4, this determination corresponds to determining whether the current command value calculated in step S2 is to the right of the third torque characteristic line L3.

[0068] If the determination in step S6 is Yes, the current command value calculation means 72 refers to the first map information 85 according to the elapsed time shown in the torque command value and counter value calculated in step S1 and obtains a first current correction value (step S7). Next, the current command value calculation means 72 adds the first current correction value obtained in step S7 to the current command value calculated in step S2 to obtain the current command value (step S8). As mentioned above, since the first current correction amount is a negative value, by adding the first current correction value to the current command value calculated in step S2, the current command value after the addition becomes smaller than the current command value calculated in step S2 by the absolute value of the first current correction amount.

[0069] Next, the current command value calculation means 72 determines whether the current command value calculated in step S8 is greater than or equal to the above-mentioned relational information reference value (step S9). If the result of the determination in step S9 is No, it means that the correction of the current command value performed in step S8 was excessive, so the current command value is set to the relational information reference value (step S10).

[0070] On the other hand, if the result of the determination in step S6 is No, the current command value calculation means 72 refers to the second map information 86 according to the elapsed time shown in the torque command value and counter value calculated in step S1 and obtains a second current correction value (step S11). Next, the current command value calculation means 72 adds the second current correction value obtained in step S11 to the current command value calculated in step S2 to obtain the current command value (step S12). Since the second current correction value is a positive value, by adding the second current correction value to the current command value calculated in step S2, the current command value after addition becomes a value that is larger than the current command value calculated in step S2 by the absolute value of the second current correction amount.

[0071] Next, the current command value calculation means 72 determines whether the current command value calculated in step S12 is greater than or equal to the above-mentioned relational information reference value (step S13). If the result of the determination in step S13 is No, it means that the correction of the current command value performed in step S12 was excessive, so the current command value is set to the relational information reference value (step S14).

[0072] The current control means 73 adjusts the duty cycle of the PWM signal that turns the switching elements of the switching power supply unit 9 on and off based on the detected value of the current sensor that detects the current supplied to the electromagnetic coil 63, so that the current supplied to the electromagnetic coil 63 is the current command value calculated in step S2, or the current command value corrected in the processing of steps S4 and S6-14, and performs feedback control. As a result, a driving force of a magnitude corresponding to the torque command value is transmitted between the housing 20 and the inner shaft 3.

[0073] (Operation and Effects of the Embodiment) According to the embodiment described above, when the torque command value transitions from a fluctuating state to a steady state, this is detected and the current command value is gradually brought closer to the value obtained by referring to the related information 82. This suppresses fluctuations in the transmitted torque due to magnetic hysteresis of magnetic path forming members such as the yoke 64 and the influence of lubricating oil interposed between multiple clutch plates, thereby improving the accuracy of the transmitted torque.

[0074] (Note) The present invention has been described above based on embodiments, but these embodiments do not limit the invention as defined in the claims. It should also be noted that not all combinations of features described in the embodiments are necessarily essential for solving the problem of the invention. Furthermore, the present invention can be implemented by omitting some components, or by adding or substituting components, without departing from its spirit. [Explanation of symbols]

[0075] 2…Drive force transmission control device 20…Housing (rotating member on the input side) 2A...Drive force transmission device 2B...Control device 3…Inner shaft (rotating member on the output side) 71…Torque command value calculation means 72...Current command value calculation means 73...Current control means 8...Memory section 82...Related information 83...First torque characteristic information 84...Second torque characteristic information 85... Map information for the first map 86... Map information for the second map

Claims

1. The system comprises a drive force transmission device that transmits a torque driving force corresponding to the current supplied to an electromagnetic coil between an input-side rotating member and an output-side rotating member, and a control device that controls the driving force transmitted between the input-side rotating member and the output-side rotating member by the current supplied to the electromagnetic coil, The control device is A storage unit that stores relational information showing the relationship between the torque transmitted between the input-side rotating member and the output-side rotating member and the magnitude of the current when the current supplied to the electromagnetic coil is kept constant, Torque command value calculation means that calculates the magnitude of the driving force to be transmitted from the input side rotating member to the output side rotating member as a torque command value, A current command value calculation means calculates the value of the current to be supplied to the electromagnetic coil according to the torque command value as a current command value, The system includes current control means for supplying a current corresponding to the current command value to the electromagnetic coil, The aforementioned relationship information stores the relationship between the torque transmitted between the input-side rotating member and the output-side rotating member and the magnitude of the current when the current supplied to the electromagnetic coil is kept constant, corresponding to a plurality of torque command values ​​from 0 to the rated torque. The current command value calculation means, when transitioning from a fluctuating state where the rate of change of the torque command value per unit time is greater than or equal to a predetermined value to a steady state where it is less than the predetermined value, gradually brings the current command value closer to a relational information reference value obtained by referring to the relational information in accordance with the torque command value. Power transmission control device.

2. The storage unit stores first map information that the current command value calculation means refers to when transitioning from a state in which the torque command value is increasing to the steady state, and second map information that the current command value calculation means refers to when transitioning from a state in which the torque command value is decreasing to the steady state. The current command value calculation means is When the torque command value transitions from a state in which it is increasing to a steady state, the current command value is corrected to decrease based on a first current correction amount obtained by referring to the first map information according to the elapsed time since the transition to the steady state. When the torque command value transitions from a state in which it is decreasing to a steady state, the current command value is corrected to increase based on a second current correction amount obtained by referring to the second map information according to the elapsed time since the transition to the steady state. The drive force transmission control device according to claim 1.

3. The absolute value of the first current correction amount obtained by referring to the first map information is greater than the absolute value of the second current correction amount obtained by referring to the second map information. The drive force transmission control device according to claim 2.