Vehicle control devices and four-wheel drive vehicles

Abstract

A vehicle control device and a four-wheel drive vehicle are provided. The vehicle control device (6) is mounted on a four-wheel drive vehicle (1) including a driving force transmission system (10). The vehicle control device (6) includes an electronic control unit. The electronic control unit calculates a command torque based on vehicle information. The electronic control unit estimates the temperature of a heat generating location in the driving force transmission system (10) based on the command torque. When the driving force corresponding to the command torque cannot be transmitted to the auxiliary driving wheel due to the magnitude of the driving force generated by the driving source or the occurrence of wheel slip, the electronic control unit estimates the temperature of the heat generating location based on an estimated value of the driving force input to the input rotating member.

Description

Technical Field

[0001] The present invention relates to a vehicle control device for a four-wheel drive vehicle, the vehicle control device being equipped with a drive force transmission system for distributing a drive force of a drive source to main drive wheels and auxiliary drive wheels, and the present invention relates to the four-wheel drive vehicle. Background Art

[0002] A vehicle control device equipped with a control unit is known, which estimates the temperature of a heat generating position of a driving force transmission system of a four-wheel drive vehicle having a main driving wheel and an auxiliary driving wheel, and when the estimated temperature is equal to or higher than a predetermined value, reduces the driving force transmitted to the auxiliary driving wheel (for example, see Japanese Unexamined Patent Application Publication No. 2002-349604 (JP 2002-349604 A) and Japanese Unexamined Patent Application Publication No. 2017-87984 (JP 2017-87984 A)). The control device controls a driving force transmission device in which the driving force transmitted to the auxiliary driving wheel side can be adjusted by a clutch, and the control device also estimates the temperature of the heat generating position by integrating the heating value calculated based on the driving force transmitted by the driving force transmission device. Summary of the invention

[0003] However, when the temperature of a heat generating location in the driving force transmission system is estimated based on the command value of the clutch engagement force in the driving force transmission device, for example when driving on a low μ road where wheel slip (idling) may occur, a temperature higher than the actual temperature may be estimated depending on the driving conditions.

[0004] The present invention can improve the accuracy of temperature estimation of a heat generating location in a driving force transmission system of a four-wheel drive vehicle.

[0005] A first aspect of the present invention relates to a vehicle control device. The vehicle control device is mounted on a four-wheel drive vehicle, which includes a driving force transmission system that distributes the driving force of a driving source to a main driving wheel and an auxiliary driving wheel. The vehicle control device controls a driving force transmission device, and the driving force transmitted to the auxiliary driving wheel can be adjusted by the driving force transmission device. The vehicle control device includes an electronic control unit. The electronic control unit is configured to calculate a command torque based on vehicle information. The command torque indicates the driving force transmitted from the input rotating member of the driving force transmission device to the output rotating member of the driving force transmission device. The electronic control unit is configured to estimate the temperature of a heat generating location in the driving force transmission system based on the command torque. The electronic control unit is configured to estimate the temperature of the heat generating location based on an estimated value of the driving force input to the input rotating member when the driving force corresponding to the command torque cannot be transmitted to the auxiliary driving wheel due to the size of the driving force generated by the driving source or the occurrence of wheel slip.

[0006] With the above-described configuration, it is possible to improve the accuracy of temperature estimation of a heat generating location in a driving force transmission system of a four-wheel drive vehicle.

[0007] A second aspect of the present invention relates to a four-wheel drive vehicle. The four-wheel drive vehicle includes: a driving force transmission system configured to distribute the driving force of a driving source to a main driving wheel and an auxiliary driving wheel; and a vehicle control device, the vehicle control device including an electronic control unit configured to control a driving force transmission device, and the driving force transmitted to the auxiliary driving wheel can be adjusted by the driving force transmission device. The electronic control unit is configured to calculate a command torque based on vehicle information, the command torque indicating the driving force transmitted from the input rotating member of the driving force transmission device to the output rotating member of the driving force transmission device. The electronic control unit is configured to estimate the temperature of a heat generating position in the driving force transmission system based on the command torque. The electronic control unit is configured to estimate the temperature of the heat generating position based on an estimated value of the driving force input to the input rotating member when the driving force corresponding to the command torque cannot be transmitted to the auxiliary driving wheel due to the size of the driving force generated by the driving source or the occurrence of wheel slip.

[0008] With the above-described configuration, it is possible to improve the accuracy of temperature estimation of a heat generating location in a driving force transmission system of a four-wheel drive vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

[0010] Figure 1 is a schematic configuration diagram of 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;

[0011] Figure 2 is a cross-sectional view of a configuration example of a driving force transmission device;

[0012] Figure 3 is a control block diagram of an example of a control configuration in a control device; and

[0013] Figure 4 is a flowchart of an example of a calculation process performed by the controller. DETAILED DESCRIPTION

[0014] Example

[0015] Will refer to Figures 1 to 4Describe the embodiments of the present invention. It should be noted that the embodiments described below are shown as preferred specific examples for implementing the present invention. Although some parts of the embodiments specifically illustrate various technically preferred matters. However, the technical scope of the present invention is not limited to these specific aspects.

[0016] Figure 1 1 is a schematic configuration diagram of 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.

[0017] like Figure 1 As shown, the four-wheel drive vehicle 1 includes: an engine 11 (as a driving source) that generates a driving force proportional to the operation amount (accelerator operation amount) of an accelerator pedal 110; a transmission 12 that changes the speed of the output of the engine 11; left and right front wheels 191, 192 (as main driving wheels) to which the driving force of the engine 11 changed by the transmission 12 is constantly transmitted; and left and right rear wheels 193, 194 (as auxiliary driving wheels) to which the driving force of the engine 11 is transmitted according to vehicle information of the four-wheel drive vehicle 1. Wheel speed sensors 101, 102, 103, 104 are arranged on the left and right front wheels 191, 192 and the left and right rear wheels 193, 194, respectively. An electric motor may be used as the driving source, or an engine and an electric motor may be combined as the driving source. In the following description, the left and right front wheels 191 , 192 and the left and right rear wheels 193 , 194 may be collectively referred to as wheels 19 .

[0018] The four-wheel drive vehicle 1 includes a driving force transmission system 10 that distributes the driving force of an engine 11 to left and right front wheels 191, 192 and left and right rear wheels 193, 194. The driving force transmission system 10 includes: a front differential 13 and a transfer case 14, which are arranged near the front wheels; a propeller shaft 15, which transmits the driving force in the front-rear direction of the vehicle; a rear differential 16, which is arranged near the rear wheels; a pinion shaft 160, which transmits the driving force to the rear differential 16; drive shafts 171, 172, which are on the left and right front wheels; drive shafts 181, 182, which are on the left and right rear wheels; and a driving force transmission device 2, which is arranged between the propeller shaft 15 and the pinion shaft 160. The driving force transmission device 2 is controlled by an on-vehicle control device 6 .

[0019] The driving force transmission device 2 transmits the driving force corresponding to the current supplied from the control device 6 from the transmission shaft 15 to the pinion shaft 160. The driving force of the engine 11 is transmitted to the left and right rear wheels 193, 194 through the driving force transmission device 2. The control device 6 can obtain: wheel speed information indicating the rotation speed of the left and right front wheels 191, 192 and the left and right rear wheels 193, 194 detected by the wheel speed sensors 101, 102, 103, 104; accelerator operation amount information indicating the operation amount of the accelerator pedal 110 detected by the accelerator pedal sensor 105; and external air temperature information detected by the external air temperature sensor 106, and controls the driving force transmission device 2 by supplying current to the driving force transmission device 2. Hereinafter, the current output by the control device 6 for controlling the driving force transmission device 2 is referred to as a control current.

[0020] The driving force of the engine 11 is transmitted to the left and right front wheels 191 and 192 through the transmission 12, the front differential 13, and the drive shafts 171 and 172 at the left and right front wheels. The front differential 13 has: a pair of side gears 131, which are connected to the drive shafts 171 and 172 at the left and right front wheels, respectively, so that the drive shafts 171 and 172 cannot rotate relative to each other; a pair of pinion gears 132, which mesh with the side gears 131, and the gear axes thereof are orthogonal to each other; a pinion gear shaft 133, which supports the pinion gear 132; and a front differential case 134, which accommodates the above-mentioned parts.

[0021] The transfer case 14 has: a pinion 141, which is fixed to the front differential case 134; and a ring gear 142, which is connected to the first end of the transmission shaft 15 on the front side of the vehicle and meshes with the pinion 141, and transmits the driving force to the transmission shaft 15. The pinion 141 and the ring gear 142 are made of hypoid gears and are lubricated by lubricating oil. The transmission shaft 15 is connected to the housing 20 of the driving force transmission device 2 at the second end on the rear side of the vehicle. The driving force transmission device 2 has: an inner shaft 23, which is rotatably arranged relative to the housing 20; and a pinion shaft 160, which is connected to the inner shaft 23 so as not to rotate relative to each other. The driving force transmission device 2 will be described in detail later.

[0022] The rear differential 16 has: a pair of side gears 161, which are connected to drive shafts 181 and 182 at the left and right rear wheels, respectively, so that the drive shafts 181 and 182 cannot rotate relative to each other; a pair of pinion gears 162, which are meshed with the side gears 161, and their gear axes are orthogonal to each other; a pinion shaft 163, which supports the pinion gears 162; a rear differential case 164, which accommodates the above-mentioned parts; and a ring gear 165, which is made of a hypoid gear and fixed to the rear differential case 164, and meshed with the pinion shaft 160.

[0023] Structure of driving force transmission device

[0024] Figure 2 2 is a cross-sectional view showing a configuration example of the driving force transmission device 2. Figure 2 , the upper portion of the rotation axis O shows the operating state (torque transmitting state) of the driving force transmission device 2, and the lower portion thereof shows the non-operating state (torque non-transmitting state) of the driving force transmission device 2. Hereinafter, the direction parallel to the rotation axis O is referred to as the axial direction.

[0025] The driving force transmission device 2 is configured to have: a housing 20 including a front housing 21 and a rear housing 22; a tubular inner shaft 23 supported to be rotatable on a common axis relative to the housing 20; a main clutch 3 arranged between the housing 20 and the inner shaft 23; a cam mechanism 4 generating a thrust for pressing the main clutch 3; and an electromagnetic clutch mechanism 5 operating the cam mechanism 4 by receiving a supply of a control current from a control device 6. The housing 20 is an example of an input rotating member of the present invention, and the inner shaft 23 is an example of an output rotating member of the present invention. Lubricating oil (not shown) is sealed inside the housing 20.

[0026] The front housing 21 has a bottomed cylindrical shape, which integrally has a cylindrical tubular portion 21a and a bottom portion 21b, and the transmission shaft 15 (see Figure 1 ) is connected to the bottom part 21b by, for example, a cross joint. A plurality of external spline protrusions 211 extending in the axial direction are formed on the inner surface of the tubular part 21a. The rear housing 22 is partially formed of an annular non-magnetic material 221 in the radial direction and rotates integrally with the front housing 21.

[0027] The inner shaft 23 is supported on the inner peripheral side of the housing 20 by bearings 24, 25, and has a plurality of internal spline protrusions 231 extending in the axial direction on the outer peripheral surface. In addition, a spline fitting portion 232 is formed on the inner surface of one end portion of the inner shaft 23, and the pinion shaft 160 (refer to Figure 1) is fitted in the spline fitting portion so as to be unable to rotate relative to each other.

[0028] The main clutch 3 includes a plurality of main outer clutch plates 31 and main inner clutch plates 32 arranged alternately in the axial direction. The outer peripheral end portions of the main outer clutch plates 31 are engaged with the outer spline protrusions 211 of the front housing 21. The inner peripheral end portions of the main inner clutch plates 32 are engaged with the inner spline protrusions 231 of the inner shaft 23.

[0029] The cam mechanism 4 is configured to have: a guide cam 41 that receives the rotational force of the housing 20 through the electromagnetic clutch mechanism 5; a main cam 42 that presses the main clutch 3 in the axial direction; and a plurality of spherical cam balls 43 that are arranged between the guide cam 41 and the main cam 42. A plurality of cam grooves 41a, 42a whose axial depths vary along the circumferential direction are formed on facing surfaces of the guide cam 41 and the main cam 42, respectively, and the cam balls 43 are arranged between the cam grooves 41a, 42a. A thrust bearing 44 is arranged between the guide cam 41 and the rear housing 22. The main cam 42 is engaged with the inner spline protrusion 231 of the inner shaft 23 so as not to rotate relative to each other and not to move axially, and the main cam is pushed toward the guide cam 41 by a disc spring 44 (as a return spring).

[0030] The electromagnetic clutch mechanism 5 is configured to have an armature 50, a plurality of guided outer clutch plates 51, a plurality of guided inner clutch plates 52, and an electromagnetic coil 53. The electromagnetic coil 53 is held in a yoke 530 supported by a bearing 26 in the rear housing 22. A control current from the control device 6 is supplied to the electromagnetic coil 53 through an electric wire 531 as an excitation current.

[0031] The guide outer clutch plates 51 and the guide inner clutch plates 52 are alternately arranged in the axial direction between the armature 50 and the rear housing 22. The end portions of the guide outer clutch plates 51 and the armature 50 at the outer peripheral side are engaged with the outer spline protrusions 211 of the front housing 21. The end portions of the guide inner clutch plates 52 at the inner peripheral side are engaged with the spline protrusions 411 of the guide cam 41.

[0032] In the driving force transmission device 2 constructed as described above, a magnetic flux is generated in the magnetic circuit G by the control current supplied to the electromagnetic coil 53, and the armature 50 is attracted toward the rear housing 22, and thus the guide outer clutch plate 51 and the guide inner clutch plate 52 are brought into frictional contact with each other. As a result, a rotational force corresponding to the control current is transmitted to the guide cam 41, and the guide cam 41 rotates relative to the main cam 42, thereby rolling the cam ball 43 in the cam grooves 41a, 42a. As the cam ball 43 rolls, a thrust for pressing the main clutch 3 is generated on the main cam 42, and a friction force is generated between the main outer clutch plate 31 and the main inner clutch plate 32. Then, the driving force is transmitted from the housing 20 to the inner shaft 23, that is, from the transmission shaft 15 to the pinion shaft 160 by the friction force. The control device 6 can adjust the driving force transmitted from the driving force transmission device 2 to the left and right rear wheels 193, 194 by increasing or decreasing the control current.

[0033] Control device structure

[0034] like Figure 1 As shown in FIG. 1 , the control device 6 includes a controller 60 having a central processing unit (CPU) (computing processing device) and a switching power supply unit 66 that switches the voltage of a direct current (DC) power supply such as a battery and supplies current to the electromagnetic coil 53 of the driving force transmission device 2. The switching power supply unit 66 has a switching element such as a transistor, switches the direct current (DC) voltage based on a pulse width modulation (PWM) signal output from the controller 60, and generates a control current to be supplied to the electromagnetic coil 53.

[0035] In the controller 60 , the CPU executes a program stored in a nonvolatile storage element to function as a torque command value calculation means 61 , a temperature estimation means 62 , an overheat protection control means 63 , a current command value calculation means 64 , and a current control means 65 .

[0036] The torque command value calculation device 61 calculates a torque command value indicating the magnitude of the driving force transmitted from the housing 20 to the inner shaft 23 based on the vehicle information. The temperature estimation device 62 estimates the temperature of the heat generating position in the driving force transmission system 10 based on the torque command value. When the heat generating position is judged to be in an overheated state by the temperature estimated by the temperature estimation device 62, the overheat protection control device 63 reduces the driving force transmitted by the driving force transmission device 2 to suppress the heat generation at the heat generating position. The current command value calculation device 64 calculates a current command value based on the torque command value, which is a target value of the control current supplied to the electromagnetic coil 53. The current control device 65 performs current feedback control so that a current corresponding to the current command value calculated by the current command value calculation device 64 is supplied to the electromagnetic coil 53.

[0037] Figure 3 is a control block diagram showing an example of a control configuration of the control device 6. In the control block diagram, the torque command value calculation unit 71, the temperature estimation unit 72, the overheat protection control unit 73, the current command value calculation unit 74, and the current control unit 75 are respectively constituted by the torque command value calculation device 61, the temperature estimation device 62, the overheat protection control device 63, the current command value calculation device 64, and the current control device 65.

[0038] The torque command value calculation unit 71 calculates the torque command value T* based on the wheel speed information of the left and right front wheels 191, 192 and the left and right rear wheels 193, 194 detected by the wheel speed sensors 101, 102, 103, 104 and the accelerator operation amount information detected by the accelerator pedal sensor 105. The wheel speed information and the accelerator operation amount information are examples of vehicle information. The torque command value calculation unit 71 sets the torque command value T* to be larger as the accelerator operation amount is larger and the front and rear wheel differential speed (which is the difference between the average speed of the left and right front wheels 191, 192 and the average speed of the left and right rear wheels 193, 194) is higher. The vehicle information is not limited to the wheel speed information and the accelerator operation amount information, and for example, the detection values ​​of various vehicle-mounted sensors such as the detection values ​​of the yaw rate sensor and the steering angle sensor can be used.

[0039] The temperature estimation unit 72 estimates the temperature of the heat generating position based on the torque command value T* calculated by the torque command value calculation unit 71, the accelerator operation amount information, the wheel speed information, and the outside air temperature information. The processing content of the temperature estimation unit 72 will be described in detail later. When the temperature calculated by the temperature estimation unit 72 is equal to or higher than the threshold value, the overheat protection control unit 73 performs a reduction correction on the torque command value T* calculated by the torque command value calculation unit 71 to calculate the correction torque command value T**.

[0040] The current command value calculation unit 74 calculates the current command value by referring to, for example, mapping information indicating the relationship between the driving force (transmission torque) transmitted by the driving force transmission device 2 and the control current. The current control unit 75 includes a deviation calculation unit 751, a proportional integral (PI) control unit 752, and a PWM control unit 753. The deviation calculation unit 751 calculates the deviation ε between the actual current value I (which is the detection value of the control current detected by the current sensor 660) and the command current value I*. The PI control unit 752 performs current feedback control by performing PI calculation on the deviation ε calculated by the deviation calculation unit 751 and calculating the duty ratio of the PWM signal output to the switching power supply unit 66 so that the actual current value I approaches the command current value I*. The PWM control unit 753 generates a PWM signal for turning on or off the switching element of the switching power supply unit 66 based on the duty ratio calculated by the PI control unit 752, and outputs the PWM signal to the switching power supply unit 66.

[0041] In the embodiment, the temperature estimation unit 72 estimates the temperature of the transfer case 14 which is a heat generating location of the drive force transmission system 10. The temperature estimation unit 72 generally calculates the temperature Temp of the transfer case 14 by estimation using the following equation (1).

[0042] Temp=K1+To+K2×H(n)···(1)

[0043] Here, K1 and K2 are coefficients set in advance based on, for example, experiments or simulations, and To is the outside air temperature detected by the outside air temperature sensor 106. H(n) is the load of the transfer case 14 in the nth calculation (n is a natural number) after the start of the engine 11. H(n) is obtained by the following equation (2).

[0044] H(n)=K3×∑{K4×T * ×Vf-K5×H(n-1)}···(2)

[0045] Here, K3, K4, and K5 are coefficients set in advance based on, for example, experiments or simulations, and T* is a torque command value calculated by the torque command value calculation unit 71. Vf is the average wheel speed of the left and right front wheels 191, 192, and H(n-1) is a previous value of the load amount of the transfer case 14. The temperature estimation unit 72 calculates the load amount of the transfer case 14 and the temperature Temp of the transfer case 14 every predetermined control cycle (for example, 5 ms). The term "K5×H(n-1)" in equation (2) corresponds to the amount of heat dissipated from the transfer case 14, and Vf corresponds to the rotation speed of the pinion 141 of the transfer case 14.

[0046] When slip (idling) occurs at the wheel 19, the driving force having a magnitude corresponding to the torque command value T* may not be transmitted from the driving force transmission device 2 to the rear differential 16. In addition, even when the driving force (input torque) transmitted from the engine 11 to the housing 20 of the driving force transmission device 2 is less than the torque command value T*, the driving force corresponding to the torque command value T* cannot be transmitted from the driving force transmission device 2 to the rear differential 16. In this case, the load amount H(n) of the transfer case 14 cannot be accurately calculated by equation (2), and therefore, the temperature Temp of the transfer case 14 cannot be accurately calculated.

[0047] Therefore, in an embodiment, when a driving force of a magnitude corresponding to the command torque T* cannot be transmitted from the driving force transmission device 2 to the left and right rear wheels 193, 194 due to the magnitude of the driving force generated by the engine 11 or slippage occurring at the wheel 19, the temperature estimation unit 72 estimates the temperature of the transfer case 14 based on an estimated value of the driving force input to the housing 20 of the driving force transmission device 2.

[0048] When slip does not occur in the wheel 19 and the driving force corresponding to the command torque T* cannot be transmitted from the driving force transmission device 2 to the left and right rear wheels 193, 194 due to the small magnitude of the driving force generated by the engine 11, the estimated value is a calculated value of the driving force transmitted from the engine 11 to the housing 20 of the driving force transmission device 2 through the transmission shaft 15. This calculated value can be obtained by, for example, multiplying the magnitude of the driving force of the engine 11 obtained by the operation amount of the accelerator pedal 110 (the torque of the crankshaft as the output shaft) by the gear ratio of the transmission 12 and the gear ratio of the transfer case 14. Hereinafter, the torque (i.e., the torque of the transmission shaft 15) obtained by multiplying the driving force generated by the engine 11 by the gear ratio of the transmission 12 and the gear ratio of the transfer case 14 is referred to as "torque on the shaft". The torque on the shaft is a converted value obtained by converting the torque of the output shaft of the engine 11 into the input torque input to the housing 20 of the driving force transmission device 2.

[0049] Furthermore, when slip occurs in at least one of the left and right rear wheels 193, 194, the estimated value of the driving force input to the housing 20 of the driving force transmission device 2 is a conversion value obtained by converting the grip of the left and right rear wheels 193, 194 where slip occurs into the torque of the propeller shaft 15 (i.e., the torque of the housing 20 of the driving force transmission device 2). Furthermore, when slip occurs in at least one of the left and right front wheels 191, 192, the estimated value of the driving force input to the housing 20 of the driving force transmission device 2 is a calculated value obtained by subtracting the conversion value obtained by converting the grip of the left and right front wheels 191, 192 where slip occurs into the torque of the housing 20 of the driving force transmission device 2 from the shaft torque. The conversion value Tg obtained by converting the grip into the torque of the housing 20 of the driving force transmission device 2 is obtained by the following equation (3).

[0050] Tg=rt / Rf×W×μ···(3)

[0051] Here, rt is the tire radius of the wheel 19, and Rf is the gear ratio of the transfer case 14. When slip occurs in one or both of the left and right front wheels 191, 192, W is the front wheel load; when slip occurs in one or both of the left and right rear wheels 193, 194, W is the rear wheel load. μ is the friction coefficient (dynamic friction coefficient) between the tire of the wheel 19 and the road surface. Here, it is assumed that the gear ratio of the transfer case 14 (paired teeth of the ring gear 142 / number of teeth of the pinion 141) and the reduction ratio of the rear differential 16 (number of teeth of the ring gear 165 / number of teeth of the pinion shaft 160) are the same.

[0052] In addition, the road surface friction coefficient μ may be a value estimated from the road surface condition imaged by, for example, an in-vehicle camera that may be used, or may be obtained by the following equation (4).

[0053]

[0054] Here, Glo is the acceleration in the front-rear direction of the vehicle, and Gla is the acceleration in the lateral direction (the width direction of the vehicle). The value of the acceleration can be obtained from the detection value of the acceleration sensor. If the road friction coefficient is zero, the acceleration in the front-rear direction of the vehicle and the acceleration in the lateral direction are both zero, and therefore, according to equation (4), the road friction coefficient can be estimated with the acceleration actually produced in the front-rear direction and the lateral direction of the vehicle.

[0055] Figure 4 2 is a flowchart of an example of a calculation process executed by the controller 60. The controller 60 repeatedly executes the process shown in the flowchart every predetermined control cycle (for example, 5 ms).

[0056] The controller 60 calculates a torque command value based on the vehicle information (step S1). Next, the controller 60 determines whether slip occurs in any one of the left and right front wheels 191, 192 and the left and right rear wheels 193, 194 among the wheels 19 (step S2). For example, the determination is made depending on whether the ratio of the rotation speed of the wheel with the fastest wheel speed to the rotation speed of the wheel with the slowest wheel speed among the wheels 19 is equal to or greater than a threshold value.

[0057] When it is determined in step S2 that slip does not occur ("No" in S2), the controller 60 determines whether the command torque is equal to or less than the shaft torque (step S3). Then, when the command torque is equal to or less than the shaft torque ("Yes" in S3), the controller 60 calculates the load amount H(n) of the transfer case 14 by equation (2) (step S4). On the other hand, when the command torque is greater than the shaft torque ("No" in S3), the controller 60 calculates the load amount H(n) of the transfer case 14 by the following equation (5) (step S5).

[0058] H(n)=K3×∑{K4×Tq×Vf-K5×H(n-1)}···(5)

[0059] Here, K3, K4, K5 and Vf are the same as in equation (2), and Tq is the shaft torque.

[0060] Furthermore, when the controller 60 determines in step S2 that slip occurs ("Yes" in S2), the controller 60 determines whether slip occurs in one or both of the left and right rear wheels 193, 194 (step S6). When slip occurs in at least one of the left and right rear wheels 193, 194 ("Yes" in S6), the controller 60 calculates the load amount H(n) of the transfer case 14 by the following equation (6) (step S7).

[0061] H(n)=K3×Σ{K4×Tg×Vf-K5×H(n-1)}···(6)

[0062] Here, K3, K4, K5 and Vf are the same as those in equation (2), and Tg is a converted value of the grip force calculated by equation (3) when W is the rear wheel load.

[0063] On the other hand, when slip does not occur in the left and right rear wheels 193, 194 but slip occurs in at least one of the left and right front wheels 191, 192 ("No" in S6), the controller 60 calculates the load H(n) of the transfer case 14 by the following equation (7) (step S8).

[0064] H(n)=K3×∑{K4×(Tq-Tg)×Vf-K5×H(n-1)}···(7)

[0065] Here, K3, K4, K5 and Vf are the same as those in equation (2), and Tq is the axial torque. Tg is the converted value of the grip force calculated by equation (3) when W is the front wheel load.

[0066] The controller 60 calculates the load amount H(n) of the transfer case 14 in any one of steps S4, S5, S7 and S8, and then calculates the temperature Temp of the transfer case 14 according to equation (1) using the calculated load amount H(n) (step S9) and determines whether the temperature Temp of the transfer case 14 is equal to or higher than a threshold value (step S10). Then, when the temperature Temp of the transfer case 14 is equal to or higher than the threshold value ("Yes" in S10), the torque command value calculated in step S1 is subjected to a reduction correction (step S11). Specifically, the reduction correction of the torque command value can be performed by multiplying the torque command value calculated in step S1 by a coefficient less than 1 and setting the value obtained by the multiplication operation as the correction torque command value, and can also be performed by subtracting a predetermined value from the torque command value and setting the value obtained by the subtraction operation as the correction torque command value. In addition, the correction torque command value can be limited to a predetermined value or less.

[0067] Then, the controller 60 calculates a current command value based on the torque command value calculated in step S1 or the corrected torque command value decremented and corrected in step S11 (step S12), and performs current feedback control so that a current corresponding to the current command value is supplied to the electromagnetic coil 53 (step S13).

[0068] In the flowchart, the operation of step S1 is as the operation of the torque command value calculation means 61, and the operations of steps S2 to S9 are as the operations of the temperature estimation means 62. Furthermore, steps S10 and S11 are as the operations of the overheat protection control means 63, the operation of step S12 is as the operation of the current command value calculation means 64, and the operation of step S13 is as the operation of the current control means 65. The processing of the above-mentioned flowchart may be modified as follows.

[0069] Modification Example 1

[0070] In the operation of step S7, when slip occurs in only one of the left and right rear wheels 193, 194 among the wheels 19, a value may be set as a conversion value of grip force, which is obtained by calculating the load of the wheel 19 where slip occurs in consideration of the acceleration in the front-rear direction and the lateral direction of the vehicle, doubling the calculated load, and applying the doubled load as a variable W to equation (3). In addition, in the operation of step S8, when slip occurs in only one of the left and right front wheels 191, 192 among the wheels 19, a value may be set as a conversion value of grip force, which is obtained by calculating the load of the wheel 19 where slip occurs in consideration of the acceleration in the front-rear direction and the lateral direction of the vehicle, doubling the calculated load, and applying the doubled load as a variable W to equation (3).

[0071] Modification Example 2

[0072] In addition to Modification Example 1, when the rear differential 16 having a differential limiting function for suppressing the differential rotation of the left and right rear wheels 193, 194 is used, a value may be set as a conversion value of the grip force, which is obtained by further multiplying the load of the wheel (slipping wheel) among the wheels 19 by a coefficient of (torque bias ratio + 1) in consideration of the acceleration in the front-rear direction and the lateral direction of the vehicle and applying the multiplied value as a variable W to equation (3). Furthermore, when the front differential 13 having a differential limiting function for suppressing the differential rotation of the left and right front wheels 191, 192 is used, a value may be set as a conversion value of the grip force, which is obtained by further multiplying the load of the wheel (slipping wheel) among the wheels 19 by a coefficient of (torque bias ratio + 1) in consideration of the acceleration in the front-rear direction and the lateral direction of the vehicle and applying the multiplied value as a variable W to equation (3).

[0073] Modification Example 3

[0074] When the road surface friction coefficient μ can be estimated individually for each wheel 19 , the μ value used in equation (3) may be an individually estimated value.

[0075] Effects of the Embodiments

[0076] According to the embodiment of the present invention described above, even when slip occurs in the wheel 19 or the torque on the shaft is less than the torque command value T, the temperature of the transfer case 14 can be estimated with high accuracy, thereby being able to suppress the reduction of the driving force transmitted by the driving force transmission device 2 more than required and appropriately perform overheat protection of the transfer case 14. In addition, according to Modification Examples 1 to 3, the temperature of the transfer case 14 can be estimated more accurately.

[0077] Additional Notes

[0078] Although 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 not all combinations of features described in the embodiment are essential to the means for solving the problems of the present invention.

[0079] The present invention can be modified appropriately without departing from the spirit of the present invention by omitting a part of the configuration or adding or replacing the configuration. For example, in the above embodiment, the case where the temperature of the transfer case 14 as the heat generating position of the driving force transmission system 10 is estimated has been described, but the present invention is not limited thereto, and for example, the temperature estimation and overheat protection of the heat generating position can be performed by setting the rear differential 16, the propeller shaft 15, or the driving force transmission device 2 as the heat generating position.

[0080] In addition, in the above embodiment, although it has been described that the driving force transmission device 2 is arranged between the drive shaft 15 and the rear differential 16, the arrangement of the driving force transmission device 2 is not limited to this, and the driving force transmission device 2 can, for example, be arranged between the rear differential 16 and the left and right rear wheels 193, 194.

[0081] In addition, in the above embodiment, although it has been described that the main clutch 3 is pressed by the cam mechanism 4 and the electromagnetic clutch mechanism 5, the present invention is not limited thereto, and the main clutch 3 may be pressed by, for example, an electric motor or a hydraulic piston.

[0082] In addition, in the above-mentioned embodiment, although the present invention has been described as being applied to a four-wheel drive vehicle 1 in which the left and right front wheels 191, 192 are main drive wheels (the driving force of the engine 11 is constantly transmitted to the main drive wheels) and the left and right rear wheels 193, 194 are auxiliary drive wheels (the driving force of the engine 11 is transmitted to the auxiliary drive wheels depending on the vehicle state), the present invention can also be applied to a four-wheel drive vehicle in which the left and right rear wheels are main drive wheels and the left and right front wheels are auxiliary drive wheels.

Claims

1. A vehicle control device (6), the vehicle control device (6) being mounted on a four-wheel drive vehicle (1) and controlling a driving force transmission device (2), the four-wheel drive vehicle (1) comprising a driving force transmission system (10), the driving force transmission system (10) distributing the driving force of a driving source to a main driving wheel and an auxiliary driving wheel, the driving force transmitted to the auxiliary driving wheel being adjustable by the driving force transmission device (2), the vehicle control device (6) being characterized in that it comprises an electronic control unit, wherein: The electronic control unit is configured to calculate a command torque based on vehicle information, the command torque indicating the driving force to be transmitted from an input rotating member of the driving force transmission device (2) to an output rotating member of the driving force transmission device (2); The electronic control unit is configured to estimate a temperature of a heat generating location in the driving force transmission system (10) based on the command torque; and The electronic control unit is configured to estimate the temperature of the heat generation location based on an estimated value of the driving force input to the input rotating member when the driving force corresponding to the command torque cannot be transmitted to the auxiliary drive wheel due to the magnitude of the driving force generated by the driving source or the occurrence of wheel slip.

2. The vehicle control device (6) according to claim 1, characterized in that: The electronic control unit is configured to estimate the temperature of the heat generation location by using a first conversion value obtained by converting a gripping force of the auxiliary drive wheel into a torque of the input rotation member as the estimation value when slip occurs in the auxiliary drive wheel.

3. The vehicle control device (6) according to claim 1, characterized in that: The electronic control unit is configured to estimate the temperature of the heat generation location when slip occurs in the main drive wheel by using a second calculated value obtained by subtracting a second converted value from a first calculated value as the estimated value, wherein the second converted value is a value obtained by converting a gripping force of the main drive wheel into a torque of the input rotating member, and the first calculated value is a calculated value of the driving force transmitted from the drive source to the input rotating member.

4. The vehicle control device (6) according to claim 2 or 3, characterized in that: The electronic control unit is configured to calculate the grip force by taking into account a load of a wheel when the slip occurs.

5. The vehicle control device (6) according to any one of claims 1 to 3, characterized in that: The electronic control unit is configured to estimate the temperature of the heat generation location by using a first calculated value as the estimated value when slip does not occur in the main drive wheels and the auxiliary drive wheels and a first calculated value is less than the command torque, the first calculated value being a calculated value of the drive force transmitted from the drive source to the input rotating member.

6. The vehicle control device (6) according to any one of claims 1 to 3, characterized in that: The electronic control unit is configured to suppress heat generation at the heat generating location by reducing the driving force transmitted by the driving force transmission device (2) when it is determined that the heat generating location is in an overheated state by the estimated temperature.

7. A four-wheel drive vehicle (1), characterized in that include: A driving force transmission system (10) configured to distribute the driving force of a driving source to a main driving wheel and an auxiliary driving wheel; as well as A vehicle control device (6), the vehicle control device (6) comprising an electronic control unit, the electronic control unit being configured to control a driving force transmission device (2), the driving force transmitted to the auxiliary driving wheel being adjustable via the driving force transmission device (2), wherein: The electronic control unit is configured to calculate a command torque based on vehicle information, the command torque indicating the driving force to be transmitted from an input rotating member of the driving force transmission device (2) to an output rotating member of the driving force transmission device (2); The electronic control unit is configured to estimate a temperature of a heat generating location in the driving force transmission system (10) based on the command torque; as well as The electronic control unit is configured to estimate the temperature of the heat generation location based on an estimated value of the driving force input to the input rotating member when the driving force corresponding to the command torque cannot be transmitted to the auxiliary drive wheel due to the magnitude of the driving force generated by the driving source or the occurrence of wheel slip.

8. The four-wheel drive vehicle (1) according to claim 7, characterized in that: The driving force transmission system (10) comprises: a transmission shaft (15) for transmitting the driving force in the front-rear direction of the four-wheel drive vehicle (1); and a transfer case (14) for transmitting the driving force to the transmission shaft (15); and The electronic control unit is configured to estimate a temperature of the transfer case as the heat generating location.

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