Center differential rotation restraint force control device

Abstract

To provide a differential rotation restriction force control device of a center differential having an increased lateral force which can be generated by a tire upon the turning.SOLUTION: A differential rotation restriction force control device of a center differential includes: a head-out state detection part 140 which is provided on a vehicle having a center differential 41 which transfers a driving force generated by a traveling power source 10 to a front wheel driving device 50 and a rear wheel driving device 60, and permits such differential rotations and a differential rotation restriction device 42 which restricts the differential rotations, and detects that the differential rotation restriction force control device of the center differential for controlling a restriction force of the differential rotation restriction device is in the turning state, and detects such a head-out state that the differential rotation restriction force control device of the center differential which controls the restriction force of the differential rotation restriction device is in the turning state and a yaw rate and a side slip angle get to the same sign; and a restriction force control part 120 which controls the restriction force so that a difference between a driving force of a front wheel by the output of the traveling power source and an absolute value of a braking force of the front wheel according to an internal part circulation torque of the center differential decreases in accordance with the detection of the head-out state.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a differential rotation restraint force control device for a center differential of an AWD vehicle. [Background technology]

[0002] For example, in an automobile such as an AWD (four-wheel drive) passenger car, the output of a driving power source such as an engine is transmitted to the front-wheel drive unit and rear-wheel drive unit via a center differential, which is a differential mechanism that allows differential rotation (difference in rotational speed) between the front and rear wheels. Known center differentials use, for example, a planetary gear set to distribute torque unevenly between the front and rear wheels (other than 50:50). It is also known to provide a center differential with a limited slip differential (LSD) that restricts differential rotation, and to vary the restraining force generated by the limited slip differential device depending on the vehicle's turning state, etc.

[0003] As a technology relating to a vehicle driving force distribution control device, for example, Patent Document 1 describes a technique for an on-demand AWD vehicle in which one of the front wheels or rear wheels is always driven and driving force can be transmitted to the other wheel via an electronically controlled coupling, in which the fastening force of the electronically controlled coupling is set according to the wheel speed and the understeer or oversteer state, and the driving force distribution is corrected according to the difference in front and rear wheel speeds and the acceleration state due to the accelerator. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-261483 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology described in Patent Document 1 increases the torque transmitted to the rear wheels when understeer occurs, reducing the drive torque of the front wheels and increasing the lateral force that the tires can generate. With this technology, even when control intervenes, drive force is generated at the front wheels as long as the driver is pressing the accelerator, so it is not possible to make maximum use of the friction force that the tires can generate as lateral force. In view of the above-mentioned problems, an object of the present invention is to provide a differential rotation restraint force control device for a center differential that increases the lateral force that can be generated by tires during cornering. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, a center differential differential rotation restraint force control device according to one aspect of the present invention is provided on a vehicle that transmits driving force generated by a power source for driving to a front-wheel drive unit that drives the front wheels and a rear-wheel drive unit that drives the rear wheels, and that has a center differential that allows differential rotation between the front-wheel drive unit and the rear-wheel drive unit, and a differential rotation restraint device that generates a restraint force that restrains the differential rotation, and that controls the restraint force of the differential rotation restraint device, and includes a head-out state detection unit that detects a head-out state in which the vehicle is in a turning state and the yaw rate and sideslip angle of the vehicle body have the same sign, and a driving force for the front wheels by the output of the power source for driving in response to the detection of the head-out state, When a difference in rotation speed occurs between the front wheels and the rear wheels, the difference is transmitted. the absolute value of the braking force of the front wheels due to the internal circulating torque of the center differential; and is equal to and a restraining force control unit that controls the restraining force so as to Generally, in a vehicle having a center differential, when a difference in rotational speed occurs between the front and rear wheels, an internal circulating torque is transmitted from the wheel with the faster rotational speed to the wheel with the slower rotational speed. A head-out state, in which the yaw rate and sideslip angle of the vehicle body have the same sign, is a vehicle posture in which the front of the vehicle (the forward side along the centerline in the vehicle width direction) is oriented toward the outside of the turn relative to the vehicle's direction of travel. In this case, the front wheels have a larger turning radius than the rear wheels, and their rotational speed is faster. In this case, the internal circulating torque generates a braking force on the front wheels and a driving force on the rear wheels. The magnitude of the internal circulating torque also changes depending on the restraining force of the center differential on the front and rear differential rotation. According to the present invention, when a head-out state occurs, the absolute value of the braking force generated on the front wheels by the internal circulating torque and the driving force of the front wheels by the output of the driving power source are calculated. is equal to By controlling the restraining force, the absolute value of the braking / driving force transmitted by the front wheels to the road surface is reduced, and the lateral force that the front tires can generate is increased. It is now possible to utilize virtually all of the friction force that the front tires can generate as lateral force, The turning ability of the vehicle can be improved.

[0008] In the present invention, a head-in state detection unit is provided that detects a head-in state in which the yaw rate and sideslip angle of the vehicle body are opposite in sign during a turning state, and the restraining force control unit calculates the absolute value of the driving force of the rear wheels due to the output of the driving power source and the braking force of the rear wheels due to the internal circulating torque of the center differential in response to the detection of the head-in state. is equal to The restraining force can be controlled so as to Furthermore, a center differential differential rotation restraint force control device according to another aspect of the present invention is provided on a vehicle that transmits driving force generated by a power source for driving to a front-wheel drive unit that drives the front wheels and a rear-wheel drive unit that drives the rear wheels, and that has a center differential that allows differential rotation between the front-wheel drive unit and the rear-wheel drive unit, and a differential rotation restraint device that generates a restraining force that restrains the differential rotation, and that controls the restraint force of the differential rotation restraint device, and includes a head-in state detection unit that detects a head-in state in which the yaw rate and sideslip angle of the vehicle body are opposite in sign during a turning state, and a driving force for the rear wheels by the output of the power source for driving in response to the detection of the head-in state, When a difference in rotation speed occurs between the front wheels and the rear wheels, the difference is transmitted. the absolute value of the braking force of the rear wheels due to the internal circulating torque of the center differential; and is equal to and a restraining force control unit that controls the restraining force so as to A head-in state, in which the yaw rate and sideslip angle of the vehicle body have opposite signs, is a vehicle posture in which the front of the vehicle is facing toward the inside of the turn relative to the vehicle's direction of travel.In this case, the rear wheels have a larger turning radius than the front wheels, and their rotational speed is faster. In this case, the internal circulating torque generates a driving force on the front wheels and a braking force on the rear wheels. According to each of these inventions, when a head-in state occurs, the absolute value of the braking force generated on the rear wheels by the internal circulating torque is and , the driving force of the rear wheels due to the output of the driving power source, is equal to By controlling the restraining force, the absolute value of the braking / driving force transmitted by the rear wheels to the road surface is reduced, and the lateral force that the rear tires can generate is increased. It is now possible to utilize virtually all of the friction force that the rear tires can generate as lateral force, Improves vehicle stability and prevents the vehicle from going into a spin 。 [Effects of the Invention]

[0009] As described above, according to the present invention, it is possible to provide a differential rotation restraint force control device for a center differential that increases the lateral force that can be generated by tires during cornering. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram schematically illustrating the configuration of a vehicle having an embodiment of a differential rotation restraint force control device for a center differential to which the present invention is applied. [Figure 2] 10A and 10B are diagrams illustrating the state of internal circulating torque in a head-out state and a head-in state. [Figure 3] 4 is a flowchart showing differential rotation restraining force control of a center differential in the embodiment. [Figure 4] 5A and 5B are diagrams illustrating the state of braking and driving forces of the front and rear wheels in a head-out state in the embodiment. [Figure 5] 5A and 5B are diagrams illustrating the state of braking and driving forces of the front and rear wheels when the vehicle is in a head-in state according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of a differential rotation restraining force control device for a center differential to which the present invention is applied will be described. The differential rotation restraint force control device for a center differential according to the embodiment is installed in an automobile such as an all-wheel drive (AWD) four-wheel passenger car, for example. FIG. 1 is a diagram showing a schematic configuration of a vehicle having a differential rotation restraining force control device for a center differential according to an embodiment.

[0012] As shown in FIG. 1, a vehicle 1 includes an engine 10, a torque converter 20, a transmission mechanism 30, an AWD transfer 40, a front differential 50, a rear differential 60, and the like.

[0013] The engine 10 is a power source for driving the vehicle 1, and is, for example, an internal combustion engine such as a gasoline engine. The torque converter 20 is a fluid coupling that transmits the output of the engine 10 to the transmission mechanism 30, and functions as a starting device that enables the vehicle to start moving from a zero vehicle speed. The torque converter 20 is provided with a lock-up clutch that directly connects the input side and the output side. The transmission mechanism 30 is, for example, a continuously variable transmission (CVT) having a variator consisting of a pair of variable pulleys and a chain, belt, etc., or a stepped AT having multiple rows of planetary gear sets, and is used to increase or decrease the output of the engine 10 input from the torque converter 20. The output of the transmission mechanism 30 is transmitted to the AWD transfer 40 .

[0014] The AWD transfer 40 is a driving force transmission device that distributes and transmits the driving force input from the speed change mechanism 30 to the front differential 50 and the rear differential 60 . The AWD transfer 40 is configured to include a center differential 41, a transfer clutch 42, and the like. The center differential 41 is configured to have, for example, a compound planetary gear set, and is a driving force distribution mechanism that distributes torque to the front differential 50 and the rear differential 60 so that the torque distribution ratio is, for example, about 35:65. The center differential 41 also functions as a differential mechanism that absorbs the differential rotation between the front differential 50 and the rear differential 60 caused by, for example, a difference in the trajectories of the front and rear wheels during cornering.

[0015] The transfer clutch 42 is a differential limiting mechanism (differential rotation limiting device, LSD) that restricts the differential between the front and rear wheel output portions of the center differential 41. The transfer clutch 42 includes, for example, a wet multi-plate clutch driven by hydraulic pressure or electromagnetic force, and its fastening force (clutch clamping force), i.e., differential limiting torque (differential rotation restricting force), is controlled by the transmission control unit 120, which will be described later. The AWD transfer 40 can adjust the driving force distribution ratio between the front and rear wheels steplessly, for example, from 35:65 to 50:50, by changing the fastening force of the transfer clutch 42.

[0016] The front differential 50 performs final deceleration on the front wheel drive force transmitted from the AWD transfer 40 and transmits it to the right front wheel 51 and the left front wheel 52. The front differential 50 also functions as a differential mechanism that absorbs the differential rotation between the right front wheel 51 and the left front wheel 52. The front differential 50, together with a drive shaft (not shown), constitutes a front wheel drive device.

[0017] The rear differential 60 performs final reduction of the rear wheel drive force transmitted from the AWD transfer 40 via a propeller shaft (not shown) and transmits it to the right rear wheel 61 and the left rear wheel 62. The rear differential 60 also functions as a differential mechanism that absorbs the differential rotation between the right rear wheel 61 and the left rear wheel 62. The rear differential 60, together with a propeller shaft and a drive shaft (not shown), constitutes a rear wheel drive device.

[0018] The vehicle is also provided with a brake device 70, which is a braking device. The braking device 70 includes a brake pedal 71, a master cylinder 72, a hydraulic control unit (HCU) 73, a brake FR 74, a brake FL 75, a brake RR 76, a brake RL 77, and the like. The brake pedal 71 is an input unit through which the driver operates the brakes. The master cylinder 72 is connected to the brake pedal 71 and pressurizes the brake fluid in response to depression of the brake pedal 71. The master cylinder 72 is provided with a vacuum booster that amplifies the input from the brake pedal 71 by using the negative pressure in the intake pipe of the engine 10.

[0019] The hydraulic control unit 73 individually increases or decreases the hydraulic pressure of the brake fluid supplied to the wheel cylinder of each wheel for, for example, antilock brake control, yaw control control, automatic brake control, and the like. The hydraulic control unit 73 includes an electric pump that pressurizes the brake fluid, and control valves that individually adjust the hydraulic pressure in each wheel cylinder.

[0020] Brakes FR74, FL75, RR76, and RL77 are provided on right front wheel 51, left front wheel 52, right rear wheel 61, and left rear wheel 62, respectively. Each brake includes a disk-shaped rotor that rotates with the wheel, and a caliper that pressurizes pads against the rotor. The caliper includes a wheel cylinder that presses the pads with the hydraulic pressure of brake fluid supplied from a hydraulic control unit 73.

[0021] The vehicle 1 includes an engine control unit 110, a transmission control unit 120, a steering control unit 130, a behavior control unit 140, etc. Each unit has, for example, an information processing unit such as a CPU, a storage unit such as a RAM or a ROM, an input / output interface, and a bus connecting these. Furthermore, each unit is communicatively connected via an in-vehicle LAN such as a CAN communication system, or directly.

[0022] The engine control unit 110 controls the engine 10 and its accessories in an integrated manner. The engine control unit 110 has a function of adjusting the output of the engine 10 . The engine control unit 110 sets the driver-requested torque based on, for example, the driver's accelerator operation amount, and controls the throttle opening, fuel injection amount, fuel injection timing, ignition timing, valve timing, EGR rate, boost pressure, etc. of the engine 10 so that the actual torque of the engine 10 matches the driver-requested torque.

[0023] The transmission control unit 120 controls the speed change mechanism 30, forward / reverse switching, and the engagement force (restriction force) of the lock-up clutch in the torque converter 20, among other things. In addition, the transmission control unit 120 has the function of changing the differential rotation restraint force by changing the fastening force of the transfer clutch 42 of the AWD transfer 40, thereby controlling the driving force distribution ratio between the front and rear wheels and the internal circulating torque. The transmission control unit 120 functions as a restraining force control section in the differential rotation restraining force control device for the center differential of the present invention.

[0024] The steering control unit 130 controls an electric power steering (EPS) device provided in a steering device (not shown). The steering control unit 130 has a function of controlling an electric motor that generates an assist force in accordance with the steering torque input to the steering wheel by the driver, for example. The steering control unit 130 is connected to a steering angle sensor 131 that detects the steering angle of the steering device.

[0025] The behavior control unit 140 controls the hydraulic control unit 73 and has the function of individually controlling the wheel cylinder hydraulic pressures (correlated with braking force) of the brakes FR74, FL75, RR76, and RL77. The behavior control unit 140 has functions such as anti-lock brake control, which periodically reduces the wheel cylinder hydraulic pressure of a wheel when the wheel locks due to braking to restore rotation, and behavior control, which generates a braking force difference between the left and right wheels when oversteer or understeer behavior occurs to suppress the yaw moment in a direction that suppresses each behavior. To perform these controls, the braking control unit 140 is connected to a vehicle speed sensor 141 that detects the rotation speed of each wheel individually, and a yaw rate sensor 142 that detects the yaw rate of the vehicle body.

[0026] The behavior control unit 140 acquires information about the steering angle detected by the steering angle sensor 131 from the steering control unit 130, and has the function of detecting a head-out state in which the front of the vehicle (the front side in the direction of the left and right central axis of the vehicle body) is directed toward the outside of the turn relative to the direction of travel of the vehicle, and a head-in state in which the front of the vehicle is directed toward the inside of the turn relative to the direction of travel of the vehicle. The behavior control unit 140 functions as a head-out state detection section and a head-in state detection section of the present invention.

[0027] FIG. 2 is a diagram showing a schematic diagram of the state of the internal circulating torque in the head-out state and the head-in state. In the following description, the vehicle's slip angle β and yaw rate γ are both positive when counterclockwise and negative when clockwise in a plan view of the vehicle seen from above. FIG. 2(a) shows the head-out state during a left turn. The head-out state is a state in which the vehicle's sideslip angle β and yaw rate γ have the same sign (both positive when turning left and both negative when turning right).

[0028] The vehicle's sideslip angle β is expressed by the following equation 1.

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[0029] In the head-out state, when comparing the right front wheel 51 with the right rear wheel 61, and the left front wheel 52 with the left rear wheel 62, the turning radius of the front wheels is larger than the turning radius of the rear wheels (the front wheels pass on the outside of the turning circle relative to the rear wheels), and therefore the rotational speed of the front wheels is larger than the rotational speed of the rear wheels. In this case, an internal circulating torque is generated from the front wheel drive unit to the rear wheel drive unit via the AWD transfer 40. As a result, as shown by the arrows in Figure 2(a), the internal circulating torque generates a braking force on the front wheels and a driving force on the rear wheels.

[0030] FIG. 2(b) shows the head-in state during a left turn. The head-in state is a state in which the vehicle's sideslip angle β and yaw rate γ have opposite signs (when turning left, the sideslip angle β is negative and the yaw rate γ is positive; when turning right, the sideslip angle β is positive and the yaw rate γ is negative). In the head-in state, when comparing the right front wheel 51 with the right rear wheel 61, and the left front wheel 52 with the left rear wheel 62, the turning radius of the rear wheels is larger than that of the front wheels (the rear wheels pass on the outside of the turn relative to the front wheels), and therefore the rotational speed of the rear wheels is larger than that of the front wheels. In this case, an internal circulating torque is generated from the rear wheel drive unit to the front wheel drive unit via the AWD transfer 40. As a result, as shown by the arrows in Figure 2(b), the internal circulating torque generates a driving force on the front wheels and a braking force on the rear wheels.

[0031] In this embodiment, the internal circulating torque of the AWD transfer 40 described above is controlled by controlling the restraining force (restraint rate) of the center differential 41 by the transfer clutch 42, thereby increasing the lateral force that the front tires can generate in a head-out state, and increasing the lateral force that the rear tires can generate in a head-in state. FIG. 3 is a flowchart showing the differential rotation restraining force control of the center differential in the embodiment. Each step will be explained in order below.

[0032] <Step S01: Obtain steering angle, vehicle speed, and required driving force> First, the behavior control unit 140 serving as a head-out state detection unit and a head-in state detection unit acquires various parameters required for control from various sensors. The behavior control unit 140 acquires information about the steering angle δ detected by the steering angle sensor 131 from the steering control unit 130 . In addition, the behavior control unit 140 acquires information relating to the vehicle speed V detected by the vehicle speed sensor 141 . Furthermore, the behavior control unit 140 acquires information relating to the driver's requested torque (requested driving force) from the engine control unit 10. Then, proceed to step S02.

[0033] <Step S02: Calculate sideslip angle and yaw rate> The behavior control unit 140 uses the above-mentioned equation 1 and the output of the yaw rate sensor 142 to calculate the vehicle's sideslip angle β and yaw rate γ. Then, proceed to step S03.

[0034] <Step S03: Head-out state / head-in state determination> The behavior control unit 140 compares the signs of the sideslip angle β and the yaw rate γ calculated in step S02. If the sideslip angle β and the yaw rate γ have the same sign, it is determined that the vehicle is in a head-out state, and the process proceeds to step S04. If the sideslip angle β and the yaw rate γ have opposite signs, it is determined that the vehicle is in a head-in state, and the process proceeds to step S05.

[0035] <Step S04: Calculation of front tire lateral force maximization constraint rate> The transmission control unit 120 calculates the constraint rate of the transfer clutch 42 (front tire lateral force maximization constraint rate) that can maximize the lateral force that can be generated by the front tire, depending on the head-out state determined by the behavior control unit 140. The restraint ratio is a parameter that indicates the restraint force (fastening force) of the transfer clutch 42, and is 0 in a free state where no restraint force is generated other than the unavoidable friction, and is 1 in a locked state where differential rotation is not permitted. Braking / driving force F due to internal circulating torque i is expressed by Equation 2.

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[0036] <Step S05: Calculation of rear tire lateral force maximization constraint ratio> The transmission control unit 120 calculates the constraint rate of the transfer clutch 42 (rear tire lateral force maximization constraint rate) that can maximize the lateral force that can be generated by the rear wheel tires, depending on the head-in state determined by the behavior control unit 140. This constraint ratio p is expressed by Equation 5.

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[0037] <Step S06: Determine upper and lower limits of calculated constraint rate> The transmission control unit 120 determines whether the restraint ratio p calculated in step S04 or step S05 is equal to or greater than 0 and equal to or less than 1 (whether it is within a range in which the transfer clutch 42 can be controlled). If the constraint rate p is equal to or greater than 0 and equal to or less than 1, the process proceeds to step S08, and otherwise the process proceeds to step S07.

[0038] <Step S07: Determine the lower limit of the calculated constraint rate> The transmission control unit 120 determines whether the restraint rate p calculated in step S04 or step S05 is smaller than zero. If the constraint rate p is smaller than 0, the process proceeds to step S09; otherwise, the constraint rate p is assumed to be larger than 1, and the process proceeds to step S10.

[0039] <Step S08: Setting the calculated constraint rate to the target constraint rate> The transmission control unit 120 sets the restraint ratio p calculated in step S04 or step S05 as a target restraint ratio used for controlling the restraint force of the transfer clutch 42. Then, proceed to step S11.

[0040] <Step S09: Set the target constraint rate to 0> The transmission control unit 120 sets the target constraint ratio to zero. Then, proceed to step S11.

[0041] <Step S10: Set the target constraint rate to 1> The transmission control unit 120 sets the target constraint ratio to one. Then, proceed to step S11.

[0042] <Step S11: Execute Transfer Clutch Binding Force Control> The transmission control unit 120 controls the restraining force (engagement force) of the transfer clutch 42 based on the set target restraint ratio. After that, the series of processes is ended (returned).

[0043] The effect of the differential rotation restraining force control of the center differential will now be described. First, a description will be given of a state in which the engine 10 generates driving torque in a head-out state (accelerator-on state). In this case, it is assumed that the turning is typically performed at a low speed with a small turning radius on a road surface with a relatively high coefficient of friction (μ). In this case, it is necessary to improve the turning ability of the vehicle.

[0044] FIG. 4 is a diagram showing the state of the braking and driving forces of the front and rear wheels in a head-out state in the embodiment. Figure 4(a) shows the driving force due to throttle operation and the braking / driving force due to internal circulating torque separately, while Figure 4(b) shows the total braking / driving force resulting from the combination of these (same as Figure 5). As described above, in a head-out state, the internal circulating torque generates a braking force on the front wheels and a driving force on the rear wheels. On the other hand, the driving force requested by the driver through accelerator operation is transmitted as driving force to the front and rear wheels via the AWD transfer 40 in a distribution set by the transmission control unit 120 . In this embodiment, the driving force of the right front wheel 51 and the left front wheel 52 required by the driver is balanced with the braking force of the right front wheel 51 and the left front wheel 52 due to the internal circulation torque, and the differential rotation restraint force is controlled so that the braking / driving force (tire generated force in the longitudinal direction) of the right front wheel 51 and the left front wheel 52 becomes zero, so that all of the friction force that can be generated by the tires of the right front wheel 51 and the left front wheel 52 can be used for lateral force. As a result, the right front wheel 51 and the left front wheel 52 are able to generate a high cornering force, improving the turning ability of the vehicle.

[0045] Next, a state in which the engine 10 generates driving torque in the head-in state (accelerator-on state) will be described. In this case, it is assumed that the vehicle is turning at high speed and with a large turning radius on a road surface with a relatively low coefficient of friction. In this case, it is important to reduce the likelihood of the vehicle going into a spin.

[0046] FIG. 5 is a diagram showing the state of the braking and driving forces of the front and rear wheels in a head-in state in the embodiment. As described above, in the head-in state, the internal circulating torque generates a driving force on the front wheels and a braking force on the rear wheels. On the other hand, the driving force requested by the driver through accelerator operation is transmitted as driving force to the front and rear wheels via the AWD transfer 40 in a distribution set by the transmission control unit 120 . In this embodiment, the driving force of the right rear wheel 61 and the left rear wheel 62 required by the driver is balanced with the braking force of the right rear wheel 61 and the left rear wheel 62 due to the internal circulation torque, and the differential rotation restraint force is controlled so that the braking / driving force (tire generated force in the longitudinal direction) of the right rear wheel 61 and the left rear wheel 62 becomes zero, so that all of the friction force that can be generated by the tires of the right rear wheel 61 and the left rear wheel 62 can be used for lateral force. As a result, the right rear wheel 61 and the left rear wheel 62 are able to generate a high cornering force, improving the stability of the vehicle and preventing the vehicle from falling into a spin state.

[0047] Next, a state in which the engine 10 is not generating drive torque (accelerator-off state), regardless of whether the state is head-out or head-in, will be described. In this case, the driver is not requesting driving force, and it is assumed that the driver wants to make a stable turn. In this embodiment, in such a case, the target restraint ratio is set to 0, the transfer clutch 42 is in a free state, and no internal circulating torque is generated, so the longitudinal forces on both the front and rear wheels can be reduced. In this case, the longitudinal forces on both the front and rear wheels consist only of the braking force of the engine brake and the brake device 70. This leaves more room for the frictional force of the front and rear wheels to be used for lateral force, allowing for stable cornering.

[0048] Furthermore, when exiting a corner (when the turning state ends), it is desirable to increase the driving force of the four wheels and accelerate the vehicle stably. In this embodiment, as the yaw rate and sideslip angle of the vehicle both approach 0, the set target restraint ratio increases and ultimately reaches 1 (locked state). This effectively utilizes the friction of the four wheels to transmit driving force to the road surface, allowing for stable acceleration.

[0049] (Variation) The present invention is not limited to the above-described embodiment, and various modifications and variations are possible, and these are also within the technical scope of the present invention. (1) The configurations of the vehicle and the differential rotation restraint force control device for the center differential are not limited to the above-described embodiment, and can be modified as appropriate. For example, in the embodiment, an engine is used as a power source for running, but this is not limited to this, and the present invention can also be applied to engine-electric hybrid vehicles and vehicles that use only an electric motor as a power source for running. (2) In the embodiment, a planetary gear type center differential is used, but this is not limiting, and other types of center differentials, such as a bevel gear type, may also be used. (3) The method for calculating the slip ratio of the vehicle and the formula for calculating the restraining force are not limited to those described in the embodiment and can be modified as appropriate. For example, in the embodiment, the equivalent CP of the front and rear tires is stored in advance as a known value, but instead, the equivalent CP may be sequentially estimated based on the behavior of the vehicle, etc. (4) In the embodiment, the control is performed depending on the head-out state and the head-in state, but a simpler configuration in which the control is performed for only one of these states may also be used. [Explanation of symbols]

[0050] 1 vehicle 10 engines 20 Torque converter 30 Transmission mechanism 40 AWD transfer 41 Center differential 42 Transfer clutch 50 Front differential 51 Right front wheel 52 Left front wheel 60 Rear differential 61 Right rear wheel 62 Left rear wheel 70 Brake device 71 Brake pedal 72 Master cylinder 73 Hydraulic control unit 74 Brake FR 75 Brake FL 76 Brake RR 77 Brake RL 110 Engine control unit 120 Transmission control unit 130 steering control unit 131 steering angle sensor 140 behavior control unit 141 vehicle speed sensor 142 Yaw rate sensor

Claims

1. A differential rotation restraint force control device for a center differential is provided on a vehicle that transmits driving force generated by a driving power source to a front-wheel drive unit that drives the front wheels and a rear-wheel drive unit that drives the rear wheels, and that has a center differential that allows differential rotation between the front-wheel drive unit and the rear-wheel drive unit, and a differential rotation restraint device that generates a restraint force that restrains the differential rotation, and that controls the restraint force of the differential rotation restraint device, a head-out state detection unit that detects a head-out state in which the vehicle is in a turning state and the yaw rate and sideslip angle of the vehicle body have the same sign; a restraining force control unit that controls the restraining force in response to detection of the head-out state so that the absolute value of the driving force of the front wheels due to the output of the driving power source and the braking force of the front wheels due to the internal circulation torque of the center differential that is transmitted when a difference in rotational speed occurs between the front wheels and the rear wheels are equal. A differential rotation restraint force control device for a center differential, characterized by:

2. a head-in state detection unit that detects a head-in state in which the yaw rate and sideslip angle of the vehicle body are opposite in sign during a turning state; The restraining force control unit controls the restraining force in response to detection of the head-in state so that an absolute value of a driving force of the rear wheels due to an output of the driving power source and an absolute value of a braking force of the rear wheels due to an internal circulating torque of the center differential are equal.

2. The differential rotation restraint force control device for a center differential according to claim 1, wherein:

3. A differential rotation restraint force control device for a center differential is provided on a vehicle that transmits driving force generated by a driving power source to a front-wheel drive unit that drives the front wheels and a rear-wheel drive unit that drives the rear wheels, and that has a center differential that allows differential rotation between the front-wheel drive unit and the rear-wheel drive unit, and a differential rotation restraint device that generates a restraint force that restrains the differential rotation, and that controls the restraint force of the differential rotation restraint device, a head-in state detection unit that detects a head-in state in which the yaw rate and sideslip angle of the vehicle body are opposite in sign during a turning state; a restraining force control unit that controls the restraining force in response to the detection of the head-in state so that the absolute value of the driving force of the rear wheels due to the output of the driving power source and the braking force of the rear wheels due to the internal circulation torque of the center differential that is transmitted when a difference in rotation speed occurs between the front wheels and the rear wheels are equal. A differential rotation restraint force control device for a center differential, characterized by:

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