Driving assistance devices

Abstract

To provide an operation support device which can encourage a driver to perform an accelerator operation increasing lateral force of a tire during turning of a vehicle.SOLUTION: An operation support device is installed in a vehicle 1 including: a transfer 40 which transfers driving force generated by a travelling power source 10 according to accelerator operation into a front wheel drive device 50 and a rear wheel drive device 60 and allows differential rotation; and a differential rotation restraining device 42 which occurs binding force to restrain differential rotation. The operation support device comprises: a target accelerator operation amount setting part 150 which sets a target accelerator operation amount according to detection of the head out state where a yaw rate γ of a vehicle body and an angle of sideslip have same sign during turning of the vehicle to decrease difference of absolute values between driving force of a front wheel by the travelling power source and brake force of the front wheel by internal circulation torque of the transfer; and an information presentation part 151 which presents information of the target accelerator operation amount to a driver.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a driving assistance device that presents a target accelerator operation amount to a driver when turning. [Background technology]

[0002] As a technology relating to the control of automobiles during cornering, for example, Patent Document 1 describes a vehicle attitude control device that generates a target yaw moment based on the deviation between a standard yaw rate and an actual yaw rate, in order to suppress understeer and tuck-in caused by accelerator operation during cornering, and applies the braking / driving force required to each wheel to achieve this target yaw moment. It also describes that an oversteer or understeer state is determined from information on vehicle behavior such as yaw rate, yaw rate deviation, vehicle speed, and lateral acceleration. Patent document 2 describes a control device for an all-wheel drive vehicle that applies hydraulic pressure to the reverse brake that constitutes the forward / reverse switching mechanism when the steering wheel is turned while the vehicle is coasting with the accelerator off and the hydraulic pressure (clamping force) of the transfer clutch is not reduced, in order to prevent abnormal noise that may arise from the gears in the drive system.This control device applies hydraulic pressure to the reverse brake that constitutes the forward / reverse switching mechanism when both the first condition, in which the torque related to the reduction drive gear becomes approximately zero, and the second condition, in which the torque related to the reduction driven gear becomes approximately zero, are met. It also describes an internal circulating torque that is exchanged between the front and rear wheels via the transfer clutch due to the differential rotation of the front and rear wheels. Furthermore, as a technique for presenting information to a driver while driving, Patent Document 3 describes a navigation device that calculates a recommended speed for a vehicle based on road condition information that indicates road conditions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-61251 A [Patent Document 2] Japanese Patent Application Publication No. 2019-166998 [Patent Document 3] International Publication No. WO2012 / 114382 Summary of the Invention [Problem to be solved by the invention]

[0004] When the vehicle is turning, in a head-out state where the front wheels pass on the outside of the turning circle relative to the rear wheels, a braking force is generated on the front wheels due to the internal circulating torque of the AWD transfer case. On the other hand, in a head-in state where the rear wheels pass on the outside of the turning circle relative to the front wheels, a braking force is generated on the rear wheels due to the internal circulating torque of the AWD transfer case. The braking force caused by such internal circulating torque reduces the lateral force generated by the tire, further promoting head-in and head-out states.

[0005] In contrast, a driver with high driving skills can apply driving force to the tires by operating the accelerator to cancel out the braking force caused by the internal circulating torque, increasing the lateral force of the tires and enabling stable driving. However, it may be difficult for an average driver to determine the optimum accelerator operation amount in this case. In view of the above-mentioned problems, an object of the present invention is to provide a driving assistance device that can prompt a driver to operate the accelerator in a manner that increases the lateral force generated by the tires when the vehicle is turning. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, a driving assistance device according to a first aspect of the present invention is a driving assistance device that is installed on a vehicle that transmits driving force generated by a driving power source in response to accelerator operation by a driver 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 transfer 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 is characterized by comprising: a head-out state detection unit that detects a head-out state in a turning state in which the yaw rate and sideslip angle of the vehicle body have the same sign; a target accelerator operation amount setting unit that sets a target accelerator operation amount that reduces the difference between the driving force of the front wheels due to the output of the driving power source and the absolute value of the braking force of the front wheels due to the internal circulation torque of the transfer in response to detection of the head-out state; and an information presentation unit that presents information related to the target accelerator operation amount to the driver. Generally, in a vehicle with an AWD (all-wheel drive) transfer, when a difference in rotational speed occurs between the front and rear wheels, internal circulating torque is transmitted from the side with the faster rotational speed to the side 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. According to the present invention, when a head-out condition occurs, a target accelerator operation amount is presented to the driver so that the difference between the absolute value of the braking force generated on the front wheels by the internal circulation torque and the driving force of the front wheels due to the output of the driving power source is reduced. This reduces the absolute value of the braking / driving force transmitted by the front wheels to the road surface, increases the lateral force that the front tires can generate, and encourages accelerator operation that can improve the vehicle's turning ability. In this case, the target accelerator operation amount setting unit can be configured to set the target accelerator operation amount in response to detection of a 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 circulating torque of the transfer are equal.

[0007] In the first aspect of the invention, a head-in state detection unit is provided that detects a head-in state in which the vehicle is in a turning state and the yaw rate and sideslip angle of the vehicle body have opposite signs, and the target accelerator operation amount setting unit can be configured to set the target accelerator operation amount so as to reduce the difference between 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 transfer case in response to the detection of the head-in state. In addition, a driving assistance device according to a second aspect of the present invention is a driving assistance device that is installed on a vehicle that transmits driving force generated by a driving power source in response to accelerator operation by a driver 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 transfer 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 is characterized by comprising: a head-in state detection unit that detects a head-in state in which the vehicle is in a turning state and the yaw rate and sideslip angle of the vehicle body have opposite signs; a target accelerator operation amount setting unit that sets a target accelerator operation amount that reduces the difference between the driving force of the rear wheels due to the output of the driving power source and the absolute value of the braking force of the rear wheels due to the internal circulation torque of the transfer in response to detection of the head-in state; and an information presentation unit that presents information related to the target accelerator operation amount to the driver. 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, by presenting the driver with a target accelerator operation amount so that the difference between the absolute value of the braking force generated at the rear wheels by the internal circulation torque and the driving force of the rear wheels due to the output of the driving power source is reduced, the absolute value of the braking / driving force transmitted by the rear wheels to the road surface is reduced, the lateral force that can be generated by the rear wheel tires is increased, the stability of the vehicle is improved, and accelerator operation that can prevent the vehicle from falling into a spin state is encouraged. In this case, the accelerator operation amount setting unit can be configured to set the target accelerator operation amount in response to the detection of a 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 circulating torque of the transfer are equal.

[0008] In each of the above inventions, the information presenting unit may be configured to present to the driver information relating to a deviation between the target accelerator operation amount and an actual accelerator operation amount. This allows the driver to easily grasp whether the accelerator operation amount should be increased or decreased, and further the amount of change in the accelerator operation amount, thereby enhancing the above-mentioned effects.

[0009] In each of the above inventions, the information presentation unit can be configured to present information regarding the target accelerator operation amount to the driver only when the steering angle of the steering device is increased or maintained and the accelerator operation amount by the driver is equal to or greater than a predetermined value. This allows information regarding the target accelerator operation amount to be presented when traveling straight with little or no difference in trajectory between the front and rear wheels, or when entering or exiting a corner where the driver places importance on deceleration or acceleration, thereby preventing a mismatch between the driver's operation and his or her sense, causing the driver to feel uncomfortable. [Effects of the Invention]

[0010] As described above, according to the present invention, it is possible to provide a driving assistance device that can prompt the driver to operate the accelerator in a manner that increases the lateral force generated by the tires when the vehicle is turning. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram schematically illustrating the configuration of a vehicle having an embodiment of a driving assistance device 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] 3 is a flowchart illustrating an operation of the driving assistance device according to the embodiment. [Figure 4] FIG. 10 is a diagram illustrating an example of a state transition when a vehicle passes through a curved road. [Figure 5] FIG. 4 is a diagram showing an example of an image display of information relating to a target throttle opening degree in the embodiment. [Figure 6] 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 7] 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

[0012] Hereinafter, an embodiment of a driving assistance device to which the present invention is applied will be described. The driving assistance device of 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 schematically illustrating the configuration of a vehicle having a driving assistance device according to an embodiment.

[0013] 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, a brake device 70, and the like.

[0014] 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 .

[0015] 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.

[0016] The transfer clutch 42 is a differential limiting mechanism (a differential rotation limiting device, LSD) that restricts the differential between the front and rear wheel side 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 restraining force), is controlled by the transmission control unit 120 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] The vehicle 1 further includes an engine control unit 110, a transmission control unit 120, a steering control unit 130, a behavior control unit 140, a driving assistance control unit 150, 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.

[0023] 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 the amount of accelerator operation by the driver detected using the accelerator pedal sensor 111, 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. In particular, the throttle opening degree has a dominant effect on the output torque of the engine, and can be used as an index showing the output state of the power source for running the vehicle.

[0024] The accelerator pedal sensor 111 is provided, for example, on an accelerator pedal that is operated by a driver's foot, and has a position encoder that detects the amount of operation of the accelerator pedal. In a gasoline engine that adjusts output using a throttle valve, the amount of accelerator pedal operation (accelerator operation amount) usually has a predetermined correlation with the throttle opening, and can often be converted into the throttle opening.

[0025] The transmission control unit 120 controls the speed change mechanism 30, forward / reverse switching, and the engagement force (restraint 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.

[0026] 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 a steering angle δ in the steering device.

[0027] 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 the direction that suppresses each behavior. To perform these controls, the behavior 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.

[0028] 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.

[0029] In the case of an AWD vehicle such as the embodiment, an internal circulating torque is generated, which is a torque exchanged between the front and rear wheels via the AWD transfer 40, depending on the difference in rotational speed (differential rotation) between the front and rear wheels due to cornering, etc. 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. FIG. 2(a) shows the head-out state. The head-out state is a state in which the vehicle's slip angle β and yaw rate γ have the same sign.

[0030] The vehicle's sideslip angle β and yaw rate γ are expressed by the following equations 1 and 2.

number

[0031] 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.

[0032] FIG. 2(b) shows the head-in state. The head-in state is a state in which the vehicle's sideslip angle β and yaw rate γ have opposite signs. 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.

[0033] The driving assistance control unit 150 is a target accelerator operation amount setting unit that sets a target accelerator operation amount that increases the tire lateral force of the front or rear wheels depending on the head-in or head-out state of the vehicle 1 based on information obtained from each unit, etc., and presents the target accelerator operation amount to the driver. An image display device 151 is connected to the driving assistance control unit 150. The image display device 151 is an information presentation unit that displays image information to the driver of the vehicle 1 . The image display device 151 may be configured to include, for example, an LCD provided on an instrument panel, an organic EL display, or a head-up display that projects an image onto the windshield. The specific display mode of the image display device 151 will be explained in detail later.

[0034] In this embodiment, in the head-out state, the braking force of the front wheels generated by the internal circulation torque of the AWD transfer 40 is canceled out by the driving force from the output torque of the engine 10, and in the head-in state, the target accelerator operation amount is presented to the driver so that the braking force of the rear wheels generated by the internal circulation torque is canceled out by the output torque of the engine 10. This increases the lateral force that the front tires can generate in a head-out state, and increases the lateral force that the rear tires can generate in a head-in state.

[0035] Internal circulating torque F i The braking / driving force due to the above is expressed by the following equation 3.

number

[0036] Total driving force of the front wheels F f_total , total driving force of rear wheels F r_total is expressed by the following Equations 4 and 5.

number

[0037] In this embodiment, driving assistance is provided to the driver by showing the appropriate accelerator opening that takes into account internal circulating torque depending on the vehicle speed and steering operation, so that even an average driver can drive in a manner similar to that of a driver with high driving skills. Specifically, in the case of a head-out state, the braking force acting on the front wheels due to the internal circulating torque is cancelled out by the driving force, and the following equations 6 and 7 (F i <F p), Equation 8, Equation 9 (F i ≧F p The target driving force F tgt Set. F tgt ×α=F i (Formula 6) F tgt =F i / α (Equation 7) F tgt ×α=F p (Formula 8) F tgt =F p / α (Equation 9) F tgt : Target driving force applied by the driver α: AWD transfer drive force distribution (distribution to front wheels) F p : Transfer clutch engagement torque

[0038] In addition, when the vehicle is in a head-in state, the braking force acting on the rear wheels is cancelled out by the driving force due to the internal circulating torque, and the following equations 10 and 11 (F i <F p ), Equation 12, Equation 13(F i ≧F p The target driving force Ftgt to be applied by the driver is set as shown below. F tgt ×(1-α)=F i (Formula 10) F tgt =F i / (1-α) (Equation 11) F tgt ×(1-α)=F p (Formula 12) F tgt =F p / (1-α) (Equation 13)

[0039] FIG. 3 is a flowchart showing the operation of the driving assistance device according to the embodiment. Each step will be explained in order below. <Step S01: Obtaining steering angle, vehicle speed, and transfer clutch engagement force> The driving assistance control unit 150 receives the steering angle δ, the vehicle speed V, and the engagement torque F of the transfer clutch 42 from the steering angle sensor 131, the vehicle speed sensor 141, and the transmission control unit 120. p Get information about. Then, proceed to step S02.

[0040] <Step S02: Calculate sideslip angle and yaw rate> The driving assistance control unit 150 calculates the sideslip angle β and the yaw rate γ using the above-mentioned formulas 1 and 2. Then, proceed to step S03.

[0041] <Step S03: Steering angle determination> The driving assistance control unit 150 compares the steering angle δ detected by the steering angle sensor 131 with a predetermined threshold value. If the steering angle δ is equal to or greater than the threshold value, the vehicle is considered to be turning, and the process proceeds to step S04; otherwise, the vehicle is considered to be traveling straight, and the process ends (returns).

[0042] <Step S04: Decision on increasing / maintaining steering angle> The driving assistance control unit 150 determines whether the steering angle δ detected by the steering angle sensor 131 has been turned further (increased) or whether it is maintained at a predetermined value or more. If the steering angle δ is being turned further or is being maintained at a value equal to or greater than a predetermined value, the process proceeds to step S05; otherwise (if the steering angle is being decreased (turned back)), the process ends.

[0043] <Step S05: Accelerator operation amount determination> The driving assistance control unit 150 determines whether or not the amount of operation of the accelerator pedal (accelerator operation amount) detected by the accelerator pedal sensor 111 is equal to or greater than a predetermined threshold value. The threshold value can be set, for example, taking into consideration an intermediate (partial) throttle opening that may occur due to accelerator operation by the driver when traveling on a normal curved road. If the accelerator operation amount is equal to or greater than the threshold, the process proceeds to step S06, assuming that the vehicle is in a partial throttle state; otherwise, the process ends, assuming that the vehicle is in an accelerator-off state.

[0044] <Step S06: Braking / driving force F i Calculation> The driving assistance control unit 150 calculates the braking / driving force F due to the longitudinal force (internal circulation torque) caused by the differential rotation of the front and rear wheels using the above-mentioned equation 3. i Calculate. Then, proceed to step S07.

[0045] <Step S07: Comparison of braking / driving force due to internal circulation torque and transfer clutch engagement torque> The driving assistance control unit 150 calculates the braking / driving force F due to the internal circulating torque calculated in step S06. i is compared with the braking / driving force Fp due to the engagement torque of the transfer clutch 42. F i F p If it is equal to or less than this, proceed to step S08, otherwise proceed to step S09.

[0046] <Step S08: Forward and backward force due to internal circulating torque = F i > The driving assistance control unit 150 calculates the braking / driving force by the internal circulating torque used to calculate the target throttle opening degree as F i Set to. Then, proceed to step S10.

[0047] <Step S09: Forward and backward force due to internal circulating torque = F p > The driving assistance control unit 150 calculates the braking / driving force by the internal circulating torque used to calculate the target throttle opening degree as F p Set to. Then, proceed to step S10.

[0048] <Step S10: Determine the sign of the sideslip angle and yaw rate> The driving assistance control unit 150 determines whether the sideslip angle β and the yaw rate γ calculated in step S02 have the same sign. If the sideslip angle β and yaw rate γ have the same sign, the vehicle is assumed to be in a head-out state and the process proceeds to step S11; if they have different signs, the vehicle is assumed to be in a head-in state and the process proceeds to step S12.

[0049] <Step S11: Calculate throttle opening angle for maximizing front wheel lateral force> The driving assistance control unit 150 uses the above-mentioned equations 6 to 9 to calculate the target driving force F for maximizing the lateral force of the front wheels (for making the longitudinal force zero). tgt Set. The driving assistance control unit 150 calculates the target driving force F tgt A target throttle opening (target accelerator operation amount) of the engine 10 is calculated so that the above equation is obtained. Then, proceed to step S13.

[0050] <Step S12: Calculating the throttle opening angle that maximizes rear wheel lateral force> The driving assistance control unit 150 uses the above-mentioned equations 10 to 13 to calculate the target driving force F for maximizing the lateral force of the rear wheels (for making the longitudinal force zero). tgt Set. The driving assistance control unit 150 calculates the target driving force F tgt A target throttle opening (target accelerator operation amount) of the engine 10 is calculated so that the above equation is obtained. Then, proceed to step S13.

[0051] <Step S13: Accelerator operation amount instruction output> The driving assistance control unit 150 causes the image display device 151 to output information relating to the target throttle opening (target accelerator operation amount) to be presented to the driver. A specific example of image display on the image display device 151 will be described in detail later. Then, the series of processes ends.

[0052] FIG. 4 is a diagram showing an example of a state transition when a vehicle passes through a curved road (corner). FIG. 4 shows, as an example, a case where the vehicle 1 passes through a U-shaped left corner. First, in the region (Z1) where the vehicle enters a curved road while braking in a straight line, there is no difference in the trajectories of the front and rear wheels, and in the calculation method of this embodiment, the internal circulation torque is calculated to be 0. At this time, the target throttle opening is also 0. In this state, information regarding the target throttle opening is not presented to the driver. (In step S03, the steering angle becomes less than the threshold value, and the process ends.)

[0053] In the turn-in region (Z2) where the brake is released at the entrance to the corner and the steering angle is applied or increased with the accelerator off, the internal circulating torque is calculated according to the degree of head-in or head-out. However, if information regarding the target throttle opening is presented to the driver in this state, the driver, who is slowly decelerating while aiming for the clipping point CP, will be prompted to apply the accelerator, which will result in a mismatch with the driver's operation and sense. In this state, information regarding the target throttle opening is not presented to the driver. (In step S05, the accelerator operation amount becomes less than the threshold value, and the process ends.)

[0054] In the area (Z3) where the throttle opening is maintained at a medium opening (partial) in the middle of the corner and the turning state is maintained, the internal circulating torque is calculated according to the degree of head-in or head-out. In such a region, it is effective to present to the driver information relating to the target throttle opening according to the embodiment, and this matches the driver's operation and sensation. Therefore, driving assistance according to the embodiment (image display of information relating to the target throttle opening (target accelerator operation amount)) can be mainly performed in such an area.

[0055] In the region (Z4) where acceleration begins at the end (exit) of the corner, the internal circulating torque is calculated according to the degree of head-in or head-out. However, in such a region, the driver intends to accelerate the vehicle by increasing the throttle opening, so if information regarding the target throttle opening is presented to the driver, there is a concern that it may restrict accelerator operation, resulting in a mismatch with the driver's operation and sensation. In this state, information regarding the target throttle opening is not presented to the driver. (In step S04, it is determined that the steering angle has returned, and the process ends.)

[0056] In the area (Z5) where the vehicle exits the corner in a straight line, there is no difference in the trajectories of the front and rear wheels, and the calculation method of this embodiment calculates the internal circulating torque to be 0. At this time, the target throttle opening degree is also 0. However, in this state, the vehicle is required to accelerate while traveling straight ahead, so it is not appropriate to present information about the target throttle opening. In this state, information regarding the target throttle opening is not presented to the driver. (In step S03, the steering angle becomes less than the threshold value, and the process ends.) In the areas Z4 and Z5, instead of presenting information about the target throttle opening, an image or the like may be displayed to prompt the driver to accelerate (to press the accelerator pedal).

[0057] FIG. 5 is a diagram showing an example of an image display of information related to a target throttle opening degree in the embodiment. As shown in FIG. 5, the image display shows the current actual throttle opening and the target throttle opening calculated by the driving assistance control unit 150 (information relating to the target accelerator operation amount), for example, in the form of a graph. In the case of a vehicle that uses an engine 10, which adjusts its output by adjusting the throttle opening, as a power source for running, the throttle opening can be converted (read) into an accelerator operation amount.

[0058] The actual throttle opening degree increases or decreases according to the increase or decrease in the accelerator operation amount (the amount of depression of the accelerator pedal) detected by the accelerator pedal sensor 111. In the example shown in FIG. 5, the actual throttle opening degree exceeds the target throttle opening degree. The image display includes information relating to the deviation between the target throttle opening and the actual throttle opening (which can be read as information relating to the deviation between the target accelerator operation amount and the accelerator operation amount). In this case, the driver operates the accelerator by releasing the accelerator pedal (reducing the accelerator operation amount) so that the actual throttle opening approaches the target throttle opening (the actual accelerator operation amount matches the target accelerator operation amount).

[0059] The effects of the above-described driving assistance control will be described below. 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 typically assumed that the vehicle is turning at a low speed with a small turning radius on a road surface with a relatively high coefficient of friction (μ). Furthermore, even on road surfaces with a relatively low coefficient of friction, there is a possibility of a head-out condition occurring, for example, when the vehicle is traveling at a low speed and the turning radius is small. In this case, it is necessary to improve the turning ability of the vehicle.

[0060] FIG. 6 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. FIG. 6(a) shows the driving force due to throttle operation and the braking / driving force due to internal circulating torque separately, while FIG. 6(b) shows the total braking / driving force resulting from the combination of these (same as in FIG. 7). 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 .

[0061] In this embodiment, the target throttle opening is set so that 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 braking / driving force (tire generated force in the longitudinal direction) of the right front wheel 51 and the left front wheel 52 becomes zero, and the driver is encouraged to operate the accelerator according to the target throttle opening, 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.

[0062] 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 typically assumed that the vehicle is turning at high speed with a large turning radius on a road surface with a relatively low coefficient of friction. Furthermore, even on road surfaces with a relatively high coefficient of friction, there is a possibility of the vehicle turning head-in, for example, when the vehicle is traveling at high speed and has a large turning radius. In this case, it is important to reduce the likelihood of the vehicle going into a spin.

[0063] FIG. 7 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 .

[0064] In this embodiment, the target throttle opening is set so that 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 braking / driving force (tire generated force in the longitudinal direction) of the right rear wheel 61 and the left rear wheel 62 becomes zero, and the driver is encouraged to operate the accelerator in accordance with the target throttle opening, 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.

[0065] According to the embodiment described above, the following effects can be obtained. (1) When a head-out condition occurs, by presenting the driver with a target throttle opening (target accelerator operation amount) so that the difference between the absolute value of the braking force generated on the front wheels by the internal circulating torque of the AWD transfer 40 and the driving force of the front wheels by the output of the engine 10 is reduced, the absolute value of the braking / driving force transmitted by the front wheels to the road surface is reduced, the lateral force that can be generated by the front wheel tires is increased, and accelerator operation that can improve the turning ability of the vehicle 1 is encouraged. (2) When a head-in state occurs, by presenting the driver with a target throttle opening (target accelerator operation amount) so that the difference between the absolute value of the braking force generated on the rear wheels by the internal circulating torque of the AWD transfer 40 and the driving force of the rear wheels due to the output of the engine 10 is reduced, the absolute value of the braking / driving force transmitted by the rear wheels to the road surface is reduced, the lateral force that can be generated by the rear wheel tires is increased, the stability of the vehicle 1 is improved, and accelerator operation that can prevent the vehicle 1 from falling into a spin state is encouraged. (3) The image display presented to the driver contains information regarding the deviation between the actual throttle opening (actual accelerator operation amount) and the target throttle opening (target accelerator operation amount), so that the driver can easily grasp whether to increase or decrease the accelerator operation amount, and further the amount of change in the accelerator operation amount, thereby promoting the above-mentioned effects. (4) By displaying information about the target throttle opening (target accelerator operation amount) as an image only when the steering angle δ of the steering device is increased or maintained and the accelerator operation amount by the driver is equal to or greater than a predetermined value (partial throttle state), information about the target throttle opening is presented when the vehicle is traveling straight and there is no or only a small difference in the trajectory between the front and rear wheels, or when the driver is entering or exiting a corner where he or she prioritizes deceleration or acceleration, thereby preventing a mismatch between the driver's operation and his or her sense, which causes the driver to feel uncomfortable.

[0066] (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 driving assistance device are not limited to the above-described embodiments and can be modified as appropriate. For example, in the embodiment, an engine is used as an example of 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. In this case, instead of the throttle opening in the embodiment, the output torque of the motor can be used as an index representing the driving force generated by the driving power source in accordance with the accelerator operation amount. (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. Alternatively, an AWD system may be used in which one of the front-wheel drive unit and the rear-wheel drive unit is directly connected to the output shaft of the speed change mechanism, and the driving force is transmitted to the other unit via a transfer clutch. (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 may be modified as appropriate. (4) In the embodiment, the driving assistance control is configured to intervene depending on whether the vehicle is in a head-out state or a head-in state. However, a simpler configuration is also possible in which the control intervenes only for one of these states. (5) In the embodiment, the method of presenting information about the target accelerator operation amount to the driver is one example, and the present invention is not limited to this and can be modified as appropriate. For example, the specific form of image display is not limited to the configuration of the embodiment and can be changed as appropriate. Furthermore, the information relating to the target accelerator operation amount may be presented to the driver by other methods in addition to or instead of the image display. For example, information may be presented to the driver through auditory sense such as voice, or tactile sense such as vibration of a member that comes into contact with the driver, such as an accelerator pedal or a seat. Furthermore, if the accelerator pedal has a reaction force generating device, the accelerator pedal operating force may be changed (typically, increased) at the target accelerator pedal operating amount. Furthermore, instead of displaying an image or the like, information relating to the target accelerator operation amount may be presented by, for example, the lighting mode (color, etc.) of an indicator lamp. (6) In the embodiment, the vehicle has an automatic transmission as an example, but the present invention is not limited to this and can also be applied to a vehicle having a manual transmission. [Explanation of symbols]

[0067] 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 111 accelerator pedal sensor 120 Transmission Control Unit 130 steering control unit 131 steering angle sensor 140 behavior control unit 141 vehicle speed sensor 142 Yaw rate sensor 150 Driving assistance control unit 151 Image display device

Claims

1. A driving assistance device provided in a vehicle that transmits driving force generated by a driving power source in response to accelerator operation by a driver 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 transfer 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 to restrain the differential rotation, 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 target accelerator operation amount setting unit that sets a target accelerator operation amount that reduces a difference between an absolute value of a driving force of the front wheels due to an output of the driving power source and a braking force of the front wheels due to an internal circulation torque of the transfer case in response to detection of the head-out state; an information presentation unit that presents information about the target accelerator operation amount to the driver; A driving assistance device comprising:

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 target accelerator operation amount setting unit sets the target accelerator operation amount such that a difference between an absolute value of a driving force of the rear wheels due to an output of the driving power source and a braking force of the rear wheels due to an internal circulation torque of the transfer case decreases in response to detection of the head-in state. The driving assistance device according to claim 1 .

3. A driving assistance device provided in a vehicle that transmits driving force generated by a driving power source in response to accelerator operation by a driver 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 transfer 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 to restrain the differential rotation, 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 target accelerator operation amount setting unit that sets a target accelerator operation amount that reduces a difference between an absolute value of a driving force of the rear wheels due to an output of the driving power source and a braking force of the rear wheels due to an internal circulation torque of the transfer case in response to detection of the head-in state; an information presentation unit that presents information about the target accelerator operation amount to the driver; A driving assistance device comprising:

4. The information presenting unit presents information regarding a deviation between the target accelerator operation amount and an actual accelerator operation amount to the driver. The driving assistance device according to claim 1 or 3, characterized in that:

5. The information presenting unit presents information about the target accelerator operation amount to the driver only when the steering angle of the steering device is increased or maintained and the accelerator operation amount by the driver is equal to or greater than a predetermined value. The driving assistance device according to claim 1 or 3, characterized in that:

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