Vehicle torque distribution control method and vehicle torque distribution control device

Abstract

To improve drivability when lateral acceleration is great.SOLUTION: The front wheel driving force distributed to a front wheel 8 can be calculated on the basis of a front wheel basic torque calculated according to the travel state of a vehicle 1 and a front wheel correction torque calculated according to lateral acceleration of the vehicle 1. The front wheel correction torque is calculated on the basis of a deviation between a detected yaw rate and a target yaw rate and a gain set to be greater as the lateral acceleration is greater. The vehicle 1 can reduce a behavior change of the vehicle 1 and improve the drivability in a region where the lateral acceleration is great.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a torque distribution control method for a vehicle and a torque distribution control device for a vehicle.

Background Art

[0002] For example, Patent Document 1 discloses a technique for improving the turning characteristics of a vehicle by increasing the driving force distribution to the front wheels when the lateral acceleration is large.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in Patent Document 1, the vehicle yaw rate is not considered, and there is a risk that the drivability may deteriorate when the lateral acceleration is large depending on the vehicle yaw rate.

Means for Solving the Problems

[0005] The torque distribution control of the vehicle in the present invention distributes the driving force from the drive source mounted on the four-wheel drive vehicle to the front and rear wheels of the vehicle, detects the vehicle yaw rate, calculates the front-wheel driving force distributed to the front wheels, and controls the distribution of the driving force in the driving force distribution mechanism based on the front-wheel driving force. The front-wheel driving force can be calculated based on the front-wheel basic torque calculated according to the running state of the vehicle and the front-wheel correction torque calculated according to the lateral acceleration of the vehicle. The front-wheel correction torque is calculated based on the deviation between the detected yaw rate and the target yaw rate and the gain calculated according to the lateral acceleration. The gain is set to increase as the lateral acceleration increases.

Effects of the Invention

[0006] According to the present invention, the maneuverability and driving stability of a vehicle can be improved in regions where lateral acceleration is high. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram illustrating the system configuration of a vehicle to which the present invention is applied. [Figure 2] A characteristic curve showing an example of the change in actual yaw rate when feedback control is applied. [Figure 3] Calculation map for target yaw rate. [Figure 4] An explanatory diagram showing an example of gain characteristics. [Figure 5] A block diagram outlining the procedure for determining the ratio of driving force distribution between the front and rear wheels. [Figure 6] An explanatory diagram showing another example of gain characteristics. [Modes for carrying out the invention]

[0008] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Figure 1 is a schematic explanatory diagram showing the system configuration of a vehicle 1 to which the present invention is applied.

[0009] Vehicle 1 is a four-wheel drive vehicle in which the internal combustion engine 2, which serves as the power source, is mounted in the engine compartment at the front of the vehicle.

[0010] Vehicle 1 includes a first propeller shaft 4 connected to the crankshaft 3 of an internal combustion engine 2, and a power conversion unit 5 through which the driving force of the internal combustion engine 2 is transmitted via the first propeller shaft 4.

[0011] The power conversion unit 5 integrates the transmission and transfer case into a single unit. It changes the drive force of the internal combustion engine 2 transmitted via the first propeller shaft 4 and distributes the changed drive force to the front and rear wheels. The transfer case corresponds to the drive force distribution mechanism and incorporates, for example, an electromagnetically driven multi-plate clutch.

[0012] The driving force distributed to the front wheels by the power conversion unit 5 is transmitted to the left and right front wheels 8 via the second propeller shaft 6 and the front wheel differential gear 7.

[0013] The driving force distributed to the rear wheels by the power conversion unit 5 is transmitted to the left and right rear wheels 10 via the rear wheel differential gear 9.

[0014] The distribution ratio of the driving force to the front wheels 8 and rear wheels 10 in the power conversion unit 5 can be changed by a command from the control unit 11, which acts as the control unit. In other words, the power conversion unit 5 is capable of changing the distribution ratio of the driving force to the front wheels 8 and rear wheels 10.

[0015] The control unit 11 receives detection signals from various sensors, including a yaw rate sensor 21 which detects the yaw rate of the vehicle 1, a lateral acceleration sensor 22 which detects the lateral acceleration of the vehicle 1, a steering angle sensor 23 which detects the steering angle of the vehicle 1, a vehicle speed sensor 24 which detects the vehicle speed of the vehicle 1, a front wheel rotation speed sensor 25 which detects the rotation speed of the front wheels 8, and a rear wheel rotation speed sensor 26 which detects the rotation speed of the rear wheels 10.

[0016] The vehicle speed sensor 24 is provided, for example, on the output shaft of the transmission of the power conversion unit 5. Alternatively, the vehicle speed sensor 24 may be omitted, and the vehicle speed may be detected using at least one of the front wheel rotation speed sensor 25 or the rear wheel rotation speed sensor 26.

[0017] The control unit 11 calculates the front-wheel drive force to be distributed to the front wheels 8 and, based on the calculated front-wheel drive force, determines the ratio of drive force distribution between the front wheels 8 and the rear wheels 10 in the moving vehicle 1. The drive force distribution ratio to the front wheels 8 is at most 50%, and the drive force distribution ratio to the front wheels 8 will never be greater than the drive force distribution ratio to the rear wheels 10.

[0018] Vehicle 1 is based on a so-called front-engine rear-drive four-wheel drive vehicle, and increases the driving force distributed to the front wheels 8 during oversteer and decreases the driving force distributed to the front wheels 8 during understeer.

[0019] FIG. 2 is a characteristic diagram showing an example of changes in the actual yaw rate when feedback control is performed so that the yaw rate (actual yaw rate) of the vehicle 1 becomes the target yaw rate. The actual yaw rate is detected by the yaw rate sensor 21.

[0020] The target yaw rate can be calculated according to, for example, the steering angle and the vehicle speed. Specifically, the target yaw rate may be calculated by referring to a preset map as shown in FIG. 3 according to the steering angle and the vehicle speed. FIG. 3 shows an example of a calculation map of the target yaw rate, and shows an example in which characteristic lines indicating the correlation between the steering angle and the target yaw rate are set for each vehicle speed. The characteristic line V1 in FIG. 3 shows an example of the target yaw rate when the vehicle speed is low (for example, 30 km / h). The characteristic line V2 in FIG. 3 shows an example of the target yaw rate when the vehicle speed is an intermediate speed (for example, 60 km / h). The characteristic line V3 in FIG. 3 shows an example of the target yaw rate when the vehicle speed is high (for example, 200 km / h). The target yaw rate is set to increase as the steering angle increases, as shown in FIG. 3. Note that the target yaw rate may be a value obtained by dividing the product of the vehicle speed and the steering angle by the wheelbase of the vehicle 1.

[0021] When the value of the actual yaw rate is smaller than the target yaw rate, since the vehicle 1 is in an understeer state, the driving force of the front wheels 8 is corrected in the direction of oversteer. When the value of the actual yaw rate is larger than the target yaw rate, since the vehicle 1 is in an oversteer state, the driving force of the front wheels 8 is corrected in the direction of understeer. That is, when the yaw rate of the vehicle 1 deviates from the target yaw rate, the driving force distributed to the front wheels 8 is corrected using the yaw rate feedback correction amount based on the yaw rate deviation.

[0022] The yaw rate feedback correction amount corresponds to the front wheel correction torque and is expressed as the product of the yaw rate deviation, gain, and coefficient.

[0023] The yaw rate deviation is the actual yaw rate minus the target yaw rate. Therefore, the yaw rate deviation will be negative if the actual yaw rate is smaller than the target yaw rate, and positive if the actual yaw rate is larger than the target yaw rate.

[0024] The gain is a positive value set according to the lateral acceleration, as shown in Figure 4. Figure 4 is an explanatory diagram showing an example of the characteristics of the gain used when calculating the yaw rate feedback correction amount.

[0025] The gain is set within a range between a predetermined first predetermined value G1 and a predetermined second predetermined value G2 that is greater than the first predetermined value G1, and is set to increase as the lateral acceleration increases.

[0026] More specifically, the gain is set to a first predetermined value G1 in a predetermined first region. The first region is the region in which the lateral acceleration is less than or equal to a predetermined first lateral acceleration threshold A1, as shown in Figure 4.

[0027] Furthermore, the gain is set such that in a predetermined second region, it increases as the lateral acceleration increases, and becomes a second predetermined value G2 when the lateral acceleration is greater than the first lateral acceleration threshold A1 and equal to a predetermined second lateral acceleration threshold A2. The second region is the region in which the lateral acceleration is greater than or equal to the first lateral acceleration threshold A1 and less than or equal to the predetermined second lateral acceleration threshold A2, as shown in Figure 4. In the example in Figure 4, in the second region, the slope of the gain (the rate of change with respect to lateral acceleration) is constant, and the gain changes in a stepwise manner.

[0028] Furthermore, the gain is set to a second predetermined value G2 in a predetermined third region. The third region is the region in which the lateral acceleration is greater than or equal to a predetermined second lateral acceleration threshold A2, as shown in Figure 4.

[0029] The coefficient is a fixed value that is a predetermined positive value.

[0030] Therefore, the yaw rate feedback correction amount will be negative if the yaw rate deviation is negative, and positive if the yaw rate deviation is positive.

[0031] If the yaw rate feedback correction amount is positive, the driving force distributed to the front wheels 8 is corrected to increase. If the yaw rate feedback correction amount is negative, the driving force distributed to the front wheels 8 is corrected to decrease. Furthermore, if the driving force distributed to the front wheels 8 increases, the driving force distributed to the rear wheels 10 decreases accordingly, and if the driving force distributed to the front wheels 8 decreases, the driving force distributed to the rear wheels 10 increases accordingly.

[0032] Here, the front-wheel drive force distributed to the front wheels 8 can be calculated based on the basic front-wheel torque calculated according to the driving conditions and the yaw rate feedback correction amount described above.

[0033] Figure 5 is a block diagram illustrating the schematic procedure (process) for determining the ratio of driving force distribution between the front wheels 8 and the rear wheels 10. In other words, Figure 5 is a block diagram illustrating the schematic of torque distribution control performed within the control unit 11.

[0034] In S1, the torque distribution to the front wheel 8 is calculated according to the difference in rotational speed between the front and rear wheels. Here, the difference in rotational speed between the front and rear wheels is the difference between the rotational speed of the front wheel 8 and the rotational speed of the rear wheel 10. The torque distribution to the front wheel 8 calculated in S1 is calculated according to the slip of the rear wheel 10, and the value becomes larger as the rear wheel 10 slips.

[0035] In S2, the torque distribution to the front wheels 8 is calculated according to the vehicle's driving force, taking into account the driving force of the internal combustion engine 2 and the gear ratio of the transmission. The torque distribution to the front wheels 8 calculated in S2 is calculated according to the estimated torque of the internal combustion engine 2 and the gear ratio of the transmission, and is calculated, for example, by using a map that correlates the torque of the internal combustion engine 2, the gear ratio of the transmission, and the torque distribution.

[0036] In S3, the initial torque distribution is calculated. The torque distribution for the front wheels 8 calculated in S3 is a preset constant value, which is set to a value necessary, for example, when vehicle 1 starts moving.

[0037] S4 receives the front wheel distribution torque calculated in S1-S3. S4 calculates the front wheel base torque by selecting the maximum of the three input distribution torques. In other words, S1-S4 represent the process of calculating the front wheel base torque. The front wheel base torque calculated in S4 is output to S6.

[0038] In S5, the yaw rate feedback correction amount is calculated.

[0039] In S6, the yaw rate feedback correction amount is added to the basic torque of the front wheels and output to S8.

[0040] In S7, for example, the front-wheel drive force during so-called VDC (Vehicle Dynamics Control) control, which is implemented when vehicle 1 is about to skid or swing its rear end, is calculated and output to S8.

[0041] In S8, one of the front-wheel drive force calculated in S6 or the front-wheel drive force calculated in S7 is selected as the front-wheel drive force and output to S9. In S8, when the attitude of vehicle 1 deteriorates to a certain extent, the front-wheel drive force calculated in S7 is selected. In normal scenes, in S8, the front-wheel drive force calculated in S6 is selected as the front-wheel drive force for the current operation. VDC control is implemented when the attitude of vehicle 1 deteriorates to a certain extent.

[0042] In S9, a predetermined rate of change limit is applied to the front-wheel drive force output from S8 to prevent the vehicle 1 from becoming unstable due to a sudden change in the drive torque of the front wheels 8. In other words, a rate of change limit is applied to prevent the rate of change of the drive torque of the front wheels 8 calculated in S8 from becoming too large.

[0043] In S10, the rear-wheel drive force is calculated using the front-wheel drive force obtained while considering the rate of change limit. In other words, in S10, the final torque distribution between the front and rear wheels is calculated.

[0044] In S11, the final distribution torque calculated in S10 is converted into a current value for current control of the multi-plate clutch of the transfer case of the power conversion unit 5.

[0045] If the gain used to calculate the yaw rate feedback correction amount is low in the region of high lateral acceleration, sufficient front-wheel drive force may not be secured, and the maneuverability and driving stability of vehicle 1 may not be guaranteed.

[0046] In the above-described embodiment, vehicle 1 can achieve a distribution of front-wheel drive force that follows changes in the vehicle's behavior by setting a large gain when calculating the yaw rate feedback correction amount in the region of high lateral acceleration. Therefore, in the region of high lateral acceleration, vehicle 1 can reduce changes in the vehicle's behavior and improve drivability. In other words, in the region of high lateral acceleration, vehicle 1 can improve the maneuverability and driving stability of vehicle 1.

[0047] Although specific embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention.

[0048] The gain may be set to have characteristics as shown in Figure 6, depending on the lateral acceleration. Figure 6 is an explanatory diagram showing another example of the gain characteristics used when calculating the yaw rate feedback correction amount. The gain in the other example with characteristics as shown in Figure 6 is a positive value set according to the lateral acceleration, and is set within a range between a predetermined first predetermined value G1 and a predetermined second predetermined value G2 that is greater than the first predetermined value G1, and is set to increase as the lateral acceleration increases.

[0049] More specifically, the gain in the other example shown in Figure 6 is set to a first predetermined value G1 in a predetermined first region. The first region in Figure 6 is the region in which the lateral acceleration is less than or equal to a predetermined first lateral acceleration threshold A3.

[0050] Furthermore, in the other example shown in Figure 6, the gain increases as the lateral acceleration increases in a predetermined second region, and is set to a second predetermined value G2 when the lateral acceleration is greater than the first lateral acceleration threshold A3 and is equal to a predetermined second lateral acceleration threshold A4. The second region in Figure 6 is the region where the lateral acceleration is greater than or equal to the first lateral acceleration threshold A3 and less than or equal to the predetermined second lateral acceleration threshold A4. In the example in Figure 6, in the second region, the slope of the gain (the rate of change with respect to lateral acceleration) is not constant, and is set to decrease as the lateral acceleration approaches the first lateral acceleration threshold A3 and the second lateral acceleration threshold A4.

[0051] Furthermore, the gain is set to a second predetermined value G2 in a predetermined third region. The third region in Figure 6 is the region in which the lateral acceleration is greater than or equal to a predetermined second lateral acceleration threshold A4.

[0052] Note that the first lateral acceleration threshold A3 in Figure 6 may be a smaller value than the first lateral acceleration threshold A1 in Figure 4. Also, the second lateral acceleration threshold A4 in Figure 6 may be a larger value than the second lateral acceleration threshold A2 in Figure 4. [Explanation of Symbols]

[0053] 1…Vehicle 2…Internal combustion engine 3…Crankshaft 4…First propeller shaft 5…Power conversion unit 6…Second propeller shaft 7…Front wheel differential gear 8…Front wheel 9…Rear wheel differential gear 10... Rear wheel 11…Control Unit

Claims

1. In a vehicle torque distribution control method that distributes driving force from a drive source mounted on a four-wheel drive vehicle to the front and rear wheels of the vehicle, The vehicle's yaw rate is detected, The system calculates the front-wheel drive force to be distributed to the front wheels, and controls the distribution of drive force in the drive force distribution mechanism based on the above front-wheel drive force. The above-mentioned front-wheel drive force can be calculated based on the basic front-wheel torque calculated according to the vehicle's driving conditions and the front-wheel correction torque calculated according to the vehicle's lateral acceleration. The above front wheel correction torque is calculated based on the difference between the detected yaw rate and the target yaw rate, and a gain calculated according to the lateral acceleration. A method for controlling the torque distribution of a vehicle, characterized in that the above gain is set to increase as the lateral acceleration increases.

2. In the first region where the lateral acceleration is below a predetermined first lateral acceleration threshold, the gain is set to a first predetermined value. In the second region where the lateral acceleration is greater than or equal to the first lateral acceleration threshold and less than or equal to a predetermined second lateral acceleration threshold that is greater than the first lateral acceleration threshold, the gain increases as the lateral acceleration increases, and is set to a second predetermined value that is greater than the first predetermined value when the lateral acceleration is at the second lateral acceleration threshold. The torque distribution control method for a vehicle according to claim 1, characterized in that in a third region where the lateral acceleration is greater than or equal to the second lateral acceleration threshold, the gain is set to the second predetermined value.

3. The torque distribution control method for a vehicle according to claim 2, characterized in that, in the second region described above, the slope of the gain is constant and the gain changes in a stepwise manner.

4. The torque distribution control method for a vehicle according to claim 2, characterized in that, in the second region described above, the slope of the gain is set to decrease as the lateral acceleration approaches the first lateral acceleration threshold and the second lateral acceleration threshold.

5. The power source installed in a four-wheel drive vehicle, A drive force distribution mechanism that distributes the drive force from the above-mentioned drive source to the front and rear wheels of the vehicle, A yaw rate detection unit that detects the yaw rate of the vehicle, The system includes a control unit that calculates the front-wheel drive force to be distributed to the front wheels so that drive force is always transmitted to at least the rear wheels, and controls the distribution of drive force in the drive force distribution mechanism based on the front-wheel drive force, The above-mentioned front-wheel drive force can be calculated based on the basic front-wheel torque calculated according to the vehicle's driving conditions and the front-wheel correction torque calculated according to the vehicle's lateral acceleration. The above front wheel correction torque is calculated based on the difference between the detected yaw rate and the target yaw rate, and a gain calculated according to the lateral acceleration. The above-mentioned gain is set to increase as the lateral acceleration increases, characterized in that it is a torque distribution control device for a vehicle.

Images