JP2007125998A - Driving force distribution control device of four-wheel-drive vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving force distribution control device of a four-wheel-drive vehicle capable of enhancing the steering stability by bringing the actual yaw rate of the vehicle close to the target yaw rate in a traveling situation in which the deviation of the yaw rate is increased while the difference in the rotational speed between front and rear wheels is hardly generated. <P>SOLUTION: The driving force distribution control device of the four-wheel-drive vehicle has a driving force distribution control means for performing the control of increasing the distribution of the driving force to a sub driving wheel as the difference in the rotational speed between front and rear wheels is large while one of the front and rear wheels is a main driving wheel, and the other is a sub driving wheel. A threshold setting means (Step S4) is provided, which sets the threshold C by a large value as the yaw rate deviation ΔΨ between the absolute value abs.(Ψ<SP>*</SP>) of the target yaw rate Ψ<SP>*</SP>and the absolute value abs.(Ψ) of the actual yaw rate Ψ is larger. The driving force distribution control means sets the value of the detected value ΔNfr of the difference in the rotational speed between front and rear wheels with the threshold C added thereto to be the controlled value of the difference in the rotational speed between front and rear wheels to be used in the control for the difference in the rotational speed between front and rear wheels. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention comprises driving force distribution control means for controlling one of the front and rear wheels to be a main driving wheel and the other to be a sub driving wheel, and to increase the driving force distribution to the sub driving wheel as the front-rear wheel rotational speed difference is larger. It belongs to the technical field of driving force distribution control devices for four-wheel drive vehicles.

Conventionally, according to the yaw rate deviation, which is the difference between the absolute value of the target yaw rate and the absolute value of the actual yaw rate, in a four-wheel drive vehicle that performs control to increase the distribution of driving force to the auxiliary driving wheels as the front and rear wheel rotational speed difference increases Then, a correction coefficient for the detected difference between the front and rear wheel rotation speeds is determined, and the driving force distribution control is performed by a value obtained by multiplying the correction coefficient and the detected difference between the front and rear wheel rotation speeds (for example, see Patent Document 1). .
JP-A-5-278488

  However, in the conventional driving force distribution control device for a four-wheel drive vehicle, there is no difference in the rotational speed of the front and rear wheels due to the road surface μ being low μ etc. However, when the behavior of the vehicle becomes unstable and the yaw rate deviation is large, no matter how large the correction coefficient is, the detected value of the front and rear wheel rotation speed difference is zero or extremely small. There was a problem that the front and rear wheel driving force distribution control that brings the actual yaw rate of the vehicle closer to the target yaw rate could not be performed, and the steering stability was lowered.

  The present invention has been made by paying attention to the above-mentioned problem, and in the driving situation in which the difference in the rotational speed of the front and rear wheels hardly occurs but the yaw rate deviation is large, the actual yaw rate of the vehicle is brought close to the target yaw rate, and the steering stability is improved. An object of the present invention is to provide a driving force distribution control device for a four-wheel drive vehicle that can contribute to the improvement of the above.

In order to achieve the above object, in the present invention, one of the front and rear wheels is a main driving wheel and the other is a sub driving wheel, and control is performed to increase the distribution of driving force to the sub driving wheel as the front and rear wheel rotational speed difference increases. In a driving force distribution control device for a four-wheel drive vehicle equipped with a driving force distribution control means,
A threshold setting unit is provided for setting a threshold with a larger value as the yaw rate deviation between the absolute value of the target yaw rate and the absolute value of the actual yaw rate is larger,
The driving force distribution control means uses a value obtained by adding the threshold value to the front and rear wheel rotation speed difference detection value as a front and rear wheel rotation speed difference control value used in front and rear wheel rotation speed difference correspondence control.

Therefore, in the driving force distribution control device for a four-wheel drive vehicle according to the present invention, when the vehicle is running, the threshold value setting means increases the threshold value as the yaw rate deviation between the absolute value of the target yaw rate and the absolute value of the actual yaw rate increases. In the driving force distribution control means, the value obtained by adding the set threshold value to the front and rear wheel rotational speed difference detection value is the front and rear wheel rotational speed difference control value used in the front and rear wheel rotational speed difference correspondence control.
In other words, a front-wheel drive-based four-wheel drive vehicle will be described as an example when driving on a low μ road such as an icy and snowy road. When the driving force distribution control according to the conventional front / rear wheel rotational speed difference detection value is executed, the front / rear wheel rotational speed difference detection value is zero or close to zero, so that the front wheel drive state remains unchanged. The driving situation in which the vehicle behavior is unstable and the yaw rate deviation is large and the vehicle behavior is unstable is not improved at all, and the steering stability is significantly lowered.
On the other hand, when traveling on low μ roads such as icy and snowy roads, a difference in rotational speed between the front and rear wheels hardly occurs, but in a traveling situation where the yaw rate deviation is large, the present invention sets a threshold value with a large value. The value obtained by adding the threshold value set to the front and rear wheel rotational speed difference detection value, that is, if the front and rear wheel rotational speed difference detection value is zero, the threshold value is the front and rear wheel rotational speed difference used in the front and rear wheel rotational speed difference correspondence control. The control value is set, and control for distributing the driving force to the rear wheel side is performed. Therefore, by shifting from the front-wheel drive state where the understeer tendency is high to the four-wheel drive state where the driving force is distributed to the rear wheels, the understeer tendency is reduced (change in the steer characteristic in the neutral steer direction), and the vehicle The actual yaw rate approaches the target yaw rate and the vehicle behavior is stabilized.
As a result, although there is almost no difference between the front and rear wheel rotational speeds, it is possible to bring the actual yaw rate of the vehicle closer to the target yaw rate in a driving situation in which the yaw rate deviation is large, thereby contributing to improvement in steering stability.

  Hereinafter, the best mode for carrying out a driving force distribution control device for a four-wheel drive vehicle of the present invention will be described based on a first embodiment shown in the drawings.

First, the configuration will be described.
FIG. 1 is an overall system diagram showing a hybrid four-wheel drive vehicle (an example of a four-wheel drive vehicle) to which the driving force distribution control device of the first embodiment is applied.
As shown in FIG. 1, the hybrid four-wheel drive vehicle with the front wheel drive base according to the first embodiment includes an engine 1 (first drive source), a front motor 2F (first drive source), and a rear motor 2R (second drive source). ), Left front wheel tire 3FL (main drive wheel), right front wheel tire 3FR (main drive wheel), left rear wheel tire 3RL (sub drive wheel), right rear wheel tire 3RR (sub drive wheel), front A differential 4F, a rear differential 4R, a front transmission 5F, and a rear transmission 5R are provided.

  The front motor 2F and rear motor 2R perform both power running and regeneration as motor generators.

  The left and right front wheel tires 3FL and 3FR are driven by at least one of the engine 1 and the front motor 2F as a drive source, and the driving force that has passed through the front transmission 5F is equally distributed by the front differential 4F.

  The left and right rear wheel tires 3RL, 3RR are driven by using only the rear motor 2R as a drive source, and the driving force that has passed through the rear transmission 5R is equally distributed by the rear differential 4R. The rear differential 4R may be capable of controlling the driving force distribution by controlling the engaging force of the differential limiting clutch set inside or by controlling the engaging force for the left clutch and the right clutch set inside.

  As shown in FIG. 1, the driving force distribution control system of the hybrid four-wheel drive vehicle of Embodiment 1 includes a wheel speed sensor 6, a steering angle sensor 7, a lateral acceleration sensor 8, a vehicle speed sensor 9, and an accelerator opening. A sensor 10, a yaw rate sensor 14, a controller 11, a high-power battery 12, a front inverter 13F, and a rear inverter 13R are provided.

  The wheel speed sensor 6 includes a left front wheel speed sensor 6FL, a right front wheel speed sensor 6FR, a left rear wheel speed sensor 6RL, and a right rear wheel speed sensor 6RR, and obtains tire rotational speed information of each wheel.

  The steering angle information is obtained from the steering angle sensor 7. Lateral acceleration information is obtained from the lateral acceleration sensor 8. Vehicle speed information is obtained from the vehicle speed sensor 9. Accelerator opening information is obtained from the accelerator opening sensor 10. Actual yaw rate information is obtained from the yaw rate 14.

  The controller 11 reads information from the wheel speed sensor 6, the steering angle sensor 7, the lateral acceleration sensor 8, the vehicle speed sensor 9, the accelerator opening sensor 10, and the yaw rate sensor 14, and basically the front and rear wheel rotational speed difference Δfr is large. The feedback control is performed to increase the driving force of the rear motor 2R, that is, to increase the driving force transmitted to the left and right rear tires 3RL and 3RR.

  The high-power battery 12 supplies electric power to both motors 2F and 2R via both inverters 13F and 13R, and also serves to collect power generated by both motors 2F and 2R.

  The front inverter 13F and the rear inverter 13R serve to supply the electric energy of the high-power battery 12 to both the motors 2F and 2R and to return the electric energy regenerated by the motors 2F and 2R to the high-power battery 12.

  FIG. 2 is a flowchart showing the flow of the driving force distribution control process executed by the controller 11 of the first embodiment. Each step will be described below (driving force distribution control means).

  In step S1, the tire rotational speed NFL, NFR, NRL, NRR from each wheel speed sensor 6 (left front wheel speed sensor 6FL, right front wheel speed sensor 6FR, left rear wheel speed sensor 6RL, right rear wheel speed sensor 6RR). Then, the steering angle θ from the steering angle sensor 7, the vehicle speed V from the vehicle speed sensor 9, and the actual yaw rate ψ from the yaw rate sensor 10 are read, and the process proceeds to step S2.

In step S2, following the reading of the tire revolutions NFL, NFR, NRL, NRR, steering angle θ, vehicle speed V, and actual yaw rate ψ in step S1, the target yaw rate ψ ^* is calculated from the steering angle θ and the vehicle speed V. Then, the target yaw rate differential value dψ ^* / dt is calculated by the differential processing of the calculated target yaw rate ψ ^{*, and} the process proceeds to step S3 (target yaw rate differential value calculating means).

In step S3, following the calculation of the target yaw rate ψ ^* and the target yaw rate differential value dψ ^* / dt in step S2, the difference between the absolute value | ψ ^* | of the target yaw rate ψ ^{* and} the absolute value | ψ | of the actual yaw rate ψ. Is calculated, and the process proceeds to step S4.

In step S4, following calculation of the yaw rate deviation Δψ in step S3, a threshold C is determined according to the yaw rate deviation Δψ, and the process proceeds to step S5 (threshold setting means).
Here, the threshold C is set to a larger value as the yaw rate deviation Δψ is larger, as shown in the threshold setting map M in FIG. Further, the threshold value C is set to a maximum value and a minimum value (C = 0) that suppress excessive driving force distribution to the left and right rear wheel tires 3RL and 3RR.

In step S5, following the determination of threshold C in step S4, the absolute value | dψ ^* / dt | of the target yaw rate differential value dψ ^* / dt calculated in step S2 is a judgment value for a sudden yaw rate change. It is determined whether or not it is equal to or less than the value α. If YES, the process proceeds to step S7, and if NO, the process proceeds to step S6.

In step S6, following the determination of | dψ ^* / dt |> α in step S5, the threshold C is set to zero, and the process proceeds to step S7.

In step S7, following the determination of | dψ ^* / dt | ≦ α in step S5 or setting of threshold value C = 0 in step S6, a rear wheel command torque is calculated, and the process proceeds to step S8.
Here, the formula for calculating the rear wheel command torque is:
Rear wheel command torque = K × {(front wheel tire rotational speed−rear wheel tire rotational speed) + threshold C}
Given in.
K is a control gain, and is given by a value based on the reciprocal of the lateral acceleration Yg from the lateral acceleration sensor 10, for example. The lateral acceleration Yg is information that combines the vehicle speed V, the steering angle θ, and the road surface μ. For example, when turning on a high μ road, the lateral acceleration Yg becomes a large value, and the control gain K is given by a small value. . Further, when turning on a low μ road, the lateral acceleration Yg becomes a small value, so that the control gain K is given a large value.
Further, (front wheel tire rotation speed−rear wheel tire rotation speed) corresponds to a detected difference between the front and rear wheel rotation speeds, and the front wheel tire rotation speed is, for example, an average value of left and right front wheel tire rotation speeds among tire rotation speeds of each wheel. The rear wheel tire rotational speed is given by the left rear wheel speed tire rotational speed average value among the tire rotational speeds of the respective wheels.

In step S8, following the calculation of the rear wheel command torque in step S7, the front wheel driving force command value is calculated by subtracting the rear wheel driving force command value from the total driving force, and the process proceeds to step S9.
Here, the “total driving force” is calculated as the driver's required driving force based on the accelerator opening information from the accelerator opening sensor 10, and the “rear wheel driving force command value” is calculated.

  In step S9, following the calculation of the front wheel driving force command value in step S8, when the electric vehicle traveling mode is selected, the front wheel driving force command value is output to the front motor 2F, and the rear wheel driving force command value is output to the rear motor 2R. To do. In the hybrid vehicle running mode, the driving force command value obtained by subtracting the estimated engine driving force from the front wheel driving force command value is output to the front motor 2F, the rear wheel driving force command value is output to the rear motor 2R, and the process proceeds to return. To do.

Next, the operation will be described.
[Driving force distribution control action]
Conventionally, in a four-wheel drive vehicle that performs control to increase the distribution of driving force to the sub-drive wheels as the front-rear wheel rotational speed difference is larger, the front and rear wheels depend on the yaw rate deviation between the absolute value of the target yaw rate and the absolute value of the actual yaw rate. A correction coefficient for the rotational speed difference detection value is determined, and driving force distribution control is performed by a value obtained by multiplying the correction coefficient by the front and rear wheel rotational speed difference detection value.

  However, when driving on low-μ roads such as icy and snowy roads, there is no difference between the front and rear wheel speeds, but even if the driver intends to drive straight due to the difference in driving resistance between the left and right wheels, the behavior of the vehicle becomes unstable and the yaw rate deviation is large. In such a case, the front / rear wheel driving force distribution will bring the vehicle's actual yaw rate closer to the target yaw rate by detecting that the detected value of the front / rear wheel rotation speed difference is zero or extremely small no matter how large the correction coefficient becomes. Control cannot be performed, and steering stability is reduced.

In the driving force distribution control device according to the first embodiment, the front and rear wheel rotation used in the front and rear wheel rotation speed difference control is a value obtained by adding a threshold value C that is larger as the yaw rate deviation Δψ is larger to the front and rear wheel rotation speed difference detection value ΔNfr. By using the number difference control value, there is almost no difference between the front and rear wheel rotation speeds, but in a driving situation where the yaw rate deviation Δψ is large, the actual yaw rate ψ of the vehicle is brought closer to the target yaw rate ψ ^* , improving steering stability. To be able to contribute.

That is, there is almost no difference between the front and rear wheel rotation speeds, but the driving situation is such that the yaw rate deviation Δψ is large, and when the target yaw rate differential value dψ ^* / dt is equal to or less than the set value α, The flow of step S1, step S2, step S3, step S4, step S5, step S7, step S8, and step S9 is repeated. In step S4, the threshold value C is set to a larger value as the yaw rate deviation Δψ is larger. In step S7, the threshold value set to the front and rear wheel rotational speed difference detection value ΔNfr (ΔNfr = front wheel tire rotational speed−rear wheel tire rotational speed). The value obtained by adding C is the front and rear wheel rotational speed difference control value used in the front and rear wheel rotational speed difference control, and as shown in FIG. 3, the rear wheel command torque is calculated based on the front and rear wheel rotational speed difference control value (ΔNfr + C). Calculated. If the horizontal axis of the rear wheel command torque map shown in FIG. 3 is replaced with the front and rear wheel rotational speed difference control value (ΔNfr + C) instead of the front and rear wheel rotational speed difference detection value ΔNfr, the solid line characteristics in FIG. 3 is a characteristic obtained by offsetting the characteristic in FIG. 3 in the direction of increasing the rear wheel command torque (the offset amount is determined by the threshold value C).

On the other hand, in a driving situation in which the difference in rotational speed between the front and rear wheels hardly occurs but the yaw rate deviation Δψ is large, and the target yaw rate differential value dψ ^* / dt exceeds the set value α, in the flowchart of FIG. Step S1, step S2, step S3, step S4, step S5, step S6, step S7, step S8, and step S9 are repeated. In step S4, the threshold C is set to a larger value as the yaw rate deviation Δψ is larger. In step S6, the set threshold C is set to zero. In step S7, the front and rear wheel rotational speed difference detection value ΔNfr is directly used as the front and rear wheel rotational speed difference control value used in the front and rear wheel rotational speed difference control, and as shown in FIG. = ΔNfr + 0), the rear wheel command torque is calculated.

  In the case of a front four-wheel drive-based hybrid four-wheel drive vehicle such as that of the first embodiment, when traveling on a low μ road such as an icy and snowy road, there is almost no difference between the front and rear wheel rotational speeds, but the yaw rate deviation is large. In the situation, when the driving force distribution control according to the conventional front and rear wheel rotational speed difference detection value is executed, the front and rear wheel rotational speed difference detection value is zero or close to zero, so that the front wheel driving state remains unchanged. The driving situation in which the vehicle behavior in which the yaw rate deviation is large and the vehicle behavior is unstable is not improved at all, and the steering stability is remarkably lowered.

On the other hand, when traveling on low μ roads such as icy and snowy roads, there is almost no difference between the front and rear wheel rotational speeds, but in a traveling situation in which the yaw rate deviation Δψ is large, in Example 1, as shown in FIG. Further, the threshold value C is set to a larger value as the yaw rate deviation Δψ is larger. And it is set as the value which added the threshold value C set to front-and-rear wheel rotation speed difference detection value (DELTA) Nfr. That is, as shown in FIG. 4, when the detected value ΔNfr of the front and rear wheels is set to zero, the value by the threshold C is set as the front and rear wheel rotational speed difference control value used in the front and rear wheel rotational speed difference corresponding control. Control to distribute the driving force to the rear wheel side is performed such that the wheel command torque TRO is calculated.
Therefore, by shifting from the front-wheel drive state where the understeer tendency is high to the four-wheel drive state where the driving force is distributed to the rear wheels, the understeer tendency is reduced (change in the steer characteristic in the neutral steer direction), and the vehicle The actual yaw rate ψ approaches the target yaw rate ψ ^*, and the vehicle behavior is stabilized.

As a result, although there is almost no difference between the front and rear wheel rotational speeds, the actual yaw rate ψ of the vehicle can be brought close to the target yaw rate ψ ^* in a driving situation in which the yaw rate deviation Δψ is large, thereby contributing to an improvement in steering stability. .

In the driving force distribution control apparatus according to the first embodiment, the threshold value setting means (step S4) sets the maximum value and the minimum value that suppress excessive driving force distribution to one of the front and rear wheels to the threshold value C set by the yaw rate deviation Δψ. Set.
For example, if the threshold set by the yaw rate deviation is not limited by the maximum and minimum values, the threshold for the rotational speed difference control becomes too large when the yaw rate deviation is large. The power distribution becomes over-distributed and the rear tires slip.
On the other hand, in the first embodiment, as shown in FIG. 6, by setting the maximum value and the minimum value for suppressing the excessive distribution of driving force to one of the front and rear wheels, the threshold value C set by the yaw rate deviation Δψ, When the yaw rate deviation Δψ is large, the threshold value C for the rotational speed difference control becomes too large, the rear wheel driving force distribution becomes excessively distributed, and the rear tires 3RL and 3RR are prevented from slipping in advance. Both tire behavior can be controlled appropriately.

In the driving force distribution control apparatus of the first embodiment, target yaw rate differential value calculating means (step S2) for calculating the target yaw rate differential value dψ ^* / dt is provided, and the driving force distribution control means is configured to provide the target yaw rate differential value dψ ^*. The threshold C is set to zero when / dt exceeds a set value α that is a judgment value of a rapid yaw rate change, and the front and rear wheel rotational speeds are set only when the target yaw rate differential value dψ ^* / dt is equal to or less than the set value α. A value obtained by adding the threshold C to the difference detection value ΔNfr is used as a front and rear wheel rotational speed difference control value used in front and rear wheel rotational speed difference correspondence control.
For example, as shown in the steering angle characteristics of FIG. 6, when the steering wheel operation is suddenly switched from right to left, the yaw rate deviation at the time of a sudden yaw rate change corresponds to the difference between the front and rear wheel speeds by feedback control. In this driving force distribution control, there is a possibility that the change in the yaw rate deviation cannot be caught up. At that time, the yaw rate deviation becomes larger, smaller, or positive / negative. Therefore, when the driving force distribution according to the first embodiment is applied, the driving force distribution is abruptly performed. Give excessive load.
On the other hand, in the first embodiment, the value obtained by adding the threshold value C to the front and rear wheel rotational speed difference detection value ΔNfr only when the target yaw rate differential value dψ ^* / dt is equal to or smaller than the set value α is used as the front and rear wheel rotational speed difference correspondence control. By using the front and rear wheel rotational speed difference control value used in the above, rapid driving force distribution is suppressed, and it is possible to reduce a sense of discomfort to the occupant due to the driving force distribution and an excessive load on driving system components.

In the driving force distribution control apparatus according to the first embodiment, the vehicle includes a front driving wheel as a main driving wheel, a rear wheel as a sub driving wheel, a first driving source for driving the front wheels by the engine 1 and the front motor 2F, and a rear motor 2R. A hybrid four-wheel drive vehicle based on a front wheel drive that includes a second drive source that drives a rear wheel, wherein the drive force distribution control means controls a drive force of a rear motor 2R that is the second drive source. To control the driving force transmitted to the left and right rear wheel tires 3RL, 3RR.
For example, a front wheel drive-based four-wheel drive vehicle has a transfer clutch such as an electromagnetic multi-plate clutch or a hydraulic clutch in the rear wheel drive system, and controls the clutch engagement force based on the drive force distribution command. There is known a system that transmits part of the driving force transmitted to the rear wheel side, but from the time when the driving force distribution command is output until the actual driving force is generated on the rear wheel → The operation flow of clutch torque generation → torque transmission between drive system components results in a response delay.
On the other hand, by controlling the driving force transmitted to the left and right rear wheel tires 3RL and 3RR by a driving force command for the rear motor 2R having high control response, an understeering tendency is caused by increasing the driving force distribution to the auxiliary driving wheels. This can be achieved with faster responsiveness compared to the driving force distribution control using the conventional transfer clutch.

Next, the effect will be described.
In the driving force distribution control device for a four-wheel drive vehicle according to the first embodiment, the following effects can be obtained.

(1) One of the front and rear wheels is a main driving wheel and the other is a sub driving wheel, and driving force distribution control means is provided for performing control to increase the driving force distribution to the sub driving wheel as the front and rear wheel rotational speed difference increases. In a four-wheel drive vehicle driving force distribution control device, a threshold value for setting a threshold value C with a larger value as the yaw rate deviation Δψ between the absolute value | ψ ^* | of the target yaw rate ψ ^{* and} the absolute value | ψ | of the actual yaw rate ψ increases. Setting means (step S4) is provided, and the driving force distribution control means uses a value obtained by adding the threshold C to the front and rear wheel rotational speed difference detection value ΔNfr in front and rear wheel rotational speed difference control. Therefore, in the driving situation where the yaw rate deviation Δψ is large, the actual yaw rate ψ of the vehicle is brought close to the target yaw rate ψ ^* to contribute to the improvement of steering stability. Can do.

  (2) The threshold value setting means (step S4) sets the maximum value and the minimum value for suppressing the excessive distribution of driving force to one of the front and rear wheels to the threshold value C set by the yaw rate deviation Δψ. When it is large, the threshold value C of the rotational speed difference control becomes too large, the rear wheel driving force distribution becomes excessively distributed, and the rear wheel tires 3RL and 3RR are prevented from slipping, thereby preventing both yaw rate and tire behavior. Can be controlled appropriately.

(3) A target yaw rate differential value calculating means (step S2) for calculating the target yaw rate differential value dψ ^* / dt is provided, and the driving force distribution control means is configured to cause the target yaw rate differential value dψ ^* / dt to change rapidly. The threshold C is set to zero when the judgment value exceeds the set value α, and the threshold C is added to the front and rear wheel rotational speed difference detection value ΔNfr only when the target yaw rate differential value dψ ^* / dt is equal to or less than the set value α. Is used as the front and rear wheel rotational speed difference control value used in the front and rear wheel rotational speed difference control, so that abrupt driving force distribution is suppressed. Overload can be reduced.

  (4) The vehicle uses a front wheel as a main drive wheel, a rear wheel as a sub drive wheel, a first drive source that drives the front wheel by the engine 1 and the front motor 2F, and a second drive that drives the rear wheel by the rear motor 2R. A front-wheel drive-based hybrid four-wheel drive vehicle, wherein the driving force distribution control means controls the driving force of the rear motor 2R that is the second driving source to control the left and right rear wheel tires 3RL, 3RR. In order to control the driving force transmitted to the vehicle, the decrease in the understeer tendency by increasing the driving force distribution to the auxiliary driving wheels is faster than the conventional driving force distribution control using a transfer clutch. Can be realized.

  As mentioned above, although the drive force distribution control apparatus of the four-wheel drive vehicle of this invention has been demonstrated based on Example 1, it is not restricted to this Example 1 about a concrete structure, Each of Claims Design changes and additions are permitted without departing from the scope of the claimed invention.

  In the first embodiment, an example of application to a four-wheel drive vehicle based on a front wheel drive is shown. However, the present invention can also be applied to a four-wheel drive vehicle based on a rear wheel drive. In this case, there is almost no difference between the front and rear wheel rotational speeds, but in a driving situation where the yaw rate deviation Δψ is large, it is possible to reduce the oversteer tendency by distributing the driving force to the front wheels.

  In the first embodiment, an example in which the maximum value and the minimum value (= 0) for suppressing excessive allocation of driving force to one of the front and rear wheels (rear wheel) is set as the threshold value setting means as the threshold value set by the yaw rate deviation. However, a negative value (a value in which the driving force is not distributed until the negative threshold value is set to zero even when the detected value of the front and rear wheel rotational speed difference is output) may be set as the minimum value.

  In the first embodiment, an example of application to a hybrid four-wheel drive vehicle having motors on the front and rear wheels has been shown. However, for example, the present invention can also be applied to a hybrid four-wheel drive vehicle having motors on the left and right rear wheels. In addition to hybrid four-wheel drive vehicles, only engines are installed as the main drive source, and sub-drive wheels are also used in engine four-wheel drive vehicles and four-wheel drive electric vehicles that transmit driving force via clutches etc. Applicable. In the first embodiment, as an example of the driving force distribution control unit, the driving force of the driving source of each of the main driving wheel and the auxiliary driving wheel is directly controlled. However, as described in the related art, in the driving system, The present invention can also be applied to a device that includes a transfer clutch, a differential limiting clutch, and the like, and controls the front and rear wheel driving force distribution by clutch engagement force control. In short, one of the front and rear wheels is a main drive wheel and the other is a sub drive wheel, and four driving force distribution control means for performing control to increase the drive force distribution to the sub drive wheel as the front and rear wheel rotational speed difference is larger. It can be applied to a wheel drive vehicle.

1 is an overall system diagram showing a hybrid four-wheel drive vehicle to which a driving force distribution control device of Embodiment 1 is applied. 3 is a flowchart illustrating a flow of a driving force distribution control process executed by the controller according to the first embodiment. It is a figure which shows the rear-wheel command torque map with respect to the front-and-rear wheel rotation speed difference control value used by the driving force distribution control of Example 1. FIG. FIG. 6 is a diagram showing a rear wheel command torque map when the horizontal axis of the rear wheel command torque map used in the driving force distribution control of the first embodiment is replaced with front and rear wheel rotation speed difference control values instead of front and rear wheel rotation speed difference detection values. is there. It is a rear-wheel driving force characteristic view with respect to the front-and-rear wheel rotational speed difference detection value explaining the situation where a threshold value is changed by the yaw rate deviation in the driving force distribution control of the first embodiment. It is a rear-wheel driving force characteristic diagram with respect to the front-and-rear wheel rotation speed difference detection value explaining the situation where the maximum value and the minimum value are set to the threshold value determined by the yaw rate deviation in the driving force distribution control of the first embodiment. 6 is a time chart for explaining a situation in which driving force distribution is not performed when the fluctuation of the target yaw rate where the target yaw rate differential value is equal to or larger than the set value is large at the time of switching steering in the driving force distribution control of the first embodiment.

Explanation of symbols

1 engine (first drive source)
2F front motor (first drive source)
2R rear motor (second drive source)
3FL left front wheel tire (main drive wheel)
3FR Right front wheel tire (main drive wheel)
3RL left rear wheel tire (sub-drive wheel)
3RR Right rear wheel tire (sub drive wheel)
4F front differential 4R rear differential 5F front transmission 5R rear transmission 6 wheel speed sensor 7 rudder angle sensor 8 lateral acceleration sensor 9 vehicle speed sensor 10 accelerator opening sensor 11 controller 12 high power battery 13F front inverter 13R rear inverter 14 yaw rate sensor

Claims (5)

Four-wheel drive equipped with driving force distribution control means for controlling one of the front and rear wheels to be the main driving wheel and the other to be the auxiliary driving wheel, and to increase the driving force distribution to the auxiliary driving wheel as the front-rear wheel rotational speed difference increases. In a driving force distribution control device for a car,
A threshold setting unit is provided for setting a threshold with a larger value as the yaw rate deviation between the absolute value of the target yaw rate and the absolute value of the actual yaw rate is larger,
The driving force distribution control means uses a value obtained by adding the threshold value to a front and rear wheel rotational speed difference detection value as a front and rear wheel rotational speed difference control value used in front and rear wheel rotational speed difference correspondence control. Driving force distribution control device for cars. In the drive force distribution control device for a four-wheel drive vehicle according to claim 1,
The threshold value setting means sets a maximum value and a minimum value for suppressing excessive distribution of driving force to one of the front and rear wheels to the threshold value set by the yaw rate deviation. . In the drive force distribution control device for a four-wheel drive vehicle according to claim 1 or 2,
A target yaw rate differential value calculating means for calculating the target yaw rate differential value is provided,
The driving force distribution control means sets the threshold to zero when the target yaw rate differential value exceeds a set value that is a judgment value of a sudden yaw rate change, and only when the target yaw rate differential value is equal to or less than a set value. A driving force distribution control device for a four-wheel drive vehicle, wherein a value obtained by adding the threshold value to a detected value of difference in front and rear wheel speed difference is used as a front and rear wheel speed difference control value used in front and rear wheel speed difference correspondence control. In the drive force distribution control device for a four-wheel drive vehicle according to any one of claims 1 to 3,
The vehicle has a front drive wheel as a main drive wheel, a rear wheel as a sub drive wheel, a first drive source for driving the front wheel by at least one of an engine and a motor, and a second drive source for driving the rear wheel by a motor. It is a front-wheel drive based hybrid four-wheel drive vehicle equipped with,
The driving force distribution control means controls the driving force transmitted to the rear wheels, which are auxiliary driving wheels, by controlling the motor driving force of the second driving source. Distribution controller. In a driving force distribution control device for a four-wheel drive vehicle, one of the front and rear wheels is a main driving wheel and the other is a sub driving wheel, and the driving force distribution to the sub driving wheel is increased as the front-rear wheel rotational speed difference increases. ,
A larger threshold value is set as the yaw rate deviation between the target yaw rate and the actual yaw rate is larger, and the value obtained by adding the threshold value to the detected value of the front and rear wheel speed difference is used for front and rear wheel speed difference control. A drive force distribution control device for a four-wheel drive vehicle, characterized in that the control value is used.

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