JP2001082199A - Driving force control device for four-wheel drive vehicle - Google Patents

Abstract

[PROBLEMS] To provide a driving force control device for a four-wheel drive vehicle capable of highly accurately estimating a vehicle speed excluding the influence of an error due to a road gradient and improving driving force control performance. . SOLUTION: In a driving force control device for controlling a drive slip of a wheel of a four-wheel drive vehicle, a longitudinal acceleration detecting means a for estimating or detecting a longitudinal acceleration generated in a vehicle, and a road surface gradient estimating means for estimating a road surface gradient. a vehicle speed estimating means b for correcting the longitudinal acceleration detected by the longitudinal acceleration detecting means a in consideration of the road surface gradient estimated by the road surface gradient estimating means g and estimating the vehicle speed from the corrected value; A driving force control unit c that controls the driving force transmitted from each wheel to the road surface based on the driving slip determination using the estimated vehicle speed by the estimation unit b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a driving force control device for a four-wheel drive vehicle.

[0002]

2. Description of the Related Art Conventionally, a driving force control device for suppressing a driving slip has been applied to a two-wheel drive vehicle in which a driving slip is liable to occur during an acceleration operation or running on a low μ road by transmitting engine driving force to only two wheels. It is often applied, and when estimating the vehicle speed which is a basic signal of the driving force control, basically, the speed of the driven wheel to which no engine driving force is transmitted (the front wheel speed in the case of a rear wheel driving vehicle) is used. The estimated vehicle speed can be accurately calculated.

On the other hand, in a four-wheel drive vehicle, since the engine driving force is distributed to the four wheels, the driving force transmitted from each wheel to the road surface is lower than that of a two-wheel drive vehicle if the engine driving force is the same. Slip is less likely to occur, and a certain amount of driving force can be generated even when the road surface μ is small, so that driving force control is rarely applied.

[0004]

When the driving force control is applied to a four-wheel drive vehicle, the four wheels are in a drive slip state. Thus, there is a problem that it is difficult to estimate with high accuracy.

[0005] This is because it is difficult to directly estimate the vehicle speed from the wheel speed when all the wheels are slipping. In particular, on extremely low μ roads, the wheel speed tends to increase the drive slip, and therefore, even if the wheel slip is suppressed by the driving force control, the estimated vehicle speed also tends to be higher than the actual vehicle speed (see FIG. 5). .

To solve such a problem, there is a method of estimating the vehicle body speed by applying the method of estimating the vehicle body speed at the time of anti-skid control in which all the wheels are in a slipping deceleration state while the slip directions of the wheels are different. That is, a sensor for detecting the longitudinal acceleration of the vehicle body is provided, and when the four wheels are slipping, the vehicle speed is estimated by changing the vehicle speed according to the longitudinal acceleration. Thus, on a flat road,
Accurate estimation of the vehicle speed can be performed (see FIG. 6).

However, in the vehicle speed estimation method using anti-skid control, a longitudinal acceleration sensor is used, so that when the road surface is steep, the influence of the road surface gradient is exerted on the longitudinal acceleration sensor. There is a problem that a correct amount of change in the vehicle speed cannot be measured. For example, if the driving force control is performed when the four wheels drive slip due to rapid acceleration on a steep downhill road surface having a small road surface μ, the output of the longitudinal acceleration sensor becomes smaller than the actual change amount of the vehicle speed. However, there is a problem that the estimated vehicle speed becomes smaller than the actual value and the vehicle stalls (see FIG. 7).

In order to solve such a problem, a method is considered in which, like the anti-skid control device, some wheels are temporarily returned to a non-slip state to approach the true vehicle speed, thereby correcting an estimation error. Can be However, when such control is performed, there is a problem that the fluctuation of the wheel speed is actually increased, and the sense of acceleration is deteriorated, for example, the fluctuation of the longitudinal acceleration of the vehicle body is caused (see FIG. 8).

The present invention has been made in view of such a problem. The present invention estimates a road surface gradient, corrects the longitudinal acceleration detected by the longitudinal acceleration detecting means according to the road surface gradient, and corrects the vehicle body with the correction value. An object of the present invention is to provide a driving force control device for a four-wheel drive vehicle that can estimate a vehicle speed with high accuracy by eliminating an influence of an error due to a road surface gradient and that can improve driving force control performance. And

[0010]

Means for solving the above problems are as follows.
It is as follows.

According to the first aspect of the present invention, there is provided a driving force control device for controlling a driving slip of wheels of a four-wheel drive vehicle.
Longitudinal acceleration detecting means for estimating or detecting longitudinal acceleration occurring in the vehicle, road gradient estimating means for estimating the gradient of the road surface, and considering the road gradient estimated by the road gradient estimating means, the longitudinal acceleration detecting means A vehicle speed estimating means for correcting the detected longitudinal acceleration and estimating the vehicle speed from the corrected value; and a driving force transmitted from each wheel to the road surface based on a drive slip determination using the estimated vehicle speed by the vehicle speed estimating means. And a driving force control means for controlling the driving force.

According to a second aspect of the present invention, there is provided a driving force control device for controlling a driving slip of wheels of a four-wheel drive vehicle,
Longitudinal acceleration detecting means for estimating or detecting longitudinal acceleration occurring in the vehicle, wheel slip convergence state determining means for determining that the slip state of each wheel is in a convergence state, and wheels according to the determination of the wheel slip convergence determining means. A vehicle speed change amount calculating means for calculating a vehicle speed change amount from the vehicle speed, and a road surface gradient is estimated based on a difference between the vehicle body speed change amount calculated by the vehicle body speed change amount calculating means and the longitudinal acceleration detected by the longitudinal acceleration detecting means. Road surface gradient estimating means, and a vehicle speed estimating means for correcting the longitudinal acceleration detected by the longitudinal acceleration detecting means in consideration of the road surface gradient estimated by the road surface gradient estimating means, and estimating the vehicle speed from the correction value. Driving force control means for controlling the driving force transmitted from each wheel to the road surface based on the drive slip determination using the estimated vehicle speed by the vehicle speed estimation means. It is characterized in.

According to the third aspect of the present invention, the first or second aspect is provided.
In the driving force control device for a four-wheel drive vehicle described above, the driving force control means uses at least one of engine output control by cutting fuel to the engine, engine output control by adjusting throttle opening, and braking force control by brake. Means for controlling the driving force.

According to a fourth aspect of the present invention, in the driving force control device for a four-wheel drive vehicle according to the first to third aspects, the longitudinal acceleration detecting means includes a longitudinal accelerometer for directly detecting the longitudinal acceleration acting on the vehicle body. It is characterized in that it is used means.

According to a fifth aspect of the present invention, in the driving force control apparatus for a four-wheel drive vehicle according to any one of the first to fourth aspects, the wheel slip convergence judging means includes at least a target wheel speed set from an estimated vehicle body speed and each The present invention is characterized in that means for judging the convergence state of the wheel slip is determined based on whether or not the deviation of the wheel from the wheel speed is within a set value.

According to a sixth aspect of the present invention, in the driving force control apparatus for a four-wheel drive vehicle according to any one of the first to fourth aspects, the wheel slip convergence judging means includes at least a target wheel speed set from an estimated vehicle body speed and each of the target wheel speeds. It is characterized in that the means for judging the convergence state of the wheel slip is determined based on whether or not the deviation of the wheel speed from the average value is within a set value.

According to a seventh aspect of the present invention, in the driving force control apparatus for a four-wheel drive vehicle according to any one of the first to sixth aspects, the vehicle body speed estimating means may be configured so that the road surface gradient estimated by the road surface gradient estimating device is equal to or more than a set value. In this case, the vehicle body speed is calculated by adding or subtracting the road surface gradient from the detected longitudinal acceleration value, and the vehicle body speed is estimated in accordance with the true vehicle body speed change amount.

According to an eighth aspect of the present invention, in the driving force control apparatus for a four-wheel drive vehicle according to any one of the first to sixth aspects, the vehicle body speed estimating means may be configured so that the road surface gradient estimated by the road surface gradient estimating device is equal to or more than a set value. In this case, the time during which this state is continued is counted, and the longitudinal acceleration is corrected by adding or subtracting the offset amount to the longitudinal acceleration detection value in accordance with the count, and the vehicle speed is corrected according to the longitudinal acceleration after this correction. It is characterized in that it is a means for estimating.

[0019]

According to the present invention, the longitudinal acceleration detecting means estimates or detects the longitudinal acceleration occurring in the vehicle, and the road gradient estimating means estimates the gradient of the road surface. In the speed estimation means,
The longitudinal acceleration detected by the longitudinal acceleration detecting means is corrected in consideration of the road surface gradient estimated by the road surface gradient estimating means, the vehicle speed is estimated from the corrected value, and the driving force control means estimates the vehicle body by the vehicle speed estimating means. The driving force transmitted from each wheel to the road surface is controlled based on the driving slip determination using the speed.

For example, if the driving force control is performed when the four wheels drive slip due to rapid acceleration on a steeply sloping road surface having a small road surface μ, the detected longitudinal acceleration becomes smaller than the actual variation of the vehicle speed. Since the vehicle speed becomes smaller, the estimated vehicle speed becomes smaller than the actual value, and there is a problem that the vehicle stalls.However, by correcting the longitudinal acceleration detected in consideration of the estimated road surface gradient, the influence of the road surface gradient is eliminated. In addition, the longitudinal acceleration information, which is the estimated information of the vehicle speed, can be changed to information having high consistency with the actual longitudinal acceleration value.

As described above, when the four-wheel drive vehicle is combined with the driving force control device for suppressing the driving slip, the longitudinal acceleration detected in consideration of the estimated road surface gradient is corrected, and the vehicle speed is estimated from the corrected value. As a result, the vehicle speed can be estimated with high accuracy while eliminating the influence of the error due to the road surface gradient, and the driving force control performance can be improved.

According to the second aspect of the present invention, the longitudinal acceleration detecting means estimates or detects the longitudinal acceleration occurring in the vehicle, and the wheel slip convergence state determining means determines that the slip state of each wheel is converging. The vehicle speed change amount calculating means calculates the vehicle speed change amount from the wheel speed in accordance with the determination of the wheel slip convergence determining means, and the road surface gradient estimating means calculates the vehicle speed change amount calculated by the vehicle speed change amount calculating means. The gradient of the road surface is estimated based on the difference between the amount of change and the longitudinal acceleration detected by the longitudinal acceleration detecting means, and the vehicle body speed estimating means considers the road surface gradient estimated by the road surface gradient estimating means and detects the front and rear directions detected by the longitudinal acceleration detecting means. The acceleration is corrected, the vehicle speed is estimated from the correction value,
In the driving force control means, the driving force transmitted from each wheel to the road surface is controlled based on the drive slip determination using the estimated vehicle speed by the vehicle speed estimation means.

Here, the relationship between the detected longitudinal acceleration and the road gradient is such that the detected longitudinal acceleration is smaller than the actual correct longitudinal acceleration on a descending road surface, and conversely, the actual correct longitudinal acceleration is on a rising gradient road surface. There is a fixed relation that the longitudinal acceleration detected from the longitudinal acceleration increases. Therefore, if the actual correct longitudinal acceleration and the detected longitudinal acceleration are known, the road surface gradient can be estimated.
On the other hand, in a driving situation where there is no drive slip, the wheel speed and the vehicle body speed match.

Accordingly, the vehicle body speed change amount is calculated from the wheel speed in accordance with the slip convergence determination, and the difference between the calculated vehicle body speed change amount and the longitudinal acceleration detected by the longitudinal acceleration detecting means is used to determine the road surface gradient. Can be estimated well. Other functions and effects are the same as those of the first aspect.

According to the third aspect of the present invention, the driving force is controlled using at least one of engine output control by cutting fuel to the engine, engine output control by adjusting the throttle opening, and braking force control by braking. You.

According to the present invention, the longitudinal acceleration is detected by using a longitudinal accelerometer which directly detects the longitudinal acceleration acting on the vehicle body.

Therefore, the longitudinal acceleration acting on the vehicle body can be detected more accurately than when the longitudinal acceleration is obtained by estimation.

According to a fifth aspect of the present invention, in the wheel slip convergence determining means, it is determined whether a deviation between at least the target wheel speed set from the estimated vehicle speed and the wheel speed of each wheel is within a set value. Thus, the convergence state of the wheel slip is determined.

According to the present invention, in the wheel slip convergence determining means, at least the deviation between the target wheel speed set from the estimated vehicle speed and the average value of the wheel speeds of the respective wheels falls within the set value. The convergence state of the wheel slip is determined based on whether or not the vehicle is slipping.

According to the present invention, when the road surface gradient estimated by the road surface gradient estimating means is equal to or higher than a set value, the vehicle body speed estimating means adjusts the road surface gradient from the detected longitudinal acceleration value. A true vehicle speed change amount is calculated, and the vehicle speed is estimated according to the true vehicle speed change amount.

According to the present invention, when the road surface gradient estimated by the road surface gradient estimating means is equal to or higher than a set value, the vehicle body speed estimating means counts the time during which this state is continued, and The longitudinal acceleration is corrected by adding or subtracting the offset amount to the longitudinal acceleration detection value according to the count, and the vehicle speed is estimated according to the corrected longitudinal acceleration.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.

First, the configuration will be described.

FIG. 1 is a conceptual diagram showing the invention according to claim 1, wherein a is longitudinal acceleration detecting means, b is vehicle speed estimating means,
c is driving force control means, and g is road surface gradient estimating means. FIG. 2 is a conceptual diagram showing the invention according to claim 2, and FIG.
Is a longitudinal acceleration detecting means, b is a vehicle speed estimating means, c is a driving force control means, d is a wheel slip convergence determining means, f is a vehicle speed change amount calculating means, and g is a road surface gradient estimating means.

(Embodiment 1) Next, Embodiment 1 corresponding to the first and second aspects of the present invention will be described.

FIG. 3 is an overall system diagram including a drive system to which the driving force control device for a four-wheel drive vehicle according to the first embodiment is applied. The vehicle to which the driving force control device of the first embodiment is applied is a four-wheel drive vehicle based on a rear wheel drive, and includes a drive system including an engine 1, a front final drive 2, a rear final drive 3, a transfer 4, a left and right front wheel. 1
0, 20, left and right rear wheels 30, 40, each rear wheel 3
The engine driving force that has passed through the transmission is directly transmitted to 0 and 40 and transmitted to the front wheels 10 and 20 via the transfer 4.

The driving force distribution control device that optimally controls the driving force distribution between the front and rear wheels while achieving both driving performance and steering performance is provided by a hydraulic actuator 6 that controls the hydraulic pressure of the wet multi-plate clutch 5. , 20 to control from a two-wheel drive state to a four-wheel drive state (rigid four-wheel drive). Left and right front wheels 10, 20,
Wheel speed sensors 11, 21, 31, and 41 for detecting wheel speeds are installed on the left and right rear wheels 30, 40, respectively, and signals from the wheel speed sensors 11, 21, 31, 41 are in a driving state. Is input to the controller 50 that controls Further, a longitudinal acceleration sensor 7 (corresponding to longitudinal acceleration detecting means) for detecting a longitudinal acceleration Xg of the vehicle and a lateral acceleration sensor 8 for detecting a lateral acceleration Yg are provided. 50 is input.

The engine output as the driving force control is controlled by giving a target driving torque Tes command to an engine controller 51 for controlling the engine output from the controller 50 and controlling the fuel cut and the throttle opening. Output is controlled. Throttle control is
This is performed by the throttle controller 52 in response to a throttle opening command from the engine controller 51. on the other hand,
The controller 50 is connected to an AT controller 53 that controls a mission, and receives a signal of a gear position. The engine driving torque Te is also input from the engine controller 51.

Next, the operation will be described.

FIG. 4 shows a flowchart of the engine output control program executed by the controller 50.
Hereinafter, each step will be described in detail.

In step 101, each wheel speed, longitudinal acceleration, lateral acceleration, and various data from each control unit are read. That is, the longitudinal acceleration Xg, the lateral acceleration Yg, each wheel speed Vwi (i = 1 to 4), the engine driving torque Te, and the gear position GR are read.

In step 102, the selected wheel speed Vfs
Is calculated. In this example, the wheel speed Vw of each wheel is filtered according to acceleration / deceleration, etc.
fi (i = 1 to 4) is calculated for each wheel, and the lowest wheel speed is selected from each Vwfi according to conditions such as braking / non-braking, for example, during acceleration, etc. to select the vehicle speed closest to the vehicle speed. Calculate the wheel speed Vfs. In particular, when the four wheels are slipping and the driving force control is activated, Vfs is calculated so that the front wheel having the lower wheel speed follows within a certain acceleration. Here, the reason why the wheel speed of the front wheels is smaller is that the driving force distributed to the front wheels tends to be smaller than that of the rear wheels due to the characteristics of the four-wheel drive device in this example. When using a four-wheel drive device, it goes without saying that there is a selection method suitable for the four-wheel drive device.

Step 103 calculates the control wheel speed Vwt. In this example, when the gear position GR is the 1st or 2nd speed, the average wheel speed of the 4 wheels is set as the control wheel speed Vwt which is the target wheel speed of the drive control. Control wheel speed Vwt. Here, the calculation of the control wheel speed Vwt is also similar to the above-described select wheel speed Vfs, depending on the characteristics of the four-wheel drive device used.For example, in the four-wheel drive device of the present embodiment, the rear wheels have slipped. Then, the driving force is distributed to the front wheels, and the slip of the rear wheels is suppressed. When the gear position is on the high gear side, the balance of the front and rear slips is left to the four-wheel drive device, and if a drive slip occurs on the front wheels with the distributed driving force, the average wheel speed of the front wheels may be controlled. In the case of the low gear, the driving torque is large, so that the four wheels immediately enter a slip state, and the distribution of the driving torque by the four-wheel drive device also increases. Is the control target,
There is a problem such as mutual interference between controls, and the average wheel speed of the four wheels is set as a control target. In a four-wheel drive device in which the distribution of the four-wheel driving force is constant, the wheel speed to be controlled may be calculated based on the weight according to the distribution.

In step 104, the convergence of the wheels is determined (corresponding to wheel slip convergence determining means). In this example, the target wheel speed Vwsi and the control wheel speed Vw calculated by the method described below are used.
When the deviation from t is within a certain set value (for example, 1 km / h), it is considered that the wheel speed is converging, and the convergence determination counter Ksu is counted up. When the convergence determination counter Ksu becomes equal to or greater than a certain set value (for example, 150 ms; 15 when the control cycle is 10 msec), it is determined that the wheel speed has converged.

In step 105, the selected wheel speed change amount dVfs is calculated. In this example, within a certain time (for example, 4
The change amount of select wheel speed dVfs is calculated according to the following equation as the change amount of the average value of the select wheel speed Vfs (for 0 msec). However, the following equation is calculated every 40 msec.

DVfs = Kg * (VF [0] + VF [1] −VF
[3]-VF [4]) where VF is the average value of the selected wheel speed Vfs and 10m
It is calculated according to the following equation for each sec. Kg is a unit conversion count.

VF = Kg * (Vfs [0] + Vfs [1] + Vfs
[2] + Vfs [3]) / 4 Here, the number in [] indicates how many cycles earlier the value is.

In step 106, the estimated road surface slope dS
(Corresponding to road surface gradient estimating means). In this example, when the convergence is determined in step 103, the estimated road surface gradient dS is calculated by the following equation.

DS = dVfs-Xg When convergence is not determined, dS = 0.

In step 107, the estimated road surface slope dS
Slope determination is made according to. In this example, the road surface gradient estimated value d
When S is equal to or more than a certain set value (for example, 0.05 g), it is determined that the road is an uphill road, and the slope determination counter Ksa is counted up. The slope determination counter Ksa has a maximum value (for example, 50), and is counted down when the estimated road surface gradient value is equal to or less than the set value.

In step 108, the longitudinal acceleration correction amount dVh is calculated according to the slope judgment. In this example, the slope determination counter Ksa is used, and when Ksa is equal to or more than the set value (for example, 15), dVh = min ((Ksa−15) * Kr, dVhmax). Here, Kr is a tuning constant, for example, 0.
01 and so on. If the value is equal to or less than the set value, dVh = 0. Further, dVhmax is a maximum limit value of the correction amount, and is set so that too large correction is not performed.

In step 109, a vehicle speed change amount Vid is calculated (corresponding to a vehicle speed change amount calculating means). In this example,
It is calculated from the longitudinal acceleration sensor value (acceleration side plus), the longitudinal acceleration correction value, and the minimum limit value Vidmin according to the following equation.

[Acceleration Judgment] Vid = max (Xg + dVh, Vidmin) Here, Vidmin is the minimum limit value of the vehicle speed change amount Vid, and is set in consideration of acceleration and driving force control. You. In this example, the weight is set to, for example, 0.05 g. The acceleration is determined by comparing the select wheel speed Vfs with the previous value of the estimated vehicle speed Vi, and when Vfs ≧ Vi (previous value), it is determined that the vehicle is accelerating.

[Determination of deceleration] Calculated by the following equation in which an offset is added to the longitudinal acceleration sensor value.

Vid = Xg-G_offset In this example, the offset is a typical slope on the market:
0.3g so that Vid does not become a positive value during deceleration.

In step 110, the estimated vehicle speed Vi is calculated (corresponding to the vehicle speed estimating means). In this example, the selected wheel speed Vfs, the vehicle speed change amount Vid, and the estimated vehicle speed Vi are calculated from the previous values according to the following equation.

[Acceleration] Vi = min (Vi (previous value) + Vid, Vfs) [Deceleration] Vi = max (Vi (previous value) + Vid, 0) That is, the vehicle speed change amount Vid is added to the previous value of Vi. Shall be added. However, when accelerating, Vfs is set to the maximum limit value, and when decelerating, 0 is set to the lower limit value. By calculating the estimated vehicle speed in this manner, the vehicle speed is such that the four-wheel drive vehicle is in a state where the four wheels are slipping and the driving force control is operating and the road surface has a gradient. Even when the estimation is difficult, the vehicle speed can be accurately estimated.

From the next step, the driving force control using the estimated vehicle speed will be described.

First, the control amount of the four-wheel drive distribution control is calculated. In step 111, a differential force limiting torque TETS controlled by the four-wheel drive power distribution device is calculated. In this example, as shown below, front and rear average wheel speeds Vff and Vrr are calculated from the wheel speeds of the respective wheels, and the differential limiting torque TETS is calculated according to the difference between the front and rear rotation speeds ΔVfr.

Vff = (Vw1 + Vw2) / 2 Vrr = (Vw3 + Vw4) / 2 ΔVfr = Vrr−Vff The differential limiting torque TETS is calculated from the longitudinal rotational speed difference ΔVfr as follows:
It is calculated according to the characteristic map shown in FIG. Note that the electronic control driving force distribution control also includes other control such as increasing the driving force distribution to the front wheels according to the increase in the rotational speed difference between the front and rear wheels, as shown in FIG. 11 attached for reference. However, it is omitted here.

In step 112, a target slip amount Sstar for driving force control is calculated. In this example, the target slip is corrected by correcting the reference target slip amount SO (for example, 2.5 km / h) by an acceleration / deceleration state, determination of straight running or turning, determination of a road surface μ, activation and deactivation of driving force control, and the like. Set the amount Sstar.

At step 113, the target wheel speed Vws is calculated. In this example, the estimated vehicle speed obtained in step 110
It is calculated from Vi and the target slip amount Sstar set in step 112 by the following equation.

Vws = Vi + Sstar In step 114, the target drive torque Tes is calculated.
In this example, first, the target wheel speed Vws obtained in step 113
And the deviation from the control wheel speed Vwt obtained in step 103 is calculated by the following equation.

Ε = Vws−Vwt Further, a target drive torque Tes, which is a command value of the F / B control (here, PID control), is calculated by the following equation according to the deviation ε.

[Driving force control is not activated] Tes = Te [Driving force control is activated] Tes = Kp * ε + Kd * dε / dt + Ki * ∫εdt where Kp, Kd and Ki are F / B gains, respectively. It is changed by gears. For example, according to the gear position, the gain is larger for the lower gear, and the gain is smaller for the higher gear. In addition, as ε increases in accordance with the wheel speed deviation ε, the gain is increased (non-linear control) to improve responsiveness.
The gain may be lowered.

In step 115, each drive signal is output. That is, a voltage command value corresponding to the target differential limiting torque TETS is output to the driving force distribution control device. Further, the target driving torque Tes is output to the engine controller 51.

In the present embodiment, the engine controller 51 receives the target torque Tes from the driving force control controller 50 and controls the fuel cut and the throttle opening in accordance with the target values. Engine output command controls. The throttle control is performed by the throttle controller 52 in response to a throttle opening command from the engine controller 51.

FIG. 10 is a time series graph (time chart) showing the operation when this control is performed.

That is, as in the case of FIG. 7, when the estimated value of the vehicle body speed is estimated to be smaller than the actual vehicle speed at the time of starting acceleration on a steep downhill, a slight decrease in acceleration occurs, Correction of the longitudinal acceleration is started by the speed convergence determination and the subsequent slope determination, and the estimated vehicle speed Vi is corrected to a larger one, so that the acceleration can be restored. Thereby, the acceleration failure is eliminated, and the acceleration performance is improved.

(Other Embodiments) In the first embodiment, the estimation of the road surface gradient is performed by calculating the vehicle speed change amount from the wheel speed in accordance with the wheel slip convergence judgment, and detecting the vehicle body speed change amount and longitudinal acceleration detection. The example of the means for estimating the gradient of the road surface based on the difference between the longitudinal accelerations detected by the means has been described.
Estimate the road gradient by a method other than that shown in the above.If there is a control system that uses the road gradient information in the installed control system, introduce the road gradient information of the control system online and use it. May be.

In the first embodiment, an example of application to an electronically controlled torque split type four-wheel drive vehicle that variably controls the driving force distribution ratio between the front and rear wheels according to the differential amount of the front and rear wheels as a four-wheel drive vehicle is shown. However, the present invention is applied to various types of four-wheel drive vehicles such as four-wheel drive vehicles, four-wheel drive vehicles using a viscous coupling, and four-wheel drive vehicles using an orifice coupling with a fixed driving force distribution ratio. Can be applied.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing the invention according to claim 1;

FIG. 2 is a conceptual diagram showing the invention according to claim 2;

FIG. 3 is an overall system diagram to which the driving force control device for the four-wheel drive vehicle according to the first embodiment is applied.

FIG. 4 is a flowchart illustrating a driving force control process according to the first embodiment.

FIG. 5 is a time chart showing an estimated vehicle speed on an extremely low μ road.

FIG. 6 is a time chart showing an estimated vehicle speed on a flat road.

FIG. 7 is a time chart showing an estimated vehicle speed on a downhill.

FIG. 8 is a time chart showing an estimated vehicle speed in a case where some of the wheels do not temporarily slip.

FIG. 9 is a characteristic map showing a relationship between a differential limiting torque TETS and a front-rear rotational speed difference ΔVfr in the first embodiment.

FIG. 10 is a time chart illustrating an operation when the control of the first embodiment is performed on a downhill.

FIG. 11 is a characteristic map showing a relationship between a front-rear rotational speed difference and a torque distribution amount to front wheels as a control example as a reference of the driving force distribution control.

[Explanation of symbols]

 Reference Signs List 1 engine 2 front final drive 3 rear final drive 4 transfer 5 wet multiple disc clutch 6 hydraulic actuator 7 longitudinal acceleration sensor 8 lateral acceleration sensor 11, 21, 31, 41 wheel speed sensor 50 control unit 51 engine control unit 52 throttle control unit 53 A / T control unit

Claims (8)

[Claims] 1. A driving force control device for controlling driving slip of wheels of a four-wheel drive vehicle, a longitudinal acceleration detecting means for estimating or detecting a longitudinal acceleration generated in a vehicle, and a road surface gradient estimating device for estimating a road surface gradient. And taking into account the road surface gradient estimated by the road surface gradient estimating means,
A vehicle speed estimating means for correcting the longitudinal acceleration detected by the longitudinal acceleration detecting means and estimating a vehicle speed from the corrected value; and a road slip from each wheel based on a drive slip determination using the estimated vehicle speed by the vehicle speed estimating means. A driving force control device for controlling a driving force transmitted to the vehicle, and a driving force control device for a four-wheel drive vehicle, comprising: 2. A driving force control device for controlling a driving slip of wheels of a four-wheel drive vehicle, a longitudinal acceleration detecting means for estimating or detecting a longitudinal acceleration occurring in the vehicle, and a slip state of each wheel being converged. Wheel slip convergence state determining means for determining the vehicle speed change amount calculating means for calculating a vehicle body speed change amount from the wheel speed in accordance with the determination of the wheel slip convergence determining means; and calculating the vehicle body speed change amount calculating means. A road surface gradient estimating unit for estimating a road surface gradient based on a difference between the vehicle body speed change amount and the longitudinal acceleration detected by the longitudinal acceleration detecting unit; taking into account the road surface gradient estimated by the road surface gradient estimating unit,
A vehicle speed estimating means for correcting the longitudinal acceleration detected by the longitudinal acceleration detecting means and estimating a vehicle speed from the corrected value; and a road slip from each wheel based on a drive slip determination using the estimated vehicle speed by the vehicle speed estimating means. A driving force control device for controlling a driving force transmitted to the vehicle, and a driving force control device for a four-wheel drive vehicle, comprising: 3. The driving force control device for a four-wheel drive vehicle according to claim 1, wherein the driving force control means includes: engine output control by cutting fuel to the engine; engine output control by adjusting throttle opening; A driving force control device for a four-wheel drive vehicle, characterized in that the driving force is controlled by using at least one of the braking force controls by the control unit. 4. A driving force control apparatus for a four-wheel drive vehicle according to claim 1, wherein said longitudinal acceleration detecting means is means for using a longitudinal accelerometer for directly detecting longitudinal acceleration acting on a vehicle body. A driving force control device for a four-wheel drive vehicle. 5. The driving force control apparatus for a four-wheel-drive vehicle according to claim 1, wherein the wheel slip convergence determining means determines at least a target wheel speed set from an estimated vehicle speed and a wheel speed of each wheel. A driving force control device for a four-wheel drive vehicle, characterized in that a means for judging a convergence state of wheel slips based on whether the deviation is within a set value or not. 6. The driving force control apparatus for a four-wheel drive vehicle according to claim 1, wherein the wheel slip convergence determining means averages at least a target wheel speed set from an estimated vehicle speed and a wheel speed of each wheel. A driving force control device for a four-wheel drive vehicle, characterized in that a means for judging a convergence state of wheel slip is determined based on whether a deviation from the value is within a set value or not. 7. The driving force control device for a four-wheel drive vehicle according to claim 1, wherein the vehicle body speed estimating means includes a longitudinal acceleration when the road surface gradient estimated by the road surface gradient estimating device is equal to or more than a set value. Means for calculating a true vehicle speed change by adding or subtracting a road surface gradient from the detected value and estimating the vehicle speed in accordance with the true vehicle speed change. Control device. 8. The driving force control apparatus for a four-wheel drive vehicle according to claim 1, wherein said vehicle body speed estimating means is configured to detect the vehicle speed when the road surface gradient estimated by the road surface gradient estimating device is equal to or greater than a set value. Means for estimating the vehicle speed in accordance with the corrected longitudinal acceleration by counting the time that the continuation is continued, adding or subtracting the offset amount to the detected longitudinal acceleration value in accordance with the count. A driving force control device for a four-wheel drive vehicle.