JP3716333B2 - Driving force control device for four-wheel drive vehicle - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a driving force control device for a four-wheel drive vehicle.
[0002]
[Prior art]
Conventionally, a driving force control device that suppresses driving slip can be applied to a two-wheel drive vehicle in which driving slip is likely to occur during acceleration operation, low μ road traveling, etc. by transmitting engine driving force to only two wheels. In many cases, when estimating the vehicle speed, which is the basic signal for driving force control, the vehicle speed is basically estimated using the speed of the driven wheel (front wheel speed for rear-wheel drive vehicles) that does not transmit the engine driving force at all. The estimated vehicle speed can be calculated with high accuracy.
[0003]
On the other hand, in the four-wheel drive vehicle, the engine drive force is distributed to the four wheels, so if the engine drive force is the same, the drive force transmitted from each wheel to the road surface is lower than the two-wheel drive vehicle, and the drive slip itself Since it is difficult to generate and a certain amount of driving force can be generated even when the road surface μ is small, the driving force control is rarely applied.
[0004]
[Problems to be solved by the invention]
Therefore, when driving force control is applied to a four-wheel drive vehicle, the four wheels are in a drive slip state, and it is difficult to accurately estimate the vehicle speed, which is the basic signal for driving force control, as in a two-wheel drive vehicle. There is a problem that.
[0005]
This is because it is difficult to estimate the vehicle body speed directly from the wheel speed when all the wheels are slipping. In particular, on extremely low μ roads and the like, the wheel speed tends to increase the driving slip, so even if the wheel slip is suppressed by the driving force control, the estimated vehicle speed tends to be higher than the actual vehicle speed (see FIG. 5). .
[0006]
To solve this problem, there is a method for estimating the vehicle body speed by applying a vehicle body speed estimating method during anti-skid control in which all the wheels are in a slipping slip state although 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 body speed is estimated by changing the vehicle body speed according to the longitudinal acceleration. This makes it possible to accurately estimate the vehicle speed on a flat road (see FIG. 6).
[0007]
However, because the vehicle speed estimation method using anti-skid control uses a longitudinal acceleration sensor, when the road surface is a steep slope, the correct vehicle body speed is affected by the influence of the road surface gradient on the longitudinal acceleration sensor. There is a problem that it is impossible to measure the amount of change. For example, when driving force control is performed when the four wheels drive and slip suddenly on a steep downhill road surface with a small road surface μ, the output of the longitudinal acceleration sensor is smaller than the actual change in vehicle speed. The estimated vehicle speed becomes smaller than the actual value, and there is a problem that the vehicle stalls (see FIG. 7).
[0008]
To solve such a problem, as in the case of the anti-skid control device, a method can be considered in which some wheels are temporarily returned to a non-slip state to approach the true vehicle speed, thereby correcting the estimation error. However, when such control is performed, there is a problem that the wheel speed is actually fluctuated and the acceleration feeling deteriorates due to the fluctuation of the longitudinal acceleration of the vehicle body (see FIG. 8).
[0009]
The present invention has been made paying attention to such problems, and estimates the road surface gradient, corrects the longitudinal acceleration detected by the longitudinal acceleration detection means according to the road surface gradient, and estimates the vehicle speed from the correction value. Thus, an object of the present invention is to provide a driving force control device for a four-wheel drive vehicle that can estimate the vehicle speed with high accuracy while eliminating the influence of an error due to a road surface gradient and improve the driving force control performance.
[0010]
[Means for Solving the Problems]
The means for solving the above problems are as follows.
[0012]
According to the first aspect of the present invention, in the driving force control device for controlling the driving slip of the wheels of the four-wheel drive vehicle, the longitudinal acceleration detecting means for estimating or detecting the longitudinal acceleration generated in the vehicle, and the slip state of each wheel converge. Wheel slip convergence state determining means for determining that the vehicle is in a state, and selecting wheel speed change amount calculation for calculating the change amount of the selected wheel speed closest to the vehicle body speed among the wheel speeds according to the determination of the wheel slip convergence determining means means and a road surface gradient estimating means the longitudinal acceleration detecting means and the select wheel speed change amount to estimate the slope of the road surface by the difference before and after the detected acceleration the select wheel speed change calculation means for calculating the road surface gradient estimating means In consideration of the estimated road surface gradient, the longitudinal acceleration detected by the longitudinal acceleration detecting means is corrected and the vehicle speed is estimated from the corrected value. Characterized in that it comprises a means, and a driving force control means for controlling the driving force transmitted to the road surface from the wheels based on the traction determination using the estimated vehicle speed by the vehicle speed estimating means.
[0013]
According to a second aspect of the present invention, in the driving force control apparatus for a four-wheel drive vehicle according to the first aspect , the driving force control means includes an engine output control by a fuel cut to the engine and an engine output control by adjusting a throttle opening. The driving force is controlled by using at least one of braking force control by the brake.
[0014]
According to a third aspect of the present invention, in the driving force control device for a four-wheel drive vehicle according to the first or second aspect, the longitudinal acceleration detecting means uses a longitudinal accelerometer that directly detects the longitudinal acceleration acting on the vehicle body. It is characterized by that.
[0015]
According to a fourth 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 third aspects, the wheel slip convergence determining means is a target wheel set based on at least a vehicle body speed estimated value. It is characterized in that it is a means for judging the convergence state of the wheel slip based on whether or not the deviation between the speed and the wheel speed of each wheel is within a set value.
[0016]
According to a fifth aspect of the present invention, in the driving force control device for a four-wheel drive vehicle according to any one of the first to third aspects, the wheel slip convergence determining means is a target wheel set based on at least a vehicle body speed estimated value. The present invention is characterized in that the means for judging the convergence state of the wheel slip is determined by whether or not the deviation between the speed and the average value of the wheel speeds of each wheel is within a set value.
[0017]
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 fifth aspects, the vehicle surface speed estimating means is configured such that the road surface gradient estimated by the road surface gradient estimating means is a road surface gradient. When the value is equal to or greater than the set value, the vehicle body speed change amount is calculated by adding or subtracting the road surface gradient from the longitudinal acceleration detection value, and the vehicle body speed is estimated according to the true vehicle body speed change amount. And
[0018]
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 fifth aspects, the vehicle body speed estimation means is configured such that the road surface gradient estimated by the road surface gradient estimation means is a road surface gradient. When the set value is exceeded, the time for which this state continues is counted, and the longitudinal acceleration is corrected by adding or subtracting the offset amount to the longitudinal acceleration detection value according to the count. It is a means for estimating the vehicle speed.
[0019]
Operation and effect of the invention
In the first aspect of the present invention, the longitudinal acceleration detection means estimates or detects the longitudinal acceleration generated in the vehicle, and the wheel slip convergence state determination means determines that the slip state of each wheel is in the convergence state. The selection wheel speed change amount calculation means calculates the change amount of the select wheel speed closest to the vehicle body speed among the wheel speeds according to the determination of the wheel slip convergence determination means, and the road surface gradient estimation means calculates the change of the selected wheel speed. The gradient of the road surface is estimated from the difference between the change amount of the selected wheel speed calculated by the amount calculation means and the longitudinal acceleration detected by the longitudinal acceleration detection means, and the vehicle body speed estimation means considers the road gradient estimated by the road surface gradient estimation means. The longitudinal acceleration detected by the longitudinal acceleration detecting means is corrected, and the vehicle body speed is estimated from the corrected value. Driving force transmitted to the road surface from the wheels based on the traction determination using the estimated vehicle speed by the speed estimating means is controlled.
[0020]
For example, when driving force control is performed when the four wheels drive and slip suddenly on a steep downhill road surface with a small road surface μ, the detected longitudinal acceleration is smaller than the actual change in vehicle speed. However, the estimated vehicle speed becomes smaller than the actual value and the vehicle stalls. However, by correcting the longitudinal acceleration detected in consideration of the estimated road gradient, the influence of the road gradient is eliminated. The longitudinal acceleration information, which is the estimated information, can be made highly consistent with the actual longitudinal acceleration value.
[0021]
Thus, when combining a four-wheel drive vehicle with a driving force control device that suppresses driving slip, correcting the longitudinal acceleration detected in consideration of the estimated road gradient, and estimating the vehicle speed from the correction value, It is possible to estimate the vehicle body speed with high accuracy without the influence of errors due to the road surface gradient, and to improve the driving force control performance.
[0023]
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 the downhill road surface, and conversely the actual longitudinal acceleration on the ascending road surface. The detected longitudinal acceleration is in a fixed relationship. 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 without driving slip, the wheel speed and the vehicle body speed coincide.
[0024]
Therefore, the change amount of the selected wheel speed closest to the vehicle body speed among the wheel speeds is calculated according to the slip convergence determination, and the difference between the calculated change amount of the selected wheel speed and the longitudinal acceleration detected by the longitudinal acceleration detecting means is calculated. By taking this, the road surface gradient can be accurately estimated.
[0025]
According to the second aspect of the invention, the driving force is controlled using at least one of engine output control by fuel cut to the engine, engine output control by adjusting the throttle opening, and braking force control by brake.
[0026]
According to the third aspect of the present invention, the longitudinal acceleration is detected by using the longitudinal accelerometer that directly detects the longitudinal acceleration acting on the vehicle body.
[0027]
Therefore, the longitudinal acceleration acting on the vehicle body can be detected more accurately than when the longitudinal acceleration is obtained by estimation.
[0028]
In the invention according to claim 4 , in the wheel slip convergence determination means, at least the wheel speed depends on whether the deviation between the target wheel speed set from the estimated vehicle body speed and the wheel speed of each wheel is within the set value. The convergence state of the slip is determined.
[0029]
In the invention according to claim 5 , in the wheel slip convergence determination means, whether or not the deviation between at least the target wheel speed set from the vehicle body speed estimated value and the average value of the wheel speed of each wheel is within the set value. Thus, the convergence state of the wheel slip is determined.
[0030]
In the invention according to claim 6 , in the vehicle body speed estimation means, when the road surface gradient estimated by the road surface gradient estimation means is greater than or equal to a set value, the true vehicle body is obtained by adjusting the road surface gradient from the longitudinal acceleration detection value. The speed change amount is calculated, and the vehicle body speed is estimated according to the true vehicle speed change amount.
[0031]
In the invention according to claim 7 , in the vehicle body speed estimation means, when the road surface gradient estimated by the road surface gradient estimation means is greater than or equal to a set value, the time during which this state continues is counted, and according to the count Thus, the longitudinal acceleration is corrected by adding or subtracting the offset amount to the longitudinal acceleration detection value, and the vehicle body speed is estimated according to the corrected longitudinal acceleration.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
[0033]
First, the configuration will be described.
[0034]
FIG. 1 is a conceptual diagram showing a reference invention, in which a is a longitudinal acceleration detection means, b is a vehicle body speed estimation means, c is a driving force control means, and g is a road surface gradient estimation means. 2 is a conceptual diagram showing the invention according to claim 1, wherein a 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 judging means, and f is a select. Wheel speed change amount calculating means, g is road surface gradient estimating means.
[0035]
(Embodiment 1)
There will be described first implementation.
[0036]
FIG. 3 is an overall system diagram including a drive system to which the drive force control apparatus for a four-wheel drive vehicle in 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 its drive system includes an engine 1, a front final drive 2, a rear final drive 3, a transfer 4, and left and right front wheels. 10, 20 and left and right rear wheels 30, 40 are provided, and the engine driving force that has passed through the transmission is directly transmitted to the rear wheels 30, 40, and is transmitted to the front wheels 10, 20 via the transfer 4. Is done.
[0037]
A driving force distribution control device that optimally controls the driving force distribution of the front and rear wheels while achieving both driving performance and steering performance is applied to the left and right front wheels 10 and 20 by a hydraulic actuator 6 that controls the hydraulic pressure of the wet multi-plate clutch 5. By transmitting the driving force, control from the two-wheel drive state to the four-wheel drive state (rigid four-wheel drive) is performed. Wheel speed sensors 11, 21, 31, 41 for detecting wheel speeds are installed on the left and right front wheels 10, 20 and the left and right rear wheels 30, 40, respectively. This signal is input to the controller 50 that controls the driving state. Further, a longitudinal acceleration sensor 7 (corresponding to longitudinal acceleration detecting means) for detecting the longitudinal acceleration Xg of the vehicle and a lateral acceleration sensor 8 for detecting the lateral acceleration Yg are provided. 50.
[0038]
In addition, the engine output control as the driving force control is performed by the controller 50 giving a target drive torque Tes command to the engine controller 51 that controls the engine output, and the engine output is controlled by controlling the fuel cut and the throttle opening. Is done. The throttle control 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 the mission, and receives a gear position signal. An engine drive torque Te is also input from the engine controller 51.
[0039]
Next, the operation will be described.
[0040]
FIG. 4 shows a flowchart of an engine output control program executed by the controller 50. Hereinafter, each step will be described in detail.
[0041]
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.
[0042]
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., and Vwfi (i = 1 to 4) closer to the vehicle body speed is calculated for each wheel, and when braking / not braking For example, the selected wheel speed Vfs closest to the vehicle body speed is calculated from each Vwfi by selecting the smallest wheel speed during acceleration, for example. In particular, in a state where the four wheels are driven to slip and the driving force control is activated, Vfs is calculated so that the wheel with the smaller wheel speed of the front wheels follows within a certain acceleration. Here, the reason why the wheel speed of the front wheel is smaller is that the driving force distributed to the front wheel tends to be smaller than the rear wheel due to the characteristics of the four-wheel drive device in this example. Needless to say, when a four-wheel drive device is used, there is a selection method suitable for the four-wheel drive device.
[0043]
Step 103 calculates the control wheel speed Vwt. In this example, when the gear position GR is 1st and 2nd speed, the average wheel speed of the four wheels is set as the control wheel speed Vwt that is the wheel speed subject to drive control, and the 3rd and 4th speeds above are the average of the front wheels. The control wheel speed is Vwt. Here, the calculation of the control wheel speed Vwt is also in accordance with the characteristics of the four-wheel drive device used as in the case of the select wheel speed Vfs described above. For example, in the four-wheel drive device of this embodiment, the rear wheels are driven and slipped. After that, 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 between 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 allocated driving force, the average wheel speed of the front wheels may be controlled. In the case of the low gear side, since the driving torque is large, the four wheels immediately enter the slip state, and the fluctuation in the distribution of driving torque by the four-wheel drive device also increases, so the fluctuation in the average wheel speed of the front wheels also increases, and only the front wheels If the control object is a control object, there is a problem that the mutual control interferes, and the average wheel speed of the four wheels is the control object. In a four-wheel drive device in which the distribution of the four-wheel drive force is constant, the control target wheel speed may be calculated by a weight according to the distribution.
[0044]
In step 104, determination of the convergence of the wheel is performed (corresponding to wheel slip convergence determination means). In this example, when the deviation between the target wheel speed Vwsi calculated by the method described later and the control wheel speed Vwt is within a certain set value (for example, 1 km / h), the wheel speed is considered to have converged. Then, the convergence judgment counter Ksu is counted up. A case where the convergence determination counter Ksu becomes equal to or greater than a certain set value (for example, 150 ms; 15 when the control period is 10 msec) is determined as the wheel speed convergence state.
[0045]
In step 105, the selected wheel speed change amount dVfs is calculated. In this example, the change amount dVfs of the selected wheel speed is calculated according to the following equation as the change amount of the average value of the selected wheel speed Vfs within a certain time (for example, for 40 msec). However, the following equation is calculated every 40 msec.
[0046]
dVfs = Kg * (VF [0] + VF [1] −VF [3] −VF [4])
Here, VF is an average value of the selected wheel speed Vfs, and is calculated according to the following formula every 10 msec. Kg is a unit conversion count.
[0047]
VF = Kg * (Vfs [0] + Vfs [1] + Vfs [2] + Vfs [3]) / 4
Here, the number in [] indicates how many cycles ago the value is.
[0048]
In step 106, a road surface gradient estimated value dS is calculated (corresponding to road surface gradient estimating means). In this example, when the convergence is determined in step 103, the road surface gradient estimated value dS is calculated by the following equation.
[0049]
dS = dVfs-Xg
If the convergence is not judged, dS = 0.
[0050]
In step 107, the slope is judged according to the road surface gradient estimated value dS. In this example, when the road surface gradient estimated value dS is equal to or greater 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 judgment counter Ksa has a maximum value (for example, 50), and is counted down when the road surface gradient estimated value becomes equal to or smaller than the set value.
[0051]
In step 108, the longitudinal acceleration correction amount dVh is calculated according to the slope judgment. In this example, the slope judgment counter Ksa is used, and when Ksa is equal to or larger than a set value (for example, 15), dVh = min ((Ksa−15) * Kr, dVhmax).
And Here, Kr is a tuning constant, for example, 0.01. If it is less than the set value, dVh = 0. Further, dVhmax is the maximum limit value of the correction amount, and is set so that correction that is too large is not performed.
[0052]
In step 109, the vehicle body speed change amount Vid is calculated (corresponding to the vehicle body speed change amount calculating means). In this example, calculation is performed according to the following equation from the longitudinal acceleration sensor value (acceleration side plus), the longitudinal acceleration correction value, and the minimum limit value Vidmin.
[0053]
[When determining acceleration]
Vid = max (Xg + dVh, Vidmin)
Here, Vidmin is a minimum limit value of the vehicle body speed change amount Vid and is set in consideration of acceleration and driving force control being performed. In this example, it is set to 0.05 g, for example. Acceleration is determined by comparing the selected 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.
[0054]
[Deceleration judgment]
It is calculated by the following formula that adds the offset to the longitudinal acceleration sensor value.
[0055]
Vid = Xg-G_offset
In this example, the offset is set to 0.3 g on a general slope on the market so that Vid does not become a positive value when decelerating.
[0056]
In step 110, an estimated vehicle speed Vi is calculated (corresponding to vehicle speed estimation means). In this example, calculation is performed according to the following equation from the previous values of the selected wheel speed Vfs, the vehicle body speed change amount Vid, and the estimated vehicle body speed Vi.
[0057]
[When accelerating]
Vi = min (Vi (previous value) + Vid, Vfs)
[Deceleration]
Vi = max (Vi (previous value) + Vid, 0)
That is, the vehicle body speed change amount Vid is added to the previous value of Vi. However, Vfs is the maximum limit value during acceleration, and 0 is the lower limit value during deceleration. By calculating the estimated vehicle speed in this way, the vehicle speed is such that the four-wheel drive vehicle is in a state where the four wheels are driving slip and the driving force control is operating, and the road surface has a gradient. Even when the estimation is severe, the vehicle speed can be estimated with high accuracy.
[0058]
From the next step, the driving force control using the estimated vehicle body speed will be described.
[0059]
First, the control amount of the four-wheel drive distribution control is calculated. In step 111, the differential force limiting torque TETS controlled by the four-wheel driving force distribution device is calculated. In this example, as shown below, 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 rotational speeds ΔVfr.
[0060]
Vff = (Vw1 + Vw2) / 2
Vrr = (Vw3 + Vw4) / 2
△ Vfr ＝ Vrr−Vff
The differential limiting torque TETS is calculated from the front-rear rotational speed difference ΔVfr according to the characteristic map shown in FIG. Note that the electronically controlled driving force distribution control includes other controls that increase the driving force distribution to the front wheels in accordance with an increase in the rotational speed difference between the front and rear wheels, as shown in FIG. 11 attached for reference. This is omitted here.
[0061]
In step 112, a target slip amount Sstar for driving force control is calculated. In this example, the target slip amount is corrected by correcting the reference target slip amount SO (for example, 2.5 km / h) by determining acceleration / deceleration, determining whether the vehicle is traveling straight or turning, determining the road surface μ, and operating / non-operating driving force control. Set the quantity Sstar.
[0062]
In step 113, the target wheel speed Vws is calculated. In this example, the estimated vehicle speed Vi obtained in step 110 and the target slip amount Sstar set in step 112 are calculated by the following equation.
[0063]
Vws = Vi + Sstar
In step 114, the target drive torque Tes is calculated. In this example, first, the deviation between the target wheel speed Vws obtained in step 113 and the control wheel speed Vwt obtained in step 103 is calculated by the following equation.
[0064]
ε = Vws−Vwt
Further, a target drive torque Tes that is a command value for F / B control (here, PID control) is calculated according to the deviation ε by the following equation.
[0065]
[When driving force control is not activated]
Tes = Te
[When driving force control is activated]
Tes = Kp * ε + Kd * dε / dt + Ki * ∫εdt
Here, Kp, Kd, and Ki are F / B gains, which are changed by gears or the like. For example, according to the gear position, the gain is increased as the gear is lower, and the gain is decreased as the gear is higher. Also, as ε increases in response to wheel speed deviation ε, the gain may be increased (non-linear control) to improve response, or on the convergence side of slip, the gain may be decreased to prevent slipping. good.
[0066]
In step 115, each drive signal is output. That is, a voltage command value corresponding to the target differential limit torque TETS is output to the driving force distribution control device. Further, the target drive torque Tes is output to the engine controller 51.
[0067]
In the present embodiment, the engine controller 51 receives the target torque Tes from the controller 50 for driving force control, and controls the fuel cut and the throttle opening in accordance with the target value, thereby outputting an engine output command. Control. The throttle control is performed by the throttle controller 52 in response to a throttle opening command from the engine controller 51.
[0068]
FIG. 10 is a time series graph (time chart) showing an operation when this control is performed.
[0069]
That is, as in the case of FIG. 7, the estimated vehicle speed is estimated to be smaller than the actual vehicle speed during start acceleration on a steep downhill. The correction of the longitudinal acceleration is started by the determination and the subsequent slope determination, and the estimated vehicle body speed Vi is corrected to a larger value, so that the acceleration can be returned. Thereby, the acceleration failure is eliminated and the acceleration performance is improved.
[0071]
In the first embodiment, an example of application to an electronically controlled torque split type four-wheel drive vehicle that variably controls the drive force distribution ratio of the front and rear wheels according to the differential amount of the front and rear wheels as a four-wheel drive vehicle has been shown. The present invention is applied to various types of four-wheel drive vehicles such as a four-wheel drive vehicle, a four-wheel drive vehicle using a viscous coupling, and a four-wheel drive vehicle using an orifice coupling depending on a fixed driving force distribution ratio. be able to.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing an invention according to claim 1;
FIG. 2 is a conceptual diagram showing an invention according to claim 2;
FIG. 3 is an overall system diagram to which the driving force control apparatus for a 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 body speed when some of the wheels are temporarily not slipped.
FIG. 9 is a characteristic map showing the relationship between differential limiting torque TETS and front-rear rotational speed difference ΔVfr in the first embodiment.
FIG. 10 is a time chart showing the operation when the control of Embodiment 1 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 the front wheels, which is a control example as a reference for driving force distribution control.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Engine 2 Front final drive 3 Rear final drive 4 Transfer 5 Wet multi-plate 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 (7)

In the driving force control device that controls the driving slip of the wheels of the four-wheel drive vehicle,
Longitudinal acceleration detection means for estimating or detecting longitudinal acceleration generated in the vehicle;
Wheel slip convergence state determination means for determining that the slip state of each wheel is in a convergence state;
Select wheel speed change amount calculating means for calculating the change amount of the selected wheel speed closest to the vehicle body speed among the wheel speeds according to the determination of the wheel slip convergence determining means;
A road gradient estimating means for estimating a gradient of a road surface due to the difference of the select wheel speed change calculation means longitudinal acceleration detected by the longitudinal acceleration detecting means and the select wheel speed change amount to be calculated,
Car body speed estimating means for correcting the longitudinal acceleration detected by the longitudinal acceleration detecting means in consideration of the road slope estimated by the road slope 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 driving slip determination using the estimated vehicle speed by the vehicle speed estimating means;
A driving force control device for a four-wheel drive vehicle. The driving force control apparatus for a four-wheel drive vehicle according to claim 1 ,
The drive force control means is a means for controlling the drive force using at least one of engine output control by fuel cut to the engine, engine output control by throttle opening adjustment, and braking force control by brake. A driving force control device for a four-wheel drive vehicle. In the driving force control device for a four-wheel drive vehicle according to claim 1 or 2 ,
4. A driving force control apparatus for a four-wheel drive vehicle, wherein the longitudinal acceleration detecting means is a means using a longitudinal accelerometer that directly detects longitudinal acceleration acting on a vehicle body. The driving force control apparatus for a four-wheel drive vehicle according to any one of claims 1 to 3 ,
The wheel slip convergence determination means is a means for determining the convergence state of the wheel slip based on whether or not the deviation between the target wheel speed set from at least the estimated vehicle speed and the wheel speed of each wheel is within the set value. A driving force control device for a four-wheel drive vehicle. The driving force control apparatus for a four-wheel drive vehicle according to any one of claims 1 to 3 ,
The wheel slip convergence determining means determines whether or not the wheel slip has converged based on whether or not a deviation between a target wheel speed set from at least a vehicle body speed estimated value and an average value of wheel speeds of each wheel is within a set value. A driving force control device for a four-wheel drive vehicle, characterized in that it is a means. The driving force control apparatus for a four-wheel drive vehicle according to any one of claims 1 to 5 ,
When the road surface gradient estimated by the road surface gradient estimating unit is greater than or equal to a set value, the vehicle body speed estimating unit calculates a true vehicle speed change amount by adding or subtracting the road surface gradient from the longitudinal acceleration detection value. A driving force control device for a four-wheel drive vehicle, characterized in that the vehicle speed is estimated in accordance with the amount of change in vehicle speed. The driving force control apparatus for a four-wheel drive vehicle according to any one of claims 1 to 5 ,
When the road surface gradient estimated by the road surface gradient estimating unit is greater than or equal to a set value, the vehicle body speed estimating unit counts the time for which this state continues, and the offset amount is added to or subtracted from the longitudinal acceleration detection value according to the count. A driving force control device for a four-wheel drive vehicle, characterized in that the longitudinal acceleration is corrected by this, and the vehicle body speed is estimated according to the corrected longitudinal acceleration.

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