JPH04293651A - Pseudo vehicle speed calculating method for four-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To improve the control capability and responsiveness by comparing both change quantities of the first vehicle speed by the lowest wheel speed and the second vehicle speed integrated with the acceleration/deceleration of a G sensor, judging the grip and slip of a wheel, and selectively using the change quantity with higher precision to calculate the pseudo vehicle speed. CONSTITUTION:Wheel speed sensors 15a-15d are provided on the right and left front wheels 8R, 8L and rear wheels 13R, 13L respectively to individually detect the wheel speed omega. A G sensor 16 is provided at the center position of a vehicle body to detect the longitudinal acceleration/deceleration G of the vehicle body. The primary acceleration/deceleration Ga of the vehicle body and the acceleration/deceleration Gb of the horizontal component of the vehicle body due to the gravitational force at the time of traveling on a slope are added and outputted. A steering angle sensor 18 detecting the steering angle phiat the time of turning is provided on a steering device 17, and these sensor signals are inputted to a slip control unit 30. The slip control unit 30 continuously calculates the pseudo vehicle speed Vr at the time of traveling under acceleration/deceleration.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for calculating a pseudo vehicle speed for use in traction control (TCS) and anti-brake control (ABS) of a four-wheel drive vehicle.

0002

BACKGROUND OF THE INVENTION In recent years, traction control to prevent slips during acceleration and anti-brake control to prevent slips during braking have been implemented in vehicles. In such control during slipping, it is essential to detect with high precision not only the wheel grip but also the ground vehicle speed during slipping. Here, particularly regarding the acceleration slip, in a vehicle having a driving wheel and a driven wheel such as a two-wheel drive vehicle, the ground vehicle speed can be directly detected from the driven wheel when the driving wheel slips. However, in the case of a four-wheel drive vehicle, since all wheels are drive wheels, all four wheels slip at the same time, and the ground speed cannot be detected as in a two-wheel drive vehicle. Therefore, when all four wheels slip at the same time, it is required to calculate a pseudo vehicle speed that matches the ground vehicle speed with high accuracy using a means other than wheel speed.

Conventionally, regarding the calculation of the above-mentioned pseudo vehicle speed, there is a prior art technique disclosed in, for example, Japanese Patent Application Laid-open No. 11470/1983. Here, it is shown that at the start of braking, the wheel speed is the initial value, and the acceleration/deceleration of the vehicle body is integrated to obtain the pseudo vehicle speed, and the integration circuit is reset at regular intervals to make the pseudo vehicle speed the same value as the wheel speed. . Furthermore, in the prior art of Japanese Patent Application Laid-Open No. 63-41273, a pseudo vehicle speed is obtained in the same manner as in the above-mentioned prior art, and the vehicle body deceleration is greater than or equal to a predetermined value, and the peak value of wheel acceleration is less than or equal to a predetermined value. Based on that,
It is shown that the integration of deceleration is stopped and the pseudo vehicle speed is determined from the wheel speed.

0004

[Problems to be Solved by the Invention] By the way, in the prior art described above, since the pseudo vehicle speed is obtained by temporarily integrating the vehicle body deceleration during braking, it is difficult to calculate the vehicle body deceleration while the vehicle is running. It is not possible to continuously calculate the pseudo vehicle speed using In addition, since the pseudo vehicle speed is calculated only from the integrated value of the G sensor's vehicle body deceleration, it is not possible to accurately calculate the pseudo vehicle speed when slipping actually occurs and when it does not occur. When an error occurs in the detected value, an error also occurs in the value of the pseudo vehicle speed, resulting in problems such as difficulty in obtaining high accuracy.

[0005] The present invention has been made in view of this point, and uses signals from wheel speed sensors and G sensors to continuously and accurately measure the grip of wheels during acceleration/deceleration and the pseudo vehicle speed when slipping. The purpose is to calculate.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a wheel speed sensor for detecting the wheel speed of each wheel;
Equipped with a G sensor that detects the acceleration/deceleration of the vehicle body, the amount of change per unit time in the first vehicle speed due to the lowest wheel speed and the second vehicle speed per unit time determined by integrating and accumulating the acceleration/deceleration of the vehicle body. If the difference between the two changes is small, calculate the pseudo vehicle speed using the first change in vehicle speed, and if it is large, use the second change in vehicle speed to continuously calculate the pseudo vehicle speed. It is calculated based on the

[0007]

[Operation] By the above method, wheel grip and slip are determined based on the difference between the amount of change in the first vehicle speed due to the lowest wheel speed and the amount of change in the second vehicle speed due to acceleration/deceleration of the vehicle body when driving in four-wheel drive. By selecting and using these highly accurate changes in grip and slip to calculate the pseudo vehicle speed, highly accurate pseudo vehicle speeds are continuously calculated during driving.

[0008]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. Referring to FIG. 2, an outline of the drive system and traction control system of a four-wheel drive vehicle will be explained. Reference numeral 1 denotes an engine, and this engine 1 is connected to a transfer device 4 such as a center differential via a clutch 2 and a transmission 3 to distribute power. One output side of the transfer device 4 has a front drive shaft 5, a front differential 6, and an axle 7.
The other output side is connected to the left and right rear wheels 13L, 13 via the rear drive shaft 9, propeller shaft 10, rear differential 11, and axle 12.
R and is configured to run in four-wheel drive.

To explain the control system, the left and right front wheels 8
Wheel speed sensors 15a to 15d are provided for the rear wheels L, 8R and the rear wheels 13L, 13R, respectively, so as to separately detect the wheel speed ω. Further, a G sensor 16 is installed at the center of the vehicle body to detect acceleration/deceleration G in the longitudinal direction of the vehicle body.
In this case, for example, the acceleration/deceleration Ga inherent to the vehicle body and the acceleration/deceleration Gb of the horizontal component of the vehicle body due to gravity when traveling on a slope are added and output. Further, the steering device 17 is provided with a steering angle sensor 18 that detects the steering angle φ during turning, and these sensor signals are input to the slip control unit 30. As will be described later, the slip control unit 30 continuously calculates a pseudo vehicle speed Vr during acceleration/deceleration driving, and calculates the pseudo vehicle speed Vr.
, wheel speed ω, steering angle φ, etc., determines a traction control signal at the time of slip, and outputs it to the engine control unit 20. The engine control unit 20 is configured to perform, for example, ignition timing retard control and fuel injection reduction control based on the traction control signal, and forcibly limit engine output to prevent slippage.

In FIG. 1, a slip control unit 30
The control system will be explained. First, to explain the control principle, the first vehicle speed Vmin can be detected by the minimum wheel speed ωmin of the four-wheel drive wheel speed ω, and the second vehicle speed VG can be detected by simultaneously integrating the integral value of the G sensor.
can be found. Therefore, when the wheels are gripped, these first and second vehicle speeds Vmin and VG change substantially in unison, and when the wheels slip during acceleration and deceleration, the first vehicle speed V
The behavior is that only min fluctuates greatly. Therefore, the first
The grip and slip of the wheels can be determined by comparing and determining the vehicle speed and the changes in the second vehicle speed ΔVmin and ΔVG. Therefore, when the wheels are gripped, the highly accurate first vehicle speed change amount ΔVmin is used to set the pseudo vehicle speed Vr.
By calculating the pseudo vehicle speed Vr using the second vehicle speed change amount ΔVG obtained from the integral value of the G sensor close to the ground vehicle speed at the time of wheel slip, the pseudo vehicle speed Vr can be continuously obtained with high accuracy. becomes possible.

Based on the above control principle, the slip control unit 30 includes a four-wheel wheel speed detection section 31 to which the signals from the wheel speed sensors 15a to 15d are input, a vehicle acceleration/deceleration detection section 32 to which the signal from the G sensor 16 is input, and a steering wheel speed detection section 32 to which the signals from the G sensor 16 are input. It has a steering angle detection section 33 into which the signal from the angle sensor 18 is input, and detects each wheel speed ω, acceleration/deceleration G, and steering angle φ. This wheel speed ω is input to the maximum wheel speed determination unit 34 to select the maximum wheel speed ωmax, and the maximum wheel speed ωmax is further input to the slip ratio calculation unit 35 and used to calculate the largest slip ratio S. The wheel speed ω is input to the first vehicle speed calculation unit 36,
A first vehicle speed Vmin is determined based on the minimum wheel speed ωmin, and this first vehicle speed Vmin is input to a change amount calculating section 37 to calculate a first vehicle speed change amount ΔVmin per unit time. The acceleration/deceleration G is also input to the change amount calculation unit 38, and by integrating the acceleration/deceleration G over the above time, the second vehicle speed change amount ΔVG per unit time is calculated, and these change amounts ΔVmin, ΔVG are It is input to the pseudo vehicle speed calculation section 39. The pseudo vehicle speed calculation unit 39 determines the wheel grip based on the absolute value of the difference between the two amounts of change and the set value K. If |ΔVG−ΔVmin|<K, the pseudo vehicle speed calculation unit 39 determines the pseudo vehicle speed Vr, V
Calculated by r=Vr+ΔVmin. In addition, if |ΔVG−ΔVmin|≧K, wheel slip is determined and the pseudo vehicle speed Vr is set to V
Calculated by r=Vr+ΔVG.

The above-mentioned pseudo vehicle speed Vr is calculated by the slip rate calculating section 35.
and the value converted to wheel speed ω and the maximum wheel speed ω
The slip rate S is calculated by subtracting it from max. Also,
The pseudo vehicle speed Vr and the steering angle φ are input to the target slip ratio setting section 40, and the target slip ratio Sd is set, for example, by a decreasing function for both the pseudo vehicle speed Vr and the steering angle φ. These slip ratios S and target slip ratio Sd are input to the control signal output section 41 to determine a traction control signal according to the difference ΔS between the two slip ratios, and output the traction control signal to the engine control unit 20.
It is designed to output to .

Next, the operation of this embodiment will be explained. First, when the transmission 3 is shifted to the driving range while the engine is running, the shifting power is input to the transfer device 4 and distributed, and is transmitted to the left and right front wheels 8L, 8R and the rear wheels 13L, 13R for four-wheel drive driving. . When driving in four-wheel drive, under conditions where the road surface μ is relatively large and the engine output is not unnecessarily large, it is possible that one of the four wheels or the front and rear wheels 8L, 8R or 13L, 13R slips. However, slippage is prevented by differential lock and torque distribution control. Therefore, most of the wheels always grip the road surface and drive while exhibiting the performance of a four-wheel drive vehicle. At this time, the first vehicle speed Vmin based on the minimum wheel speed ωmin and the first vehicle speed The vehicle speeds VG of 2 are equal and change substantially in unison as shown in the grip range of FIG. On the other hand, if the road surface μ decreases extremely or the engine output increases, the grip force of the four wheels will eventually decrease and four-wheel slip will occur.
Only the first vehicle speed Vmin suddenly increases as shown in FIG. At this time, signals from the wheel speed sensors 15a to 15d, the G sensor 16, and the steering angle sensor 18 are input to the slip control unit 30 and processed. That is, the minimum wheel speed ωmi
The amount of change ΔVmin per unit time of the first vehicle speed Vmin due to n and the amount of change ΔVG per unit time of the second vehicle speed VG obtained by integrating acceleration/deceleration are calculated, and the difference between these amounts of change ΔVmin and ΔVG is calculated. Based on this, a pseudo vehicle speed Vr is calculated. Therefore, when the difference in the amount of change is small as in the case of wheel grip mentioned above, the first vehicle speed Vmin with high accuracy
Pseudo vehicle speed Vr is calculated using the amount of change ΔVmin,
When the difference in the amount of change exceeds the set value K, wheel slip is determined, and the amount of change ΔV in the second vehicle speed VG, which is close to the ground vehicle speed, is determined.
Pseudo vehicle speed Vr is calculated using G. In this way, the minimum wheel speed ωmin, the amount of change ΔVmin based on acceleration/deceleration G, and the amount of change ΔVmin,
By selectively using ΔVG, the pseudo vehicle speed Vr is always calculated continuously with high accuracy.

The pseudo vehicle speed Vr calculated as described above is used together with the steering angle φ as a setting element for the target slip ratio Sd.
The slip rate S is determined by the pseudo vehicle speed Vr and the maximum wheel speed ωmax.
is calculated. Therefore, if wheel slip occurs when the pseudo vehicle speed Vr and steering angle φ are small, such as when starting straight ahead, the target slip rate Sd will be approximately 20% when the driving force is maximum due to the slip-drive force characteristic. % is set to a large value, and the slip rate S calculated by this and calculation is
A traction control signal based on the difference ΔS is output to the engine control unit 20, and the engine output is controlled to be forcibly reduced. This reduces the driving force on the wheel side, prevents four-wheel slip, and performs traction control to ensure an optimal slip ratio.

[0015] In addition, in calculating the pseudo vehicle speed Vr, both changes ΔV
Since the absolute value of the difference between min and ΔVG is used, it is possible to determine whether there is wheel slip due to four-wheel locking during braking and calculate the pseudo vehicle speed Vr based on the amount of change ΔVG in acceleration/deceleration G. Therefore, in this case, the pseudo vehicle speed Vr
This makes it possible to perform anti-brake control accurately.

Referring to FIG. 4, a second embodiment of the present invention will be described. In this embodiment, when the output value of the G sensor 16 includes an error, the value of the pseudo vehicle speed Vr is parallel to the first vehicle speed Vmin corresponding to the actual vehicle speed with a predetermined deviation when the wheels are gripped. This is to avoid this problem, which may not converge when set to . Therefore, the first vehicle speed Vmin based on the minimum wheel speed ωmin, the pseudo vehicle speed Vr
, a convergence correction unit 45 to which changes ΔVmin and ΔVG in the first and second vehicle speeds are input. And ΔVmin>0
, When the vehicle speed increases with ΔVG>0, only when Vmin>Vr, and when the wheel grip has |ΔVG−Vmin|<K,
A predetermined correction amount +a is determined and output to the pseudo vehicle speed calculation section 39. Also, when the vehicle speed decreases with ΔVmin<0, ΔVG<0, only when Vmin<Vr, |ΔVG−Vmi
When the wheel grip is n|<K, a predetermined correction amount -a is determined and similarly output to the pseudo vehicle speed calculation section 39. and,
The pseudo vehicle speed calculation unit 39 is configured to correct the pseudo vehicle speed Vr by adding or subtracting the correction amount ±a.

According to this embodiment, when the pseudo vehicle speed Vr is smaller than the first vehicle speed Vmin during wheel grip, as shown in FIG. 5 in the case of acceleration, due to the error of the G sensor 16, the pseudo vehicle speed Vr is corrected to increase over time, and both vehicle speeds Vmin and Vr converge. Furthermore, the pseudo vehicle speed Vr is higher than the first vehicle speed Vmi.
If it is larger than n, the pseudo vehicle speed Vr is corrected to decrease during wheel grip during deceleration and similarly converges.

Referring to FIG. 6, a third embodiment of the present invention will be described. This embodiment is a measure for initializing the pseudo vehicle speed Vr, and includes a zero adjustment section 46 into which the minimum wheel speed ωmin and acceleration/deceleration G are input. The conditions for stopping the vehicle are that the minimum wheel speed ωmin is zero for a predetermined period of time, the minimum wheel speed ωmin is zero, the acceleration/deceleration G is also approximately zero, the minimum wheel speed ωmin is zero, and the G sensor 16 The following three conditions are set: the output in the low frequency range excluding the DC component is approximately zero, and when any of these conditions is met, the pseudo vehicle speed calculation unit 39 is forced to set the pseudo vehicle speed Vr to zero. It has become.

According to this embodiment, if an error occurs in the value of the pseudo vehicle speed Vr due to the integration of the integral of the acceleration/deceleration G, the pseudo vehicle speed Vr is adjusted to zero every time the vehicle stops. It becomes possible to perform traction control with high precision.

Referring to FIG. 7, a fourth embodiment of the present invention will be described. This embodiment is a measure against zero adjustment of the G sensor 16. That is, errors in the G sensor 16 occur due to its installation and aging, but also due to the number of passengers, displacement of the suspension, inclination of the vehicle body due to inclination, etc., and errors occur due to individual differences in each vehicle. If the acceleration/deceleration G is detected and the pseudo vehicle speed Vr is calculated with such an error included, the accuracy of the value of the pseudo vehicle speed Vr will inevitably decrease. Therefore, in order to deal with these errors, the detected value of the acceleration/deceleration G may be adjusted based on the zero point of the G sensor 16 when the vehicle is stopped. Therefore, the output signal of the G sensor 16, the minimum wheel speed ωmi
n, P position signal of gear position sensor 23, door switch 2
It has a zero adjustment section 47 into which the signal No. 4 is input. Then, the P position signal is input, the minimum wheel speed ωmin is zero for a predetermined period of time, the minimum wheel speed ωmin is zero, and the G sensor 1
6's output is also approximately zero, the minimum wheel speed ωmin is zero, and G
When either of the following conditions is satisfied: the output of the sensor 16 in the low frequency range excluding the DC component is approximately zero, and the door close signal is input, the zero point value Go of the output of the G sensor 16 at this time is determined as the vehicle body acceleration/deceleration. It is output to the detection unit 32. Vehicle body acceleration/deceleration detection section 32
calculates the acceleration/deceleration G from the value Gt of the G sensor 16 at a certain point in time and the zero point value Go as follows. G=Gt-Go

According to this embodiment, the G sensor 1 is activated every time the vehicle is stopped.
The zero point value Go of the G sensor 16 is determined in accordance with the error of the G sensor 6 itself, the error of the tilt of the vehicle body due to the number of passengers, etc. and,
When calculating the acceleration/deceleration G using the signal Gt of the G sensor 16 while driving, the above zero point value Go is always subtracted, so that the vehicle acceleration/deceleration G is accurately detected and the accuracy of calculating the pseudo vehicle speed Vr is improved. It becomes possible to improve.

Although the embodiments of the present invention have been described above, the present invention is not limited thereto.

[0023]

[Effects of the Invention] As explained above, according to the present invention,
In calculating the pseudo vehicle speed of a four-wheel drive vehicle, accuracy is determined by comparing the amount of change in both the first vehicle speed based on the lowest wheel speed and the second vehicle speed obtained by integrating the acceleration/deceleration of the G sensor, and determining the grip and slip of the wheels. Since the pseudo vehicle speed is calculated by selecting and using a large amount of change, it is possible to continuously calculate the pseudo vehicle speed with high accuracy during acceleration and deceleration driving. Therefore, traction control and anti-brake control during slipping can be performed accurately, and since the pseudo vehicle speed is calculated by determining the grip and slip of the wheels, controllability, responsiveness, etc. are improved. Second
In this embodiment, since the pseudo vehicle speed is corrected so as to converge to the first vehicle speed when the wheels are gripped, accuracy and the like are improved. In the third embodiment, the pseudo vehicle speed is adjusted to zero when stopped,
In the fourth embodiment, since the G sensor is zero-adjusted, errors in integrating and accumulating the G sensor output and acceleration/deceleration can be accurately corrected, and the accuracy of calculating the pseudo vehicle speed can be improved. It can be further improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a pseudo vehicle speed calculation method for a four-wheel drive vehicle according to the present invention.

FIG. 2 is a configuration diagram showing a drive system and traction control system of a four-wheel drive vehicle to which the present invention is applied.

FIG. 3 is a diagram showing how the first and second vehicle speeds and pseudo vehicle speeds change during accelerated driving.

FIG. 4 is a block diagram of main parts of a second embodiment of the present invention.

FIG. 5 is a diagram showing a convergence state of pseudo vehicle speed during acceleration driving.

FIG. 6 is a block diagram of main parts of a third embodiment of the present invention.

FIG. 7 is a block diagram of main parts of a fourth embodiment of the present invention.

[Explanation of symbols]

15a-15d Wheel speed sensor 16 G sensor 30 Slip control unit 36 First vehicle speed calculation unit 37, 38 Change amount calculation section 39 Pseudo vehicle speed calculation unit

Claims (6)

[Claims] Claim 1: A wheel speed sensor that detects the wheel speed of each wheel and a G sensor that detects the acceleration/deceleration of the vehicle body, the amount of change per unit time in the first vehicle speed due to the lowest wheel speed, and the acceleration/deceleration of the vehicle body. and the amount of change per unit time in the second vehicle speed, which is obtained by integrating and accumulating the amount of change in the second vehicle speed, and if the difference between the two amounts of change is small, calculate the pseudo vehicle speed using the amount of change in the first vehicle speed, A method for calculating a pseudo vehicle speed of a four-wheel drive vehicle, characterized in that if the amount of change in the second vehicle speed is large, the pseudo vehicle speed is continuously calculated using the amount of change in the second vehicle speed. 2. The pseudo vehicle speed of a four-wheel drive vehicle according to claim 1, wherein the pseudo vehicle speed is calculated by comparing an absolute value of a difference in the amount of change between the first and second vehicle speeds with a set value. Vehicle speed calculation method. Claim 3: The pseudo vehicle speed is based on the actual slip rate,
2. The pseudo vehicle speed calculation method for a four-wheel drive vehicle according to claim 1, further comprising outputting a traction control signal that is used to calculate target slip ratios and is determined by these slip ratios. 4. The pseudo vehicle speed of the four-wheel drive vehicle according to claim 1, wherein when the pseudo vehicle speed deviates from the first vehicle speed during wheel grip, the pseudo vehicle speed is corrected so as to converge. Calculation method. 5. The method for calculating a pseudo vehicle speed of a four-wheel drive vehicle according to claim 1, wherein the pseudo vehicle speed is forcibly set to zero under the determination conditions when the vehicle is stopped. 6. According to the zero point of the G sensor when the vehicle is stopped,
2. The pseudo vehicle speed calculation method for a four-wheel drive vehicle according to claim 1, wherein the acceleration/deceleration value is corrected based on the output value of a G sensor while the vehicle is running.