JPH0668496B2 - Vehicle speed estimation calculation method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for estimating and calculating a vehicle body speed from wheel speeds, and in particular, by changing the range of values that the estimated vehicle body speed can take with time. This is intended to improve the estimation accuracy.

[Conventional technology]

Since slip due to wheel lock during braking deteriorates steerability, the anti-skid control device optimally controls the brake hydraulic pressure by monitoring the difference between the wheel speed and the vehicle body speed. The wheel speeds are as shown in FIG. 4 for the wheels FR, EL, RR, R.
It can be obtained directly from the wheel speed sensors WS1 to WS4 provided for each L. On the other hand, the vehicle body speed must be determined by separately providing a vehicle body speed sensor such as a ground speed sensor or by estimating and calculating from the wheel speed. ACT1 to ACT3 are actuators that control the brake hydraulic pressure of each wheel.

FIG. 5 is an explanatory diagram of a conventional vehicle body speed estimation method.
_Tn-3 , _Tn-2 , ... Are calculation times, Vn _-2 , V
_{n-1, V n} is the estimated vehicle speed at each time _{point, V xn} is the current wheel speed. In this method, when the vehicle speed is calculated at regular intervals, it is estimated that the change in the vehicle speed (acceleration, deceleration) cannot exceed a certain value due to the characteristics of the vehicle and the road surface. Based on the vehicle body speed V _n-1 , the range that the estimated vehicle body speed V _n can take this time is limited, and V _{n is} calculated by the following equation within the range.

V _n = MED (V _xn , V _nU , V _nD ) ... The above equation is a function that selects an intermediate value from V _xn , V _nU , and V _nD . Further, V _nU = V _n-1 + ΔV _U V _nD = V _n-1 −ΔV _D , and + ΔV _U and −ΔV _D are in a range that V _n can take.

That is, as shown in FIG. 5, if V _xn <V _nD , then V _n = V _nD . _Further , if V _nD <V _xn <V _nU , then V _n = V _xn , and if V _xn > V _nU , then V _n = V _nU. Therefore, V _n is V _nU as the upper limit and V _nD is the lower limit. It is decided within that range.

These limit values ΔV _U and ΔV _D are calculated as follows.

(1) The maximum value of the descent limit ΔV _D road surface μ is about 1.0 on concrete road surface. Therefore, the maximum deceleration of the vehicle is 1G (9.8m / s ² ),
More than that is usually impossible. If the calculation interval of the vehicle body speed is ΔT, the lower limit value Δ of the vehicle body speed within ΔT
V _D is 9.8 · ΔT (m / s). Therefore, if ΔT = 4 ms, then ΔV _D ≈0.04 (m / s).

(2) Ascent limit ΔV _U Acceleration depends on the vehicle, although it depends on the vehicle.
5G is the upper limit of increase. Therefore, when calculated in the same manner as in (1), ΔV _U ≈0.02 (m / s).

However, when estimating the vehicle speed from the wheel speed,
Since the estimated vehicle body speed drops much faster than the actual vehicle body speed (see FIG. 6), the value of ΔV _U can be changed in order to quickly correct the estimated vehicle body speed as shown in FIG. 7 when the wheel speed is restored.
It must be a value that is sufficiently larger than equation (3) (if a vehicle speed sensor, equation (3) can be left unchanged).

[Problems to be solved by the invention]

The present invention intends to improve the steerability by accelerating the start time point of the anti-skid control by adopting a calculation method capable of making the estimated vehicle body speed closer to the actual vehicle body speed when the wheel speed suddenly drops. It is what

[Means for solving problems]

The present invention is a method for estimating and calculating a vehicle body speed in a predetermined calculation cycle, which is estimated from a difference ΔV _n-1 between a previous estimated vehicle body speed V _n-1 and an estimated vehicle body speed V _{n-2 two} times before. An upper limit value V _nU and a lower limit value V _nD are provided to the estimated vehicle speed V _n to limit them by the following equation and V _nU = V _n-1 -ΔV _n-1 + ΔV _U V _nD = V _n-1 -ΔV _{n -1} -ΔV _D However, ΔV _U : rising limit value ΔV _D : falling limit value The current wheel speed V _xn obtained from the wheel speed sensor and the above-mentioned V _nU and V _nD are selected as medium values. is characterized in that the current estimated vehicle speed V _n.

[Action]

The deceleration of the vehicle body increases as the brake hydraulic pressure increases, but the increase rate of the brake pressure is 1000 kg / c even during sudden braking.
It is about m ² / s, but it depends on the vehicle, but it is generally 1G (9.8m / s).
It takes 100 ms or more to increase the brake hydraulic pressure to 100 kg / cm ² to obtain the deceleration of s ² ). Therefore, it is possible to accurately estimate the vehicle body speed by making the limit value of the vehicle body speed small initially and gradually increasing it.

In the anti-skid control, the control starts when the difference between the estimated vehicle speed and the wheel speed becomes a certain value or more.Therefore, by decreasing the start time, the drop in the wheel speed can be reduced and the steerability can be improved. You can

〔Example〕

FIG. 1 is an explanatory view showing an embodiment of the present invention, in which V _n-2 is an estimated vehicle speed _{two times} before, V _n-1 is a previous estimated vehicle speed, V _n is an estimated vehicle speed this time, and V _nU is The upper limit value V _nD of the current estimated vehicle speed is the lower limit value of the current estimated vehicle speed,
V _xn is the current wheel speed.

V _nU = V _n-1 -ΔV _n-1 + ΔV _U V _nD = V _n-1 -ΔV _n-1 -ΔV _D where ΔV _n-1 = V _n-2 -V _n-1 and ΔV _U is the rising limit value, and ΔV _D is the falling limit value. The calculation formula of the estimated vehicle body speed V _n this time is V _n = MED (V _xn , V _nU , V _nD ), which is the same as the formula.

However, since the calculation method of V _nU and V _nD is different, Δ
Even if V _U and ΔV _D have the same values as in the conventional case, since the range of the estimated vehicle body speed V _n changes depending on ΔV _n−1 , the values are close to the actual vehicle body speed (see FIG. 6). As a result, the responsiveness of anti-skid control is improved. Figure 2 shows this.
(b) shows the response of anti-skid control as the brake hydraulic pressure. FIG. 3 is an explanatory view of the conventional anti-skid control, and shows that the responsiveness is poor due to a large change in brake hydraulic pressure due to a large drop in wheel speed.

In order to _prevent V _nU and V _nD from changing with time and _exceeding the limits of acceleration and deceleration of the vehicle, the following settings can be made.

V _nU = V _n-1 + MIN (V _n-1 -V _n-2 + ΔV _U , ΔV _UMAX ) V _nD = V _n-1 + MIN (V _n-2 -V _n-1 + ΔV _D , ΔV _DMAX ) MIN (,) is a function that selects the smaller of the two values, and ΔV _UMAX and ΔV _DMAX are the maximum values of ΔV _U and ΔV _D , respectively.

When the present invention is applied to the case where the vehicle speed is calculated from the vehicle speed sensor (Doppler type, spatial filter type), abnormal data can be removed and the vehicle speed can be calculated accurately.

[Effects of the Invention] As described above, according to the present invention, it is possible to accurately perform the estimation calculation of the vehicle body speed. Therefore, if it is used for anti-skid control, the responsiveness can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of antiskid control to which the present invention is applied, FIG. 3 is an explanatory diagram of conventional antiskid control, and FIG. 4 is an antiskid control. FIG. 5 is an explanatory diagram of a conventional vehicle body speed estimation method, FIG. 6 is an explanatory diagram of speed change during braking, and FIG. 7 is an explanatory diagram of wheel speed recovery. In the figure, WS is a wheel speed sensor, FR, FL, RR, RL
Is a wheel, and ACT is a brake control actuator.

Claims (1)

[Claims] 1. A method for estimating and calculating a vehicle body speed at a predetermined calculation cycle, which is estimated from a difference ΔV _n-1 between a previous estimated vehicle body speed V _n-1 and an estimated vehicle speed V _{n-2 two} times before. Of the estimated vehicle speed V _n of the upper limit value V _nU and the lower limit value V _nD
And limiting them by the following equation, V _nU = V _n-1 -ΔV _n-1 + ΔV _U V _nD = V _n-1 -ΔV _n-1 -ΔV _D However, ΔV _U : rise limit value ΔV _D : _Lower limit value A vehicle body characterized by selecting a medium value from the current wheel speed V _xn obtained from a wheel speed sensor and the above-mentioned V _nU and V _nD to be the current estimated vehicle body speed V _n Speed estimation calculation method.