JPS5934159A - Car speed detecting method - Google Patents

Abstract

PURPOSE:To obtain an inexpensive device which requires no operation, by obtaining a gate time being proportional to a car speed, counting the number of clock pulses in this gate time, and obtaining a pulse being proportional to the car speed. CONSTITUTION:A frequency divider 2 divide a pulse from a car speed pulse generator 1, and obtains T1 being the first gate time. A monostable multivibrator 3 obtains T2 being the second gate time which is set by rise of the pulse from the frequency divider 2 and is reset after a constant interval of time. An RS flip- flop 4 obtains T3 being the third gate time which is set by fall of the pulse from the frequency divider 2 and is reset by fall of the pulse from the monostable multivibrator 3. A car speed signal is obtained by counting a clock in this third gate time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vehicle speed detection method that can be used to detect the vehicle speed in a constant speed driving system of an automobile, in principle an autodriving system.

An autodrive device is a device that maintains the speed at that point when the driver turns on the autodrive switch while driving. The accelerator is controlled by an actuator such as a vacuum servo or a motor, and the vehicle is always driven at a constant speed.

Vehicle speed detection is an essential requirement for this autodrive device, but the vehicle speed pulse conventionally used as a vehicle speed signal is a pulse train obtained by a reed switch that is opened and closed by a magnet rotated by a speedometer cable. However, in general, with this method, only 4 pulses can be obtained per revolution of the speedometer cable.

Therefore, if an attempt is made to obtain a vehicle speed signal by counting the number of pulses, the sampling time will be extremely long, and this method cannot be applied to a device with a fast control cycle such as an automatic drive device.

Therefore, there is a method of detecting the vehicle speed by the number of pulses obtained by counting the period of the vehicle speed pulse with the reference clock pulse, but the number of pulses N obtained by this method is as shown by the broken line in Figure 1. Since it is inversely proportional to vehicle speed, this N
In order to obtain the desired vehicle speed, calculations are required, which has the disadvantage of making the device complicated and expensive.

On the other hand, in automatic drive control, the absolute vehicle speed is not so necessary, and only the change between the set vehicle speed and the traveling vehicle speed is 8 times, so there is also a method of controlling the actuator using the change ΔN of the number of pulses N described above. However, according to this method, the resolution when detecting changes in vehicle speed (vehicle speed change angle represented by one pulse, vehicle speed V÷number of pulses N) changes dramatically at each vehicle speed, as shown by the broken line in Figure 2, and therefore it becomes necessary to make corrections. However, similar to the above, there are drawbacks such as a complicated device and high cost.

The present invention aims to rectify the above-mentioned drawbacks, and its purpose is to provide a vehicle speed detection method in which the speed b pulse train of the sampling time can be adjusted without complicated calculations or corrections.

Next, the vehicle speed detection method of the present invention will be explained with reference to FIGS. 3 and 4.

In FIG. 3, 1 is a known vehicle speed pulse generator that outputs a pulse proportional to the vehicle speed, and 2 is a pulse generator 1 whose pulse frequency is divided to obtain a first gate time T1. The frequency divider 3 is set at the rising edge of the pulse from the frequency divider 2 and is reset after a certain period of time to obtain the second gate time T, which is a monostable multi. 4 is the pulse from the frequency divider 2↓ The RS flip 70 knob (hereinafter simply referred to as FF
), 5 is a clock pulse generator with a constant period t, 6 is an AND circuit that manually spans the output of the FF 4 and the output of the clock pulse generator 5, and 1 is the AND circuit 6.
This is a counter that counts the output of the device.

Incidentally, FIG. 4 shows the output waveforms of each circuit in the block diagram of FIG. 3 above.

Next, to explain the operation, in Fig. 4, 'I'
,! Since T2 - T1, it is clear that T3 changes in proportion to the vehicle speed. That is, since T1 changes depending on the vehicle speed detection pulse, T! is constant. From T + t
- The subtracted value T8 changes in proportion to the vehicle speed.

Below, we will explain why the value obtained by dividing T3 required at the third gate time by the period t of the clock pulse, that is, the count number N that indicates the vehicle speed, is appropriate as a control signal for the autodrive device. The count number N is expressed by the following equation.

here, Eye: Division ratio N: Determined by the characteristics of the vehicle speed pulse V: Vehicle speed So, Then, the relationship between vehicle speed and H is expressed.

As mentioned above, in controlling an autodrive device, it is not necessary to know the absolute vehicle speed, but only to be able to reliably know changes in vehicle speed. (equivalent to a change of 1n/H) is a value sufficient for use in automatic drive control, then the change in N can be used as a change in vehicle speed.

Therefore, if we change the resolution to humans, becomes.

Here, assume that the vehicle speed pulse is 4 pulses per revolution of the speedometer cable, and that the speedometer cable is 637 rpm when running at 60mm/H.
K=1.413.

Under these conditions, m and T2 + tl each change,
All you have to do is select the combination that minimizes the change in each vehicle speed of m = 4 r T 2 =
(L 2 ・sea, t = 320 μse
We selected combination c.

The results of the above equations (1) and (2) for this combination K are shown as solid lines in FIGS. 1 and 2. Please note that due to the nature of auto drive and Japanese domestic regulations, the vehicle speed range is 40~
120 &/H.

From Figure 2, the lowest value of MU is 0.18 km/H1 and the highest value is 0.25 hot/H, and this difference is 0.07 km/H1.
km/H, and during actual auto drive driving, the vehicle speed change is limited to about ±5 kIn/H, so when driving at 90kIn/H, for example, this difference is 1-1.
It becomes only about 0.017cm/H. That's all, Δ
Auto drive control can be performed by treating N as ΔV.

In addition, in the actual auto drive 1tiII m, the interval for controlling the actuator is 0.1~
About 0.2 sec is appropriate, and the vehicle speed resolution during control is also 0.2br/H (5 pulses zb++/H)
A certain degree is sufficient.

Note that although the above-described embodiment shows a combination of discrete elements, it goes without saying that the system may be assembled using a microcomputer. In this case, R
Since the OM area can be significantly saved, other functions can be processed within the same computer.

As described above, in the present invention, a gate time proportional to the vehicle speed is observed, and the number of clock pulses within this gate time is counted to obtain a pulse proportional to the vehicle speed.
It is suitable for use as a control signal for auto drive equipment, and therefore does not require complicated calculations or corrections.
This has the advantage that a control device can be manufactured at low cost.

[Brief explanation of drawings]

Figure 1 is a diagram showing speed changes with respect to vehicle speed pulses;
The figure is a diagram showing the vehicle speed change 'jk caused by one pulse.
The figure is a block diagram showing an example of implementing the method of the present invention, and FIG. 4 is a timing chart showing the outputs of each circuit.

Claims (1)

[Claims] A first gate time obtained by dividing a vehicle speed pulse that changes in proportion to the vehicle speed, a second gate time that is set at the rise of the first gate time and reset after a predetermined time, and the first gate time A third gate time is set at the falling edge of the gate time and reset at nine o'clock at the falling edge of the second gate time. A vehicle speed detection method that obtains the number of pulses.