JPS60225066A - Vehicle speed detector - Google Patents

Abstract

PURPOSE:To get rid of effect from chattering and noises without use of any complicated filter by providing an interrupt mode for the rising and falling to calculate the vehicle speed from the time of receiving a pulse. CONSTITUTION:When interrupt is initiated at the rising time t1 of a pulse P1, it is switched over to the rising trigger mode. This allows the triggering of interrupt at the rising time t7 of a pulse P4 at the next time. Subsequently, interrupt is trigered at the rising time t8 of a pulse P2. At the next step 11, the interrupt mode is changed to the falling trigger mode. then, interrupt is triggered at the falling time t2 of the pulse P2 an done again at the falling of a pulse P5. The change of the interrupt mode is made. Then, interrupt is triggered at the rising time t9 of a pulse P30. Subsequently, interrupt is triggered at the rising time of a pulse P31 and then done at the falling thereof. It is changed to the rising trigger mode from the falling trigger mode. In the end, the time t1, t5 and t3 is memorized in the falling processing and time t8 and t10 done in the rising processing. Thus, the effect of chattering or the like can be reduced using either of the processings.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a method for detecting the vehicle speed of an automobile, and more particularly to a method for detecting the vehicle speed by processing a pulse signal of a vehicle speed sensor that generates a pulse signal with a repetition frequency proportional to the vehicle speed. This invention relates to a vehicle speed detection method.

Prior Art and Problems This type of conventional vehicle speed detection method uses a pulse signal (P) with a repetition frequency proportional to the vehicle speed, as shown in FIG.
I, P2. P3 indicates each pulse) is input to the interrupt terminal of the microcomputer, an interrupt is generated at the falling edge of the pulse signal, and the frequency of the periodic acid of the pulse signal can be measured by detecting the timing tl-t3 of this interrupt. It is carried out in

By the way, the vehicle speed is determined by rotating a magnet whose N and S poles are alternately magnetized in the circumferential direction according to the vehicle speed using the speed cable of the vehicle, and obtaining the on/off state of a reed switch near the magnet as a pulse signal. In sensors, etc., as shown in FIG. 1(b), narrow pulses P5. P6 and a narrow pulse P4 due to noise often appear. In addition, the same figure (b)
Pulse P30. P31 indicates a state in which pulse P3 is divided by chattering pulse P6. For this reason, for example, if an interrupt is generated at the fall of the Ehahals signal from the 1' level to the o'' level, an interrupt will be generated at the falling time of the normal pulse B, t2.t3, as well as the pulse P5.P6 due to chattering. Therefore, an interrupt is generated at times t5 and t6, and an interrupt is also generated by the noise pulse P4, so in the conventional method, the timing when the interrupt occurs is simply determined as the falling edge of a normal pulse signal. Therefore, t1~t4.t2~t5.t6
- L3 is recognized as one cycle, and the accuracy of the calculated speed is extremely poor.

One possible way to improve this problem is to apply a hardware filter to the pulse signal to remove pulses due to chattering before inputting it to the interrupt terminal of the microcomputer. However, the maximum value of the pulse width due to chattering in the pulse signal of a standard vehicle speed sensor is close to 1 m5ec, which is the minimum pulse width of the regular pulse at level "1" and level "θ" at high speed. It is difficult to reliably remove only chattering pulses with a simple RC filter, and there is a drawback that a complicated filter is required.

Purpose of the Invention The present invention improves these conventional drawbacks, and
The purpose is to be able to sufficiently remove the effects of chattering and noise without using complex filters.

Structure of the Invention The gist of the present invention is to provide a vehicle speed detection method for detecting vehicle speed by processing a pulse signal of a vehicle speed sensor that generates a pulse signal with a repetition frequency proportional to the vehicle speed. The first one that is interrupted by
The pulse signal is inputted to the interrupt terminal of a microcomputer that can select by program an interrupt mode in which an interrupt mode occurs and a second interrupt mode in which an interrupt occurs at the falling edge of a signal applied to the interrupt terminal. In the interrupt mode, it is determined whether or not the level of the pulse signal does not change for a predetermined period of time from the time of the interrupt, and when it changes, the interrupt processing is immediately terminated, and when it does not change, the interrupt mode is changed to the opposite mode, and In at least one of the interrupt modes, the time of the interrupt or the time related thereto is temporarily stored as the pulse reception time and the interrupt processing is terminated, and the vehicle speed is determined from the pulse reception time sequentially stored through multiple interrupt processing. The problem lies in the vehicle speed detection method that calculates the vehicle speed.

The operation of the present invention will be explained with reference to the pulse signal waveform diagram of FIG. 2(a). 1(a) has the same waveform as FIG. 1(b), and in addition to the regular pulses PI and P2°, there are noise pulses P4. Chattering pulse P5. Chattering pulse P
Pulse P30.6 divided by P30. P31 appears.

For convenience of explanation, the microcomputer was originally designed as shown in Figure 2 (b).
), it is assumed that the mode is a falling trigger mode in which an interrupt occurs at the falling edge of the signal applied to the interrupt terminal. Furthermore, since the width of the noise pulse is narrow, the maximum chattering time T (for example, 1 m5ec) is set as the predetermined time for determining whether there is no change in the signal.

When the microcomputer is first interrupted at the falling edge (tl) of the pulse P1, it determines in this interrupt processing whether the level of the pulse signal does not change for a predetermined time T from the time of the interrupt. The pulse P1 is a regular pulse without chattering, and in such a case, the level of the pulse signal does not change for a predetermined time T after an interrupt is generated at the falling edge (tl) of the pulse P1. This is because the minimum width of the @θ″ level of the pulse is T(l
m5ec) or more. In such a case, the microcomputer temporarily stores the time of the interrupt (tl) or the time when the discrimination ends (tl+T) as the pulse reception time, and also sets the interrupt mode by the program to generate an interrupt at the rising edge of the signal applied to the interrupt terminal. Switch to rising trigger mode. Therefore, next time, an interrupt is generated at the rising edge of pulse P4 (tl). However, since the pulse P4 is a noise pulse and the level of the pulse signal changes within a predetermined time T from the time of the interrupt (tl), the interrupt processing is promptly terminated, and the pulse reception processing and interrupt mode change are not performed. .

Therefore, an interrupt will be generated next time at the rising edge of pulse P2 (t8). This pulse P2 is a regular pulse, and the level of the pulse signal does not change for a predetermined time T from the time of the interrupt (t8), so the time of the interrupt (t8) or the time when the determination is finished (t8+T) is temporarily the pulse reception time. is stored and the interrupt mode is changed to falling trigger mode.

Next, an interrupt is generated at the falling edge of pulse P2 (t2), but since chattering pulse P5 appears immediately after, it does not change for a predetermined time 'r, and pulse reception processing 2 interrupt mode change processing is performed. Not possible. and,
When an interrupt is generated at the falling edge of pulse P5, the level of the pulse signal does not change for a predetermined period of time from the time of the interrupt (t5).
+T) is temporarily stored as the pulse acceptance time and the interrupt mode is changed. Therefore, next pulse P30
An interrupt is generated at the rising edge of (t9).

However, since the pulse P30 has a narrower width due to the chattering pulse P6, the pulse reception process 1 interrupt mode change process is not performed. Therefore, an interrupt is generated at the next rising edge of pulse P31 (110), and the interrupt time (tlO) or time (tl0+T) is temporarily stored and the interrupt mode is changed. Next, an interrupt is generated at the falling edge of the pulse P31, and the interrupt time (t3) or time (t3+T) is temporarily stored, and the interrupt mode is changed from the falling trigger mode to the rising trigger mode.

After all, in the above processing, in the falling trigger mode interrupt processing, the time (tl) or the time (t 1 +T)
, time (t5) or time (15-)T).

The time (t3) or the time (t3+T) is stored respectively, and in the interrupt processing in the rising trigger mode, the time (t3) or the time (t3+T) is stored.
t8), time (t8+T), time (tlO), or time (tlo+T), respectively. Therefore, by using either the pulse reception time stored in the falling trigger mode or the pulse reception time stored in the rising trigger mode, the effects of chattering and noise can be reduced, and vehicle speed can be determined more accurately than conventional methods. It is something that can be detected. In the above description, pulse reception processing was performed in both the rising mode and the falling mode, but either one of the processings may be omitted. Furthermore, the vehicle speed may be calculated for each pulse by subtracting the current pulse reception time from the previous pulse reception time, or it may be calculated by averaging the cycles of multiple pulses. .

Embodiment of the Invention FIG. 3 is a block diagram showing an example of the hardware configuration of a device implementing the present invention. Reference numeral 1 denotes a magnet that is rotated according to the vehicle speed by a speed cable (not shown), and in the circumferential direction of the magnet. The N and S poles are magnetized alternately for a total of 4 poles. The reed switch 2 is placed close to the magnet 1 and turns on and off in response to the rotation of the magnet 1. One end of the reed switch 2 is grounded, and the other end is connected to a buffer 3 that performs amplification, waveform shaping, level adjustment, etc., and a pulse signal as shown in FIG. 2(a) is obtained from the buffer 3. The microcomputer 4 has an interrupt function that allows a program to select a falling trigger mode in which an interrupt occurs at the falling edge of an input signal applied to the interrupt terminal INT, and a rising trigger mode in which an interrupt occurs at the rising edge of the input signal. In addition, ROM, RAM, etc. are CPL
It is a so-called one-chip microcomputer integrated on the same chip as I. It also has the function of inputting the interrupt terminal INT and reading the health signal. Microcomputers having such functions have been well known. The microcomputer 4 may be a microcomputer dedicated to vehicle speed detection that sends the detected vehicle speed to the outside from its output port, or may be a microcomputer for so-called automobile engine control, fuel injection, etc. that also performs other processing. It's okay. Note that ■c is a power supply.

The microcomputer 4 responds to the falling of the pulse signal from the "1" level to the "0" level or from the "0" level to the "0" level as shown in FIG. 2(a), depending on the current interrupt mode.
An interrupt is generated when the voltage rises to the 1'' level, and the interrupt processing as shown in FIG. If it is the falling trigger mode, execute the falling mode processing from step 32 onwards, and if it is the rising trigger mode, execute the falling mode processing in step 3.
Execute rising mode processing of 8 or less.

In the falling mode process, first, the value of the first loop counter LPCI set in the RAM area is set to n (
S2). This n is the maximum chattering time (T),
This is the value divided by the execution time required to complete one cycle of steps S3→S4→S5-33. Note that a hardware timer such as a built-in timer can also be used to measure the predetermined time T. Next, it is determined whether the level of the interrupt terminal INT, that is, the level of the pulse signal output from the buffer 3, is "0" or not (S2). If it is "1", the pulse signal is Since the level has changed, interrupt processing is ended and the process returns to the main routine. Furthermore, if the level of the interrupt terminal INT is "O", the value of the first loop counter LPCI is subtracted by 1 (S4), and the process of determining whether the value of the loop counter LPCI is zero (S5) is performed as a loop counter. Repeat until the content of LPCI becomes zero or the level of the interrupt terminal INT becomes 1'. Then, if the level of the interrupt terminal INT becomes 1' before the content of the first loop counter LPCI becomes zero, When the interrupt processing is finished and the contents of the loop counter LPCI become zero before the level of the interrupt terminal INT becomes "1", the mode is switched to the rising trigger mode (S6), and the vehicle speed pulse reception processing is executed (S7). Return to the main routine.Vehicle speed pulse reception processing is processing that temporarily stores the time when the current interrupt occurs or the time when the content of the first loop counter LPCI becomes zero in a certain area such as RAM. .

In addition, in the rising mode processing, first, the value of the second loop counter LPC2 set in the RAM area is set to n''
shall be. This n' is the value obtained by dividing the maximum chattering time (T) by the execution time required to go through steps S9→SIO→Sll→S9. Next, interrupt terminal I
To determine whether the NT level is “1” or not, S9), “θ”
', the interrupt processing ends and returns to the main routine. Also, if the level of the interrupt terminal INT is 1'', the value of the second loop counter LPC2 is subtracted by 1 (310), and the process of determining whether the value of the loop counter LPC2 is zero (S11) is performed as a loop counter. This process is repeated until the contents of LPC2 become zero or the level of the interrupt terminal TNT becomes 0''. Then, the second loop counter L P
If the level of the interrupt terminal INT becomes "0" before the contents of C2 become zero, the interrupt processing ends, and the interrupt terminal
If the contents of the loop counter LPCI become zero before the level of T becomes 0'', the falling edge switches to retrigger mode (
S12), return to the main routine.

In the main routine, the vehicle speed is detected by a known method based on the pulse reception times that are sequentially and temporarily stored in the interrupt process.

Although the acceptance process is performed in the falling trigger mode in FIG. 4, the acceptance process may be performed in the rising trigger mode. Also, the output of buffer 3 is connected to the interrupt terminal INT.
This may be done by inputting the pulse signal into the input port and monitoring the level of the input port to see if the level of the pulse signal changes.

As described in detail, the present invention has the advantage of being able to eliminate the effects of chattering and noise without the need for externally providing a complicated filter using hardware, and can reduce vehicle speeds at economical speeds. Detection becomes possible. Furthermore, some types of chattering include, for example, chattering that is repeatedly turned on and off every 100 μsec and whose duration exceeds 1 m5 ec, but the present invention has the advantage of being able to eliminate the effects of such chattering.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional vehicle speed detection method, FIG. 2 is an explanatory diagram of a vehicle speed detection method of the present invention, FIG. 3 is a block diagram showing an example of the hardware configuration of a device implementing the present invention, and FIG. The figure is a flowchart showing an example of interrupt processing by the microcomputer 4. 1 is a magnet, 2 is a reed switch, 3 is a buffer, ・1)
)4 is a microcomputer. Patent Applicant Fujitsu Ten Ltd. Representative Patent Attorney Tamamushi 5 1 person outside the department No. 1 t+t? is second mouth

Claims (1)

[Claims] In the vehicle speed detection method of detecting vehicle speed by processing the pulse signal of a vehicle speed sensor that generates a pulse signal with a repetition frequency proportional to the vehicle speed, a first interrupt mode in which an interrupt occurs at the rising edge of a signal applied to an interrupt terminal; The pulse signal is input to the interrupt terminal of a microcomputer that can select by program a second interrupt mode in which an interrupt occurs at the falling edge of a signal applied to the terminal; In the second interrupt mode, it is determined whether or not the level of the pulse signal does not change for a predetermined period of time from the time of the interrupt, and if it changes, the interrupt processing is promptly terminated, and if it does not change, the interrupt mode is changed to the opposite mode. At the same time, in at least one of the interrupt modes, the time of the interrupt or the time related thereto is temporarily stored as the pulse reception time, and the interrupt processing is terminated, and the pulse reception time sequentially stored through multiple interrupt processing is A vehicle speed J11 method characterized in that the vehicle speed is calculated.