JPS60225067A - Vehicle speed detection - Google Patents

Abstract

PURPOSE:To enable the removal of effect from chattering without use of any complicated filter by inhibiting the subsequent interrupt processing when a pulse receiving processing is done in the interrupt processing. CONSTITUTION:Inhibition is done by masking the interrupt on a program in the interrupt processing. Then, after the masking of interrupt, as the level of a pulse signal will not be ''1'' continuously upto halfway in a pulse P<2>, no interrupt is triggered with the falling of the noise P<5> and the falling time t<4> is overridden. Then, after the masking of interrupt is released halfway in the pulse P<2>, the falling of the subsequent pulse P<4> is applied again while the masking of interrupt is done by a program. The masking continues halfway in the pulse P30 and interrupt is triggered at the falling of the pulse P30. Then, the interrupt processing starts at the falling of the subsequent pulse P31. In the end, the time t<1>, t<5> and t<3> is memorized as pulse receiving time respectively and thus, the detection of the vehicle speed can be performed accurately.

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 timings t1 to 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), a narrow pulse P5 due to reed switch chattering and a narrow positive pulse P5 due to noise are generated. A negative polarity pulse P6 often appears.

It should be noted that pulse P30. of the figure (b). P31 indicates a state in which the pulse P3 is divided by the negative pulse P6. Therefore, for example, if an interrupt is generated when the pulse signal falls from the "1" level to the "0" level, an interrupt will be generated at the normal pulse falling time B, t2°t3, and the pulse P4 due to chattering will be generated. An interrupt is also generated at time t4 due to the noise pulse P5. P6 also generates an interrupt at times t5 and t6, and in the conventional method, the timing at which the interrupt occurs is simply determined as the falling edge of a regular pulse signal, so it seems that the interrupt occurs between t1 and t6.
t4. t2-t5. There is a drawback that t6 to t3 is recognized as one cycle, and the accuracy of the calculated speed becomes extremely poor.

One possible way to improve this problem is to filter the pulse signal to remove chattering pulses and noise pulses 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 normal pulse at high speeds of level "1" and level "0", so it can be calculated simply by The RC filter has the disadvantage that it is difficult to reliably remove only chattering pulses and requires a complicated filter.

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 Generally, a chattering pulse has a narrower pulse width than a regular pulse. Therefore, if it is determined whether the level of the pulse signal does not change for a certain period of time after an interrupt occurs, it can be determined that if the level does not change, it is a regular pulse, and if it changes, it is a chattering pulse. but,
If this method alone is used, it is not possible to remove the influence of noise pulses that appear near the middle of the 0'' level of the pulse signal, such as noise pulse P5 in FIG. In general processing other than processing, the level of the pulse signal applied to the interrupt terminal is detected at predetermined time intervals, and when the predetermined level continues for a predetermined time or more, the next interrupt processing is permitted, and pulse reception processing is performed in the interrupt processing. When the pulse width of the noise pulse P5 is narrow, the next interrupt processing is disabled when the noise pulse P5 is narrow. Even at the falling edge of the noise pulse P5 at t4, interrupt processing remains prohibited, making it possible to eliminate the influence of the noise pulse.

Embodiment of the Invention An embodiment of the present invention will be described 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, chattering pulses P4. Noise pulse P5. Noise pulse P6
Pulse divided by P30. P3] appears.

The microcomputer performs general processing as shown in Figure (b).
The level of the pulse signal is sampled at the timing shown in . The sampling period is T Hwin, which is the minimum value of the pulse width of the predetermined level so that the predetermined level of the pulse signal (here, the level "1") can be sampled at least twice consecutively even at high vehicle speeds. Set to Hll1in/2 or less. 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 T for determining whether there is no change in the signal.

FIG. 2(C) is a diagram showing the state of enabling and disabling interrupts. Enablement is achieved by canceling the interrupt mask using a microcomputer program when a level of "1" is detected twice in a row. This is done by masking interrupts by a program during interrupt processing. That is, assuming that the interrupt is initially masked, the interrupt mask is canceled when "1 level" is detected twice in succession during the pulse P1, and an interrupt is generated at the falling edge of the pulse P1. When an interrupt occurs, it is determined whether the level of the pulse signal does not change for a predetermined time T from the time of the interrupt (tl), and if it has changed, it is immediately processed without performing pulse reception processing or interrupt mask cancellation processing. If the process ends and there is no change, at the time of interrupt (tl) or at the time of determination (t 1 +T)
A pulse reception process for temporarily storing the pulse reception time as a pulse reception time and a process for masking interrupts are performed. Pulse P1
is a regular pulse, and the level of the pulse signal does not change for a predetermined time T, so the time (tl) etc. are stored and interrupts are masked.

After interrupt masking is performed, the level of the pulse signal does not become "1" continuously until the middle of pulse P2, so
No interrupt is generated when the noise P5 falls, and the falling edge (t4) is ignored.

If the interrupt mask is released in the middle of pulse P2, an interrupt is generated at the falling edge of pulse P2. However, pulse P
Since pulse P4 due to chattering is generated immediately after 2,
The level of the pulse signal changes within a predetermined time T from the time of interrupt (t2), and the microcomputer does not perform storage processing or setting of an interrupt mask at the time of interrupt (t2), etc. Therefore, an interrupt will be issued again at the next falling edge of pulse P4. This time, at the time of interrupt (t
Since the level of the pulse signal does not change for a predetermined time T from 5), at the time of interrupt (t5) or at the time of determination (t 5 +T)
is temporarily stored as the pulse reception time, and the interrupt is masked by the program.

This interrupt masking continues until the middle of pulse P30. Then, when the mask is released, an interrupt is generated at the falling edge of pulse P30. However, since the level of the pulse signal changes within a predetermined time from the time of interrupt (t6) due to the noise pulse P6, the pulse reception process and the interrupt mask setting process are not performed. Then, the next pulse P
The pulse reception process and the interrupt mask setting process are performed by the interrupt process at the falling edge of signal 31.

After all, in the above process, the pulse reception time is the time (t
l) or time (tl+T), time (t5), or time (t
5+T), time (t3), or time (t 3 +T), respectively.

Therefore, it is more accurate than the conventional method (vehicle speed can be detected).In the above explanation, we have explained the case where an interrupt is generated at the falling edge of the pulse signal, but it is also possible to generate an interrupt at the rising edge of the pulse signal. Good.The vehicle speed can be calculated for each pulse by subtracting the current pulse reception time from the previous pulse reception time, or it can be calculated by averaging the periods of multiple pulses. Also good.

FIG. 3 is a block diagram showing an example of the hardware configuration of a device that implements the above method. 1 is a magnet that is rotated according to the vehicle speed by a speed cable (not shown), and has N and S poles in the circumferential direction. A total of 4 poles are magnetized alternately. The reed switch 2 is placed close to the magnet 1, and
It performs on/off operation according to the rotation of. 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 also has a masking function that allows a program to specify whether or not an interrupt will be generated at the fall of the input signal applied to the interrupt terminal INT, and the ROM, RAM, etc. are integrated into the same chip as the CPU. It was a so-called 1,000-knob microcomputer.

It also has a function of reading the input level of the interrupt terminal INT. 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 boat.
It may also be a microcomputer for so-called automobile engine control, fuel injection, etc. that also performs other processes. Note that ■o is a power source.

In general processing other than interrupt processing, the microcomputer 4 performs processing as shown in FIG. 4, for example, at intervals of THmjn/2 or less. That is, the level of the interrupt terminal INT is detected (sl), and if the level is "0", it is stored in the RAM etc. as the current terminal level and the process is terminated (32.35), and if the level is "1", it is the previous terminal level. It is determined whether or not is "1" by referring to a value stored in a RAM or the like (S3). Then, if the previous level is "o", the process goes to step S5 and ends, and if the previous level is also "1", the level is "1" for a predetermined period of time, so the program allows interrupts and cancels the mask. after(
34), and the process ends through step s5.

FIG. 5 is a flowchart showing an example of interrupt processing by the microcomputer 4. When an interrupt occurs, the microcomputer 4 first sets the value of the loop counter PC set in the RAM area to n (Sll). This n is the maximum chuckling time (T) in step S12.
→S13-S14-S12 It is the value divided by the execution time required to complete one round. Note that a hardware timer such as a built-in timer can also be used to measure the predetermined time T. Next, the level of the interrupt terminal INT, that is, the level of the pulse signal output from the buffer 3 is "0".
If it is "1", the level of the pulse signal has changed within the predetermined time T from the time of the interrupt, so the interrupt processing is ended and the process returns to the main routine.

Furthermore, if the level of the interrupt terminal INT is 0'', the value of the loop counter LPC is subtracted by 1 (513), and the process of determining whether the value of the loop counter LPC is zero (S14) is performed when the contents of the loop counter LPC are This is repeated until the level becomes zero or the level of the interrupt terminal INT becomes 1''. If the level of the interrupt terminal INT becomes '1' before the content of the loop counter LPC becomes zero, the interrupt processing is terminated, and the content of the loop counter LPC becomes '1' before the level of the interrupt terminal INT becomes '1'. When it becomes zero, the vehicle speed pulse reception process is executed (515), and after setting an interrupt mask by the program (316), the process returns to the main routine. This is a process of temporarily storing the time or the time when the contents of the loop counter LPC become zero in a certain area such as a RAM.

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 processing. Also, buffer 3
The output from the input port may be inputted to the interrupt terminal INT and the input port, and monitoring of whether the level of the pulse signal changes and sampling of the pulse signal may be performed by inputting from the input port.

In Figures 6 and 7, interrupts are not disabled or enabled by setting or unmasking interrupts, but by enabling interrupts, but by ignoring or not interrupts during interrupt processing. FIG. 6 corresponds to FIG. 4, and FIG. 7 corresponds to FIG. 5.

The difference between FIG. 6 and FIG. 4 is that step S4 in FIG. 4 allows interrupts, whereas setting flag 8 set in the RAM area, etc. to 1 specifies that interrupts are to be allowed. It is at the point where it was made (S4'). Furthermore, the difference between FIG. 7 and FIG. 5 is that before step Sll in FIG.
0 is added, and if it is 1, the process after step Sll is executed, and if it is 0, it is returned immediately, and step 8 is set to flag A for step S16.
It is at the point replaced by 16゛.

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 an embodiment 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, FIG. 5 is a flowchart showing an example of general processing other than interrupt processing by the microcomputer 4, and FIG. 6 shows another example of the interrupt processing by the microcomputer 4. Flowchart FIG. 7 is a flowchart showing another example of general processing other than interrupt processing of the microcomputer 4. 1 is a magnet, 2 is a reed switch 7, 3 is a buffer, and 4 is a microcomputer. Patent Applicant Fujitsu Ten Ltd. Representative Patent Attorney Tamamushi Go 1 person outside the department 11 Fig. tHt2 t3 Fig. 2 Fig. 30 r Fig. 4 Fig. 5 Fig. 6 Fig. 7

Claims (1)

[Scope of Claims] (1) In a vehicle speed detection method in which a vehicle speed is detected by processing a pulse signal of a vehicle speed sensor that generates a pulse signal with a repetition frequency proportional to the vehicle speed, a predetermined edge of a signal applied to an interrupt terminal is used. The pulse signal is input to the interrupt terminal of the microcomputer where the interrupt is to be performed, and in the separate processing, it is determined whether the level of the pulse signal does not change for a predetermined period of time from the time of the interrupt, and if it has changed, the interrupt is processed. If there is no change, the time of the interrupt or the time related to it is stored as the pulse acceptance time, and the next interrupt processing is prohibited, the interrupt processing is ended, and the general operations other than the interrupt processing are detecting the level of the pulse signal applied to the interrupt terminal in the process at predetermined time intervals, and when the predetermined level continues for more than a predetermined time, performing a process of permitting the next interrupt process;
A vehicle speed detection method characterized in that vehicle speed is calculated from pulse reception times sequentially stored through a plurality of interrupt processings. (2. In the vehicle speed detection method according to claim 1, the process of prohibiting the next interrupt process in the interrupt process is to mask the interrupt by a program, and the process of disabling the next interrupt process in the general process is to A vehicle speed detection method characterized in that the processing is to cancel the interrupt mask by a program. (3) In the vehicle speed detection method according to claim 1, prohibition of the next interrupt processing in the interrupt processing. The process is a process of switching the program so that it returns promptly even if an interrupt occurs, and the process of permitting the next interrupt process in the general process is a process of restoring the program switched by the switching process. Characteristic vehicle speed detection method.