Speed detecting method and apparatus

• US 4,584,528 A
• Filed: 02/25/1982
• Issued: 04/22/1986
• Est. Priority Date: 02/28/1981
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Matsuda, Toshihiko, Ohmae, Tsutomu, Tachikawa, Makoto
• Primary Examiner(s): Krawczewicz, Stanley T.
• Assistant Examiner(s): Solis, Jose M.
• Application Number:
  US06/352,083
• Time in Patent Office: 1,517 Days
• Field of Search: 324/166, 324/178, 324/161, 328/129, 377/20, 377/24
• US Class Current: 324/166
• CPC Class Codes: G01P 3/489 Digital circuits therefor

Abstract

A counter is provided to count an output pulse which a pulse generator generates each time a vehicle moves by a predetermined distance. A microprocessor is provided to actuate a timer in synchronism with the leading edges of the output pulse from the pulse generator. The timer is set to a constant time interval during which the speed of the vehicle is to be detected. The microprocessor calculates the speed of the vehicle from the count of the counter which count is a value during the time interval from when the timer starts to operate to when the pulse generator generates a pulse just before or after the end point of the set time interval. Thus, the speed of the vehicle can be detected with good resolution and precision.

Claims

1. A speed detecting apparatus comprising:

a pulse generator means for generating a first pulse each time a vehicle moves by a predetermined distance;

first counting means for counting the first pulses delivered from said pulse generator means;

oscillator means for generating a clock pulse with a constant frequency higher than the frequency of generation of said first pulse;

second counting means for counting the clock pulses delivered from said oscillator means;

interruption pulse generating means for generating an interruption pulse in synchronism with the generation of said first pulse;

timer means for generating a time interruption pulse each time a set time interval has lapsed; and

microprocessor means responsive to receipt of said interruption pulse and said time interruption pulse for calculating the speed of said vehicle on the basis of a count value of said first counting means during a time interval from when a pulse is generated by said pulse generator at or adjacent the measuring start point of said set time interval to when a pulse is generated by said pulse generator just before or after the end point of said set time interval and a count value of said second counting means during said time interval, said microprocessor means operating to control said interruption pulse generating means so as to selectively inhibit the generation of said interruption pulse.

2. A speed detecting apparatus according to claim 1, wherein said timer starts counting said set time interval in response to a pulse generated by said pulse generator means.

3. A speed detecting apparatus according to claim 1, wherein said microprocessor allows the generation of said interruption pulse only during a time interval from the reception of said time interruption pulse to when said interruption pulse generating means generates an interruption pulse.

4. A speed detecting apparatus according to claim 1, further comprises reset pulse generating means for generating a reset pulse each time a first pulse is generated from said pulse generator means to thereby reset said second counting means, wherein said microcomputer determines the speed of said vehicle on the basis of a count value of said first counting means and a value obtained by subtracting a count value of said second counting means at a time point where the time interruption pulse is generated from a count value of said second counting means at the end point of said set time interval.

5. A speed detecting apparatus according to claim 1, wherein said timer makes said set time interval larger when a change of speed of said vehicle is less than a set value.

6. A speed detecting apparatus comprising:

pulse generator means for generating a first pulse each time a vehicle moves by a predetermined distance;

first counting means for counting the first pulses delivered from said pulse generator means;

oscillator means for generating a clock pulse with a constant frequency higher than the frequency of generation of said first pulse;

second counting means for counting the clock pulses delivered from said oscillator means;

interruption pulse generating means for generating an interruption pulse in synchronism with the generation of said first pulse;

timer means for generating a time interruption pulse each time set time interval has lapsed; and

microprocessor means responsive to receipt of said interruption pulse and said time interruption pulse for

(a) initiating the start of said timer means,

(b) inhibiting operation of said interruption pulse generating means during the period after said timer means has been started and prior to generation of said time interruption pulse,

(c) reading the contents of said first and second counting means following the receipt of said time interruption pulse, and

(d) calculating the speed of said vehicle on the basis of the read contents of said first and second counting means.

7. A speed detecting apparatus according to claim 6, wherein said microprocessor means initiates the start of said timer means in response to receipt of an interruption pulse.

8. A speed detecting apparatus according to claim 6, further including means for resetting said second counting means in response to each generation of a first pulse.

9. A speed detecting apparatus according to claim 8, wherein said first and second counting means are read immediately following the receipt of said time interruption pulse.

10. A speed detecting apparatus according to claim 6, wherein said microprocessor means is responsive to receipt of said time interruption pulse for removing the inhibition of operation of said interrupt pulse generating means and operates to read the contents of said first and second counting means in response to receipt of an interruption pulse after receipt of said time interruption pulse.