Synchronous timer vehicle speed measurement

• US 6,219,624 B1
• Filed: 08/03/1998
• Issued: 04/17/2001
• Est. Priority Date: 08/03/1998
• Status: Expired due to Fees

• Current Assignee: Visteon Global Technologies Incorporated (Visteon Corporation)
• Original Assignee: Visteon Global Technologies Incorporated (Visteon Corporation)
• Inventors: Russ, Ronald Paul
• Primary Examiner(s): Assouad, Patrick
• Application Number:
  US09/128,604
• Time in Patent Office: 988 Days
• Field of Search: 702/75, 702/96, 702/147, 702/148, 701/74, 701/75, 327/24, 327/26, 327/31
• US Class Current: 702/75
• CPC Class Codes: G01P 3/489 Digital circuits therefor

Abstract

A method of measuring the period of a vehicle speed signal is disclosed that includes the steps of accumulating predetermined time interval increments between first and second rising edges of the signal, calculating a remainder time interval upon detection of the second edge of the signal and adding the remainder to the accumulated increments value to obtain the period, and calculating an average period from a plurality of consecutive period measurements. If the accumulated value exceeds a predetermined maximum value before the second edge occurs, the maximum value is used in calculating the average.

Claims

1. A method of measuring the period of a signal comprising a sequence of the following steps:

detecting a first edge of said signal;

accumulating predetermined time interval increments between edges of the signal;

if the current value of the accumulated increments is equal to or greater than a predetermined maximum value, terminating the period measurement and storing said maximum value as the period measurement value;

if said current value is less than said predetermined maximum value, calculating a remainder time interval upon detection of a second edge of said signal and modifying said current value to account for the calculated remainder and storing modified current value as the period measurement value; and

calculating an average period from a plurality of consecutive period measurement values.

2. The method of claim 1 wherein the value of a free running timer is stored upon detection of a signal edge;

said increments are generated by a retriggerable timer that is triggered upon detection of a signal edge; and

said period measurement values are stored in an N stage FiFo buffer for use in the average calculation.

3. The method of claim 1 wherein period measurement starts with said first edge by setting a retriggerable timer to generate interrupts at the end of a predetermined time interval, a current speed value is increased by said time interval each time said interrupt is generated and period measurement ends with said second edge or when said current speed value exceed a predetermined maximum value.

4. The method of claim 3 wherein a free running counter is used to identify the times of said edges and the occurrence of the interrupt preceeding an edge in order to calculate a remainder value to be added to said current speed value to determine the period of the signal.

5. The method of claim 4 wherein said signal is a vehicle speed signal and the value of the average period is used to drive a speed display.

6. A method of measuring and displaying vehicle speed based on the period of a vehicle speed signal comprising a sequence of the following steps:

executing an input capture routine upon detection of a first transition in said speed signal to initiate the determination of a current speed period value;

executing an output compare routine upon each expiration of a predetermined time interval following said detection of a transition in said speed signal;

executing a speedometer update routine after a plurality of said periods;

said capture routine accumulating predetermined time interval increments between transitions of the speed signal and adding a calculated remainder time interval equal to the difference in time between execution of said capture routine and the previous execution of said compare routine to obtain said current speed period value and storing said current value;

if the accumulated increments equal or exceed a predetermined maximum value prior to detection of a second transition, terminating the period measurement and storing said maximum value;

calculating an average period from a plurality of values stored.

7. Apparatus for measuring and displaying vehicle speed based on the period of a vehicle speed signal comprising:

detecting means for detecting a first transition in said speed signal to initiate the determination of a current speed period value;

calculating means for accumulating predetermined time interval increments subsequent to said first transition and prior to a second transition of the speed signal;

memory means for storing a maximum current period if the accumulated increments exceed a maximum period;

said calculating means calculating any remainder time interval upon the detection of said second transition between the time of the second transition and expiration of the previous time increment;

said calculating means adding said remainder time interval to said accumulated increments and storing the sum as a current period in said memory means;

means for calculating an average period from a plurality of the most recent periods stored.