Rangeable speedometer/odometer

• US 4,491,007 A
• Filed: 12/02/1982
• Issued: 01/01/1985
• Est. Priority Date: 12/02/1982
• Status: Expired due to Fees

• Current Assignee: Beede Electrical Instrument Company Incorporated
• Original Assignee: Beede Electrical Instrument Company Incorporated
• Inventors: Crowdes, George J. Jr.
• Primary Examiner(s): Gill, James J.
• Application Number:
  US06/446,222
• Time in Patent Office: 761 Days
• Field of Search: 73/2, 324/166, 324/171, 324/167
• US Class Current: 73/1.37
• CPC Class Codes: G01C 22/02 by conversion into electric waveforms and subsequent integration, e.g. using tachometer generator G01C22/002, G01C22/004, G01C22/006 take precedence
• CPC Class Codes: G01P 3/50 for measuring linear speed G01P3/56 takes precedence

Abstract

The present invention describes an adjustable speedometer/odometer to accommodate various vehicle drive configurations such as a variety of vehicle tire size and rear axle ratios. The range adjustment is made at the factory or by service personnel, and is implemented by a plurality of switches, insuring a positive selection of the desired range value, thereby eliminating the need for calibration. The conventional mechanical speedometer/odometer and speedometer cable are replaced by a signal transducer mounted on the transmission, and an electronic speedometer unit. The transducer sends signal pulses to the electronic speedometer unit that displays the vehicle speed and distance travelled, by a moving-magnet meter and an incremental counter, respectively. In addition, the range of the speedometer/odometer is switched to accommodate a dual-axle ratio differential according to a signal from an axle mounted switch. The speedometer/odometer range value is changed according to a constant proportion representing the difference in the two axle ratios. Moreover, the present invention is adaptable to receive signal pulses derived from a variety of vehicle locations, and is adaptable for other indicator applications, such as a tachometer.

Claims

1. A rangeable speedometer receiving a pulse signal having a pulse rate corresponding to velocity to be measured, comprising:

pulse integrator means to produce an analog voltage output in a relationship to said pulse signal and including a selectable ranging network for changing the relationship of said pulse integrator output voltage to said pulse signal, said relationship including at least one of system nonlinearities, offsets, and distortions;

a speedometer drive circuit providing a speedometer drive signal according to said pulse integrator output signal; and

a speedometer indicator providing a visual representation according to said speedometer drive signal, wherein said ranging network includes a switch selectable network comprising a plurality of switched resistances of values in decrementing sequences, said switch selectable network being adjusted to approximate the desired ranging network according to at least one of said nonlinearities, signal distortions, and said relationship to provide accurate representation of the velocity to be measured.

2. The speedometer of claim 1 wherein:

said pulse integrator means includes a charge pump circuit.

3. The speedometer of claim 2 further including:

odometer means providing a cumulative indication of distance travelled according to said pulse integrator output signal.

4. The speedometer of claim 3 wherein said odometer includes:

an incremented numeric indicator; and

a pulse generator providing a pulse sequence to said incremental numeric indicator according to said pulse integrator output signal.

5. The speedometer of claim 1 wherein:

said speedometer indicator comprises an air core meter; and

said speedometer drive circuit provides sine and cosine drive signals to said speedometer indicator according to said pulse integrator output signal.

6. The speedometer of claim 1, further including:

second switching network to reduce said integrator output voltage by a constant proportion, said second switching network being activated by a range select signal.

7. The speedometer of claim 6, wherein:

said second switching network includes a field-effect transistor.

8. The speedometer of claim 6, wherein:

said range select signal is activated by a change in axle ratio.

9. For use in a wheeled vehicle having a selected tire size and a selected drive axle ratio, an adjustable speedometer/odometer comprising:

means to receive a periodic signal according to said selected tire size and said selected axle ratio and the velocity of said vehicle;

frequency to voltage converter means receiving said periodic signal providing a charge signal related to the period of the received signal;

a range network receiving said charge signal and producing a scaled output signal of discrete intervals having a proportional relationship to said received charge signal;

a speedometer indicator;

speedometer driver means receiving said scaled output signal and providing a corresponding speedometer drive signal to said speedometer indicator;

an odometer indicator; and

odometer drive means receiving said scaled output signal and providing a corresponding odometer drive signal to said odometer indicator, wherein

the relationship between the input frequency and output voltage of said frequency to voltage converter including at least one of signal errors, comprising system offset, distortion and nonlinearities; and

said range network includes a plurality of resistors to form a voltage divider, and switch means for range network adjustment selectively connected to at least one of said plurality of resistors to provide a correction in the indications of both said speedometer and odometer indicator for at least one of said signal errors, change in tire size and change in axle ratio.

10. A method of calibrating a speedometer providing an indication of speed in response to an input signal and having a switchably adjustable selectable range adjustment, said method comprising the steps of:

determining the nonlinear relationship between input signal and indicated speed incuding factors comprising the correspondence between input signal and true speed, signal nonlinearities, offsets, and distortions;

calculating the appropriate adjustment of said selectable range adjustment to include correction for said factors, wherein said indication of speed corresponds to said true speed; and

switchably adjusting said selectable range adjustment to provide a correspondence between the indication of speed and the true speed.