Tachometer

• US 20040133394A1
• Filed: 01/06/2003
• Published: 07/08/2004
• Est. Priority Date: 01/06/2003
• Status: Active Grant

• Current Assignee: Auto Meter Products Incorporated
• Original Assignee: Innova Electronics Corporation (Innova Telematics Solutions)
• Inventors: Huang, David, Andreasen, Keith
• Granted Patent: US 6,868,369 B2
• Time in Patent Office: Days
• US Class Current: 702/182
• CPC Class Codes: G01P 1/07 Indicating devices, e.g. for remote indication indicating working conditions of vehicles G07C5/00
• CPC Class Codes: G01P 3/4807 by using circuits for the detection of the pulses delivered by the ignition system of an internal combustion engine

Abstract

A tachometer used to measure a speed of an engine. The tachometer includes a pickup, a counter circuit, a conversion circuit, an automatic switching device, an indicator and a meter display. The inductive pickup may be disposed around a spark plug wire of the engine to generate a pulse signal in response to a current flowing through the spark plug wire. The pulse signals are then counted by the counter circuit and input to the conversion circuit therefrom. The conversion circuit typically includes a plurality of lookup tables, each having mapped information correlating the pulse signals to the engine speed for a particular number of engine cylinders. The automatic switching device is operative to call up alternate lookup tables, e.g. each time when the electrical system of the engine is turned on. The display may be display the number of engine cylinders called up by the automatic switching device and measured engine speed.

Claims

1. A tachometer for measuring the speed of an engine, comprising:

an inductive pickup disposed about a spark plug wire and operative to detect current pulses flowing through the spark plug wire and to generate pickup pulse signals in response thereto;

a counter circuit for counting the pulse signals generated by the inductive pickup;

a conversion circuit, including a plurality of lookup tables, each lookup table having mapped information correlating pickup pulse signal frequency to engine speed information for a predetermined number of engine cylinders;

an automatic switching device, operative to sequentially access one of the lookup tables; and

a meter display operative to display the engine speed information.

2. The tachometer according to claim 1, further comprising a filter coupled to the inductive pickup for filtering the pulse signals corresponding to exhaust sparks.

3. The tachometer according to claim 1, wherein the filter is operative to filter out pulse signals having a pulse width shorter than a predetermined length.

4. The tachometer according to claim 3, wherein the predetermined value is about “

”

.²

²Please provide the predetermined value.

5. The tachometer according to claim 2, wherein the filter is operative to filter out pulse signals less then a predetermined voltage level.

6. The tachometer according to claim 1, wherein the conversion circuit comprises a plurality of lookup tables each corresponding to an engine having a different number of cylinders.

7. A tachometer operative for measuring the speed of an engine with a predetermined number of engine cylinders, the tachometer comprising:

a connector, inserted to a terminal of a spark plug and a terminal of an ignition coil of an engine, the connector being operative to tap current spikes generated by the ignition coil, and to generate pickup pulse signals in response thereto;

a counter circuit for counting the pulse signals generated by the inductive pickup;

a conversion circuit, including a plurality of converting circuits each being operative to convert the pickup pulse signals to engine speed information for a predetermined number of engine cylinders;

an automatic switching device, operative to select one of the converting circuits; and

a meter display, operative to display the engine speed information.

8. The tachometer according to claim 7, wherein each of the converting circuits includes a lookup table having mapped information correlating the pickup pulse signal frequency to engine speed information for a predetermined number of engine cylinders.

9. The tachometer according to claim 7, further comprising a filter connected to the connector.

10. The tachometer according to claim 7, further comprising a filter operative to filter out pickup pulse signals having an amplitude smaller than a predetermined value.

11. The tachometer according to claim 10, wherein the predetermined value about ? volts.

12. The tachometer according to claim 7, further comprising an inductive pickup disposed around the spark plug wire and operative to generate pickup pulse signals in response to current pulses flowing through the spark plug wire.

13. The tachometer according to claim 12, wherein the inductive pickup is coupled to the conversion circuit.

14. The method according to claim 12, further comprising a sensing device operative to sense the presence of pickup pulse signals from the connector to the conversion in response thereto and to block pickup pulse signals from the inductive pickup.