Engine operation detecting circuit for a visual display

Information

  • Patent Grant
  • 6377168
  • Patent Number
    6,377,168
  • Date Filed
    Thursday, September 7, 2000
    24 years ago
  • Date Issued
    Tuesday, April 23, 2002
    23 years ago
Abstract
A timing circuit for providing an output to a microcontroller indicating whether an engine is operating, wherein the engine has a magneto. The circuit includes a triac coupled to the magneto for switching output generating circuitry between an engine on condition to an engine off condition in response to an operating condition of the engine. The output generating circuitry provides a signal indicating that the engine is not operating to the microcontroller when the circuitry is in an engine off condition and provides a signal indicating that the engine is operating to the microcontroller when the circuitry is in an engine on condition.
Description




FIELD OF THE INVENTION




The invention relates to a visual display circuit for monitoring and displaying the operation of a combustion engine and more particularly concerns an circuit for monitoring the operation time of a riding lawn mower.




BACKGROUND ART




Hour meters of various types are commercially available both as an add on device to a combustion engine or supplied as part of a vehicle that has a combustion engine. The hour meter provides information about the amount of time the engine has been operating. This information is useful for scheduling maintenance necessary at predetermined engine run times. In addition, hour meters may be used on test vehicles to calculate the durability of engine components as a function of engine run time.




U.S. Pat. No. 5,644,491 to Fiske et al. concerns a self contained multi-function engine monitor and timer for providing engine running time, job time, service time and tachometer functions. The engine monitor employs a spark sensor in the form of a pick up wire wrapped around a spark plug wire. The spark plug current flowing through the spark plug wire induces a voltage across the coil of the pick up wire. This voltage is sensed by a microcomputer and is used to determine a variety of engine functions. Circuitry is required to filter the signal from the pick up wire to make it suitable for input to the microcomputer.




U.S. Pat. No. 4,617,639 to Paine concerns an hour meter apparatus and method for use with industrial vehicles. The hour meter increments time interval registers whenever the ignition switch of the vehicle is in a position indicating that the vehicle is in operation. Because the hour meter is activated by the ignition switch of the vehicle, engine time may be logged when the ignition switch is turned to the on position, but the vehicle's engine is not running.




SUMMARY OF THE INVENTION




The present invention concerns a timing circuit for providing an output to a monitoring circuit indicating whether an engine having a magneto is operating. In a preferred embodiment, the monitoring circuit is a microcontroller. The timing circuit includes switching means, such as a triac in an exemplary embodiment, coupled to the magneto for switching output generating circuitry between an engine on condition and an engine off condition in response to an operating condition of the engine. The output generating circuitry provides a signal indicating that the engine is not operating to the microcontroller when the circuitry is in an engine off condition and provides a signal indicating that the engine is operating to the microcontroller when the circuitry is in an engine on condition.




In an exemplary embodiment, the triac is activated by pulses generated by the magneto when the engine is operating to place the output generating circuitry in the engine on condition. The triac operates in a conducting mode and the circuitry includes a capacitor that discharges to ground through the triac thereby maintaining the output circuitry in the engine on condition. The triac is deactivated when the magneto is not generating pulses to place the output generating circuitry in the engine off condition such that the triac does not conduct current. The circuitry includes a transistor that switches on when the triac is not conducting current to maintain the output circuitry in the engine off condition.




In an embodiment of the present invention, the microcontroller senses a voltage at the capacitor and records a time between drops in said voltage to determine the RPM of the engine.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a block diagram of an hour meter apparatus that features the engine operation detection circuit of the present invention;





FIG. 2

is a schematic diagram of a circuit constructed in accordance with one embodiment of the present invention that provides an output signal indicative of an operating status of the engine; and





FIGS. 3A and 3B

depict waveforms of a magneto signal that triggers the circuit of FIG.


2


.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT





FIG. 1

depicts an hour meter


10


for use with a small combustion engine such as is found in a lawn tractor. The hour meter


10


is coupled to a vehicle battery


22


. The battery is in turn coupled to a low voltage detecting circuit


24


that activates a low voltage indicating LED


25


mounted to a riding lawn mower dashboard (not shown). The vehicle battery


22


energizes a power supply and filtering circuit


23


that supplies power to a microcontroller


50


.




The hour meter


10


is also coupled to a primary coil of the engine magneto


21


. The magneto includes a transformer secondary inductively coupled to the primary that transmits large voltages (approximately 20 kilovolts) to the spark plug each time current through the magneto primary is disrupted. U.S. Pat. No. 4,270,509 to Tharman discloses a typical small engine magneto system for use with a lawn mower and is incorporated herein by reference. An engine operation detection circuit


30


, shown in greater detail in

FIG. 2

, receives pulses from the magneto


21


and provides an output indicative of an engine operating condition to the microcontroller


50


. An LCD display


60


mounted to the lawn mower dashboard is coupled to the microcontroller


50


and displays the hours of run time on the engine being monitored by the hour meter.





FIG. 2

illustrates a schematic diagram of an engine operation detection circuit


30


constructed in accordance with a preferred embodiment of the invention. The circuit senses a magneto (or engine kill) signal from a small gasoline combustion engine such as those produced by Briggs and Stratton, Kohler, Tecumseh, and converts it into a DC voltage suitable for use as a digital input to a microcontroller. Voltage pulses (examples shown in

FIG. 3

) from the magneto


21


(

FIG. 1

) pass through a current limiting resistor


31


and to a gate input


35


G to a triac


35


. A triac commercially available from S.G.S. Thompson having model number Z0103DN has proven suitable for use in the present invention. A benefit of the triac is that it will be turned on by either positive or negative polarity magneto pulses of most small gasoline combustion engines. A resistor


33


serves as a pull up resistor, and a resistor


32


limits the current discharged through the triac


35


from a capacitor


36


. A zener diode


37


(such as model number ZMM5228B from Diodes, Inc.) prevents the voltage at the capacitor


36


from turning a transistor


38


on until a certain voltage level is achieved. A model number FMMTA06 from Zetex transistor has proven suitable for use in the present invention. A resistor


34


serves as a pull up resistor and provides for a suitable input level at an output


39


to the microcontroller


50


.




When no pulses are present at the input to the triac


35


, the triac remains off, and the capacitor


36


charges through the resistor


33


. When the zener diode's


37


zener voltage is exceeded, the transistor


38


turns on and pulls the output to the microcontroller


50


low to indicate to the microcontroller that the engine is not running.




When magneto pulses are present at the input to the triac


35


, the triac


35


turns on and discharges the capacitor


36


, preventing the transistor


38


from turning on.

FIGS. 3A and 3B

depict voltage pulses as a function of time from two typical small engine magnetos


21


.

FIG. 3A

depicts a voltage pulse from an inductive type magneto on a Briggs and Stratton engine.

FIG. 3B

depicts a voltage pulse from a capacitor discharge type magneto on a Tecumseh engine. As can be seen by a comparison of the pulses shown in

FIGS. 3A and 3B

, the circuit of the present invention can process pulses of either polarity from a wide variety of small gasoline engines. The magneto


21


is coupled to the triac gate input


35


G. The triac is active (and thus discharges the capacitor) during the “triac on” time indicated in

FIGS. 3A and 3B

. The discharge characteristics of the capacitor are tuned so that the capacitor's voltage remains below the zener voltage of the zener diode during the time the triac is off so that the transistor remains non conducting when pulses are present. Thus the output is pulled up to 5 volts output from the power supply


23


to signal the microcontroller that the engine is running.




The circuit


30


can be used to enable/disable a microprocessor incrementing of the display


60


so that the microprocessor only accumulates time while the engine is actually running. In another embodiment, the signal at the capacitor


36


could be sensed by the microcontroller


50


(sense location shown in dashed line) to detect engine RPM by recording the time between drops in the voltage at the capacitor


36


.




Several embodiments of the invention have been described with a degree of particularity. It is the intent that the invention encompass all alterations and modifications from these embodiments falling within the spirit or scope of the appended claims.



Claims
  • 1. A timing circuit for providing an output signal to a monitoring circuit indicating whether an engine is operating, wherein said engine has a magneto, said circuit comprising:a) switching means coupled to said magneto for periodically switching on and off in response to an operating condition of said engine; and b) output generating circuitry coupled to said switching means for providing a signal indicating that said engine is not operating when said engine is in an off condition and providing a different signal when said engine is in an on condition.
  • 2. The timing circuit of claim 1 wherein said switching means comprises a solid state switch.
  • 3. The timing circuit of claim 1 wherein said switching means comprises a thyristor.
  • 4. The timing circuit of claim 1 wherein said switching means comprises a triac.
  • 5. The timing circuit of claim 2 wherein said solid state switch is activated by pulses generated by said magneto when said engine is operating to place said output generating circuitry in said on condition with said solid state switch in a conducting mode and wherein said circuitry comprises a capacitor that discharges to ground through said solid state switch thereby maintaining said output circuitry in said on condition.
  • 6. The timing circuit of claim 2 wherein said solid state switch is deactivated when said magneto is not generating pulses to place said output generating circuitry in said off condition with the solid state switch not conducting current and wherein said circuitry comprises a transistor that switches to a conducting mode when said solid state switch is not conducting current to maintain said output circuitry in said off condition.
  • 7. The timing circuit of claim 1 wherein said monitoring circuit comprises a microcontroller.
  • 8. The timing circuit of claim 1 comprising a display for displaying a number of hours said engine has operated.
  • 9. A timing circuit for providing an output signal to a microcontroller indicating whether an engine is operating, wherein said engine has a magneto that generates pulses when said engine is operating, said circuit comprising:a) a thyristor coupled to said magneto for periodically switching on and off in response to an operating condition of said engine, wherein said thyristor conducts current when said magneto is generating pulses and does not conduct current when said magneto is not generating pulses; b) output generating circuitry coupled to said thyristor comprising a capacitor and a switching transistor, said capacitor coupled between said thyristor and a base input of the switching transistor such that when said magneto is generating pulses said capacitor discharges through said thyristor and maintains said switching transistor in an nonconducting mode to provide a signal indicating that said engine is operating to said microcontroller and wherein said capacitor is coupled to said transistor through a zener diode such that when said magneto is not generating pulses and said thyristor is not conducting said capacitor charges beyond a zener voltage of said zener diode to switch said transistor to conducting mode to provide a signal indicating that said engine is not operating to said microcontroller.
  • 10. The timing circuit of claim 9 wherein said thyristor comprises a triac.
  • 11. The timing circuit of claim 9 further comprising a sensing means coupled to said microcontroller sensing a voltage at said capacitor and wherein said microcontroller records a time between drops in said voltage to determine the RPM of said engine.
  • 12. The timing circuit of claim 9 comprising a display for displaying a number of hours said engine has been operated.
  • 13. A method of providing an output to a microcontroller indicating whether an engine is operating, wherein said engine has a magneto, comprising the steps of:a) coupling a switching means across a magneto coil that generates a spark plug voltage; b) charging a capacitor to a voltage; c) routing magneto generated pulses of either a positive or negative polarity to the switching means to activate the switching means and provide a discharge path to ground to said capacitor; and d) said capacitor to determine an operating condition of said engine.
  • 14. The method of claim 13 wherein said causing step is accomplished by routing said magneto generated pulses to said input switching means to disconnect said discharge path and cause said capacitor to charge.
  • 15. A timing apparatus for monitoring and displaying the operation time of an engine of a riding lawn mower comprising:a) a microcontroller comprising an engine monitoring circuit; b) a timing circuit for providing an output signal to said monitoring circuit indicating whether an engine is operating, wherein said engine has a magneto, said circuit comprising: i) switching means coupled to said magneto for periodically switching on and off in response to an operating condition of said engine; and ii) output generating circuitry coupled to said switching means for providing a signal indicating that said engine is not operating to when said engine is in an off condition and providing a different signal when said engine is in an on condition; and c) a display for displaying a number of hours said engine has operated.
US Referenced Citations (20)
Number Name Date Kind
3992070 Dunn et al. Nov 1976 A
4129037 Toalson Dec 1978 A
4144862 Estkowski Mar 1979 A
4181883 Beeghly et al. Jan 1980 A
4187927 Byrne Feb 1980 A
4280457 Bloxham Jul 1981 A
4613939 Paine Sep 1986 A
4617639 Paine Oct 1986 A
4642787 McCarthy et al. Feb 1987 A
4742297 Heaton et al. May 1988 A
5065320 Hayashi et al. Nov 1991 A
5138995 Erhard Aug 1992 A
5150568 White Sep 1992 A
5375977 Hill Dec 1994 A
5642284 Parupalli et al. Jun 1997 A
5644491 Fiske et al. Jul 1997 A
5730098 Sasaki et al. Mar 1998 A
5857159 Dickrell et al. Jan 1999 A
5869776 Vuong et al. Feb 1999 A
5913911 Beck et al. Jun 1999 A