Engine operating time hour meters for outdoor power equipment including riding lawn mowers, lawn and agricultural tractors, snowmobiles, snowblowers, jet skis, boats, all terrain vehicles, bulldozers, generators, etc. are well known. Such engine operating time hour meters are provided, among other things, to let the owner and/or manufacturer know how long the equipment has been operated, when the equipment is due for repair/maintenance service, whether the equipment is still under warranty, etc.
With the widespread use of digital circuitry, digital engine operating time hour meters generally have replaced the old style mechanical hour meters which utilized rotating wheels. Digital hour meters provide improved accuracy and a digital display of accumulated hours. One shortcoming of some digital and mechanical prior art hour meters is that they accumulate hours of use of the equipment as soon as the ignition key or switch is turned on. Such hour meters provide an inaccurate measure of engine use. There may be instances where the ignition switch is on and the engine is not running, for example, an operator may inadvertently leave the ignition key in the on position after use of the equipment is completed and the engine is off. If the hour meter is accumulating time when the ignition switch is on the accumulated hours on the hour meter will overstate the true engine operating hours. Since warranty and service intervals are generally based on hours of engine operation, accumulating hours on the hour meter when the ignition key is on will result in premature indication that maintenance is needed and/or premature expiration of warranty, both to the disadvantage and dissatisfaction of the equipment owner.
As the manufacturer and owner of power equipment generally want to know the hours that the most expensive component of the equipment, namely, the engine has been operated, it is desired to have an hour meter that accumulates hours only when the engine is actually on. Certain prior art hour meters have attempted to address this issue. Generally, such prior art hour meters include two terminals which are coupled to the engine battery (generally 12 volts DC) and further include a third or enable terminal. Such hour meters only accumulate hours when the third terminal is enabled, that is, the third terminal receives a signal indicating that the engine is operating. One prior art hour meter utilizes three terminals, two of which are coupled to an internal DC power source of the hour meter and a third terminal is coupled to a spark plug wire and only accumulates time if the spark plug is firing. A disadvantage of such three terminal hour meters is that they necessarily include three terminals, two for power and a third terminal which must be enabled for accumulation of time. An additional disadvantage of the three terminal hour meter with an internal power source is that the power source eventually runs down necessitating a new power source being installed.
What is needed is a digital hour meter that utilizes only two terminals and accumulates engine operating time only when the engine is operating. What is also needed is a digital hour meter that is powered by a magneto of the engine and only accumulates engine operating time when the magneto is powering the hour meter. What is also needed is a versatile digital hour meter that can be powered by an engine magneto or the engine battery and is polarity insensitive.