Patent Application
20110061355
This invention relates generally to grass mowing equipment, and more specifically to a grass mowing machine with an engine speed and voltage limiter for an engine driven alternator or generator supplying power directly to one or more electric reel drive motors.
Grass mowing machines such as walk behind greens mowers may include one or more cutting reels driven by electric motors. An electric reel drive motors may be bidirectional and variable speed, meaning it can spin forward or reverse and at a range of rotational speeds. An electric reel drive motor may be powered directly by an engine driven alternator or generator system.
For example, the alternator or generator may be a 48-V, 180 amp alternator that is belt-driven by an internal combustion engine. The alternator or generator may supply power to an electrical bus for the cutting reel circuit. The bus voltage may be unregulated. Other circuits, including starter, safety interlocks, lights, and accessory circuits, may be separately powered by a 12-V battery.
An electric reel drive motor on a grass mowing machine may have a motor controller that regulates power to the motor. The controller may maintain a consistent reel rotational speed across a wide throttle range, to maintain a desired cut quality, or may vary the speed in response to operator commands or other inputs.
Typically, internal combustion engines on grass mowing machines have governors that attempt to run the engine at specific speeds. However, engine speed may not be limited if the governor is overridden or abnormal fuel/air conditions are encountered. If that occurs, output voltage of the generator or alternator to the voltage bus may exceed the upper voltage limit of a motor controller.
There is a need for a grass mowing machine that limits the output voltage of an alternator or generator on a voltage bus for powering one or more electric reel drive motors. There is a need for a grass mowing machine that limits engine speed for an electric reel drive motor powered directly by an engine driven alternator or generator system. There is a need for a grass mowing machine that can prevent the output voltage of an alternator or generator on the voltage bus from exceeding the upper voltage limit of a motor controller for an electric reel drive motor.
A grass mowing machine with a reel mower cutting unit having spiral cutting blades rotating on a horizontal axis in close proximity to a bedknife. An internal combustion engine with spark ignition is mounted to a frame supported by a traction drum coupled to the engine and rotating to move the machine forward during mowing. An electric reel drive motor is mounted to a side panel of the reel mower cutting unit and is powered directly by an engine driven alternator supplying power to an electrical bus to which the electric reel drive motor is connected. An engine speed and voltage limiting module is connected between the alternator and the spark ignition. The engine speed and voltage limiting module senses the voltage on the electrical bus and closes a kill switch to prevent spark ignition if the sensed voltage exceeds a specified threshold.
In
A preferred embodiment of the engine speed and voltage limiter is shown on a walk behind greensmower, but the present invention also may be provided on other grass mowing machines such as riding greensmowers, fairway mowers, or other grass mowing machines having one or more reel mower cutting units.
The reel mower cutting unit may be rotated by electric reel drive motor 24. The electric motor may be mounted to a side panel on the left or right sides of the cutting unit. The electric reel drive motor may be bidirectional and variable speed, meaning that it can spin forward or reverse and at a range of rotational speeds. The electric reel drive motor may be powered directly by engine driven alternator 26 connected to an electrical bus.
For example, the engine driven alternator may be a 48-V, 180 amp alternator that is belt-driven by the internal combustion engine. The alternator may be designed to supply constant power to an electrical bus for the cutting reel circuit at a specified engine speed. However, the bus voltage may be unregulated, and engine speed may not be limited if the governor is overridden or abnormal fuel/air conditions are encountered. If that occurs, output voltage of the generator or alternator to the voltage bus may exceed the upper voltage limit of a motor controller.
The grass mowing machine also may include other circuits, including starter, safety interlocks, lights, and accessory circuits, that are separately powered by a 12-V battery.
In one embodiment, electric reel drive motor 24 may be connected to and controlled by electronic motor controller 30. The controller may be connected to the electrical bus to regulate power to the motor. The controller may be configured to run the motor at a consistent reel rotational speed across a wide throttle range, to maintain a desired cut quality, or may vary the speed in response to operator commands or other inputs.
In an embodiment shown in
In one embodiment, the engine speed and voltage limiter module includes zener diode 38 connected to the alternator output. The zener diode may permit current in a reverse direction only if the voltage exceeds a threshold value exceeding the desired or normal bus voltage of 48 volts. For example, the threshold may be 68 volts. If the voltage exceeds the threshold, current flows through the zener diode and triggers solid state switch 44, which reduces firing pulses to the spark plug by bypassing the current flow through the ignition primary. Solid state switch 44 may be a silicon controlled rectifier (SCR) 44 between the zener diode and kill switch 40. Resistor 42 also may be included in the engine speed and voltage limiter module between the zener diode and engine ground.
In one embodiment, kill switch 40 may be connected between the engine speed and voltage limiter module 14 and ground. The grass mowing machine also may use the kill switch for one or more other safety interlocks to stop firing pulses to the spark plug.
Having described a preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.
