Diaphragm pump motor driven by a pulse width modulator circuit and activated by a pressure switch

#1. Field of the Invention

#The present invention relates to a pump assembly.

#2. Background Information

#FIG. 1 is a graph showing a characteristic curve of a prior art pump;

#FIG. 2 is a schematic of an embodiment of a hydraulic system of the present invention;

#FIG. 3 is a schematic of a control circuit for a pump motor of the hydraulic system;

#In general the present invention includes a pump assembly that has a control circuit and a pressure switch which control the operation of a pump motor. The motor drives a positive displacement pump that is coupled to a fluid system. The control circuit includes a pulse width modulator circuit. The control circuit is activated when a pressure switch senses that a line pressure of the fluid system is below a threshold value. The control circuit can either operate in a continuous mode to provide a constant signal to the motor, or a pulse regulating mode to provide a series of pulses to the motor.

#The pulses begin with a minimum width and gradually increase until a predetermined current limit has been attained, or the motor reaches a full speed with the control circuit in a continuous on state. The speed of the motor will then correspond to the flow demanded by the fluid system. The energy provided by the pulses is varied as a function of changes in peak current drawn by the motor. The peak current is sensed and used to determine the pulse width. Changing the pulse energy varies the speed of the motor.

#In general the pulse width and thus pulse energy is reduced with sensed increases in the peak motor current. The lower pulse energy slows down the motor. Thus the pump will slow down and reduce output flow with increasing output pressure. The output flow of the pump can thus vary proportionately to demand. If the pressure exceeds an upper threshold value, the pressure-switch deactivates power to the control circuits to turn off the pump.