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Electronic control for a hydraulic system to drive an auxiliary power source is provided, with an application as a system for controlling the operation of a hydraulically driven AC generator. The system includes a hydraulic pump, a hydraulic motor drivably connected to the generator, and a fluid cir

Electronic control for a hydraulic system to drive an auxiliary power source is provided, with an application as a system for controlling the operation of a hydraulically driven AC generator. The system includes a hydraulic pump, a hydraulic motor drivably connected to the generator, and a fluid circuit for circulating fluid from the pump to the motor and back. The feedback circuit contains a feedback conduit to feedback the motor. The system also includes a proportional servo control valve assembly for controlling the fluid conduits and a control circuit for controlling the control valve assembly to thereby control the flow of fluid to the motor. Sensors for measuring the operating parameters of the system and an operator interface module are both able to influence the operation of the system.

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1. A hydraulic system for driving an auxiliary power source, located aboard a vehicle having a primary power source, at a substantially constant speed despite fluctuations in rotational speed of the primary power source, the system comprising: a hydraulic pump drivably connectable to the primary pow

1. A hydraulic system for driving an auxiliary power source, located aboard a vehicle having a primary power source, at a substantially constant speed despite fluctuations in rotational speed of the primary power source, the system comprising: a hydraulic pump drivably connectable to the primary power source, the pump having an inlet for receiving fluid, an outlet for discharging fluid under pressure, and a pump displacement control inlet for receiving fluid to control displacement of the pump;a hydraulic motor drivably connectable to an auxiliary power source, the motor having an inlet for receiving fluid under pressure and an outlet for discharging spent fluid;a fluid circuit including a supply conduit for conducting fluid discharged by the pump to the motor, a return conduit for returning fluid discharged by the motor to the pump, and a feedback conduit directly connected to the pump displacement control inlet;a control valve assembly interposed between the outlet of the pump and both the inlet of the motor and the feedback conduit, the control valve assembly having a housing including a valve chamber with a valve disposed therein, a solenoid drivably connectable to the valve for selecting moving the valve within the valve chamber between an opened position and a closed position; anda control circuit in communication with the control valve assembly for controlling the control valve assembly and hence fluid flow to both of the motor and the pump displacement control inlet. 2. The system of claim 1 wherein the control circuit comprises: an output sensor coupled to the auxiliary power source for determining output frequency of the auxiliary power source;a reference signal generator for generating a reference signal indicative of a desired output frequency; anda comparing sub-circuit for comparing the sensed output frequency with the reference signal and for generating a control signal controlling the control valve assembly such that supply of fluid to the motor is sufficient for the auxiliary power source to maintain the desired output frequency. 3. The system of claim 1 wherein the control circuit comprises: a speed sensor for determining rotational speed of the motor;a reference signal generator for generating a reference signal indicative of a desired rotational speed; anda comparing sub-circuit for comparing sensed rotational speed of the motor with the reference signal and for generating a control signal controlling the control valve assembly such that supply of fluid to the motor is sufficient for the motor to maintain the desired rotational speed. 4. The system of claim 1 wherein: the control valve assembly is an electro-hydraulic servo control valve assembly. 5. The system of claim 1 wherein: the control circuit comprises a pressure sensor for determining hydraulic pressure of the fluid, wherein the control circuit controls the control valve assembly to begin system operation when hydraulic pressure is sufficient and to shut down system operation when hydraulic pressure is deficient. 6. The system of claim 1 wherein the control circuit comprises: a temperature sensor disposed in the fluid circuit for sensing temperature of the fluid; anda system controller having a fluid pre-heating sub-circuit for generating a control signal controlling the control valve assembly such that fluid is restricted entirely from the motor until safe fluid temperature is obtained. 7. The system of claim 6 wherein: the system controller of the control circuit further comprises a power ramping sub-circuit for generating a control signal controlling the control valve assembly when sufficient fluid temperature is obtained such that fluid is supplied gradually to the motor thereby gradually powering the motor. 8. The system of claim 6 wherein: the system controller of the control circuit further comprises an over temperature shutdown sub-circuit for generating a control signal controlling the control valve assembly when the fluid temperature becomes too hot for safe operation such that fluid is restricted from the motor thereby shutting down the auxiliary power source. 9. The system of claim 8 wherein: the control circuit further comprises an emergency override accessible by an operator for instructing the system controller to continue system operation when unsafe operating conditions exist. 10. The system of claim 1 further comprising: an interface module having a display in communication with the control circuit for displaying real time system operating characteristics to an operator. 11. The system of claim 10 further comprising: a diagnostic memory in communication with the control circuit to record abnormal operating conditions and faults for subsequent retrieval by an operator via the display. 12. The system of claim 10 wherein: the interface module is operable to display fault and alarm conditions. 13. The system of claim 1 wherein: the fluid circuit further comprises a fluid reservoir;wherein the control circuit comprises a fluid level sensor disposed in the fluid reservoir for generating a fluid level fault when the fluid level falls below a first minimum fluid level and for generating a control signal shutting down the system when the fluid level falls below a second minimum level. 14. The system of claim 1 wherein: the fluid circuit further comprises a fluid filter disposed serially with respect to the return conduit. 15. The system of claim 1 wherein the fluid circuit further comprises: a fluid cooler disposed serially with respect to the return conduit;an electrically operated fan disposed adjacent the fluid cooler to pass ambient air through the fluid cooler; anda thermostat disposed proximate the fluid cooler to operate the fan when fluid contained within the fluid cooler attains a temperature exceeding a predetermined temperature. 16. The system of claim 15 wherein: the fluid circuit further comprises a fluid filter disposed serially with respect to the return conduit and a fluid reservoir;wherein the system further comprises a housing enclosing the motor, the control valve assembly, the fluid cooler, the fan, the fluid filter, and the fluid reservoir whereby the motor, the control valve assembly, the fluid cooler, the fan, the fluid filter, and the fluid reservoir are installable as a unit on the chassis of the vehicle. 17. The system of claim 16 wherein: the fluid cooler and the fan are disposed in an orientation such to direct exhausted air upward to provide reduced space for mounting adjacent to side walls of the housing thereby taking advantage of rising heat tending not to re-circulate back into the housing resulting in cooling efficiency. 18. The system of claim 16 wherein: the fluid cooler and the fan are disposed in an orientation such to direct exhausted air downward to provide reduced space for mounting adjacent to side walls of the housing thereby providing cooling efficiency by drawing cooler overhead air into the system and exhausting air into lower vehicle space heatable by the operation of other equipment. 19. The system of claim 16 wherein: the housing comprises a closed tolerance enclosure interposed between the fluid cooler and the fan for providing a generally evenly distributable air flow from the fan through the fluid cooler. 20. The system of claim 15 wherein: the control circuit comprises a sub-circuit for providing electrical communication to manually control the fan by input from an interface module. 21. The system of claim 20 wherein: manual control of the fan is used to troubleshoot system installation by commanding the fan to be on or off as desired. 22. The system of claim 1 wherein: the auxiliary power source is a generator. 23. The system of claim 22 wherein the control circuit comprises: an output sensor coupled to the generator for determining output voltage of the generator;a reference signal provider for providing a reference signal indicative of a desired output voltage; anda comparing sub-circuit for comparing sensed output voltage of the generator and the desired output voltage and for generating a control signal controlling the control valve assembly such that supply of fluid to the motor is sufficient for the generator to maintain the desired output voltage. 24. The system of claim 22 wherein: the generator has output conductors and a circuit breaker for opening a circuit connected to the output conductors. 25. The system of claim 1 wherein: the fluid circuit further comprises a fluid reservoir and a venturi boost for drawing fluid from the fluid reservoir into the fluid circuit. 26. The system of claim 1 wherein: the control circuit comprises electrical communication for providing automatic shut down of user prioritized specific vehicle component AC power loads to alleviate overload or over-temperature conditions for maintaining safe operation of the auxiliary power source. 27. The system of claim 26 wherein: the control circuit receives feedback from an over-temperature sensor for communicating the need for shutting down vehicle AC components. 28. The system of claim 26 wherein: the control circuit further comprises electrical communication alerting a user that vehicle component AC power loads previously shut down are ready for restarting as a result of determined safer temperature conditions. 29. The system of claim 1 wherein: the control circuit comprises a temperature sensor disposed in an air intake of the primary power source for sensing ambient temperature to be used in communication with an interface module for displaying a user alert of temperature differential. 30. The system of claim 1 wherein: the control circuit comprises a sub-circuit for providing electrical communication to manually control the control valve assembly by input from an interface module. 31. The system of claim 30 wherein: manual control of the control valve assembly to command the valve to be fully opened or closed enables troubleshoot system installation. 32. A method for operating a hydraulic system, the method comprising: sensing temperature of hydraulic fluid in a fluid circuit;if the temperature of the fluid is below a safe operating temperature, then warming the fluid by circulating the fluid through portions of the fluid circuit while restricting the fluid from the fluid circuit to a hydraulic motor; andincrementally supplying fluid from the fluid circuit to the motor once the temperature of the fluid reaches the safe operating temperature in order to bring the motor up to a desired speed so that full power operation can commence;wherein incrementally supplying fluid from the fluid circuit to the motor includes incrementally closing a hydraulic proportional valve disposed within the fluid circuit such that fluid is gradually conducted from a motor supply conduit of the fluid circuit in fluid communication with the motor in order to gradually supply power to the motor. 33. The method of claim 32 wherein: warming the fluid includes maintaining closed the proportional valve such that fluid is entirely restricted from the fluid circuit to the motor. 34. A method for operating a hydraulic system, the method comprising: sensing temperature of hydraulic fluid in a fluid circuit;if the temperature of the fluid is below a safe operating temperature, then warming the fluid by circulating the fluid through portions of the fluid circuit;apportioning fluid from the fluid circuit to a hydraulic motor once the temperature of the fluid reaches the safe operating temperature in order to bring the motor up to a desired speed so that full power operation can commence; andsensing output characteristics of the motor;wherein apportioning fluid from the fluid circuit to the motor includes comparing sensed motor output characteristics with predetermined output characteristics and selectively controlling a hydraulic proportional valve disposed in the fluid circuit to move incrementally such that fluid is proportionally restricted from the fluid circuit to the motor. 35. The method of claim 34 further comprising: preventing over-temperature damage to the hydraulic system when the temperature of the fluid exceeds safe operating temperature. 36. The method of claim 35 wherein preventing over-temperature damage comprises: annunciating existence of over-temperature condition to an operator when the temperature of the fluid obtains a first high temperature;triggering a timer to begin counting down a specified time when the temperature of the fluid obtains a higher second high temperature; andrestricting all fluid from the fluid circuit to the motor when the timer has expired. 37. The method of claim 36 wherein: restricting all fluid from the fluid circuit to the motor includes closing the proportional valve such that fluid is blocked from the fluid circuit to the motor. 38. The method of claim 36 further comprising: overriding the restricting step upon receipt of an emergency override instruction from an operator to prevent shutdown and keep the hydraulic system running. 39. The method of claim 34 further comprising: sensing pressure of the fluid in the fluid circuit;commencing operation of an auxiliary power source if the pressure of the fluid is sufficient by controlling the hydraulic proportional valve to meter fluid from the fluid circuit to the motor in order for the motor to drive an auxiliary power source coupled to the motor; andceasing operation of the auxiliary power source if the pressure of the fluid is deficient by opening the proportional valve to feedback all fluid flow from the fluid circuit to the motor. 40. A method for controlling a hydraulic system driven by an engine onboard a vehicle for supplying stable AC power despite fluctuations in engine speed, the method comprising: sensing pressure of fluid in a fluid circuit;sensing temperature of the fluid;commencing operation of an auxiliary power source if the pressure and temperature of the fluid are sufficient;ceasing operation of the auxiliary power source if at least one of the pressure and temperature of the fluid is deficient by fully opening a hydraulic proportional valve disposed in the fluid circuit to feedback all fluid flow from the fluid circuit to a hydraulic motor coupled to the auxiliary power source;warming the fluid by circulating the fluid through the fluid circuit while restricting the fluid to the motor, if the temperature of the fluid is below a safe operating temperature;supplying the fluid gradually from the fluid circuit to the motor once the temperature of the fluid reaches the safe operating temperature in order to gradually bring the motor up to a desired speed such that full operation can commence;sensing output characteristics of the motor; andapportioning fluid flow from the fluid circuit to the motor in order to maintain constant motor output characteristics. 41. The method of claim 40 further comprising: preventing over-temperature damage to the hydraulic system when the temperature of the fluid exceeds the safe operating temperature.