Noise reduction apparatus and method

Abstract

An apparatus and method for operating an auxiliary hydraulic load at low noise levels. A pump having a capacity which is sufficiently large to supply the load with the necessary volume of hydraulic fluid at relatively low pump speeds is driven by an engine operating at a speed near its idling speed. Throttle control means control the fuel supply to the engine at a level sufficient to drive the pump while maintaining the engine speed near its idling speed. When the engine speed is increased to a predetermined level in excess of its idling speed, means are provided to maintain the output from the pump at or below a predetermined flow rate to not overload the pump means or the auxiliary load. The pump may include a variable displacement pump or a plurality of fixed displacement pumps with means to vary the pump output in response to the pressure demand from the auxiliary load to maintain the torque input requirements for the pump below a predetermined level. The throttle control means may be actuated in response to the pressure demands of the auxiliary load to vary the torque from the engine in response to the torque input required for operation of the pump while the engine is operating at a speed near its idling speed.

I claim: 
     
       1. A noise reduction apparatus for operating a variable volume and variable pressure auxiliary load, said apparatus comprising: pump means having a capacity which is sufficiently large to supply said load at a relatively low pump speed;   said pump means including a plurality of fixed displacement pumps supplying hydraulic fluid to the variable load;   means to vary the number of pumps supplying fluid to the load in response to the demands of the load;   engine means operably connected to said pump means for supplying power to said pump means in performing a secondary work function at a speed near the idling speed of said engine means;   throttle control means governing the flow of fuel to the engine means to maintain its horsepower output at a level sufficient to operate the pump means while maintaining the speed of said engine means at a speed near its idling speed; and   means to maintain the flow rate from the pump means at a sufficiently low level to not exceed the capacity of the pump means or the auxiliary load when the engine speed is increased to a predetermined level in excess of its idling speed;   whereby the engine means operates in the low noise level region of speeds near its idling speed or less when supplying power for the pump means in operating the variable volume and variable pressure load, and the pump means and auxiliary load are protected from use in excess of their capacity when the engine means is operating at increased speeds.   
     
     
       2. A noise reduction apparatus as defined in claim 1 wherein the number of fixed displacement pumps supplying fluid to the variable load is decreased when the pressure demands of the load are increased to maintain the torque required to drive the pumps below a predetermined level. 
     
     
       3. A noise reduction apparatus for operating a variable volume and variable pressure auxiliary hydraulic load comprising: a variable pressure and variable volume pump means;   engine means operably connected to the pump means for supplying power to the pump means in performing a secondary work function at speeds near the idling speed of the engine means;   a fluid reservoir in flow communication with the pump means and the auxiliary load to provide a variable volume of hydraulic fluid for operation of the variable load;   means to vary the output pressure and volume of hydraulic fluid from the pump means in response to the demands of the variable load;   said pump means including a plurality of fixed displacement pumps with the number of pumps supplying fluid to the variable load being varied in response to the demands of the variable load;   throttle control means governing the flow of fuel to the engine means to maintain a torque output of the engine means at a level sufficient to operate the pump means under various loading conditions imposed by the variable load;   said throttle control means being actuated in response to the volume and pressure of fluid discharged by the pump means to the variable load, and   means to maintain the flow rate of fluid to the variable load at or below a predetermined level.   
     
     
       4. In combination, a throttle control device for varying the quantity of fuel fed to an engine and a plurality of fixed displacement pumps driven by the engine and providing hydraulic fluid to drive a variable load comprising: means to vary the number of pumps discharging hydraulic fluid to the load in response to the demands of the load;   first sensing means to transmit pressure to the throttle control device from the pumps with the transmitted pressure being proportional to the number of pumps discharging fluid to the variable load;   second sensing means to transmit pressure to the throttle control device with the transmitted pressure being proportional to the pressure of the hydraulic fluid fed to the load by the pumps;   first pressure receiving means in the throttle control device for receiving pressure from the first sensing means;   second pressure receiving means in the throttle control device for receiving pressure from the second sensing means, and   means in the throttle control device actuatable by the first and second pressure receiving means to transmit movement to the engine throttle with the degree of movement being dependent on both the pressure and volume of fluid discharged by the pumps, whereby   the torque output of the engine is varied in response to the torque input required to drive the pumps.   
     
     
       5. The combination of claim 4 wherein the throttle control device includes a movable piston having differential pressure receiving areas, with one of said areas receiving the pressure from the first sensing means and another of said areas receiving the pressure from the second sensing means, and   said piston being operably connected to the engine throttle control to transmit movement to the throttle control in response to the volume and pressure of fluid discharged to the load by the pumps.   
     
     
       6. The throttle control device of claim 5 including spring means resiliently biasing said piston to a retracted position and imposing a resistive force to movement of said piston. 
     
     
       7. The throttle control device of claim 6 including a gap between the spring means and the piston when the piston is in a retracted position, whereby the initial movement of the piston in response to pressure received from the pump is relatively rapid to provide a quick initial response of the throttle control device when the pumps begin their operation.   
     
     
       8. The combination of claim 4 including stop means in the throttle control device to limit the degree of movement imparted to the engine throttle.