Noise reduction apparatus and method

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.

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.