Hydraulic system

Abstract

A method includes providing a hydraulic pump with an outlet, a main orifice having an inlet communicating with the pump outlet, and a main orifice outlet. Further provided are a flow orifice, an amplification orifice, and an amplification orifice outlet, means for generating an output signal representative of a fluid pressure, and a pump controller for controlling the hydraulic pump in response to the output signal. The flow orifice and the amplification orifices each define an area, with these areas defining a ratio, and with the main orifice and the ratio being variable. The method includes operating the system in a first mode so as to define a first mode ratio and operating the system in a second mode so as to define a second mode ratio, so that the ratio is controlled differently in the first mode and the second mode.

1 . A method of operating a hydraulic system including providing
 a hydraulic pump having a pump outlet,   a main orifice having a main orifice inlet in fluid communication with the pump outlet and a main orifice outlet for supplying pressurized fluid to a service,   a flow orifice having a flow orifice inlet for sensing a pressure representative of a pressure at the pump outlet and a flow orifice outlet,   an amplification orifice having an amplification orifice inlet in fluid communication with the flow orifice outlet and an amplification orifice outlet for sensing a pressure representative of a pressure at a service,   means for generating an output signal representative of a fluid pressure between the flow orifice outlet and the amplification orifice inlet,   and a pump controller for controlling the hydraulic pump in response to the output signal,   the flow orifice defining a flow orifice cross section area and   the amplification orifice defining an amplification orifice cross section area,   the flow orifice cross section area and the amplification orifice cross section area defining a ratio,   in which the main orifice is variable and the ratio is variable,   the method further comprising the steps of operating the system in a first mode so as to define a first mode ratio regime and operating the system in a second mode so as to define a second mode ratio regime,   so that the first mode ratio regime is different to the second mode ratio regime.   
     
     
         2 . A method as defined in  claim 1  wherein when operating the system in the first mode the first mode ratio regime is to have a fixed ratio. 
     
     
         3 . A method as defined in  claim 2  wherein the first mode ratio regime fixes the ratio at one of greater than 1 and less than 1 and equal to 1. 
     
     
         4 . A method as defined in  claim 1  wherein when operating the system in the first mode the first mode ratio regime is to have a variable ratio. 
     
     
         5 . A method as defined in  claim 4  wherein the variable ratio excludes a ratio of one of greater than 1 and less than 1. 
     
     
         6 . A method as defined in  claim 1  wherein when operating the system in the second mode the second mode ratio regime is to have a fixed ratio. 
     
     
         7 . A method as defined in  claim 1  wherein when operating the system in the second mode the second mode ratio regime is to have a variable ratio. 
     
     
         8 . A method as defined in  claim 1 , the method further comprising the steps of operating the system in a third mode so as to define a third mode ratio regime so that the ratio is controlled differently in the first mode and the second mode and the third mode wherein when operating the system in the third mode the third mode ratio regime is to have a fixed ratio. 
     
     
         9 . A method as defined in  claim 1 , the method further comprising the steps of operating the system in a third mode so as to define a third mode ratio regime so that the ratio is controlled differently in the first mode and the second mode and the third mode wherein when operating the system in the third mode the third mode ratio regime is to have a variable ratio. 
     
     
         10 . A method as defined in  claim 1  wherein the amplification orifice outlet is in fluid communication with a service. 
     
     
         11 . A method as defined in  claim 1  in which the flow orifice is variable. 
     
     
         12 . A method as defined in  claim 11  in which the amplification orifice is variable. 
     
     
         13 . A method as defined in  claim 1  in which the flow orifice is fixed. 
     
     
         14 . A method as defined in  claim 1  in which the amplification orifice is fixed. 
     
     
         15 . A method as defined in  claim 1  wherein the hydraulic pump is a variable displacement hydraulic pump having a pump margin pressure and the controller is configured to vary a margin pressure of the main orifice relative to the pump margin pressure in response to the output signal. 
     
     
         16 . A method as defined in  claim 1  in which the hydraulic pump is a fixed displacement hydraulic pump, having a pump margin pressure defined by a bypass regulator valve and the controller is configured to vary a margin pressure of the main orifice relative to the pump margin pressure in response to the output signal. 
     
     
         17 . A method as defined in  claim 15  wherein the controller is configured to increase the margin pressure of the main orifice relative to the pump margin pressure in response to the output signal. 
     
     
         18 . A hydraulic system including
 a hydraulic pump having a pump outlet,   a main orifice having a main orifice inlet in fluid communication with the pump outlet and a main orifice outlet for supplying pressurized fluid to a service,   a flow orifice having a flow orifice inlet for sensing a pressure representative of a pressure at the pump outlet and a flow orifice outlet,   an amplification orifice having an amplification orifice inlet in fluid communication with the flow orifice outlet and an amplification orifice outlet for sensing a pressure representative of a pressure at a service,   means for generating an output signal representative of a fluid pressure between the flow orifice outlet and the amplification orifice inlet,   and a pump controller for controlling the hydraulic pump in response to the output signal,   the flow orifice defining a flow orifice cross section area and   the amplification orifice defining an amplification orifice cross section area,   the flow orifice cross section area and the amplification orifice cross section area defining a ratio,   in which the main orifice is variable and the ratio is variable,   the main orifice defining a main orifice margin pressure, the system being configured to vary the main orifice margin pressure by varying the ratio.   
     
     
         19 . A hydraulic system as defined in  claim 18  wherein the pump defines a pump margin pressure and the system is configured to vary the main orifice margin pressure relative to the pump margin pressure. 
     
     
         20 . A hydraulic system as defined in  claim 19  wherein the main orifice margin pressure is greater than the pump margin pressure.