Power steering system with auxiliary pump

Claim 2

A vehicle power steering system which comprises: a primary pump having an output line and a return line; a secondary pump having an output line and a return line; means connected with said primary pump output line for sensing mass flow rate of fluid therein; and valve means connected to, and for controlling fluid flow in, said primary and secondary output and return lines, said valve means being connected to said sensing means and being responsive at a predetermined mass flow rate sensed thereby to alter the fluid flow circuits of said primary and secondary pumps.

Claim 3

A vehicle power steering system in accordance with claim 1, wherein said means for sensing mass flow rate of fluid comprises an orifice connected with said primary pump output line.

Claim 4

A vehicle power steering system in accordance with claim 2, wherein said means for sensing mass flow rate of fluid further includes one-way valve means connected in series with said orifice.

Claim 5

A vehicle power steering system, which comprises: a primary pump having an output line and a return line; a secondary pump having an output line and a return line; means connected with said primary pump output line for sensing mass flow rate of fluid therein; a steering assist mechanism; and transfer valve means connected to, and for controlling fluid flow in, said primary and secondary output and return lines, said valve means having a first position in which said primary pump output and return lines are connected to said steering assist mechanism and wherein said secondary pump output and return lines are connected together by said valve means, and said valve means having a second position wherein said secondary pump output and return lines are connected to said steering assist mechanism for fluid flow therethrough.

Claim 6

A vehicle power steering system, which comprises: a primary pump having an output line and a return line; a secondary pump having an output line and a return line; means connected with said primary pump output line for sensing mass flow rate of fluid therein; a steering assist mechanism; and transfer valve means connected to, and for controlling fluid flow in, said primary and secondary output and return lines, said valve means having a first position in which said primary pump output and return lines are connected to said steering assist mechanism and wherein said secondary pump output and return lines are connected together by said valve means, and said valve means having a second position wherein said secondary pump output and return lines are connected to said steering assist mechanism for fluid flow therethrough.

Claim 7

A vehicle power steering system in accordance with claim 4, wherein said means for sensing mass flow rate of fluid comprises fluid flow restrictive means for producing a fluid pressure differential.

Claim 8

A vehicle power steering system in accordance with claim 4, wherein said means for sensing mass flow rate of fluid comprises an orifice connected in series with one-way valve means to produce a pressure differential in the fluid output from said primary pump when said valve means are in said first position.

Claim 9

A vehicle power steering system in accordance with claim 6, wherein said transfer valve means further include means responsive to a reduction below a predetermined level of the pressure differential across said orifice and one-way valve means to shift said transfer valve means from its first position to its second position.

Claim 10

A vehicle power steering system in accordance with claim 7, wherein said transfer valve means has a third unstable intermediate position wherein the output from said steering assist mechanism is connected to said return lines of said primary and secondary pumps.

Claim 11

A vehicle hydraulic power steering system, which comprises: a primary hydraulic fluid pump having an output line and a return line; an auxiliary hydraulic fluid pump having an output line and a return line; a fluid-controlled open-center-valve steering assist mechanism having input and output lines connected thereto; a transfer valve connected to the inpuT and output lines of said steering assist mechanism, to the ouput line of said auxiliary pump, and to the return lines of said primary and auxiliary pumps, said transfer valve having a first position wherein said output line of said steering assist mechanism is connected to said return line of said primary pump and wherein said output line of said auxiliary pump is connected to said return line of said auxiliary pump, and said transfer valve having a second position wherein said output line of said auxiliary pump is connected to said input line of said steering assist mechanism and wherein said output line of said steering assist mechanism is connected to said return line of said auxiliary pump, said transfer valve further including first pilot means connected to said output line of said primary pump for urging said transfer valve to its first position and second pilot means connected to said input line of said steering assist mechanism for urging said transfer valve to its second position; and orifice and one-way valve means for sensing mass flow rate of fluid flowing therethrough, said orifice and one-way valve means being connected between said output line of said primary pump and said input line of said steering assist mechanism.

Claim 12

A vehicle hydraulic power steering system, which comprises: a primary hydraulic fluid pump having an output line and a return line; an auxiliary hydraulic fluid pump having an output line and a return line; a fluid-controlled open-center-valve steering assist mechanism having input and output lines connected thereto; a transfer valve connected to the inpuT and output lines of said steering assist mechanism, to the ouput line of said auxiliary pump, and to the return lines of said primary and auxiliary pumps, said transfer valve having a first position wherein said output line of said steering assist mechanism is connected to said return line of said primary pump and wherein said output line of said auxiliary pump is connected to said return line of said auxiliary pump, and said transfer valve having a second position wherein said output line of said auxiliary pump is connected to said input line of said steering assist mechanism and wherein said output line of said steering assist mechanism is connected to said return line of said auxiliary pump, said transfer valve further including first pilot means connected to said output line of said primary pump for urging said transfer valve to its first position and second pilot means connected to said input line of said steering assist mechanism for urging said transfer valve to its second position; and orifice and one-way valve means for sensing mass flow rate of fluid flowing therethrough, said orifice and one-way valve means being connected between said output line of said primary pump and said input line of said steering assist mechanism.

Claim 13

A vehicle hydraulic power steering system in accordance with claim 9, wherein said transfer valve has a third unstable intermediate position wherein said output line of said steering assist mechanism is connected to said return lines of said primary and auxiliary pumps.

Claim 14

In a vehicle hydraulic power steering system including a primary pump and an auxiliary pump and a steering assist mechanism connected to a transfer valve having a first position wherein said primary pump is connected to said steering assist mechanism and having a second position wherein said auxiliary pump is connected to said steering assist mechanism, the improvement which comprises, in combination, means for sensing mass flow rate of fluid from said primary pump and for producing a pressure differential corresponding thereto; and means for holding said valve in said first position when said pressure differential is above a predetermined level and for holding said valve in said second position when said pressure differential is below said predetermined level.

Claim 15

In a vehicle hydraulic power steering system including a primary pump and an auxiliary pump and a steering assist mechanism connected to a transfer valve having a first position wherein said primary pump is connected to said steering assist mechanism and having a second position wherein said auxiliary pump is connected to said steering assist mechanism, the improvement which comprises, in combination, means for sensing mass flow rate of fluid from said primary pump and for producing a pressure differential corresponding thereto; and means for holding said valve in said first position when said pressure differential is above a predetermined level and for holding said valve in said second position when said pressure differential is below said predetermined level.