Hydraulic system for variable assist power steering system
First Claim
1. A variable assist power steering system for a vehicle including a steering wheel, a pump, a reservoir, a power cylinder adapted to be connected to a steering linkage, the power cylinder defining two chambers, comprising:
- a control valve including valve elements relatively displaceable in response to a first predetermined variable in the form of a steering torque applied by the steering wheel to define therebetween two parallel fluid flow paths connected between the pump and the reservoir to produce a pressure differential between the two chambers of the power cylinder in response to said first predetermined variable, said two parallel fluid flow paths including connections communicating with the two chambers of the power cylinder, respectively, each of said two parallel fluid flow paths being divided into an upstream section and a downstream section with respect to said connection thereof;
each of said upstream and downstream sections of said two parallel fluid flow paths including a main variable flow restrictor having an orifice area variable with said first predetermined variable;
whereinone of said upstream and downstream sections of each of said two parallel fluid flow paths includes an additional variable flow restrictor having an orifice area variable with said first predetermined variable and arranged in series with that one of said main variable flow restrictors which is included by said one section, said additional variable flow restrictor and said one main variable flow restrictor being disposed on the same side from one of said connections such that said additional variable flow orifice is disposed less far from said one connection than said one main variable flow restrictor is;
a pair of bypass paths, each having one end communicating with one of said two parallel fluid flow paths at said connection of said one parallel fluid flow path and an opposite end communicating with the other of said two parallel fluid flow path at a portion which is disposed more far from said connection of said the other parallel fluid flow path than said additional variable flow restrictor is but less far from said connection of said the other parallel fluid flow path than said main variable flow restrictor is;
each of said bypass paths has arranged therein at least one variable flow orifice valve which has an orifice area variable in a different manner from the manner of variation the orifice areas of said main and additional variable flow restrictors.
1 Assignment
0 Petitions
Accused Products
Abstract
A variable assist power steering system employing a fluid distributor circuit of the open center type is disclosed. The fluid distributor circuit includes two parallel fluid flow paths connected to both chambers of a power cylinder respectively to produce a pressure differential between the both cylinder chambers in response to steering torque. For modulating the valve characteristics, two additional variable flow restrictors are arranged in series with two main variable flow restrictors and two bypass paths are arranged to bypass the main variable flow restrictors, respectively. The bypass paths are provided with variable flow orifice valves, respectively, which valves are controlled in response to a turning direction of a steering wheel and also to some external signal, such as vehicle speed.
25 Citations
11 Claims
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1. A variable assist power steering system for a vehicle including a steering wheel, a pump, a reservoir, a power cylinder adapted to be connected to a steering linkage, the power cylinder defining two chambers, comprising:
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a control valve including valve elements relatively displaceable in response to a first predetermined variable in the form of a steering torque applied by the steering wheel to define therebetween two parallel fluid flow paths connected between the pump and the reservoir to produce a pressure differential between the two chambers of the power cylinder in response to said first predetermined variable, said two parallel fluid flow paths including connections communicating with the two chambers of the power cylinder, respectively, each of said two parallel fluid flow paths being divided into an upstream section and a downstream section with respect to said connection thereof; each of said upstream and downstream sections of said two parallel fluid flow paths including a main variable flow restrictor having an orifice area variable with said first predetermined variable; wherein one of said upstream and downstream sections of each of said two parallel fluid flow paths includes an additional variable flow restrictor having an orifice area variable with said first predetermined variable and arranged in series with that one of said main variable flow restrictors which is included by said one section, said additional variable flow restrictor and said one main variable flow restrictor being disposed on the same side from one of said connections such that said additional variable flow orifice is disposed less far from said one connection than said one main variable flow restrictor is; a pair of bypass paths, each having one end communicating with one of said two parallel fluid flow paths at said connection of said one parallel fluid flow path and an opposite end communicating with the other of said two parallel fluid flow path at a portion which is disposed more far from said connection of said the other parallel fluid flow path than said additional variable flow restrictor is but less far from said connection of said the other parallel fluid flow path than said main variable flow restrictor is; each of said bypass paths has arranged therein at least one variable flow orifice valve which has an orifice area variable in a different manner from the manner of variation the orifice areas of said main and additional variable flow restrictors. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A variable assist power steering system for a vehicle including a steering wheel, a pump, a reservoir, a power cylinder adapted to be connected to a steering linkage, the power cylinder defining two chambers, comprising:
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a control valve including valve elements relatively displaceable in response to a first predetermined variable in the form of a steering torque applied by the steering wheel to define therebetween two parallel fluid flow paths connected between the pump and the reservoir to produce a pressure differential between the two chambers of the power cylinder in response to said first predetermined variable, said two parallel fluid flow paths including connections communicating with the two chambers of the power cylinder, respectively, each of said two parallel fluid flow paths being divided into an upstream section and a downstream section with respect to said connection thereof; each of said upstream and downstream sections of said two parallel fluid flow paths including a main variable flow restrictor having an orifice area variable with said first predetermined variable; wherein one of said upstream and downstream sections of each of said two parallel fluid flow paths includes an additional variable flow restrictor having an orifice area variable with said first predetermined variable and arranged in series with that one of said main variable flow restrictors which is included by said one section, said additional variable flow restrictor and said one main variable flow restrictor being disposed on the same side from one of said connections such that said additional variable flow orifice is disposed less far from said one connection than said one main variable flow restrictor is; a pair of bypass paths, each having one end communicating with one of said two parallel fluid flow paths at said connection of said one parallel fluid flow path and an opposite end communicating with the other of said two parallel fluid flow path at a portion which is disposed more far from said connection of said the other parallel fluid flow path than said additional variable flow restrictor is but less far from said connection of said the other parallel fluid flow path than said main variable flow restrictor is; each of said bypass paths has arranged therein a variable flow orifice valve which has an orifice area variable in a different manner from the manner of variation of the orifice areas of said main and additional variable flow restrictors; and means for controlling said variable flow orifice valve of one of said bypass paths to close said orifice area thereof when said orifice area of the other of said bypass paths is opened. - View Dependent Claims (9, 10, 11)
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Specification