Hydraulic-power control device for power-assisted steering system

Claim 2

A hydraulic-power control device for controlling hydraulic power to be supplied by a constant delivery pump to a hydraulic reaction chamber of a servo mechanism of a power-assisted steering system of a motor vehicle, which device comprises a steering-control valve unit which is responsive to steering resistance from front wheels of the motor vehicle and which is hydraulically connected to said pump for controlling the fluid pressure of the pump delivery to develop a steering-assistance fluid pressure in accordance with the steering resistance, speedsensitive control means responsive to driving speed of the motor vehicle and producing an electric signal which is representative of the vehicle driving speed, a pressure control valve unit responsive to said steering-assistance fluid pressure and to said electric signal and producing a control signal which is related to said steering-assistance fluid pressure and said electric signal, and a booster unit hydraulically connected to said pump, reaction chamber and steering control valve unit for varying a fluid pressure to be directed to said reaction chamber in accordance with said control signal.

Claim 3

A hydraulic-power control deviCe according to claim 1, in which said pressure control valve unit is hydromechanically connected to said booster unit and said steering-control valve unit for supplying to the booster unit a mechanical signal as said control signal in accordance with said steering-assistance fluid pressure and said electric signal.

Claim 4

A hydraulic-power control device according to claim 2, in which said booster unit comprises first and second balanced valves each having opposed, smaller and larger working faces, the smaller working faces being subjected to respective input pressures to the valves and the larger working faces being subjected to respective output pressures from the valves, the input pressure to the first balanced valve and the output pressure from the second balanced valves corresponding respectively to said pump delivery and steering-assistance fluid pressures, a first passageway for providing fluid communication between an input side of said first balanced valve and an output side of said second balanced valve through output and input sides of said first and second balanced valve respectively, said first passageway being provided with first and second adjustable flow restrictions intervening between the input and output sides of said first and second balanced valves respectively, said flow restrictions being adjustable by movements respectively of said first and second balanced valves due to differences between the input and output pressures acting upon the respective valves, and a second passageway providing interruptible fluid communication between the output sides of said first and second balanced valves for varying each of the output pressure from said first and second balanced valves in accordance with said mechanical signal which is supplied by said pressure control valve unit.

Claim 5

A hydraulic-power control device according to claim 3, in which said pressure control valve unit comprises first and second electromagnetic actuating means which are energized in accordance with said electric signal supplied from said speed-sensitive control means, and first and second fluid flow control valves operatively connected to said first and second electromagnetic actuating means, respectively, each for being actuated when the associated actuating means is energized, said first and second fluid flow control valves being positioned in association with said output sides of said first and second balanced valves of the booster unit for controlling said second passageway to vary each of the output pressures from said first and second balanced valves.

Claim 6

A hydraulic-power control device according to claim 1, in which said pressure control valve unit is hydraulically connected to said booster unit and said steering-control valve unit and supplying to said booster unit a signal fluid pressure as said control signal in accordance with said steering-assistance fluid pressure and said electric signal.

Claim 7

A hydraulic-power control device according to claim 5, in which said pressure control valve unit comprises a first valve member which is operable to cut off said steering-assistance fluid pressure to be directed to said booster unit when actuated, a second valve member which is operable to relieve said steering-assistance fluid pressure at a limited rate when actuated, and first and second electromagnetic actuating means connected to said speed-sensitive control means and respectively associated with the first and second valve members for actuating these valve members when energized, said first electromagnetic actuating means being energized when said electric signal represents a vehicle driving speed which is lower than a predetermined relatively low level and said second electromagnetic actuating means being actuated when said electric signal represents a vehicle driving speed higher than a relatively high level.

Claim 8

A hydaulic-power control device according to claim 6, in which said pressure control valve unit further comprises a first passageway which is hydrauliCally connected at its inlet side to said booster unit and at its outlet side to said steering-control valve unit through a flow restriction, said first valve member being positioned to shut-off said first passageway posterior to said flow restriction when actuated, and a second passageway leading at one end from said first passageway through a flow restriction and at the other opened to the outside of the pressure control valve unit, said second valve member being positioned to shut off said second passageway posterior to the flow restriction therein.

Claim 9

A hydraulic-power control device according to claim 6, in which speed-sensitive control means comprises a vehicle speed detector for detecting said driving speed of the motor vehicle and producing a signal voltage substantially proportional to the detected driving speed and an elecric control circuit which is connected at its input terminal to said vehicle speed detector and at its output terminal to said first and second electromagnetic actuating means for energizing the first electromagnetic means when said signal voltage represents said vehicle driving speed lower than said relatively low level and energizing the second electromagnetic means when said signal voltage represents said vehicle driving speed higher than said relatively high level.

Claim 10

A hydraulic-power control device according to claim 8, in which said electric control circuit comprises first and second Schmidt trigger circuits respectively having trigger levels corresponding to said relatively low and relatively high levels, said second Schmidt trigger circuit being connected to said second electromagnetic actuating means, and a NOT-gate circuit connected at its input terminal to said first Schmidt trigger circuit and at its output terminal to said first electromagnetic actuating means.

Claim 11

A hydraulic-power control device according to claim 5, in which said booster unit comprises a directional balanced valve having opposed, larger and smaller working faces, the larger working face being subjected to signal fluid pressure and the smaller working face being subjected to the pressure to said pump delivery, and a pressure-control passageway providing fluid communication between said pump and said steering-control valve unit through an adjustable flow restriction which is adjustable by movement of said directional balanced valve, said restriction being constricted or even closed when said balanced valve is moved by a force resulting from said signal fluid pressure acting upon said larger working face of the valve overcoming a force resulting from the pump delivery pressure acting upon said smaller working face of the valve for giving rise to an increase in the pump delivery pressure which is to be directed to said reaction chamber.

Claim 12

A hydraulic-power control device according to claim 10, in which said booster unit further comprises a valved passageway leading at one end from a pump side of said pressure-control passageway and opened at the other to the outside for draining off an excess of the pump delivery when the pump delivery pressure rises beyond a predetermined level.

Claim 13

A hydraulic-power control device according to claim 11, in which said booster unit further comprises a spring-loaded pressure relief valve interposed between ends of said valve passageway to bias the valved passageway to be closed and to open the valved passageway when a pressure difference thereacross exceeds a predetermined level.

Claim 14

A hydraulic-power control device according to claim 12, in which said pressure relief valve has self-maintaining characteristics by which the pressure relief valve is held at rest while said pressure difference is greater than a predetermined level.

Claim 15

A hydraulic-power control device according to claim 10, in which said booster unit further comprises a valved passageway leading at one end from a steering-control valve unit side of said pressure-control passageway and opened to the outside at its other end for Draining off an excess of the steering-assistance fluid when the pressure thereof rises beyond a predetermined level.

Claim 16

A hydraulic-power control device according to claim 14, in which said booster unit further comprises a pressure spring-loaded pressure relief valve interposed between ends of said valve passageway to bias the valved passageway to be closed and to open the valved passageway when a pressure difference thereacross exceeds a predetermined level.

Claim 17

A hydraulic-power control device according to claim 15, in which said pressure relief valve has self-maintaining characteristics by which the pressure relief valve is held at rest while said pressure difference is greater than a predetermined level.

Claim 18

A hydraulic-power control device for controlling hydraulic power to be supplied from a constant delivery pump to a hydraulic reaction chamber of a servo mechanism of a power-assisted steering system of a motor vehicle, comprising a steering-control valve unit which is responsive to steering resistance from front wheels of the motor vehicle and which is hydraulically connected to said pump for controlling the fluid pressure of the pump delivery to develop a steering-assistance fluid pressure in accordance with the steering resistance, speed-sensitive control means which is responsive to a driving speed of said motor vehicle for producing an electric signal representative of the vehicle driving speed, a pressure control valve unit hydraulically connected to said steering-control valve unit and electrically connected to said speed-sensitive control means for producing a signal fluid pressure in accordance with the steering-assistance fluid pressure and said electric signal supplied therefrom, and a booster unit hydraulically connected to said pump, reaction chamber, steering-control valve unit and pressure control valve unit for multiplying a fluid pressure which is to be directed to said reaction chamber in accordance with said signal fluid pressure when said vehicle driving speed represented by said electric signal is higher than a predetermined level.

Claim 19

A hydraulic-power control device for controlling hydraulic power to be supplied from a constant delivery pump to a hydraulic reaction chamber of a servo mechanism of a power-assisted steering system of a motor vehicle, comprising a steering-control valve unit which is responsive to steering resistance from front wheels of the motor vehicle and which is hydraulically connected to said pump for controlling the fluid pressure of the pump delivery to develop a steering-assistance fluid pressure in accordance with the steering resistance, speed-sensitive control means which is responsive to a driving speed of said motor vehicle for producing an electric signal representative of the vehicle driving speed, a pressure control valve unit hydraulically connected to said steering-control valve unit and electrically connected to said speed-sensitive control means for producing a signal fluid pressure in accordance with the steering-assistance fluid pressure and said electric signal supplied therefrom, and a booster unit hydraulically connected to said pump, reaction chamber, steering-control valve unit and pressure control valve unit for multiplying a fluid pressure which is to be directed to said reaction chamber in accordance with said signal fluid pressure when said vehicle driving speed represented by said electric signal is higher than a predetermined level.

Claim 20

A hydraulic-power control device according to claim 17, in which said booster unit comprises a housing structure having formed therein fluid lines including a port communicating with said pump and said reaction chamber, a port communicating with said steering-control valve unit and with an input side of said pressure control valve unit, a port communicating with an output side of said pressure control valve unit and a bore into which all the said ports are open, and a directional balanced valve axially slidably received in said bore and having a land which has a smaller working face sub-jected to the pump delivery pressure through said port communicating with said pump and a larger working face subjected to said signal fluid pressure through said port communicating with said output side of said pressure control valve unit, said balanced valve defining in said bore an adjustable orifice which is closed and opened as said balanced valve is moved due to difference between opposing forces resulting from the fluid pressure acting upon the smaller and larger working faces of said land, said orifice providing communication between the ports communicating respectively with said pump and said steering-control valve unit when opened.

Claim 21

A hydraulic-power control device according to claim 18, in which said booster unit further comprises first and second bypass passageway each opened at one end to the outside of said housing structure, said first bypass passageway bypassing said orifice and said second bypass passageway leading from said port commu-nicating with said steering-control valve unit, and first and second spring-loaded pressure relief valves disposed in said first and second bypass passageways respectively, each of said pressure relief valves being biased to close the associated bypass passage and moved to open the bypass passageway when the fluid pressure obtaining anterior thereto rises beyOnd a predetermined level for draining off an excess of the fluid pressure.

Claim 22

A hydraulic-power control device according to claim 17, in which said pressure control valve unit comprises a housing structure having formed therein a first fluid passage having an inlet port communicating with an output side of said booster unit and an outlet port communicating with an input side of said booster unit, a flow restriction intervening between the inlet and outlet ports of said first fluid passage and a second fluid passage communicating through a flow restriction with said first fluid passage posterior to the flow restriction therein and opened to the outside of said housing structure, first and second flow shut-off valves projecting respectively into first and second fluid passages posterior to the respective flow restrictions and biased to open said first and second fluid passages, and actuating means associated with said flow shut-off valves and electrically connected to said speed-sensitive control means for moving each of said shut-off valves in accordance with said electric signal.

Claim 23

A hydraulic-power control device according to claim 20, in which said actuating means comprises first and second solenoid devices respectively having plungers engaging with said first and second flow shut-off valves and having retracted positions when the respective solenoid devices are de-energized, said plungers being protruded when the respective solenoid devices are energized by said electric signal for moving the associated flow shut-off valves to close said first and second fluid passages independently of each other.

Claim 24

A hydraulic-power control device according to claim 21, in which said speed-sensitive control means comprises a vehicle-pseed detector responsive to the driving speed of the motor vehicle and producing a d.c. signal voltage proportional to the detected vehicle driving speed, converting means for converting said d.c. signal voltage into an a.c. signal voltage, and switch means which is connected to said converting means and which is operable to produce said electric signal to energize said first solenoid device only when said signal voltage represents a vehicle driving speed lower than a predetermined relatively low level and to energize said second solenoid device only when said signal voltage represents a vehicle driving speed which is higher than a predetermined relatively high level.

Claim 25

A hydraulic-power control device according to claim 22, in which said switch means comprises first and second Schmidt trigger circuits having trigger levels respectively corresponding to said predetermined relatively low and relatively high levels, said second Schmidt trigger circuit being connected to said second solenoid device, and a NOT-gate circuit connected between said first Schmidt trigger circuit and said first solenoid device.

Claim 26

A hydraulic-power control device for controlling hydraulic power to be supplied from a constant delivery pump to a hydraulic reaction chamber of a servo mechanism of a power-assisted steering system of a motor vehicle, comprising a steering-control valve unit which is responsive to steering resistance from front wheels of the motor vehicle and which is hydraulically connected to said pump for controlling the pump delivery pressure to develop steering-assistance fluid pressure in accordance with said steering resistance, speed-sensitive control means which is responsive to a driving speed of said motor vehicle for producing an electric signal representative of the vehicle driving speed, a pressure control valve unit hydromechanically connected to said steering-control valve unit and electrically connected to said speed-sensitive control means for producing a mechanical signal in accordance with said electric signal, and a booster unit hydraulically connected to said pump, reaction chamber and steering-control valve unit and hydromechanically connected to said pressure control valve unit for multiplying a fluid pressure Which is to be directed to said reaction chamber when said vehicle driving speed represented by said electric signal is higher than a predetermined level.

Claim 27

A hydraulic-power control device for controlling hydraulic power to be supplied from a constant delivery pump to a hydraulic reaction chamber of a servo mechanism of a power-assisted steering system of a motor vehicle, comprising a steering-control valve unit which is responsive to steering resistance from front wheels of the motor vehicle and which is hydraulically connected to said pump for controlling the pump delivery pressure to develop steering-assistance fluid pressure in accordance with said steering resistance, speed-sensitive control means which is responsive to a driving speed of said motor vehicle for producing an electric signal representative of the vehicle driving speed, a pressure control valve unit hydromechanically connected to said steering-control valve unit and electrically connected to said speed-sensitive control means for producing a mechanical signal in accordance with said electric signal, and a booster unit hydraulically connected to said pump, reaction chamber and steering-control valve unit and hydromechanically connected to said pressure control valve unit for multiplying a fluid pressure Which is to be directed to said reaction chamber when said vehicle driving speed represented by said electric signal is higher than a predetermined level.

Claim 28

A hydraulic-power control device according to claim 24, in which said booster unit comprises a housing structure having formed therein a port communciating with said pump and reaction chamber, a port communicating with said steering-control valve unit, a first bore anteriorly communicating with said port communicating with said pump and reaction chamber, a second bore posteriorly communicating with said port communicating with said steering-control valve unit, said first and second bores communicating with each other through an intermediate passage, a first pressure acting chamber anteriorly communicating with said port communicating with said pump and posteriorly communicating with said intermediate passage, a second pressure acting chamber communicating anteriorly with said first pressure acting chamber and said intermediate passage and posteriorly with said port communicating with said steering-control valve unit and first and second directional balanced valves respectively axially slidably received in said first and second bores, each of said balanced valves having a land and a constriction defining an adjustable flow restriction in the associated bore, the land of said balanced valve having a smaller working face subjected to the pump delivery pressure and a larger working face subjected to a fluid pressure in said first pressure acting chamber and the land of said second balanced valve having a smaller working face subjected to a fluid pressure in said intermediate passage and a larger working face subjected to a fluid pressure in said second pressure working chamber the adjustable flow restriction in said first bore intervening between said port communicating with said pump and said intermediate passage and the adjustable flow restriction in said second bore intervening between said intermediate passage and said port communicating with said steering-control valve unit, each of the adjustable flow restrictions being closed and opened as the associated balanced valve is axially moved due to difference between opposing forces resulting from the fluid pressures acting on both working faces of its land, said pressure control valve comprising first and second spring-loaded fluid shut-off valves projecting toward said first and second pressure acting chambers, respectively, said first fluid shut-off valve being axially movable between postions establishing and interrupting fluid communication between said first pressure acting chamber and said port communicating with said pump and biased to establish such communication and said second fluid shut-off valve being axially movable between positions establishing and interrupting fluid communication between said second pressure acting chamber and said port communicating with said steering-control valve and biased to interrupt such commnication, and first and second valve actuating means associated with said first and second fluid shut-off valves and electrically connected to said speed-sensitive control means for moving said first fluid shut-off valve to interrupt said fluid communication and moving said second fluid shut-off valve to establish said fluid communication when energized by said electric signal.

Claim 29

A hydraulic-power control device according to claim 24, in which said booster unit comprises a housing structure having formed therein a port communicating with said pump and reaction chamber, a port communicating with said steering control valve unit, a first bore anteriorly communicating with said port communicating with the pump and reaction chamber, a second bore posteriorly communicating with said port communicating with said steering-control valve unit, said first and second bores communicating with each other through an intermediate passage, first and second pressure acting chambers communicating respectively with said intermediate pAssage and said port communicating with said steering-control valve unit, and a drain passage having one end opened to the outside of said housing structure and branch ends disposed adjacent said first and second pressure acting chambers, and first and second directional balanced valves respectively axially slidably received in said first and second bores, each of said balanced valves having a land and a constriction defining an adjustable flow restriction in the associated bore, the land of said first balanced valve having a smaller working face subjected to the pump delivery pressure and a larger working face subjected to the fluid pressure in said first pressure acting chamber and the land of said second balanced valve having a smaller working face subjected to the fluid pressure in said intermediate passage and a larger working face subjected to the steering-assistance fluid pressure in said port communicating with said steering-control valve unit, the adjustable flow restriction in said first bore intervening between said port communicating with said pump and said intermediate passage and the adjustable flow restriction in said second bore intervening between said intermediate passage and said port communicating with said steering-control valve unit, each of the adjustable flow restrictions being closed and opened as the associated balanced valve is axially moved due to difference between opposing faces resulting from the fluid pressures acting upon both working faces of its land, said pressure control valve unit comprising first and second spring-loaded fluid shut-off valves projecting toward said first and second pressure acting chambers and axially movable between positions to close and open the chambers, respectively, each of said fluid shut-off valves being formed with a fluid passage having one end open to the associated pressure acting chamber and the other end opened and positioned to be in alignment with each of said branch ends of said drain passage when the fluid shut-off valve is in a position to close the associated pressure acting chamber, said first fluid shut-off valve being biased to open said first pressure acting chamber and said second fluid shut-off valve being biased to close said second pressure acting chamber, and first and second valve actuating means associated with said first and second fluid shut-off valves and electrically connected to said speed-sensitive control means for moving said first fluid shut-off valve to a position to close said first pressure acting chamber and moving said second fluid shut-off valve to open said second pressure acting chamber when energized by said electric signal.

Claim 30

A hydraulic-power control device according to claim 26, in which said booster unit further comprises first and second bypass passageways which are opened each at one end to the outside of said housing structure, said first bypass passageway bypassing said first adjustable flow restriction and said second bypass passageway leading from said port communicating with said steering-control valve unit, and first and second spring-loaded pressure relief valves disposed respectively in said first and second bypass passageways, each of said pressure relief valves being biased to close the associated bypass passageway and moved to open the passageway when the fluid pressure obtaining anterior thereto rises beyond a predetermined level for draining off an excess of the fluid pressure therefrom.

Claim 31

A hydraulic-power control device according to claim 26, in which said speed sensitive control means comprising a vehicle-speed detector responsive to the driving speed of the motor vehicle and producing a d.c. signal voltage proportional to the detected vehicle driving speed, converting means for converting said d.c. signal voltage into an a.c. signal voltage, and switch means which is connected to said converting means and which is operable to produce said electric signal to selectively energize said first and second valve actuating means in aCcordance with said a.c. signal voltage.

Claim 32

A hydraulic-power control device according to claim 28, in which said switch means comprises first, second, third and fourth Schmidt trigger circuits connected to said converting means, said first and third Schmidt trigger circuits having a common trigger level which is in agreement with a predetermined reference voltage, said second Schmidt trigger circuit having a trigger level lower than said common trigger level and said fourth Schmidt trigger circuit having a trigger level which is higher than said common trigger level, said first Schmidt trigger circuit being connected to said second valve actuating means, first and second NOT-gate circuits connected to said second and fourth Schmidt trigger circuits, an AND-gate circuit connected to said third Schmidt trigger circuit and said second NOT-gate circuit, and an OR-gate circuit connected at its input terminal to said first NOT-gate circuit and said AND-gate circuit and at its output terminal to said first valve actuating means.