Abstract: A power steering system includes: a first drain passage for draining an oil pressure from a first oil passage, a second drain passage for draining the oil pressure from a second oil passage, and a pair of a first and second switch valves. When one of the first oil passage and the second oil passage is so pressurized by an operation of a reversible oil pump as to have an increased internal pressure, the pair of the first switch valve and the second switch valve allow the following: i) closing one of the first drain passage and the second drain passage which one is connected to the oil passage having the thus increased internal pressure, while ii) opening the other of the first drain passage and the second drain passage which other is connected to the oil passage that is so depressurized as to have a decreased internal pressure.

Abstract: A power steering system for a vehicle, comprises a steering shaft connected to a steering mechanism. A hydraulic power cylinder is provided for assisting a steering effort of the steering mechanism. A reversible pump is provided having first and second discharge ports which are respectively connected through first and second hydraulic lines with two hydraulic pressure chambers of the hydraulic power cylinder so that the two hydraulic pressure chambers are respectively provided with hydraulic pressures. A driving device is provided for driving the reversible pump to rightly and reversely rotate. A differential pressure regulating valve is disposed in the hydraulic circuit to maintain pressure at least in the first and second hydraulic lines at a level of atmospheric pressure or higher in an inoperative condition of the reversible pump.

Abstract: A first fluid passage extends from a first outlet/inlet port of a hydraulic pump to a first work chamber of a power cylinder, and a second fluid passage extends from a second outlet/inlet port of the pump to a second work chamber of the power cylinder. A switch system switches the role of the first and second outlet/inlet ports in accordance with a turning direction of a steering wheel. Flow control mechanisms are respectively incorporated with the first and second fluid passages, so that a controlled flow of hydraulic fluid from the hydraulic pump to the first or second work chamber and vice versa are appropriately carried out thereby providing the driver with a comfortable steering feeling. A bypass arrangement may be provided between the first and second fluid passages to deal with a residual pressure that would be remained in the first or second work chamber when the hydraulic pump is under inoperative condition.

Abstract: A power steering system includes: a first drain passage for draining an oil pressure from a first oil passage, a second drain passage for draining the oil pressure from a second oil passage, and a pair of a first and second switch valves. When one of the first oil passage and the second oil passage is so pressurized by an operation of a reversible oil pump as to have an increased internal pressure, the pair of the first switch valve and the second switch valve allow the following: i) closing one of the first drain passage and the second drain passage which one is connected to the oil passage having the thus increased internal pressure, while ii) opening the other of the first drain passage and the second drain passage which other is connected to the oil passage that is so depressurized as to have a decreased internal pressure.

Abstract: A power steering system and a method of charging the power steering system with hydraulic fluid are provided. Hydraulic fluid is selectively supplied to hydraulic chambers of a power cylinder via oil passages from a reversible pump, according to a steering torque. In addition, a bypass passage is provided between oil passages. A normally open switching valve is provided in the bypass passage. When the system is assembled, the hydraulic fluid is supplied from an oil reservoir via the switching valve or the reversible pump, and circulated in the hydraulic circuit. The air in the hydraulic circuit is discharged via the switching valve.

Abstract: To provide a nonvolatile memory microcomputer with which a step of testing a microcomputer unit using a logic tester can be omitted, thereby reducing the testing cost. A memory tester supplies test data and expectation data to the nonvolatile memory microcomputer, and the nonvolatile memory microcomputer stores them in a nonvolatile memory. Subsequently, upon receiving an address signal, the nonvolatile memory outputs a test signal and an expectation signal based on test data and expectation data corresponding to the address signal. The test signal is supplied to a circuit block in the microcomputer unit, to drive the circuit block. The circuit block returns a test result signal, which is output to the memory tester together with the expectation signal. The memory tester compares the test result signal and the expectation signal, to judge whether the microcomputer unit operates correctly.

Abstract: A power steering system includes first and second drain passages connected to the first and second passages, respectively, and first and second passage switching valves arranged at connections of the first and second drain passages and the first and second passages, respectively. When a hydraulic pump operates to discharge the hydraulic pressure to the first passage, the first passage switching valve provides fluid communication between pump-side and cylinder-side portions of the first passage and closes off the first drain passage. And when the hydraulic pump stops, the first switching valve provides fluid communication between the cylinder-side portion of the first passage and the first drain passage.

Abstract: A power steering system includes: a first drain passage for draining an oil pressure from a first oil passage, a second drain passage for draining the oil pressure from a second oil passage, and a pair of a first and second switch valves. When one of the first oil passage and the second oil passage is so pressurized by an operation of a reversible oil pump as to have an increased internal pressure, the pair of the first switch valve and the second switch valve allow the following: i) closing one of the first drain passage and the second drain passage which one is connected to the oil passage having the thus increased internal pressure, while ii) opening the other of the first drain passage and the second drain passage which other is connected to the oil passage that is so depressurized as to have a decreased internal pressure.

Abstract: A power steering system for a vehicle, comprises a steering shaft connected to a steering mechanism. A hydraulic power cylinder is provided for assisting a steering effort of the steering mechanism. A reversible pump is provided having first and second discharge ports which are respectively connected through first and second hydraulic lines with two hydraulic pressure chambers of the hydraulic power cylinder so that the two hydraulic pressure chambers are respectively provided with hydraulic pressures. A driving device is provided for driving the reversible pump to rightly and reversely rotate. A differential pressure regulating valve is disposed in the hydraulic circuit to maintain pressure at least in the first and second hydraulic lines at a level of atmospheric pressure or higher in an inoperative condition of the reversible pump.

Abstract: A power steering system is provided which comprises a bypass conduit connecting between first and second communication conduits and having bypass conduit ports. A pair of valves disposed in the bypass conduit for selectively opening and closing the bypass conduit ports in response to the pressure fluid from the pressure source. The valves are adapted to provide communication between the first and second communication conduits when the hydraulic pressure source is inoperative.

Abstract: A first fluid passage extends from a first outlet/inlet port of a hydraulic pump to a first work chamber of a power cylinder, and a second fluid passage extends from a second outlet/inlet port of the pump to a second work chamber of the power cylinder. A switch system switches the role of the first and second outlet/inlet ports in accordance with a turning direction of a steering wheel. Flow control mechanisms are respectively incorporated with the first and second fluid passages, so that a controlled flow of hydraulic fluid from the hydraulic pump to the first or second work chamber and vice versa are appropriately carried out thereby providing the driver with a comfortable steering feeling. A bypass arrangement may be provided between the first and second fluid passages to deal with a residual pressure that would be remained in the first or second work chamber when the hydraulic pump is under inoperative condition.

Abstract: A power steering system is provided which comprises a bypass conduit connecting between first and second communication conduits and having bypass conduit ports. A pair of valves disposed in the bypass conduit for selectively opening and closing the bypass conduit ports in response to the pressure fluid from the pressure source. The valves are adapted to provide communication between the first and second communication conduits when the hydraulic pressure source is inoperative.