Toyoda Koki Kabushiki Kaisha

Katsuhisa Mori

Mikio Suzuki

Kyosuke Haga

Hiroshi Suzuki

Yoshiharu Inaguma

Hideya Kato

Kenichi Fukumura

Tsuneo Tanaka

Hideaki Sugiyama

In a power steering apparatus having a control valve with a first control valve portion and a second control valve portion to enhance rigidity of a steering operation, an amount of an overlapping portion of an overlap variable orifice is designed larger than an amount of an unlapping portion of an untapped variable orifice in the control valve because of dispersion during manufacture. When the overlap variable orifice finishes overlapping, the unlapped variable orifice has already started unlapping. Therefore, since the overlap variable orifice and the unlapped variable orifice never become unlapping form simultaneously regardless of the dispersion, the control valve is capable of minimizing a difference of the flow between a plurality of the second control valve portion. As a result, the power steering apparatus relative to the invention prevents enlargement of noise caused by an unbalance of the flow between a plurality of the second control valve portions in the control valve.

Power steering apparatus

In a power steering apparatus comprising a pump, a reservior, a power cylinder having two opposite chambers, and a rotary control vale, the rotary control valve consists of a first control portion which communicates between the pump and the reservior, and a second control portion which communicates not only between the pump and the reservior but also with the power cylinder. In the first control portion, each of four underlapping variable orifices is so provided as to take the form of underlap in itself. In the second control portion, two underlapping variable orifices are provided on the side of the pump, and besides each of two overlapping variable orifices is so provided as to take the form of overlap in itself on the side of the reservior. In this manner, while a steering wheel is operated within a predetermined angle, an opening area of the overlapping variable orifice changes little. When the steering wheel is operated beyond the predetermined valve, the opening are increases sufficiently according to steering operation. As a result, a differential pressure between the chambers is prevented from originating at and around the neutral position of the steering wheel. Consequently, as for steering feeling, the rigidity of the steering operation at and around the neutral position is enhanced, and furthermore, a beginning point where the power assist is produced by operating the steering wheel from its neutral position is distinguished.

Power steering system including a rotary control valve with multiple

A power steering apparatus is composed a fluid source for discharging pressurized fluid, a power cylinder, a control valve responsive to operation of a steering wheel for supplying the power cylinder with pressurized fluid from the fluid source, and a reservoir. The control valve has a first control portion for controlling the flow of pressurized fluid from the fluid source to the reservoir, and a second control portion for controlling the flow of pressurized fluid to the power cylinder. The first control portion has four paths communicating with the fluid source and the reservoir, and each of the four paths is formed with a center-open variable orifice which opens when the control valve is in a neutral state. The second control portion has two supply paths communicating with the fluid source and a pair of chambers of the power cylinder, each of the two supply paths is formed with a semi-center-open variable orifice which opens when the control valve is in the neutral state, and two drain paths communicating with the chambers of the power cylinder and the reservoir, each of the two drain paths is formed with a center-closed variable orifice of which closes when the control valve is in the neutral state.

Hydraulic power steering apparatus

A power steering apparatus comprises a fluid source for supplying pressurized fluid, a power cylinder having a pair of fluid chambers, a control valve, and a drain control mechanism. The control valve is composed of first and second control portions. The first control portion has four paths connecting the fluid source and the reservoir, and each of the four paths is formed with a variable orifice of center-open type. The second control portion has two supply paths communicating the fluid source with the fluid chambers of the power cylinder, each of the supply paths being formed with a variable orifice of center-open type, and two drain paths communicating the fluid chambers with the reservoir, each of the drain paths being formed with a variable orifice of center-closed type. The drain control mechanism is responsive to differential pressure between the fluid chambers of the power cylinder to control the communication of one fluid chamber under high pressure with the reservoir, and is responsive to a vehicle speed to control the communication of both fluid chambers with the reservoir.

A power steering apparatus having a fluid source for discharging pressurized fluid, a power cylinder, a control valve responsive to operation of a steering wheel for supplying the power cylinder with pressurized fluid from the fluid source, and a reservoir. The control valve has a first control portion for controlling the flow of pressurized fluid from the fluid source to the reservoir, and a second control portion for controlling the flow of pressurized fluid to the power cylinder. The first control portion has two paths connecting the fluid source and the reservoir, each of the paths being formed with at least one variable orifice of a center-open type which opens when the control valve is in a neutral state. The second control portion has two supply paths communicating with the fluid source and a pair of chambers of the power cylinder, each of the supply paths being formed with a variable orifice of a center-close type which closes when the control valve is in the neutral state, and two drain paths communicating with the pair of chambers and the reservoir, each of the drain paths being formed with a variable orifice of a center-open type which opens when the control valve is in the neutral state.

A power steering apparatus having a hydraulic pump for outputting a pressurized fluid, an assist force generation mechanism hydraulically connected to the pump through a supply passage to generate an assist force in response to rotation of a steering wheel, wherein the assist force generation mechanism has a characteristic that the back pressure thereof increases when the steering wheel is rotated. The power steering apparatus further comprises a flow control valve having a spool which is moved in response to a pressure drop at a metering orifice disposed in the middle of the supply passage, so as to control the flow rate of the pressurized fluid to be constant. The spring chamber of the flow control valve is connected to a reservoir through a drain passage, and a drain valve is disposed in the drain passage for allowing the flow of pressurized fluid from the spring chamber to the reservoir when the back pressure of the assist force generation mechanism is low, and for prohibiting the flow of the pressurized fluid when the back pressure of the assist force generation mechanism increases.

A rotary servovalve includes a valve sleeve formed with a supply port for connection to a source of fluid under pressure and distribution ports respectively for connection to opposite fluid chambers of a hydraulic power cylinder, the valve sleeve being formed at the inner periphery thereof with circumferentially spaced sleeve channels respectively in open communication with the supply and distribution ports, and a valve rotor coupled with the valve sleeve for relative rotation thereto, the valve rotor being formed thereon with circumferentially spaced control lands which are arranged to correspond with the sleeve channels when the servovalve is in a neutral position. The control lands corresponding with the sleeve channels in open communication with the distribution ports are each formed larger in width than the corresponding sleeve channel and smaller in height than the control land corresponding with the sleeve channel in open communication with the supply port to define a predetermined clearance for restricting the flow of fluid discharged from and supplied into the distribution ports when the servovalve is in the neutral position.

Growing community of inventors

Okazaki, Japan

Katsuhisa Mori