The present invention relates to a fluid control valve device suitably used as a rotary fluid channel switching valve in a power steering apparatus of a hydraulic type or the like for reducing a steering wheel operating force of, e.g., an automobile and, more particularly, to an improvement in a rotary fluid control valve device for controlling distribution of a fluid pressure by relative rotational displacement between a rotor and a sleeve.
A fluid control valve device of this type is used as a fluid channel switching valve in a power steering apparatus or the like to operate a power cylinder as a movable unit in accordance with a steering wheel operation, thereby generating an auxiliary steering force during a steering operation. Various types of such a fluid control valve device have been conventionally proposed as disclosed in, e.g., Japanese Patent Laid-Open No. 57-178971 and Japanese Utility Model Publication No. 63-30613. That is, in this fluid channel switching valve, a rotor formed integrally with an input shaft (stab shaft) of a steering wheel and a sleeve formed integrally with its output shaft (pinion shaft) are assembled to be rotationally displaced relative to each other and arranged in a valve housing. A plurality of channel grooves formed in the outer circumferential surface of the rotor and the inner circumferential surface of the sleeve in their circumferential direction are connected to channels communicating with an oil pump as a fluid pressure generating source, an oil tank, and right and left cylinder chambers constituting a power cylinder, thereby easily and properly switching fluid channels of a fluid pressure circuit (hydraulic circuit). In addition, the arrangement of the device is simple.
One of problems posed when the above rotary fluid control valve device is used as a fluid channel switching valve in a power steering apparatus is a noise problem. That is, in the hydraulic circuit extending from the pump to the right and left cylinder chambers or to the tank through the pressurized oil channels in the fluid channel switching valve, an abrupt increase or decrease in a fluid channel sectional area forms a turbulence, a vortex, or the like in a flow of a pressurized oil in the pressurized oil channels constituted by the channel grooves or land portions formed in the rotor and the sleeve of the control valve and channel holes formed to open in the grooves or the land portions, thereby generating a fluid sound (so-called shoo sound). More specifically, when a wide or narrow portion, a bent portion, a branch portion, or the like is present in the fluid channel through which the pressurized oil flows, since a pressure variation is caused to form a turbulence or a vortex, generation of the fluid sound is more or less inevitable. However, this fluid sound is desired to be minimized in the fluid channel switching valve of this type.
Especially in the above rotary fluid channel switching valve for use in a power steering apparatus, the channel grooves and the land portions formed in the sleeve inner circumferential surface and the rotor outer circumferential surface are selectively combined by the relative rotational displacement therebetween, thereby connecting or disconnecting the fluid channels to perform switching between the fluid channels. Throttle portions formed between side edge portions of the land portions for controlling connection/disconnection of the fluid channels abruptly change the fluid channel sectional area because the side edge portions are formed as sharp corner portions. Therefore, a turbulence or a vortex is inevitably formed in the flow of a pressurized oil flowing from an input port of the pump into the channel grooves. For this reason, Japanese Utility Model Publication No. 63-38138, for example, proposes an arrangement in which the throttle portion defined between the two side edges of the channel grooves communicating with the input port or the two side edges of the land portions is formed to have a structure which does not cause much change in fluid channel sectional area by forming the shape of the side edge portion into an inclined surface shape, thereby solving the noise problem. However, this arrangement is still unsatisfactory to prevent the fluid sound caused by the flow of a pressurized oil. Therefore, a demand has arisen for a countermeasure capable of solving the above noise problem with a comparatively simple and inexpensive arrangement.
In addition, this noise problem similarly arises in channel grooves or a fluid discharge hole portion communicating with a return port to the tank in the above rotary fluid channel switching valve. Therefore, this point must also be considered.