Patent Application
20080092537
The present invention relates to a piston-type hydraulic fluid reservoir (or working liquid reservoir) which can store a working liquid of a hydraulic circuit, and more particularly to a reservoir technique which forms a hydraulic chamber into a donut shape thus making the movement of a piston smoother.
For example, a vehicle-use brake hydraulic control circuit such as an anti-lock brake device includes a working liquid reservoir which temporarily stores a working liquid released from a wheel cylinder. Although a capacity of the working liquid reservoir is small, the working liquid flows into or flows out from working liquid reservoir each time a brake control is performed. The working liquid reservoir is, in general, of a piston type, wherein a piston defines a hydraulic chamber and a gas chamber in the inside of a cylinder bore. The movement of the piston is relatively frequent and hence, it is important to effectively guide the piston.
As a technique which guides the piston, there has been known a technique which guides the piston at two points (that is, two portions). This two-point guide technique can surely perform the guiding compared to the general one-point guiding and also can shorten an axial length of the piston and hence the two-point guide technique is effective in the miniaturization of the working liquid reservoir.
Patent document 1 (Japanese Utility Model Laid-open Publication Hei5(1993)-65730 describes a technique in which a hydraulic chamber is defined by a piston head, a guide shaft having a small diameter is mounted on a side of the piston head which is positioned in a gas chamber which is positioned opposite to the hydraulic chamber, and the small-diameter guide shaft is made to penetrate a plug member (a member which closes the gas chamber). To focus an attention to the movement of the piston head, the movement of the piston head is guided at two portions, that is, by an outer peripheral portion of the large-sized piston head per se and an outer peripheral portion of the small-sized guide shaft which is integrally formed with the piston head.
The guiding of the piston side at two portions as described in patent document 1 is basically effective in guiding the piston smoothly. However, the hydraulic chamber defined by the piston maintains the same cylindrical type as in the case of one-point guide and hence, an opening of a passage through which a working liquid flows into or flows out from the cylindrical type hydraulic chamber is also deviated or offset with respect to the hydraulic chamber. Accordingly, the flow of the working liquid which enters or is discharged from the hydraulic chamber is disturbed and hence, there exists a possibility that a force which impedes the smooth movement of the piston is generated although an amount of the force may be considerably small. In this respect under a present circumstance in which the miniaturization of the working liquid reservoir per se is in progress, to ensure the more rapid responsiveness in a brake control, as one of external factors which influences the motion of the piston, it is required to ensure the smooth inflow of the working liquid into the hydraulic chamber and the smooth outflow of the working liquid from the hydraulic chamber.
Accordingly, it is an object of the present invention to provide a novel type of a working liquid reservoir which ensures the smoother inflow of a working liquid into a hydraulic chamber and the smoother outflow of the working liquid from the hydraulic chamber on a premise that a piston is guided at two points.
Other objects of the present invention will become apparent from the explanation made hereinafter.
In the present invention, a hydraulic chamber which stores a working liquid is formed into a donut shape, and an opening of a passage for the working liquid is arranged at a center portion of the donut. Due to such a constitution, the turbulence attributed to the flow of the working liquid (turbulence which impedes the smooth movement of a piston) can be minimized. Accordingly, the present invention has constitutional features in following points.
(A) A housing has a second cylinder bore whose diameter is smaller than a diameter of a cylinder bore which defines the hydraulic chamber at the center of a bottom portion of the cylinder bore.
(B) The piston which is movably fitted into the cylinder bore has the stepped structure and includes a large-diameter portion which is fitted into the cylinder bore and a small-diameter portion which is fitted into the second cylinder bore and hence, the hydraulic chamber in the inside of the cylinder bore is formed into a donut shape.
(C) A communication passage is formed between an inner peripheral wall of the second cylinder bore and an outer periphery of the small-diameter portion of the piston, and the working liquid reciprocates between the donut-shaped hydraulic chamber and an external hydraulic circuit through the communication passage.
In the working liquid reservoir of the present invention, a two-point guide of the moving piston is constituted of two portions on the large-diameter portion and the small-diameter portion, that is, the two-point guide of the moving piston is constituted of the small-diameter portion which is filled with the working liquid besides the outer periphery of the large-diameter piston. The small-diameter portion is positioned in the midst of the passage in which the working liquid flows and hence, the working liquid functions as a lubricant and makes a guiding function smooth thus preventing wear attributed to guiding. Further, two portions of the piston are guided by cylinder bores and hence, compared to a case in which a guiding function is obtained by making use of a separate member joined to a piston (see the above-mentioned patent document 1), the piston can be surely guided thus making the movement of the piston smoother.
In a preferred embodiment of the present invention, in the small-diameter portion of the piston which constitutes one guide, a plurality of groove passages which extends along the axial direction of the small-diameter portion may be formed. Here, a land portion between neighboring groove passages functions as a guide wall which guides the movement of the piston.
The tandem-type master cylinder 10 has two independent ports 11, 12, and two pipe connection ports 511, 512 are formed in a housing of a hydraulic control unit 50 corresponding to two ports 11, 12. Further, the housing of the hydraulic control unit 50 includes four separate pipe connection ports 521, 522, 523, 524 corresponding to four wheel cylinders 201 to 204.
Further, the hydraulic control unit 50 includes four normally-opened solenoid valves EV and four normally-closed solenoid valves AV corresponding to four wheel cylinders 201 to 204. Further, the hydraulic control unit 50 includes a pump 30 which is driven by an electric motor M. The pump 30 is constituted of coupled plunger pumps, and a brake liquid pressure is applied to the respective wheel cylinders 201 to 204 through the normally-opened respective solenoid valves EV while a brake liquid pressure of the respective wheel cylinders 201 to 204 is released to the working liquid reservoir 70 through the normally-closed respective solenoid valves AV. It may be appreciated that along with the anti-lock control, the working liquid in the circuit flows into or flows out from the working liquid reservoir 70 in response to operations of the pump 30 and the respective solenoid valves EV, AV. Accordingly, to ensure the smooth and rapid brake control, it is necessary to perform the inflow and the outflow of the working liquid with respect to the working liquid reservoir 70.
The working liquid reservoir 70 is a piston-type reservoir with a capacity of approximately 3 cc. The working liquid reservoir 70 is housed in a block-like housing of the hydraulic control unit 50.
The housing 550 of the hydraulic control unit 50 is a molded product made of aluminum metal or aluminum-based alloy. The housing 550 includes a chamber which houses the respective solenoid valves EV, AV and the like therein and, respective pipe connection ports 511, 512, 521 to 524 are formed in side surfaces of the chamber. The housing 550 defines a cylinder bore 560 for constituting the working liquid reservoir 70 together with a plurality of these chamber spaces.
The cylinder bore 560 is a stop bore which opens in one surface of the housing 550 (one surface being positioned downwardly when the housing 550 is set). A most portion of the cylinder bore 560 from a depth of the bore to the vicinity of an opening portion has a uniform diameter, and the opening portion of the cylinder bore 560 which follows the most portion of the cylinder bore 560 has a two-stepped portion. This two-stepped constitution of the stepped portion at the opening portion of the cylinder bore 560 is provided for fixing a lid member 72 by press-fitting and caulking. The lid member 72 is made of metal and hermetically seals the cylinder bore 560 by fixing.
In the inside of the cylinder bore 560 which is hermetically sealed by the lid member 72, besides a resin-made piston 74, a conical compression spring 76 which pushes the piston 74 in the depth direction of the cylinder bore 560 is arranged. What must be noted here is that the piston 74 is configured to possess the stepped structure which allows a two-point guide. The piston 74 is integrally provided with a large-diameter portion 74L which is snugly fitted into the cylinder bore 560, a small-diameter portion 74S which extends in the axial direction from one surface of the large-diameter portion 74L, and a projecting portion 74P which is arranged on a side opposite to the small-diameter portion 74S. The small-diameter portion 74S and the projecting portion 74P are respectively positioned at the center on both sides of the large-diameter portion 74L and hence, three components consisting of the large-diameter portion 74L, the small-diameter portion 74S and the projecting portion 74P are coaxially aligned with each other. The projecting portion 74P is positioned inside the compression spring 76 and performs a function of stably supporting the compression spring 76 and performs a function as a stopper for restricting a stroke of the piston 74. Here, in a full-stroke state shown on the right side of
The large-diameter portion 74L of the piston 74 supports an O-ring 73 in a groove formed in an outer periphery thereof thus defining the inside of the cylinder bore 560 into a hydraulic chamber 82 and a gas chamber 80. A gas in the gas chamber 80 is usually air but an inert gas such as nitrogen or helium may be used. It is preferable that the gas chamber 80 constitutes a gas spring thus compensating for a spring force of the compression spring 76.
Here, due to the formation of the small-diameter portion 74S on the piston 74, the hydraulic chamber 82 is formed into a donut shape. Accordingly, the housing 550 has a second cylinder bore 562 at a center of a bottom portion of the cylinder bore 560 which defines the hydraulic chamber 82. The second cylinder bore 562 is a guide hole which receives the small-diameter portion 74S of the piston 74 and, further, functions as a hole to form a communication passage for allowing the hydraulic chamber 82 to communicate with the solenoid valve AV, the pump 30 or the like. By collectively arranging the communication passage to the small-diameter portion 74S of the piston 74, the working liquid reservoir can be designed while alleviating the restriction on the position and the size (diameter) of working liquid reservoir.
Accordingly, when the working liquid flows into or flows out from the hydraulic chamber 82, the piston 74 is guided by two portions on the respective outer peripheries of the large-diameter portion 74L and the small-diameter portion 74S and hence, the piston 74 is moved smoothly without becoming eccentric. Further, when the piston 74 moves, the working liquid flows into or flows out from the donut-shaped hydraulic chamber 82 through the groove passages 90 formed on the outer periphery of the small-diameter portion 74S and hence, there is no possibility that a force which disturbs the movement of the piston 74 (for example, an eccentric force) is generated attributed to the inflow and outflow of the working liquid. Further, the working liquid which flows into the groove passages 90 lubricates the outer periphery of the small-diameter portion 74S and hence, it is possible to obviate the wear as in the case of an operation in air.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-344813 | Nov 2004 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP05/21740 | 11/26/2005 | WO | 5/9/2007 |
