GB2147674A

GB2147674A - Double-action type master cylinder

Info

Publication number: GB2147674A
Application number: GB08421983A
Authority: GB
Inventors: Shozo Sakaguchi; Riichiro Sugimoto
Original assignee: Jidosha Kiki Co Ltd
Current assignee: Jidosha Kiki Co Ltd
Priority date: 1983-09-06
Filing date: 1984-08-31
Publication date: 1985-05-15
Also published as: GB2147674B; GB8421983D0; JPS6045256U

Abstract

A double-action type master cylinder is provided with a blow-off valve arrangement which comprises a ball (51) urged towards its seat (56) by a spring (53). A liquid impounding region (57) is formed between the valve body (54) and the ball (51) and a plate (52) engaging the upper portion of the ball (51). An annular gap (58) provides the outlet for said liquid impounding region (57). The arrangement reduces valve oscillation and the resulting noise. Plate (52) and ball (51) may be integrally formed (Fig 3 not shown). <IMAGE>

Description

SPECIFICATION Double-action type master cylinder The present invention relates to a double-action type master cylinder for supplying pressure liquid to a brake actuator.

Heretofore, a double-action type master cylinder shown in Figure 1 has been used as a device for supplying pressure liquid to a cylinder of a brake actuator. In the Figure 1, numeral 1 denotes a cylinder body 2, a supply chamber provided in a cylinder having a large diameter, 3 a pressure chmaber provided in a cylinder having a small diameter, 4 a primary piston operated by a brake pedal of a vehicle (not shown), 5 and 6 a large diameter portion and a small diameter portion of the primary piston 4, respectively, 10 a boss communicating with a reservoir (not shown) and 11 a relief valve.

The relief valve 11 is composed of an annular valve body 12, an orifice 13, a valve seat 134, a steel ball 15 operated as a valve, a coil spring 16 which always urges the steel ball 15 to close the valve, a cap 17 supporting the coil spring 16 and having a flow-way therein, a supply path 18, and a resilient seal member 19 which opens the supply path 18 when pressure in the supply chamber 2 is negative.

Numeral 20 denotes a supply port through which the supply chamber 2 communicates with a valve chamber 21, 22 a relief port, 23 a cup seal which is fitted into the small diameter portion 6 of the primary piston 4, and 24 a return spring.

The arrangement is such that the diameter of the cylinder for the supply chamber 2 is larger than that of the cylinder for the pressure chamber 3 as described above to supply a large amount of liquid at the beginning of operation. When the pressure in the supply chamber 2 becomes larger than a preset opening pressure as the primary piston 4 moves, the relief valve 11 opens so that the liquid flows out of the supply chamber 2 toward the reservoir, whereas when the pressure in the supply chamber 2 becomes lower than a preset supply pressure, the resilient seal member 19 opens so that the liquid is supplied from the reservoir through the supply path 18 to the supply chamber 2.

In the relief valve 11, the valve member i.e. the steel ball 15 is urged by means of the coil spring 16.

Accordingly, the characteristic of the spring is linear.

Furthermore, there is a limitation in structure and hence the spring constant is required to be large.

Consequently, the valve resonates and produces self-oscillation due to a jet stream of the liquid from the orifice in operation and produces a strange sound.

It is an object of the present invention in view of the above problem to provide a double-action type master cylinder which eliminates the drawback of the conventional relief valve mechanism and does not produce any strange sound.

The present invention consists in a double-action type master cylinder including a pressure chamber having a small diameter, a supply chamber having a large diameter, a relief valve for passing liquid from said supply chamber to a reservoir when pressure in said supply chamber exceeds an opening pressure and a supply valve for supplying liquid from said reservoir to said supply chamber when pressure in said supply chamber is lower than a supply pressure, the valve member of said relief valve being urged toward a valve seat of a valve body so that said relief valve closes an orifice provided between said reservoir and said supply chamber, wherein a liquid impounding portion is formed by said valve and said valve body downstream of said valve seat where said valve member of said relief valve is in contact with said valve seat and an outlet of said liquid impounding portion is formed by a small gap.

In the accompanying drawings: Figure 1 is a sectional view of a prior art doubleaction type master cylinder; Figure 2 is an enlarged partial sectional view of a relief valve of a double-action type master cylinder according to an embodiment of the present invention, and Figure 3 is a sectional view of a valve according to another embodiment of the present invention.

An embodiment of the present invention will now be described with reference to Figure 2 in which a relief valve 50 comprises a ball 51 and a plate 52 contacting the upper portion ofthe ball 51. Numeral 53 denotes a spring which always urges the valve 50 downward, 54 a valve body, 55 an orifice which communicates with the supply chamber, 56 a valve seat, 57 a liquid impounding portion formed between the valve body 54 and the ball 51 and the plate 52, and 58 an annular gap formed between the plate 52 and the valve body 54. A locating portion 59 for the spring is formed in the plate 52.

When a brake pedal is operated, the primary piston moves and the liquid pressure in the supply chamber increases. When the liquid pressure exceeds a preset opening pressure, the liquid in the supply chamberthrusts the ball 51 upwardly from the orifice 55 to move the ball 51 from the valve seat 56 so that the liquid flows into the liquid impounding portion 57. The liquid flowing into this portion 57 gradually flows out through the annular gap 58 formed between the valve body 54 and the plate 52 toward the reservoir.

The liquid flowing into the liquid impounding portion 57 by pushing the ball 51 upwardly temporarily remains in the liquid impounding portion 57 without flowing out directly toward the reservoir.

The valve 50 is thus maintained in the raised condition. Accordingly, since any variation in the pressure difference as in the prior art is not produced in the vicinity of the valve seat 56 where the valve 50 abuts against the valve seat 56, there is no room to generate energy for producing self-oscillation in synchronism with movement of the valve 50, and hence the valve does not oscillate and produce any strange sound.

Figure 3 shows another embodiment of the present invention, in which a part-spherical portion 61 corresponding to the ball 51 in the above embodiment and a plate-like portion 62 corresponding to the plate 52 in the above embodiment are united to form a relief valve 60.

As described above, according to the doubleaction type master cylinder of the present invention, since the relief valve is provided with the liquid impounding portion formed of the valve and the valve body downstream of the valve seat where the valve is in contact with the valve seat and an inet of the liquid impounding portion is formed of a portion of the valve seat where the valve is in contact with the valve seat, an outlet of the liquid impounding portion being formed by the small gap provided between the valve and the valve body, it is difficult to produce any variation in the pressure difference in the vicinity of the valve seat which is generate in synchronism with movement of the valve and is energy for the self-oscillation in the prior art, and hence occurrence of the strange sound is effectively prevented.

Claims

1. A double-action type master cylinder including a pressure chamber having a small diameter, a supply chamber having a large diameter, a relief valve for passing liquid from said supply chamber to a reservoir when pressure in said supply chamber exceeds an opening pressure and a supply valve for supplying liquid from said reservoirto said supply chamber when pressure in said supply chamber is lower than a supply pressure, the valve member of said relief valve being urged toward a valve seat of a valve body so that said relief valve closes an orifice provided between said reservoir and said supply chamber, wherein a liquid impounding portion is formed by said valve and said valve body downstream of said valve seat where said valve member of said relief valve is in contact with said valve seat and an outlet of said liquid impounding portion is formed by a small gap.

2. A double-action type master cylinder according to claim 1, wherein said valve member of said relief valve is formed of a ball abutting said valve seat of said valve body and a plate which is urged to press against said ball.

3. A double-action type master cylinder according to claim 1, wherein said valve member of said relief valve is formed buy a part-spherical portion abutting said valve seat of valve body and a plate-like portion which is urged to press against said part-spherical portion, said latter portion and said plate-like portion being integrally formed.

4. A double-action type master cylinder substantially as hereinbefore described with reference to the accompanying drawings of Figures 2 and 3.