GB2147962A

GB2147962A - A hydraulic brake system of a wheeled motor vehicle

Info

Publication number: GB2147962A
Application number: GB08237021A
Authority: GB
Inventors: Yoshio Otsuka; Tomohiro Ishihara
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1982-12-30
Filing date: 1982-12-31
Publication date: 1985-05-22
Also published as: DE3248651A1

Abstract

In a hydraulic brake system including a master cylinder (10), a brake cylinder (14a, 14b, 14c and 14d) of each road wheel, and piping (16) connecting the master cylinder (10) with the brake cylinders, there is disposed a restrictor member (18a, 18b, 18c and 18d) in the piping (16) to dampen the brake fluid flow through the piping. The restrictor may be disposed in a brake cylinder (Fig. 4, not shown). <IMAGE>

Description

SPECIFICATION A hydraulic brake system of a wheeled motor vehicle The present invention relates to a hydraulic brake system of a wheeled motor vehicle, and more particularly to an improved hydraulic brake system which can eliminate or at least lessen the "brake judder" and "skid" phenomena.

According to the present invention, there is provided a hydraulic brake system of a wheeled motor vehicle, which comprises a master cylinder for producing a hydraulic pressure when operated, a brake cylinder for braking a road wheel when a hydraulic pressure is applied thereto, piping connecting the master cylinder with the brake cylinder, and a restrictor member disposed in the piping for damping the brake fluid flow through the piping.

Objects and advantages of the present invention will be come clear from the following description when taken in conjunction with the accompanying drawings, in which: Figure 1 is a schematic drawing of a conventional hydraulic brake system; Figure 2 is a drawing similar to Fig. 1, but showing an embodiment of the present invention; Figure 3 is a sectional view of a restrictor member which is employed in the system of Fig. 2; and Figure 4 is a sectional view of a wheel brake cylinder equipped with a restrictor member, showing a part of a hydraulic brake system of a second embodiment of the present invention.

Prior to describing the invention, a conventional hydraulic brake system will be outlined with reference to Fig. 1 in order to clarify the invention.

Referring to Fig. 1, there is shown the conventional hydraulic brake system which is applied to a four wheel-motor vehicle. The system comprises a master cylinder 10 actuated by a brake pedal 12, brake cylinders 1 4a and 1 4b for front road wheels, brake cylinders 1 4c and 1 4d for rear road wheels, and piping 1 6 connecting the master cylinder 10 with the brake cylinders 14a, 14b, 1 4c and 14d.

When, in operation, the brake pedal 1 2 is depressed, it moves a piston 1 0a within the master cylinder 10, forcing hydraulic fluid throughout the piping 1 6 and into the brake cylinders 14a, 14b, 1 4c and 14d of each wheel. It causes pistons (no numerals) of the brake cylinders 14a, 14b, 1 4c and 14d to move which, in turn, forces the brake shoes (or brake pads in the case of disc brake) against the brake drums (or discs) to retard the movement.

However, this type of brake system has suffered from the drawback that as the brake drums (or discs) are not perfectly circular (or flat) and/or the brake linings (or pads) provided on the shoes (or callipers) are inevitably not perfectly smooth, upon application of the brakes, the brake shoes (or discs) tend to vibrate producing a pulsation which is transmitted back through the brake fluid to the master cylinder whereat this vibrational energy is transmitted to the vehicle body (via the brake pedal for example) to produce an annoying vibration or noise. (This phenomenon is called "brake judder").

Furthermore, this type brake system tends to induce the dangerous skid phenomenon in that upon rapid application of the brakes, the rear wheels lock under such hard braking.

This is because the excessively high brake pressure generated upon such hard braking is directly applied to the rear wheel brake cylinders 1 4c and 1 4d irrespective of the reduction in the effective weight applied on the rear wheels. Although this drawback may be solved by providing the system with an antilock device (such as a proportioning valve, a limiting valve or the like), this measure causes increased cost of the system.

It is thus an essential object of the present invention to provide an improved and economical hydraulic brake system which is free of the above-mentioned drawbacks.

Referring to Fig. 2, there is shown a first embodiment of the present invention. In the drawing, the same parts as those of the conventional hydraulic brake system of Fig. 1 are designated by the same numerals. According to this embodiment, four restrictor members 18a, 18b, 1 8c and 1 8d are respectively disposed in the pipes 16a, 1 6b, 1 6c and 1 6d of the piping 1 6 which lead to the respective wheel brake cylinders 14a, 14b, 14c and 14d. As is clearly shown in Fig. 3, each restrictor member 1 8 (that is, 18a, 18b, 1 8c or 18d) has a straight passage 20 formed therethrough.The passage 20 consists of two larger bore sections 20a positioned at opposed ends of the passage 20, two medium bore sections 20b positioned inside of the larger bore sections 20a, and a smaller bore section 20c positioned between the medium bore section 20b. In assembly, connectors 22 are used which are screwed into the larger bore sections 20a. Each medium bore section 20b has throughout the length there of a uniform cross section which is identical to that of the passage of the pipe 16. The smaller bore section 20c of the passage 20 has throughout the length thereof a uniform cross section which is smaller than that of the medium bore section 20b, and thus acts as a restrictor proper.Experiments have revealed that when the inner diameter of the pipe 1 6 is within a range from about 3 mm to about 3.5 mm, employing a restrictor, having a diameter (d) of about 0.6 mm to about 0.8 mm produces desired results.

When, in operation, the brake pedal 1 2 is rapidly depressed for achieving hard braking, excessively high brake pressure is generated by the master cylinder 10 and is directed toward the brake cylinders 14a, 14b, 1 4c and 1 4d of the road wheels. During this brake application, the brake fluid directed to each brake cylinder is subjected to flow restriction by the bore section 20c delaying the time when the pressure actually applied to the brake cylinder reaches the pressure applied to the piping 1 6 upstream of the bore section 20c.During this so-called "time delay", the driver can moderate the depression of the brake pedal 1 2. With this braking operation, the brake cylinder of each wheel is prevented from being applied with such an excessively high pressure which would cause locking of the road wheels. Thus, the dangerous skid phenomenon does not occur, or at least lessens.

Furthermore, the undersirable pulsation caused by the aforementioned matters is damped by the smaller bore section 20c, thus eliminating or at least lessening the brake judder phenomenon.

Referring to Fig. 4, there is shown, but partially, a second embodiment of the present invention. In this second embodiment, the means corresponding to the restrictor member 1 8 of the first embodiment is provided by a connecting tube 24 which is fixed in a fluid passage 1 4e of the brake cylinder 14, holding an end of the pipe 1 6. As shown, the passage of the connecting tube 24 has throughout the length thereof a uniform cross section (d) which is smaller than that of the inner diameter of the pipe 1 6. Designated by reference 1 4f is an air bleeder of the brake cylinder 14.

In this second embodiment, substantially the same advantageous functions as those in the first embodiment are achieved.

Claims

1. A hydraulic brake system of a wheeled motor vehicle, comprising: a master cylinder for producing a hydraulic pressure when operated; a brake cylinder for braking a road wheel when a hydraulic pressure is applied thereto; piping connecting said master cylinder with said brake cylinder; and a restrictor member disposed in said piping for damping the brake fluid flow through said piping.

2. A hydraulic brake system as claimed in claim 1, in which a portion of the passage in said restrictor member has throughout the length thereof a uniform cross section which is smaller than that of the inner diameter of said piping.

3. A hydraulic brake system as claimed in claim 2, in which the inner diameter of the passage portion of the restrictor member is within a range from approximately 0.6 mm to approximately 0.8 mm.

4. A hydraulic brake system as claimed in claim 3, in which the inner diameter of said piping is within a range from approximately 3 mm to 3.5 mm.

5. A hydraulic brake system as claimed in claim 4, in which said restrictor member is a connecting tube which is tightly disposed in a fluid passage formed in said brake cylinder.

6. A hydraulic brake system substantially as disclosed in the specification with reference to Figs. 2 and 3, and Fig. 4 of the accompanying drawings.