GB2188712A - Vehicle parking brakes - Google Patents

Abstract

An operation mechanism for a parking brake pedal rotatably mounted on a stationary structure in a vehicle compartment comprises a cylinder type air damper interposed between the structure and the pedal to dampen the return of the pedal from its depressed position. The air damper includes a cylinder body 41, a piston 43 axially slidably disposed within the cylinder body to internally subdivide the cylinder body into front and rear air chambers R1, R2, a piston rod 42 having one end integral with the piston and extending outwardly from the cylinder body through the rear air chamber in an air-tight manner, and a throttle element 46 disposed in the piston for permitting therethrough a flow of air between the air chambers. The piston 43 is integrally formed with an annular projection 46a which is arranged in surrounding relationship with the throttle element 46 in the front air chamber. The annular projection of the piston acts as a separator for a lubricant for sealing the piston. <IMAGE>

Description

SPECIFICATION Vehicle parking brakes The invention relates to parking brakes for wheeled vehicles, that is to say to an operation mechanism for a parking brake pedal, a lock for the pedal in its depressed position, and a release mechanism.

Such a conventional operation mechanism has been proposed in Japanese Utility Model Early Publication No. 54-11443, wherein an oil damper is provided for the impact caused by the return movement of the pedal. Use for a long period of time leads to oil leakage caused by wear or the fatigue of seal members, and results in oil stains in the vehicle compartment. In manufacture, it is necessary to form a one-way valve or an orifice in the damper piston in a precise manner, and this results in an increase in cost.

To solve such problems as described above, an operation mechanism for a parking brake pedal has been proposed in a copending UK Patent Application No. 8607562 (GB 2175375A) in our name, which operation mechanism comprises a lock and a release mechanism as above, and a damper cylinder for the return of the pedal from the depressed position. In use, lubricant such as grease is applied between the cylinder and a piston slidable therein. However, the lubricant tends to adhere to an end surface of the piston and so to penetrate and impede the throttle element.

This causes trouble in operation of the air damper.

According to the present invention the piston is formed with an annular projection surrounding the throttle for preventing penetration by lubricant. The projection also acts a separator for the lubricant for sealing the piston.

Preferably, the annular projection has at its outer end a radial annular flange to help prevent the lubricant from passing the projection.

An annular cup seal is preferably disposed in an annular groove in the outer periphery of the piston for storage of lubricant and sealing the piston. The annular cup seal is arranged to permit the flow of air on depression of the pedal and to block the flow of air on return of the pedal. The throttle may comprise an element of porous sintered metal in an end bore in the piston.

The mechanism of the invention can be free of oil which might leak and stain, and is comparatively inexpensive to manufacture to an appropriate standard. The annular projection of the piston is useful to prevent adherence of the lubricant to the throttle during an assembly of the air damper, and to protect the throttle from abutment against an end wall of the cylinder on excessive forward movement of the piston.

Drawings: Figure 1 is a side view of an operation mechanism in accordance with the invention; Figure 2 is a rear view of the mechanism in Figure 1; Figure 3 is a longitudinal section of a cylinder type air damper in Figures 1 and 2; Figure 4 is an enlarged sectional view of a damper piston in Figure 3; Figure 5 illustrates a modification of the damper piston in Figure 3; and Figure 6 illustrates a piston in the mechanism in our earlier Uk Patent Application mentioned above showing the adherence of grease to an end of the piston.

In the Figures 1 and 2, a foot pedal 10, a locking mechanism 20, a release mechanism 30, and a cylinder type air damper 40 are shown. The foot pedal 10 is arranged to operate a parking brake (not shown) of a wheeled vehicle. The foot pedal 10 has an arm 11 which is formed at its upper end with a sector gear 12 and provided at its lower end with a pedal 13. The foot pedal arm 11 is placed between a stationary base plate 51 secured to a body structure of the vehicle and an attachment plate 52 secured in parallel to the stationary base plate 51. Thus, the foot pedal arm 11 is rotatably mounted on a stepped lateral bolt 14 which is threaded into the attachment plate 52 through the stationary base plate 51 and fastened by a nut.The foot pedal arm 11 has a front end portion operatively connected to the parking brake by means of a parking brake cable 60 and is biased counterclockwise by means of a return spring (not shown) assembled within the parking brake. When the foot pedal 10 is in a released position, the foot pedal arm 11 is in engagement with a rubber stopper 59 which is fixed to a rear portion of the stationary base plate 51. When the pedal 13 is depressed, the foot pedal arm 11 rotates clockwise about the lateral bolt 14 to operate the parking brake through the brake cable 60.

A normally closed switch 58 is arranged adjacent the rubber stopper 59 and fixed to the stationary base plate 51 to be opened by engagement with the foot pedal arm 11.

The locking mechanism 20 includes a latch member 21 which is formed at its one end with a pawl 21a engageable with the sector gear 12 of foot pedal arm 11. The latch member 21 is placed between the stationary base plate 51 and the attachment plate 52 and rotatably mounted on a lateral support pin 23 fastened to the stationary base plate 51 through an upper portion of attachment plate 52. A tension spring 22 is fixed at its one end to an outer peripheral flange 51a of stationary base plate 51 and connected at its other end to another end of latch member 21 to bias the latch member 21 clockwise. When the foot pedal 10 is in the released position, the pawl 21a of latch member 21 is resiliently engaged with a non-toothed upper end of foot pedal arm 11 under load of the tension spring 22.When the foot pedal 10 is depressed to cause clockwise rotation of the sector gear 12, the pawl 21a of latch member 21 is brought into engagement with a portion of the sector gear 12 to lock the foot pedal 10 in its depressed position.

The release mechanism 30 is arranged to release the foot pedal 10 from its locked position. The release mechanism 30 includes a release lever 31, a release cable 32, a compression coil spring 33, a release knob 34 and a release stopper 35. The release lever 31 is placed at the outside of attachment plate 52 and rotatably mounted at its upper end on a lateral support pin 36 fastened to the stationary base plate 51 through the attachment plate 52. The release lever 31 has an arm 31a engageable with the latch member 21. The compression coil spring 33 is anchored at its one end to the attachment plate 52 and engaged at its other end with the lower end of release lever 31 to bias the release lever 31 clockwise.The release lever 31 is further connected at its lower end to the release knob 34 by means of the release cable 32, and the release knob 34 is supported in place by means of the release stopper 35 which is fixedly mounted on a stationary structure in the vehicle compartment.

When the release knob 34 is retained by the release stopper 35 in its inoperative position, the arm 31a of release lever 31 is separated from the latch member 21 under load of the compression coil spring 33. When the release knob 34 is pulled by the driver to cause counterclockwise rotation of the release lever 31 against the compression coil spring 33, the latch member 21 is rotated counterclockwise by engagement with the arm 31a of release lever 31 to disengage the pawl 21a of latch member 21 from the sector gear 12 of foot pedal arm 11.

As shown in Figs, 1 and 2, the cylinder type air damper 40 is interposed between the foot pedal arm 11 and a bracket 53 secured to a front end portion of the outer peripheral flange 51 a of stationary base plate 51. As shown in Fig. 3, the air damper 40 comprises a cylinder body 41, a piston rod 42 integrally provided with a piston 43, and a closure member 44. The cylinder body 41 has a closed end 41a pivoted to a lateral stepped bolt 54 fixed to the bracket 53 by means of a nut 55 fastened thereto, while the piston rod 42 is provided at its outer end with an end fitting 42a which is pivoted to a lateral stepped bolt 56 secured to an intermediate portion of foot pedal arm 11 by means of a nut 57 fastened thereto.The piston 43 is axially slidably disposed within the cylinder body 41 through an annular cup seal 45 to subdivide the interior of cylinder body 41 into front and rear air chambers R, and R2. The annular cup seal 45 is disposed within an annular groove 43a which is formed in the outer periphery of piston 43 to store therein lubricant such as grease for sealing the piston 43. The piston 43 is formed therein with a passage H for communication between the front and rear air chambers R, and R2 and is further formed therein with an end bore Ha in communication with the passage H.An interchangeable throttle element 46 made of porous material such as porous sintered metal is fixedly coupled within the end bore Ha of piston 43 and arranged in the front air chamber R1 to permit therethrough a flow of air between the air chambers R, and R2 thereby to cause a pneumatic resistance acting on the piston 43. The closure member 44 is disposed within an opening end portion of the cylinder body 41 through an O-ring 47A and fixed in place by means of a pair of axially spaced annular retainers 48A and 48B. The closure member 44 is provided at its inner periphery with an Oring 47B through which the piston rod 42 extends outwardly.

In the cylinder type air damper 40, it is to be noted that as shown clearly in Fig. 4, the damper piston 43 is integrally formed with an annular projection 46a which is arranged in surrounding relationship with the throttle element 46 within the front air chamber R,. The annular projection 46a of piston 43 acts as a separator for preventing the lubricant from penetrating into the throttle element 46. Preferably, as shown in Fig. 5, the annular projection 46a of piston 43 is formed at its outer end with a radial annular flange 46b for preventing the lubricant from penetrating into the annular projection 46a.

In depression of the foot pedal 10, the parking brake cable 60 is pulled by the foot pedal arm 11 to operate the parking brake, and subsequently the locking mechanism 20 acts to lock the foot pedal 10 in its depressed position. In this instance, the piston rod 42 and piston 43 are moved forwards by depression of the foot pedal 10 to compress the air in the front air chamber R, and to expand the rear air chamber R2. During such forward movement of the piston rod 42 and piston 43, the throttle element 46 acts to permit the flow of air passing through the passage H from the front air chamber R1 into the rear air chamber R2, and simultaneously the annular cup seal 45 acts to permit the flow of air passing therethrough from the front air chamber R1 into the rear air chamber R2. Additionally, the pressure in the front air chamber R1 does not increase because of a sufficient capacity of the front air chamber R,. Thus, the foot pedal 10 is smoothly depressed without any resistance acting thereon.

When the release knob 34 is pulled by the driver to rotate the release lever 31 counterclockwise against the compression coil spring 33, the latch member 21 is rotated counterclockwise by engagement with the arm 31a of release lever 31 to release lock of the foot pedal 10, and subsequently the foot pedal 10 is returned to the release position under load of the return spring of the parking brake. In this instance, the piston rod 42 and piston 43 are moved backwards under the load of the return spring to compress the air in the rear air chamber R2 and to expand the front air chamber R,.During such backward movement of the piston rod 42 and piston 43, the annular cup seal 45 acts to block the flow of air from the rear air chamber R2 into the front air chamber R1, and the throttle element 46 acts to throttle the flow of air passing therethrough from the rear air chamber R2 into the front air chamber R, across the passage H. Thus, the pneumatic resistance acting on the piston 43 increases up to a maximum value in accordance with approach of the piston 43 to its backward stroke end to retard the backward movement of foot pedal 10 thereby to reduce an impact acting on the rubber stopper 59 caused by abutment against the foot pedal 10.

In the operation mechanism described above, it is to be noted that the cylinder type air damper 40 is adapted as a damper for the foot pedal 10 to avoid problems such as stain of the vehicle compartment caused by oil leakage in use of a conventional cylinder type oil damper. Even if the sealing function of O-rings 47A and 47B is decreased by use for a long period of time, only the dampening function of the air damper will be slightly decreased without causing any other problems. In the air damper 40, the throttle element 46 is disposed within the end bore Ha of piston 43 for communication between the air chambers R, and R2. For this reason, it is not necessary to form a conventional orifice in the piston in a precise manner or to provide a conventional one-way valve in the piston.It is, therefore, able to simplify the construction of the air damper so as to reduce the manufacturing cost. In addition, the dampening function of the air damper 40 can be adjusted in a simple manner by replacement of the throttle element 46 with another throttle element having a different throttle property.

Furthermore, in operation of the air damper 40, the annular projection 46a of piston 43 is useful to prevent the lubricant from penetrating into the throttle element 46 and is also useful to prevent adherence of the lubricant to the throttle element 46 during an assembly process of the air damper. Additionally, the annular projection 46a of piston 43 is useful to protect the throttle element from abutment against an internal end wall of the cylinder body 41 in excessive forward movement of the piston 43.

Although in the above embodiment and modification, the annular cup seal 45 has been adapted to the piston 43, it may be replaced with an O-ring. In such a case, it is desirable that the throttle element 46 is selected in consideration with a pneumatic resistance acting on the piston 43 in depression of the foot pedal 10. Furthermore, the front air chamber R, in the cylinder body 41 may be communicated with the atmospheric air to reduce the resistance acting on the piston 43 in depression of the foot pedal 10. In such a case, it is desirable that an air filter is provided to prevent entry of dust into the front air chamber R,.

Claims (6)

1. An operation mechanism for a parking brake pedal of a wheeled vehicle comprising a lock for the pedal in a depressed position, a release mechanism for the lock, a damper for the return of the pedal from the depressed position, the damper being in the form of a cylinder with a piston slidable in the cylinder and a throttle for permitting a flow of air through the piston, the piston being formed with an annular projection surrounding the throttle for preventing penetration by lubricant.

2. An operation mechanism as claimed in claim 1 in which the annular projection has at its outer end a radial annular flange.

3. An operation mechanism as claimed in claim 1 or claim 2 comprising an annular cup seal in an annular groove in the outer periphery of the damper piston for storage of lubricant, the annular cup seal being arranged to permit the flow of air on depression of the pedal and to block the flow of air on return of the pedal.

4. An operation mechanism as claimed in any preceding claim in which the throttle comprises an element of porous sintered metal in an end bore in the piston.

5. An operation mechanism for a parking brake pedal substantially as herein described with reference to Figures 1 to 4 of the drawings.

6. An operation mechanism according to claim 5 as modified by Figure 5 of the drawings.