GB2196416A

GB2196416A - Handbrake lever mechanism for automobiles

Info

Publication number: GB2196416A
Application number: GB08625387A
Authority: GB
Inventors: Frank Christopher Price; David Geoffrey Fairburn
Original assignee: REARSBY AUTOMOTIVE Ltd
Current assignee: REARSBY AUTOMOTIVE Ltd
Priority date: 1986-10-23
Filing date: 1986-10-23
Publication date: 1988-04-27
Anticipated expiration: 2006-10-23
Also published as: GB2196416B; GB8625387D0

Abstract

A handbrake lever mechanism for an automobile comprises a handbrake lever 10 which is formed from sheet metal bent into a generally U-shaped section, a rearward portion 10b of that U-shape enclosing a pivotal mounting for the handbrake lever. Also enclosed within the portion 10b is a mechanism comprising a pair of plates 28 pivotally mounted at 32 which support a cam follower 38, so that the initial few degrees of movement of the handbrake lever 10 result in an appreciable movement of a cable connector 36 mounted between the plates 28 by pivot pin 32. Continued movement of the handbrake lever results in a much higher mechanical advantage. The initial movement takes up the slack in the handbrake cable, whereas continued movement is effective to apply the brakes. The shape of the cam track 40 formed in the mounting 12 can be altered at will to provide the optimum characteristic for the handbrake lever mechanism, which has no unsightly surface-mounted parts or cable anchorages. In an alternative embodiment (Fig. 5, not shown) the cam track (50) is formed in each of the plates 28 and the cam follower (46) is mounted on the handbrake lever 10 between opposite sides of the U-shaped mounting portion 10b. <IMAGE>

Description

SPECIFICATION Handbrake lever mechanism for automobiles Field of the Invention The invention relates to handbrake levers for automobiles, and in particular to such levers designed to provide a variable mechanical advantage over the range of lever movement.

Background Art A handbrake lever in a modern motor vehicle has an acceptable feel to the user if it has a short range of movement between fully 'off" and fully "on". Ideally the brake should be actuated and held firmly engaged after only a very few "clicks" of the pawl-and-ratchet detent mechanism.

Against this desideratum there must be set the requirement, in a self-adjusting cable brake system, for the cable to go slack when the brakes are released. Different cable adjustment mechanisms have different amounts of slack, but 7 mm of slack is not unusual. This slack must be taken up before the brake can be applied, and there is therefore a design constraint on handbrake lever designers, encouraging low ratio levers. A low ratio lever is one that results in more millimetres of cable pull for a given angle of lever actuation than a higher ratio lever. Also, it is common for ratchet teeth to be omitted from the lower part of the handbrake quadrant of the pawland-ratchet detent mechanism so that the handbrake lever traverses one quarter or more of its maximum travel before the first "click" is heard.

An opposing design constraint exists when disc brakes are fitted to the rear wheels and are actuated by the handbrake cable. Disc brakes require a higher operating force than drum brakes, and it is desirable for the handbrake lever to have a high ratio, to give a greater mechanical advantage, and a smaller increment of cable pull per ratchet tooth so that the higher operating force can be maintained.

It has been proposed to overcome the conflict between these opposing design constraints by arranging for the mechanical advantage of the handbrake lever to vary over its range of movement. Thus initial movement is at a lower ratio than later movement. This has been achieved by mounting an eccentric cable guide on the handbrake lever, and drawing the cable around the guide to an anchorage point on the lever. The eccentricity is such that, as the lever is rotated, the distance between the pivotal axis of the lever and the point at which the cable leaves the guide tangentially for the brakes varies, with a resulting variation in the mechanical advantage or lever ratio.

Generally speaking, the change in the ratio as the lever is operated varies through the whole of the lever movement, with a cable pull per increment of angular movement being typically from 30% to 80% more at the start of the lever movement than at the end of the permitted range of lever movement.

Disadvantages of the above proposal are that an unsightly cable holder has to be mounted on the handbrake lever, and must be shrouded or covered; the change of ratio is limited and is distributed over all or a significant proportion of the lever movement; and the line of cable pull changes as the lever is operated. Despite these disadvantages, and despite the cost of the proposal this mechanism is in current production and fitted as original equipment on some motor cars.

An alternative solution to the same problem, not aimed at the original equipment market, is described in DE OS 2714432. A saddleshaped cable anchorage unit is secured to a portion of the handbrake lever between the pivot and the handgrip, and carries a prim-ary lever one end of which anchors the ends of a pair of cables and the other end of which is a tail which engages and is actuated by the untoothed portion of the handbrake quadrant of the pawl-and-ratchet detent mechanism. Advantages of the mechanism are that the change of mechanical advantage, from low ratio to higher ratio, is confined to the first few degrees of lever movement, with a constant ratio thereafter; and that a greater proportional increase in the mechanical advantage is obtainable than with the eccentric cable guide discussed above.Disadvantages are an excessive and intolerable bulkiness of the saddle carried on the handbrake lever well forwardly of its pivot, needing excessive shrouding; a dramatic change in the line of cable pull particularly over the first few degrees of lever movement; and the carrying of an equalizer bar 3 (to equalize the tensions in the two cables) on the handbrake lever itself. Normally such equalizer bars are out of sight beneath the vehicle floor.

A desirable handbrake lever would have the change in ratio considerably higher than either of the above proposals and readily variable to match the optimum amount of slack required by the brake adjuster with which it is to be used. It would provide a constant or reasonably constant line or direction of pull during the whole of its range of movement. It would be slim, not adding appreciably to the overall width of the original handbrake lever and not requiring costly and unsightly shrouding. And finally it would be inexpensive as compared with the solutions to the problem discussed above.

Disclosure of the Invention The invention provides a handbrake lever mechanism for an automobile, comprising a handbrake lever formed from sheet metal with a generally U-shaped section mounting portion pivotally secured to a mounting with a detent pawl carried by the lever within the U-shaped section being engageable with ratchet teeth on a quadrant portion of the mounting, and cam plate means mounted within the U-shaped section mounting portion and having cam and pivot means thereon, cooperating with different ones of the handbrake lever and mounting, and also having a cable anchorage thereon, arranged on generally the opposite side of the pivotal axis of the lever to the said pivot means.

The cam plate means may comprise one or two cam plates. Preferably two cam plates are used, one on each side of the mounting and connected together to move only in unison.

The cable anchorage may then be mounted between the two cam plates. Even when two such cam plates are used, the assembly of cam plate means and cable anchorage is according to the invention mounted within the U-shaped section rear mounting portion of the handbrake lever which need be made only fractionally wider to accommodate the extra components. The need for additional shrouding to shield and hide surface componentsmounted on the outside of the handbrake lever is thereby avoided.

If the pivot means on the cam plate means cooperates with, and establishes a pivotal connection of the cam plate means on, the handbrake lever itself, then the cam means is preferably a cam follower cooperating with a cam track in the mounting. The cam track preferably has a short initial section of steep cam slope, to cause relatively rapid pivotal movement of the cam plate -means relative to the handbrake lever during the initial few degrees of lever movement; followed by a continuation section of less steep cam slope, or zero cam gradient, or even a reverse cam gradient, to cause less rapid pivotal movement of the cam plate means relative to the handbrake lever, or no such relative pivotal movement, or even slight reverse relative pivotal movement during continued lever movement.If there is no relative pivotal movement between the cam plate means and the handbrake lever during this continued lever movement then the handbrake lever and cam plate means move as one, with all of the mechanical advantage being supplied by the spacing of the cable anchorage and pivotal axis of the handbrake lever. If a small reverse pivotal movement is provided for by the shape of the cam track, then an enhanced mechanical advantage can be provided over some or all of the range of continued lever movement.

If the pivot means on the cam plate means cooperates with, and establishes a pivotal connection of the cam plate means on, the mounting, then the cam means is preferably a cam track in the cam plate means cooperating with a cam follower on the handbrake lever.

The same criteria govern the shape of the cam track as have been discussed above.

The relative disposition of the cable anchorage and the pivot means on opposite sides of the pivotal axis of the handbrake lever ensures that the line of pull on the cable is substantially constant over the whole range of lever movement. Absolute linearity of the direction of pull can be obtained according to the invention by causing the cable anchorage to run in a straight guide track provided by or mounted on the mounting, and by providing a floating connection between the cam plate means and the pivot means or the cable anchorage, to accommodate the constraint to absolute linearity of direction of pull.

All of the above advantageous design features can be obtained according to the invention with components that are housed within, and shrouded by, a handbrake lever which has a mounting portion of a U-shaped section only marginally wider than that of conventional handbrakes. The avoidance of surfacemounted components and cable anchorages is of tremendous commercial advantage, and the flexibility of design is such that a mechanical advantage after the first two notches of a continuous evenly toothed ratchet quadrant can easily be 400% of that during the first two notches.To the driver, that means that all of the slack in a brake cable can be taken up in a very short initial movement of the lever, accompanied by one or at most two "clicks", whereupon further lever movement provides a constant and increased mechanical effort that can be precisely tailored to suit the brake characteristics of the vehicle.

Drawings: Figure 1 is a side elevation of a handbrake lever mechanism according to this invention; Figure 2 is the same side elevation as Figure 1, with part of the handbrake lever shown cut away to illustrate the mechanism shrouded therein; Figure 3 is a partial section taken along the line Ill-Ill of Figure 1; Figure 4 is a detail from Figure 3, showing the range of movement of the three linkage points of the cam plate during brake actuation; Figure 5 is a partly cut away view similar to that of Figure 2, through an alternative embodiment of the invention; Figure 6 is a cut away view similar to that of Figure 2 through a modification of the handbrake lever assembly of Figures 1 to 4; and Figure 7 is a cut away view similar to that of Figure 2 through a further modification of the handbrake lever assembly of Figures 1 to 4.

Best Modes for Carrying out the Invention Referring first to Figures 1 to 3, the handbrake- lever mechanism of the invention comprises handbrake lever 10 pivotally mounted on a mounting 12 which in use is bolted se curely to the floor of the vehicle. The hand brake lever 10 is formed as a pressing from sheet steel, a forward portion 10a being formed into a substantially closed housing for a pawl release mechanism (to be described below), and a rearward portion 10b being a mounting portion of generally U-shaped section. The pivotal mounting of the handbrake lever 10 comprises a pivot pin 14 fast to opposite sides of the U-shaped mounting portion 10b and passing through a pivot hole formed in the mounting 12.

At the extreme forward end of the hand brake lever 10 there is a moulded hand grip 16 provided with a conventional release button 18 depression of which actuates a push rod 20 (Figures 2 and 4) which releases a pawl 22 from the ratchet teeth 24 of a quadrant portion 26 of the mounting 12. The re lease button 18, push rod 20, pawl 22 and ratchet teeth 24 together make up a conventional brake release mechanism, the significant feature of that illustrated in Figures 1-to 3 being that the ratchet teeth 24 extend over the full arcuate length of the quadrant portion 26. In conventional release mechanisms there is a lower portion of the quadrant which is without ratchet teeth, so that initial movement of the handbrake lever to take up slack in the brake cable is not accompanied by the clicking of the pawl in the ratchet teeth.

It will be seen from Figure 3 that the generally U-shaped rear mounting portion 10b of the handbrake lever 10 is made marginally wider than the forward portion 10a. This change in width is to accommodate a pair of cam plates 28 mounted one on each side of the mounting 12, but both contained within the U-shaped mounting portion 10b. The shape of each cam plate 28 is clearly illustrated in Figures 2 to 4. Each has an aperture 30 formed therein, of a size and position such that the cam plate can move freely without fouling the pivot pin 14.

The cam plates 28 are pivotally mounted at 32 on the handbrake lever 10. The pivotal mounting 32 is located generally directly above the pivot pin 14. On the opposite side of the pivot pin 14, that is generally directly below the pivot pin, a connecting pin 34 connects together the two can plates 28 and supports a cable connector 36. Forwardly of the pivot pin 14 the cam plates 28 support a cam follower 38 which is a roller rotatably mounted on a shaft which extends between the two cam plates. The cam follower 38 moves in a cam track 40 formed in the mounting 12 immediately behind the ratchet teeth 24 of the quadrant portion 26.

The shape of the cam track 40 is such that during the first few degrees of movement of the handbrake lever 10 the cam follower 38 rides up a steeply inclined portion 42, causing a rapid rotation of the cam plates 28 about their pivotal mounting 32 in the clockwise sense as viewed in Figures 2 and 4. The remainder of the cam track 40 is generally arcuate about the pivot pin 14, so that there is no further camming of the cam plates 28. It should be appreciated, however, that the shape of the cam track 40 can be chosen at the discretion of the designer, e.g. to continue the same cam action resulting in continued clockwise pivotal movement of the cam plates 28 about their pivotal mounting 32, but at a lesser rate.Alternatively the inclination of the upper portion of the cam track 40 could be such that the initial clockwise rotation of the cam plates 28 about their pivotal mounting 32 is replaced by a small anticlockwise relative rotation, thereby producing a greater mechanical advantage as the handbrake is tightened.

Figure 4 illustrates very clearly the practical results of the cam track shape illustrated in Figures 2 and 4. As the handbrake lever 10 is raised, so the pivotal mounting 32 moves successively through positions 32a, 32b, 32c and 32d. This is accompanied by a corresponding movement of the cam follower 38 throught positions 38a to 38b, and corresponding movement of the connecting pin 34 through positions 34a to 34d. It will be seen that an initial very small movement of the handbrake lever results in sufficient movement of the connecting pin 34 and cable connector 36 to take up all the slack in the handbrake cable, with continued movement of the handbrake lever resulting in brake actuation with a much higher mechanical advantage.

Figure 5 shows a further embodiment of a handbrake lever mechanism according to the invention, in which parts similar in design and function to those of the preceding embodiment have been identified with the same reference numerals. In Figure 5, the cam plates 28 are pivotally mounted at 44 on the mounting 12 rather than on the handbrake lever 10, and a. -cam follower 46 is mounted on the handbrake lever 10 between opposite sides of the U-shaped mounting portion 10b. The cam follower 46 is freely movable in an arcuate recess 48 formed in the mounting 12 immediately behind the ratchet teeth 24, and cooperates with a cam track 50 formed in each of the cam plates 28.

The function of the embodiment of Figure 5 is exactly the same as that of the first embodiment described. The initial few degrees of movement of the handbrake lever 10 results in movement of the cam follower 46 along a steeply inclined portion 52 of the cam track 50, resulting in a relatively rapid rotation of the cam plates 28 about their pivotal mounting 44. Continued handbrake movement is accompanied by a much more gradual rotation of the cam plates 28, resulting in a much higher mechanical advantage of the handbrake mechanism.

In both embodiments described so far, the line of movement of the cable connector 36 is a generally arcuate line as best seen from the four illustrated positions of the connecting pin 34 shown in Figure 4. The radius of the arcuate movement in the embodiment of Figure 5 is greater than that of Figure 4, resulting in a line of movement that morely closely approximates straight linear movement. The modifications of Figure 6 and Figure 7 can be adopted to constrain the movement of the cable connector 36 to a precise straight linear movement along the line 54. In each modification, a further cam track 56 is formed in a portion of the mounting 12 which is bent out of the plane of the cam plates 28. The connecting pin 34 mounting the cable connector 36 is formed with a cam follower tail portion which extends beyond the cam plates 28 and into the cam track 56.A lost motion connection 58 between the connecting pin 34 and the cam plates 28 (Figure 6) or a lost motion connection 60 between the pivotal mounting 32 and the cam plates 28 (Figure 7) permits the cam track 56 to constrain the movement of the cable connector 36 to the line 54. Each lost motion connection comprises a pair of elongated holes in the cam plates 28 permitting a limited amount of longitudinal movement of the appropriate pin- therein as the cam plates rotate. This construction is particularly suitable for situations in which the cable connector 36 mounts a rod which passes through bushings in the vehicle floor to an equalizer for a pair of brake cables.

In each of the embodiments illustrated, the entire mechanism is readily contained within the rear U-shaped mounting portion 10b of the handbrake lever 10, which gives the mechanism the maximum strength coupled with the maximum possible neatness.

Claims

1. A handbrake lever mechanism for an automobile, comprising a handbrake lever formed from sheet metal with a generally U-shaped section mounting portion pivotally secured to a mounting with a detent pawl carried by the lever within the U-shaped section being engageable with ratchet teeth on a quadrant portion of the mounting, and cam plate means mounted within the U-shaped section mounting portion and having cam and pivot means thereon, cooperating with different ones of the handbrake lever and mounting, and also having a cable anchorage thereon, arranged on generally the opposite side of the pivotal axis of the lever to the said pivot means.

2. A handbrake lever mechanism according to claim 1, wherein the pivot means on the cam plates means cooperates with and establishes a pivotal connection of the cam plate means on the handbrake lever, and the cam means comprises a cam follower cooperating with a cam track in the mounting.

3. A handbrake lever mechanism according to claim 1, wherein the pivot means on the cam plate means cooperates with, and establishes a pivotal connection of the cam plate means on, the mounting, and the cam means comprises a cam track in the cam plate means cooperating with a cam follower on the handbrake lever.

4. A handbrake lever mechanism according to any preceding claim, further comprising a cam track in the mounting cooperating with the cable anchorage to constrain the movement of the cable anchorage to a precise straight linear movement which is accommodated by a lost motion linkage between the cam plate means and the handbrake lever, or between the cam plate means and the cable anchorage.

5. A handbrake lever mechanism for an automobile, substantially as described herein with reference to Figures 1 to 4 of the drawings.

6. A handbrake lever mechanism for an automobile, substantially as described herein with reference to Figure 5 of the drawings.

7. A handbrake lever mechanism for an automobile substantially as described herein with reference to Figures 1 to 4 as modified by Figure 6 of the drawings.

8. A handbrake lever mechanism for an automobile, substantially as described herein with reference to Figure 4 as modified by Figure 7 of the drawings.