GB2474008A

GB2474008A - Brake bias adjustment mechanism

Info

Publication number: GB2474008A
Application number: GB0915026A
Authority: GB
Inventors: Philip Smith; William Bailey
Original assignee: Alcon Components Ltd
Current assignee: Alcon Components Ltd
Priority date: 2009-08-27
Filing date: 2009-08-27
Publication date: 2011-04-06
Also published as: GB0915026D0

Abstract

The present invention provides a vehicle brake bias adjustment mechanism 46 having a balance bar 56 which is pivotably connectable at each end thereof to a respective brake master cylinder 42,44, a pivot body 64 having a through aperture 62 through which the balance bar 56 extends such that the pivot body 64 is provided intermediate the ends of the balance bar 56, and a pivot housing 70 within which the pivot body 64 is pivotably mounted about a pivot axis 104, the pivot housing 70 having an abutment surface 84 which, in use, rests against a reaction surface 31 of a vehicle, wherein the pivot body 64 has a rotatatable element mounted therein which is in driving engagement with the balance bar 56, the rotatable element being rotatable so as to move the pivot body 64 and pivot housing 70 along the balance bar 56 and thereby move the pivot axis 104 of the pivot body 64 relative to the ends of the balance bar 56, the brake bias adjustment mechanism further having a driver operable actuator 108 to rotate the rotatable element. The brake bias mechanism preferably comprises a rack and pinion mechanism.

Description

Brake Bias Adjuster Mechanism The present invention relates to a vehicle brake bias adjuster mechanism. The present invention further relates to a vehicle brake assembly including a brake pedal, two hydraulic cylinders and a brake bias adjuster mechanism, and to a vehicle having such an assembly.

Hydraulic brake systems in high performance or race vehicles typically include dual master cylinders to isolate the front and rear hydraulic braking circuits. This allows the braking force to be varied between the front and rear of the vehicle, with master cylinders of different diameter possibly being chosen to apportion the braking force to suit the particular characteristics of the vehicle.

Referring to figures 1 and 2 there is shown a typical brake master cylinder and pedal arrangement generally designated 10. The arrangement 10 includes a pair of brake master cylinders 12,14, and a brake bias adjuster mechanism generally designated 16.

The master cylinders 12,14 each comprise a housing 18,20 and a rod 22,24. The rods 22,24 of the master cylinders 12,14 are pivotably connected to a pedal 30 by a pedal bar 13. The master cylinder housings 18,20 are pivotably connected to a threaded adjuster rod 26 which is mounted to a pivot 28 that allows a driver to fine tune the front to rear setting or brake bias to compensate for changes that occur during a race.

The threaded adjuster rod 26 is received in a correspondingly threaded aperture of pivot 28. The pivot 28 is pivotably mounted in a base 29 which rests against a reaction surface 31, such as a vehicle bulkhead. The base 29 is movable relative to the reaction surface 31 as indicated by arrows 33,35 by the rotation of the threaded adjuster rod 26 in the threaded aperture of the pivot 28. The brake bias will typically need to be adjusted during a race to achieve maximum braking efficiency without wheel lockup by taking into account such factors as reducing fuel load, tyre wear and changing track conditions.

The above described system enables the brake bias to be adjusted by moving the pivot 28 between the master cylinders 12,14 so that more force is applied to either the front master cylinder (more front brake) or more to the rear master cylinder (more rear brake). The driver can make the adjustment as required by turning a knob 32, which, via a flexible cable 34, turns the adjuster rod 26, changing the distance between each master cylinder 12,14 and the pivot axis of the pivot 28 by means of the screw thread on the adjuster rod 26. The full range of adjustment of the brake bias adjuster mechanism 16 is commonly six full turns of the knob 32 in each direction from a mid position where the front to rear brake balance is equal. The six full turns of the knob 32 in turn rotate the adjuster rod 26 by six full turns. The knob 32 has click-stop positions that give the driver a degree of control, often graduated in Y4 turn increments.

The above described system does however have the following drawbacks. The configuration of the brake bias adjuster mechanism 16 means that cable 34 must connect with the adjuster rod 26 at more or less right angles to where it connects to the knob 32. The bending the cable 34 through substantially 90 degrees in what is often a short distance can cause a loss of efficiency due to binding in the cable 34. Actuation of the master cylinders 12,14 by depressing the brake pedal typically tightens the angle through which the cable 34 bends. This can be seen by comparing the angle a through which the cable 34 turns between figures 1 and 2 which correspond, respectively, to a brake off position of the master cylinders 12,14 and a brake on position of the master cylinders 12,14. Occasionally the driver will turn the knob 32 and friction in the cable 34 will be greater than the torque generated, with the result that the adjuster rod 26 does not turn. This process can continue until wind-up in the cable 34 eventually turns the adjuster rod 26 by more turns than the driver originally intended. As the angle through which the cable 34 bends increases as a result of the vehicle brakes being applied the resistance to movement of the cable 34 may also increase.

With a full range of typically six turns of the knob 32 in each direction, in the heat of a race it is difficult for the driver to keep track of exactly where the brake bias is set, so that unnecessary adjustments are often made, resulting in loss of braking efficiency and increased lap times. Also, clearance between the threaded adjuster rod 26 arid the threaded aperture of the pivot 28 creates undesirable play in the brake bias adjuster mechanism 16 that may affect the selected front to rear brake bias setting.

According to a first aspect of the present invention there is provided a vehicle brake bias adjustment mechanism having a balance bar which is pivotably connectable at each end to a brake master cylinder, a pivot body having a through aperture through which the balance bar extends such that the pivot body is provided intermediate the ends of the balance bar, and a pivot housing within which the pivot body is pivotably mounted about a pivot axis, the pivot housing having an abutment surface which, in use, rests against a reaction surface of a vehicle, wherein the pivot body has a rotatable element mounted therein which is in driving engagement with the balance bar, the rotatable element being rotatable so as to move the pivot body and pivot housing along the balance bar and thereby move the pivot axis of the pivot body relative to the ends of the balance bar, the brake bias adjustment mechanism further having a driver operable actuator to rotate the rotatable element The rotatable element is provided with a drive formation which is engaged with a corresponding drive formation of the balance bar. The drive formation of the rotatable element may take the form of a plurality of teeth provided around the rotatable element. The rotatable element may take the form of a pinion. The corresponding drive formation of the balance bar may take the form of a plurality of teeth spaced along at least a portion of the length of the balance bar to provide a rack with which the pinion is engaged. The rack may be formed directly into the balance bar.

Alternatively, the rack may be formed on a member fixed to the balance bar. For example, the rack may be provided on a sleeve which is fitted to the balance bar.

The pinion may be connected to a pinion shaft which extends from the pivot body.

The pinion shaft may by inclined relative to the pivot axis of the pivot body.

The driver operable actuator may comprise a rotatable actuation member provided at a location remote to the pivot body and a rotatable connecting member extending to the rotatable element of the pivot body. A gear arrangement may be provided between the rotatable actuation member and the rotatable element of the pivot body such that rotation of the rotatable actuation member through a given angle results in lesser rotation of the rotatable element of the pivot body. The rotatable connecting member may be flexible and comprise a sheathed cable. In an alternative embodiment the rotatable connecting member may be substantially rigid.

The rotatable actuation member may comprise a rod or lever. The gear arrangement may be configured such that less than one rotation of the rotatable actuation member results in the full range of movement of the pivot body and pivot axis relative to the balance bar.

According to a second aspect of the present invention, there is provided a vehicle brake assembly comprising a first brake master cylinder, a second brake master cylinder, a pedal bar pivotably connected between respective first ends of the master cylinders, a brake pedal connected to the pedal bar and a brake pedal bias adjustment mechanism according to the first aspect of the invention connected between respective second ends of the brake master cylinders.

According to a third aspect of the present invention there is provided a road vehicle having the brake pedal bias adjustment mechanism according to the first aspect of the invention or the brake assembly according to the second aspect.

An embodiment of the present invention will now be described with reference to the accompanying drawings in which: Figures 1 and 2 show plan views of a prior art brake pedal, hydraulic cylinder and brake bias adjuster mechanism; Figure 3 shows a plan view of a brake pedal, hydraulic cylinder and brake bias adjuster mechanism according to the present invention; Figure 4 shows a cross-sectional view of a portion of the brake bias adjuster mechanism of figure 3; and Figure 5 shows a side view of said portion of the brake bias adjuster mechanism.

Referring to figures 3 to 5, there is shown a brake master cylinder and pedal arrangement generally designated 40. The arrangement 40 includes a pair of brake master cylinders 42,44, and a brake bias adjuster mechanism generally designated 46.

The master cylinders 42,44 each comprise a housing 48,50 and a rod 52,54. The master cylinder rods 52,54 are joined by a pedal bar 110 to which a brake pedal 112 is connected. The brake bias adjuster mechanism 46 includes a balance bar 56 upon which there are provided a plurality of teeth (not shown) forming a rack 58. In the embodiment shown the rack 58 is provided on a central portion 60 of the bar 56 which has a larger diameter than the respective ends of the bar 56. The respective ends of the bar 56 are provided with collars 63 which, in use, locate the master cylinder housings 48,50 to the bar 56. The balance bar 56 is pivotably mounted at each end to a respective master cylinder housing 48,50. In an alternative embodiment, the rack 58 may be provided on a sleeve which is fitted over and fixed to the bar 56. The sleeve may be pinned or welded to the bar 56.

The rack 58 extends through a through aperture 62 of a pivot body 64. The pivot body 64 comprises a substantially cylindrical mid portion 66 within which the through aperture 62 is provided, the pivot body having a trunnion 68a,68b at each end thereof.

The pivot body 64 is provided within an open sided pivot housing 70. The pivot housing 70 includes a first or lower bearing recess 72 provided in a lower portion 73 of the housing 70 and within which one of the pivot body trurmions 68a is received. The housing 70 is further provided with an upper portion 75 having a cap 74 defining a second or upper bearing recess 76 within which the other of the pivot body trunnions 68b is received. The cap 74 has a circumferential lip 77 which engages a circumferential seat 78 of an aperture 80 of the upper portion 75 of the pivot housing 70. The cap 74 is retained to the pivot housing 70 by a circlip 82. The pivot housing is provided with an abutment face 84 which, in use, rests against a fixed surface 31 of the vehicle to which the brake bias adjuster mechanism 46 is fitted and, in use, is movable relative thereto. The abutment face 84 is provided on a mid portion 85 of the housing 70 which joins the lower 73 and upper 75 portions of the housing 70. The fixed surface 31 may be part of the structure of the vehicle, for example, a bulkhead or interior body wall of the vehicle. Alternatively, the fixed surface may form part of an assembly that is fitted to the vehicle, for example, part of a pedal box assembly. An opening 86 of the pivot housing 70 is defined between the lower, upper and mid portions 73,75,85 is sized such that pivot body 64 and bar 56 are able to pivot through an arc of approximately +1-9 degrees about a central position.

The pivot body 64 is further provided with a pinion 88 which is engaged with the rack 58 of the bar 56. The pinion 88 is provided within a recess 90 of the pivot body 64.

The recess 90 extends through the pivot body 64 and comprises a larger diameter portion 92 within which the toothed pinion gear 94 is provided and a smaller diameter portion 96 within which a pinion shaft 98 is provided. The larger diameter portion 92 of the recess 90 faces the portion of the pivot housing 70 upon which the abutment face 84 is provided and thus is not generally visible. The smaller diameter portion 96 is accessible through the opening 86 of the pivot housing 70. The pinion shaft 98 extends through a central bore of the pinion 88 and is secured to the pinion 88 by a threaded fastener 100. The axis of rotation 102 of the pinion 88 and pinion shaft 98 intersects the pivot axis 104 of the pivot body 64.

As can be readily seen from figure 4 the axis of rotation of the pinion is inclined upwardly in the direction of the upper portion 75 of the housing 70. It will be appreciated that the brake bias adjustment mechanism 46 is typically positioned in a lower region of a vehicle in close relation to the vehicle brake pedal. The pinion shaft 98 thus extends from the brake bias adjuster mechanism 46 upwardly in the direction of the driver of the vehicle to which the bias adjuster 46 is fitted, in use. As will be described in greater detail below, this inclination of the pinion shaft 98 assists in ensuring the connection between the brake bias adjuster mechanism 46 and a driver operable means of adjust the brake bias is not as convoluted as in the prior art. It will be appreciated that the inclination angle shown is not intended to be limiting and, depending upon the installation requirements of the and corresponding configuration of the pivot body may be inclined by a greater or lesser amount.

In order to rotate the pinion shaft 98 there is provided a sheathed cable 106 which is connected to a rotatable knob 108. In Figure 3 the cable 106 and knob 108 are shown to be positioned in the region between the master cylinder rods 52,54. This schematic representation is not intended to illustrate the actual position of the knob 108 which will typically be mounted to the dashboard of a vehicle within easy reach of the driver.

As the cable 106 extends from the knob 108 to a position between the master cylinders 42,44, the cable 106 can be routed in a much more linear fashion than in the prior art type adjuster. An optional gear arrangement 114 is shown between the cable 106 and the knob 108. The gear arrangement 114 may be configured so as to reduce the number of turns required at the knob 108 to shift the pivot axis 104 between the limits of its movement relative to the balance bar 56.

The benefits of the present invention over the prior art include the following: As the pinion is orientated towards the adjuster knob, the cable can be more or less straight, without the need for a right angle turn. In an alternative embodiment a solid rod could be used in place of the cable, with one or more universal joints being provided to compensate for any misalignment. This arrangement would eliminate the problem of wind-up in the adjuster cable.

As the cable or rod is connected to the pinion rather than the end of the adjuster rod, movement of the cable end or rod as the balance bar rotates on the pivot axis during depression of the brake pedal is minimal. Therefore the effect on the chosen brake bias setting of the cable or rod resisting rotational movement of the adjuster knob by wind-up or binding is much reduced.

By selecting an appropriate tooth pitch on the rack and pinion, the full range of travel in one direction (equivalent to six turns of the adjuster rod of the prior art arrangement) can be achieved with less than 450 rotation of the pinion. Using an appropriate speed reducing gear arrangement at the adjuster knob, one full turn or less of the knob may provide the full range of adjustment in one direction. In which case, the knob may be replaced by a rotating lever. The lever may be arranged such that it points to an upright twelve o'clock position on the dashboard to indicate the mid position of the brake bias adjuster and points to respective end positions either side of the twelve o'clock position to indicate full front or rear brake bias. A number of equally spaced click stops may be provided between the 12 o'clock and end position. The lever would thus give the driver a simple and quick visual indication as to where the brake bias is set rather than needing to remember how many turns of the knob have been made. In one embodiment the lever may be fully rotatable between the end positions through an arc of 356 degrees and configured such that it is movable through an arc of 178 degrees to either side of the mid position.

Free play in mating parts is almost eliminated by the use of a precision rack and a pinion. The brake bias adjustment mechanism of the present invention may be integrated into the pedal box of a vehicle or, alternatively be provided separate to the pedal box. S 9

Claims

CLAIMS1. A vehicle brake bias adjustment mechanism having a balance bar which is pivotably connectable at each end thereof to a respective brake master cylinder, a pivot body having a through aperture through which the balance bar extends such that the pivot body is provided intermediate the ends of the balance bar, and a pivot housing within which the pivot body is pivotably mounted about a pivot axis, the pivot housing having an abutment surface which, in use, rests against a reaction surface of a vehicle, wherein the pivot body has a rotatatable element mounted therein which is in driving engagement with the balance bar, the rotatable element being rotatable so as to move the pivot body and pivot housing along the balance bar and thereby move the pivot axis of the pivot body relative to the ends of the balance bar, the brake bias adjustment mechanism further having a driver operable actuator to rotate the rotatable element.
2. A vehicle brake bias adjustment mechanism according to claim 1 wherein the rotatable element is provided with a drive formation which is engaged with a corresponding drive formation of the balance bar.
3. A vehicle brake bias adjustment mechanism according to claim 2 wherein the drive formation of the rotatable element comprises a plurality of teeth provided around the rotatable element.
4. A vehicle brake bias adjustment mechanism according to claim 3 wherein the rotatable element is a pinion.
5. A vehicle brake bias adjustment mechanism according to claim 4 wherein pinion is connected to a pinion shaft which extends from the pivot body, the pinion shaft being inclined relative to the pivot axis of the pivot body.
6. A vehicle brake bias adjustment mechanism according to claim 2 or claims 3 to when dependent upon claim 2 wherein the corresponding drive formation of the balance bar comprises a plurality of teeth spaced along at least a portion of the length of the balance bar to define a rack
7. A vehicle brake bias adjustment mechanism according to claim 6 wherein the rack formed directly in the balance bar.
8. A vehicle brake bias adjustment mechanism according to claim 6 wherein the rack is formed on a member fixed to the balance bar.
9. A vehicle brake bias adjustment mechanism according to any preceding claim wherein the driver operable actuator comprises a rotatable actuation member provided at a location remote to the pivot body and a rotatable connecting member extending to the rotatable element of the pivot body.
10. A vehicle brake bias adjustment mechanism according to claim 9 wherein a gear arrangement is provided between the rotatable actuation member and the rotatable element of the pivot body such that rotation of the rotatable actuation member through a given angle results in lesser rotation of the rotatable element of the pivot body.
11. A vehicle brake bias adjustment mechanism according to claim 10 wherein the gear arrangement is configured such that less than one rotation of the rotatable actuation member results in the full range of movement of the pivot body and pivot axis relative to the balance bar.
12. A vehicle brake assembly comprising a first brake master cylinder, a second brake master cylinder, a pedal bar pivotably connected between respective first ends of the master cylinders, a brake pedal connected to the pedal bar and a brake pedal bias adjustment mechanism according to any preceding claim and connected between respective second ends of the brake master cylinders.
13. A road vehicle having the brake pedal bias adjustment mechanism according to claims 1 to 11 or the brake assembly according to claim 12.