GB2321682A

GB2321682A - A hydraulic brake system for a motorcycle

Info

Publication number: GB2321682A
Application number: GB9702160A
Authority: GB
Inventors: Jonathan Paul Tait; Richard Arnold Bass
Original assignee: Automotive Products PLC
Current assignee: Automotive Products PLC
Priority date: 1997-02-01
Filing date: 1997-02-01
Publication date: 1998-08-05
Anticipated expiration: 2017-02-01
Also published as: GB9702160D0; GB2321682B

Abstract

A hydraulic brake system for a motorcycle comprises a lever 60 which operates each of two master cylinders 21, 21A via a linkage 50, each master cylinder includes a piston to generate a brake fluid pressure to operate an associated brake circuit 20, 20A with each brake circuit operating to brake the same wheel 11. The master cylinder pistons are interconnected to each other via the linkage to give a pre-determined, and possibly adjustable, brake fluid pressure relationship between each brake circuit during braking (the braking pressures may be the same or different). The ratio L:M and the lever span S are adjustable. The master cylinders and/or brake calipers may have different piston diameters, the working surfaces of each disc and/or pad could be different, and the circuits may contain different brake fluids. The linkage 50 is such that if one brake circuit fails the other will be pressurised.

Description

A BRAKING SYSTEM The present invention relates to a hydraulic brake systems for motor cycles.

It is an object of the present invention to produce an improved form of a hydraulic braking system for a motor cycle which is particularly suitable for use on the front wheel of a motorcycle having two front disc brakes.

According to the present invention there is provided a hydraulic brake system for a motorcycle comprising a lever which operates each of two master cylinders via a linkage, each master cylinder including a piston to generate a brake fluid pressure to operate an associated brake circuit, each brake circuit operating to brake the same wheel, the master cylinder pistons being inter-connected to each other via the linkage to give a pre determined brake fluid pressure relationship between each brake circuit during braking.

The invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a schematic view of a hydraulic brake system according to the present invention; Figure 2 is a plan view of the master cylinder and lever arrangement of figure 1; Figure 2A is an enlarged cutaway view of part of figure 2; Figure 3 is a general section view of one of the master cylinders of figure 2; Figure 4 is an isometric view of the master cylinder and lever arrangement of figure 2; and Figure 5 is a section view of the linkage taken along the line AA of figure 2.

With reference figures 1 to 5 there is shown a hydraulic brake system 10 for a motor cycle. The system includes two independent brake circuits 20 and 20A, operated by a lever 60. Each brake circuit operates a brake calliper 40 40A which pushes corresponding brake pads 41, 41A onto a corresponding brake disc 42, 42A. Both discs are attached to the front wheel 11 of the motor cycle. In this specification the term motorcycle includes the combination of a motorcycle and side car and also a three wheeled vehicle having only one wheel at the front .Individually the wheel 11, brake discs 42, 42A, brake pads 41, 41A and callipers 40,40A are all well known in the art. The calipers 40, 40A are of the opposed piston type.

Typically the calliper 40 would be mounted on the front telescopic forks of the motorcycle are one side of the wheel and the caliper 40A would be similarly mounted on the other side of the wheel.

Each brake circuit also includes a master cylinder 21, 21 A hydraulic fluid reservoir 12, 12A hoses 13, 13A to connect the outlet from each fluid reservoir to the inlet of the appropriate master cylinder and hoses 14, 14A to connect the outlet from each master cylinder to the inlet to the appropriate brake calliper 40, 40A.Each brake circuit is also primed with hydraulic fluid 18, 18A.

The master cylinders are mounted parallel and adjacent to each other. The body 22, 22A of each master cylinder is integral with a mounting bracket 15, which attaches to the handle bar 17 ofthe motor cycle, and also integral with a lever pivot bracket 16.

The principle of operation of both brake circuits 20, 20A is the same and as such only the operation of circuit 20 will be described in detail. Equivalent components in brake circuit 20A are indicated by the suffix 'A'.

Master cylinder 21 comprises a body 22 with a bore 23 with a closed end 24 and an open end 25. A cap 26 is sealingly mounted on the opened 25 of the bore 23. The master cylinder also includes a piston 27. One end 28 of piston 27 includes a seal 29 which seals the piston against the bore to prevent passage of fluid past the piston during braking. The other end 30 of piston 27 is formed as a pull rod 34 part of which projects through the cap 26. A seal 31 in the cap 26 prevents loss of hydraulic fluid during braking.

A hole 32 connects the fluid in the bore 23 with the fluid in the reservoir 12. Braking is achieved by applying a tensile force to the pull rod 34 which moves the piston which is then moved away from the closed end 24 of the bore 23 causing the seal to move past hole 32 The hydraulic fluid that was situated between the cap 26 and the end 28 ofthe piston 27 is then displaced to operate the associated calliper 40. Upon release of the brake the spring 33 returns the piston to its 'at rest' position (as shown in figure 3).

The pull rod 34 has a fork 35 formed at the end remote from seal 29.

A pin 36 is held fast at each of its ends in corresponding holes 37 formed in the fork. A connection means in the form of a bar 50 (see fig 5)has slotted holes 51 and 51A, one at each end. Each end ofthe bar 50 is positioned between the appropriate forks 35, 35A with the pins 36, 36A passing through the appropriate slotted holes 51, 51A.

Brake lever 60 is pivotally mounted via pivot 69 on the lever pivot bracket 16. The pivot 69 consists of a pin 61, rotationally fast with the lever each end of the pin being pivotable in a block 62, 62' (only 62' shown) each of which are rotationally fast with the pivot bracket 16. Each block 62, 62' is mounted in a slotted hole 63, 63' (only 63' shown). The pin is mounted in a slotted hole 64 in the lever and can be moved along the slot 64 via an axially fixed screw thread 65. The screw thread can be turned by a thumb wheel 66.

End 67 of brake lever 60 has a hole 68 which is parallel to the axis of pin 61.A ring 70 is mounted in the hole 68 between a shoulder 68B and circlip 68C.Between the shoulder 68B and the ring 70 there are a number (in this case two) of shims 68E. The ring 70 has a hexagonal portion 71 at one end to allow the ring to be rotated in the hold 68 for adjustment.. The ring can be locked in position by grub screw 68D following an adjustment.

A spherical bearing 80 is mounted in a hole 72 in the ring 70 between a shoulder 73 and a circlip 74. The end ofthe hole 72 adjacent the hexagonal portion 71 is of reduced diameter D. The bar 50 passes through hole 72 in the ring 70 and is supported by the spherical bearing 80.

It should be noted that the axis 68' of the hole 68 is eccentric to the axis 72' of the hole 72 in ring 70.

Operation of the lever is as follows: a) The lever 60 is pulled towards the handle bar 17 causing it to rotate about pivot 69. End 67 of lever 60 moves away from the handle bar 17 causing the bar 50 to apply a tensile load to each pull rod 34, 34A of each master cylinder 21, 21A.

Operation of each brake circuit is then as previously described. There is usually a tolerance mis-match between the braking components of each brake circuit 20 and 20A which requires one of the pistons 27 or 27A to move further than the other piston. This slight mis match is catered for because the bar 50 is mounted on the spherical bearing 80 and the axis 50' of the Bar 50 can tilt slightly, as required, relative to the axis 72' of the hole 72.

b) When the lever 60 is released the brake system returns to the at rest position under the influence of springs 33, 33A, and the axis 50' and 72' become co-incident again (see fig 5 ).

Should one brake circuit fail (say circuit 20), the corresponding piston 27 is unable to generate any pressure in circuit 20 and as the brake is applied all the force applied to the lever 60 can only be reacted by tension in the pull rod 34A of the functioning circuit 20A.

Under these circumstances the bar 50 tilts until abutment portion 52 of bar 50 contacts the edge 75 of hole 72 whereupon tension can be applied to pull rod 34A thus maintaining a limited amount of braking to wheel 11. Similarly should brake circuit 20A fail the bar 50 will tilt until abutment portion 52 contacts the edge 76 of hole 72 whereupon tension can be applied to pull rod 34 and a limited amount of braking of wheel 11 is still possible.

The slotted holes 51 of bar 50 allow the pins to slide slightly relative to the bar and ensure that the tensile force applied to the pistons 27, 27A acts directly along the axis 23', 23A' of the appropriate bores 23, 23A should the bar be tilted during braking. Similarly the pivot 61 and blocks 62, 62' allow the lever to slide as the brake is operated which ensures that the movement of the spherical bearings is linear (as opposed to arcuate) and the tensile force being applied to the pistons 27, 27A is again directly along the axis 23', 24A' of the appropriate bores.

In an altemative embodiment one end only of the bar could have a non slotted hole, and if the bar tilted slightly during braking it could slide in the bearing 80 and the slotted end of the bar could also slide on the pin to allow the tensile load to be applied to the pistons 27, 27A along the axis 23', 23A' of the appropriate bores.

As previously described adjustment ofthe pin 61 via screw thread 65 and thumb wheel 66 causes the pin to move relative to the lever 60. This has the effect of adjusting the lever ratio i.e. the ratio L:M where L is the distance between the pin axis 61' and the bar axis 50' and M is the distance between the pin axis 61' and position R on the lever 60 where the force to move the lever is applied. Thus the lever ratio can be adjusted within limits to suit different riders and different riding conditions. Note that adjustment of pin 61 does not affect the lever span S i.e. the distance between the position R on the lever 60 and the handle bar axis 17' with the brake in the at rest position.

As previously described the ring 70 can be rotated relative to the hole 68 and locked in any described position by grub screw 68D. The primary effect of such an adjustment is to alter the lever span S due to the eccentricity of axis 68' of hole 68 of lever 60 relative to axis 72' of hole 72 of ring 70. Thus it is possible to alter the lever spans within limits to suit different riders and riding conditions. A secondary effect of adjusting ring 70 is to slightly modify the lever ratio L:M, however this can be reset via adjustment of pivot pin 61 if necessary.

The above description of a braking system assumes that each half of the system are identical in operation, but this need not be the case for example:a) the working surface of each discs (i.e. the surface contacted by the brake pads) could be different e.g. of a different material and/or of a different construction.

Typical materials would be steel, chrome, or carbon carbon, typical construction would be a flat disc, a slotted disc, or a drilled disc.

b) the working surface of each pad (i.e. the surface contacted by the brake disc) could be different e.g. of a different material and/or of a different construction.

c) the piston diameter of the brake callipers could be different.

d) the piston diameter of the master cylinders could be different.

e) the force applied to each master cylinder piston could be different.

A particular brake set up on a motor cycle is a compromise between say wet weather versus dry weather braking performance or peak braking versus brake fade performance.

The use of a braking system according to the present invention allows a better compromise to be reached. For example the parameters (a) to (e) mentioned above could be altered on one brake circuit to provide optimum dry weather braking (to the detriment of wet weather braking performance on that brake circuit) some or all of the same parameters could be different on the other brake circuit to ensure optimum wet weather braking performance (to the detriment of dry weather braking performance that brake circuit) and such an arrangement can be advantageous.

In particular further embodiments of the present invention could have different master cylinder bore diameters or the load applied to each master cylinder piston could be different (e.g. by off setting the spherical bearing 80 towards one or the other ends of bar 50) and this allows each brake circuit to operate at a different pressure. This has heretofore not been possible with motorcycles having only one brake circuit operating the brake of one wheel.

In the embodiment shown in figures 1 to 5 the bearing 80 can be off set by removing one or both shims 68 from between the ring 70 and shoulder 68B and re-positioning it/them between the ring 70 and circlip 68. In further embodiments different adjustment methods are possible.

Embodiments of the present invention can be particularly advantageous when used on the front wheel of a motorcycle because this wheel often performs the majority of the braking.

This is witnessed by the fact that several modern road going motor cycles are capable of lifting the rear wheel of the motorcycle during heavy braking of the front wheel. Typically the relatively short wheel base and relatively high centre of gravity of the combination of the motorcycle and rider contribute to this undesirable effect. Conversely typical modern road going motor car will always have is rear wheels in contact with the road surface and as such they are always able to contribute to the braking of the vehicle.

Claims

1. A hydraulic brake system for a motorcycle comprising a lever which operates each of two master cylinders via a linkage, each master cylinder including a piston to generate a brake fluid pressure to operate an associated brake circuit, each brake circuit operating to brake the same wheel, the master cylinder pistons being inter connected to each other via the linkage to give a pre determined brake fluid pressure relationship between each brake circuit during braking.

2. A hydraulic braking system as defined in Claim 1 in which the brake fluid pressure generated in each brake circuit during braking is the same.

3. A hydraulic brake system as defined in Claim 1 in which the brake fluid pressure generated in each brake circuit during braking is different.

4. A hydraulic brake system as defined in any previous claim in which the ratio of the brake fluid pressure generated in one circuit, to the brake fluid pressure generated in the other circuit is adjustable.

5. A hydraulic brake system as defined in any previous claim in which the lever applies a force to each of the pistons during braking via the linkage and the force applied to each piston is the same.

6. A hydraulic brake system as defined in anyone of Claims 1 to 4 in which the lever applies a force to each of the pistons during braking via the linkage and the force applied to each piston is different.

7. A hydraulic brake system as defined in Claims 5 or 6 in which the ratio of the force applied to one piston to the force applied to the other piston is adjustable.

8. A hydraulic brake system as defined in any preceding claim in which the linkage can tilt to a limited extent relative to the lever and relative to each piston so that if one brake circuit fails the other brake circuit is still operable.

9. A hydraulic brake system as defined in Claim 8 in which the tilting of the linkage is limited by an abutment on the linkage contacting an abutment on a component fixed relative to the lever.

10. Aaster cylinder is sealingly sideable in a bore of the appropriate master cylinder and the diameter of each bore is different.

11. A hydraulic brake system as defined in any previous claim in which each brake circuit operates a corresponding brake calliper which in operation pushes the working surfaces of one or more corresponding brake pads onto the working face of one or more brake discs.

12. A hydraulic brake system as defined in Claim 11 in which the working surface of at least one brake pad associated with one brake circuit is different from the working surface of a brake pad associated with the other brake circuits.

13. A hydraulic brake system as defined in Claims 11 or 12 in which each brake circuit acts on a separate disc brake, and the working surface of one disc brake is different from the working surface of the other disc brake.

14. A hydraulic brake system as defined in any previous claim in which the linkage comprises a bar mounted in a bore of the lever, each end of the bar being attached to the piston of the corresponding master cylinder.

15. A hydraulic brake system as defined in Claim 14 in which the bar is mounted in a spherical bearing in the lever to allow the bar to tilt relative to the lever.

16. A hydraulic brake system as defined in Claim 14 or 15 in which each end of the bar has a slotted hole through which passes a corresponding pin held fast with the corresponding piston, each pin sliding relative to the corresponding slot should the bar tilt as the brake is applied, to ensure the force applied to each piston is along a line coincident with the axis of the corresponding bore of the appropriate master cylinder.

17. A hydraulic brake system as defined in anyone of Claims 14 to 16 in which the bar is mounted in a bore of a ring, the ring being mounted in the bore of the lever, the bore of the ring being eccentric with the bore of the lever and the ring being rotatable relative to the lever to adjust the lever ratio.

18. A hydraulic brake system as defined in anyone of Claims 14 to 17 in which the point of action of a force applied to the bar by the lever is adjustable to modify the ratio of the forces applied to one piston to the force applied to the other piston during braking.

19. A hydraulic brake system as defined in anyone of Claims 14 to 18 in which the lever is mounted on a handle bar and the distance from the handle bar to the lever is adjustable.

20. A hydraulic brake system comprising a lever which operates to pressurise brake fluid in each of two brake circuits, each brake circuit operating to brake the same wheel in which during braking, the brake fluid pressure in one brake circuit is different from the brake fluid pressure in the other brake circuit.