GB2456664A

GB2456664A - Master cylinder having an operating lever of which the mechanical advantage may be adjusted

Info

Publication number: GB2456664A
Application number: GB0900762A
Authority: GB
Inventors: Walter Emil Saunders; Philip John Tucker
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-01-18
Filing date: 2009-01-19
Publication date: 2009-07-29
Anticipated expiration: 2029-01-19
Also published as: GB0800928D0; GB0900762D0; GB2456664B

Abstract

An hydraulic cylinder 10, preferably for a motorcycle, has a piston slidable in a master cylinder body 11 with an operating mechanism including a lever 13 pivoted by means of a link 21 to the body 11 and connected to a piston rod 15. A guide 31 (or 33, figs 2,3 and 5) is arranged to keep the piston rod 15 substantially in line with the bore of the cylinder. A screw-threaded adjuster 27,30 connects the link 21 to the lever 13 such that the effective pivot point 23 is adjustable along the length of the lever. This allows adjustment of the mechanical advantage whenever required by a rider.

Description

MASTER CYLINDER ASSEMBLY

This invention relates to an hydraulic master cylinder assembly which is arranged to allow adjustment of the mechanical advantage of an operating lever of that assembly.

Hydraulic master cylinders are used extensively for the operation of brakes and clutches on cars and motorcycles. A typical master cylinder has a main body defining a cylinder within which a piston slides and an operating mechanism including a pivoted lever driving a piston rod so that movement of the lever expels fluid out of the cylinder. In order to achieve the required performance, the diameter of the cylinder must be selected having regard to the mechanical advantage of the operating lever and the volume of fluid which must be moved to effect operation of the brakes or clutch. In a case where no servo assistance is available (such as is usually the case on a motorcycle), a careful selection must be made for the cylinder diameter, brake calliper or clutch slave cylinder diameter and the mechanical arrangement of the operating lever, in order to ensure sufficient fluid can be moved with acceptable loads on the operating lever.

On racing motorcycles, the performance of the brakes and clutch will often change with the temperature of the hydraulic fluid and of the friction surfaces. It has been recognised that it would be advantageous to be able to adjust the mechanical advantage of the operating lever in the course of a race, to compensate for overheated fluid, over sensitive brakes or when tyre grip is reduced, to help avoid wheel locking under braking. Reducing the volume of fluid pumped for a given operating lever movement would give greater performance and sensitivity, for example allowing for friction surfaces which may not be a optimum working temperature.

To address the above issues, there have been proposals for master cylinder assemblies where the effective mechanical advantage of the operating mechanism can be adjusted. One such proposal addresses the problem by having a guide with linear bearings for a piston actuating rod and arranging the operating lever to pull the piston rod, rather than pushing it in the conventional way. Such an arrangement is somewhat complex and it has been found that it is possible for there to be uneven wear and stiction in the mechanism, leading to less than perfect operation, which is unacceptable in a racing environment.

According to this invention, there is provided an hydraulic master cylinder assembly comprising a body defining an hydraulic cylinder, a piston slidable in the cylinder and an operating mechanism to drive the piston deeper into the cylinder, which mechanism comprises an operating lever, a piston rod operatively connecting with the piston, a first pivotal connection connecting the piston rod to the lever part-way between the ends thereof, guide means for maintaining the line of action of the piston rod substantially aligned with the axis of the cylinder, and first link pivoted at one end to the body and its other end defining a fulcrum for pivoting movement of the lever, the position of the fulcrum along the length of the lever with respect to the first pivotal connection being adjustable thereby to allow adjustment of the mechanical advantage of the lever.

It will be appreciated that the master cylinder assembly of this invention allows ready adjustment of the mechanical advantage of the operating mechanism for the piston of the assembly, in a simple and reliable manner.

This is achieved by providing a link pivoted at its two ends respectively to the operating lever and to the master cylinder body, the pivotal connection of the link to the lever serving as the fulcrum for the lever and being adjustable along the length thereof, relative to the connection of the piston rod thereto. It is possible to arrange a master cylinder of this invention so as to resemble a conventional motorcycle master cylinder and so facilitate the installation on a motorcycle, without requiring any modification to the motorcycle, and yet allow immediate control of the operation of the master cylinder.

The guide means serves to maintain the axis of the piston rod substantially in alignment with the axis of the cylinder and one or more guide rails may be provided for this purpose, the or each guide rail being mounted on the body and the piston rod or the first pivotal connection being associated therewith. Another possibility is for there to be a rod guide mounted in or adjacent the open mouth of the bore and through which the piston rod extends to be guided thereby. A preferred embodiment of this invention employs a second link pivoted at one end to the body and at its other end to the lever, at or adjacent the first pivotal connection thereof -that is, the connection between the lever and the piston rod. In order to minimise lateral movement of the piston rod, the second link should extend generally parallel to a line passing through the first pivotal connection and the fulcrum, when the lever is in a rest position -that is, before operation to expel hydraulic fluid out of the cylinder.

Similarly, it is preferred for the first link to extend generally normal to that line, when the lever is in its rest position.

Preferably, the lever is provided with a slot extending along the length thereof and there is a second pivotal connection serving as the fulcrum and which locates in the slot, to connect the other end of the first link to the lever.

Advantageously, there is a link pin extending through that slot and through a bore in the other end of the first link, the link pin having a transverse hole to which a screw-threaded adjuster connects. Rotation of the adjuster will then adjust the position of the second pivotal connection, along the length of the slot, so varying the mechanical advantage of the lever.

In addition to the adjustment of the mechanical advantage of the lever, it is preferred for the position of the piston rod to be adjustable with respect to the lever, thereby to allow fine adjustment of the operating conditions of the master cylinder. For this purpose, the piston rod may be screw-threaded to the first pivotal connection whereby rotation of the piston rod adjusts the projecting length of that piston rod beyond the first pivotal connection.

Preferably, for both the above-mentioned screw-threaded adjustable connections, there is a respective locking arrangement to prevent inadvertent or unintentional rotation of the adjuster. For example, a spring-loaded click-stop arrangement may be provided for this purpose.

Embodiments of this invention may employ a pair of first links pivoted to both the master cylinder body and the lever, with one link to each side of the lever. In an alternative arrangement, a single first link is received in a central aperture in the lever. Similarly, though two second links may be provided, one to each side of the lever, an alternative possibility would be to have a single second link again disposed centrally in a further aperture in the lever.

Advantageously, the master cylinder assembly may be constructed to have a pair of parallel hydraulic cylinders each fitted with a respective piston and each having an associated operating mechanism. The levers of the two mechanisms may each have a manually operable portion which is arranged for operation independently of the other. For this purpose, the two portions may extend essentially contiguously, generally in alignment with each other. Such an arrangement may conveniently be employed on a racing motorcycle to permit independent operation of the front brake and rear brake, or the clutch and one of the front and rear brakes.

By way of example only, several specific embodiments of master cylinder assemblies of this invention will now be described in detail, reference being made to the accompanying drawings in which:-Figure 1 diagrammatically illustrates a first embodiment of an adjustable master cylinder assembly of this invention; Figure 2 illustrates, partly in section, a second embodiment of an adjustable master cylinder assembly; Figure 3 is a detail sectional view on the adjustment mechanism used in the second embodiment, with the section plane at 900 to that of Figure 2; Figures 4A and 4B are respectively end and side views on an adjuster screw used in the adjustment mechanism of Figure 3; Figure 5 diagrammatically illustrates a third embodiment of an adjustable master cylinder assembly, incorporating two cylinders in parallel each having an associate adjustable operating mechanism; and Figure 6 is an end view on the assembly of Figure 5; Referring initially to Figure 1, there is shown a master cylinder assembly intended for use with a motorcycle, for operating either the front brake or the clutch. The master cylinder assembly 10 has a main body 11 provided with a clamp 12 for securing the body to a handlebar (not shown). The assembly further has an operating lever 13 (only the root end of which is shown in Figure 1) and which, in use, will extend generally parallel to the handlebar such that a rider may squeeze the lever towards the handlebar to operate the master cylinder and so operate the front brake or clutch as appropriate.

The body 11 of the master cylinder assembly 10 defines an hydraulic cylinder 14 within which is slidably mounted a piston (not shown) for driving hydraulic fluid out of the cylinder. A piston rod 15 bears on the piston and is pivoted to the operating lever 13 by means of a rod pin 16 journalled in the operating lever. The rod pin has a threaded bore 17 extending diametrically thereacross partway between the ends thereof and aligned with an aperture 18 in the lever, the piston rod 15 extending through the aperture and being in threaded engagement with the bore 17. The rod 15 is provided with a knurled adjuster head 19 whereby the rod may be rotated to adjust the position thereof with respect to the rod pin 16 and so to adjust the extension of the rod beyond the lever 13.

The operating lever 13 is connected to the body 11 by means of a pair of first links 21 disposed one to each side of the lever and pivoted at their respective ends to the body and the lever. The lever 13 has a slot 22 formed therein, a link pin 23 being slidably located in that slot and the one ends 24 of the first links 21 being pivoted to the two ends respectively of that link pin. The first links are held on to the link pin 23 by means of circlips engaged in grooves in the pin. The other ends 25 of the first links 21 are pivoted to the body 11 by means of a shaft 26 threaded into a hole formed in the body.

The link pin 23 serves as a fulcrum for pivoting movement of the lever 13, on operation of the master cylinder. An adjustment mechanism is provided to control the position of the link pin 23 along the length of the slot 22. This mechanism includes an adjuster pin 27 fitted into a hole 28 formed through the lever 13 adjacent the end thereof. A further aperture is formed in the end face of the lever and extends into the slot 22 and the adjuster pin has a transverse threaded bore which is aligned with that further aperture. An adjustment screw extends through the further aperture and is in threaded engagement with the transverse threaded bore of the adjuster pin 27. The link pin 23 is received on a plain end portion of the screw 30 and is retained on that end portion by means of a further circlip.

The master cylinder assembly is also provided with a guide arrangement for the rod pin 16, to ensure that the rod pin 16 moves substantially in alignment with the bore of the cylinder 14 during operation of the lever 13. In Figure 1, there is shown a disc-shaped guide 31 fitted into the open end of the cylinder 14 and defining a central bore in which the piston rod 15 is a close sliding fit, the guide being held in place by a circlip located in a groove cut into the cylinder at the open end thereof. Another possibility would be to provide a pair of guide rails (not shown) which project from the body 12 and locate the rod pin 16 for axial sliding movement along the length of the rails. Whatever guide arrangement is chosen, it will be appreciated that the objective is smoothly to guide the piston rod for movement into and out of the cylinder in alignment with the cylinder bore, without giving rise to any significant friction or stiction, either or both of which would impair the operation of the master cylinder.

In use, the mechanical advantage of the operating mechanism may be adjusted by rotating the screw 30, to position the link pin 23 at a required location along the length of the slot 22. In the position shown in Figure 1, the mechanical advantage of that mechanism is at its lowest setting with movement of the operating lever producing relatively large movements of the piston rod 15. If the screw is turned to move the link pin 23 nearer the rod pin 16, the mechanical advantage of the mechanism increases and will be at a maximum when the link pin is at the end of the slot 22 nearer the rod pin 16.

Figures 2 and 3 show a modified form of the master cylinder assembly of Figure 1 and like parts with those of Figure 1 are given like reference characters. Those parts will not be described again here. In the arrangement of Figure 1, a guide 31 or pair of guide rails (not shown) are provided to guide the movement of the piston rod, to ensure the rod remains essentially coaxial with the cylinder 14. In the arrangement of Figures 2 and 3, a pair of second links 33 are provided, one to each side of the operating lever 13 (shown in full in Figure 2) and pivoted at their first ends 34 to the rod pin 16 and at their second ends 35 to a lug 36 projecting from the body 12. Also shown in Figure 2 are the internal details of the cylinder 14 within the body 12 and also the piston 37 provided with seals 38.

In use, the second links 33 control movement of the rod pin 16 such that the pin will follow an arcuate path centred on the pivotal connection between those links 33 and the lug 36, as the lever 13 is operated. By having the second links 33 extending substantially at 900 to the piston rod 15 in the rest position as shown in Figure 2, the deviation of the rod pin 16 from a true axial position will be relatively small during operation of the lever. To accommodate that deviation, the piston rod 15 is provided with a ball end 39 which is received in a part spherical socket in the piston 37 whereby articulation may occur between the end of the piston rod and the piston. Further, the ball end and socket serve to locate the piston rod centrally in the piston.

Figure 3 illustrates a click-stop mechanism used in conjunction with the adjuster screw 30, shown separately in Figures 4A and 4B. The threaded shaft of the adjuster screw 30 is formed with three equi-spaced axially-extending grooves 41 (also shown in Figure 1). The adjuster pin 27 has an axially-projecting boss 42 within which is formed a bore leading to the threaded hole 28. A ball is received in that bore and is spring- loaded to engage the grooves 41, the ball and its spring being held in place by means of a grub screw 43 received in the boss 42.

A similar click-stop mechanism is provided for the piston rod 15. This too is formed with at least one, but preferably three, axially-extending grooves which are engaged by a spring-loaded ball located in an axial hole 44 extending through the rod pin 16, and held in place by an end cap 45.

Figures 5 and 6 illustrate a third embodiment of master cylinder assembly generally corresponding to the second embodiment and again like parts are given like reference characters; these parts will not be described again here. The master cylinder assembly of Figures 5 and 6 differs from that of Figures 2 and 3 in that two cylinders 50,51 are formed side-by-side in the body 52, each cylinder being provided with its own operating mechanism including an independent operating lever. One of those mechanisms and its operating lever is the same as that as has been described with reference to Figures 2 and 3. The other mechanism is functionally the same but has a much shorter operating lever 54 the manually grippable part 55 of which is disposed within arcuate section 56 of lever 13.

Each operating mechanism has its own pair of first and second links pivoted as described above to the respective operating lever and also to the master cylinder body 52. Further, each operating mechanism has an arrangement corresponding to that described above with reference to Figures 2 and 3, for adjusting both the position of the piston rod with respect to the lever and the position of the link pin 23 along the length of the slot 22 of the respective lever 13 or 54.

When the master cylinder assembly of Figures 5 and 6 is used on a motorcycle, the cylinder associated with the larger lever 13 may be arranged to operate the front brake and the cylinder associated with the smaller lever 54 to operate the rear brake, possibly in parallel with the conventional foot brake arrangement for the rear brake. In this case, the master cylinder assembly would be mounted on the right-hand handlebar and the index finger of a rider will be used to operate the smaller lever 54, with that finger passing through the opening defined between part 55 of lever 54 and section 56 of lever 13. The remaining three fingers of the rider will be used to operate the larger lever 13, on the part thereof beyond section 56.

The master cylinder assembly of Figures 5 and 6 could instead be used on the left-hand handlebar, to allow operation of the clutch and rear brake. Yet another possibility would be to allow operation of the clutch and front brake, for example in the case of a disabled rider having limited right hand mobility.

Claims

1. An hydraulic master cylinder assembly comprising a body defining an hydraulic cylinder, a piston slidable in the cylinder and an operating mechanism to drive the piston deeper into the cylinder, which mechanism comprises an operating lever, a piston rod operatively connecting with the piston, a first pivotal connection connecting the piston rod to the lever part-way between the ends thereof, guide means for maintaining the line of action of the piston rod substantially aligned with the axis of the cylinder, and first link pivoted at one end to the body and its other end defining a fulcrum for pivoting movement of the lever, the position of the fulcrum along the length of the lever with respect to the first pivotal connection being adjustable thereby to allow adjustment of the mechanical advantage of the lever.

2. A cylinder assembly as claimed in claim 1, wherein the guide means comprises a second link pivoted at one end to the body and at its other end to the lever at or adjacent said first pivotal connection.

3. A cylinder assembly as claimed in claim 2, wherein the second link extends generally parallel to a line passing through the first pivotal connection and the fulcrum when the lever is in a rest position.

4. A cylinder assembly as claimed in any of the preceding claims, wherein first link extends generally normal to a line passing through the first pivotal connection and the fulcrum when the lever is in a rest position.

5. A cylinder assembly as claimed in any of the preceding claims, wherein the lever is provided with a slot extending along the length thereof and there is a second pivotal connection serving as said fulcrum which second pivotal connection locates in the slot and connects the other end of the first link to the lever. -12-

6. A cylinder assembly as claimed in claim 5, wherein said second pivotal connection comprises a link pin extending through the slot and through a bore in the other end of the first link, the link pin having a transverse hole through which a screw-threaded adjuster extends whereby the position along the length of the slot of the second pivotal connection is adjustable.

7. A cylinder assembly as claimed in claim 6, wherein an adjuster pin is pivoted to the lever to extend parallel to but spaced from the link pin, the adjuster pin also having a transverse bore through which said screw-threaded adjuster also extends.

8. A cylinder assembly as claimed in claim 7, wherein the transverse hole in the adjuster pin is threaded and the screw-threaded adjuster is threadingly engaged therewith, the screw-threaded adjuster being rotatably connected to the link pin.

9. A cylinder assembly as claimed in any of claims 6 to 8, wherein the screw-threaded adjuster is provided with a locking arrangement to resist unintentional adjusting rotation thereof.

10. A cylinder assembly as claimed in any of the preceding claims, wherein the first link comprises a pair of parallel links spaced apart with the lever extending therebetween.

11. A cylinder assembly as claimed in any of the preceding claims, wherein said first pivotal connection pivotally connects said other end of the second link to the lever.

12. A cylinder assembly as claimed in claim 11, wherein said first pivotal connection comprises a connecting pin extending through aligned bores in the lever and the first link and having a transverse hole through which the piston rod extends.

13. A cylinder assembly as claimed in claim 12, wherein the transverse hole is threaded and the piston rod is adjustably threaded in said hole.

14. An cylinder assembly as claimed in claim 13, wherein the piston rod is provided with a locking arrangement to resist unintentional adjusting rotation thereof.

15. A cylinder assembly as claimed in any of the preceding claims, wherein the second link comprises a pair of parallel links spaced apart with the lever extending therebetween.

16. A cylinder assembly as claimed in any of the preceding claims, wherein the body defines a pair of parallel hydraulic cylinders each fitted with a respective piston and having an associated operating mechanism, the levers of the two mechanisms each having a manually-operable portion and arranged so that the two portions extend essentially contiguously, generally in alignment with each other.

is

17. An hydraulic master cylinder assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.