AN IMPROVED DISC BRAKE SYSTEM

FIELD OF THE INVENTION

[0001] The present invention generally relates to a disc brake system and more particularly pertains to a brake caliper assembly for a straddle type vehicle.

BACKGROUND OF THE INVENTION

[0002] Disc brakes are increasingly provided in modern vehicles for better braking response, shorter stopping distances and efficient heat dissipation as drum brakes became ineffective to take care of these problems owing to increased vehicle power and speed. A simple disc brake system present at a front or rear wheel of a vehicle comprises of a control lever, a master cylinder assembly actuated by the control lever, a fluid hose, a disc mounted at the respective wheel hub and a caliper assembly operably connected to the master cylinder assembly through the fluid hose to receive brake fluid pressure from the master cylinder through the fluid hose. The caliper assembly further comprises of at least one piston operated by the brake fluid pressure in furtherance of which the brake pads clamp the disc on opposite disc surfaces. The engagement between the brake pads and the disc is a frictional contact that converts the kinetic energy of the moving vehicle to thermal energy and effectuates the brakes.

[0003] Various types of calipers like a floating caliper, fixed caliper and radial mounted caliper are known to be used in a disc brake system. The floating type caliper assembly design is more economical and light weight compared to both fixed and radial mounted calipers. A typical disc brake system comprising a floating type caliper assembly is shown in FIG. 1(a). It comprises of a caliper body 101, a fixed brake pad 201 and a movable brake pad 202 respectively supported on the caliper body 101, a piston 108 operated by the brake fluid 109 in the caliper body 101, a carrier support (plate) 106 anchored with vehicle frame (front fork or rear swing arm), at least two parallel guide pins 102, 104 rigidly connected to the carrier plate 106 and supporting the caliper body 101 through sliding joints. The direction of the sliding movement between the caliper body 101 and the guide pins is in lateral direction which is perpendicular to the opposite surfaces of the disc operating with the brake pad for braking.

[0004] The piston 108 is located on one side of caliper body 101 only. The movable brake pad 202 is supported on the piston side of the caliper body and is actuated by the piston 108 in lateral direction normal to the operating surface of the disc 107. The fixed brake pad 201 is supported by the caliper body through contact joints, being disposed proximately to the disc 107 and anchored by the caliper body 101 or with carrier plate 106 against disc friction. Thus, the fixed brake pad 201 is supported on an opposite side of the movable brake pad 202. Both the aforementioned brake pads are made of friction material and steel back plate.

[0005] FIG. 1 (b) shows a schematic view of a typical disc brake system including a floating type caliper assembly according to the prior art. The orientation of the fixed brake pad is fully constrained by and purely dependent on the caliper body only, whereas the orientation of the movable brake pad is only based on the piston, which is having some degree of freedom (tilting) with respect to the caliper body due to inherent clearance between the piston and caliper bore on the caliper body. When a force is applied on the control lever of the vehicle, it builds hydraulic pressure in the master cylinder located therein and the hydraulic pressure, transmitted from the master cylinder assembly to the caliper assembly through the brake hose, is applied on the piston in the caliper assembly to actuate the movable pad against the disc. At the same time, a reaction force of the piston acts on the caliper body by means of the same fluid pressure. This causes the caliper body to move in a direction opposite to that of the piston and actuates the fixed pad against the disc from other side of the movable pad. This phenomenon of starting of simultaneous engagement of both the brake pads with the disc on the opposite surfaces of the disc to attain a quick response in friction and thereby achieving brake torque is known as "brake bite".

[0006] Nonetheless, the current design of floating type caliper assembly in a disc brake system leads to poor braking response, uneven brake pad wear and poor brake bite, substantially caused due to inherent offset between brake pad load on caliper body and support reaction of the major guide pin 102 on the caliper body.

[0007] When braking is applied, the caliper body having such offset is tilted about an axis along disc radial line and with respect to disc surface due to the disc friction (brake reaction). In general, leading side of the movable pad is moved towards the disc in a greater measure than the trailing side due to the couple generated by disc friction. But, in case of fixed pad, trailing side is moved more towards the disc than leading side due to caliper body tilting and this is quite opposite to movable pad.

[0008] Thus both movable and fixed pads are tilted in same direction, for example in clockwise direction as shown in FIG. 2. This leads to poor clamping of brake pads over the disc surface since maximum contact pressure of each brake pad is at different position on each side of the disc. For example, fixed brake pad has maximum contact pressure with disc at its trailing side whereas movable brake pad has maximum contact pressure with disc at its leading side. This can cause disc bending which slacks to have any firm clamping of the pads.

[0009] Hence, the present subject matter is directed to overcome all or any of the problems as set forth above and obviate the lacunae in the prior art Therefore it is an object of the present invention to disclose a fluid operated disc brake system for vehicles capable of obtaining higher braking bite and optimum braking pressure at each side of the disc surface without attenuating the braking efficiency. Another object of the present invention is to disclose a fluid operated disc brake system capable of imparting a better brake feel to an operator of the vehicle and reducing uneven brake pad wear.

SUMMARY OF THE INVENTION

[00010] To this end, the present invention discloses a fluid operated disc brake system for a vehicle comprising: a caliper assembly slidably supported in the axial direction of a disc attached to and rotating with a wheel of the vehicle, the said caliper assembly further comprising at least one piston controlled movable brake pad engaging with one surface of the said disc and at least one fixed brake pad engaging with another surface of the disc, the movable brake pad and the fixed brake pad positioned opposite to each other and secured to the caliper body, the said disc sandwiched between the fixed brake pad and the movable brake pad, a carrier plate supporting the caliper body through at least one guide pin; characterised in that, the said guide pin is laterally disposed with a lateral offset for its support to caliper body in such a way that under brake torque, the caliper body tilts about any axis along disc radial line and in a direction opposite to the tilt of the movable brake pad, wherein when the said disc brake system is operable, the said fixed and movable brake pad tilt about axes along disc radial line in mutually opposite direction with respect to the disc contact surfaces and clamp the disc simultaneously at opposite contact surfaces of the said disc, but at the same location on the disc.

[00011] According to an aspect of the present invention, the guide pin supporting the caliper body is laterally disposed from the carrier plate and towards the same side of the fixed brake pad and a portion of the caliper body supported by the guide pin is also laterally disposed from the fixed pad and opposite to the movable pad, in such a way that a couple acting on the caliper body about an axis along disc radial line is opposite to direction of titling of movable pad wherein the said fixed and movable brake pad tilt about axes along disc radial line and in mutually opposite direction with respect to the disc contact surfaces and clamp the disc simultaneously at the opposite contact surfaces of the said disc, but at the same location on the disc.

[00012] The foregoing objectives and summary provide only a brief introduction to the present subject matter. To fully appreciate these and other objects of the present subject matter as well as the subject matter itself, all of which will become apparent to those skilled in the art, the ensuing detailed description of the subject matter and the claims should be read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[00013] The above and other features, aspects, and advantages of the subject matter will be better understood with regard to the following description, appended claims and accompanying drawings where:

FIG. 1(a) shows a sectional pictorial view of a typical floating type caliper assembly of a disc brake system according to the prior art, sectioned along its piston and major guide pin axes.

FIG. 1 (b) shows a schematic view of a typical disc brake system including a floating type caliper assembly according to the prior art.

FIG. 2 shows the movement of a typical disc brake and the forces acting on the disc brake system of FIG. 1(a) and 1(b) under the braking torque.

FIG. 3 shows a side view of a concerned two wheeled vehicle capable to incorporate the present invention.

FIG. 4 depicts a schematic view of an improved disc brake system according to the present invention when viewed from front side and sectioned along its piston axis.

FIG. 5 shows the operation of the improved disc brake system according to the present invention under vehicle static conditions.

FIG. 6 shows a schematic view of the improved disc brake system and the forces acting on it under the effect of the braking torque and when viewed from front side and sectioned along its piston axis.

DETAILED DESCRIPTION OF THE INVENTION

[00014] The solution for this problem is to provide an offset of caliper body support reaction with respect to disc plane in such a way the caliper body can be tilted in a direction opposite to tilting of the movable pad under the reaction of brake torque. This enables both fixed and movable pads to tilt mutually opposite directions with respect to the disc surface so that leading side of both the pads are pressed against corresponding disc surfaces more than the other (trailing) side of the pads. It creates self-energizing effect simultaneously on both the pads, which then enhance the clamping force against the disc without any laterally bending of the disc. It also reduces the overall response delay. Hence braking performance and dynamic feel and pad wear life are improved.

[00015] In order that those skilled in the art can understand the present invention, the invention is further described below so that various features of the brake system with an improved floating type caliper assembly proposed here are discernible from the description thereof set out hereunder. However these descriptions and the appended drawings are only used for those skilled in the art to understand the objects, features, and characteristics of the present invention and not to be used to confine the scope and spirit of the present invention. In the supporting FIGs, the same reference numerals are given to members and parts having the same functions.

[00016] In the ensuing exemplary embodiments, the vehicle is a straddle type vehicle capable of holding a disc brake system at front wheel or rear wheel or both wheels. However it is contemplated that the concepts of the present invention may be applied to other types of vehicles within the spirit and scope of this invention including a scooter type motorcycle, three wheeled vehicles and four wheeled vehicles also. The present invention is restricted to a disc brake system with floating type caliper assembly and is now explained with the help of rendered drawings.

[00017] FIG. 3 shows a side view of a concerned two wheeled vehicle in the form of a motorcycle capable to incorporate the present invention. The motorcycle M comprises a body frame assembly made up of a number of tubes welded together. The motorcycle M has a steerable front wheel 11 and a driven rear wheel 12. The body frame primarily includes a head pipe 1 disposed at a front end of the body frame, a main tube running across the longitudinal axis of the motorcycle M and enclosed by several motorcycle components, and a down tube 2. A front fork 3 may be connected to the head pipe 1 by any known type of suspension system and rotatably carries the front wheel 11. The head pipe 1 supports a steering shaft (not shown) disposed inside the head pipe 1. The upper and lower ends of the steering shaft are fixed on an upper bracket and the under bracket. The front end of the main tube and an upper end of the down tube 2 are connected to the head pipe 1. The down tube 2 extends obliquely downward in front of an engine 15 from the head pipe 1 whereas the main tube extends rearward from the front end thereof. A front fender 4 is provided below the under bracket to avoid the motorcycle and its occupants from being splashed with mud. A fuel tank 5 is disposed above the main tube for storing the fuel for propelling the motorcycle M. A seat 6 for a driver and a pillion is further provided, with the said seat 6 being placed behind the fuel tank 5 and rearwardly of the main tube.

[00018] The rear wheel 12 revolves about a sprocket splined shaft (or central axle) 13. The axle 13 is supported at each end by a swing arm 14, the swing arm in turn pivotally connected to the body frame of the motorcycle M by a rear suspension 10. Generally a motorcycle may use any of the two arrangements for rear suspensions, namely dual suspension and mono suspension. However the present motorcycle is exemplified through a dual suspension system. The dual suspensions are fixed at their upper ends to the motorcycle frame. Their lower ends are fixed to the swing arm 14.

[00019] The anterior portion of the motorcycle placed forward to the fuel tank 5 comprises of a headlamp assembly, the headlamp assembly further comprising a headlamp 8 and a visor 7 placed forward to a handlebar assembly. The handle bar assembly further comprises of a handle bar 9 extending transversely to the vehicle and several control switches for various motorcycle operations.

[00020] The said motorcycle M is powered by an internal combustion engine (hereinafter "engine") 15 disposed below the main tube and supported by the down tube 2. The engine may be liquid-cooled or air-cooled. Drive force output from the engine 15 is transmitted to the rear wheel 12 through a transmission system. The transmission system includes a clutch actuated by a clutch lever placed forwardly to one side of the handle bar 9, a gear box and a chain drive. The transfer of power from the engine to the rear wheel takes place generally by disengaging the clutch by pulling the clutch lever and thereafter manually shifting the gears in the gear box through a foot pedal 16 manually operated by the operator of the motorcycle M.

[00021] A fluid operated disc brake system with a disc 107 and a floating type caliper assembly 101 is connected to the front wheel 11 of the motorcycle according to the present invention. FIG. 4 shows the schematic view of floating type caliper assembly of the disc brake system. The disc brake system comprises of a caliper assembly slidably supported in the axial direction of the disc 107 attached to and rotating with the front wheel 11 of the vehicle, the said caliper assembly further comprising at least one piston controlled movable brake pad 202 engaging with one surface of the said disc 107 and at least one fixed brake pad 201 engaging with another surface of the disc 107, and a carrier plate 106' supporting the caliper body 101' through at least one guide pin 102'. The movable brake pad 202 and the fixed brake pad 201 are positioned opposite to each other and secured to the caliper body 101' and the disc 107 is sandwiched between the fixed brake pad and the movable brake pad. The fixed brake pad and a movable brake pad and piston perform known functions, except as otherwise indicated.

[00022] In a preferred embodiment, the guide pin is a major guide pin (referred to as "guide pin" in the said and subsequent figures). The guide pin 102' is rigidly secured to the carrier plate 106' and supporting the floating type caliper body 101'. A portion of the caliper body 101' supported by the guide pin 102' is laterally disposed from the fixed brake pad 201 and opposite to the movable brake pad 202. The guide pin 102' is laterally disposed from the carrier plate 106' opposite to the movable brake pad 202 as well as laterally extended beyond the fixed brake pad 201. The guide pin and the portion of the caliper body supported by the former are radially disposed outward from the outer circumference of the disc. Thus the major guide pin and the said portion of the caliper body are on opposite side of the movable brake pad and they maintain adequate clearance with the disc.

[00023] Initially when braking is applied through the control lever (not shown), both the movable brake pad 202 and fixed brake pad 201 are actuated against the disc 107 on opposite surfaces, by means of hydraulic pressure acting on the piston 108 enclosed in the caliper body 101'. As long as the vehicle is in static condition, both the brake pads are clamped against the disc on the opposite surfaces and aligned along the disc contact surfaces as shown in FIG. 5.

[00024] However whenever brakes are applied on the moving vehicle, the said fixed and movable brake pad tilt about axes along disc radial line in mutually opposite direction with respect to the disc contact surfaces, mainly due to mutually opposite couples generated on the movable brake pad and caliper body by disc frictional forces. The response of the caliper body and the brake pads under disc frictional forces according to the present invention is shown in FIG. 6. The leading side of both the brake pads are pressed against corresponding disc surfaces more than the other (trailing) side of the brake pads. Thus under the present invention, both the brake pads apply equal pressure on the disc at any contact point on the disc at same angular position and on opposite disc surfaces thereby result in higher braking bite on the disc. They clamp the disc simultaneously at opposite contact surfaces of the said disc, but at the same location on the disc.

[00025] Therefore in the present invention, the caliper body is slidably supported by the guide pin, with an offset of caliper body support reaction from the disc in the same side of the fixed pad. This is quite opposite to the conventional floating type caliper assembly where both the brake pads tilt in the same direction leading to poor pad clamping over the disc surface. The minor (second) support of the caliper body by minor guide pin can be as it is in the present art.

[00026] From the foregoing description, it will be appreciated that the present invention offers many advantages. The present invention provides a negative offset of caliper body support reaction with respect to disc plane in such a way that the caliper body can be tilted in a direction opposite to tilting of the movable pad due to disc frictional forces. This enables both the fixed and movable pads to tilt in mutually opposite directions with respect to the disc contact surfaces so that the leading side of both the pads is pressed against corresponding disc surface more than the other (trailing) side of the pads.

[00027] It enhances the clamping force against the disc without any lateral bending of the disc thereby reducing the overall braking response delay and stopping distance or stopping time. Hence braking performance and dynamic feel and pad wear life are improved. Additionally the braking bite can also be easily perceived by the operator of the vehicle which leads to his satisfaction and higher level of rider confidence to use the braking. The present disc brake system can be used with front or rear or both wheels and also along with a hydraulic system.

[00028] The present subject matter is thus described. The movable brake pad is movable through a sliding effect with respect to the caliper body. The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore the forgoing description is to be considered exemplary, rather than limiting, and the true scope of the invention is that described in the appended claims.

We claim:

1. A fluid operated disc brake system for a vehicle comprising:

a caliper assembly slidably supported in the axial direction of a disc attached to and rotating with a wheel of the vehicle, the said caliper assembly further comprising at least one piston controlled movable brake pad engaging with one surface of the said disc and at least one fixed brake pad engaging with another surface of the disc, the movable brake pad and the fixed brake pad positioned opposite to each other and secured to the caliper body, the said disc sandwiched between the fixed brake pad and the movable brake pad,

a carrier plate supporting the caliper body through at least one guide pin,
characterised in that,

the said guide pin is laterally disposed with a lateral offset for its support to caliper body in such a way that under brake torque, the caliper body tilts about any axis along disc radial line and in a direction opposite to the tilt of the movable brake pad,

wherein when the said disc brake system is operable, the said fixed and movable brake pad tilt about axes along disc radial line in mutually opposite direction with respect to the disc contact surfaces and clamp the disc simultaneously at opposite contact surfaces of the said disc, but at the same location on the disc.

2. The fluid operated disc brake system as claimed in claim 1, wherein the guide pin supporting the caliper body is laterally disposed from the carrier plate and towards the same side of the fixed brake pad and a portion of the caliper body supported by the guide pin is also laterally disposed from the fixed pad and opposite to the movable pad, in such a way that a couple acting on the caliper body about an axis along disc radial line is opposite to direction of titling of movable pad wherein the said fixed and movable brake pad tilt about axes along disc radial line and in mutually opposite direction with respect to the disc contact surfaces and clamp the disc simultaneously at the opposite contact surfaces of the said disc, but at the same location on the disc.

3. The fluid operated disc brake system as claimed in claim 1, wherein the said disc brake system is capable of being used in association with a front wheel or a rear wheel or both wheels of the said vehicle.

4. The fluid operated disc brake system as claimed in any of the preceding claims wherein the said disc brake system is capable of being used with hydraulic system.