GB2468303A

GB2468303A - Brake operating lever having a pivot point between a brake pedal and a connection for a master cylinder

Info

Publication number: GB2468303A
Application number: GB0903591A
Authority: GB
Inventors: Barry Lett
Original assignee: Gordon Murray Design Ltd
Current assignee: Gordon Murray Design Ltd
Priority date: 2009-03-03
Filing date: 2009-03-03
Publication date: 2010-09-08
Also published as: GB0903591D0

Abstract

A braking system for a vehicle comprising a master cylinder 36 and a pivoting operating lever 22, the operating lever 22 having a brake pedal 24 at one end and being arranged to act on a piston moveable within the master cylinder, wherein the operating lever 22 is pivoted at a point 20 along its length that is between the brake pedal 24 at the point 30 at which it acts on the piston. The brake master cylinder 36 and any associated servo unit 34 (via which the lever may be acting on the piston) can then be mounted above and behind the lever 22, taking them away from the impact zone to the front of the vehicle. A braking system is also disclosed, in which the master cylinder piston moves in a direction opposite to the brake pedal.

Description

Vehicle Braking System

FIELD OF THE INVENTION

The present invention relates to a vehicle braking system.

BACKGROUND ART

Most modern braking systems for vehicles comprise a brake pedal located within the cabin, a brake master cylinder that converts a force applied to the brake pedal into a hydraulic pressure, and brake callipers containing pistons that convert the hydraulic pressure to a clamping force that is applied to a friction material -either brake pads pressed against a brake disc, or brake shoes pressed against a brake drum.

The brake master cylinder comprises an elongate cylinder within which slide (usually) two pistons, each supplying hydraulic pressure to one of two separate braking circuits so that the system as a whole has a degree of redundancy. A force applied to the brake pedal is multiplied by a lever action and transmitted to the pistons. Reservoirs of brake fluid are mounted to the master cylinder in order to keep the circuits topped up with fluid.

The brake pedal must (obviously) be located at a low point within the cabin, in the driver's footwell. To provide easy access to the fluid reservoirs for servicing purposes, the master cylinder needs to be located at an elevated location -usually within the engine compartment, in front of the driver. The brake pedal is therefore usually fitted to the lower end of a lever arm pivoted at its upper end, with the connection to the brake master cylinder at a point along the lever arm below the pivot but above the pedal. The relative positioning of the pedal, the pivot and the connection to the brake master cylinder is dictated by the desired mechanical advantage.

SUMMARY OF THE INVENTION

Given recent increases in fuel costs and urban traffic congestion, together with the need to reduce CO2 emissions, there is a drive to design and manufacture smaller and more space efficient vehicles. Although designed to be small, any such vehicle still has to satisfy existing expectations of cabin space (for reasons of occupant comfort) and be capable of accommodating all the component hardware requirements needed to ensure correct functionality within the vehicle architecture.

In addition to these requirements, a modern vehicle must also satisfy mandatory safety requirements for both passengers and pedestrians. This requirement is probably the biggest threat to achieving the overall size reduction necessary to make a difference to city traffic and parking congestion evident today. In order to meet these crash performance and occupant injury levels, expected in a modern road going vehicle, space must be designed into the overall size to accommodate crumple zones. These crumple zones are required to minimize the body deceleration generated by an impact with another vehicle or large object. Typically in the range of 250 -400mm (depending on the type and weight of vehicle) the crumple zone must be free of "hard" non-compressible components, thus permitting the body to be decelerated and its kinetic energy to be absorbed.

Pedestrian impact legislation also requires deformation clearances to enable a pedestrian head form, lower leg and upper leg to be decelerated thereby rninimising serious injury in the event of being hit by a car. The laboratory testing for this requirement means that (typically) clearances from 55 to 80mm are needed between the outer body surface and any non-deformable component beneath that surface. This requirement has recently driven considerable packaging and construction changes to the front of vehicles.

Typically, the brake master cylinder and booster (servo) components are packaged at the front of the vehicle as noted above. The master cylinder push rod is directly connected to the brake pedal, between the pivot centre and the pedal pad (the distance being driven by the required mechanical ratio of pedal stroke to cylinder stroke). In this configuration the booster and master cylinder face forwards in the vehicle and are mounted ahead of the front cabin bulkhead.

This conventional installation enables the hydraulic connections and brake fluid reservoir to be accessed from the front service compartment (i.e. the engine bay of a front-engined car) and mounted directly to the front bulkhead -in a RHD or LHD installation the front bulkhead receives local reinforcement from the RH or LH front longitudinal member.

The brake booster and master cylinder assembly is non-compressible and therefore can significantly affect the overall performance of the vehicle in a crash, if it is contacted at any stage during a crash event. Due to practical installation constraints it also needs to be mounted relatively high on the front bulkhead. If this position conflicts with the pedestrian impact mark up zones (which it can be expected to do) then the front bonnet surface will have to be placed approximately 80mm above the highest point of the master cylinder and booster, to minimise injury to pedestrians and comply with the applicable regulations.

With a conventional brake booster installation, realising the desired overall dimensions of the compact vehicle together with the passive safety targets is not possible. The front overhang dimension would need to be increased by 200- 250mm, and the bonnet height would need to be raised in order to give adequate pedestrian protection.

This arrangement works well for the (relatively) large cars that are presently commonplace. With minor design adjustments, it has been accommodated even in smaller city cars such as the Mercedes A-Class, and the Toyota Yaris and Aygo. In the production of an extremely compact city car of the type that we envisage, this is not possible since there will not be enough space ahead of the driver's foot to accommodate the lever arm, the brake master cylinder, and an impact-absorbing structure.

The present invention therefore provides a braking system for a vehicle, comprising a master cylinder and a pivoting operating lever, the operating lever having a brake pedal at one end and being arranged to act on a piston moveable within the master cylinder, wherein the operating lever is pivoted at a point along its length that is between the brake pedal at the point at which it acts on the piston.

As a result, the piston will move in a direction opposite to that of the brake pedal -as the driver pushes the brake pedal towards the front of the vehicle, the piston will move toward the rear. In addition, the brake master cylinder and any associated servo unit (via which the lever may be acting on the piston) can be mounted above and behind the lever, taking them away from the impact zone to the front of the vehicle.

The pivot will usually be located on the operating lever at a location closer to the point at which it acts on the piston than to the pedal, to offer a mechanical advantage to the braking system.

The present invention also provides an operating lever for a vehicle braking system comprising a brake pedal at one end, a connection for a brake master cylinder, and a pivot point between the brake pedal and the connection.

The present invention further provides a vehicle having a braking system comprising a master cylinder and a pivoting operating lever, the operating lever having a brake pedal at one end and being arranged to act on a piston moveable within the master cylinder, wherein the operating lever is connected to the vehicle chassis via a pivot located at a point along its length that is between the brake pedal at the point at which it acts on the piston.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described by way of example, with reference to the accompanying figures in which the sole figure 1 is a vertical section through the front part of a vehicle incorporating the braking system of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

We propose to employ the same components as a conventional braking system, for reasons of supply and reliability, but to repackage them in a manner that permits conformity with both front end crash crumple zone and pedestrian impact deformation requirements. Rather than position the booster and master cylinder assembly to face forward (so it is accessible from the front of the car) according to the present invention it is turned through 1800 so that it faces rearwards. This change moves the non-compressible mass of the assembly away from the crumple zone (under the windshield). To maintain correct functionality with the booster re-orientated, the push rod is actuated by an actuator link rather than directly from the pedal. Service access to the fluid reservoir can be achieved via a suitable opening hatch or by remotely positioning the reservoir.

This arrangement is illustrated in figure 1. A tubular frame chassis 10, shown in dotted lines, supports vehicle bodywork 12 and rolling gear including a front wheel 14. The chassis 10 includes a cross member 16 and supporting risers 18, onto which is mounted the braking system of the present invention.

Specifically, a pivot 20 extends between the risers 18 and carries an operating lever 22. This pivots at a point along its length, and has a relatively long extension downwards towards a pedal pad 24 which can be operated by the foot 26 of a driver 28. In the opposite direction, the operating lever 22 extends upwardly beyond the pivot 20 to an attachment point 30. Thus, as the pedal pad 24 is pushed downward and forward by the driver 28, the attachment point moves rearwardly as the operating lever 22 pivots.

A master cylinder push rod 32 is connected to the attachment point 30.

This passes through a vacuum servo 34 and into the brake master cylinder 36.

Of conventional design, the push rod 32, vacuum servo 34 and brake master cylinder 36 are mounted in a rearward-facing orientation, i.e. with the brake master cylinder 36 located rearward relative to the vacuum servo 34. They are mounted to a suitable bracket 38 supported on the pivot 20 and the cross member 16, so as to provide a rigid and secure location.

In this way, the brake master cylinder 36 is oriented away from the vehicle body work 12 and a significant spacing 40 is provided between the front edge of the vehicle bodywork and the first rigid item. This spacing can allow for the necessary pedestrian impact requirements.

In addition to the main advantage of protecting the impact deformation space on a small vehicle a small front overhang, a vehicle assembly benefit can also be obtained through the invention. Previously, the installation into the vehicle was dependant on the requirement to position the brake pedal inside the cabin. This necessitated that the components be assembled from inside the car, whilst positioning the booster and master cylinder assembly in the front service compartment from outside the car. The above-described system can be installed as one module that includes the complete brake pedal and booster assembly.

This aspect of the vehicle assembly should give a reduction in assembly time, and also permits a complete assembly unit to be supplied as a quality assured module that can be installed directly to the vehicle.

It will of course be understood that many variations may be made to the above-described embodiment without departing from the scope of the present invention.

Claims

CLAIMS1. A braking system for a vehicle, comprising a master cylinder and a pivoting operating lever, the operating lever having a brake pedal at one end and being arranged to act on a piston moveable within the master cylinder, wherein the operating lever is pivoted at a point along its length that is between the brake pedal at the point at which it acts on the piston.
2. A braking system for a vehicle according to claim 1 in which the piston moves in a direction opposite to that of the brake pedal.
3. A braking system for a vehicle according to claim 1 or claim 2 in which the pivot is located on the operating lever at a location closer to the point at which it acts on the piston than to the pedal.
4. A braking system for a vehicle according to any one of the preceding claims in which the lever acts on the piston via a servo unit.
5. An operating lever for a vehicle braking system comprising a brake pedal at one end, a connection for a brake master cylinder, and a pivot point between the brake pedal and the connection.
6. A vehicle having a braking system comprising a master cylinder and a pivoting operating lever, the operating lever having a brake pedal at one end and being arranged to act on a piston moveable within the master cylinder, wherein the operating lever is connected to the vehicle chassis via a pivot located at a point along its length that is between the brake pedal at the point at which it acts on the piston.
7. A braking system for a vehicle, comprising a master cylinder and a brake pedal arranged to act on a piston moveable within the master cylinder, in which the piston moves in a direction opposite to that of the brake pedal.
8. A braking system for a vehicle substantially as described herein with reference to and/or as illustrated in the accompanying figures.