GB2213890A - Vehicle having compressed air and hydraulic operated brakes - Google Patents

Abstract

A heavy road vehicle with independent front wheel suspension has a compressed air operable braking system including a foot operable brake controlling valve (5), output air pressures from which operate conventional roar wheel brake actuators (10;11) and a hand operable valve (16) operating air pressure responsive spring brakes (12, 13) for secondary or parking brake operation and wherein a compressed air output pressure line (6) from the foot operable valve is connected to hydraulic master cylinders (20, 21) which control the application of hydraulic braking pressure to front wheel actuators (27, 28). <IMAGE>

Description

Motor Vehicle with Fluid Pressure Operable Braking System.

This invention relates to a motor vehicle with a fluid pressure operable braking system, particularly a compressed air operable braking system.

Compressed air operable braking systems for heavy road vehicles usually comprise compressed air pressure operable actuators mounted on the vehicle axles in close proximity to the disc brakes or drum brakes of the respective wheels of the vehicle. Typically, where the brakes are drum brakes, the are operated by 'S cams through levers, such levers often incorporating slack adjusters. Such actuators tend to be quite bulky and are required to be arranged to be positioned well clear of any suspension components and steering linkages. Some such vehicles have independent suspensions on one or more axles and in this case there may be insufficient room in proximity of the wheels to accommodate the compressed air operable actuators.

The object of the present invention is, therefore, to provide such a vehicle with a compressed air operable braking system in spite of the fact that insufficient room exists for compressed air operable actuators in proximity of the wheels.

According to the present invention there is provided a motor vehicle having a compressed air operable braking system, said vehicle having front and rear wheel axles at least the rear wheel axle being provided with brakes operable by pneumatic pressure actuators and the front wheels of the front wheel exle being provided with brakes operable by hydraulic pressure actuators connected via flexible pipe connections to hydraulic master cylinder rear operable by compressed air actuators.

In order that the invention may be more clearly understood and readily carried into effect, the same will be further described by way of example with reference to the accompanying drawings of which: Fig. 1 illustrates a compressed air braking system of a vehicle in accordance with the invention and, Fig. 2 and 3 illustrate alternative embodiments.

Referring to Fig. 1, this shows a brake system of a passenger bus in accordance with the invention, the passenger bus having independent front wheel suspensions. The compressed air braking system is provided with reservoirs 1, 2 and 3 which are charged in conventional manner, via a multicircuit protection valve 4, from an engine-driven compressor and an air dryer neither of which are shown in the drawing.

Reservoirs 1 and 2 provide compressed air sources for a driver's foot-operable dual valve 56 providing separate outputs on lines 6 and 7 to front and rear axle brakes.

Line 7 is connected as a control input to a relay valve 8, the supply to which is derived also from reservoir 2. The output of relay valve 8 appears on line 9 and is connected to respective pressure inputs of service actuator portions 10 and 11 of respective combined spring and service actuators 12 and 13. These actuators are pivotally coupled to respective brake levers 14 and 15 of S-cam operated brake brake mechanisms of the wheels of the rear axle of the vehicle.

The reservoir 3 is connected as a supply source to a separate manually operable hand valve 16 fitted in the driver's cab of the vehicle and the output of which is connected as one input to a double check valve 17, the second input of which is connected to the line 9. The output line 18 of the double check valve is connected via a quick release valve 19 to respective control pressure ports of the spring brake portions of actuators 12 and 13.

The output line 6 of the dual foot valve 5 is connected in common to compressed air actuators 20 and 21 which are mounted integrally on the chassis of the vehicle with hydraulic master cylinders 22 and 23 having a common hydraulic fluid reservoir 24. Flexible hydraulic pressure output lines 25 and 26 of the respective master cylinders are connected to the respective independently suspended front wheel axle mounted hydraulic pressure slave cylinders 27 and 28 which in turn are pivotally linked to brake levers and slack adjusters 29 and 30 of the respective S-cam operated brake mechanisms of independently suspended front wheel axle of the vehicle.

In operation of the compressed air braking system of Fig.1, the reservoirs 1, 2 and 3 are charged in known manner from the mentioned compressor through the mentioned air dryer and the multi-circuit protection valve 4. The multi-circuit protection valve operates to ensure that in the event of failure of one of the reservoirs or the associated connections thereto, the other reservoirs are still able to acquire a predetermined pressure.

In normal operation of the vehicle the driver will depress the pedal of the dual foot valve 5 in order to apply to service brakes and decelerate the vehicle. The pressure thus produced in the line 7 is applied as a control pressure to relay valve 8 which relays a proportion of the pressure from the reservoir 2 to the service actuator portions 10 and 11, associated with the rear axle of the vehicle. These actuators, therefore, oeprate the rear wheel brakes via levers 14 and 15.

At the same time, the independent pressure which is produced in line 6, as derived from reservoir 1, is applied to the actuators 20 and 21 to produce corresponding hydraulic pressures in master cylinders 22 and 23. These hydraulic pressures are applied via lines 25 and 26 to slave cylinders 27 and 28. These cylinders then apply output forces to the brake levers 29 and 30 of the brake mechanisms of the respective front wheels of the vehicle. It will be appreciated that the master cylinders 22 and 23 are replenished with hydraulic fluid from reservoir 24 in a conventional manner and the available stroke and effective area of the master cylinders is chosen to provide appreciably more than the maximum operating volume of hydraulic fluid required by slave cylinders 27 and 28.

The manually operable brake control valve 16 is normally in a position where it applies full reservoir pressure from the reservoir 3 via the double check valve 17 to output line 18.

The pressure thus acts via the release valve 19 to hold the spring brake portions of the double actuators 12 and 13 in their inoperative positions. In order to apply the spring brakes the driver may move the handle of the control valve 16 into a brakes applied position giving a reduced or zero output pressure on line 18, whereby the spring brakes are respectively partially or fully released in secondary or parking operation. The double check valve 17 operates in known manner to prevent compounding of a service brake application with spring brake force. This happens because the pressure on line 18 is selected by the valve 17 to be the largest of the two pressures applied to valve 17.

Referring to Fig. 2, this illustrates an alternative manner of connecting the hydraulic salve cylinders 27 and 28 to the hydraulic master cylinders. By interconnecting the hydraulic lines to both sides of the front wheels of the vehicle as shown it is ensured that the pressures are balanced.

In the further alternative of Fig. 3, the respective master cylinders are provided with separate reservoirs but otherwise the arrangement is the same as that of Fig. 1.

By virtue of the invention it is possible to provide a vehicle with a compressed air braking system although there may not be sufficient space for an operated actuator adjacent to the brake levers. The hydraulic slave cylinders which are connected to the brake levers are appreciably smaller than the air-actuators which can now be more conveniently located where space permits.

Having due regard for the fact that the driver's cab of vehicles such as passenger buses, for which the present invention is particularly applicable, is usually located over the front axles the hydraulic master cylinders are themselves located very close to the foot valve 5. The response time for the front axle brakes is therefore advantageously shorter than the response time for the air operated rear axle brakes, whilst retaining the overall advantages of air brake systems.

Although the vehicle considered in the foregoing has only one axle at the front and one axle at the rear, the invention can readily be applied to vehicles with more than one axle at the front or the rear. If the vehicle has two steered pairs of wheels these may each be provided with hydraulic slave cylinders which are pressurised from air pressure actuated master cylinders as described in the foregoing.

Claims (6)

1. A motor vehicle having a compressed air operable braking system, said vehicle having front and rear wheel axles at least the rear wheel axle being provided with brakes operable by pneumatic pressure actuators and the front wheels of the front wheel axle being provided with brakes operable by hydraulic pressure actuators connected via flexible pipe connections to hydraulic master cylinder rear operable by compressed air actuators.

2. A motor vehicle as claimed in claim 1, wherein a separate hydraulic master cylinder is provided for the brakes of the wheels on each side of the front wheel axle.

3. A motor vehicle as claimed in claim 2, wherein said separate master cylinders are provided with separate fluid reservoirs.

4. A motor vehicle as claimed in clam 1, 2 or 3 wherein said wheels on each side of the front wheel axle are independently suspended.

5. A motor vehicle as claimed in claim 1, 2, 3 or 4 wherein the hydraulic pressure actuators are coupled to the respective brake mechanisms via brake levers which incorporate slack adjusters.

6. A motor vehicle including a brake system substantially as described herein with reference to Fig. 1, or Fig. 1 and Fig 2 or Fig. 1 and Fig. 3 of the accompanying drawings.