GB2140109A - Tandem-axle rear suspension - Google Patents

Abstract

In a vehicle having a tandem- axle rear suspension provided with a load-sensitive road wheel braking arrangement, the respective tandem axles 22, 24 are connected by way of motion-transmitting linkage 56 to a Bowden cable 54 for actuation of a brake valve control element 44 for varying the ratio of fluid pressure supplied to road wheel brakes of the respective tandem axles in accordance with the axle loading. The arrangement is such that normal ride movement of the tandem axles is transmitted by way of the Bowden cable to produce a differential load-dependent actuation movement of the brake valve control element, whereas on pure rocking movement of the tandem axle suspension the sleeve 60 and core 58 of the Bowden cable move conjointly, without affecting the position of the brake valve control element. <IMAGE>

Description

SPECIFICATION Tandem-axle rear suspension This invention relates to a vehicle having a tandem-axle rear suspension provided with a load-sensitive road wheel braking arrangement.

The invention is particularly concerned with a balanced-beam (so-called "walking beam") type of suspension.

A balanced-beam suspension is one in which a pair of tandem axles can rock about a central pivot without deflecting the main road spring. In practice, the axles can be controlled by control arms, a see-saw type of beam, by a leaf spring, or by any combination of these.

By law, a tandem axle type of rear suspension must include a load-sensing valve to compensate for the load change which occurs when the vehicle is unladen. The load change at the rear axle of a heavy vehicle can for example be within the range of 11/2 to 11 tonnes.

A further factor is that with such heavy vehicles, a considerable degree of servo assistance is provided for the brakes.

By the present invention, from one aspect, there is provided a vehicle having a tandemaxle rear suspension fitted with a load-sensitive road wheel braking arrangement, in which a Bowden cable is connected to actuate the control element of a single brake valve for proportioning a supply of pressure fluid between the road wheel brakes of both tandem axles of a balanced-beam rear suspension, and the Bowden cable is connected by way of motion-transmitting linkage to both tandem axles such that on simultaneous rise and fall movement of the tandem axles the Bowden cable produces corresponding load-dependent actuation movement of the control element of the brake valve, Whereas on conjoint pivotal movement of the tandem axles about a common suspension pivot the Bowden cable is without effect on the position of the control element of the brake valve.

According to this invention, also, from another point of view, there is provided a vehicle having a tandem-axle rear suspension fitted with a load-sensitive road wheel braking arrangement, in which a suspension pivot is mounted on a frame portion of the vehicle, first and second axles for respective opposed pairs of road wheels of the vehicle are connected to the suspension pivot by a suspension means permitting rise and fall movement of the first and second axles simultaneously and indedendently relative to the frame portion, and also conjoint pivotal movement of the first and second axles about the suspension pivot, and a single brake valve is arranged to proportion a supply of pressure fluid to wheel brakes for the road wheels of the first and second axles in accordance with the position of a control element of the brake valve relative to a reaction portion of the brake valve via a Bowden cable comprising a flexible core slidably disposed within a flexible sleeve, in that at the output end of the Bowden cable the core is connected to the control element of the brake valve and the sleeve is connected to the reaction portion of the brake valve, and at the input end of the Bowden cable the core and sleeve are connected by way of motion-transmitting linkage one to the first axle and the other to the second axle, such that rise and fall movement of the first and second axles simultaneously relative to the frame portion of the vehicle produces sliding movement of the core relative to the sleeve, for actuation of the control element of the brake valve, whereas conjoint pivotal movement of the first and second axles about the suspension pivot produces conjoint movement of the core and sleeve at the input end of the Bowden cable, without actuation of the control element of the brake valve.

In such a vehicle in accordance with the present invention, one brake valve (specifically, one load-sensing valve) is sufficient to provide the necessary regulation of the air flow to the brakes of both axles of the tandem axle rear suspension. This results in a considerable cost saving as compared with the use of separate valves for the respective tandem axles, and also a corresponding weight saving, and additionally makes it possible to use a less complex piping arrangement than if two valves were used.

Effectively, the linkage between the axles and the brake valve relays to the valve only the mean rear suspension movement, whilst ignoring axle movement resulting solely from suspension rock.

As well as being potentially cheaper, the proposed arrangement can be substantially more accurate in operation than existing arrangements.

Broadly, the Bowden cable transmits a movement which represents the difference in the angular movement at the pivots of the respective tandem axle control or positionsensing arms, and thus transmits a movement which is indicative of the travel of the respective axles.

If the tandem axles are guided by centrally mounted and oppositely directed control arms having relatively closely spaced pivotal connections to the frame portion of the vehicle, a suitable motion-transmitting linkage comprises a pair of cantilever arms mounted on the respective control arms and pivotally connected (for example by respective clevis connections) to the sleeve and the core respectively of the Bowden cable.

In principle, it would be possible to omit the control arms (for example, with control of tandem axle movement by the main suspen sion springs), and put the cantilever arms directly on one of the suspension springs.

Alternatively, light position-sensing arms, for example made of sheet metal, could be provided solely to operate the load-sensing valve system.

The drawing shows a fragmentary and somewhat schematic perspective view of a preferred form of tandem-axle rear suspension with a load-sensitive road wheel braking arrangement in a vehicle in accordance with the present invention.

As is shown in the drawing, a frame portion 10 of a heavy-duty motor vehicle includes a laterally spaced pair of longitudinally extending side frame members 1 2 interconnected by a cross-member 14.

In the region of the cross-member 14, outrigger portions 1 6 (of which only one is shown in the drawing) extend laterally outwardly from the respective side frame members, and a main suspension spring 1 8 is pivotally mounted at a central pivot region 20 thereof to each of the outrigger portions 16.

The end portions-of the main suspension spring 1 8 are located by way of spring sliders (not shown) to first and second tandem axles 22 and 24 respectively, such that the tandem axles are arranged respectively forwardly and rearwardly of the cross-member 14.

For controlling the movement of the tandem axles, a longitudinally extending upper control arm 26 is pivotally connected to an upstanding bracket 28 formed on the first tandem axle 22 and to a bracket 30 secured to the cross-member 14, and correspondingly an oppositely directed upper control arm 32 is pivotally connected by way of respective brackets 34 and 36 to the second tandem axle 24 and to the cross-member 14. The two brackets 30 and 36 on the cross-mernber 14 are arranged adjacent each other, on opposite sides of the cross-member.

Each tandem axle is also provided with a laterally spaced pair of longitudinally extending lower control arms. The drawing shows one of these lower control arms for each tandem axle, namely a control arm 38 pivotally connected to a lower part of the outrigger portion 1 6 and to a depending bracket on the first tandem axle 22, and an oppositely directed longitudinally extending control arm 40 pivotally connected to a lower part of the outrigger portion 1 6 and to a depending bracket on the second tandem axle 24.

Mounted in a part of one of the side frame members 1 2 there is a brake valve 42 that is arranged to supply pressure fluid from a conventional manually operable brake servo (not shown) to conventional wheel brakes (not shown) of opposed pairs of road wheels (likewise not shown) that are rotatably mounted at the outboard ends of the first and second tandem axles 22 and 24 respectively. The brake valve 42 is shown as having a control element in the form of a T-shaped actuating lever 44 that is mounted on a pivot 46 and is spring-biased by means of a coil spring 48.

The brake valve 42 has a clevis-type input connection for varying the position of the actuating lever 44, to vary the ratio of braking pressure being supplied to the road wheel brakes of the first and second tandem axles.

The brake valve 42 also includes a reaction portion 52 constituted by a portion of the housing of the brake valve, by way of which the brake valve is mounted within the part of the side frame member 1 2, the side frame member being constituted by a U-section gir der.

The brake valve 42 is arranged to be actuated in accordance with movement of the first and second tandem axles 22 and 24, via a Bowden cable 54 that is connected between the input connection 50 for the brake valve and a motion-transmitting linkage 56 associated with the first and second control arms 26 and 32.

The Bowden cable 54 is of conventional construction, comprising a flexible core 58 slidably disposed within a flexible sleeve 60.

At the output end of the Bowden cable 54, the sleeve 60 of the cable is mounted on a bent-over flange portion 62 of the housing portion 52 of the brake valve 42, with adjustment being provided by means of an adjusting screw 64. The flexible core 58, surrounded by a protective gaiter 66, is connected to the clevis-type input connection 50 to the brake valve 42.

The motion-transmitting linkage 56 that is connected between the first and second control arms 26 and 32 and the Bowden cable 54 includes a first cantilever arm 68 projecting laterally from the first control arm 26, in the region of the bracket 30, in a generally upward direction, and correspondingly a second cantilever arm 70 extending laterally from the second control arm 32, in the region of the bracket 36, in a generally upward direction. The first cantilever arm 68 is pivotally connected, by way of a clevis connection 72 incorporating an adjusting nut 74, to a straight projecting portion 76 of the flexible core 58 of the Bowden cable 54.

The second cantilever arm 70 is pivotally connected, by way of a somewhat similar clevis connection 78, to a straight tubular extension portion 80 of the flexible sleeve 60 of the Bowden cable 54, a protective gaiter 82 being mounted between the free end of the tubular extension portion 80 and the straight projecting portion ?6 of the core of the Bowden cable.

During operation of the vehicle, normal ride movements as the rear wheels move up and down relative to the frame portion of the vehicle cause oppositely directed movements of the first and second cantilever arms 68 and 70 such that there is relative sliding move ment of the flexible core 58 and flexible sleeve 60 of the Bowden cable 54, whereby the Bowden cable can transmit to the brake valve 42 a net movement indicative of the vertical movements of the first and second tandem axles, for establishing an appropriate relationship between the brake pressures supplied to the road wheel brakes of the first and second tandem axles, in accordance with the prevailing vehicle loading.

However, in the event of the wheels on one of the tandem axles meeting an obstruction, such that there is rocking of the tandem axle suspension as a whole about its suspension pivot, the first and second cantilever arms 68 and 70 act to cause translational movement of the flexible core 58 and flexible sleeve 60 of the Bowden cable 54 in the same direction and by the same amount (assuming pure rocking movement), such that the Bowden cable merely flexes as a whole, without causing any change in the position of the actuating lever 44 of the brake valve 42.

The tandem-axle rear suspension and loadsensitive wheel braking arrangement as described is simple, inasmuch as it involves only a single load-sensing brake valve, and is robust and effective in operation. This permits a useful cost and weight saving, and a less complex brake pipe arrangement than would be required with a conventional type of configuration utilising a separate brake proportioning valve for each of the tandem axles.

Claims (11)

1. A vehicle having a tandem-axle rear suspension fitted with a load-sensitive road wheel braking arrangement, in which a Bowden cable is connected to actuate the control element of a single brake valve for proportioning a supply of pressure fluid between the road wheel brakes of both tandem axles of a balanced-beam rear suspension, and the Bowden cable is connected by way of motiontransmitting linkage to both tandem axles such that on simultaneous rise and fall movement of the tandem axles the Bowden cable produces corresponding load-dependent actuation movement of the control element of the brake valve, whereas on conjoint pivotal movement of the tandem axles about a common suspension pivot the Bowden cable is without effect on the position of the control element of the brake valve.

2. A vehicle having a tandem-axle rear suspension fitted with a load-sensitive braking arrangement, in which a suspension pivot is mounted on a frame portion of the vehicle, first and second axles for respective opposed pairs of road wheels of the vehicle are connected to the suspension pivot by a suspension means permitting rise and fall movement of the first and second axles simultaneously and independently relative to the frame portion, and also conjoint pivotal movement of the first and second axles about the suspension pivot, and a single brake valve is arranged to proportion a supply of pressure fluid to wheel brakes for the road wheels of the first and second axles in accordance with the position of a control element of the brake valve relative to a reaction portion of the brake valve via a Bowden cable comprising a flexible core slidably disposed within a flexible sleeve, in that at the output end of the Bowden cable the core is connected to the control element of the brake valve and the sleeve is connected to the reaction portion of the brake valve, and at the input end of the Bowden cable the core and sleeves are connected by way of motion-transmitting linkage one to the first axle and the other to the second axle, such that rise and fall movement of the first and second axles simultaneously relative to the frame portion of the vehicle produces sliding movement of the core relative to the sleeve, for actuation of the control elements of the brake valve, whereas conjoint pivotal movement of the first and second axles about the suspension pivot produces conjoint movement of the core and sleeve at the input end of the Bowden cable, without actuation of the control element of the brake valve.

3. A vehicle according to claim 2, in which the motion-transmitting linkage connecting the core and sleeve at the input end of the Bowden cable to the first and second tandem axles respectively comprises a pair of cantilever arms that are connected to participate in movement of the respective tandem axles and are pivotally connected to the core and sleeve respectively of the Bowden cable.

4. A vehicle according to claim 3, in which the cantilever arms are mounted on respective oppositely directed pivotal control arms for the tandem axles.

5. A vehicle according to claim 4, in which the pivotal connections between the cantilever arms and the core and sleeve respectively of the Bowden cable are located in the region of a pair of pivotal connections between the respective control arms and the frame portion of the vehicle.

6. A vehicle according to any one of claims 2 to 5, in which, on each side of a vertical longitudinally extending centre plane of the vehicle, the first and second tandem axles are connected to respective end portions of a leaf spring that is pivotally mounted at its central region to the frame portion of the vehicle by means of the suspension pivot.

7. A vehicle according to any one of claims 2 to 6, in which the reaction portion of the brake valve is secured to the frame portion of the vehicle, and the part of the Bowden cable between the input and output ends of the cable is free to flex in response to movement of the tandem axles.

8. A vehicle according to any one of claims 2 to 7, in which the brake valve has an inlet arranged to be supplied with pressure fluid by a manually operable brake servo, the brake valve also has first and second outlets connected to supply pressure fluid to the wheel brakes of the first and second tandem axles respectively, and the brake valve is effective to proportion the fluid pressure from the inlet to the first and second outlets such that the ratio between the fluid pressure at the first outlet to the fluid pressure at the second outlet corresponds to the position of the control element of the brake valve.

9. A vehicle according to any one of claims 2 to 8, in which the Bowden cable includes an adjusting screw for adjustment means at the output end of the cable.

10. A vehicle according to any one of claims 2 to 9, in which the Bowden cable includes adjustment means in the form of an adjusting nut co-operating with a clevis connection forming a pivotal portion of the motion-transmitting linkage between one of the tandem axles and the core of the Bowden cable.

11. A vehicle having a tandem-axle rear suspension provided with a load-sensitive road wheel braking arrangement, substantially as hereinbefore particularly described and as shown in the accompanying drawing.