GB2349436A

GB2349436A - Vehicle brake servo assemblies

Info

Publication number: GB2349436A
Application number: GB9909885A
Authority: GB
Inventors: Michael Neil Basnett
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1999-04-29
Filing date: 1999-04-29
Publication date: 2000-11-01
Also published as: GB9909885D0

Abstract

A vehicle brake servo 16 is mounted directly onto the front side of a bulkhead panel 10 which has channels formed in it. These channels together with the rear face 22 of the servo form air inlet ducts 48a, 48b, 48c for feeding air from the engine compartment into an air inlet chamber 50 defined by a domed portion 36 of a pedal box 24. This produces a compact servo assembly with a low number of parts which is quiet in operation. The domed portion may be replaced by a cup-shaped member of moulded plastics material separate from and attached to the pedal box.

Description

Vehicle Brake Servo Assemblies The present invention relates to brake servo assemblies in vehicles, and in particular to the supply of air, generally at atmospheric pressure, to the rear of the servo.

Conventional servos have a lower pressure air chamber towards the front to which a vacuum is applied and a higher pressure chamber towards the rear to which air at atmospheric pressure can be applied, the difference in pressure between these two chambers providing the activating force of the servo. It is known to be advantageous to supply air to the rear of a servo from the front of the bulkhead between the passenger compartment and the engine compartment, because this produces less noise in the passenger compartment than when air is supplied directly from the passenger compartment. However, known ways of doing this usually require the addition of an additional component between the front of the bulkhead and the servo body through which air can flow radially inwards from the outer edge of the servo towards the aperture through the bulkhead through which it must then flow to reach the rear of the servo. This increases the cost of the system and also requires the servo to be mounted further forwards, generally by about 8 to 10 mm. This can cause problems in meeting crash safety regulations because the servo is moved closer to the engine.

It is also known from DE19523309 to provide air ducts from the engine compartment to the rear of the serve which are formed partly by a groove formed in the rear wall of the servo and partly by the bulkhead. However this requires modification of the servo which can be a disadvantage, and also requires the servo to be longer so that it can accommodate the grove. It therefore also results in the front of the servo being closer to the engine.

Accordingly the present invention provides a vehicle having a bulkhead, a brake servo mounted on the forward side of the bulkhead and having two chambers, the pressure difference between which can be used to actuate the servo, and air supply means for supplying air from in front of the bulkhead to one of the chambers, wherein the air supply means includes a duct partly defined by a channel formed in part of the bulkhead and partly defined by the servo.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a section through a braking system of a vehicle according to the invention, and Figure 2 is a front view of the bulkhead forming part of the system shown in Figure 1.

Referring to the drawings, a vehicle includes a bulkhead 10 separating its engine compartment 12 to the front from its passenger compartment 14 to the rear. Mounted on the front side of the bulkhead 10 is a brake servo 16, a rear part 18 of which extends rearwards through an aperture 20 in the bulkhead into the passenger compartment 14. The rear face 22 of the servo around the rear part 18 is substantially flat and is held in contact with the bulkhead 10.

A pedal box 24 is mounted on the rear side of the bulkhead 10 and comprises a generally flat part 26 with mounting holes 28 through it through which pass mounting bolts 30, a pedal bracket portion 32 on which a brake pedal 34 is pivotably mounted, and a central domed housing portion 36 which encloses the rear portion 18 of the brake servo. This housing portion 36 has a circular side wall 38 and an end wall 40 which has an aperture 42 through it through which a pushrod 44 extends, providing the input from the pedal 34 to the servo 16.

The bulkhead 10 has three channels 46a, 46b, 46c formed in it which extend radially of the servo, each having an outer end 47a which is radially outside the area of contact between the rear face 22 of the servo and the bulkhead 10, and an inner end 47b which opens into the aperture 20 through the bulkhead. These channels are formed by deforming respective regions of the bulkhead panel out of the general plane of that panel towards the rear, so the channels are open to the front of the bulkhead, having sides 52 and a base 54 to the rear of the general plane of the bulkhead. These channels 46a, 46b, 46c are covered over most of their length by the rear face 22 of the servo to form air ducts 48a, 48b, 48c leading from the engine compartment 12 to the edge of the aperture 20 through the bulkhead 10.

The domed housing part 36 of the pedal box 24 is larger than the rear part 18 of the servo, and an air inlet chamber 50 is therefore formed between them. In particular its side wall 38 is of a larger diameter than the widest part 52 of the rear part 18 of the servo, so the air ducts 48 open into the air inlet chamber 50 at their inner ends. A seal 54 is provided between the bulkhead 10 and the flat part 26 of the pedal box which extends around the aperture 20. This is formed from a bead of mastic which is extruded into a groove in the front face of the pedal box, although it will be appreciated that other forms of seal could be used. The pushrod 44 is sealed to the edges of the aperture 42 in the pedal box by a seal 56. This is shown as a rolling seal which provides a good airtight seal, but it might in some cases be advantageous to use another type of seal, such as a sliding seal, which might provide better sound insulation. The servo, which is of a conventional form having a lower pressure air chamber towards the front to which a vacuum is applied and a higher pressure chamber towards the rear to which air at atmospheric pressure can be supplied, the difference in pressure between these two chambers providing the activating force of the servo, has an air inlet 58 in the rear end of its rear portion 18 which allows air into the higher pressure chamber.

This air inlet 58 opens into the air inlet chamber 50.

In use, when the brake pedal 34 is depressed the pushrod 44 opens valves which close off any connection between the higher and lower pressure chambers and open the higher pressure chamber so that it is connected to the air inlet 58.

Because a vacuum is applied to the lower pressure chamber the two chambers are then at different pressures as is required to activate the servo. The air flowing into the inlet 58 flows from the engine compartment 12 into the outer ends of the air ducts 48a, 48b, 48c, inwards along those ducts into the inlet chamber 50, and from there into the inlet 58. Because this air does not come from the passenger compartment, and because the air inlet chamber 50 is mostly separated from the passenger compartment by the rigid domed part 36 of the pedal box, the noise produced by the servo in the passenger compartment is relatively low. Also, because the air ducts are formed to the rear of the plane of the bulkhead 10, the servo 16 is mounted as far to the rear as possible.

It should be noted that, in the embodiment shown, the air ducts 48a, 48b, 48c all have their outer ends below their inner ends. This is to inhibit the flow of moisture into the air inlet chamber 50 from the engine compartment through the air ducts.

As an alternative to the embodiment described, it is possible to make the housing forming the outer wall of the air inlet chamber from a separate component and attach it to the rear of the pedal box. In other words the domed central part 36 of the pedal box could be replaced by a cup-shaped member, formed for example from moulded plastics material. The pedal box would then simply have an aperture through it through which the rear part of the servo would extend, and the cup-shaped member would fit over this aperture. However forming the housing integrally with the pedal box as shown has the additional advantage that it greatly increases the stiffness of the pedal box.

Claims

CLAIMS 1. A vehicle having a bulkhead, a brake servo mounted on the forward side of the bulkhead and having two chambers, the pressure difference between which can be used to actuate the servo, and air supply means for supplying air from in front of the bulkhead to one of the chambers, wherein the air supply means includes a duct partly defined by a channel formed in part of the bulkhead and partly defined by the servo.
2. A vehicle according to claim 1 wherein the servo has a substantially flat rear surface part of which is contact with the bulkhead on either side of the duct and the duct is formed between said rear surface and the bulkhead.
3. A vehicle according to claim 1 or claim 2 wherein the duct extends substantially radially inwards relative to the servo.
4. A vehicle according to any foregoing claim wherein the duct extends in a direction substantially parallel to the plane of the bulkhead.
5. A vehicle according to any foregoing claim wherein the duct has a radially outer end into which air is arranged to flow in use from the engine compartment and an inner end out of which air is arranged to flow in use towards said one of the chambers, the outer end being arranged to be, in use, lower than the inner end thereby to inhibit the flow of water from the outer end to the inner end.
6. A vehicle according to any foregoing claim wherein the servo includes a rear portion extending through the bulkhead into the passenger compartment and the vehicle further comprises a rigid housing means around said rear portion, wherein a gap between the housing means and said rear portion forms a further part of the air supply means.
7. A vehicle having a bulkhead, a brake servo mounted on the forward side of the bulkhead and having two chambers, the pressure difference between which can be used to actuate the servo, and a rear portion extending through the bulkhead into the passenger compartment, and air supply means for supplying air from in front of the bulkhead to one of the chambers, wherein the vehicle further comprises a rigid housing means around the rear portion of the servo and the air supply means includes a chamber formed between said housing means and the rear portion of the servo.
8. A vehicle according to claim 6 or claim 7 further comprising a pedal box mounted on the rear side of the bulkhead, wherein a part of the pedal box forms the housing means.
9. A vehicle according to claim 6 or claim 7 further comprising a pedal box mounted on the rear side of the bulkhead, wherein the housing means is formed separately from the pedal box.
10. A vehicle according to any one of claims 6 to 9 wherein the housing means has an end wall with an aperture therethrough through which a pushrod extends, and a seal is provided between the housing means and the pushrod.
11. A vehicle according to claim 10 wherein the seal is a rolling seal.
12. A vehicle including a braking system substantially as hereinbefore described with reference to the accompanying drawings.