GB2344860A

GB2344860A - Pneumatically-operated boosters for vehicle braking systems

Info

Publication number: GB2344860A
Application number: GB9827466A
Authority: GB
Inventors: Brendan Casey; Sean Byrnes
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1998-12-15
Filing date: 1998-12-15
Publication date: 2000-06-21
Anticipated expiration: 2018-12-15
Also published as: GB9827466D0; GB2344860B

Abstract

A pneumatically-operated booster for a vehicle braking system comprises a reaction assembly constituted by a reaction disc (81, Fig.2) of elastomeric material and a rigid ratio disc 82, the disc 82 being carried by a screw-threaded stem 90 which, in response to rotation of an input member 50, is rotatable relative to a non-rotatable part 51, 97 to adjust the spacing (83) between the ratio disc and the reaction disc, in turn to determine the "jump-in" characteristics. As illustrated, the non-rotatable part is a valve member 51, whereas, in an alternative embodiment, the valve member 51 and the stem 90 are rotatable relative to a non-rotatable nut 97.

Description

IMPROVEMENTS IN PNEUMATICALLY-OPERATED BOOSTERS FOR VEHICLE BRAKING SYSTEMS This invention relates to pneumatically-operated boosters for vehicle braking systems of the kind in which a wall is movable in a booster housing when subjected to pressure differential in order to augment a brake-applying force from the pedal which, in turn, is applied to a master cylinder, and the pressure differential is controlled by a control valve mechanism operated by the pedal.

In known boosters of the kind set forth the pedal acts on the valve mechanism through an input member, and a brake-applying force is transmitted to the master cylinder through an output member, a reaction force or"feel"being transmitted back to the pedal through a reaction assembly disposed between the output member and the valve. Normally the reaction assembly comprises a reaction disc of elastomeric material and a rigid ratio disc. A clearance between the two discs which determines characteristics of the booster is set to meet the characteristics required and this clearance has an important influence on the so called "jump-in"effect."Jump-in"is defined as the initial reaction or"feel"of the booster at the very beginning of a pedal actuation. This has an important influence on the pedal feel recognised by the driver.

An adjustment procedure is known in which a constant pressure (vacuum) chamber of a complete booster is connected to a vacuum source and subsequently the variable pressure chamber is vented to atmosphere as a result of a force applied to the input rod. The output force is measured and compared with the required characteristics of the booster. If the output force meets the necessary requirements, the procedure has been completed successfully. If not, the control valve mechanism has to be disassembled and the ratio disc has to be replaced with another disc of a different thickness. Such a procedure is time consuming, complicated and expensive.

It is also difficult to maintain closely the manufacturing tolerances of the components of the booster which influence the"jump-in"effect.

According to our invention in a booster of the kind set forth having a reaction assembly comprising a reaction disc of elastomeric material and a rigid ratio disc, the ratio disc is carried by a screw-threaded stem which in response to rotation of the input member is rotatable relative to an nonrotatable part to adjust the axial spacing between the ratio disc and the reaction disc.

The desired clearance can be set simply by rotation of the input member.

Once set the clearance can be measured using a test brake.

The input member may co-operate directly with the stem. Alternatively, in a modification, it may act on the stem through a valve member of the control valve mechanism which is itself rotatable.

In each construction a detachable drive coupling is provided between the input member and the stem itself, or between the input member and the valve member.

The drive coupling may comprise an adaptation of a spherical end fitting by which the input member acts on, and is coupled to, the valve member of the control valve mechanism.

When the input member acts directly on the stem the end fitting may have a co-axial cross recess for detachable co-operation with a complementary formation at the adjacent end of the threaded stem, the stem having a screw threaded engagement in a threaded bore in the valve member which is held against rotation, for example by the presence of a conventional key which defines a back stop for the control valve. In such a case the friction between the key and the valve member is greater than the torque needed to impart a rotary movement to the threaded extension.

A clearance between the spherical end fitting and the threaded extension is needed to allow an angular movement of plus or minus 5 articulation of the input member.

When the input member acts to rotate the threaded extension through the valve member, the spherical end fitting is adapted to define a hexagonal bore-shaped drive head portion received within a recess in the valve member which is of complementary outline. Such a head portion allows the transfer of any rotational movement to the valve member. The opposite end of the valve member is formed with a stepped recess of noncircular outline in which an axial extension on the threaded stem is slidably received to impart rotational movement of the valve member to the threaded stem, the stem being screwed through a threaded bore in a nut, suitably in a form of a circular ring element fixed to the valve housing.

The non-circular recess and extension may be of any convenient outline, for example quadratic or triangular in shape.

A known booster and modifications showing two embodiments of the present invention are illustrated in the accompanying drawings in which: Figure 1 is a longitudinal section through a known booster of the vacuum-suspended type; Figure 2 is a longitudinal section, on an enlarged scale, of the control valve mechanism incorporated in the booster of Figure 1; Figure 3 is a longitudinal section through the control valve mechanism illustrating a modification in accordance with the present invention; and Figure 4 is a view similar to Figure 3 but illustrating a different construction.

The known vacuum-suspended tandem pneumatic booster illustrated in Figures 1 and 2 of the drawings comprise a housing 1. The interior of the housing is divided into front and rear compartments 5 and 6 by means of an annular partition 7.

The first movable wall 9 divides the front compartment 5 into a front pressure chamber 10 of constant pressure and a rear variable pressure chamber 11. Similarly the second movable wall 12 divides the rear compartment 6 into a front constant pressure chamber 13 and a rear variable pressure chamber 14.

Each movable wall 9 comprises a piston 15 supported by a rolling diaphragm 16.

The movable walls 9 and 12 are adapted to be assembled to a central hub member 31 which defines the housing for a control valve mechanism 32.

The valve mechanism 32 comprises a pedal-operated input member in the form of a rod 50 coupled at its inner end to a poppet valve member 51 comprising a piston which is guided to slide in an axial bore 52 in the hub member 31. The valve member 51 is formed at its outer most end with a valve seating 54. An annular valve head 55 at the inner end of the flexible valve member 56 is urged by means of a spring towards the valve seating 54 and an annular valve head 59 on the hub member 51.

Air is admitted into the valve mechanism 32 through a filter 60 in the outer end of the hub member 31 and which forms an abutment for a conical helical spring 61 acting as a return spring for the rod 50 and to hold the valve member 56 against an abutment in the hub member 31.

The poppet valve member 51 is provided with the radial slot 62, and a key 63 fitted into the slot 62 projects radially from the valve member 51. The key 63 is so positioned as to allow free displacement of the valve member 51 with respect to the hub member 31 during operation of the booster, but to abut against the housing 1 on release of the pedal to define a balanced position for the valve mechanism 32.

The two constant pressure chambers 10 and 13 are connected to vacuum, suitably the inlet manifold of a vehicle, through a non-return valve connection 70 with the two chambers 10 and 13 permanently interconnected. In a normal brakes off position the variable pressure chambers 11 and 14 are held under slight atmospheric pressure through the interior of a boot 34 and the valve mechanism 32 since, in such a position, the valve head 55 is just contacting the seating 59 by the engagement of the seating 54 with the valve head 55 in the position determined by the engagement of the key 63 with the housing 1. A reaction assembly 80 is located between the valve member 51 and an output member in the form of a rod 83 which acts on a master cylinder.

The reaction assembly 80 comprises a reaction disc 81 of elastomeric material and a rigid ratio disc 82 disposed between the reaction disc 81 and the valve member 51. A small clearance 83 between the discs 81 and 82 determines the"jump-in"effect as defined herein.

In operation of the booster the valve seat 59 is already in abutment with the valve head 55 with the valve mechanism 32 in the balanced position due to the engagement of the key 63 with the housing 1. A brakeapplying force applied to the rod 50 causes the seating 54 to separate from the valve head 55 with the result that air is admitted into the two rear compartments 11 and 14 to energise the booster. Thereafter the booster operates with the two movable walls 9 and 12 moving in tandem to augment the force applied to the output member 84 in response to the pedal-operating force. A reaction force or"feel"is transmitted back to the pedal through the reaction assembly 80.

In the modified valve mechanism 32 illustrated in Figure 3 of the accompanying drawings which illustrate a first embodiment of the invention, the ratio disc 82 is carried from a screw threaded stem 90 which, in turn, is screwed through a threaded bore 91 extending through the poppet valve member 51. A spherical fitting 92 at the inner end of the rod 50 and which forms an articulated connection with the valve member 51 is adapted to form a detachable drive coupling 93 with the stem 90. As illustrated the spherical fitting 92 is formed with a two-axial cross recess 93, of similar configuration to"Phillips drive"system, adapted to co-operate with a complementary formation 94 at the end of the stem 90 remote from the rigid ratio disc 82. Rotational movement of the rod 50 is then transferred directly to the stem 90 to adjust the axial spacing between the disc 82 and the reaction disc 81 and with the valve member 51 being held against rotation since the friction between the key 63 and the valve member 51 is greater than the torque required to screw the threaded stem 90 to achieve axial movement of the disc 80.

A clearance between the two complementary parts 93 and 94 is needed to allow an angular movement of plus or minus 5 to accommodate articulation of the input rod 50.

Rotation of the input rod 50 can adjust the axial spacing between the discs 81 and 82, thereby determine the"jump-in"characteristics of the booster.

In the construction illustrated in Figure 4 of the accompanying drawings the threaded bore in the valve member 51 is replaced by a blind bore 95 of non-circular outline and which slidably receives an extension 96 of complementary outline extending from the free end of the threaded stem 90. The extension 90 is screwed through a threaded bore in a nut 97 in the form of a circular member fixed against rotation with respect to the hub 31.

Rotation is imparted through the threaded stem 90 by rotation of the valve member 51 itself. This is achieved by adapting the part-spherical fitting 92 to an hexagonal outline and to forming the recess in the valve member 51 which it is received of a similar outline.

Rotation of the rod 51 can therefore be transmitted through the helical engagement of the spherical fitting 92 with the valve member 51 and through the sliding engagement between the extension 92 in the non circular blind bore 95. Since the nut 97 is held against rotation the rigid disc 82 can be moved axially and relative to the reaction disc 81 in order to determine"jump-in"characteristics of the booster.

Claims

CLAIMS 1. A booster of the kind set forth having a reaction assembly comprising a reaction disc of elastomeric material and a rigid ratio disc, in which the ratio disc is carried by a screw-threaded stem which in response to rotation of the input member is rotatable relative to an nonrotatable part to adjust the axial spacing between the ratio disc and the reaction disc.
2. A booster as characterised in Claim 1, in which the input number co-operating directly with the stem.
3. A booster as claimed in Claim 1, in which a detachable device coupling is provided between the input member and the stem itself.
4. A booster as claimed in Claim 1, in which the input member acts on the stem through a valve member of the control valve mechanism which is itself rotatable.
5. A booster as claimed in claim 4 in which a detachable drive coupling is provided between the input member and the valve member.
6. A booster as claims in Claim 3 or Claim 5, in which the drive coupling comprises an adaptation of a spherical end fitting by which the input member acts on, and is coupled to, the valve member of the control valve mechanism.
7. A booster as claimed in Claim 6, in which the input member acts directly on the stem and the end fitting has a co-axial cross recess for detachable co-operation with a complementary formation at the adjacent end of the threaded stem, the stem having a screw threaded engagement in a threaded bore in the valve member which is held against rotation.
8. A booster as claimed in Claim 7, in which friction between a key defining a back stop for the control valve and the valve member is greater than the torque needed to impart a rotary movement to the threaded extension.
9. A booster as claimed in any of claims 6 to 8, in which a clearance between the spherical end fitting and the threaded extension is arranged to allow an angular movement of plus or minus 5 articulation of the input member.
10. A booster as claimed in Claim 6, in which the input member acts to rotate the threaded extension through the valve member, and the spherical end fitting is adapted to define a hexagonal bore-shaped drive head portion received within a recess in the valve member which is of complementary outline whereby rotational movement is transferred to the valve member, the opposite end of the valve member being formed with a stepped recess of non-circular outline in which an axial extension on the threaded stem is slidably received to impart rotational movement of the valve member to the threaded stem, the stem being screwed through a threaded bore in a nut fixed to the valve housing.
11. A booster as claimed in Claim 10, in which the non-circular recess and extension are quadratic or triangular in shape.
12. A booster substantially described herein with reference to and as illustrated in Figures 3 and 4 of the accompanying drawings.

12. A booster substantially as claimed herein with reference to any illustration in Figures 3 and 4 of the accompanying drawings.

Amendments to the claims have been filed as follows 1. A booster of the kind set forth having a reaction assembly comprising a reaction disc of elastomeric material and a rigid ratio disc, in which the ratio disc has a screw-threaded stem which in response to rotation of the input member is rotatable relative to an non-rotatable part to adjust the axial spacing between the ratio disc and the reaction disc.

2. A booster as characterised in Claim 1, in which the input number co-operating directly with the stem.

3. A booster as claimed in Claim 1, in which a detachable device coupling is provided between the input member and the stem itself.

4. A booster as claimed in Claim 1, in which the input member acts on the stem through a valve member of the control valve mechanism which is itself rotatable.

5. A booster as claimed in claim 4 in which a detachable drive coupling is provided between the input member and the valve member.

6. A booster as claims in Claim 3 or Claim 5, in which the drive coupling comprises an adaptation of a spherical end fitting by which the input member acts on, and is coupled to, the valve member of the control valve mechanism.

7. A booster as claimed in Claim 6, in which the input member acts directly on the stem and the end fitting has a co-axial cross recess for detachable co-operation with a complementary formation at the adjacent end of the threaded stem, the stem having a screw threaded engagement in a threaded bore in the valve member which is held against rotation.

8. A booster as claimed in Claim 7, in which friction between a key defining a back stop for the control valve and the valve member is greater than the torque needed to impart a rotary movement to the threaded extension.

9. A booster as claimed in any of claims 6 to 8, in which a clearance between the spherical end fitting and the threaded extension is arranged to allow an angular movement of plus or minus 5 articulation of the input member.

10. A booster as claimed in Claim 6, in which the input member acts to rotate the threaded extension through the valve member, and the spherical end fitting is adapted to define a hexagonal bore-shaped drive head portion received within a recess in the valve member which is of complementary outline whereby rotational movement is transferred to the valve member, the opposite end of the valve member being formed with a stepped recess of non-circular outline in which an axial extension on the threaded stem is slidably received to impart rotational movement of the valve member to the threaded stem, the stem being screwed through a threaded bore in a nut fixed to the valve housing.

11. A booster as claimed in Claim 10, in which the non-circular recess and extension are quadratic or triangular in shape.