GB2069641A - Improvements in flywheel mechanisms for fluid-pressure operated anti-skid braking systems - Google Patents

Abstract

In an anti-skid braking system, an over arm clutch (44) is provided in a flywheel mechanism (3) comprising a flywheel (6) rotatably mounted on a shaft (2) driven from a braked wheel for axial movement relative to the shaft (2), a thrust member (8) mounted on, and keyed against rotation and axial movement with respect to, the shaft (2), and a ball and ramp mechanism 11 located between the thrust member (8) and a reaction plate (13) in clutched engagement with the flywheel (16). The ball and ramp mechanism comprises balls (19) located in angularly spaced recesses (16, 17) in adjacent faces of the thrust member (8) and the reaction plate (13). Relative rotation between the thrust member (8) and the reaction plate (13) causes the balls (19) to ride up ramps defined by the sides of the recesses (16, 17) to move the flywheel (6) axially away from the thrust member (8). Upon such movement the flywheel (6) acts on a lever (24) to operate a dump valve (5) for controlling a brake-applying fluid-pressure. An overrun clutch (44) between the flywheel (6) and the reaction plate (13) allows operation of the dump valve (5) to be maintained when the ball and ramp mechanism (11) is fully expanded. <IMAGE>

Description

SPECIFICATION Improvements in flywheel mchanisms for fluid-pressure operated anit-skid braking systems This invention relates to flywheel mechanisms for fluid-pressure operated anti-skid braking systems of the kind comprising a flywheel which is rotatably mounted on a shaft adapted to be driven from a braked wheel, a thrust member mounted on, and keyed against rotation with respect to, the shaft, and camming means disposed between the flywheel and the thrust member and through which rotation of the shaft is imparted to the flywheel from the thrust member, the camming means being so constructed and arranged that relative rotation between the flywheel and the thrust member as a result of excessive deceleration of the shaft is accompanied by relative movement between the flywheel and the thrust member in an axial direction to operate pressure-regulating means for controlling a brake-applying fluid-pressure.

In some known flywheel mechanisms of the kind set forth the flywheel is restrained against axial movement with respect to the shaft, and the thrust member is axially movable with respect to the shaft to operate the pressure regulating means, the thrust member being guided for axial sliding movement on splines on the shaft.

Apart from the fact that such known flywheel mechanisms are expensive to manufacture due to the cost of producing the splines, the reliability of such mechanisms is also in doubt due to the provision of the splines to provide the sliding axial engagement between the thrust member and the shaft. In particular, after an extended period in service and an extended period of non-use of the flywheel mechanism without the thrust member sliding on the shaft, the splines may becorne fouled with foreign matter, or otherwise damaged.This might either prevent the thrust member from sliding on the shaft to initiate skid control, or more likely and more seriously. cause the thrust member to stick in an axially displaced position in which the pressure-regulating means, suitably a pressure dump valve, are operated to control, and suitably relieve, the brake-applying fluid-pressure thereby causing brake failure.

In another known flywheel mechanism of the kind set forth the camming means comprises a helical cam surface constituted by screw-tilreaded engagement between the flywheel and the shaft and by means of which the flywheel is mounted on the shaft.

According to our invention in a flywheel mechanism of the kind set forth the thrust member is keyed against rotation and axial movement with respect to the shaft, and the flywheel is mounted on the shaft for relative axial movement and relative rotation with respect to the shaft as dictated by the camming means, the flywheel being adapted to cooperate with the pressure-regulating means, and the camming means being separate from the mounting for the flywheel on the shaft and located between the thrust member and a second member in clutched engagement with the flywheel so that the flywheel can overrun to maintain operation of the pressure-regulating means, when the camming means is fully expanded.

This simplifies the construction and increases reliability since a splined or other screw-threaded connection between the flywheel and the shaft can be avoided, and the combined rotational and axial movement of the flywheel alleviates any tendency for it to stick.

For example, the thrust member may be keyed to the shaft by means of a single key or a radial pin, and the flywheel may be jour nalled for rotation on a plain or roller bearing on the shaft on which the flywheel is also axially slidable.

Preferably the bearing is directly beneath the mass centre of the flywheel to provide a balanced assembly.

Conveniently the flywheel is urged by a spring towards the thrust member so that the camming means is clamped there between at all times.

The camming means conveniently comprises a ball and ramp mechanism in which balls are located in angularly spaced recesses in adjacent faces of the thrust member and the second member which comprises a reaction plate, relative rotation between the thrust member and the reaction plate at least in one direction causing the balls to ride up ramps defined by the sides of the recessses to cause the flywheel to be urged axially away from the thrust member.

Three embodiments of our invention are illustrated in the accompanying drawings in which: Figure 1 is a longitudinal section through a flywheel mechanism for a fluid-pressure operated anti-skid braking system; Figure 2 is a longitudinal section through another flywheel mechanism; and Figure 3 is a section similar to Fig. 2 but showing a modification.

The flywheel mechanism illustrated in Fig.

1 of the accompanying drawings comprises a housing 1 from opposie ends of which project opposite ends of a shaft 2. At one end the shaft 2 is coupled to a wheel to be braked and at the opposite end provides a mounting for a flywheel asembly 3. At an intermediate point in its length the shaft 2 is provided with eccentric cam 4 forming the drive mechanism for a pump of a modulator and pump assem bly (not shown) for controlling a brake-applying fluid pressure in response to operation of a dump valve 5. The modulator and pump assembly forms the subject of our co-pending G.B. Patent Applications 8,005,304 and 8,005,305, and need not be described further herein.

The flywheel assembly 3 comprises a flywheel 6 which is journalled for rotation on a roller bearing 7 on the shaft 2, a radial thrust member 8 in the form of plate which has an outwardly directed axial flange 9 through which the thrust member 8 is keyed against relative rotation and axial movement with respect to the end of the shaft 2 by means of a diametrical pin 1 0. and a ball and ramp mechanism 11 clamped between the thrust member 8 and plain face 1 2 at the base of an annular recess in the adjacent end of the flywheel. An annular clearance 1 0a is provided between the thrust member 8 and the shaft 2 so that the thrust member 8 can move radially through a limited distance to compensate for tolerance variations in the mechanism 11.

The ball and ramp mechanism 11 comprises an annular reaction plate 1 3 which encircles, and is mounted on, the hub 14 of the flywheel 6 by means of a one-way drive unit 1 5 of the roller type. The reaction plate 1 3 engages at one end with the face 1 2 to form a friction overrun clutch 44 biassed by a compression spring 20, and at the other end has a plain face in which is located a series of angularly spaced recesses 1 6 corresponding with, and superimposed upon, complementary recesses 1 7 in the adjacent face of the thrust member 8. Balls 1 9 are disposed in corresponding pairs of the recesses 16 and 1 7.

The reaction plate 1 3 is urged towards the thrust member 8 by the compression spring 20 of large diameter which is housed within the recess in the flywheel 6 and acts between a radial abutment 21 adjacent to the outer end of the recess and a radial flange 22 on a dished-shape abutment member 23 which reacts the force in the spring 20 at a single point against the end of the shaft 2 to which the thrust member 8 is keyed.

The dump valve 5 is normally closed and is operated by a lever 24 which is pivotably mounted at an intermediate point in its length on the housing 1. A spring 25 acts on the lever 24 to urge it at its outer end in a direction to hold the dump valve 5 closed, and the inner end of the lever 24 is normally spaced from a plain thrust washer 26 upon which the adjacent inner face of the flywheel 6 acts.

When the wheel is rotating in a "brakesoff" condition, or when the brake is applied normally in a non-skid condition, the thrust member 8 rotates with the shaft 2, and the flywheel 6 is driven with it at the same speed through the ball and ramp mechanism 11, and then to the one-way drive 1 5 and the overrun clutch 44.

If the deceleration of the wheel is excessive, the speed of rotation of the shaft 2 is reduced suddenly. However, due to its inertia, the flywheel 6 runs on and thus causes relative rotation to take place between the thrust member 8 and the reaction plate 13. The balls 1 9 ride up ramps comprising end walls of the recesses 1 6 and 1 7 so that simultaneously the reaction plate 1 3 and the flywheel 6 move axially relatively away from the thrust member 8. This moves the lever 24 angularly to permit the dump valve 5 to open and affect relief of the brake-applying fluid pressure as described in our co-pending G.B. Patent Application Nos. 8,005,304 and 8,005,305, referred to above.

Once the dump valve 5 has been opened fully, the reaction plate 1 3 rotates with the thrust member 8 to maintain the ball and ramp mechanism 11 in the expanded condition, but the flywheel 6 is permitted to rotate relative to the reaction plate 1 3 by slipping the overrun clutch 44 and the one-way drive 1 5. Thus the flywheel 6 decelerates at a rate determined by the torque sustained by the overrun clutch 44 and the rate of deceleration of the shaft 2.

Following brake release, the wheel will reaccelerate and as the wheel speed again approaches more closely the speed of rotation of the flywheel 6, the flywheel 6 can be moved angularly and axially in the opposite direction by the force in the spring 20, so that the components of the mechanism are returned to the position shown in the drawings, and the brakes can be re-applied.

The wheel may continue to accelerate during an initial period of the brake-application phase and on high ii road surfaces this rate of acceleration could exceed the setting of the clutch 44. The one-way drive 1 5 ensures that the flywheel 6 is accelerated with the shaft 2 during this period.

In the construction illustrated in Fig. 2 the one-way drive 15 of the roller type is replaced by a pawl and ratchet device 30 of the face type located between the face 1 2 and the reaction plate 13. An annular clearance 31 is; provided between the reaction plate 1 3 and the hub 14 of the flywheel so that the reaction plate 1 3 can move radially to compensate for tolerance variations in the ball and ramp mechanism 11, and clearance between the thrust member 8 and the shaft 2 is eliminated.

The thrust washer 26 is replaced by a thrust bearing 32 contained within a cage 37, and a compression spring 33, which replaces the large diameter spring 20, acts between the thrust bearing 32 and a sleeve 34 which is pressed onto the shaft 2 and is slotted at 35 to accept projections 36 on the cage 37 to prevent the cage 37 from rotating. Finally the flywheel 6 rotates on a plain bearing 38 on the shaft 2.

The construction and operation of the embodiment of Fig. 2 is otherwise the same as that of Fig. 1 and corresponding reference numerals have been applied to corresponding parts.

In the modified construction illustrated in Fig. 3 the diametrical pin 10 is omitted and the thrust member 8 is keyed to the shaft 2 against rotation by means of a woodruff key 40.

The free end of the shaft 2 has a threaded portion 41 of reduced diameter to receive a castellated nut 42 which clamps a washer 43 against the thrust member 8.

The construction and operation of the embodiment of Fig. 3 is otherwise the same as Fig. 2 and corresponding reference numerals have been applied again to corresponding parts.

In a further modification the sleeve 34 may be omitted and the compression spring 33 may act between the thrust bearing and a suitable abutment face provided in the housing.

In another modification, the one-way drive 1 5 or the pawl and ratchet device 30 may be omitted, the overrun clutch being relied upon to provide all the torque necessary to drive and accelerate the flywheel. This may be acceptable when the vehicle wheels have a relatively high rotational inertia so that high rates of wheel acceleration are unlikely to be encountered. Alternatively, when the wheel has a low inertia the one-way drive may again be omitted provided the torque setting of the overrun clutch is increased.

Claims (11)

1. A flywheel mechanism of the kind set forth in which the thrust member is keyed against rotation and axial movement with respect to the shaft, and the flywheel is mounted on the shaft for relative axial movement and relative rotation with respect to the shaft as dictated by the camming means, the flywheel being adapted to co-operate with the pressure-regulating means, and the camming means being separate from the mounting for the flywheel on the shaft and located between the thrust member and a second member in clutched engagement with the flywheel so that the flywheel can overrun to maintain operation of the pressure-regulating means, when the camming means is fully expanded.

2. A flywheel mechanism as claimed in Claim 1, in which the thrust member is keyed to the shaft by a single key or a radial pin.

3. A flywheel mechanism as described in Claim 1 or Claim 2, in which the flywheel is journailed for rotation on a plain or rqller bearing on the shaft on which the flywheel is also axially slidable.

4. A flywheel mechanism as claimed in Claim 3, in which the bearing is directly beneath the mass centre of the flywheel to provide a balanced assembly.

5. A flywheel mechanism as claimed in any preceding claim, in which the flywheel is urged by a spring towards the thrust member so that the camming means is clamped therebetween at all times.

6. A flywheel mechanism as claimed in any preceding claim, in which the camming means comprises a ball and ramp mechanism in which balls are located in angularly spaced recesses in adjacent faces of the thrust member and the second member which comprises a reaction plate, relative rotation between the thrust member and the reaction plate at least in one direction causing the balls to ride up ramps defined by the sides of the recesses to cause the flywheel to be urged axially away from the thrust member.

7. A flywheel mechanism as claimed in Claim 6, in which the reaction plate is mounted on the hub of the fly wheel by means of a one-way drive unit of the roller type.

8. A flywheel mechanism as claimed in Claim 7, in which an annular clearance is provided between the thrust member and the shaft so that the thrust member can move radially through a limited distance to compensate for tolerance variations in the ball and ramp mechanism.

9. A flywheel mechanism as claimed in Claim 6, in which the reaction plate is coupled to the flywheel by means of a pawl and ratchet device of the face type.

1 0. A flywheel mechanism as claimed in Claim 9, in which an annular clearance is provided between the reaction plate and the hub of the flywheel so that the reaction plate can move radially through a limited distance to compensate for tolerance variations in the ball and ramp mechanism.

11. A flywheel mechanism as claimed in any preceding claim, in which the flywheel acts on the inner end of a lever to operate a dump valve which comprises the pressureregulating means, the lever being pivotably mounted at an intermediate point of its length, and a spring being provided to act on the lever to urge the outer end of the lever in a direction to close the dump valve.

1 2. A flywheel mechanism as claimed in Claim 11, in which the flywheel acts on the inner end of the lever through a plain thrust washer which is normally spaced from the inner end of the lever.

1 3. A flywheel mechanism as claimed in Claim 5, or any one of the Claims 6 to 1 2 as appended directly or indirectly to Claim 5, in which the spring which urges the flywheel towards the thrust member is housed within a recess in the flywheel and acts between a radial abutment surface adjacent to the outer end of the said recess and a radial flange on an abutment member which reacts the force in the spring at a single point against the end of the shaft at which the thrust member is keyed.

1 4. A flywheel mechanism as claimed in Claim 11, in which the flywheel acts on the inner end of the lever through a thrust bearing contained within a cage.

1 5. A flywheel mechanism as claimed in Claim 14 as appended to Claim 5, in which the spring which urges the flywheel towards the thrust member acts between the thrust bearing and a sleeve which is pressed onto the shaft and is slotted to receive projections on the cage to prevent the cage from rotating.

1 6. A flywheel mechanism as claimed in any preceding claim, in which the thrust member is keyed to the shaft against rotation by a woodruff key, and a nut threaded onto the end of the shaft to which the thrust member is keyed clamps a washer against the thrust member.

1 7. A flywheel mechanism of the kind set forth substantially as herein described with reference to Fig. 1 of the accompanying drawings.

1 8. A flywheel mechanism of the kind set forth substantially as herein described with reference to Fig. 2 of the accompanying drawings.

1 9. A flywheel mechanism as claimed in Claim 1 8 but modified substantially as herein described with reference to Fig. 3 of the accompanying drawings.