WHEELS AND BRAKES FOR VEHICLES

2) Technical Field

This invention relates to wheels and brakes for vehicles. In one embodiment, it is particularly concerned with wheels and braking systems for use on racing cars .

3) Background Art

In wheel and brake assemblies for automotive vehicles, the brakes are either of the known disc brake type or of the known brake shoe type. In the brake shoe type, brake shoes have brake linings securely mounted thereon. The brake shoes are moveable, by various types of mechanical and/or fluid operated means, upon braking actions in which the shoes are caused to approach inner cylindrical surfaces of brake drums of the wheels, pressurized engagement of the brake linings with these brake drum surfaces effecting the braking action. Braking systems are undoubtedly extremely efficient in their action and have been, and are, used extensively throughout the automotive vehicle industry. In fact, every road vehicle appears to use either the brake shoe type of brake or the disc brake type. Further, both of these types of mechanism are shown extensively throughout the world in patent specifications and in magazine or ocher publications.

An inordinate amount of repair time is necessary for the purpose of replacing brake linings . This is particularly the case when replacing brake linings as the brake shoes themselves need to be removed and this may be an extremely intricate operation. The time taken for repair may not, under normal circumstances, be particularly important. In contrast, however, if the brake lining replacement were to be done upon a racing car during a pit stop in a racing car event, the time expended would be extremely important and may be crucial to the outcome of the race. While racing cars are subject to rigorous and high mechanical stresses during racing, which

includes rapid brake lining wear inevitably leading to pit stops during a race, any time spent on a pit stop for any form of maintenance or repair of brakes may be considered as wasted time in the race. For this reason, pit stop time for brake lining replacement generally is not done, even though there may be loss in braking efficiency which could lead to accidents if no such replacement is undertaken.

Among the patents which relate to this general subject matter of which applicant is aware are the following: US Patent No. 2,016,435, patented October 8, 1935, by B. Isiden; US Patent No. 3,989,305,, patented November 2, 1970, by H. Umeda, et al; and Japanese Publication JP 403282026, published December 1991, of Hino Motors, Ltd.

4) Disclosure of the Invention

According to the present invention, a wheel is provided which includes a generally-cylindrical wheel rim for mounting a tire thereon. A wheel disc carries the wheel rim and extends radially-inwardly from the wheel rim towards a rotational axis of the wheel for mounting the wheel upon a rotatably-driven, or free-wheeling rotatable wheel support of a vehicle. A cylindrical support secured to the wheel disc is disposed radially-inwardly of the wheel rim. The wheel is characterized by a radially- inwardly facing arcuate brake lining structure of constant radius, the brake lining structure including an exposed curved surface which is formed of friction material, the brake lining structure being secured to the cylindrical support, the brake lining structure extending at least partially around, and having a centre of radius coincident with, the rotational axis of the wheel.

According to the present invention, a wheel assembly is also provided for an automotive vehicle, the wheel assembly including in combination the generally- cylindrical wheel rim described above and a rotatably- driven or free-wheeling wheel support which is secured to

a non-rotational part of the vehicle along the rotational axis of the wheel. The combination is characterized not only by a radially-inwardly facing arcuate brake lining structure of constant radius, the brake lining structure including an exposed curved surface which is formed of friction material, the brake lining structure being secured to the cylindrical support, the brake lining structure extending at least partially around, and having a centre of radius coincident with, the rotational axis of the wheel, but also by a plurality of arcuate brake arms having radially-opposed outer curved surfaces which are mounted upon the non-rotatable part of the vehicle in spaced positions around a rotational axis of the wheel support. Structure is also provided for moving the arcuate brake arms in a braking action radially-outwardly from inactive positions towards the brake lining structure, and for returning the brake arms radially- inwardly upon termination of the braking action.

Various other features of the wheel of this invention are characterized as follows: the cylindrical support comprises a radially-inwardly facing surface extending substantially continuously around the rotational axis of the wheel; the brake lining structure comprises brake pads which are rigidly secured to the radially-inwardly facing surface; the brake lining structure comprises a plurality of brake pads which are secured to a surrounding brake lining carrier, the brake lining carrier and the cylindrical support being co-operable detachably and securely to mount the brake lining carrier radially- inwardly of the cylindrical support with the plurality of brake pads facing radially-inwards towards the rotational axis of the wheel; the cylindrical support comprises a radially-inwardly directed cylindrical support surface to which the brake pads are secured, the brake lining carrier having an outer circumferential surface which is complementary to the cylindrical support, and including securing elements provided for securing the cylindrical

support and the circumferential surface of the brake lining carrier in engagement with one another, the securing elements comprising a plurality of screw elements which are spaced apart angularly around the rotational axis of the wheel and which extend radially through respective aligned holes in the brake lining carrier and in the cylindrical support; the cylindrical support and the circumferential surface are both cylindrical and are complementary to one another; the cylindrical support comprises a cylindrical element which is spaced radially- inwardly of, and which is concentric with, the generally- cylindrical wheel rim, and which includes heat.dissipation members for dissipation of heat which is generated by braking action of the brake arms against the brake pads; the heat dissipating members comprises heat removal fins, which may be spiral in configuration, extending into a hollow annular region from the cylindrical support towards the wheel rim; and the annular chamber within which the fins are disposed has apertures communicating between front faces and rear faces thereof, for the passage of cooling air therethrough.

Various other features of the combination of this invention are characterized as follows: the arcuate brake arms comprise a pair of diametrically opposed arms, with each end of each the arm being operably connected to a fluid operated cylinder mechanism for moving the brake arm on a braking action, the structure for the return of the brake arms including at least one tension spring; the structure for moving the brake arms on a braking action includes an element for applying fluid pressure to move the brake arms on the braking action and for relaxing the fluid pressure upon termination of the braking action; an element is provided for effecting movement of the brake arms to further positions which are further radially- inwardly of their inactive positions, the element for effecting such movement of the brake arms comprising structure for drawing pressurized fluid from the braking

system; a master cylinder and a valve are disposed between the master cylinder and the structure for drawing pressurized fluid from the system so as to disconnect the pressurized fluid in the master cylinder from the remainder of the system during operation of the means for drawing the pressurized fluid from the braking system; the structure for drawing pressurized fluid from the braking system includes a piston and cylinder assembly having a piston within a cylinder, one end of the cylinder being connected to the braking system, movement of the piston in one direction within the cylinder drawing pressurized fluid from the braking system into the cylinder ;• the valve is held in its normally open position by a torsion spring, the valve being urged towards its closed position by a counterbalancing tension spring, the tension spring being operated by vertical movement of an operating rod which is coupled to the piston.

In the wheel defined above according to the present invention, the brake lining structure may be applied directly to the support of the wheel. This support may comprise an inwardly facing cylindrical surface to which the frictional material lining structure is directly mounted. Alternatively, the wheel may have a support for securing a frictional material brake lining assembly, e.g., brake pads thereto, the brake lining assembly comprising the brake lining structure or brake pads which is secured to a surrounding brake lining carrier. The brake lining assembly is then mounted upon the wheel by co-operation between the brake lining carrier and the support. In this arrangement, the brake lining carrier is detachably secured in position with the brake lining structure facing radially-inwards towards the rotational axis of the wheel.

In a preferred arrangement, the support and the brake lining assembly have complementary cylindrical surfaces which engage each other when the brake lining assembly is assembled to the support surface. The support is

support itself be a cylindrical element which is spaced inwardly of the wheel rim and is concentric therewith to provide an annular chamber there between.

The brake arms may be a diametrically opposed pair of arcuate arms, with each end of each the arm being operably connected to a fluid operated cylinder mechanism for moving the brake arm on a braking action, and the return means comprises at least one tension spring.

With the combination of wheel and wheel support according to the invention provided on a vehicle, the braking system is preferably a fluid operated system and the structure for effecting movement of the brake arms to the further positions which are further radially-inwardly operates to draw pressurized fluid from the system. Hence, the resilient elements are permitted to move the brake arms to their further inner positions. Thus, upon removal of a wheel, a greater distance is created between the inner peripheral surface of each wheel and the brake arms, thereby decreasing the possibility of binding between the wheel and the brake arms with resultant easing of wheel removal.

To ensure that the master cylinder of the braking system does not suffer damage as the pressurized fluid is drawn from the system, the valve previously described is preferably provided as a butterfly valve which is closed so as to separate the fluid within the master cylinder from the remainder of the system. 5) Brief Description of the Drawings In the accompanying drawings, Figure 1 is a diagrammatic plan view showing the basic layout of a braking system as used upon a vehicle;

Figure 2 is a side elevational view of the embodiment in the form of a wheel and brake lining assembly of the vehicle taken along line II-II in Figure 1 and to a larger scale, parts of the wheel being removed for clarity;

Figure 3 is a view similar to Figure 2 of the brake lining assembly;

Figure 4 is a view similar to Figure 2 of the wheel;

Figure 5 is a multicross-sectional view of the wheel assembly of Figure 2 taken along line V-V in Figure 2;

Figure 6 is a view similar to Figure 5 of part of a wheel and brake lining assembly forming a modification of that embodiment;

Figure 7 is an isometric view at one corner position of part of the braking system;

Figure 8 is a view similar to Figure 2 and showing the position of the elements of the assembly during a braking action;

Figure 9 is a side elevational view, partly in cross- section, and to a greatly enlarged scale, of a device for drawing pressurized fluid from the fluid brake system used in that embodiment;

Figure 10 is in an enlarged cross-sectional side elevational view of a valve mechanism incorporated in the device of Figure 9;

Figure 11 is a view similar to Figure 2 and showing a parking brake arrangement which is incorporated into a wheel assembly of the embodiment; and

Figures 12 to 15 are views of emergency or parking brakes embodying features of this invention, in which:

Figure 12 is a side elevational view similar to Figure 11 showing another parking brake embodiment incorporated into a wheel assembly of one embodiment of this invention;

Figure 13 is a side elevational view similar to Figure 12 showing yet another parking brake embodiment incorporated into a wheel assembly of one embodiment of this invention;

Figure 14 is a top plan view of the parking brake embodiments of either Figure 12 or Figure 13 showing the use with either a hydraulic braking system or with a cable system; and

Figure 15 is a top plan view of still another parking brake embodiment whose side elevational view is generally

similar to the views of Figure 12 or Figure 13, but showing the use with a pneumatic braking system. 6) Best Mode For Carrying Out The Invention

As shown diagrammatically in Figure l, an automobile 10 shown in chain dotted, incorporates a wheel and braking assembly of this invention comprising front wheel assemblies 12 and rear wheel assemblies 14, (of which at least one assembly may be driven, and another assembly may be free-wheeling) , a braking system controlled by a master cylinder 16 of conventional construction, and fluid pressurized lines 18 extending from the master cylinder 16 to each of the wheel assemblies 12, 14.

The construction of each of the driven wheel assemblies 14, which includes part of the invented braking system, is illustrated in Figures 2 to 8 inclusive.

As shown in Figures 2, 5 and 6, each rear wheel assembly comprises a wheel 20 comprising a wheel rim 22 upon which a pneumatic tire 24 is mounted in conventional fashion. The wheel has an inwardly extending pressed wheel disc 26 for mounting the wheel rim concentrically with the rotational axis of the wheel (see Figure 5 and 6) . The wheel disc 26 is omitted from Figure 2 and from other Figures similar to Figure 2 for the purpose of showing other details. The wheel disc 26 is detachably secured by a plurality of retaining nuts and studs 28 to a back plate 30 which is secured to a driving half shaft 32 which is rotatably mounted in conventional fashion within a driven axle 34 of the vehicle. The wheel 20 differs from conventional wheels in that it is provided with part of the braking system, i.e., it has a brake lining structure, as will now be described, which includes exposed surfaces which are formed of friction material, forming an essential element of this invention securely mounted thereon. In respect of each wheel assembly 12, 14, and as shown particularly by Figures 2 and 5, two arcuate brake arms 60 are provided. ( While conventionally these

elements are known as "brake shoes" a more accurate description for the present invention is "brake arm" . Henceforth that term "brake arm" or"arcuate brake arm" will be used.) These arcuate brake arms 60 are in diametrically opposite positions relative to the rotational axis of the wheel and are mounted so that each arcuate brake arm 60 is operated simultaneously by two parallel fluid operated cylinders 62, which are also diametrically opposed across the rotational axis of the wheel. Each cylinder 62 has two opposite operational ends which operate one against each of the opposite shoes 60 so as to centralize the arcuate brake arms 60 in operation. As shown in Figure 2, each of the arcuate brake arms 60 has an outer arcuate surface 64 which extends approximately 120 degrees around the rotational axis of the wheel. In the full outline inactive position of the arcuate brake arms 60 shown in Figure 2, the surfaces 64 are spaced from the inner peripheral surface 65 of the brake lining structure provided by the brake linings 44. In these positions, two tension springs 66 (see Figure 2) mounted between opposing ends of the arcuate brake arms 60 pull the arcuate brake arms 60 radially-inwards so that two driving extensions 68 of each arcuate brake arm 60, which engage plungers 70 of the cylinders 62 (see particularly Figure 5) force the plungers 70 inwards against the pressure of the fluid in the braking system with the master cylinder inactivated.

The two cylinders 62 are securely mounted in their relative positions upon a backing plate 72 of open rectangular structure, the backing plate 72 being secured through holes 74 (see Figure 2) by two screws to a mounting structure 76 (see Figure 5) forming part of the non-rotatable portion of the wheel mounting structure, e.g., the non-rotatable portion of the axle 34. The mounting structure 76 is omitted from Figure 2 and from similar Figures for the sake of clarity of other features. Each cylinder 62 is secured in position by spaced-apart

nuts 78 (see Figure 5) received upon studs which are securely mounted to the cylinders 62 and passing through bores which are suitably positioned in the backing plate 72. A fluid pressurized line 18 (see Figures l and 5) extends to a substantially-mid-position of the respective cylinder 62 for simultaneously operating both of the plungers 70 and a bleed valve (not seen) which is suitably positioned upon each cylinder 62. Each cylinder 62 is provided with its own elongate rectangular open cover plate 82 as shown particularly in Figure 7. This cover plate 82 is secured at each end by two screws 84 to the backing plate 72 (see Figure 7) . Each cover, plate 82 serves to hold an individual driving extension 68 of the arcuate brake arm 60 in a location which is slideably mounted within a complementary shaped slot 86 in the backing plate 72, whereby the driving extension 68 is guided in its sliding movement during movement of the arcuate brake arm 60.

The structure of a driving wheel assembly has been described in this embodiment. Such driving wheel may be a rear wheel assembly or it may be a front wheel assembly. Furthermore, both front and rear wheel assemblies may be driven, as in a four-wheel drive vehicle. The main features of the structure are similar for a non-driving wheel assembly, e.g., where the non-driving assembly is securely mounted upon a short free-wheeling rotatable mounting within a fixed wheel assembly structure as is conventional with vehicle constructions. The construction of the non-driving wheel assemblies is, therefore, not required to be described.

The four brake linings 44 need not be attached to the ring 42, but as shown in the modification of Figure 6, may be rivetted directly to the cylindrical element 50 of the wheel. As shown in Figures 3 and 4, a brake lining assembly 40 comprises a brake lining carrier in the form of a rigid cylindrical metal ring 42 having an inner cylindrical

surface to which is secured a brake lining structure 41 whose exposed arcuate surface is formed from friction material, and which extends partially around such surface, and having a constant radius. The brake lining structure 41 whose exposed arcuate surface is formed from friction material, is provided by four such arcuate brake linings 44, each of which subtends an angle of slightly less than 90 degrees around the common centre of radius of the brake linings 44 and of the ring 42. The brake linings 44 are assembled with their radially-outer peripheral surfaces engaging the inner cylindrical surface of the ring 42 and are secured by conventional rivetting or bonding techniques. Ends of the brake linings are slightly spaced apart, as shown, so that the lining structure does, in fact, extend substantially-continuously around the inside surface of the ring 42. Between spaced apart ends of the brake linings 44, the ring 42 is provided with through holes (not shown) into which a screw-threaded means extends, e.g., attachment screws 46, to secure the brake lining assembly to an inner peripheral cylindrical surface 48 (see Figure 5) of a support for the brake lining structure and provided by the wheel. This support comprises a cylindrical element 50 which is spaced radially-inwards from the wheel rim 22 while being concentric therewith. It follows, therefore, that the brake lining assembly is detachably mounted to the cylindrical element support 50 by the angularly spaced apart screws 46 which pass through the holes in the ring ₄ 2 and are received within screw-threaded holes in the support. Alternatively, they may extend through the cylindrical element support 50 as shown in Figures 2 and ₄ to be secured in place by attachment nuts 52. Hence, the wheel structure 20 differs from conventional structures in that it has the brake lining assembly 40 attached directly thereto, and this brake lining assembly 40 may be removed from the wheel for replacement purposes if desired.

As it is expected that the cylindrical element support 50 will be caused to absorb heat during brake usage, and particularly if it is used upon the racing car, it is desirable to provide some structure for assisting in heat removal. For this purpose, a plurality of radially- extending heat removal fins 54 may be provided within an annular chamber 154 between wheel rim 22 and cylindrical element support 50, the fins being optionally of spiral configuration, to assist in cooling air flow. These fins 54 are spaced apart angularly around the rotational axis and are welded both to the cylindrical element 50 and to the wheel rim 22 for heat removal (see Figures- 2 and 4) . Circulation of air around and between the fins 54 is effective in removing heat from the cylindrical element 50 during usage. To assist in air circulation between the fins 54, outer regions of the wheel disc 26 are provided with a plurality of apertures 156 therethrough (see Figures 5 and 6) . The inner region of the wheel disc has an open internal face 155. Thus, cooling air passes between the fins 54 and through the openings 155,156, i.e., from side to side of the wheel in the direction of the arrows 158 (see Figures 5 and 6) .

In order to minimize any problems associated with removal of a wheel 20 from the vehicle 10 in the embodiment as shown, the vehicle 10 also is provided with structure for drawing pressurized fluid from the braking system when the arcuate brake arms 60 are in their inactive, i.e. non-braking, positions. This enables the resilient springs 66, to move and retain the arcuate brake arms 60 to positions which are further radially-inwards of their inactive positions. This structure for drawing the pressurized fluid from the system comprises a piston and cylinder arrangement 90 (see Figure 9) which is disposed in a position in the pressurized line 18 which is adjacent to the master cylinder 16 as shown by Figures 1 and 9.

The piston and cylinder assembly 90 comprises a cylinder

92 which is open at one end onto the line 18 and which is

provided with a bleed valve 94. The cylinder 92 contains a piston 96 having one end 98 forming one side of the line 18 at the position of the piston 96. At the other end, the piston 96 is attached to a coaxial operating rod 100 which extends through the housing of the cylinder 92 and is connected to an operating handle 102. The piston 96 is normally biased into the position shown in Figure 9 with its one end 98 defining one side of the line 18, by means of a compression spring 104 which encircles the rod 100 to urge the piston 96 in the required direction. Handle 102 which is vertically movably mounted in bushing 121 operates rod 100.

To ensure that no damage can result to the master cylinder 16 during operation of the piston and cylinder arrangement 90, a valve arrangement 110 is positioned in the line 18 between the master cylinder 16 and the piston and cylinder arrangement 90. As shown in Figures 9 and 10, this valve arrangement 110 comprises a butterfly valve 112 which is normally in the chain-dotted open position in Figure 10 to enable the master cylinder 16 to operate the braking system. This butterfly valve 112 is held in its normal open position by a torsion spring 113 (see Figure 9) which acts as an outside link 114 to move the butterfly valve 112 counterclockwise about its pivot. At the pivot, the outside link 114 is secured to a rotatable pin 117 in the valve housing 119, the butterfly valve 112 also being secured to the pin 117. Because of road dirt, spring 116 extending between pin 117 and arm 123 which is secured to bushing 121 is preferably protected by a dirt cover plate (not shown) . Tension spring 116 operates butterfly valve

112. In this position, the butterfly valve 112 engages seals 118 which are provided around the inner surface of a valve chamber 119 within which the butterfly valve 112 is accommodated. The butterfly valve 112 moves into its closed position immediately when the piston 96 commences to move towards its downward position (shown in chain- dotted in Figure 9) , whereby the master cylinder 16

becomes separated from the rest of the braking system so that fluid cannot be drawn from the master cylinder 16. Upon return of the piston 96 to its upper position shown in Figure 9, the butterfly valve 112 is reopened. As an alternative to the structure for the operation of the piston 96 described in the embodiment of Figure 9, the piston 96 may be moved electrically by operation of a switch (not shown) .

In addition, the vehicle 10 of the embodiment described herein has an emergency brake provided and which is operable at each wheel assembly. As shown by Figure 11, this emergency or parking brake conveniently may comprise an actuation disc 120 which is freely rotatably mounted around the axis of rotation of the wheel, the actuation disc 120 being attached at one radial position to an operating cable 122. The actuation disc 120 is operably connected to each arcuate brake arm 60 by an operating link 124 which is pivoted at its two respective ends to the arcuate brake arm 60 and to the actuating disc 120. As shown in Figure 11, with the brake not operated, the links 124 lie in the full outline position with the arcuate brake arms in their inactive positions.

As shown in Figure 12, the emergency or parking brake includes a backing plate 250 supporting an actuation disc 220, which is freely-rotatably mounted around the axis of rotation of the wheel, at axle 230. The actuator disc 220 is attached at one radial position to a cable 222 at connection point 232 on first lower arm 234 of actuator disc 220. The actuator disc 220 is operatively connected to each of the arcuate brake arms 260 by two links 236, namely, one downwardly and one upwardly, obliquely- oriented operating link 236 at pivot points 238, and to the arcuate brake arms 260 at pivot points 240. The arcuate brake arms 260 are anchored to the backing plate 250 at 180-degree-spaced-apart anchor points 242. A second upper arm 244 of actuator plate 220 is attached to the rod end of an hydraulic operating piston 246. Figure

12 shows the emergency or parking brake in its non-engaged orientation with the operating links 236 permitting the arcuate brake arms to lie in their inactive positions.

As shown in Figure 13, the emergency or parking brake includes a backing plate 350 supporting an actuation disc 320, which is freely-rotatably mounted around the axis of rotation of the wheel, at axle 230. The actuator disc 320 is attached at one radial position to a cable 322 at connection point 332 on first lower arm 334 of actuator disc 320. The actuator disc 320 is operatively connected to each of the arcuate brake arms by two upwardly- obliquely-oriented operating links 336 at pivot points 338, and to the arcuate brake arms 260 at pivot points 340. The arcuate brake arms 260 are anchored to the backing plate 350 at vicinal anchor points 342. A second upper arm 344 of actuator plate 320 is attached to the rod end of an hydraulic operating piston 346. Figure 13 shows the emergency or parking brake in its non-engaged orientation with the operating links 336 permitting the arcuate brake arms 260 to lie in their inactive positions.

Figure 14 need not be described in great detail since the reference numbers used are the same as, and indicate the same elements as, those in Figure 12 or Figure 13.

However, Figure 14 additionally shows the orientation of the upper and lower arm on the actuator disc and the hydraulic hose connection 252/352.

Figure 15 shows an embodiment which differs from the embodiments shown in Figures 12 to 14 in that there is only one arm 444 which extends upwardly from actuator disc 420. The operating linkage arms 236/336 are the same as shown and described for the embodiments shown in Figures 12 to 14. 7) Industrial Applicability

In use of the vehicle and with each of the wheel and braking assemblies rotating, normally the arcuate brake arms are spaced away from the inner peripheral surface of the brake lining structure. However, should it be

required to apply braking pressure to the wheel and braking assemblies, then the master cylinder is operated in conventional fashion and this increases the fluid pressure in each of the cylinders to force each of the arcuate brake arms radially-outwardly, in which they perform a braking action by pressurized engagement against the inner peripheral surfaces of the brake lining structure.

Removal of the wheel for tire replacement or repair is quickly done by removal of the wheel retaining nuts and the wheel is withdrawn. As will be noticed, this wheel withdrawal also removes the brake lining assembly from the vehicle. Should it be noticed at this time that the brake lining assembly be worn at this time, a replacement wheel with a mounted tire may be used as a replacement, the new wheel having a new and unworn brake lining assembly of this invention mounted to it. Hence the tire and the brake lining may be changed simultaneously. This operation in the case of a racing car, particularly, saves valuable time during a pit stop while maintaining the vehicle in first class racing condition.

Operation of the piston is manual by pulling the handle out from the cylinder which urges the piston downwardly, thereby enlarging a chamber within the cylinder at one side of the line. As the chamber within the cylinder becomes enlarged, fluid within the line is drawn into such enlarging chamber. This has the effect of reducing the resistance of the fluid in the braking system, whereby the springs urge the arcuate brake arms closer together. As will be realized, with the arcuate brake arms in these further inner positions, the distance between the arcuate brake arms and the brake lining structure is increased, thereby easing removal of the wheel from the vehicle. Wheel removal and replacement may, therefore, be performed in a faster time than is normally possible.

The butterfly valve is closed as the handle commences to move out from the cylinder to draw fluid from the line. This closure of the butterfly valve is performed by a tension spring which connects the free end of the link to an arm which extends radially-outwardly from a nut member. The nut member is non-rotatably held in screw threaded reception upon the lower end of the operating rod which has a screw thread for the purpose. The tension spring is infinitely stronger than the torsion spring. Immediately the handle commences to move downwardly, the tension spring (which is slightly relaxed in the upper position of the handle) overcomes the torsion spring to .pivot the link, pin and butterfly valve clockwise to move the butterfly valve to the closed position. In this position, the butterfly valve engages seals which are provided around the inner surface of valve chamber within which the butterfly valve is accommodated. The master cylinder thus becomes separated from the rest of the braking system immediately the handle starts to move downwardly so that fluid cannot be drawn from the master cylinder.

Downward movement of the rod and the handle also draws the nut member down. When the handle reaches its lower position, and in order to hold the piston in its lower position and retain the brake fluid in the cylinder, the handle is then turned to rotate the rod in the nut, so that the handle engages a stationary holding means to hold the handle in the down position. When it is required to dispel brake fluid from the cylinder, the handle is rotated to disengage it from its holding means and is then forced upwards, thereby pushing the piston to its upper position. Immediately before the end of this movement, the tension spring slackens to enable the torsion spring to return the valve into the open position.

To operate the emergency brake shown in Figure 11, the cable is pulled to rotate the disc counterclockwise until the links move the brake shoes radially-outwardly to

apply sufficient braking pressure to the surfaces of the brake linings.

To operate the emergency brake shown in Figure 12, operation of the cable causes rotation of the actuator disc and results in arm operating hydraulic piston to power the movement of the arcuate brake arm, either to engage or to disengage the emergency or parking brake.

To operate the emergency brake shown in Figure 13, operation of the cable causes rotation of the actuator disc and results in arm operating hydraulic piston to power the movement of the arcuate brake arm, either to engage or to disengage the emergency or parking, brake.

To operate the emergency brake shown in Figure 15, operation of this emergency or parking brake is by way of compressed air admitted through air hose to operate a pneumatic piston to cause arm to rotate to power the movement of the arcuate brake arms, either to engage or to disengage the emergency or parking brake.

Further, the alternative emergency brake systems may be used to some effect, instead of the piston and cylinder arrangement shown in Figures 9 and 10, for the purpose of reducing the fluid pressure within the braking system so as to enable the arcuate brake arms to be moved further radially-inwards by the tension springs. This operation may be effected by relaxing the cable so that the disc is caused to move clockwise under the pressure of springs from the inactive position, thereby drawing the arcuate brake arms from their inactive positions to further inward positions. The construction of the embodiment shown may be incorporated either into a conventional automotive vehicle or a racing vehicle. In the case of a conventional automotive vehicle, it may be prudent to incorporate an electrical switch (not shown) in the ignition system which operates dependent upon the position of the piston. Thus, this switch would enable the vehicle to be started with an ignition key only when the piston is in its upper

position, i.e. with the arcuate brake arms in the inoperative position. However, with the piston moved downwardly from its upper position, and with at least some of the pressure removed from the braking system, the switch would be automatically opened and this will prevent starting of the engine of the vehicle upon operation of the ignition switch. The vehicle thus cannot be operated with the pressure reduced within the brake line by use of the piston and cylinder arrangement. The present invention has therefore provided wheel and brake structures in which the problems of unexpected brake failure are minimized or are avoided completely. The wheel defined above according to the present invention is provided with its own arcuate brake lining structure, including a portion which is formed of friction material. Thus, the wheel, upon removal from the vehicle may be replaced immediately with another wheel also having its own brake lining structure including a portion which is formed of friction material which serves as a replacement for the brake lining structure carried upon the previously used wheel. It follows, therefore, that wheel replacement for any purpose, including that of providing a new tire upon the vehicle, is automatically accompanied by a replacement brake lining structure including a portion which is formed of friction material. The addition of the brake lining structure including a portion which is formed of friction material in this manner requires no additional time as it is effected simultaneously with the wheel and tire replacement. Hence, in certain situations, e.g., in racing car events, where tires and wheels are replaced during the course of a race, a racing car may be equipped throughout the whole of a race with adequate braking facility without increasing the amount of pit stop time required during the race.