GB1561396A - Internal shoe drum brakes - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO INTERNAL SHOE DRUM BRAKES (71) We, AUTOMOTIVE PRODUCTS LIMITED, a British Company of Tachbrook Road, Leamington Spa, Warwickshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : This invention relates to internal shoe drum brakes for vehicles and to braking systems incorporating such brakes.

An object of this invention is to provide a new and improved internal shoe drum brake.

According to one aspect of this invention there is provided an internal shoe drum brake for a vehicle which includes two brake shoes and a brake shoe expander for exerting a brake applying thrust which acts to urge one end of one of the brake shoes away from the adjacent one end of the other brake shoe, wherein one arm of a lever which has two such arms extends between the brake shoe expander and said one end of said one brake shoe and the other of said two arms extends between the other end of said other brake shoe and the adjacent other end of said one brake shoe, the lever being adapted to be fulcrumed about an axis which is substantially midway between said one end of said one brake shoe and said other end of said other brake shoe when the brake is installed in a vehicle for use. and the two arms being orientated one with respect to the other so that the brake applying thrust that is exerted by the brake shoe expander is transmitted to said one end of said one brake shoe by said one arm and said other arm is in contact with said other end of said other brake shoe when the brake applying thrust is transmitted to said one end of said one brake shoe to apply substantially one half of said thrust to said other end of said other brake shoe.

Preferably the brake includes another brake shoe expander which is operable to exert a brake applying thrust which acts to urge the other end of said other brake shoe away from the other end of said one brake shoe, said other arm of the lever extending between the other brake shoe expander and said other end of said other brake shoe so that the brake applying thrust that is exterted by said other brake shoe expander is transmitted to said other end of said other brake shoe by said other arm. The lever serves to ensure that the forces exerted by operation of the two brake shoe expanders to separate said one end of said one brake shoe from the adjacent end of said other brake shoe and to separate said other end of said other brake shoe from said other end of said one brake shoe are balanced so that initial contact of the two brake shoes with the brake drum is simultaneous with the advantageous result that the two brakes shoes wear substantially equally.

Preferably the or each brake shoe ex pander is operable by the action of fluid pressure. The or each brake shoe expander preferably is an internal hydraulic wheel cylinder and conveniently is single ended.

An internal shoe drum brake which is an embodiment of this invention and which includes two brake shoe expanders which are operable by the action of fluid pressure is particularly convenient for use as a brake of a fluid pressure braking system according to another aspect of the invention and which comprises one sub-system for supplying fluid pressure to actuate one group of brake shoe expanders which are operable to apply brakes to one group of wheels which- comprises the wheel to which the aforesaid brake that is an embodiment of this invention is fitted at least, and another sub-system for supplying fluid pressure to actuate another group of brake shoe expanders which are operable to apply brakes to another group of wheels which includes said wheel to which the brake that is an embodiment of this invention is fitted and at least one other wheel of the vehicle that is not included in said one group of wheels. Such an internal shoe drum brake in which this invention is embodied is operable by either sub-system in the event of failure of the other sub-system to provide half the braking force that it would provide in similar circumstances if the two sub-systems are operating normally.

Also the incidence of distortion of the drum and the undesirable differential displacement of components of the brake that follows such drum distortion which can be caused by the fluid pressure that is supplied by one of the sub-systems to actuate one of the shoe expanders being different from the fluid pressure that is supplied by the other sub-system to actuate the other expander is minimised because the lever of such an internal shoe drum brake in which this invention is embodied serves to distribute the brake applying thrust that is exerted by the two brake shoe expanders substantially equally between the respective ends of the two brake shoes so that the braking force applied by each brake shoe to the brake drum is substantially equal to the braking force that is exerted by the other brake shoe to the brake drum.

Each arm of the lever may be connected to the adjacent end of the respective brake shoe by a respective resilient link which acts to hold that arm in contact with the adjacent end of the respective brake shoe, in which case if the or each brake shoe expander is an internal hydraulic wheel cylinder a respective piston of the respective internal hydraulic wheel cylinder may be spring loaded into contact with that arm. Alternatively a piston of the or each internal hydraulic wheel cylinder that acts upon a respective one of the arms of the lever to exert a brake applying thrust upon that arm may be connected to the adjacent end of the respective brake shoe by a respective resilient link which spans the respective lever arm and acts to hold that piston in contact with that arm and that arm in contact with that adjacent brake shoe end. The central portion of the lever may provide an anchorage for one end of each of a pair of coil springs, the other end of each coil spring being connected to a respective one of the brake shoes between the ends of that brake shoe so that the pair of coil springs serve as the return springs of the drum brake.

The lever may be adapted to interact with a mechanism which is operable by a hand brake lever so that the drum brake can be operated by the hand brake lever for the emergency braking if desired. The lever may be journaled upon a component of a wheel hub of the vehicle when the drum brake is installed as a brake for a respective wheel so that the lever is fulcrumed about said axis. Preferably the said wheel hub component is a part of the wheel suspension which supports the brake drum and the wheel for rotation relative to it, the lever having an annular portion at its centre, the annular portion receiving the wheel hub component. Conveniently the wheel is a front wheel of a front wheel drive motor car.

Figure 1 is a diagrammatic illustration of one form of hydraulic braking system in which this invention is embodied; Figure 2 is a schematic illustration of the installation of an internal shoe drum brake which is one of the front brakes of the hydraulic braking system illustrated in Figure 1; Figure 3 is a section on the line Ill-rn of Figure 2; Figure 4 is a fragmentary view, similar to part of Figure 2, which shows one modification of the internal shoe drum brake shown in Figures 2 and 3; Figure 5 is a fragmentary view, similar to another part of Figure 2, which shows another modification of the internal shoe drum brake shown in Figures 2 and 3; Figure 6 is a section on the line VI-VI of Figure 5; and Figure 7 is a fragmentary view showing a modified detail of the internal shoe drum brake shown in Figures 5 and 6.

Referring to Fig. 1, a front wheel drive vehicle has a two-shoe internal shoe drum brake 11, 12 fitted to each front wheel and a two-shoe internal shoe drum brake 13, 14 fitted to each rear wheel. The drum brakes 11 to 14 are actuated by fluid pressure, being hydraulic brakes in which the brake shoe expanders are two internal hydraulic wheel cylinders.

A tandem master cylinder 15 has two liquid pressure outlets. One of the liquid pressure outlets is connected to one of the two internal hydraulic wheel cylinders of each front brake 11, 12 by a main pipe 16 and a respective one of two branch pipes 17 and 18. The other liquid pressure outlet is connected to the other of the two internal hydraulic wheel cylinders of each front brake 11, 12, by a main pipe 19 and a respective one of two branch pipes 21 and 22, and to the two internal hydraulic wheel cylinders of each rear brake 13, 14 by a primary branch pipe 23, which is connected to the main pipe 19 between the tandem master cylinder and the two branch pipes 17 and 18, and a respective one of two secondary branch pipes 24 and 25. A pressure cylinder and the two branch pipes 17 and 18, and a respective one of two secondary branch pipes 24 and 25. A pressure reducing valve 26 is fitted into the primary branch pipe 23. Hence the liquid pressure braking system of the vehicle is of the kind which comprises one sub-system, namely the main pipe 16 and the two branch pipes 17 and 18, for supplying hydraulic pressure to wheel cylinders of the front wheel brakes 11 and 12, and another subsystem, namely the main pipe 19, the branch pipes 21 and 22, the primary branch pipe 23 and the secondary branch pipes 24 and 25, for supplying hydraulic pressure to wheel cylinders of the front wheel brakes 11 and 12 and the rear wheel brakes 13 and 14.

Each front wheel is supported by a suspension assembly. The two front wheel suspension assemblies are similar and that for the front wheel to which the brake 11 is fitted will be described now in detail with reference to Figures 2 and 3. It comprises a tubular hub component 27 and has an internal annular rib 28. The rib 28 serves as a spacer between the radially outer races of a pair of ball bearing assemblies (not shown) by which a stub axle (not shown) is supported for rotation within the bore of the tubular hub component 27. The outboard end of the stub axle carries the brake drum (not shown) of the drum brake 11 and the usual studs for the wheel nuts by which the front wheel is secured to the stub axle. The inboard end of the stub axle is connected in the usual manner by a universal drive coupling to a transmission drive shaft. The inboard end of the hub component 27 is connected by upper and lower suspension arms (not shown) to the body of the vehicle, each suspension arm being connected to the hub component 27 by a pin and socket joint (not shown).

The two shoes 29 and 31 of the two shoe internal shoe drum brake 11 are supported in a conventional manner by an annular back plate 32. The back plate 32 is secured by setscrews 33 to three lugs 34 which are formed in the radially outer surface of the tubular hub component 27 substantially midway between the ends of that component 27. A cylindrical surface 35, which has been formed by machining the outer surface of the hub component 27, extends from the lugs 34 towards the outboard end of the hub component 27 and stops short of that outboard end, being separated from that outboard end by a frusto-conical outer surface portion 36 which extends to that outboard end of the hub component 27. The hub component 27 is spigotted into the central aperture of the annular back plate 32 so that the latter is located radially by engagement of its inner periphery with the cylindrical surface 35.

A single ended wheel cylinder 37 has its cylinder body 38 fixed to the back plate 32 and mounted between one pair of adjacent ends 39 and 41 of the shoes 29 and 31. The closed end wall 42 of the cylinder body 38 serves as a fixed abutment for the adjacent end 41 of the brake shoe 31.

Another single ended wheel cylinder 43 has its cylinder body 44 fixed to the back plate 32 and mounted between the other pair of adjacent ends 45 and 46 of the brake shoes 29 and 31. The closed end wall 47 of the cylinder body 44 serves as a fixed abutment for the adjacent end 45 of the brake shoe 29.

A lever 48 has a central tubular portion 49 which is journaled upon that part of the tubular hub component 27 upon which the cylindrical surface 35 is formed, and a diametrically opposed pair of arms 51 and 52. The arm 51 extends between the end 39 of the brake shoe 29 and the piston 53 of the wheel cylinder 37. The arm 52 extends between the end 46 of the brake shoe 31 and the piston 54 of the wheel cylinder 43, or, in other words, between the end 46 of the shoe 31 and the adjacent end 45 of the shoe 29. Each piston 53, 54 projects into a respective arcuate recess 55, 56 which is formed in the adjacent face of the respective arm 51, 52 and the web 57, 58 of each brake shoe 29 and 31 at the respective end 39, 46 projects into another arcuate recess 59, 61 which is formed in the adjacent face of the respective arm 51, 52. Hence the lever 48 is located axially with respect to the tubular hub component 27 by the engagement of the pistons 53 and 54 in the respective recesses 55 and 56 and is fulcrumed about an axis which is substantially midway between the end 39 of brake shoe 29 and the end 46 of shoe 31. Circumferentially spaced recesses 62 are formed in the inner surface of the central tubular portion 49 of the lever 48.

Two ears 63 and 64 are formed in the outer surface of the central tubular portion of the lever 48 substantially diametrically opposite one another. A coil spring 65, 66 serves as the brake release spring for each brake shoe 29, 31. Each release coil spring 65, 66 has one of its end turns formed as a hook 67, 68 which is hooked into an aperture 69, 71 in the web 57, 58 of the respective brake shoe 29, 31, and a tang 72, 73 at its other end. The end of each tang 72, 73 is hooked around a respective one of the ears 63 and 64 so that each brake shoe 29, 31 is urged radially inwardly by the respective release coil spring 65, 66.

Each arm 51, 52 is connected to the end 39, 46 of the web 57, 58 of the respective brake shoe 29, 31 that is received within its arcuate recess 59, 61, by a respective resilient link 74, 75. Each resilient link 74, 75 comprises a coil spring, which has one of its end turns abutting one side of the web 57, 58 of the respective brake shoe 29, 31, and a bent tang which extends from the other end turn of the coil spring through the centre of the coil spring and through a hole 76, 77 in the web 57, 58 of the respective brake shoe 29, 31, that portion of the tang that projects from the respective hole 76, 77 opposite the turns of the coil spring being looped and its end spigotted into a hole (see Figure 3) which is formed in the respective arm 51, 52 of the lever 48.

Manually operable adjusting means provided for each brake shoe 29, 31 comprise a circular disc 78, 79 which is supported upon the back plate 32 for rotation about its centre and which is held frictionally against such rotation, for example by a dished washer, and a peg 81, 82 which is mounted eccentrically upon the disc 78, 79 and which projects into a substantially 'D'shaped aperture 83, 84 which is formed in the web 57, 58 of the respective brake shoe 29, 31. Such adjusting means are sometimes referred to as "eccentric peg" adjusters.

The branch pipe 21 communicates with the interior of the single ended wheel cylinder 37 between its piston 53 and its closed end wall 42. The branch pipe 17 communicates with the interior of the single ended wheel cylinder 43 between its piston 54 and its closed end wall 47.

Substantially the same liquid pressure is fed to the two wheel cylinders 37 and 43 when the braking system is functioning normally and the tandem master cylinder 15 is operated to apply the brakes. The thrust from each piston 53, 54 is transmitted to the adjacent end 39, 46 of the respective brake shoe 29, 31 by the intervening arm 51, 52 of the lever 48. The lever 48 ensures that brake applying thrust is applied to the leading end 39, 46 of each brake shoe 29, 31 simultaneously and that its magnitude and direction relative to that brake shoe 29, 31 is the same as the magnitude and direction of the brake applying thrust supplied to the leading end 39, 46 of the other brake shoe 29, 31. Hence the two brake shoes 29 and 31 are applied to the surrounding brake drum simultaneously so that the friction facings carried by the two brake shoes 29 and 31 wear substantially evenly.

If there is a failure in the supply of liquid pressure to one of the wheel cylinders 37 and 43, the brake applying thrust exerted by the piston 53, 54 of the other wheel cylinder 37, 43 is divided substantially equally between the leading ends 39 and 46 of the two brake shoes 29 and 31 by the action of the two armed lever 48 so that the total braking force applied by the two brake shoes 29 and 31 to the brake drum is substantially half the braking force that would be applied if they were applied by the action of liquid pressure in both the wheel cylinders 37 and 43.

The surfaces of the arcuate recesses 55, 56, 59 and 61 formed in the arms 51 and 52 of the lever 48 and the circumferentiallyspaced portions of the inner surface of the central tubular portion of that lever 48 that engage tubular hub component 27 may be coated with a low friction material if desired.

The lever 48 may be adapted to coact with a hand brake lever linkage, for example by the provision of ratchet teeth on its outer edge which are engaged by a pawl which is incorporated in the hand brake lever mechanism, so that the lever 48 can be rotated about the tubular hub component 27 by operation of the hand brake lever to apply the brake shoes 29 and 31 to the surrounding brake drum for emergency braking. In such an arrangement, the eccentric peg adjuster described above which include the circular discs 78 and 79 and eccentric pegs 81 and 82 would be replaced by some other form of adjusting device which enables adjustment of the hand brake lever mechanism as well as adjustment of the service brake operating mechanism. The known type of adjusting device which incorporates a snail cam would be a suitable form of adjusting device for this purpose. In practice the loading of resilient links 74 and 75 of the internal shoe drum brake that is described above with reference to Figures 2 and 3 is insufficient to prevent the arms 51 and 52 being separated from the adjacent ends 39 and 46 of the brake shoes 29 and 31 by the action of the brake release springs 65 and 66 once movement of the brake shoes 29 and 31 away from the drum is stopped by abutment of the straight edge portions of the D-shaped apertures 83 and 84 with the respective pegs 81 and 82 of the eccentric peg adjusters. Each wheel cylinder 37, 43 may be provided with a light com pression spring which reacts against the respective closed end wall 42, 47 and urges the respective piston 53, 54 towards the respective arm 51, 52 in order to prevent that arm 51, 52 being separated from the adjacent end 39, 46 of the respective brake shoe 29, 31. Other modifications of the internal shoe drum brake that is described above with reference to Figures 2 and 3 which are intended to oppose the tendency for the arms 51 and 52 to be separated from the respective adjacent ends 39 and 46 of the brake shoes 29 and 31 will be described now with reference to Figures 4, 5, 6 and 7.

Components shown in Figures 2 and 3 are identified by the same reference numerals and will not be described again fully.

Figure 4 shows the provision of a plate 85 which is bolted to the arm 52 and which extends between the back plate 32 and the web 58. An aperture 86 is formed in the plate 85 and the eccentric peg 82 projects into it. The shape and location of the aper ture 86 in relation to the shape and location of the aperture 84 in the web 58 of the brake shoe 31 is such that the peg 82 cooperates with the periphery of the aperture 86 to limit movement of the arm 52 towards the respective wheel cylinder 43, and thus to limit movement of the brake shoe 31 away from the drum and rotation of the lever 48 due to the action of the release springs. The eccentric peg adjuster which interacts with the brake shoe 29 is redundant and may be removed or rendered inoperative by locating its peg so that there is always a clearance between it and the periphery of the respective D-shaped aperture or by shortening or removing that peg. The peg 82 may be shortened so that it projects into the aperture 86 but not into the aperture 84 rather than take care to ensure that the relative location of the apertures 84 and 86 is such that the peg 82 co-operates with the periphery of the aperture 86 and not with the periphery of the aperture 84.

Referring now to Figures 5 and 6, the bent tank of the resilient link 74A connects the end 39 of the web 57 of the brake shoe 29 to the piston 53A of the respective wheel cylinder 37 rather than to the arm 51A that extends between them, the end of the bent tang being inserted into a hole in the piston 53A. An identical link 75A (not shown) similarly connects the end 46 of the other brake shoe 31 to the piston of the other wheel cylinder 43. These two resilient links 74A and 75A are arranged to ensure that the brake shoes and the pistons of the two wheel cylinders move together.

Figure 5 also shows that the tang 73 of the release spring 66 is booked into an aperture in a lug 64A of the central tubular portion 49 of the lever 48A rather than being engaged in an ear as described with reference to Figures 2 and 3. The arms 51A and 52A (not shown) of the lever 48A are modified so that the pistons of the wheel cylinders 37 and 43 engage the side faces of those arms rather than projecting into recesses in those arms. The recesses 55 and 56, which are described with reference to Figures 2 and 3, are omitted. Figure 5 shows that the end of the piston 53A that engages the arm 51A is spherical, the side face of the arm 51A that it engages being flat. Figure 7 shows that the end of the piston 53B may be flat and may engage a domed projection 87 fonned by the adjacent side face of the arm 51B with which is co-operates.

Figure 6 shows a modification in the manner in which the lever 48A is mounted on the tubular hub component 27A and located axially with respect to that component 27A as compared with the arrange ment described above with reference to Figures 2 and 3.

The machined cylindrical surface 35A of the hub component 27A upon which the lever 48A is journaled, extends inwardly from the frusto-conical outer surface portion 36 to a shoulder 88 which is spaced from the lugs 34 and the inner peripheral portion of the back plate 32 by a larger diameter portion 89 of the hub component 27A. The lever 48 is located axially upon the hub component 27A by abutment of one of its sides with the shoulder 88 and by a circlip 91 which is fitted into a circumferential groove 92 formed in the machined surface 35A adjacent the frusto-conical outer surface portion 36.

WHAT WE CLAIM IS: 1. An internal shoe drum brake for a vehicle which includes two brake shoes and a brake shoe expander for exerting a brake applying thrust which acts to urge one end of one of the brake shoes away from the adjacent one nd of the other brake shoe, wherein one arm of a lever which has two such arms extends between the brake shoe expander and said one end of said one brake shoe and the other of said two arms extends between the other end of said other brake shoe and the adjacent other end of said one brake shoe, the lever being adapted to be fulcrumed about an axis which is substantially midway between said one end of said one brake shoe and said other end of said other brake shoe when the brake is installed in a vehicle for use, and the two arms being orientated one with respect to the other so that brake applying thrust that is exerted by the brake shoe expander is transmitted to said one end of said one brake shoe by said one arm and said other arm is in contact with said other end of said other brake shoe when the brake applying thrust is transmitted to said one end of said one brake shoe to apply substantially one half of said thrust to said other end of said other brake shoe.

2. An internal shoe drum brake according to Claim 1, which includes another brake shoe expander which is operable to exert a brake applying thrust which acts to urge the other end of said other brake shoe away from the other end of said one brake shoe, said other arm of the lever extending between the other brake shoe expander and said other end of said other brake shoe so that the brake applying thrust that is exerted by said other brake shoe expander is transmitted to said other end of said other brake shoe by said other arm.

3. An internal shoe drum brake according to Claim 1 or Claim 2, wherein the or each brake shoe expander is operable by the action of fluid pressure.

4. An internal shoe drum brake according to Claim 3, wherein the or each brake shoe expander is an internal hydraulic wheel cylinder.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (16)

**WARNING** start of CLMS field may overlap end of DESC **. ture 86 in relation to the shape and location of the aperture 84 in the web 58 of the brake shoe 31 is such that the peg 82 cooperates with the periphery of the aperture 86 to limit movement of the arm 52 towards the respective wheel cylinder 43, and thus to limit movement of the brake shoe 31 away from the drum and rotation of the lever 48 due to the action of the release springs. The eccentric peg adjuster which interacts with the brake shoe 29 is redundant and may be removed or rendered inoperative by locating its peg so that there is always a clearance between it and the periphery of the respective D-shaped aperture or by shortening or removing that peg. The peg 82 may be shortened so that it projects into the aperture 86 but not into the aperture 84 rather than take care to ensure that the relative location of the apertures 84 and 86 is such that the peg 82 co-operates with the periphery of the aperture 86 and not with the periphery of the aperture 84. Referring now to Figures 5 and 6, the bent tank of the resilient link 74A connects the end 39 of the web 57 of the brake shoe 29 to the piston 53A of the respective wheel cylinder 37 rather than to the arm 51A that extends between them, the end of the bent tang being inserted into a hole in the piston 53A. An identical link 75A (not shown) similarly connects the end 46 of the other brake shoe 31 to the piston of the other wheel cylinder 43. These two resilient links 74A and 75A are arranged to ensure that the brake shoes and the pistons of the two wheel cylinders move together. Figure 5 also shows that the tang 73 of the release spring 66 is booked into an aperture in a lug 64A of the central tubular portion 49 of the lever 48A rather than being engaged in an ear as described with reference to Figures 2 and 3. The arms 51A and 52A (not shown) of the lever 48A are modified so that the pistons of the wheel cylinders 37 and 43 engage the side faces of those arms rather than projecting into recesses in those arms. The recesses 55 and 56, which are described with reference to Figures 2 and 3, are omitted. Figure 5 shows that the end of the piston 53A that engages the arm 51A is spherical, the side face of the arm 51A that it engages being flat. Figure 7 shows that the end of the piston 53B may be flat and may engage a domed projection 87 fonned by the adjacent side face of the arm 51B with which is co-operates. Figure 6 shows a modification in the manner in which the lever 48A is mounted on the tubular hub component 27A and located axially with respect to that component 27A as compared with the arrange ment described above with reference to Figures 2 and 3. The machined cylindrical surface 35A of the hub component 27A upon which the lever 48A is journaled, extends inwardly from the frusto-conical outer surface portion 36 to a shoulder 88 which is spaced from the lugs 34 and the inner peripheral portion of the back plate 32 by a larger diameter portion 89 of the hub component 27A. The lever 48 is located axially upon the hub component 27A by abutment of one of its sides with the shoulder 88 and by a circlip 91 which is fitted into a circumferential groove 92 formed in the machined surface 35A adjacent the frusto-conical outer surface portion 36. WHAT WE CLAIM IS:

1. An internal shoe drum brake for a vehicle which includes two brake shoes and a brake shoe expander for exerting a brake applying thrust which acts to urge one end of one of the brake shoes away from the adjacent one nd of the other brake shoe, wherein one arm of a lever which has two such arms extends between the brake shoe expander and said one end of said one brake shoe and the other of said two arms extends between the other end of said other brake shoe and the adjacent other end of said one brake shoe, the lever being adapted to be fulcrumed about an axis which is substantially midway between said one end of said one brake shoe and said other end of said other brake shoe when the brake is installed in a vehicle for use, and the two arms being orientated one with respect to the other so that brake applying thrust that is exerted by the brake shoe expander is transmitted to said one end of said one brake shoe by said one arm and said other arm is in contact with said other end of said other brake shoe when the brake applying thrust is transmitted to said one end of said one brake shoe to apply substantially one half of said thrust to said other end of said other brake shoe.

2. An internal shoe drum brake according to Claim 1, which includes another brake shoe expander which is operable to exert a brake applying thrust which acts to urge the other end of said other brake shoe away from the other end of said one brake shoe, said other arm of the lever extending between the other brake shoe expander and said other end of said other brake shoe so that the brake applying thrust that is exerted by said other brake shoe expander is transmitted to said other end of said other brake shoe by said other arm.

3. An internal shoe drum brake according to Claim 1 or Claim 2, wherein the or each brake shoe expander is operable by the action of fluid pressure.

4. An internal shoe drum brake according to Claim 3, wherein the or each brake shoe expander is an internal hydraulic wheel cylinder.

5. An internal shoe drum brake accord

ing to Claim 4, wherein the or each internal wheel cylinder is single ended.

6. An internal shoe drum brake according to any one of Claims 1 to 5, wherein each arm of the lever is connected to the adjacent end of the respective brake shoe by a respective resilient link which acts to hold that arm in contact with the adjacent end of the respective brake shoe.

7. An internal shoe drum brake according to Claim 6 when appended to Claims 2 and 5, wherein a piston of each internal hydraulic wheel cylinder is spring loaded into contact with the respective arm.

8. An internal shoe drum brake accordin the Claim 3 or Claim 4, wherein a piston of the or each internal hydraulic wheel cylinder that acts upon a respective one of the arms of the lever to exert a brake applying thrust upon that arm is connected to the adjacent end of the respective brake shoe by a respective resilient link which spans the respective lever arm and acts to hold that piston in contact with that arm and that arm in contact with that adjacent brake shoe end.

9. An internal shoe drum brake according to any one of Claims 1 to 8, wherein the central portion of the lever provides an anchorage for one end of each of a pair of coil springs, the other end of each coil spring being connected to a respective one of the brake shoes between the ends of that brake shoe so that the pair of coil springs serve as the return springs of the drum brake.

10. A fluid pressure braking system which comprises one sub-system for supplying fluid pressure to actuate one group of brake shoe expanders which are operable to apply brakes to one group of wheels which comprises a wheel to which an internal shoe drum brake according to Claim 2 or any one of Claims 3 to 9 when appended to Claim 2 is fitted at least, and another sub-system for supplying fluid pressure to actuate another group of brake shoe expanders which are operable to apply brakes to another group of wheels which includes said wheel to which said internal shoe drum brake is fitted and at least one other wheel of the vehicle that is not included in said one group of wheels.

11. A fluid pressure braking system according to Claim 10, wherein the lever of said internal shoe drum brake that is fitted to said wheel that is common to the two sub-systems is adapted to interact with a mechanism which is operable by a hand brake lever so that said internal shoe drum brake can be operated by the hand brake lever for emergency braking if desired.

12. A fluid pressure braking system according to Claim 10 or Claim 11, wherein the lever is journaled upon a component of a wheel hub of the vehicle so that the lever is fulcrumed about said axis.

13. A fluid pressure braking system according to Claim 12, wherein the said wheel hub component is a part of the wheel suspension which supports the brake drum and said wheel for rotation relative to it, the lever having an annular portion at its centre, the annular portion receiving the wheel hub component.

14. A fluid pressure braking system according to any one of Claims 10 to 13, wherein the wheel is a front wheel of a front wheel drive motor car.

15. An internal shoe drum brake substantially as described hereinbefore with reference to and as illustrated in Figures 2 and 3, or substantially as described hereinbefore with reference to and as illustrated in Figures 2 and 3 and modified substantially as described hereinbefore with reference to and as illustrated in Figure 4, Figures 5 and 6, or Figure 7 of the accompanying drawings.

16. A liquid pressure braking system substantially as described hereinbefore with reference to and as illustrated in Figures 1 to 3, or substantially as described hereinbefore with reference to and as illustrated in Figures 1 to 3 and modified substantially as described hereinbefore with reference to and as illustrated in Figure 4, Figures 5 and 6, or Figure 7 of the accompanying drawings.