ELECTRIC HUB DRIVE WITH BRAKING ASSEMBLY

Abstract

Some embodiments are directed to an electric hub drive with a braking assembly. The hub drive includes a housing; a rotary drive transmission system mounted within the housing; and a braking assembly positioned within the housing. The braking assembly includes a braking formation that is coupled to be rotationally driven by the rotary drive transmission system. Advantageously or preferably, the braking formation is coupled to be rotationally driven by a part of the rotary drive transmission system that has a higher angular velocity than the output shaft. This enables the braking formation to rotate at a faster speed than the wheel hub.

Claims

1. An electric hub drive comprising: a housing; a rotary drive transmission system including an input shaft, output shaft, and a torque transfer arrangement to effect a rotational coupling between the input shaft and the output shaft mounted within the housing; and a braking assembly including a braking formation positioned within the housing, the braking formation being coupled to be rotationally driven by the drive transmission system.

2. The hub drive of claim 1, wherein the braking formation is carried on a drive shaft coupled to be driven rotationally by the drive transmission system.

3. The hub drive of claim 1, wherein the braking formation is a friction formation selectively engageable against one or more complementary friction surfaces carried within the housing.

4. The hub drive of claim 1, wherein the braking formation includes at least one brake disc.

5. The hub drive of claim 4, wherein at least one brake disc is mounted co-axially on a shaft coupled to be driven rotationally by the drive transmission system.

6. The hub drive of claim 1, wherein the braking formation is coupled to be rotationally driven at an angular velocity equal to or greater than that of the output shaft of the hub drive.

7. The hub drive of claim 6, wherein the braking formation is coupled to be rotationally driven at an angular velocity greater than that of the output shaft of the hub drive.

8. The hub drive of claim 7, wherein the rotary drive transmission system includes a gearing assembly configured to reduce a higher input shaft angular velocity to a lower output shaft angular velocity and the braking formation is coupled to be rotationally driven by a part of the gearing assembly having an angular velocity greater than that of the output shaft.

9. The hub drive of claim 8, wherein the gearing assembly includes a final reduction gear the output of which reduction gear drives the output shaft of the hub drive, and the braking formation has a torque coupling to an input of the reduction gear.

10. The hub drive of claim 3, wherein the friction surface(s) comprise the surfaces of one or more brake pads carried within the housing.

11. The hub drive of claim 10, wherein a plurality of brake pads are provided on one or more carrier formations.

12. The hub drive of claim 11, wherein the plurality of brake pads are provided disposed across the surface of each of one or more carrier formations in the form of carrier discs.

13. The hub drive of claim 12, wherein the braking formation comprises at least one brake disc, and wherein a pair of said carrier discs are provided, one disposed on either side of the brake disc, so as to engage a respective surface of the brake disc and effect a braking action in use.

14. The hub drive of claim 3, wherein the braking assembly further comprises an actuation means to effect selective engagement and disengagement of the braking formation against the friction surface(s).

15. The hub drive of claim 1, wherein the hub drive has an inboard side for positioning proximal to a vehicle and an outboard side for positioning distal to a vehicle, and the braking formation is positioned on the inboard side.

16. The hub drive of claim 1, further comprising an electric motor having a motor rotor for driving the hub drive input shaft mounted within the housing.

17. The hub drive of claim 1, further comprising a gearing assembly wherein the motor rotor is interposed between the barking formation and the gearing assembly.

18. The hub drive of claim 1, wherein the housing is adapted to fit within the wheel rim of a wheel.

19. The hub drive of claim 1, wherein the housing is cooled.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Some embodiments will now be described by way of example only, and with reference to the accompanying drawings, in which:

[0026] FIG. 1 is a schematic cross-section of an electric wheel hub braking system in accordance with some embodiments; and

[0027] FIG. 2 is an exploded view of a brake disc and pads suitable for use with a braking system in accordance with some embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] In some embodiments, it has been appreciated that it is not necessary to position a brake disc within the radial space between the inner surface of a wheel rim and a hub drive in order to provide sufficient braking at even high torques. In accordance with some embodiments, an electric hub drive includes a housing, a rotary drive transmission system including an input shaft, and output shaft, and a torque transfer arrangement to effect a rotational coupling between the input shaft and the output shaft mounted within the housing, and a braking assembly in accordance with the principles of some embodiments positioned within the housing. The braking mechanism is driven by a torque coupling to the drive transmission system, and in a particular preferred case to a part of the transmission system that has the same or a greater angular velocity than the output shaft that drives the wheel such that it rotates faster than or at the same speed as the wheel during braking.

[0029] FIG. 1 is a schematic cross-section of an electric hub drive system including an electric hub drive incorporating a braking system in accordance with some embodiments. An electric hub drive system 1 includes an electric hub drive 4 to drive a wheel including a wheel rim 2 on a wheel bearing 16 sealed by seal 17, the wheel rim generally having the form of an open cylinder, with an inner surface and an outer surface with a tire 3 mounted radially on the outer surface of the wheel rim 2 for contact with the terrain on which a vehicle (not shown) carrying the wheel hub will drive over.

[0030] The volume described by the inner surface of the open cylinder of the wheel rim 2 contains the electric hub drive 4. The hub drive 4 includes a housing 5 for example of aluminium, containing an electric drive mechanism, a braking assembly, and a drive transmission system including gearing assembly to transmit drive from the electric drive mechanism to the driven wheel.

[0031] The electric drive mechanism includes a rotary electric motor 9 mounted within the housing. The motor is positioned co-axially around the shaft 6. A gearing system in the embodiment includes a selectively active gear change set 10 and a fixed ratio output reduction gear 11. An oil cooler system 15 cools the gearbox.

[0032] The braking assembly includes a shaft 6 mounted within the housing 5, and a braking formation 7, mounted on the shaft 6, such that the braking formation 7 is rotatably driven by the shaft 6. In this embodiment the braking formation 7 is a brake disc, which is mounted co-axially on the drive shaft 6. In other words, the drive shaft 6 passes through the centre of the brake disc.

[0033] The gearing assemblies 10, 11 are positioned axially with respect to the shaft 6. This ensures that the brake disc 7, the motor 9 and the gearing assemblies 10, 11 are arranged axially with each other and the shaft 6. This arrangement is enhanced or optimised to fit all the required components for the hub drive within both the radial space allowed by the wheel rim 2 and the transverse space available to the hub assembly for practical use on a vehicle.

[0034] The hub drive 4 has an inboard side for positioning proximal to a vehicle and an outboard side for positioning distal to a vehicle. The brake disc 7 is preferably positioned on the inboard side of the assembly. This is advantageous since this is the side with the stationary casing for connection to the suspension system and to which the braked pad assemblies can be mounted. The outer part of the casing rotates with the wheel.

[0035] In order to apply sufficient braking by friction with the brake disc 7, a plurality of brake pads 12 are mounted within the housing 5 on cooled discs and adapted to contact the brake disc 7. The arrangement is shown in greater detail in FIG. 2.

[0036] Advantageously or preferably, the shaft 6 is torque coupled to a part of the drive transmission system that is rotating at higher speed than the speed output to the wheels. In the embodiment, the shaft 6 is torque coupled to the input side of the output reduction gear 11. The input side of the reduction gear has a higher angular velocity than the output side driving the wheels. Thus the brake disc rotates at a faster speed than the wheels. Typically the input side of the reduction gear will run four times faster than the output side and hence than the wheel, such that the torque capacity of the brake is four times lower than it would be if it were braking the wheel directly. The size of the brake disc 7, the brake pads 12 and the force required to operate the brake are reduce proportionally allowing for a reduction in size and mass compared with existing braking assemblies.

[0037] As shown in FIG. 1, the housing 5 is adapted to fit within the wheel rim 2. The housing 5 may be cooled using a cooling mechanism 14, which may be, for example, a water cooling mechanism. The use of water cooling instead of air cooling allows the system to be sealed to prevent ingress of dirt. The water cooled hub structure cools the brake pads, as well as the motor housing and the gearbox casing. The gear box is cooled and lubricated by a fixed volume of oil contained inside the hub. This oil fills the gap between the cooled structure supporting the gearbox and the rotating outer casing. A narrow gap is provided with heat transfer features so that the shearing action of the oil in the gap aids heat transferheat transfer from static oil is otherwise poor.

[0038] Ideally, the brake disc 7 is rotationally coupled to the shaft 6 but is free to move axially, and may be mounted on splines, axial pins, a key way or other connection mechanism to effect this.

[0039] The brake disc 7 may be a metal brake disc, such as a steel brake disc, or a composite material, such as a carbon fibre brake disc. The brake disc may be closed or vented, and may be cooled. As noted a closed water cooled system is preferred allowing the housing 5 to be completely sealed from the ingress of external elements such as water, dust, mud and dirt.

[0040] The brake pads 12 may be formed from materials having ideal frictional relationships with the brake disc material, such as sintered metallic materials or bonded organic materials.

[0041] FIG. 2 illustrates an advantageous or preferred embodiment of disc brake assembly with brake components disassembled.

[0042] A brake disc 21 is provided to be mounted on and rotated with a drive shaft, in the preferred case at an angular velocity that is greater than that of the hub output shaft, and for example by coupling to the input stage of a final reduction gear as described with reference to FIG. 1. The brake disc is annular and provided on the inside with splines whereby it rotates with the shaft but floats axially.

[0043] Paired brake pad assemblies are provided either side of the brake disc. An inner brake pad assembly 22 is fixed in the hub case and includes a carrier disc that carries a plurality of brake pads 23 covering essentially its entire surface. The brake pad assembly is water cooled. An outer brake pad assembly 24 including a carrier disc again covered essentially on its entire surface by a plurality of brake pads 23, is mounted within the hub case to moveable axially by a brake actuator (not shown). The outer brake pad assembly is again water cooled.

[0044] Under action of the brake actuator, engagement is effected between the brake disc and the paired brake pad assemblies, effecting retardation of the brake disc, and hence of the shaft, and hence because the shaft is torque coupled to the hub drive transmission and for example to the input of the output reduction gear, effects braking of the hub drive and of the wheel.

[0045] Although in the embodiment a single brake disc is used, a possible configuration, for example for a higher capacity brake, might be to have a plurality of discs stacked axially. In such an arrangement a carrier disc that carries a plurality of brake pads on each of its opposed faces may then be provided between each adjacent pair of discs in the stacked array.

[0046] The hub drive may be adapted for regenerative braking.

[0047] Although in the embodiment shown in FIG. 1 it is advantageous to position the braking mechanism on the inboard side of the hub drive with the gearing assembly 10, 11 on the outboard side and the electric motor 9 positioned centrally, it is possible to arrange the components differently whilst still maintaining their axial arrangement and thus taking advantage of the main benefits of some embodiments. For example, the braking mechanism may be positioned on the outboard side, or centrally.

[0048] These and other advantages of some embodiments will be apparent from the appended claims.