Field of the Invention

The present invention relates to a torque transmitting device and relates particularly, though not exclusively, to a constant velocity hub for transmitting torque from the drive train of a vehicle engine operating at constant velocity to a wheel of the vehicle.

Background to the Invention

Concern for the environment and increased awareness of the impact of climate change are providing incentives for motor vehicle manufacturers to produce vehicles with reduced exhaust emissions. The increased cost of fossil fuels is also providing incentives for producing vehicles with improved fuel economy, and for electric and hybrid vehicles. It is well known that one of the principal causes of increased vehicle emissions and reduced fuel economy is the constant fluctuations in engine load and speed typically encountered when driving in unban traffic. If the vehicle engine could be operated at a substantially constant velocity, then a significant reduction in exhaust emissions and improved fuel economy could be achieved. Furthermore, operating the vehicle engine at a substantially constant velocity would also result in increased engine reliability and efficiency, with a corresponding reduction in service requirements and increase in serviceable life of the vehicle.

The present invention was developed with a view to providing a torque transmitting device that allows the vehicle engine to operate at substantially constant velocity whilst transmitting torque to the wheels as the vehicle accelerates or decelerates through different speeds, terrain or load-carrying requirements. However it will become apparent that the invention is equally applicable to many other applications where a torque needs to be transmitted from a power source, such as an electric motor or internal combustion engine, to a rotating driven load. The present invention also provides a braking device for retarding rotation of a rotating load, which operates on a similar principle to the torque transmitting device.

The previous discussion of the background to the invention is provided for illustrative purposes only and is not to be taken as an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge in Australia or elsewhere as at the priority date of this application.

Summary of the Invention

According to one aspect of the present invention there is provided a torque transmitting device for transmitting torque from a power source to a rotating driven load, the device comprising: a cylindrical assembly adapted to be mechanically coupled via its outer circumference to the rotating driven load, and provided with a port on its inner circumference; a rotor assembly adapted to be mechanically coupled to the power source and rotatably mounted within the cylindrical assembly so as to form together with the port a fluid chamber between the rotor assembly and the inner circumference of the cylindrical assembly, the rotor assembly comprising a plurality of pistons at angularly spaced intervals, each piston being movable between a retracted position and an extended position in which it extends into the fluid chamber; and, a hydraulic fluid provided in the fluid chamber whereby, in use, upon activation of the pistons an hydraulic lock is formed between the rotor assembly and the cylindrical assembly to transmit torque from the rotor assembly to the cylindrical assembly.

Typically the port in the cylindrical assembly is one of a plurality of ports at angularly spaced intervals on its inner circumference. Preferably the angular spacing between the pistons is offset relative to the spacing of the ports. Preferably the rotor assembly comprises a flywheel and the pistons are radially mounted and extend through an outer circumference of the flywheel into the fluid chamber. Preferably the fluid chamber is a sealed chamber and the pistons are adapted to trap hydraulic fluid between two of the pistons in their extended position. Typically the hydraulic fluid in the fluid chamber is pressurised. Preferably when the pistons are actuated the hydraulic fluid in the fluid chamber is further pressurised as the pistons extend into the fluid chamber. Preferably the width of the pistons is machined to match exactly the width of the fluid chamber. Preferably the ports in the cylindrical assembly are of circular cross-section with a diameter that exactly matches that of the pistons.

Typically in their fully extended position the clearance between the top of each piston and the inner circumference of the cylindrical assembly is less than one thousandth of an inch. The top surface of each piston is typically precision- machined to match the angle of curvature of the inner circumference of the cylindrical assembly. As the flywheel continues to rotate within the cylindrical assembly and the pistons are actuated, the pistons sweep hydraulic fluid before them and peak pressure occurs when a piston covers one of the ports.

Preferably each piston is slidably received in its own piston sleeve. The piston sleeves are preferably mounted in radially extending bores provided in the flywheel. The sleeves are preferably designed to limit the travel of the respective pistons to their extended position. An annular lip is preferably provided on a lower edge of each piston and is adapted to engage with a lower edge of the corresponding piston sleeve to limit the travel of the piston.

Preferably the flywheel is fixed to a stub axle of the rotor assembly, which is rotatably supported in the cylindrical assembly by a plurality of bearings. Hydraulic fluid for actuating the pistons is preferably pumped through a fluid circuit extending through the stub axle. The hydraulic fluid in the fluid circuit is typically pressurised by an external actuator provided on a closed loop hydraulic line, to actuate the pistons. When the pressure is released the pistons return to their retracted position by virtue of the preset pressure of the hydraulic fluid within the sealed fluid chamber. An additional fluid circuit is provided within the stub axle for circulating coolant through the rotor assembly, and removing heat generated during operation of the torque transmitting device.

In a preferred embodiment the device is in the form of a hub for transmitting power from a motor vehicle engine to a wheel of the motor vehicle, the rotor assembly being mechanically coupled to a drive train of the engine and the cylindrical assembly being mechanically coupled to the wheel. The hydraulic fluid in the fluid circuit is typically pressurised by foot pressure, for example, applied to the motor vehicle accelerator pedal on a closed loop hydraulic line, to actuate the pistons. Advantageously the motor vehicle engine is operated at substantially constant velocity to reduce vehicle emissions and improve engine efficiency, and the hub is one of a plurality of hubs transmitting engine torque to a corresponding plurality of the vehicle wheels.

Advantageously the torque transmitting device also incorporates a braking device for retarding rotation of a rotating load, which operates on the same principle as the torque transmitting device. The braking device comprises a cylindrical assembly, which it preferably shares with the torque transmitting device, and which is adapted to be mechanically coupled via its outer circumference to the rotating load. The cylindrical assembly is preferably provided with a second plurality of ports at angularly spaced intervals on its inner circumference. As with the first plurality of ports, the second plurality of ports are angularly spaced at uniform intervals on the inner circumference of the cylindrical assembly.

The braking device preferably further comprises a stator assembly adapted to be mechanically coupled to a stationary structure and mounted within the cylindrical assembly so as to form a second sealed fluid chamber between the stator assembly and the inner circumference of the cylindrical assembly. The stator assembly preferably comprises a stator housing with a second plurality of radially mounted pistons extending through its outer circumference into the fluid chamber at angularly spaced intervals. The angular spacing between the pistons in the second plurality of pistons is offset relative to the spacing of the ports in the second plurality of ports. Preferably the second fluid chamber is a sealed chamber and the pistons are adapted to trap hydraulic fluid between two of the pistons in their extended position.

According to another aspect of the present invention there is provided a braking device for retarding rotation of a rotating load, the device comprising: a cylindrical assembly adapted to be mechanically coupled via its outer circumference to the rotating load, and provided with a port at on its inner circumference; a stator assembly adapted to be mechanically coupled to a stationary structure and mounted within the cylindrical assembly so as to form together with the port a fluid chamber between the stator assembly and the inner circumference of the cylindrical assembly, the stator assembly comprising a plurality of pistons at angularly spaced intervals, each piston being movable between a retracted position and an extended position in which it extends into the fluid chamber; and, a hydraulic fluid provided in the fluid chamber whereby, in use, upon activation of the pistons an hydraulic lock is formed between the stator assembly and the cylindrical assembly to retard rotation of the cylindrical assembly relative to the stator assembly. Typically the port in the cylindrical assembly is one of a plurality of ports at angularly spaced intervals on its inner circumference. Preferably the angular spacing between the pistons is offset relative to the spacing of the ports. Preferably the stator assembly comprises a stator housing and the pistons are radially mounted and extend through an outer circumference of the housing into the fluid chamber. Preferably the fluid chamber is a sealed chamber and the pistons are adapted to trap hydraulic fluid between two of the pistons in their extended position.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. Likewise the word "preferably" or variations such as "preferred", will be understood to imply that a stated integer or group of integers is desirable but not essential to the working of the invention. Brief Description of the Drawings

The nature of the invention will be better understood from the following detailed description of a specific embodiment of a torque transmitting device and braking device, given by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a preferred embodiment of the torque transmitting device of the present invention in the form of a constant velocity hub for a motor vehicle wheel;

Figure 2 is a longitudinal section view through the device of Figure 1 ;

Figure 3 is an exploded view of the internal components of the device of Figure 1;

Figures 4 (a) and (b) are an end view and a side view respectively of the external component of the device of Figure 1 ;

Figure 5 (a) is a simplified exploded view of part of the device of Figure 1 ^' ·

Figures 5 (b) and (c) illustrate operation of the device of Figure 1 and the onset of hydraulic lock;

Figure 6 is a longitudinal section view through the rotor assembly of the device of Figure 1 ;

Figure 7 is a section view of the rotor assembly through the line A-A of Figure 6; and,

Figure 8 is a longitudinal section view through the stator assembly of the device of Figure 1. Detailed Description of Preferred Embodiments

A preferred embodiment of torque transmitting device 10 in accordance with the invention, as illustrated in Figures 1 to 8, comprises a cylindrical assembly 12 adapted to be mechanically coupled via its outer circumference to a rotating driven load. In the illustrated embodiment the device is in the form of a constant velocity hub 10 for transmitting power from a motor vehicle engine (not shown) to a wheel 14 of the motor vehicle, the cylindrical assembly 12 of the hub being mechanically coupled to a vehicle brake disc and wheel assembly of the wheel 14. The cylindrical assembly 12 preferably comprises a hollow steel cylinder 16 provided with a plurality of ports 18 at angularly spaced intervals on its inner circumference (see Figures 2 and 4). In Figure 4 the ports 18 are shown passing all the way through from the inner surface of the cylinder 16 to its outer surface. However in the assembled device each port 18 is sealed shut at the outer surface of the cylinder 16, as shown in Figure 2. In this embodiment there are three ports 18 angularly spaced at uniform intervals of 120° on the inner circumference of the cylinder 16.

The device 10 further comprises a rotor assembly 20 adapted to be mechanically coupled to the power source and rotatably mounted within the cylindrical assembly 12 so as to form together with the ports 18 a sealed fluid chamber 22 between the rotor assembly 20 and the inner circumference of the cylinder 16. The rotor assembly 20 comprises a drive flywheel 24 having a plurality of radially mounted pistons 26 extending through its outer circumference into the fluid chamber 22 at angularly spaced intervals (see Figures 3, 6 and 7). The angular spacing between the pistons 26 is offset relative to the spacing of the ports 18 in the cylinder 16. In this embodiment there are four pistons 26 angularly spaced at uniform intervals of 90° around the circumference of the flywheel 24.

The sealed fluid chamber 22 is formed in the gap between the outer circumference of the drive flywheel 24 and the inner circumference of the cylinder 16, and is bounded by two annular fluid seals 28 provided in 6 connection with the outer circumference of the flywheel 24 (see Figure 6). The fluid seals 28 are preferably made from a synthetic rubber material, and are received in respective annular grooves provided in the outer surface of the flywheel 24 to form a tight seal against the inner surface of the cylinder 16. A fixed volume of hydraulic fluid is provided in the fluid chamber 22 whereby, in use, upon activation of the pistons 26 an hydraulic lock is formed between the flywheel 24 and the cylinder 16 to transmit torque from the rotor assembly 20 to the cylindrical assembly 12. Any suitable hydraulic fluid may be employed; however the preferred fluid is onoethylene Glycol. The manner in which the hydraulic lock is formed will now be described with reference to Figures 5 and 7.

As shown in Figure 5 (a) the flywheel 24 of the rotor assembly 20 is rotatably received in the cylinder 16 of the cylindrical assembly 12, and the two annular fluid seals 28 contain the hydraulic fluid in the fluid chamber 22. The hydraulic fluid in the chamber 22 is pressurised. The width of the pistons 26 is machined to match exactly the width of the fluid chamber 22, and they slightly protrude into the fluid chamber in their extended position. The ports 18 in the cylindrical assembly are preferably of circular cross-section with a diameter that exactly matches that of the pistons 26. The pistons 26 are actuated by a separate hydraulic circuit as will be further described below. Prior to actuation, the pistons 26 are held in their retracted position, as shown in Figure 5 (b), due to pre-load pressure within the chamber 22. This allows the flywheel 24 to rotate freely (freewheel) with no resistance or pressure exerted on the cylinder 16, which means that no torque is transmitted to the cylindrical assembly 12. However when the pistons 26 are actuated the hydraulic fluid in the chamber 22 is further pressurised as the pistons extend into the fluid chamber 22. In their fully extended position the clearance between the top of each piston 26 and the inner surface of the cylinder 16 is less than one thousandth of an inch. As the flywheel 24 continues to rotate within the cylindrical assembly 12, the pistons 26 sweep hydraulic fluid before them. Peak pressure occurs when a piston 26a covers a port 18a as shown in Figures 5 (c) and 7. The spiked release of this pressure (as the piston 26a begins to uncover the port 18a) against the immediately following piston 26b is what creates the hydraulic lock. Because the hydraulic fluid has nowhere to escape to it is trapped in the space 27 between the piston 26b and the port 18a. The pressurised fluid trapped within the space 27 presses down on the piston 26a via port 18a and it this hydraulic lock which then locks the cylinder 16 to the flywheel 24 and forces it to rotate with the flywheel 24. Because the angular positions of the pistons 26 are offset with respect to the ports 18, hydraulic lock can occur at any of the ports 18. With relatively low loads, such as in smaller motor vehicles, it may be desirable to provide a smoother transition to an hydraulic lock condition so as to minimise vibration. For this purpose a circumferentially extending bleed groove or metering groove may be provided (not illustrated) within the sealed fluid chamber. The metering groove is formed in the inner surface of the cylinder 16, and starts just after the previous port 18 and extends substantially the full distance between adjacent ports 18. The groove allows for a build-up of compression in a more controlled way to eliminate vibration.

Each piston 26 is received in its own piston sleeve 30, as can be seen most clearly in Figure 3. The piston sleeves 30 are received in radially extending bores provided in the flywheel 24 and secured with grub screws. The sleeves 30 are designed to limit the travel of the respective pistons 26 to their extended position. An annular lip 32 provided on the lower edge of the piston 26 engages with the lower edge of the corresponding piston sleeve 30 to limit the travel of the piston 26. The top surface of each piston 26 is precision- machined to match the angle of curvature of the inner surface of the cylinder 16.

The flywheel 24 is fixed to a stub axle 34 of the rotor assembly 20, which is rotatably supported in the cylindrical assembly by a plurality of bearings 36, 38 and 40. Hydraulic fluid for actuating the pistons 26 is pumped through a fluid circuit 42 extending through the stub axle 34, as can be seen most clearly in Figures 2 and 6. The hydraulic fluid in the fluid circuit 42 is pressurised by foot pressure, Tor example, applied to the accelerator pedal on a closed loop hydraulic line, to actuate the pistons 26. When the foot pressure is released the pistons 26 return to their retracted position by virtue of the preset pressure of the hydraulic fluid within the sealed fluid chamber 22. An additional fluid circuit 44 is provided within the stub axle 34 (see Figure 2) for circulating coolant through the rotor assembly 20, and removing heat generated during operation of the torque transmitting device 10.

Advantageously the device 10 also incorporates a braking device for retarding rotation of a rotating load, which operates on the same principle as the torque transmitting device. The braking device comprises a cylindrical assembly 12, which in this embodiment it shares with the torque transmitting device, and which is adapted to be mechanically coupled via its outer circumference to the rotating load. The cylinder 16 of the cylindrical assembly 12 is provided with a second plurality of ports 48 at angularly spaced intervals on its inner circumference. As with the ports 18, there are three ports 48 angularly spaced at uniform intervals of 120° on the inner circumference of the cylinder 16.

The braking device 10 further comprises a stator assembly 50 adapted to be mechanically coupled to a stationary structure and mounted within the cylindrical assembly 12 so as to form a sealed fluid chamber 52 between the stator assembly 50 and the inner circumference of the cylindrical assembly 12. Similar to the flywheel 24, the stator assembly 50 comprises a stator housing 54 with a plurality of radially mounted pistons 56 extending through its outer circumference into the fluid chamber 52 at angularly spaced intervals. The angular spacing between the pistons is offset relative to the spacing of the ports 48 in the cylinder 16. In this embodiment there are four pistons 56 angularly spaced at uniform intervals of 90° around the circumference of the stator housing 54.

A hydraulic fluid is provided in the fluid chamber 52 whereby, in use, upon activation of the pistons 56 an hydraulic lock is formed between the stator housing 54 and the cylindrical assembly 12 to retard rotation of the cylindrical assembly 12 relative to the stator assembly 50. The stator assembly is U2011/000043

11 rotatably mounted on the stub axle 34 by means of bearing 58, and also rotatably supported within the cylinder 16 of the cylindrical assembly 12 by bearing 60. The stator assembly 50 itself is secured to the vehicle differential housing or the suspension fulcrum on front and four wheel drives, to prevent rotation of the braking device (when the pistons 56 create an hydraulic lock against the cylinder assembly).

The brake pistons 56 are substantially identical to the flywheel pistons 26. The arrangement of the brake , pistons 56 in the stator housing 54 is substantially identical to that of the pistons 26 in the flywheel 24, and therefore will not be described again. The manner in which the hydraulic lock is formed between the stator housing 54 and the cylindrical assembly 12 is also substantially the same as described above, and will also not be described again here. A hydraulic circuit 62 is provided within the stator assembly 50 for supplying hydraulic fluid to actuate the pistons 48. The brake pistons 56 typically utilise actuation fluid from the existing vehicle brake system or a dedicated common brake master cylinder system.

A typical operating sequence of the constant velocity hub 10 will now be described. After the engine is started, the driver selects Drive or the highest gear of the vehicle. A manual throttle control on the vehicle steering wheel provides + or - control of the engine speed (rpm) via the vehicle's electronic Engine Management System (EMS). The stub axle 34, together with the drive flywheel 24, is now rotating at the same rpm as the engine. Advantageously the motor vehicle engine is operated at substantially constant velocity to reduce vehicle emissions and improve engine efficiency, and the constant velocity hub 10 is one of four hubs transmitting engine torque to all four of the respective vehicle wheels (in a four wheel drive vehicle).

Applying foot pressure to the vehicle accelerator pedal forces hydraulic fluid to actuate the drive pistons 26 which creates an hydraulic lock in the hub 10 and moves the vehicle's wheels. When foot pressure is released the drive pistons retract and the flywheel 24 will continue to spin but no torque is transmitted to the wheels. To assist the vehicle brakes, the hub brake pistons 56 can be actuated to lock the wheel to the stator assembly 50 when required. The EMS will monitor braking time and return engine RPM to idle when the brakes are applied for more than five seconds. Handbrake operation may also initiate the hub brake. If 2000 rpm engine speed corresponds to 80 km/hr, and the driver wishes to increase the vehicle speed or engine horsepower, the throttle control on the steering wheel is used to raise the rpm steadily. When reverse gear is required, the brake pistons 56 and drive pistons 26 are extended to stop the hub flywheel 24 from rotating and to facilitate the change in direction of the drive train. Releasing braking pressure will retract both sets of pistons. The hub 10 operates the same in forward and reverse. The result is smooth vehicle operations without engine speed fluctuations or raised rpm for gear changes. High load conditions or difficult 4X4 requirements may still require the driver to utilize the vehicle gearbox or transmission. Whilst in the illustrated embodiment the rotor assembly 20 of the torque transmitting device and stator assembly 50 of the braking device are both incorporated in a common cylindrical assembly 12, clearly the torque transmitting device and the braking device can also be built as independent units. Now that a preferred embodiment of the torque transmitting device and braking device have been described in detail, it will be apparent that they provides a number of advantages over the prior art, including the following:

(i) Device control is based on producing an hydraulic lock between the actuating pistons and the cylindrical assembly for both drive and braking. (ii) No external pressure or pump is required.

(iii) The existing drive train rotates the flywheel inside the cylindrical assembly.

(iv) The relationship between engine speed and rotation of the hub does not change. When the hydraulic lock is achieved the ratio is 1:1 with the drive motor. (v) Vehicle emissions can be kept to a minimum by maintaining the engine speed substantially constant.

(vi) Improved fuel economy can be achieved because the vehicle engine speed is kept substantially constant.

It will be readily apparent to persons skilled in the relevant arts that various modifications and improvements may be made to the foregoing embodiments, in addition to those already described, without departing from the basic inventive concepts of the present invention. For example, the number, shape and configuration of the pistons and ports can be varied from that shown in the illustrated embodiment; the only limitation is that the arrangement must be capable of forming an hydraulic lock. Therefore, it will be appreciated that the scope of the invention is not limited to the specific embodiments described and is to be determined from the appended claims.