GB2187824A

GB2187824A - Fluid coupling transmission

Info

Publication number: GB2187824A
Application number: GB08606408A
Authority: GB
Inventors: Anthony George Shute
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-03-14
Filing date: 1986-03-14
Publication date: 1987-09-16
Anticipated expiration: 2006-03-14
Also published as: GB2187824B; GB8606408D0

Abstract

A fluid coupling (27) for a power transmission system of a front wheel drive vehicle provides, where necessary, a four wheel drive facility for the vehicle. The coupling (27) comprises an enclosed rotary fluid pump (27) having a chamber (28) permanently filled with fluid which is trapped in the chamber. An input shaft (16) from the vehicle power unit is connected to the housing (29) of the pump and the output shafts (18) to the rear wheels are connected to independent rotors (32) (33) in the pump. Rotational movement of the rotors relative to the housing results in a pressure build-up within the pump which can cause the rotors to lock-up relative to the housing if, for example, the front drive wheels slip and there is a substantial difference between the speeds of the front and rear wheels. <IMAGE>

Description

SPECIFICATION A fluid coupling This invention relates to fluid couplings and in particular to fluid couplings used in power transmission systems of four wheel drive vehicles, especially permanent front wheel drive vehicles with a four wheel drive facility.

A problem associated with front wheel drive vehicles of the above type is the cost associated with drive couplings between the permanent drive axle and the other axle of the vehicle.

This invention seeks to provide a low cost and/or low weight fluid coupling differential that will allow relative rotational movement between each wheel in the different axle, and between the permanent drive axle and the other axle of the vehicle, as well as providing a facility for locking-up the drive between the two axles.

Accordingly there is provided a fluid coupling for transmitting rotational drive from an input shaft to an output shaft, and in which the coupling comprises an enclosed rotary fluid pump having fluid trapped therein, the input shaft being connected to a first member of the pump and an output shaft connected to a second member of the pump so that relative rotational movement betwen the first and second members of the pump resuits in a fluid pressure build up within the pump which can prevent rotational movement between said members. The term 'fluid pump' is equally meant to embrace 'fluid motor', and fluid dampers.

A fluid coupling of the above type can be advantageously incorporated into a power transmission system for a vehicle, particularly a front wheel drive automobile with a transverse engine layout.

The pump utilised in the fluid coupling is preferably a sliding-vane, or roller vane type in which a bore in a cylindrical housing is eccentrically off-set relative to a rotor. However other types of pumps such as gear pumps or turbine type pumps could possibly be utilised.

The invention will be described with reference to the accompanying drawings in which: Figure 1 is a power transmission system for a front wheel drive automobile with a transverse engine layout.

Figure 2 is a section through a fluid coupled as used in the power transmission system illustrated in Fig. 1.

Figure 3 is a section through the fluid coupling of Fig. 2, and Figure 4 is a section on the line 4-4 of Fig.

3.

In Fig. 1 there is illustrated a motor vehicle power transmission system, particularly but not necessarily for a front wheel drive automobile and which can provide for a four wheel drive facility for the vehicle when necessary.

The vehicle power unit 11, is preferably a transverse engine which is connected via a gearbox/differential unit 12 to a pair of drive shafts 13 which connect with the primary drive wheels of the vehicle, in this case the two front wheels. The gearbox/differential 12 is also permanently connected with a transmission shaft 14 which connects the power unit 11 with the rear wheels (not shown). The transmission shaft 14 is any typical modern transmission shaft and can comprise two parts 14A and 14B connected through a Hooke's joint 15 (universal joint).

The transmission shaft 14 is driven simultaneously with the drive shafts 13 to the front wheels and is connected with the input shaft 16 of a fluid coupling 17 which has a pair of output shafts 18 which are connected via drive shafts 19 to the rear wheels (not shown) of the vehicle.

With reference now to Fig. 2, the input shaft 16 of the fluid coupling 1 7 is mounted in a pair of bearings 21 and 22 located in a differential casing 23 such that the shaft 16 is aligned longitudinally of the vehicle and can rotate freely within the casing 23. A bevel/hypoid gear 24 on the end of the input shaft 16 meshes with a circular gear 25 arranged so that it's axis of rotation is transverse of the vehicle.

The circular gear 25 is mounted externally on the fluid coupling 17 which is also located within the casing 23. The fluid coupling 17 has a pair of output shafts 18 which are connected via the drive flange 26 to the drive shaft 19 of the rear wheels. The fluid coupling 1 7 comprises an enclosed rotary fluid pump 27 having fluid restrained therein i.e. the fluid cannot enter or escape from a cylindrical chamber 28 within the pump but may have controlled leakage or valving therein which can be so arranegd to provide a free wheel facility. A suitable fluid for use within the pump is a typical ATF (Automobile Transmission Fluid) a hydraulic fluid of the type utilised in vehicle braking systems, or a high viscosity silicone fluid.

The rotary pump 27 comprises a housing 29 having the cylindrical chamber eccentrically off-set therein and which is rotatably mounted within the casing 23 on a pair of bearing 31 for rotation coaxially with the transverse axis of the circular gear 25. A pair of rotors 32 and 33, rotate coaxially with said transverse axis, and each has four sliding vanes 34 therein which are swept by the bore of the chamber as it turns around the rotors with the housing 29. The two rotors 32 and 33 are independent of each other and are separated by a plate 36. In the present fluid pump 27 each rotor 32 or 33 is mounted on a respective one of the output shafts 1 8 which are sealingly rotatable within the pump housing 29 and which extend coaxially and outwardly of the housing.The chamber 28 is arranged axi ally off-set within the housing 29, with the output shafts 18, housing 27 and circular gear 25 all being coaxial.

The gear ratios of the bevel gear 24 on the input shaft and the circular gear on the housing 27 are arranged such that the housing 27 normally rotates at the same rotational speed as the shafts 18 to the rear wheels.

In operation the fluid coupling functions in the following manner: (i) When a front wheel drive vehicle is driving along a route under normal driving conditions the rotors 32 and 33 are driven via the shafts to rotate at the rotational speed of the rear wheels, and the housing 29 is also driven by the input shaft 16 to rotate at the same speed so that there is substantially no rotative movement between the rotors 32 and 33 and the housing 29.

(ii) If the vehicle turns a corner so that one rear wheel rotates at a different speed as the other rear wheel then the rotors 32 and 33 rotate at different speeds. This will result in at least one of the rotors 32 and 33 rotating relative to the housing 29 thereby causing the vanes 24 to sweep the chamber 28. Leakage of fluid past the vanes will allow limited relative rotational movement without any substantial loads being put onto the housing or the pump rotor so that the fluid coupling act as a differential and allows for different rotation speeds between each rear wheel.

(iii) When the rotational speed between the wheels on the front axle and the wheels on the rear axle varies slightly as in the case of when there is a slight difference in the rolling circumference between the front and rear tyres, the fluid leakage past the vanes in the fluid coupling will allow for relative rotational movement between the rotors 32 and 33 on the one hand and the housing 29 on the other hand. Thus the fluid coupling 27 prevents wind up of the transmission shaft 14 between the front wheel drive and the rear wheel drive.

(iv) In the event of a substantial difference in rotational speed between the front wheels of the vehicle and the rear wheels of the vehicle, for example, during front wheel slip when either or both front wheels would be rotating faster than the rear wheels, the rotors 32 or 33 would be relatively rotating within the housing 29. This will cause a pressure build up within the fluid in the pump because not all the fluid displaced by the vanes can leak past the vanes 34. The build of pressure within the housing will therefore gradually slow down movement between the rotors 32 and 33 and the housing 29 and may even lock-up the rotor relative to the housing. Thus the fluid coupling 28 can act as a limited slip differential and eventually lock-up for full four wheel drive to the rear wheels.

The vehicle power transmission system as described has several advantages over present four wheel drive systems which utilise expensive fluid couplings. It provides a low cost system that eliminates the centre differential used on many four wheel drive systems and retains front wheel drive dominance on a front wheel drive car. It is envisaged that the system can also be applied to rear wheel drive rear engined vehicles and multi axle drive systems.

Claims

1. A fluid coupling for transmitting rotational drive from an input shaft to an output shaft and in which the coupling comprises an enclosed rotary fluid pump having fluid trapped therein, the input shaft being connected to a first member of the pump and the output shaft being connected to a second member of the pump so that relative rotational movement between the first and second members of the pump results in a fluid pressure build up within the pump which can prevent rotational movement between said members.

2. A fluid coupling as claimed in Claim 1, wherein the input shaft is connected with the housing of the pump, and the output shaft is connected with a rotary body within the housing.

3. A fluid coupling as claimed in Claim 2, wherein the pump is of the type having a sliding or roller vane rotor arranged within an eccentric bore off-set relative to the housing and the output shaft is coaxial to the rotor and connected thereto.

4. A fluid coupling as claimed in Claim 2 or Claim 3, wherein there are two output shafts each of which is connected with a respective rotary body within the housing, the two rotary bodies being rotatable relative to each other.

5. A power transmission system for a motor vehicle and including a fluid coupling as claimed in Claim 4 wherein the input shaft is connected to the vehicle power unit, and the two output shafts extend oppositely and connect to the wheels on an axle not being the primary driving axle of the vehicle.

6. A power transmission system as claimed in Claim 5 wherein the fluid coupling is housed in a casing, the pump housing being rotatably mounted within the casing for rotation about an axis transverse of the vehicle.

The input shaft is mounted in the casing longitudinally of the vehicle and connects with gears arranged externally of the housing, and the output shafts are arranged coaxially with said transverse axis.

7. A motor vehicle having a power transmission unit as claimed in Claim 5 or Claim 6.

8. A motor vehicle as claimed in Claim 7 wherein the vehicle is a front wheel drive vehicle and in which the power transmission system is located in the transmission system between the power unit and a rear axle of the vehicle.

9. A fluid coupling substantially as described herein and with reference to Fig. 2 of the accompanying drawing.

10. A motor vehicle power transmission system substantially as described herein and with reference to Fig. 1 of the accompanying drawings.