GB2221964A - Automatic variable speed gear comprising planetary gearing and speed responsive coupling - Google Patents

Abstract

An automatic variable speed gear has rotatable input and output members (1, 2) interconnected by a low ratio planetary gear drive (3) and a parallel speed responsive coupling preferably a centrifugal clutch (5). When drive is initially applied through the input shaft (1) it is transmitted at a low ratio to the output shaft (2) through the planetary gear drive (3). As the speed of the output shaft (2) increases the speed responsive coupling transmits a slipping higher ratio drive to the output shaft (2) partially superseding that provided by the planetary gear drive (3). When the output shaft (2) reaches a predetermined speed responsive coupling provides a solid direct drive superseding the planetary gear drive. The speed responsive coupling may alternatively be a plate clutch, a cone clutch, a multi-disc clutch or an electromagnetic clutch. <IMAGE>

Description

Title: Automatic variable speed gear The present invention relates to automatic variable speed gears.

The object of this invention is to provide a simple and efficient automatic variable speed gear or gearbox which is also capable of providing gear ratio changes in an infinitely variable manner. The gear is primarily, but not exclusively, intended for road or other land vehicle use including rail traction.

Accordingly, the present invention provides an automatic variable speed gear comprising; a rotatable input member; a rotatable output member; a speed responsive coupling between said input End output members; and a low ratio planetary gear drive arranged in parallel with said speed responsive coupling and interconnecting said input and output members for transmitting drive therebetween; and wherein said speed responsive coupling is operable in response to said output member reaching a first rotary speed to transmit drive through said coupling from said input member to said output member, said drive at least partially superseding that provided by said planetary gear and is operable in response to said output member falling below a second, rotary speed to remove said drive through said coupling.

Preferably the first and second speeds are the same speed.

The present invention is further described hereinafter, by way of example, with reference to the accompanying drawing; which is a diagrammatic axial plane section of a speed gear according to the invention. Any speed ratios or other values quoted in the following description are given by way of example only.

The input drive shaft 1 drives the output driven shaft 2 by a basically low ratio planetary gear drive 3 shown consisting of a sun pinion 31 on the input shaft 1 meshing with planetary gear wheels 30 carried by respective axially parallel shafts 33 journalled in a housing 4 which serves as a carrier for the planetary gear drive 3 and is uni-directionally rotatable about the co-axial input and output shafts 1, 2 in a manner later described.

The shafts 33 further carry planetary gears or pinions 34 meshing with a sun gear wheel 32 on the output shaft 2. All gear wheels and pinions are rotationally fast with their respective shafts and duplicated, triplicated or other suitable equi-spaced arrangements of planetary gear wheels and pinions 30, 34 can be provided as appropriate for balanced operation.

Acting between the input and output shafts 1, 2 is a speed responsive coupling 5 shown in the form of a centrifugal clutch in which centrifugally acting clutch elements or shoes 50 carried at 53 by a back plate 52 fast on the output shaft 2 operate within a drum 51 carried by the input shaft 1 and fast therewith. Other suitable types of clutch or coupling activated by centrifugal force due to the speed of rotation of the output shaft 2 may be employed as later referred to.

When the output shaft 2 is subject to considerable load such as starting from rest in the case of vehicle application of the gear, the input shaft 1 imparts a basic low ratio drive (e.g. 4.2 : 1) to the output shaft 2 through the planetary gear drive 3. As the speed of rotation of the input and output shafts 1, 2 increases, particularly of the output shaft 2 on accelerating motion of the vehicle, the centrifugal action of the clutch shoes 50 brings them into frictional contact with the inner peripheral surface of the drum 51. This results initially in a slipping higher ratio direct drive partially superseding that provided by the planetary gear drive 3 which latter then adopts a corresponding planetary motion together with rotation of the gear box housing 4.

Upon the output shaft 2 reaching or exceeding a predetermined speed (typically 1000 rpm) the clutch 5 provides a substantially solid direct drive between the input and output shafts 1, 2 with rotation of the planetary gear drive and gear box housing in a unitary manner therewith, the planetary gear wheels 30 and pinions 34 then no longer rotating about their own axes.

When the output shaft slows down to the predetermined speed as the load on the output shaft increases e.g. on the vehicle ascending a hill, or on braking and/or on reduction of driving power input from the engine, the converse to the above described operation of the gear box occurs. Thus it will be appreciated that the variable gear drive provided is self adapting to such varying conditions of operation in an automatic and infinitely variable manner between the basic low ratio drive of the planetary gear system 3 and the direct drive of the centrifugal clutch 5.

Furthermore, and when operative, the planetary gear 3 provides a constant mesh drive whilst at all times the entire gear provides a positive drive between the input and output shafts 1, 2 either by the planetary gear 3 or by the clutch 5 or by a combination of both. Rotation of the housing 4 and particularly the aforesaid unitary rotation of the entire gear provides a flywheel action for smooth operation of the gear and of the transmission effected.

A further advantageous feature of the gear is that as the clutch shoes 50 engage the inner periphery of the drum 51, the latter is already rotating at greater speed so that a smooth engagement of the clutch is obtained with no inertia to overcome. In fact on the output shaft 2 rotating at or about 1000 rpm and where the basic low ratio drive of the planetary gear 3 is 4.2 : 1 the input shaft will be rotating at a speed of about 4000 rpm just prior to full engagement of the clutch so that adequate power input and torque from the engine can be developed for transmission by, or mainly by, the planetary gear 3.

On the other hand as the speed of rotation of both the input and output shafts 2, 3 reduces under solid drive conditions such speed can fall to about or below 1000 rpm before the clutch disengages. Thus the engine speed of the vehicle can be reduced to a comparatively low speed before the solid drive is disengaged whilst on disengagement relatively high engine rpm can be employed for effective acceleration through the planetary gear 3 back to solid drive conditions as the clutch 5 is activated.

These aspects of the gear are particularly advantageous when driving the vehicle under varying traffic conditions.

For the purpose of starting from rest or under other considerable load conditions provision is made for preventing back rotation of the housing 4 so that its rotation is uni-directional i.e. in the direction of operative rotation of the transmitted gear drive. Such provision may be effected by ratchet, free wheel or one way clutch mechanism (not shown) acting between the housing 4 and relatively fixed structure acting as a reaction member. Preferably a ball or roller type free wheel mechanism is employed for silent operation.

If desired a plate or multi-disc or cone clutch may be employed at 5 operated by a centrifugal weight mechanism driven by the output shaft 2, whilst if desired an electromagnetic clutch or an electro-magnetically operated clutch such as a multi-disc clutch may be used.

A centrifuqal governor or other suitable device driven by the output could be employed to control and/or activate the electro-magnetic means of the clutch.

Particularly where there is little or no physical contact between the clutch elements of an electro-magnetic clutch frictional contact and resulting wear would be avoided or reduced to a minimum. A simple manual override mechanism could be installed to override the governor which controls the electo-magnetic clutch.

Torque convertors and fluid or viscous couplings would function in a different and undesirable way as they would be affected by, if not controlled by, the speed of rotation of the input shaft. Therefore such clutches are unsuitable for the purpose of this invention.

The gear ratios of the meshing gear wheels and pinions of the planetary gear drive 3 can be selected to suit particular application of the gear.

For vehicle use an operable or automatic primary clutch or coupling would be provided acting between the engine or other prime mover and the input shaft 1 so that the engine can idle without driving the gear e.g., when the vehicle is stationery in traffic conditions.

Again especially for vehicle use a separate operable reverse gear would have to be provided and located in the transmission between the variable speed gear and final drive to the driven road or like wheels of the vehicle in view of the requirements for uni-directional rotation of the housing 4. The reverse gear could be contained within a fixed casing also accommodating the entire variable speed gear and serving as a reaction member for the uni-directional rotation of the housing 4 as well as providing a lubricant bath for the gear trains of the variable speed and reverse gears.

Together with the operating advantages already referred to above it is believed that, particularly in the form herein described, a variable speed gear according to this invention is capable of efficient operation especially when compared with known forms of torque convertor. As will also be apparent the gear can be of simple,compact and inexpensive construction which can be of robust and durable form to withstand hard usage. There are also few moving parts especially when the gear is operating in high ratio direct drive.

Although particularly suited for vehicle use, the gear is capable of a wide range of practical applications e.g. in various kinds of machinery.

Claims (15)

1. An automatic variable speed gear comprises a low ratio planetary gear drive between input and output rotary members and a centrifugal clutch or other suitable speed responsive coupling acting between said members and. activated by the speed of rotation of the output rotary member on the latter exceeding a predetermined speed of rotation, said clutch or coupling on engagement providing a higher ratio or direct drive between said members partially or fully superseding that provided by the planetary gear drive with corresponding planetary motion of the latter and vice versa dependent on the rotational speed of the output rotary member exceeding or falling below the predetermined speed in accordance with operating conditions of the gear.

2. An automatic variable speed gear comprising a rotatable input member; a rotatable output member; a suitable speed responsive coupling between said input and output members; and a low ratio planetary gear drive arranged in parallel with said speed responsive coupling and interconnecting said input and output members for transmitting drive therebetween; and wherein said speed responsive coupling is operable in response to said output member reaching a first rotary speed to transmit drive through said couplings from said input member to said ouput member, said drive at least partially superseding that provided by said planetary gear, and is operable in response to said ouput member falling below a second, rotary speed to remove said drive through said coupling.

3. An automatic variable speed gear as claimed in claim 2 wherein said first and second speeds are the same speed.

4. An automatic variable speed gear as claimed in claim 1, 2 or 3 wherein said drive is a higher ratio drive or a direct drive fully superseding that provided by said planetary gear.

5. An automatic variable speed gear as claimed in claim 1 or 2 or 3 or4 wherein said speed responsive coupling is operable to transmit drive through said coupling at a drive ratio variable, in dependence on the rotary speed of said ouput member, between a higher ratio drive and a direct drive.

6. An automatic variable speed gear as claimed in claim 5 wherein said drive ratio is variable from a higher drive ratio to a direct drive in response to the rotary speed of said output member increasing from said first predetermined speed to a third predetermined speed.

7. An automatic variable speed gear as claimed in claim 6 wherein said third predetermined speed is substantially 1000rpm.

8. An automatic variable speed gear as claimed in any preceding claim wherein said second predetermined speed is substantially 1000rpm.

9. An automatic variable speed gear as claimed in any preceding claim further comprising means for preventing rotation of said planetary gear in a direction opposite to that of the operative rotation of the transmitted gear drive.

10. An automatic variable speed gear as claimed in any preceding claim wherein said speed responsive coupling is a centrifugal clutch.

11. An automatic variable speed gear as claimed in claim 10 wherein said clutch is a plate clutch.

12. An automatic variable speed gear as claimed in claim 10 wherein said clutch is a multi-disc clutch.

13. An automatic variable speed gear as claimed in claim 10 wherein said clutch is a cone clutch.

14. An automatic variable speed gear as claimed in claim 10 wherein said clutch is an electromagnetic clutch.

15. An automatic variable speed gear substantially as hereinbefore described with reference to the accompanying drawings.