GB2100384A - Rotary transmission - Google Patents

Abstract

A motor vehicle engine (11), drive clutch (12) and manual change transmission (13) combination has automatic change speed means including a controller (20) and means (16, 19) responsive to the controller to both change the state of engagement of the drive clutch (12) and select a required transmission speed ratio, an engine brake (17, 18) responsive also to the controller (20) is provided to brake the engine during a speed ratio change to substantially synchronise engine speed with transmission input shaft speed. <IMAGE>

Description

SPECIFICATION Rotary transmission This invention relates to automatically controlled rotary transmissions particularly, though not exclusively, suitable for motor vehicles.

In motor vehicles such transmissions have hitherto been fundamentally different from the manual transmission counterparts both in design and operation. To satisfy public demand and maximise sales vehicle manufacturers are anxious to offer both manual and fully automatic versions of a particular model. Automatic transmissions are almost universally more bulky than the manual transmissions they are intended to replace and this imposes severe constraints on the initial vehicle design parameters. Indeed, it has proved increasingly difficult to provide fully automatic transmissions for the transverse-engined frontwheel-drive vehicles which are becoming more prevalent.

Automatic transmissions are less fuel efficient than the equivalent manual transmission because, for example, they incorporate torque converters for drive take-up from rest. They frequently have a lower number of speed ratios which affects not only their comparative fuel economy, but also the comparative vehicle performance.

Automatic transmissions are in general less well understood than manual transmissions and thus can pose service and reliability problems.

Furthermore, the manufacturers spares inventory is increased.

An automatic transmission option is usually an expensive extra and thus can add a considerable percentage to the cost of small vehicles.

Our Patent Application No. 80 37290 (Publication No. 2 064 028) proposes an automatic transmission which offers an improvement in most respects over conventional automatic transmissions, it is relatively cheap, fuel efficient and has substantial parts commonality with an equivalent manual transmission. It has the disadvantage that the transmission design must be slightly changed to suit the principle of operation.

A fully automatically controlled transmission which uses the same clutch and gearbox as an equivalent manual transmission would be an acceptable solution to the above-mentioned problems but although such control has been proposed it has never been wholly successful due to the problems of clutch engagement whiist retaining full driver command of the vehicle engine.

Examination of the problem of clutch control has shown that the clutch is required to perform two functions on engagement, firstly initial engagement to synchronise engine speed and transmission input speed and secondly final engagement to transmit drive. In a manually controlled transmission the experienced vehicle driver judges the rate of clutch engagement to achieve a perfect ratio change under all conditions of speed and load but this has proved extremely difficult with fully automatic control.

Solutions have been proposed which isolate the vehicle driver from the engine throttle during a ratio change so easing the conditions for clutch engagement. These have not proved acceptable because the period of isolation, although very short, has proved too long for the driver who requires instant throttle response.

The present invention seeks to provide a fully automatically controlled transmission using an equivalent manual control gearbox and drive clutch and which overcomes the afore-mentioned problems by providing means other than the drive clutch to substantially synchronise engine and transmission input shaft speeds during a ratio change.

According to the invention there is provided a motor vehicle engine, drive clutch and manual change transmission combination having automatic change speed means including a controller and means responsive to the controller to both change the state of engagement of the drive clutch and select a required transmission speed ratio, characterised thereby that further means also responsive to the controller are provided to brake the engine during a speed ratio change to substantially synchronise engine speed with transmission input shaft speed.

Preferably said further means comprise a friction brake which may act directly on the engine crankshaft.

Other features of the invention are included in the following description of two preferred embodiments shown, by way of example only, in the accompanying drawings in which: Fig. 1 is a schematic illustration of an engine, clutch and gearbox combination according to the invention; Fig. 2 is a schematic axial section through a conventional manual gearbox suitable for a front wheel drive vehicle; and Fig. 3 shows the transmission of Fig. 2 as modified in accordance with the present invention.

With reference to Fig. 1 there is shown a motor vehicle engine 1 1, belihousing 12 containing a conventional drive clutch (not shown) gearbox 1 3 and output shaft 1 4. A clutch release arm 1 5 is actuated by a hydraulic cylinder 16.

The nose of the engine crankshaft carries a brake disc 17, a co-operating brake caliper 18 being mounted on the engine 11. The caliper reaction loads could alternatively be transmitted direct to the vehicle frame by some suitable means which allowed relative engine/frame movement.

Movement of the gearbox manual gear lever (shown in dotted outline) is controlled by a selector mechanism 1 9 having actuators which guide the gear lever to select the desired speed ratio. The gear lever need however only be long enough to be engagable by the mechanism 1 9 which can be mounted on top of the gearbox.

Selector mechanisms of this kind have been previously proposed for manual controlled gearboxes.

A transmission controller 20, which may include a microprocessor and memory, is provided to control the clutch cylinder 16, brake caliper 1 8 and selector mechanism 1 9 to effect speed ratio changes in the manner described hereafter.

The controller 20 is provided with input signals for parameters such as engine speed, throttle opening and road speed in order that it can determine when a ratio change is to be effected.

All change speed automatic transmissions incorporate such controllers which are well understood in the automatic transmission art.

It is intended that the transmission be drive controlled by the use of a conventional automatic transmission selector lever having the usual DRIVE, NEUTRAL and REVERSE positions.

Operation of the transmision is as follows:- With the vehicle engine running the driver shifts the selector lever to DRIVE and the controller 20 causes the selector mechanism to almost simultaneously engage first speed ratio.

Depression of the vehicle accelerator pedal causes the controller 20 to effect progressive engagement of the drive clutch until the vehicle is rolling and the clutch fully engaged. The rate of clutch engagement will be dependent for example on throttle position, vehicle load etc. One suitable clutch engagement system is described in our copending patent application No. 81.03582 but other systems may be equally applicable.

As vehicle road speed increases, the controller 20 will cause a speed ratio upchange to take place which includes the necessary steps of automatically disengaging the drive clutch, selecting the next required speed ratio and reengaging the drive clutch.

During a speed ratio upchange engine speed must fall to match the newly selected transmission input speed. In a conventional transmission the drive clutch synchronises engine and transmission input speed at initial engagement. In the present transmission the brake 17, 18 is engaged, whilst the next required speed ratio is being selected, to bring the engine to approximately synchronous speed with the transmission. Thus the conditions for clutch reengagement are greatly simplified very fast and smooth clutch engagement being possible since the engine flywheel and clutch driven plate are pre-synchronised.

An additional input to the controller 20 of engine speed is required, devices to give such an input are commercially available eg. use of a magnetic pick-up and toothed wheel (engine starter ring).

It is anticipated that the technique of using a brake to synchronise clutch engagement can result in smooth and accurate ratio changes within a time of 0.5-1.0 seconds or better.

For speed ratio downchanges the engine speed must rise to match the newly selected transmission input speed. Where the throttle is applied during downchanges the controller 20 will allow engine speed to rise to synchronous speed and then momentarily engage the engine brake to hold engine speed for clutch re-engagement.

Throttle off downchanges will require the clutch to synchronise engine and gearbox speed.

However, since the transmitted torque between engine and gearbox is very low and rapid change speed not of the essence such synchronisation is well within the capacity of the clutch.

A subsidiary advantage of the use of an engine brake is that clutch driven plate life may be prolonged since the energy input into the driven plate during the worst ratio change, ie. a full throttle upchange, is reduced. This is because the brake dissipates the energy that would otherwise be absorbed by the clutch in reducing engine speed to synchronous speed.

Although the engine brake has been described as a disc brake mounted on the crankshaft nose other configurations are possible, for example, where the crankshaft nose bearing is not suitable a wet plate brake at the rear of the crankshaft may be acceptable.

With reference to Figs. 2 and 3 there is shown an output shaft 21 from a vehicle engine (not shown) for connection through a drive clutch 22 to the input shaft 23 of a vehicle gearbox 24.

First, second, third and fourth speed drive gear wheels, respectively 25, 26, 27, 28 are in mesh with respective driven gear wheels 32, 33, 34, 35 journalled for individual rotation on an output shaft 31.

The driven gear wheels are connectable to the output shaft 31 by synchroniser assemblies 36, 37, shiftable in response to movement of a transmission gear lever. The output shaft 31 is for connection to a differential gear for the vehicle drive wheels.

Such a transmission and its method of operation is well known.

The modification to the transmission according to the invention is to continue the engine output shaft 11 through the gear cluster 25, 26, 27, 28 to a brake 29 mounted at the other side of the transmission.

In this way the engine/clutch/gearbox unit installation requirement is substantially unchanged, the size of the continuation shaft 21 a being determined by the duty required of the brake. No changes to the vehicle engine are required, as might for example where the engine brake is mounted on the crankshaft nose.

The engine/clutch/gearbox unit can remain in its originally installed position, no substantial changes to engine mountings, length of drive shafts, etc. being required. This feature is of special importance for small engine, front wheel drive cars where installation space is at a premium.

A further advantage of the invention is that it is relatively straightforward to convert a vehicle for which both transmissions are available from manual to fully automatic mode according to demand.

Claims (4)

1. A motor vehicle engine, drive clutch and manual change transmission combination having automatic change speed means including a controller and means responsive to the controller to both change the state of engagement of the drive clutch and select a required transmission speed ratio characterised thereby that further means also responsive to the controller are provided to brake the engine during a speed ratio change to substantially synchronise engine speed with transmission input shaft speed.

2. A transmission combination according to Claim 1, characterised thereby that said further means comprise a friction brake.

3. A transmission combination according to Claim 2, characterised thereby that said manualchange transmission includes an input shaft and an output shaft with gear trains therebetween, said engine brake being located at the other side of the transmission to said drive clutch and driven by an auxiliary shaft through the input shaft.

4. A motor vehicle engine, drive clutch and manual change transmission combination substantially as described herein with reference to Fig. 1 or Fig. 3 of the accompanying drawings.