GB2291147A - Vehicle drive transmission has overdrive epicyclic gear set integrated with fl uid coupling - Google Patents

Abstract

A motor vehicle drive transmission system comprises a fluid coupling (59) having an impeller driven by a power input shaft and a turbine driving the power output shaft, and an epicyclic gear set (51 - 57) in which the planet gear carrier (52) is driven by the power input shaft (53), the annulus gear (57) is connected to the turbine and the sun gear (51) carries a disc (48) which can be locked against rotation by braking means (43) engageable thereon whereby when the disc and sun gear are released to rotate, the transmission provides a continuously variable drive ratio over a predetermined range, and when the disc and sun gear are locked, the transmission provides a fixed overdrive ratio. The braking means (43) is preferably a calliper brake operated by an electric motor via a lever and linkage system. The motor is preferably controlled so as to disable the overdrive below a predetermined vehicle speed. <IMAGE>

Description

MOTOR VEHICLE DRIVE TRANSMISSION SYSTEM Field of the Invention This invention relates to a motor vehicle drive transmission system.

Background to the Invention My earlier application published under number 2 249 812 discloses and claims a torque multiplier device which can form part of a motor vehicle drive transmission system to provide continuously variable gearing. In the device, an input drive shaft drives the sun gear of an epicyclic gear set while an output drive shaft is driven by the annulus gear of the gear set. A fluid coupling has a turbine driving the annulus gear and an impeller driven by the planet gear carrier of the epicyclic gear set.

An objective of the present invention is to enhance the performance of the universal ratio transmission system by the addition of a mechanical overdrive mechanism to avoid the inherent power loss in the fluid coupling, whose otherwise necessary features are not appropriate to high speed cruising, and also to effect substantial savings in fuel consumption and engine wear in conditions of moderate torque requirements, for example at speeds above 40 mph, or approximately 2200 engine rpm. In such conditions the overdrive could be arranged to engage automatically if the overdrive selector switch were in the on position.

A solid mechanical drive within the speed range of start to cruise is not feasible nor is it desirable with the universal ratio transmission system of the type which is the subject of my earlier application. This relies on the fluid coupling to effect its main feature of a universally adjusting ratio between the input and output elements when acceleration is partly achieved by gradual reduction of the torque requirements without higher revving of the engine. An exception is when conditions are such that rapid acceleration is essential, in which instance the driver is free to apply unlimited power to the engine and then engage the overdrive at a much greater speed.

Summarv of the Invention According to the invention, a motor vehicle drive transmission system comprises a fluid coupling having an impeller driven by a power input shaft and a turbine driving the power output shaft, and an epicyclic gear set in which the planet gear carrier is driven by the power input shaft, the annulus gear is connected to the turbine and the sun gear carries a disk which can be locked against rotation by breaking means engageable thereon, whereby when the disk and sun gear are released to rotate, the transmission provides a continuously variable drive ratio over a predetermined range, and when the disk and sun gear are locked, the transmission provides a fixed overdrive ratio.

Preferably, a caliper brake system is provided to stop rotation of the disk and sun gear to engage overdrive. The caliper brake system is preferably operated by a lever and linkage system which is arranged to provide a large mechanical advantage to an electric motor which rotates in one direction to engage overdrive and in the other direction to disengage the overdrive. The motor may be operated by means of an on/off switch mounted conveniently on the gear lever. Electrical controls may be provided to enable instant forward or reverse drive of the motor from the switch without the need for completion of the engage or disengage sequence. The electrical controls may incorporate an inhibitor which disables the overdrive when the vehicle slows, stops or is reversed with the switch left in the on position.The inhibitor switch is preferably designed to be sensitive to the rate of rotation of the output shaft, the critical speed typically being in the region of 1800 to 2200 rpm according to the vehicle drive train specification. The overdrive may be readily disengaged by the control switch, for example for rapid acceleration.

The overdrive ratio is achieved by the basic principle of stopping the sun gear of an epicyclic arrangement and driving the annulus gear at above engine speed from the planet gears whose carrier cage is driven at engine speed. A caliper brake arrangement, applied to a large diameter disc, may be used to hold the sun gear stationary.

The brake is suitably applied by an electric motor using a worm drive on its main axis to rotate a large gear wheel having a crank lever splined to its axis. By virtue of a worm and gear drive method, the crank lever is inert when in either the on or off position. The electrical circuit in the motor and the command circuits are designed to enable the motor to rotate in either direction, i.e. clockwise to engage overdrive and anti-clockwise to disengage overdrive.

Alternatively, the overdrive could be operated by a hydraulic system using either a caliper brake mechanism as described in this specification, or a band-brake using electronic controls.

It is believed that the device of the invention would offer increased fuel economy for a motor vehicle, particularly for motorway cruising and the like, by avoiding slippage in the fluid coupling which is estimated to cause losses of up to 6%. Engine braking is provided during deceleration from speeds above, say, 40 mph, and below this speed the inhibitor switch in the electrical controls will cancel the overdrive to allow the vehicle brakes to be applied. Acceleration at speeds above 40 mph will be improved, since the inherent slippage in the fluid coupling will be overcome by virtue of the drive from the engine to drive axle being mechanically solid with overdrive engaged.At speeds below 40 mph, the fluid coupling provides, in conjunction with the epicyclic gear set, a universally changing ratio between the engine and the driven axle from approximately 4:1 at the start of drive up to 1:1 at operating speeds, for example.

The transmission system is ideally suited to city driving and will greatly relieve driving stresses by requiring only two-pedal operation, without the need to disengage forward drive when the vehicle is stopped. With the engine running at idling speed, the handbrake can be applied.

Brief Description of the Drawings In the drawings, which illustrate a preferred embodiment ofthe invention: Figure 1 shows a sectional view of the brake mechanism and the overdrive gear Set mounted ahead of the fluid coupling; Figures 2a to 2c are respectively side, front and top plan views of the brake mechanism; Figure 3 is a side view showing the brake operating level connected by rod and compression spring to the electric motor; Figures 4a to 4c are respectively side, front and top plan views of the electric motor for the brake mechanism; and Figure 5 is a diagrammatic layout of the overdrive electric circuits, and sectional views of switches.

Detailed Description of the Illustrated Embodiment In the motor vehicle transmission system of the invention, as illustrated in the drawings, a main power input shaft 53 drives the planet carrier cage 52 of the epicyclic gear set through a spline 54. The central boss 55 ofthe planet carrier cage 52 rotates within and provides the bearing for the sun gear 51 of the epicyclic set, the planet gears 56 driving the annulus gear 57, which is connected by cogs 58 to the turbine casing 59 of the fluid coupling. A brake disc 48 is secured to the sun gear 51 and is held stationary by a caliper brake unit 43 which is mounted within an aluminium or iron casting secured to the main transmission casing by means of screws 13 through holes 44.

The brake is applied by an external lever 2 (Figure 3) splined to a crank spindle 3 and secured with a nut 1. Brake levers 4 are connected to the spindle 3 via links 45 and pivots 49 such that, when the spindle 3 is rotated anti-clockwise, the levers 4 are pulled inwardly together. The brake shoes 46 are secured to the levers 4 by trunnion pins 47 which enable parallel alignment of the shoes with the brake disc 48, and the inward pull on the levers 4 urges the shoes against the disc 48 to brake the disc.

The brake lever 2 is operated by a rod 5 via a collet 7, nut 8 and compression spring 6. The other end of the rod 5 is secured by a connecting pin 15 to a crank lever 14 on an electric motor 11. To pennit articulation over its length of travel, the brake lever 2 is designed to locate on a hemispherical seating 9, which is adjusted in position by a stiff nut 10. The rod 5 is threaded over part of its length to accommodate manufacturing and installation tolerances and to enable correct set-up of the on/off switch illustrated in Figures 4a to 4c.

As may be seen from Figures 4a and 4c, the electric motor 11 has a two-way limit switch 16 mounted thereon via a swivel mounting 17. The switch 16 is operated by a plunger rod 18 connected to the crank lever 14 by a pin 19 operating in a slot 20.

The limit switch 16 has electrical connectors (Fig 4c) which are designed to enable the power to the motor 11 to be cut at the end of the on/off sequence and simultaneously to reset the motor circuit to the opposing direction of rotation.

Figure 4b shows the motor and the brake lever in end elevation, with the limit switch 16 omitted. As may be seen from Figure 4c, the motor 11 is conveniently mounted on the side ofthe transmission casing by a bracket 21 and screws 22.

Figure 5 shows diagrammatically a typical installation of the electrical circuit required to operate the overdrive caliper brake. The driver-operated switch 23 is situated within the gear lever knob. The illustration shows the switch in the off position, which caused the motor 11 to turn anti-clockwise and thus release the overdrive brake mechanism.

The signal from the driver switch 23 passes through the limit switch 16 and simultaneously to the circuit selector switch 24 which alters the contacts 25 for close-wise or anti-clockwise rotation of the motor 11. Switch 24 also cuts the power to its solenoid 26 by alternating the position of the contacts 27.

The solenoid plunger 28 is mounted on a shaft 29 which pushes or pulls a spring toggle arrangement 30 to a position approximately 3 degrees over the neutral load centre before the contacts 27 are disconnected. In doing so, the centre pin of toggle 30 travels within a slot 31 and makes contact with shaft a 32 which carries the contacts 25 and 27, which are held against the terminals by means of the spring loading in a second toggle arrangement 33, the position of which is alternated by the action of the first toggle arrangement 30 in completing its stroke after the solenoid plunger 28 has moved it past the neutral load centre. The first toggle arrangement 30 is designed to have sufficient travel and also greater spring loading by which to overcome and re-set the position ofthe second toggle arrangement 33.

A similar two stage over-centre spring toggle arrangement 34 is employed to control the operation of the two-way limit switch 16 to select the on or off setting of the contact 35 in the limit switch 16 and so complete the circuit to the motor 11, and at the same time, changing the position of the contacts 27 to cut off its own power. The power to the motor 11 is picked up by a plug 39 which connects to the limit switch 16 and is regulated by a plug 40 which connects to the selector switch 24. A plug 41 which also connects to the switch 24 supplies power to the armature brushes, and alternating current flow to the field windings to enable forward and reverse rotation of the motor. Plug 42 also connects to the selector switch 24 and enables two way travel of the solenoid plunger 28.

The electric motor is mounted on the side of the gear box as determined by packaging convenience, and its crank lever is connected to the brake lever by a rod which applies a loading to the brake lever through a coil spring which is compressed by a specific amount prior to the motor power being cut off by its limit switch.

The brake rod is designed to facilitate setting-up adjustment, and also to apply a specific pre-load to the compression spring to ensure that the correct load is applied to the brake for efficient operation of the overdrive.

Principles of operation The overdrive brake unit is designed as a complete sub-assembly and is fitted through an aperture in the transmission housing, and is operated by an externally mounted lever which is connected by a rod and spring arrangement to the crank lever on the electric motor as previously described.

The brake shoes are lined with appropriate material for effective use in transmission lubrication, and the linkage is designed to provide a small electric motor with sufficient mechanical advantage so that adequate braking effort can be applied.

In accordance with this requirement, the pull on the brake lever is applied through a coil spring 6 (Fig 3) which is adjusted to a predetermined loading in accordance with the setting of the circuit cut-off sequence of the clockwise rotation ofthe electric motor, and will provide a static loading of approximately 10 kg on the brake lever, which is equivalent to 50 kg at the brake pads.

The brake release sequence is effected by anti-clockwise rotation of the electric motor, by which action the load in the coil spring 6 will be relaxed, and there will also be an allowance of free travel included in the initial setting to allow the brake pads to clear the brake disc prior to the power being cut off by limit switch 16.

The electric motor 11 has a worm and gear drive mechanism providing a ratio in the region of 10 to 1, so that the drive is inert when the power is shut off by the limit switch 16, and the crank lever 14 on the motor can maintain the required static pull on the brake lever 2.

The epicyclic gear arrangement is mounted forward of the E3 fluid coupling as shown in Figure 1, and according to the chosen gear sizes will provide overdrive in the range 27 to 36 per cent. This particular arrangement provides a mechanical connection within the drive train from engine to drive axle and avoids the power loss of the fluid coupling during conditions of high speed cruising, and also for best economy for low torque motoring at speeds in the region of 45 to 50 mph when the over-drive switch may stay in the on position.

The overdrive feature is completely controllable by the driver from the switch on the gear lever, but included in the electrical circuit there is a relay switch 36 (Figure 5) which is activated by a signal from a transducer connected to the speedometer pick-up point. The fUnction of the relay switch is to disable the overdrive in conditions when the functions of the fluid coupling are essential for slowing, stopping and reversing, in which circumstances it will over-ride the command switch if this should be left in the on position.

When the overdrive is switched off at the command switch this also cuts the power to the transducer circuit to avoid the relay switch continuously reacting to changing operating speeds which could adversely affect the durability of its coil windings.

Claims (9)

1. A motor vehicle drive transmission system, comprising a fluid coupling having an impeller driven by a power input shaft and a turbine driving the power output shaft, and an epicyclic gear set in which the planet gear carrier is driven by the power input shaft, the annulus gear is connected to the turbine and the sun gear carries a disc which can be locked against rotation by braking means engageable thereon, whereby when the disc and sun gear are released to rotate, the transmission provides a continuously variable drive ratio over a predetermined range, and when the disc and sun gear are locked, the transmission provides a fixed overdrive ratio.

2 A transmission system according to Claim 1, wherein a calliper brake system is provided to stop rotation of the disc and sun gear to engage overdrive.

3. A transmission system according to Claim 2, wherein the calliper brake system is operated by an electric motor via a lever and linkage system.

4. A transmission system according to Claim 3, wherein the electric motor has a worm gear in driving engagement with a gear wheel driving a crank lever operating the calliper brake via a control rod.

5. A transmission system according to Claim 3 or 4, wherein the motor is controlled by electrical controls incorporating inhibitor means arranged to disable the overdrive below a pre-determined vehicle speed.

6. A transmission system according to Claim 2, wherein the calliper brake system is operated by hydraulic means.

7. A transmission system according to Claim 1. wherein a band-brake is provided to stop rotation of the disc and sun gear to engage overdrive.

8. A motor vehicle drive transmission system, substantially as described with reference to, or as shown in, the drawings.

9. A motor vehicle incorporating a drive transmission system according to any preceding claim.