GB2383101A

GB2383101A - Regenerative braking device with uni-directional clutches

Info

Publication number: GB2383101A
Application number: GB0130028A
Authority: GB
Inventors: Roger David Harrison
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-12-15
Filing date: 2001-12-15
Publication date: 2003-06-18
Also published as: GB0130028D0

Abstract

A regenerative braking device comprises epicyclic or differential gearing and two uni-directional clutches 1, 3 which transmits power from an input shaft 2, driven by an electric motor, to an output shaft 4 that is fixed to a ring gear 5. The uni-directional clutch 1 has an outer portion which drives shaft 2 while uni-directional clutch 3 has an inner portion that drives output shaft 4. Thus when brake 7 is applied to planetary carrier 8 the direction of the output shaft 4 is reversed so that clutch 3 overruns and the output shaft 4 drives the ring gear 5 which rotates planet gears 6, around shafts 10, which drives sun gear 11 in the opposite direction, thereby causing the clutch 1 to engage a pulley and drive the motor backwards in an opposite direction then when it was driving a load. Energy being transmitted back through the input shaft 2 may be harnessed to drive a generator or compressor etc. the proportion of a maximum braking torque may be controlled electronically by pulse width modulation or similar methods.

Description

Description Brake Operated Clutch for Regenerative Braking.

Motors driving loads are often used as brakes to retard that load, but the kinetic energy that exists is often wasted. Regenerative braking enables this energy to be saved. This is achieved by converting the energy into a form that can be used later by the motor, e. g. electricity or compressed air.

The relationship between a motor and a load can be considered in three modes: 1. Driving; Motor is driving the load.

2. Coasting; No power is transmitted from the motor to the load or visa versa.

3. Braking; When the load is being retarded by the motor.

A direct connection can achieve all three but energy is wasted in coast mode, as the motor requires energy to drive itself.

The problem facing designers of regenerative braking systems in the past has been the smooth introduction of the braking effect. A clutch mechanism has often been used to disconnect the motor for coasting but engagement and disengagement have to be controlled. The characteristics of both engaging and disengaging are similar and may not ideally match those required by the take up of drive and release of the motor for coasting.

This invention enables driving of the load by the motor, coasting with the motor stationary and an easily controlled application of regenerative braking.

Notes for the drawings: Fig 1 and 3 show the mechanisms assembled, fig 2 and 4 are exploded view of the same device. The motor or driving device is not shown but the input power is to be transmitted by the toothed belt although any other rotational power transmitting mechanism would be suitable. Figures land 2 refer to the epycyclic form, figs 3 and 4 refer to the bevel gear form. It could be considered that the difference between these forms is radial power transmission (epicyclic) and axial power transmission (bevel gear version). The text describes the epicyclic form only. For bevel gear transmission the names can be directly changed as in the following table. Most of the parts are identical in the two versions but the following identifies the different descriptions depending on the differential form used.

Item or drawing ref No Figs 1 and 2 Figs 3 and 4 Uni-directional clutch Uni-directional clutch 2 Input shaft Input shaft 3 Uni-directional clutch Uni-directional clutch 4 Output shaft Output shaft 5 Ring gear Output bevel gear 6 Planet gears Pinion gears 7 Brake Brake 8 Bake disc Bake disc 9 Planet carrier Differential cage 10 Planet gear pivots Pinion gear pivots 11 Sun gear Input bevel gear The function of this device is described in its operation in the following three modes.

Driving: The motor is driving the load, the device transmits the torque to the load through the two uni-directional clutch devices. The uni-directional clutch (1) is turned by the pulley in an anticlockwise direction so that it engages and transmits torque through the shaft (2) which in turn engages the uni-directional clutch (3) this drives the output shaft (4) anti clockwise. It may be observed that the two uni-directional clutches are mounted in opposite directions even though they both transmit power when rotating in the same direction. This is because uni-directional clutch (1) is transmitting torque from its outer to the inner where as uni-directional clutch (2) is transmitting torque from the inner to the outer. The following actions are as a result of these rotations but not important in terms of the power transmission: The sun gear (10) is fixed to the shaft (2) this turns the planet gears (6). As the ring gear (5) is fixed to the output shaft (4) the brake disc (8) rotates at the same speed and direction as these components. If the brake was applied this would slow the motor although this is considered of no practical use.

Coasting: The uni-directional clutch (1) slips allowing the motor to remain idle. The ring gear is driven by the output shaft the planet gears, carrier and brake all rotate with the ring gear. If the brake is now applied then the device changes to braking mode.

In both of the above cases the gears turn with the output shaft but do not transmit any power.

Braking: The ring gear (5), which is mounted on the output shaft, turns in an anti-clockwise direction, this action then turns the planet gears (6). If the brake disc (8) is retarded by the brake (7) the planet carrier (9) that is connected to the disc (8), is also retarded. The planets now turn on their pivots (9) in an anti clockwise direction. The planet gears now turn the sun gear (10) and the shaft on which it is fixed (2) in a clockwise direction, which is opposite to the output shaft (4). The input shaft (2) now drives the uni-directional clutch (1) and the pulley in the opposite direction to that when the motor was driving the load. Power can then be utilized for regeneration.

There are 3 groups of gears in a differential, sun, planet and ring. The sun and ring gears are usually connected directly to a drive, brake or load etc however, the planet gears are not, it is the planet gear carrier that is used to transmit the power. The planets, (usually more than one), act as idler gears and the axles or pivots transfer the load to the carrier. If the planet carrier is held stationary then the sun and ring gears rotate in opposite directions, this feature is used when the device is in braking mode, hence the reverse direction. If we regard the ring gear as having positive rotation and the planet carrier as zero then the sun gear has a negative rotation. Consequently for the motor to drive the load forwards through the differential then the uni-directional clutch that prevents the relative rotation between these groups may be located in any of three locations.

1. Between the sun gear and ring gear as in figs 1 and 2, this is preferred, as the gears are not loaded when driving; all the torque is transmitted through the clutch.

2. Between the planet gear carrier and the ring gear, when driving this option puts load on the sun and planet gears although they do not rotate with relative to one another.

3. Between the sun gear and the planet carrier, as in position 2 this puts load on the planet gears and ring gear.

The diagrams 1 and 2 show an epicyclic gear unit, these are often referred to as differentials, although the more common form is a bevel gear differential shown in figs 3 and 4. A bevel gear differential could be used in the same way; this would give a ratio of 1: 1 when used in braking mode. In the case of a bevel gear differential the brake would retard the pinion gear carrier. An advantage of using the epicyclic form of differential is that the drive to the motor can be faster than the input speed from the load. This can be useful in increasing the regenerative speed output available and therefore, the maximum braking torque, for any given load speed.

The proportion of the maximum braking torque is often controlled electronically by pulse width modulation or similar methods of rapidly connecting and disconnecting the motor electrically. This results in an average time of connection and hence braking effect. In the case of a direct current electric motor the E. M. F (voltage) is proportional to speed so an increase in speed ratio would give a higher E. M. F for any given load speed. As the load speed diminishes on braking the E. M. F. drops so if regenerative effect is to be maintained instead of plug braking (dissipating the energy through a resister) then a transformer of some kind is required. Alternatively if the motor windings are shorted out until the current reaches a level at which if stopped by breaking the circuit, a transient E. M. F. is induced by inductance. This method induces large motor currents, which can cause the motor to overheat. As the load speed decreases the increase in motor speed provided by the speed ratio increase will postpone the need for these more elaborate solutions. If these solutions are then used the power that the associated circuitry handles will be lower and so the components could be reduced in size.

Claims

1. A drive mechanism where the power source drives through a uni-directional clutch and then a gearbox to the load, where the gearbox can be reversed enabling the load to drive the power source backwards through the same uni-directional clutch.

2. A mechanism as in claim 1 where the gearbox is a differential type and the reverse drive is achieved by retarding the planet gear carrier (or differential cage).

3. A mechanism as in claim 2 where the forward drive through the gearbox is achieved by another uni-directional clutch between the sun gear and ring gear (input bevel gear and output bevel gear).

4. A mechanism as in claim 2 where the forward drive through the gearbox is achieved by another uni-directional clutch between the planet gear carrier and the ring gear output shaft (differential cage and the output bevel pinion).

5. A mechanism as in claim 2 where the forward drive through the gearbox is achieved by another uni directional clutch between the sun gear and the planet carrier (input bevel pinion and the differential cage).

6. A device as in claims 2 to 5 where the differential gearbox used is of an epicyclic type (fig 1 and 2) giving a forward drive ratio of 1: 1 and a reverse drive ratio other than 1: 1.

7. A device as in claims 2 to 6 where the degree of load braking is controlled by varying the degree of brake application to the planet gear carrier (or differential cage).

8. A device as in any of the preceding claims where the power transmitted from the load to the power source is collected for later use (regenerative braking).