GB2291950A

GB2291950A - Drive transfer system with energy storage

Info

Publication number: GB2291950A
Application number: GB9415922A
Authority: GB
Inventors: James Michael Gilbert; Paul Michael Taylor; Robert Oldaker
Original assignee: University of Hull
Current assignee: University of Hull
Priority date: 1994-08-04
Filing date: 1994-08-04
Publication date: 1996-02-07
Also published as: GB9415922D0

Abstract

A drive transfer system for transferring drive from an input drive shaft 13 to an output drive shaft 16 comprises a spring 10 for temporarily storing energy from the input drive shaft and coupling means in the form of a clutch 11 and a brake 12 for transferring the stored energy to the output drive shaft. A control arrangement, 18 - 21, repeatedly switches the coupling means between different operating states to regulate the angular velocity/torque of the output drive shaft 16. The control system may monitor angular positions and/or velocities of input and output shafts, and may use optical encoding. A ratchet may be used instead of a clutch. <IMAGE>

Description

DRIVE TRANSFER SYSTEMS This invention relates to drive transfer systems, and the invention relates particularly, though not exclusively, to such systems which are used as variable ratio gear boxes.

According to the invention there is provided a drive transfer system for transferring drive from an input drive shaft to an output drive shaft, the system comprising energy-storage means for temporarily storing energy derived from the input drive shaft coupling means for coupling the energy storage means to the output drive shaft and or to the input drive shaft, the coupling means having a first operating state in which energy from the input drive shaft is stored in the energy storage means and a second operating state in which stored energy is transferred from the energy storage means to the output drive shaft, and control means for repeatedly switching the coupling means between said first and second operating states.

In a preferred embodiment of the invention, the energy-storage means may comprise a rotational elastic element such as a spring and the coupling means may comprise the combination of a clutch and a brake. These components may be so arranged as to provide step-up, step-down or a combination of step-up and step-down drive transfer systems. Also, a rotary inertial body may be provided to determine the rotational sense of the output drive shaft.

The control means may switch the coupling means between the first and second operating states cyclically, and the coupling means may be decoupled from the output drive shaft for a part of each cycle.

Embodiments of the invention are now described, by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates a drive transfer system according to the invention; Figure 2 illustrates an operating cycle of the system shown in Figure 1, and Figures 3 to 5 show further embodiments of drive transfer systems according to the invention.

Referring to Figure 1, the drive transfer system has an energy storage unit in the form of a coil spring 10 and a coupling unit in the form of a clutch 11 and an associated brake 12.

One end of spring 10 is connected to a rotary drive shaft 13 (the input drive shaft) and the opposite end of the spring is connected to a first plate 11' of clutch 11 via an intermediate rotary shaft 14. A second plate 11" of clutch 11 is connected to a load 15 via a further rotary drive shaft 16 (the output drive shaft).

In operation of the system, the input drive shaft 13 is driven by motor 17 connected to a power supply 18.

The clutch 11 and brake 12 are engaged and disengaged cyclically, to establish a desired angular velocity and torque of the output drive shaft 16.

As shown in Figure 2, each operating cycle of the system is of fixed duration T and consists of three phases; namely, a "Load Energy" phase, a "Transfer Energy" phase and a "Wait" phase.

During the "Load Energy" phase, clutch 11 is disengaged and brake 12 is engaged so that rotational energy from the input drive shaft 13 is stored in spring 10, the amount of stored energy being dependent upon the variable time interval tl, for which the brake is applied. At the end of the time interval tl, brake 12 is disengaged and clutch 11 is simultaneously engaged causing energy stored in spring 10 to be transferred to load 15 via the intermediate and output drive shafts 14,16.

When all, or a predetermined portion of the energy stored in spring 10 has been transferred to load 15, clutch 11 is disengaged (the "Wait" phase) allowing the output drive shaft 16 (and load 15) to run freely, and the system will remain in this condition until the end of the current cycle (i.e. until time T).

As the angular velocity of the output drive shaft 16 increases, the torque transferred will decrease, and for an output angular velocity lower than the input angular velocity, the torque applied to the load will be limited to the maximum input torque. Accordingly, the configuration shown in Figure 1 is more appropriate for effecting a step-up in angular velocity.

In this particular example, the angular velocity of the output drive shaft is determined, inter alia, by the amount of energy stored in spring 10 which, in turn, depends on the duration t of the "Load Energy" phase.

The time interval tl is controlled by a feedback control system. Referring again to Figure 1, the feedback control system comprises optical encoders 18,19,20 arranged to monitor the angular positions of drive shafts 13,14,16 respectively, and the output from each encoder is supplied to a processor 21 (eg a personal computer PC) via an encoder counter 22. The processor 21 is programmed to evaluate the correct time interval tl for a desired angular velocity of the output drive shaft, and outputs control signals C effective to engage and disengage the clutch 11 and brake 12 at the required times.

The processor 21 also compares the outputs from encoders 18 and 19, which are positioned at opposite ends of spring 10 to determine when all, or a predetermined portion of the stored energy in the spring has been transferred to the output drive shaft 16. When this determination is made, the processor produces a respective control signal which is effective to disengage the clutch to initiate the "Wait" period.

The time interval tl may be evaluated according to the expression: tl k =k (vl-v2), where k is a constant and vl and v2 are respectively the desired and the actual angular velocities of the output drive shaft.

In this example, the angular velocity of the output drive shaft is controlled by varying the time interval tl during which energy is stored in spring 10, and provided there are no excessive frictional losses, the longer the time interval tl, the greater the load angular velocity. Thus, if the load angular velocity should fall below a desired value, the time interval tl will be increased, giving a corresponding increase in the load angular velocity and, conversely, if the load angular velocity is higher than a desired value, the time interval t will be decreased giving a corresponding decrease in load angular velocity.

In another embodiment of the invention, the time interval t during which energy is stored in spring 10 is held at a preset, constant value, and the interval T of successive cycles is varied, as necessary, to control the average rate at which energy is transferred to the load.

As before, such control may be effected using a feedback control system such as that shown in Figure 1.

Figures 3 to 5 are diagramatic illustrations of further embodiments of drive transfer systems according to the present invention.

Figure 3 shows a system which is similar to that of Figure 1. However, in Figure 3, the coupling unit (i.e.

clutch 11 and brake 12) is positioned on the opposite side of spring 10 to that shown in Figure 1.

At the start of each operating cycle, clutch 11 is engaged and brake 12 is disengaged so that rotational energy will be transferred from the input drive shaft to the spring 10. The clutch 11 is then disengaged and brake 12 is engaged whereby the torque in spring 10 causes the output drive shaft 16 (and load 15) to accelerate. The brake is then released for a period and the clutch re-engaged for the next operating cycle.

In contrast to the system shown in Figure 1, the system of Figure 3 is only capable of producing a reduction in angular velocity between the input and output drive shaft (a step-down arrangement), but can produce an increased torque.

Referring to Figure 4, the energy storage unit comprises a spring 20 of which one end is attached to an intermediate drive shaft 21 and of which the opposite end is anchored in fixed relationship to that shaft. In this embodiment, the coupling unit comprises two clutches 22,23 which couple the intermediate drive shaft 21 to the input and the output drive shafts 24,25 respectively.

At the start of each operating cycle, clutch 22 is engaged and clutch 23 is disengaged, causing rotational energy to be transferred from the input drive shaft 24 and stored in spring 20, the amount of stored energy being dependent on the time tl for which the clutch 22 is engaged. Clutch 22 is then disengaged and clutch 23 engaged causing the stored energy to be transferred from spring 20 to the output drive shaft 25, causing its angular velocity to increase, but in the opposite sense to that of the input drive shaft 24. When all, or a predetermined portion of the stored energy has been transferred from spring 20 to the output drive shaft 25 (and so to the load 26), clutch 23 is disengaged allowing the output drive shaft 25 to run freely until it receives further rotational energy from spring 20 during the next operating cycle.

This operation can be effected by means of a feedback control system similar to that described with reference to Figure 1. Again, as described hereinbefore, the time interval t during which energy is stored in spring 20 could alternatively be held at a preset constant value, and the period T of successive cycles could be varied as necessary to control the average rate at which energy is transferred to the load.

The embodiment shown in Figure 5, is similar to that of Figure 4, but has an additional rotational inertial body 27 positioned between spring 20 and the second clutch 23. With this configuration, when clutch 22 is disengaged, the inertial body 27 will oscillate, and, depending on when clutch 23 is engaged, the torque applied to the output drive shaft 25 (and to the load 26) will either be in the same sense as that of the input drive shaft or in the opposite sense. The timing of the engagement of clutch 23 can be controlled by monitoring the position of an appropriate rotary shaft using an encoder in a feedback control system similar to that described with reference to Figure 1.

The configurations described with reference to Figures 4 and 5 are capable of producing either an increase or a decrease in angular velocity between the input and output drive shafts (i.e. a step-up or a step-down arrangement), and the configuration of Figure 5 may be used to effect drive in either rotational sense.

In the above-described embodiments, a ratchet device may be used in place of a clutch, and in the embodiments described with reference to Figures 4 and 5 the clutch 23 may be replaced by a ratchet device.

It will be appreciated that the described embodiments have a wide range of applications for which it is desired to transfer drive from an input rotary drive shaft to an output rotary drive shaft, and they find particular, though not exclusive application in variable ratio gearboxes.

Claims

1. A drive transfer system for transferring drive from an input drive shaft to an output drive shaft, the system comprising energy-storage means for temporarily storing energy derived from the input drive shaft, coupling means for coupling the energy storage means to the output drive shaft and or to the input drive shaft, the coupling means having a first operating state in which energy from the input drive shaft is stored in the energy storage means and a second operating state in which stored energy is transferred from the energy storage means to the output drive shaft, and control means for repeatedly switching the coupling means between said first and second operating states.

2. A drive transfer system as claimed in claim 1 wherein the control means switches the coupling means from said second operating state to said first operating state via a third operating state in which the output drive shaft is free running.

3. A drive transfer system as claimed in claim 2 wherein the control means switches the coupling means from the second to the third operating states when a predetermined portion of the energy stored in the energy-storage means has been transferred to the output drive shaft.

4. A drive transfer system as claimed in claim 2 wherein the control means switches the coupling means from the second to the third operating states when the energy stored in the energy-storage means has all been transferred to the output drive shaft.

5. A drive transfer system as claimed in claims 1 to 4 wherein the control means causes the coupling means to operate in the first operating state for a time interval related to a difference between a desired and the actual angular velocity of the output drive shaft.

6. A drive transfer system as claimed in claims 1 to 4 wherein the control means causes the coupling means to operate in the first operating state for successive preset intervals of time, and switches the coupling means between the first and second operating states at a rate related to a difference between a desired and the actual angular velocity of the output drive shaft.

7. A drive transfer system as claimed in any one of claims 1 to 6 wherein the control means comprises means for monitoring the angular positions and/or angular velocites of the input and output drive shafts and processing means for controlling the coupling means in dependence on the output from said monitoring means.

8. A drive transfer system as claimed in claim 6 wherein the monitoring means comprises optical encoder means.

9. A drive transfer system as claimed in any one of claims 1 to 8 wherein the energy storage means comprises a spring.

10. A drive transfer system as claimed in any one of claims 1 to 9 wherein the coupling means is positioned between the energy-storage means and the output drive shaft.

11. A drive transfer system as claimed in claim 10 wherein the coupling means comprises the combination of a brake and a clutch or the combination of a brake and a ratchet device.

12. A drive transfer system as claimed in claim 10 or claim 11 wherein in said first operating state of the coupling means the brake is engaged and the clutch or ratchet device is disengaged and in the second operating state of the coupling means the brake is disengaged and the clutch or ratchet device is engaged.

13. A drive transfer system as claimed in any one of claims 1 to 9 wherein the coupling means comprises the combination of a first coupling element for coupling the input drive shaft to the energy-storage means and a second coupling element for coupling the output drive shaft to the energy-storage means, wherein in the first operating state of the coupling means the first coupling element is engaged and the second coupling element is disengaged and in the second operating state of the coupling means the second coupling element is engaged and the first coupling element is disengaged.

14. A drive transfer system as claimed in claim 13 wherein the first and second coupling elements are both clutches.

15. A drive transfer system as claimed in claim 13 wherein the second coupling element is a ratchet device.

16. A drive transfer system as claimed in any one of claims 13 to 15 including a rotary inertial body positioned between the second coupling element and the energy-storage means.

17. A drive transfer system as claimed in any one of claims 1 to 9 wherein the coupling means is positioned between the input drive shaft and the energy-storage means.

18. A drive transfer system as claimed in claim 17 wherein the coupling means comprises the combination of a brake and a clutch or the combination of a brake and a ratchet device.

19. A drive transfer system substantially as herein described with reference to the accompanying drawings.

20. Use of a drive transfer system as claimed in any one of claims 1 to 19 as a variable ratio gearbox.