IE990786A1

IE990786A1 - A power control device

Info

Publication number: IE990786A1
Application number: IE19990786A
Authority: IE
Inventors: Gerald David Francis; Victor Anthony Nagle; Stanley Sturdy
Original assignee: Sturdy Francis Nagle & Co Ltd
Priority date: 1999-09-21
Filing date: 1999-09-21
Publication date: 2001-04-04
Also published as: GB0022923D0; GB2357163A; GB2357163B

Abstract

A power control device (10), particularly a power control device for use in a vehicle powered by an electric motor (11), such as a golf trolley, connected to a power source therefore (12), comprises means (17,18) for detecting and measuring fluctuations in the current flow to the motor (11) in use, means (19) for determining the speed of the motor (11) on the basis of the measured fluctuations, and means (16,19) for controlling the speed of the motor (11), the relationship between the speed of the motor (11) and the power being supplied thereto being maintained thereby within predetermined limits. The device enables avoidance of damage to the power and drive elements of the vehicle and at the same time increases user comfort without prohibitively impacting on production costs. <Figure 1>

Description

A power control device This invention relates to a power control device and, in particular, to a power control device for use in a vehicle powered by an electric motor.

There are many examples of vehicles which can be, and are, powered by electric motors. These include wheelchairs, mopeds, golf trolleys and the like. i Using the example of a golf trolley, this will usually comprise a j motor to drive the wheels via an arrangement of gears and a power Ί source for the motor, typically a battery. j The trolley is usually controlled by one or more controls which jean be adjusted manually by the user to vary the speed of the motor in jsome way or other. In their simplest form these controls will comprise jan on/off switch and some type of “throttle” controlling the power Supplied to the motor. A drive module connects the controls, the power source and the motor in order to provide the appropriate impulses to the power source in response to the settings of the controls to adjust the speed of the motor.

Conventional motorised golf trolleys do however suffer from a number of drawbacks, caused by a variety of circumstances, resulting in damage to motor, power source and gears. Examples of situations which can lead to damage include: sudden stalls caused, for example, by encountering an obstacle.

The sudden increase in current can lead to permanent damage to the motor windings within a few seconds. In a prolonged stall the current build up can also detrimentally affect the power source; the trolley being held stationary on an incline by applying a low power setting. Because this stall effect is usually not detected, it is the largest single cause of damage in conventional golf trolleys and can cause serious cumulative damage to the motor with eventual failure; and sudden start shock caused by turning the power setting to full on from off. This causes damage to both motor and gears due to the sudden transition from off to full on and, because of a temporary short circuit from motor to the power source, damage of the latter can also occur. Similar effects occur when the power is suddenly turned off.

In addition, conventional golf trolleys require the user to repeatedly adjust the controls for moving the trolley forward in order to maintain a desired speed or to move the trolley even a short distance. This can be awkward and tiresome.

Similar concerns apply to all vehicles driven in this manner.

Although there are individual solutions available for solving these problems, such as sensors for monitoring motor movement and/or detecting current surge, bimetallic strips for reacting to overheating, sophisticated cruise control systems and the like, these tend to increase significantly the cost of the vehicle particularly in the case of smaller vehicles such as golf trolleys.

There is therefore a need for a power control device which will avoid damage to the power and drive elements of the vehicle and at the same time increase user comfort without prohibitively impacting on production costs.

It is the object of the present invention to provide a power control device which will address these needs.

The present invention therefore provides a power control device for use in a vehicle powered by an electric motor connected to a power source therefor, which comprises means for detecting and measuring fluctuations in the current flow to the motor in use, means for determining the speed of the motor on the basis of the measured fluctuations, and means for controlling the speed of the motor such that the relationship between the speed of the motor and the power being supplied thereto is maintained within predetermined limits.

Determining motor speed on the basis of detection and measurement of fluctuations in the current flowing to the motor eliminates the need for separate sensors.

Providing means whereby the speed of the motor and the power supplied thereto are maintained within predetermined limits enables inappropriate and potentially damaging extremes of power to be avoided.

Preferably, the means for determining the speed of the motor and the means for controlling the speed of the motor form part of a feedback system which adjusts the level of power supplied to the motor from the power source.

In this way switching systems can be employed which enable adjustments to the power supplied to the motor to be made virtually instantaneously upon determining the motor speed.

Typically, the fluctuations in the current are those due to changes in the magnetic attraction/repulsion effect as the rotor poles pass towards and away from the stator poles in the motor.

This has the advantage that the fluctuations used to determine the speed are signals which are generated by an electric motor in normal operation.

Any suitable electronic component can be used to detect and measure the fluctuations and the choice thereof will be evident to the skilled person.

The amplitude of such fluctuations will typically be very small usually in the microvolt range. For example, in the case of fluctuations resulting from the attraction/repulsion effect they are in the range of between 1 kHz and 40kHz. It is therefore preferred that the fluctuations in current are amplified before reaching the feedback system.

This amplification allows minor differences to be more readily and precisely determined thus providing enhanced accuracy and reliability.

Preferably, the feedback system incorporates a micro-controller. In this micro-controller signals from the key components in the drive and power systems are received and read, appropriate responses to these signals computed and impulses provided back to the key components. Typically such a micro-controller will be in the form of a programmable microchip.

Micro-controllers of this general type will be known to the skilled person who will be able to program the same to carry out the functions required in a power control device according to the present invention.

In order to minimise the risk of damage occurring to the elements of the power and drive systems, the time during which extreme conditions obtain should be kept as short as possible without interfering with the normal functioning of the vehicle.

Therefore, in a preferred embodiment of the invention, the predetermined limits are chosen such that the supply of power from the power source is cut off if the speed of the motor and the power being supplied thereto fail to conform to the predetermined limits within a predetermined time period.

Preferably, the predetermined time period is shorter than the time after which damage would occur to the motor, to the power source or to other components of the vehicle if the supply of power were not cut off.

The actual length of the predetermined time period will depend on the specifications of the particular power and drive elements chosen.

Preferably, the power source is a battery, especially a rechargeable battery. In order to minimise production costs a standard twelve volt dry cell battery for use with a corresponding electric motor can be employed.

It is preferred that the power is transferred from the power source to the motor as a series of on/off pulses of modulated width such that the ratio of the time during which the power to the motor is on to the time when it is off determines the speed of the motor.

In this manner the length of time during which the motor is subjected to current from the power source within a fixed time period can be regulated such that it is always commensurate with the level of power required to achieve or maintain the desired speed or a measured speed. This effectively eliminates the risk of the motor being subjected to prolonged bursts of excessive power or sudden switching off of power. This could otherwise occur, particularly in situations where the vehicle comes to a sudden unexpected stop or where a user moves abruptly to a full on or full off position on a manual control, if present.

The pulse speed preferably lies between 10 kHz and 50 kHz, especially between 25 kHz and 35 kHz.

In the power control device according to the invention, it is preferred that means are provided which enable a user of the vehicle to stop and start the vehicle and to select a desired constant motor speed.

Preferably the means is an analog switch, the precise setting of which is converted to a digital signal which is passed to the power control device.

A preferred such switch is a potentiometer.

Providing such user control means can enable a user of the vehicle to start and stop the vehicle, to select a desired constant speed (“cruise control”), to move the vehicle a prescribed distance or to select other appropriate functions.

In order to enhance the convenience of the vehicle, the power control device will preferably include means that allow the level of power supplied to the motor to be adjusted so as to permit the vehicle to travel a pre-determined distance followed by an adjustment of the level of power to cause the vehicle to stop.

Such a feature is particularly useful in golf trolleys as it will enable the user to set the vehicle to move a few yards independently and then come to a stop without the need for the user to have her or his hands on the controls.

It is further preferred that the predetermined limits are chosen such that the power being supplied to the motor at a given speed does not significantly exceed that which the motor would be expected to use when travelling constantly and unhindered at that same speed.

This feature not only enables the power control device to maintain a constant speed as chosen by the user but allows for elimination of excesses of current which are out of step with the speed of the motor and which if unchecked would cause damage to the power or drive elements of the vehicle.

Preferably, the predetermined limits are chosen such that the power being supplied to the motor will cut off after a predetermined time period unless the motor speed has reached a certain minimum value.

This feature is particularly intended to prevent too high a level of power flowing to the motor for a period which would be long enough to cause damage to either the motor or gears themselves or to the power source through possible short circuit effects. Such situations include in particular those where the vehicle meets an obstruction or where a user inadvertently or intentionally uses the motor to maintain the vehicle in a stationary position on a hill.

It is also preferred that the predetermined limits are chosen such that the rate of increase or decrease in the level of power supplied to the motor remains under control independently of any changes in settings applied by the user.

This feature can be used for example to prevent damage being caused to the motor and gears and/or the power source in situations where a user moves a manual control switch to a full on or full off position suddenly rather than gradually.

As mentioned herein, the power control device according to the invention can be employed in any motorised vehicle which is driven by an electric motor connected to a power source. Examples of such devices include wheelchairs, lawnmowers, mopeds, golf carts and the like.

The power control device is particularly useful where the vehicle is a golf trolley. These vehicles are also known as power caddies and are designed to carry a golf bag with a complement of clubs.

It is an advantage of the power control device according to the invention that it can be incorporated into an existing design of a motorised vehicle in place of the original power control device with little, if any, need to modify the remaining elements and systems of the vehicle.

In general terms the invention also concerns a method of regulating the speed of a vehicle powered by an electric motor connected to a power source therefor, which comprises: a) detecting and measuring fluctuations in the current flow to the motor in use; IE99O786 b) determining the rotational speed of the motor on the basis of the measured fluctuations; c) adjusting the power supply to the motor in response to the determined speed of the motor, such that the relationship between the speed of the motor and the power being supplied thereto is maintained within predetermined limits.

The invention will be further illustrated by the following description of embodiments thereof, given by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a block diagram representing the key elements in the power control device according to the invention as installed in a golf trolley and their relationship with each other and with the components of the drive and power systems.

Fig. 2 is a graph of power (volts) versus time representing the transfer of power from the power source to the motor.

Fig. 3 is a flowchart providing a schematic representation of the operation of the power control device of Fig. 1.

In Fig 1 there is indicated generally at 10 a schematic representation of a power control device according to the invention.

The power control device 10 is connected between a direct current motor 11 and a 12V dry cell battery 12 having a positive terminal 13 and a negative terminal 14. A manual speed control 15, in the form of a potentiometer, is also connected to the power control device 10.

The motor 11 and the battery 12 are connected to the power control device 10 via a drive switching unit 16 and a detector 17 for detecting microvolt fluctuations in the current provided to the motor 11 from the battery 12. The detector 17 is connected to an amplifier 18 where the microvolt fluctuations are amplified before being received and read by a micro-controller 19. The micro-controller 19 is also connected to the drive switching unit 16. The manual speed control 15 is connected to the power control device 10 through the micro-controller 19.

The micro-controller 19 compares the actual speed of the motor 11 with the power setting and adjusts the power accordingly by way of feedback until the desired speed is attained.

The micro-controller 19 switches the battery 12 to the motor 11 through the drive switching unit 16 using pulse width modulation.

In Fig. 2 the supply of power from the battery 12 to the motor 11 by pulse width modulation is illustrated in graphic form. On the ordinate the power supply to the motor 11 from the battery 12 is shown in volts with 0V representing off and 5 V representing full on. The arrows along the abscissa mark off equal time periods. The ratio of on to off per unit time determines the speed of the motor. The graph indicates speed increasing from zero to full speed, with pairs of peaks indicating intermediate speed settings.

Fig. 3 is a flowchart in which certain key functions of the power control device are indicated as boxes. Diamond-shaped boxes indicate points where determinations of alternatives are made and rectangular boxes indicate actions contingent upon such determinations or settings of components. Arrows indicate the direction of flow of information and instruction.

In use, these functions operate as follows. After setting up the trolley with the manual speed control 15 in an “off’ or “reset” setting a user shifts the manual speed control 15 to a desired “on” setting. This setting will be received and read by the micro-controller 19 and compared with the speed of the motor 11 calculated in the microcontroller 19 based upon the data received from the detector 17 through ίο the amplifier 18. If the correct speed has not been achieved, the microcontroller 19 will determine whether the speed is too fast or too slow. Based upon this information a signal will be passed from the microcontroller 19 to the drive switching unit 16 which will decrease or increase the power supplied to the motor 11 from the battery 12 to decrease or increase the motor speed. The micro-controller 19 will then continue to monitor the speed of the motor 11 and compare signals until the desired speed is achieved.

In the case where an increase in speed has been computed, the 10 micro-controller 19 will check the motor speed and if the speed has not increased will check again after 4 seconds. In the event that the speed has still not increased upon this second check, the micro-controller 19 will cease transmitting to the drive switching unit 16 and power will cease to be supplied from the battery 12 to the motor 11.

Such a cessation of power supply would take place for example where the motor 11 is unable to attain the desired speed due to the trolley being unable to move forward because of an obstruction or the like.

Claims

1. A power control device for use in a vehicle powered by an electric motor connected to a power source therefor, which comprises means for detecting and measuring fluctuations in the current flow to the motor in use, means for determining the speed of the motor on the basis of the measured fluctuations, and means for controlling the speed of the motor such that the relationship between the speed of the motor and the power being supplied thereto is maintained within predetermined limits.

2. A power control device according to Claim 1, wherein the means for determining the speed of the motor and the means for controlling the speed of the motor form part of a feedback system which adjusts the level of power supplied to the motor from the power source.

3. A power control device according to Claim 1 or 2, wherein the fluctuations in the current are those due to changes in the magnetic attraction/repulsion effect as the rotor poles pass towards and away from the stator poles in the motor.

4. A power control device according to any preceding claim, wherein the fluctuations are in the range of between 1kHz and 40kHz.

5. A power control device according to any one of Claims 2 to 4, wherein the fluctuations in current are amplified before reaching the feedback system.

6. A power control device according to any one of Claims 2 to 5, wherein the feedback system incorporates a micro-controller.

7. A power control device according to any preceding claim, wherein the predetermined limits are chosen such that the supply of power from the power source is cut off if the speed of the motor and the power being supplied thereto fail to conform to the predetermined limits within a predetermined time period.

8. A power control device according to Claim 7, wherein the predetermined time period is shorter than the time after which damage would occur to the motor, to the power source or to other components of the vehicle if the supply of power were not cut off.

9. A power control device according to any preceding claim, wherein the power source is a battery.

10. A power control device according to any preceding claim, wherein power is transferred from the power source to the motor as a series of on/off pulses of modulated width such that the ratio of the time during which the power to the motor is on to the time when it is off determines the speed of the motor.

11. A power control device according to Claim 10, wherein the pulse speed lies between 10 kHz and 50 kHz.

12. A power control device according to Claim 10 or 11, wherein the pulse speed lies between 25 kHz and 35 kHz.

13. A power control device according to any preceding claim, wherein means are provided which enable a user of the vehicle to stop and start the vehicle and to select a desired constant motor speed.

14. A power control device according to Claim 13, wherein the means is an analog switch, the precise setting of which is converted to a digital signal which is passed to the power control device.

15. A power control device according to Claim 14, wherein the switch is a potentiometer.

16. A power control device according to any preceding claim, which includes means that allow the level of power supplied to the motor to be adjusted so as to permit the vehicle to travel a predetermined distance followed by an adjustment of the level of power to cause the vehicle to stop.

17. A power control device according to any preceding claim, wherein the predetermined limits are chosen such that the power being supplied to the motor at a given speed does not significantly exceed that which the motor would be expected to use when travelling constantly and unhindered at that same speed.

18. A power control device according to any preceding claim, wherein the predetermined limits are chosen such that the power being supplied to the motor will cut off after a predetermined time period unless the motor speed has reached a certain minimum value.

19. A power control device according to Claim 13, wherein the predetermined limits are chosen such that the rate of increase or decrease in the level of power supplied to the motor remains under control independently of any changes in settings applied by the user.

20. A power control device according to any preceding claim, wherein the vehicle is a golf trolley.

21. A method of regulating the speed of a vehicle powered by an electric motor connected to a power source therefor, which comprises: a) detecting and measuring fluctuations in the current flow to the motor in use; b) determining the rotational speed of the motor on the basis of the measured fluctuations; c) adjusting the power supply to the motor in response to the determined speed of the motor, such that the relationship between the speed of the motor and the power being supplied thereto is maintained within predetermined limits.

22. A power control device according to Claim 1, substantially as hereinbefore described with particular reference to and as illustrated in Fig. 1 of the accompanying drawings.