GB2335797A

GB2335797A - Control system for an electrically powered actuator

Info

Publication number: GB2335797A
Application number: GB9809144A
Authority: GB
Inventors: Wilfred Ward Smith
Original assignee: BTR Industries Ltd; Dunlop Ltd
Current assignee: BTR Industries Ltd; Dunlop Ltd
Priority date: 1998-03-11
Filing date: 1998-04-30
Publication date: 1999-09-29
Also published as: GB9805040D0; GB9809144D0

Abstract

A method or means of controlling an electrically powered actuator comprises monitoring the current flow through an actuator device and switching the current off when the current level reaches a first predetermined level Da and restoring the current when the current level falls to a second predetermined level Dm such that the actuator is held in an activated mode. The first predetermined current level Da may be within plus or minus 15% of the activation current level 1a of the actuator or it may be equal to or less than the activation current level 1a. The second predetermined current level Dm may be between 5% and 20% above the current level Im required to hold the actuator in the activated mode. The control system may provide efficient, small and light weight actuators which may be used within vehicles.

Description

2335797 1.

"CONTROL OF ELECTRICALLY POWERED ACTUATION DEVICE" This invention relates to a method of and means for control of an electrically powered actuation device and in particular, but not exclusively, a device powered by an electrical supply having a variable, substantially unregulated, voltage characteristic. The invention is particularly applicable to the control of a device which possesses both resistive and inductive electrical impedances.

The invention relates in particular, but not exclusively, to a method of and means for control of an electrical solenoid such as is used in an automotive vehicle, for exanple as part of a vehicle suspension control system and which is powered by the vehicle battery.

The working voltage and working (ambient) temperature of a device, such as a solenoid, used in an automotive application can vary significantly. For example the working voltage may vary between 10.5 and 16 volts and the working (ambient) temperature range may be between -320C and +950C. This can create operating difficulties. For example at a low ambient temperature, especially when combined with a high instantaneous supply voltage, there is a high wattage in the solenoid and a risk of the solenoid windings over heating due to the rate of heat generation in the windings exceeding the rate of heat dissipation.

Another operating difficulty potentially can arise at a high ambient temperature. To ensure availability of sufficient force to actuate the solenoid, especially when a high ambient temperature (i.e. high resistance in the solenoid coil) is combined with a low instantaneous supply voltage, it is necessary to provide the solenoid with a higher number of coil turns than necessary when operating at a lower temperature.

In consequence of these operating extremes it is usual to provide a solenoid coil which has a wattage rating much greater than is required to move the solenoid piston. That results in additional weight and cost.

The present invention seeks to provide an improved method of and means for control of an electrically powered actuation device, such as an inductive device, e.g. a solenoid, used in an automotive vehicle.

2.

In accordance with one aspect of the present invention operating means for control of an electrically powered actuation device selectively operable to be in a first operating mode or a second operating mode comprises monitoring means for substantially continuously monitoring the current flow through the device and control means for controlling the supply of energy to the device at least when the device is required to be held in a f irst operating mode, wherein said control means switches of f the supply of electrical energy when the current level in the device reaches a f irst current datum level which is related to that current level which is sufficient to cause actuation of the device to said f irst operating mode and wherein said control means restores the supply of electrical energy to the device when the current level in the device f alls to close to the minimum level required to maintain the device in said first operating mode.

In accordance with another aspect of the present invention a method for the control of an electrically powered actuation device selectively operable to be in a f irst operating mode or a second operating mode comprises substantially continuously monitoring the current f low in the actuation device thereby to enable the supply of electrical energy to the device to be switched off when the current level reaches a f irst current datum level which is related to that current level which is sufficient to cause actuation of the device to a f irst operating mode and to enable the supply of electrical energy to be restored when the current level in the device falls to close to the minimum level required to maintain the device in said first operating mode.

The actuation device typically is of a kind, such as a solenoid, which has a coil or other component that exhibits an electrical impedance comprising resistance and inductive characteristics.

The actuation device may comprise an electrical solenoid having a piston member movable to said f irst operating position from a second operating position when electrical energy is applied to the solenoid coil, and said piston member being maintainable in said first operating position by a flow of current through the coil.

The f irst current datum level preferably is within plus or minus 15%, more preferably within plus or minus 5%, of that current level sufficient to cause actuation of the device to a first operating mode. The datum level i 3.

may be a level which is selected to be less than or 1 to, but not greater than, that current level required for actuation of the device to a first operating mode.

The monitored current level which causes the supply of electrical energy to be restored preferably is no greater than 20% greater than the minimum level required to maintain the device in said first operating mode. Preferably said current level which causes the supply of electrical energy to be restored is always at least 5% greater than said minimum level current. The monitored current level may be selected to be between 5% and 15% above the minimum level.

The spacing of the two current datum levels will affect the frequency of the on-off switching process for the control of the solenoid power supply. A reduction of that spacing will increase the switching frequency. The switching frequency will depend also on the supply voltage and temperature because these will affect the rate of both current build up and current decay.

To minimise the required power rating of a solenoid the invention teaches a requirement that both current datum levels should be as low as possible subject to the requirement that the first datum level must always be above the second, lower datum level, that the second datum level must always be above the minimum current required to maintain the solenoid in a first operating mode, e.g. activated, and that the datum levels are not so close together that the resulting on-off switching cycle frequency is beyond the capabilities of a microprocessor or other component part of a switching system of the control means.

In accordance with the invention, in the control of a solenoid, the inductive impedance of the coil causes the current flow in the coil to lag behind the voltage. It is that characteristic which is utilised in accordance with the invention so as to limit the current flow and thereby the wattage in the coil.

The method and means of the present invention are particularly applicable to solenoids as used in an automotive vehicle, for example to control fluid flow in a vehicle suspension as described in our co-pending UK Patent Application No. 9724444.6 filed on 19th November 1997. Solenoids used in 4 automotive vehicles commonly are required to operate over the above mentioned temperature range and also the aforedescribed voltage range which results from variation of the battery output voltage.

The control means may be provided in combination, e.g. in series, with a switch device operable to select between a first and a second operating mode. Alternatively the control means may operate also as a switch device.

The invention provides also an operating system comprising an operating means of the invention and an actuation device under the control of said operating means.

Embodiments of the invention will now be described, by way of example, with reference to the Drawings wherein:- Figure 1 is a circuit diagram of part of a vehicle suspension control; Figure 2 shows one example of the current flow in the solenoid coil of the circuit of Figure 1; Figure 3 shows the voltage applied to the solenoid coil when it is maintained in a first operating mode.

Figure 4 shows a switching arrangement for four solenoids and a current sensor facility; Figure 5 shows another example of the current flow in the solenoid coil of the circuit of Figure 1, and Figure 6 shows the solenoid voltage supply function for the current flow shown in Figure 5.

Referring to Figure 1, flow of suspension system fluid from pipe 10 to pipe 11 is controlled by a valve 12 which is normally closed but can be opened by operation of an associated solenoid 14 to move the solenoid plunger 13 to a f irst operating mode position at which it holds the valve in an open position.

The vehicle battery 15 is available to provide a supply of electrical energy to the solenoid coil when a switch 16 is closed, i.e. when the fluid valve 12 is to be opened.

5.

A current control device 17 lies between the switch 16 and the solenoid 14 and operates as described below to protect the solenoid coil from overload and overheating but at the same time ensures maintenance of the valve 12 in the required open condition. The control device 17 monitors the actual current f low in the solenoid coil and temporarily switches off the supply from the battery when the current has reached a first datum level 20 (see Figure 2) which is sufficient to ensure that the solenoid is able to move the valve 12 f rom a closed to an open condition. Supply of electrical energy from the battery to the coil is restored when the coil current level falls to less than 10% above a second datum level 21. For as long as the valve is required to remain open the current control device 17 continues to switch the battery supply off and on, resulting in an applied voltage of a pulse waveform 18 as shown in Figure 3. Figure 3 shows that voltage is applied for only a part, typically as low as 30%, of the time for which the valve is maintained open. Significant reduction of energy consumption and risk of solenoid overheating is thereby achieved.

Typically the control device 17 and switch 16 will be part of a control device system controlling four valves 12 each associated with a respective one of four vehicle wheel suspensions. To enable the solenoid current to be monitored when the switch 16 or similar component temporarily switches of f the battery supply, the control device system may comprise an arrangement as shown in Figure 4.

In Figure 4, four solenoid switches and the current sensor are shown. The sensor comprises in particular a resistor and an amplifier. The only additions required to the switching system for monitoring the decay current are the back EMF diodes.

When a solenoid is switched on, current flows through the switch, the solenoid coil and the current sensor resistor. When the solenoid is switched off, the current decays from the solenoid through the sensor resistor and the back EMF diode, so enabling current monitoring.

In the above described embodiment the first current datum level equals the current level necessary to activate the solenoid to an "on" condition, but the second current datum level is slightly above the current level necessary to hold the "oW' condition.

6.

In a second embodiment now described with reference to Figures 5 and 6, the first current datum level (Da) is below the current level (Ia) necessary to activate an "on" condition, but again the second current datum level (Dm) is slightly above the current level (Im) necessary to maintain that "on" condition.

Figures 5 and 6 show the profiles against time of solenoid current and supply voltage.

Two current datum levels, Da and Dm, are shown. Dm, the lower of these two levels, lies just above Im. The upper datum level, Da, is set to a value above Dm. Subsequent to initial switch-on of the solenoid when current must be allowed to build up to the value Ia which is sufficient for actuation, the supply voltage will be switched off and the current in the solenoid allowed to fall to the level Dm. The supply voltage is then restored and the solenoid current rises to the level Da, at which point the supply voltage is switched off again. This process is repeated for as long as the solenoid is to be maintained in the operating position.

7.

Claims

CLAIMS:

1. An operating method for the control of an electrically powered actuation device selectively operable to be in a first operating mode or a second operating mode comprises substantially continuously monitoring the current flow in the actuation device thereby to enable the supply of electrical energy to the device to be switched off when the current level reaches a first current datum level which is related to that current level which is sufficient to cause actuation of the device to a first operating mode and to enable the supply of electrical energy to be restored when the current level in the device falls to close to the minimum level required to maintain the device in said first operating mode.

2. Method according to claim 1, wherein the first c = ent datum level is set to within plus or minus 15% of the current level which is sufficient to cause actuation of the device to a first operating mode.

3. Method according to claim 2, wherein the first current datum level is set to within plus or minus 5% of the current level which is sufficient to cause actuation of the device to said first operating mode.

4. Method according to any one of the preceding claims, wherein said f irst datum level is set to be less than or equal to that current level required for actuation of the device to said first operating mode.

5. Method according to any one of the preceding claims, wherein the monitored current level which causes the supply of electrical energy to be restored is no greater than 20% greater than the minimum level required to maintain the device in said first operating mode.

6. Method according to claim 5, wherein said monitored current level is between 5% and 15% above said minimum level.

7. Method according to any one of the preceding claims, and as applied to the control of an actuation device which possesses both resistive and inductive impedances.

8. Method according to claim 1 and substantially as hereinbefore described.

8.

9. Operating means f or control of an electrically powered actuation device selectively operable to be in a f irst operating mode or a second operating mode comprises monitoring means for substantially continuously monitoring the current f low through the device and control means for controlling the supply of energy to the device at least when the device is required to be held in a f irst operating mode, wherein said control means switches off the supply of electrical energy when the current level in the device reaches a first current datum level which is related to that current level which is sufficient to cause actuation of the device to said first operating mode and wherein said control means restores the supply of electrical energy to the device when the current level in the device falls to close to the minimum level required to maintain the device in said first operating mode.

10. Operating means according to claim 9, wherein said f irst current datum level is set to within plus or minus 15% of the current level which is sufficient to cause actuation of the device to a first operating mode.

11. Operating means according to claim 10, wherein said f irst current datum level is set to within plus or minus 5% of the current level which is sufficient to cause actuation of the device to said first operating mode.

12. Operating means according to any one of claim 9 to 11, wherein said f irst datum level is set to be less than or equal to that current level required for actuation of the device.

13. operating means according to any one of claims 9 to 13, wherein the control means causes the supply of electrical energy to be restored only when the monitored current level is no greater than 20% above the minimum current level required to maintain the device in said first operating mode.

14. Operating means according to claim 13, wherein the control means restores the supply of electrical energy when the monitored current level falls to a level between 5% and 15% above said minimujn level.

15. Operating means according to claim 9 and substantially as hereinbefore described.

1 9.

16. Operating system comprising operating means according to any one of claims 9 to 15 and an electrically powered actuation device under the control of said operating means.

17. Operating system according to claim 16, wherein said actuation device possesses both resistive and inductive impedances.

18. Operating system accordixig to claim 16 or claim 17, and adapted for operation in accordance with an operating method according to any one of claims 1 to 8.