GB2099235A - Electrically-operable actuator - Google Patents

Abstract

A control system for controlling the position of a movable element, e.g. a flap valve in a vehicle heating and/or ventilating system, includes a miniature electric-motor driven actuator having a linearly displaceable and reciprocable output member (17) for coupling to the element, and electrical circuit means for controlling operation of the actuator motor (110) and thereby position of the element. The member (17) is displaced axially within a bore (117) by the motor (110) through a reduction gear arrangement (112) disposed in a space intermediate two parts (113 and 115) of the actuator housing and having a rotatable output gear (132) surrounding the member (17) which is journalled in the part (115) and which drivingly engages the member (17) by means of co-operating screw-threads. Circuits described energise the motor for a predetermined duration in response to switch actuation (Figure 2, now shown), de- energise the motor on reaching a predetermined level of monitored current such as when the motor stalls at end of travel, (Figure 3, not shown), and circuit for positioning member 17 in accordance with the position of a manually- operable element (Figures 4, 5, not shown). <IMAGE>

Description

SPECIFICATION Control systems This invention relates to control systems, and is especially concerned with control systems for controlling the operation of flap valves of vehicle heating and/or ventilating equipment.

Heretofore, flap valves used in vehicle heating and/or ventilating equipment for directing flow of air and for blending streams of hot and cold air have commonly been operated by means of mechanical linkages, such as, for example, Bowden cables connected to manually-operable levers on the vehicle dashboard.

However, this method of operating the flap valves of such equipment suffers from the disadvantage that the location of the unit which houses the flap valves in the vehicle has been dictated to a certain extent by the positioning of the manually-operable levers on the vehicle dashboard. In this respect, the unit housing these flap valves has usually been positioned adjacent the vehicle dashboard in order not to complicate unnecessarily the mechanical linkages between the manually-operable levers and the flap valves.

It has also been proposed to use vacuum operated servo motors regulated by dashboard-mounted pneumatic valves to control the operation of flap valves in vehicle heating and ventilating equipment.

Although the above disadvantage associated with mechanical linkage is substantially overcome by the adoption of vacuum operated servo motors, such as a system introduces a different disadvantage in that it is essential that the pneumatic circuitry controlling the servo motors be air-tight, with the subsequent result that the equipment becomes expensive to install and maintain.

It is an object of the present invention to provide a control system suitable for use in a vehicle heating and/or ventilating equipment which does not suffer from the above disadvantages.

According to the present invention, there is provided a control system for controlling the position of a moveable element comprising an electrically operable actuator having output means which is to be connected to the moveable element and electrical circuit means for controlling operation of the actuator and thereby the position of the moveable element, the actuator including a housing having a first part defining a recess in which an electric motor is disposed and a bore in which an elongate member comprising the output means is mounted for linear reciprocating movement, and a second part mounted on the first part defining therebetween a space into which the output shaft of the motor projects and having an aperture therein in axial alignment with the bore through which the elongate member extends, and reduction gearing disposed in the space including an input gear mounted on the motor output shaft and an output gearjournalled in the aperture of the second part which surrounds the elongate output member and which has an internal screw-thread that co-operates with an external screw-thread on the elongate output member such that rotation of the output gear by the electric motor causes axial displacement of the elongate member within the bore, and wherein the electrical circuit means is arranged to control energisation of the electric motor so as to vary the axial displacement of the elongate member within the bore and thereby to control the position of the moveable element.

A thrust washer may be disposed between a radially-extending surface of the output gear and a surface of the second part of the housing. A further thrust washer may be disposed between a second surface of the output gear and a surface of the first part of the housing, the output gear being captively retained between the two thrust washers to inhibit axial movement thereof.

The actuator may include a tube disposed in the bore of the first part of the housing in which the elongate member is slidably mounted. This tube preferably extends out of the bore into an axial recess in the output gear so as to act as a bearing for the outpt gear.

The housing of the actuator may conveniently be formed of plastics material.

The electric circuit means of the control system may include a switching device and, in such case, may be arranged to energise the motor of the actuator for a predetermined duration in response to actuation of the switching device, or may alternatively be arranged, following energisation of the motor by actuation of the switching means, to monitor electric current supplied to the motor and to deenergise the motor in response to a predetermined level of current being reached, indicative of, for example, stall of the motor at the end of travel of the moveable element.

The electric circuit means may instead include a variable input device having a manually-operable element adjustable between two extreme positions and means for providing a signal indicative of the position of the elongate member of the actuator and be arranged to control energisation of the electric motor so as to position the elongate member in accordance with the position of the manuallyoperable element.

Various forms of control systems in accordance with the present invention and incorporated in vehicle heating and ventilating equipment will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of one form of control system; Figure 2 shows part of an electrical circuit of the control system of Figure 1; Figure 3 is a schematic diagram of another form of control system; Figure 4 is a schematic diagram of a further form of control system; Figure 5 shows part of an electrical circuit of the control system of Figure 3; Figure 6 shows an electrical actuator of the control systems of Figures 1,3 or 4 mounted on a vehicle heater unit; and Figure 7 is a cross sectional view of the electric actuator shown in Figure 6.

Referring to Figures 1 and 2, there is shown a control system for deflecting a flap valve 10 of a vehicle heating and ventilating equipment from one to another of two predetermined positions. Such a flap valve is commonly used in vehicle heating and ventilating equipment to direct a flow of air from one outlet of the equipment to another.

The flap valve 10 is mounted for pivotal movement on a shaft between a first position in which the flap valve 10 lies adjacent a stop 12, and a second position in which the flap valve 10 lies adjacent a stop 13. An arm 15 is securely attached to one end of the shaft 11 and is pivotally coupled at 16 to a linearly-moveable recipricating actuating member 17 of a 12 volt D.C. miniature electric actuator 18 of a screw and nut type. The actuator 18 is described in greater detail with reference to Figure 7.

Energisation of the miniature actuator 18 is controlled by a manually-operable switching mechanism 19, suitably located on the dashboard of the vehicle, and a control circuit 21.

Referring in particular to Figure 2, the control circuit 21 generally comprises a timing circuit which is actuated by manually operating the switching mechanism 19 to supply power for a predetermined period of time to the 12 volt D.C. miniature electric actuator 18. The switching mechanism 19, besides controlling the actuation of the timing circuit 21, is also effective to control the direction of current supplied to the actuator 18, and this the direction of travel of the actuating member 17.In this respect, the switching mechanism 19 includes a pair of ganged switches 19a and 19b each of which has a contact member 23 that is moveable between two fixed contacts 24 and 25 such that, when the moveable contact members 23 are in engagement with their respective contacts 24, electric current passes through the electric motor of the actuator 18 in a first direction to cause the actuating member 17 to travel in a first direction, and when the moveable contact members 23 are in engagementwith their respective contacts 25, electric current passes through the motor in the opposite direction, thereby causing member 17 to move in the opposite direction.

The moveable contact member 23 of the switch 19a is connected via a diode 27 to a line 28 coupled to a source of positive potential, such as the positive terminal of the vehicle's battery. The moveable contact member 23 of the switching mechanism 1 9b is connected via a resistor 30 and the collector and emitter terminals of a switching transistor 31, to a line 32 coupled to a source of negative potential on the vehicle. The base of the transistor 31 is coupled, through a resistor, to the output pin number 3 of a linear l.C. timer 34, for example, an NE 555 or similar.

The input pin number 2 of the timer circuit 34 is connected to the line 28 via a resistor 36 and to the line 32 via an R-C circuit 37 and a moveable contact member 38 of the switching mechanism 19. The R-C circuit 37 has two branches each of which contains a capacitor 39 and a resistor 40 in parallel and a fixed contact member 41. The moveable contact member 38 of the switching mechanism 19 is coupled mechanically to the ganged contact members 19a and 19b such that when the members 19a and 19b are switched from one to the other of the fixed contacts 24 and 25, the movable contact member 38 moves from one of the fixed contacts 41 to engage with the other of the fixed contacts 41.

The timer circuit 34 operates to supply current to the base of the transistor 31 for a predetermined duration, thereby switching on the transistor 31 and energising the electric motor of the actuator 18 for a corresponding period of time. As previously mentioned, the direction of current flow through the actuator 18, and therefore the direction of movement of the member 17, is dependent upon the position of the moveable contact member 23 of the switching mechanism 19.

A pulse is generated by the R-C circuit 37 each time the switching mechanism 19 is operated. This pulse is passed to the input pin number 2 of the timer 34 and initiates the supply of current to the base of the transistor 31 from the output pin number 3, the current being maintained for a predetermined period of time to control the energisation of the actuator 18 as previously described. The duration of the period for which the timer circuit 34 supplies current from its output pin number 3 to the base of the transistor 31 is determined by the value of signals fed to input pin numbers 6 and 7. To this end, the input pin members 6 and 7 of the timer circuit 34 are connected through a variable resistor 43 and a fixed resistor 44 to the line 28, and through the capacitor 45 to the line 32.By adjusting the value of the variable resistor 43, the duration of the period for which current is supplied to the base of the transitor 31 is regulated to meet the particular requirements of the actuator 18.

In operation then, the switching mechanism 19, mounted on the vehicle dashboard, is manually operated to move the contacts 19a and 19b into engagement with the fixed contacts 24. At the same time, the moveable contact 38 is brought into engagement with one of the fixed contacts to provide a voltage spike at the input pin number 2 of the timer circuit 34. Upon receipt of this voltage spike, the timer circuit 34 is actuated and supplies a signal from its output pin number 3 to the base of the transistor 31 to switch the transistor 31 on and energise the electric motor of the actuator 18.

Energisation of the actuator's motor causes the actuating member 17 to be linearly displaced which in turn pivots the flap valve 10 about the shaft 11 from its position adjacent the stop 12. The period of time for which the servo motor 18 is energised is limited to the time taken for the flap valve 10 to be pivotted from its position adjacent the stop 12 to its position adjacent the stop 13 and this period of time is determined by the appropriate adjustment of the variable resistor 43.

To return the flap valve 10 to its original position adjacent the stop 12, the switching mechanism is operated in the opposite sense such that the moveable contacts 19a and 19b are moved back into engagement with the other of the fixed contacts 41.

The R-C circuit 37 and the timer circuit 34 then operate in the previously described manner to supply current to the motor of the actuator 18 only this time the direction of current through the motor is reversed by the switching mechanism 19 so that the member 17 is moved in the opposite direction and returns the flap valve 10 to its original position.

With reference to Figure 3, there is shown another form of control system for moving a flap valve 10 between two predetermined positions. In this control system, certain elements are identical with those shown in Figures 1 and 2, and, as such, have been designated with the same reference numerals.

The actuator 18 is supplied with power from the vehicle battery through a control circuit 50 which is operated by two push-button switches 51 and 52 mounted on the vehicle dashboard. Depression of the push-button switch 51 is effective to actuate the control circuit 51 and supply power along the lines 53 and 54 to the motor of the actuator 18 in a first direction so as to move the flap valve 10 to its second position, whilst depression of the pushbutton switch 52 is effective to supply current to the motor in the reverse direction so as to return the flap valve 10 from its second position back to its first position.

The control circuit 50 monitors electrical current to the actuator 18 and includes sensing means which senses the characteristic current rise in current level along the lines 53 and 53 that occurs upon motor stall when the flap valve 10 has reached the end of its permissible travel, that is, when the flap valve 10 is abutting against either the stop 12 or the stop 12 or the stop 13. The control circuit 50 responds to this characteristic current rise to inhibit further supply of current to the actuator 18, thereby de-energizing the actuator 18.

Referring now to Figures 4 and 5, there is shown a further form of control system for use in a vehicle heating and ventilating equipment. In this embodiment, a flap valve is moveable between two predetermined extreme positions and is also selectively operable to move to a position intermediate those two extreme positions. Such a flap valve is commonly provided in a vehicle heating and ventilating equipment for blending hot and cold streams of air to obtain an output stream of air having a desired temperature within the range determined by the temperatures of the hot and cold streams. The control system includes a pivotally-mounted flap valve 10 and an actuator 18 similarto those described with reference to Figures 1 and 2.The actuator 18 is energised by a control circuit, generally designated 60 (shown in greater detail in Figure 5), which includes a slider-type variable resistor 61 mounted on the dashboard ofthe vehicle. The control circuit 60 also includes a variable resistor 62 that is coupled to the flap valve 10 so as to provide a feedback signal indicative of the position of the flap valve 10. The control circuit 60 generally comprises a Wheatstone bridge circuit 65 and a differential amplifier circuit 66.

The Wheatstone bridge circuit 65 has four arms 67,68,69 and 70, the variable resistors 61 and 62 forming part of the arms 67 and 69 respectively, and is connected at the junctions between the arms 67 and 69, and 68 and 70 to a source of electrical potential, such as the vehicle battery, along the lines 71 and 72. The other two junctions of the Wheatstone bridge, that is, the junctions between the arms 67 and 68, and 69 and 70, are connected to a switching circuit 73 comprising the transistors 74,75,76 and 77. The switching circuit 73 responds to an imbalance between the arms 67 and 69 of the Wheatstone bridge to suply a signal along eitherthe output 80 or the output 81 in dependence upon whether the resistive value of the arm 67 is greater or lower than that of the arm 69.

The differential amplifier circuit 66 comprises a plurality of transistors 84 to 89 which are interconnected in a known manner to supply power from the lines 71 and 72 to the actuator 18.

The base of transistor 84 is connected to the output 80 of the switching circuit 73 so that, when a signal appears along the output 80, the transistor 84 is switched on. The transistor 84, in turn, switches transistors 85 and 86 which supply current from the line 72 though the electric motor of the actuator 18 to the return line 71.

In a similar manner the base of the transistor 89 is connected to the output 81 of the switching circuit 73 so that, when a signal appears along the output 81, the transitor 89 is switched on. The transistor 89, in turn, switches transistors 87 and 88 to supply current to the actuator 18, only this time the current flows through the actuator 18 in the reverse direction.

In operation, movement of the manually-operable variable resistor 61 causes an imbalance between the arms 67 and 69 of the Wheatstone bridge circuit 65 that results in a signal at either the output 80 or the output 81 of the circuit 65 according to whether the resistive value of the arm 67 is above or below the resistive value of the arm 69. The differential amplifier circuit 66 responds to the signal at output 80 or output 81 and supplies electric current to the actuator 18 in the appropriate direction. The actuator 18 operates to pivots the flap valve 10 until the resistive value of the variable resistor 62 is increased or decreased as the case may be to restore the arms 67 and 69 of the Wheatstone bridge 65 to a balanced condition, at which time the signal at the output 80 or 81 disappears and the actuator 18 is de-energised.

The control system shown in Figure 5 is calibrated such that positioning of the slider of the variable resistor 61 at its extreme positions will result in the flap valve 10 being positioned against the stops 12 and 13.

In mechanical control systems it is well known that the temperature of the air stream which has been blended from hot and cold air streams by a flap valve is not directly proportional to the extent of movement of the manually-operable lever controlling the flap valve. That is, the change of temperature of the blended air as a result of movement of the lever along its track from one extreme position to, say, half way along the track, does not correspond to the change of temperature of the blended air streams as a result of movement of the lever from half way along its track to its other extreme position. This phenomenon is attributed to the use of a flap valve for blending purposes but can be counteracted to a certain extent in the control system shown in Figures 4 and 5 by employing variable resistors 61 and 62 which have a non-uniform resistance characteristic.

In this way, the extend of movement of the flap 10 is not directly proportional to the extent of movement of the slider of the variable resistor 61 but varies in a non-uniform manner.

It is envisaged that one of the fixed-value resistors in the arm 67 of the Wheatstone bridge circuit 65 shown in Figure 5 may be replaced by a thermistor, which is located in, for example, the passengercarrying compartment of the vehicle, to maintain automatically the temperature of the air within the passenger-carrying compartment at a predetermined level which is set by the variable resistor 61.

It is also envisaged that the variable resistor 61 may be replaced by a resistor switch in which any one or more of a plurality of series-connected fixed-value resistors may be switched into the arm 67 of the Wheatstone bridge circuit 65 in order to move the flap valve 10 to discrete intermediate positions determined by the value of the fixed resistances.

The electronic circuit shown in Figure 5, apart from the variable resistances may be contained in a single integrated circuit.

Figure 6 of the accompanying drawings shows a typical installation of an actuator 18 on the side of a vehicle heater housing 100. The actuator 18 is mounted on a bracket 102 carried by the housing 100 with its actuating member 17 pivotaliy connected to the arm 15 secured to one end of the shaft 11 of the flap valve 10. The flap valve 10 in this particular installation is being used to control air flow through an outlet slot 101 in the heater housing 100.

The actuator 18 of the aforementioned arrangements will now be described with reference to Figure 7. The actuator 18 comprises a miniature 12 volt DC electric motor 110 and a reduction gear arrangement, generally designated 112, through which drive is transmitted to the actuating member 17, all of which are carried in a housing 111 of moulded glass-filled nylon or ABS plastics material.

The housing 111 comprises a first part 113 having a generally cylindrical recess 114 containing the motor 110, and a second part 115 secured to the part 113 by means of rivets (not shown) constituting a cover and defining with the part 113 a space in which the reduction gear arrangement is enclosed and into which the motor shaft protrudes.

An end wall 119 of the recess 114 defines a boss 120 that engages with and locates one end of the motor 110. The wall 119 also has apertures in which electrical terminals 121 of the motor are mounted.

The other end of the motor 110 is supported by a shoulder 122 on the cover 115 that extends around the motor hub.

The part 113 of the housing 111 includes a tubular portion 116 whose bore 117 is slightly tapered and supports an open-ended steel tube 118. The elongate actuating member 17, which is externally screw-threaded along a major portion of its length, is slidably mounted within the tube 118. The tube 118 projects out of the bore 117 into the space defined between the cover 115 and the part 113 and provides a bearing surface for the elongate actuating member 17. In the position shown in Figure 7, the member 17 is seen as extending completely therethrough, although in actual operation of the actuator the member 17 can be displaced with respect to the tube 118 such that it extends only part way through the tube.

Drive is transmitted from the motor 110 to the actuating member 17 through the reduction gear arrangement 112. This comprises a metal pinion gear 130 mounted on the motor shaft, an output drive gear 132 of glass-filled nylon material surrounding the member 17, and an intermediate gear 131,also of glass-filled nylon material, which is rotatably mounted on a spigot 135 formed integrally on the cover 115. the gear 131 has a first gearwheel 133 in meshing relationship with the pinion gear 130 and a second gear wheel 134, of smaller diameter, in meshing relationship with an externally-toothed part 136 of the drive gear 132.

The drive gear 132 has a cylindrical portion 137 constituting a hub which isjournalled in a correspondingly-shaped cylindrical aperture 138 in the cover 115 that is axially aligned with the bore 117 and through which the member 17 extends. An axial bore 139 extending through the drive gear 132 has a first portion 140 which is a push fit over the projecting end of the tube 118, with the tube 118 acting as a bearing surface for the gear 132, and a second portion 141 that is screw-threaded and engages with the external screw-thread on the actuating member 17.

A P.T.F.E. thrust washer 142 is disposed between respective radially extending surfaces of the cover 115 and the drive gear 132. Afurther P.T.F.E. thrust washer 143 is disposed around the bearing tube 118 between a radial end face of the drive gear 132 and a wall of the housing part 113, with the drive gear 132 captively retained between the two thrust washers 142 and 143 and prevented from axial movement.

Apertures, such as shown at 144, are provided in the housing 111 for mounting purposes.

The actuating member 17 is preferably made of glass-filled nylon, although if it is desired to increase the length of stroke of the actuating member 17 by increasing its length, the member 17 may be fornmed from stainless steel to provide additional strength. The screw-thread adjacent the coupling end of the actuating member 17 is removed to root diameter over a length longer than the bore portion 141 so as to prevent jamming should over-run of the actuating member 17 occur.

Upon energisation of the motor 110, the drive gear 132 is rotated, via the pinion gear 130 and intermediate gear 131, around the actuating member 17 whereby the member 17 is linearly displaced as a result of co-operation between its screw-thread and the internal screw-thread of the drive gear 132.

Reversal of the direction of electrical current supplied to the motor 110 results in linear displacement of the actuating member 17 in the opposite direction.

The end of the actuating member 17 may be operatively coupled to the flap valve mechanism of the aforementioned arrangements using any suitable means.

Claims (13)

1. A control system for controlling the position of a moveable element comprising an electricallyoperable actuator having output means which is to be connected on said moveable element and eiectrical circuit means for controlling operation of the said actuator and thereby the position of said moveable element, said actuator including a housing having a first part defining a recess in which an electric motor is disposed and a bore in which an elongate member comprising said output means is mounted for linear reciprocating movement, and a second part mounted on the first part defining therebetween a space into which the output shaft of said motor projects and having an aperture therein in axial alignment with said bore through which said elongate member extends, and reduction gearing disposed in said space including an input gear mounted on said motor output shaft and an output gearjournalled in the said aperture of said second partwhich surrounds said elongate member and which has an internal screw-thread that co-operates with an external screw-thread on said elongate member such that rotation of said output gear by said electric motor causes axial displacement of said elongate member within said bore, and wherein said electrical circuit means is arranged to control energisation of the electric motor so as to vary the axial displacement of the elongate member within said bore and thereby to control the positon of said moveable element.

2. A control system according to Claim 1, wherein a thrust washer is disposed between a radiallyextending surface of said output gear and a surface of said second part of the housing.

3. A control system according to Claim 2, wherein a further thrust washer is disposed between a second radially-extending surface of said output gear and a surface of said first part of the housing, the output gear being captively retained between said two thrust washers to inhibit axial movement thereof.

4. Acontrol system according to any one ofthe preceding Claims, wherein said actuator includes a tube disposed in said bore of the first part of the housing in which said elongate member is slidably mounted.

5. A control system according to Claim 4, wherein said tube extends out of said bore into an axially-extending recess in said output gear to act as a bearing for the output gear.

6. A control system according to any one of the preceding Claims, wherein said reduction gearing includes a gear intermediate said input and output gears which is journalled on a spigot formed integrally with said second part of said housing.

7. A control system according to any one of the preceding Claims, wherein said housing is of plastics material.

8. A control system according to any one of the preceding Claims, wherein said electrical circuit means includes a switching device and is arranged to energise said electric motor of said actuatorfora predetermined period of time in response to actuation of said switching device.

9. A control system according to any one of Claims 1 to 7, wherein said electrical circuit means includes a switching device which is operable to effect energisation of said electric motor of the actuator and means for monitoring electrical current supplied to the electric motor during its energisation and de-energising the motor in response to a predetermined level of electric current being reached.

Claims 1 to 7, wherein said electrical circuit means includes a switching device which is operable to effect energisation of said electric motor of the actuator and means for monitoring electrical current supplied to the electric motor during its energisation and de-energising the motor in response to a predetermined level of electric current being reached.

10. A control system according to any one of Claims 1 to 7, wherein said electrical circuit means includes a variable input device having a manuallyoperable element adjustable between two extreme positions and means for providing a signal indicative of the position of the elongate member of said actuator, wherein the electrical circuit means is arranged to control energisation of the electric motor of said actuator so as to position said elongate member in accordance with the position of said manually-operable element of the input device.

11. A control system substantially as hereinbefore described with reference to Figures 1,2,6 and 7 of the accompanying drawings.

12. A control system substantially as herein be fore described with reference to Figures 3,6 and 7 of the accompanying drawings.

13. A control system substantially as hereinbefore described with reference to Figures 4,5,6 and 7 of the accompanying drawings.