Electrical Control Systems

Abstract

An electrical control system, particularly for a choke cable on a vehicle, includes a pair of electromagnets, each of which when energized moves the choke cable back from its operative position to its inoperative position. The first electromagnet is energized when the engine temperature rises to a predetermined value, moves the choke cable back, and brings the second electromagnet into the circuit in series with a resistor which determines when the second electromagnet is energized. When the second electromagnet is energized, it moves the choke cable back further, and brings the first electromagnet back into the circuit in series with a resistor which determines the engine temperature at which the first electromagnet is energized again. This sequence continues until the choke cable returns to its rest position. Other parameters can be controlled in a similar way.

Description

This invention relates to electrical control systems for operating a pair of electromagnets alternately in response to variations of a parameter.

A system according to the invention comprises in combination a pair of supply lines, a resistor connected across the supply lines, the resistor having a value which varies with said parameter, a first electromagnet having one end connected to one of said supply lines and its other end connected to the movable contact of a multiposition switch having a plurality of operative fixed contacts, a plurality of preset resistors connecting said operative contacts to the other supply line, a second electromagnet having one end connected to one of the supply lines and its other end connected to the movable contact of a second multiposition switch having a plurality of operative fixed contacts, a plurality of preset resistors connecting the operative fixed contacts of the second switch to the other supply line, the arrangement of the electromagnets and switches being such that at any given time the resistor having a value dependent on the parameter is connected between the lines in parallel with a series combination including one of the preset resistors and one of the electromagnets, current flow through a preset resistor to an electromagnet being insufficient to energize the electromagnet, and the system further including means for energizing one of the electromagnets whenever the value of the resistor associated with the varying parameter reaches a value determined by the preset resistor in use at that moment, each of said switches having a plurality of nonoperative fixed contacts intermediate the operative fixed contacts, and the arrangement being such that when either electromagnet is energized, both switches are moved onto their next fixed contact, the circuit to the energized electromagnet is broken, and the switch associated with the other electromagnet moves onto an operative fixed contact to connect a further preset resistor in series with the said other electromagnet between the supply lines.

The accompanying drawing is a circuit diagram illustrating one example of the invention.

Referring to the drawing, the battery 10 of a road vehicle has its negative terminal connected to an earth supply line 12, and its positive terminal connected through a switch 13 which is closed only when the voltage regulator of the vehicle is operating, and resistors 11, 14 in series with the switch 13, to a supply line 15, the voltage between the lines 15 and 12 being stabilized by a Zener diode 16, connected between the junction of the resistors 11, 14 and the line 12. The arrangement further includes a first rotary or other multiposition switch having a movable contact 17 which is movable in use sequentially over fixed contacts 22, 21, 20, 19, 18 in that order. The contacts 18, 20, 22 are operative fixed contacts, the contacts 18 and 20 being connected respectively to one end of each of two preset resistors 23, 24 the other ends of these resistors being connected through a diode 51 to the line 15. The contact 22 is connected to a supply line 25 connected to the positive battery terminal through the switch 13 and the contacts 19 and 21 are nonoperative fixed contacts. The movable contact 17 is connected to the line 12 through an electromagnet 28.

A second rotary or other multiposition switch is also provided having a movable contact 29 which is movable in use sequentially over fixed contacts 34, 33, 32, 31, 30 in that order. The contacts 30, 32 and 34 are nonoperative, but the contacts 31 and 33 are operative and are connected through resistors 35 and 36 respectively to the cathode of the diode 51. The movable contact 29 is connected to the line 12 through a second electromagnet 37.

The line 15 is connected through a resistor 26 to the base of an NPN-transistor 38, having its base connected through a variable resistor 39 and a thermistor 52 in parallel to the line 12, its emitter connected to the line 12 and its collector connected through a resistor 41 to the line 25. The collector of the transistors 38 is further connected through a diode 42 to the gate of a thyristor 43, the anode of which is connected to the line 25, the gate of which is connected through a resistor 53 to the line 12, and the cathode of which is connected through diodes 44, 45, 46 and 47 respectively to the contacts 18, 20, 31 and 33. Finally, a resistor 27 having a value determined by some variable parameter is connected across the lines 15, 12.

Although of course the arrangement can be used for a variety of purposes, the specific example described is for use in a vehicle having an automatic choke control. The choke is moved to its operative position manually, but is returned to its nonoperative position with increasing engine temperature by the electromagnets 28 and 37, which require to be energized in turn. For the purposes of the present description, all that is required to be known is that the electromagnets 28 and 37 are to be energized alternately, and that the resistor 27 is sensitive to engine temperature, and has a sharply decreasing resistance with increasing temperature. Typically a resistor is used having a resistance of 2,300 ohms at minus 5.degree. C., falling to 175 ohms at 55.degree. C.

In use, when the choke knob is pulled out, the contacts 29 and 17 are moved into engagement with the contacts 34 and 22 respectively. When the engine is started, then once the speed of the generator reaches a predetermined value, the voltage regulator operates and closes the contact 13. The electromagnet 28 is now energized by way of the contacts 22, 17, energization of the electromagnet 28 serving to move the choke cable back towards its inoperative position, but in addition moving the contact 17 onto the contact 21 and the contact 29 onto the contact 33. The circuit to the electromagnet 28 is now broken, and the electromagnet 37 is not energized, because the current flowing in the electromagnet 37 by way of the resistors 11, 14, the diode 51 and the resistor 36 is insufficient to energize the electromagnet 37. However, when the temperature sensed by the resistor 27 rises to a predetermined value, then the value of the resistor 27 will fall to a level at which the transistor 38 turns off, and current flows by way of the resistor 41 and diode 42 to turn on the thyristor 43. Current can now flow through the diode 47 to energize the electromagnet 37, which moves the choke cable further back towards its inoperative position, and in addition moves the contact 29 onto the contact 32 and the contact 17 onto the contact 20. The circuit to the electromagnet 37 is now broken, and the electromagnet 28 is not energized because current is flowing to it only through the paths 11, 14, 51 and 24. At this stage the thyristor 43 is again off, because its circuit was broken upon movement of the contact 29 from the contact 33.

When the engine temperature rises further, the thyristor 43 is turned on again and the electromagnet 28 is energized by way of the diode 45. The contacts 17 and 29 now step onto the contacts 19 and 35 respectively, and the sequence continues with the electromagnet 37 being energized by way of the diode 46 when the engine temperature has risen further, whereupon the contacts 17 and 29 step to the position shown. Finally, the electromagnet 28 is energized by way of the diode 44, at which point the choke cable is in its inoperative position and the contacts 17 and 29 are stepped to their final off position.

It will be appreciated that the engine temperatures at which the choke cable is moved back step by step are determined by suitable choice of the resistors 23, 24 35 and 36.

The thermistor 52 caters for changes in ambient temperature, and it will be appreciated that the overall effect of the circuit is to return the choke gradually to its inoperative position as the temperature of the engine increases.

It will be appreciated that the circuit can be used to control other arrangements in response to variation of a parameter.

Claims

Having thus described my invention what I claim as new and desire to secure by Letters patent is:

1. An electrical control system for operating a pair of electromagnets alternately in response to variations of a parameter, comprising in combination a pair of supply lines, a resistor connected across the supply lines, the resistor having a value which varies with said parameter, a first electromagnet having one end connected to one of said supply lines and its other end connected to the movable contact of a multiposition switch having a plurality of operative fixed contacts, a plurality of preset resistors connecting said operative contacts to the other supply line, a second electromagnet having one end connected to one of the supply lines and its other end connected to the movable contact of a second multiposition switch having a plurality of operative fixed contacts, a plurality of preset resistors connecting the operative fixed contacts of the second switch to the other supply line, the arrangement of the electromagnets and switches being such that at any given time the resistor having a value dependent on the parameter is connected between the lines in parallel with a series combination including one of the preset resistors and one of the electromagnets, current flow through a preset resistor to an electromagnet, being insufficient to energize the electromagnet, and the system further including means for energizing one of the electromagnets whenever the value of the resistor associated with the varying parameter reaches a value determined by the preset resistor in use at that moment, each of said switches having a plurality of nonoperative fixed contacts intermediate the operative fixed contacts, and the arrangement being such that when either electromagnet is energized, both switches are moved onto their next fixed contact, the circuit to the energized electromagnet is broken, and the switch associated with the other electromagnet moves onto an operative fixed contact to connect a further preset resistor in series with the said other electromagnet between the supply lines.