GB2193589A

GB2193589A - Electric switching circuit

Info

Publication number: GB2193589A
Application number: GB08619243A
Authority: GB
Inventors: Gary Chris Fulks
Original assignee: Delco Chassis Overseas Corp
Current assignee: Delco Chassis Overseas Corp
Priority date: 1986-08-06
Filing date: 1986-08-06
Publication date: 1988-02-10
Anticipated expiration: 2006-08-06
Also published as: GB8619243D0; GB2193589B

Abstract

An electric switching circuit comprises: an electronic control unit (1) having an input terminal (2) and connected to electric apparatus (7) to be actuated; a first switch (3) connected between the input terminal and a line at a first predetermined voltage level; and a second switch (4) connected between the input terminal and a line (5) at a second predetermined voltage level (B+) which is different from the first predetermined voltage level; the electronic control unit monitoring an input signal at the input terminal to determine if the first switch is closed, or if the second switch is closed, or if neither switch is closed, and actuating the electric apparatus in accordance with the monitored voltage level. <IMAGE>

Description

SPECIFICATION Electric switching circuit This invention relates to an electric switching circuit, and in particular, a tristate switching circuit. Such an electric switching circuit has particular, though not exclusive, application in motor vehicles, and can be used for controlling the switching of wiper motors, central door locking motors, or other electric motors or apparatus.

In a known arrangement, a switch is connected between an electronic control unit (ECU) and ground. An electric motor or other electric apparatus is connected to the ECU.

Closing or opening of the switch actuates the electric motor or other electric apparatus. This arrangement has the disadvantage that a separate electric wire is required for each switched command (for example, on a wiper motor, a separate electric wire is required for fast wipe, normal wipe, pulsed wipe, etc.), and hence requires the use of a considerable amount of electric wire in a motor vehicle. In another known arrangement, usually referred to as voltage level multiplexing, a number of resistors are connected in series between the ECU and ground, with a separate switch connected between each junction of two adjacent resistors and ground. Closing different switches results in different voltage levels being received by the ECU, which then actuates the electric apparatus in accordance with, and dependent on, the voltage level monitored.Whilst this arrangement reduces the amount of electric wire required (to a single electric wire connected between the resistors and the ECU), it is still costly because of the number of resistors required. This arrangement is also disliked by motor vehicle manufacturers because of the need to incorporate large numbers of resistors in the steering column of the motor vehicle.

The object of the present invention is to overcome the disadvantages of the above mentioned known arrangements.

An electric switching circuit in accordance with the present invention comprises an electronic control unit having an input terminal, the electronic control unit being connected to electric apparatus to be actuated; a first switch connected between the input terminal and a line at a first predetermined voltage level; and a second switch connected between the input terminal and a line at a second predetermined voltage level which is different from the first predetermined voltage level, the electronic control unit monitoring an input signal at the input terminal to determine if the first switch is closed, or if the second switch is closed, or if neither switch is closed, and actuating the electric apparatus in accordance with the monitored voltage level.

Preferably the first predetermined voltage level is ground.

In the present invention, a single electric wire (connected between a common terminal of the first and second switches and the input terminal) provides a choice of three commands, and removes the need for a large number of resistors. By doubling up this arrangement, the present invention can provide a choice of nine commands for only two electric wires.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a simplified diagram of an electric switching circuit in accordance with the present invention; Figure 2 is a diagram of an alternative embodiment of an electric switching circuit in accordance with the invention; Figures 3A to 3E are voltage waveforms on the sense and enable lines and at the input terminal of the electric switching circuit of Figure 2; and Figure 4 is a flow diagram used in a modified arrangement of the electric switching circuit of Figure 2.

Referring to Figure 1, the electric switching circuit comprises an electronic control unit (ECU) 1 having an input terminal 2; a first switch 3 connected between the input terminal and a first predetermined voltage level of ground; and a second switch 4 connected between the input terminal and a line 5 at a second predetermined voltage level of B+. A single electric wire 6 is connected between the input terminal 2 and the first and second switches 3,4. Electric apparatus 7 is connected to the ECU 1 and is actuated in accordance with an input signal monitored at the input terminal 2 by the ECU.The input signal at the input terminal 2 is dependent on the state of the first and second switches 3,4, and can have an open circuit configuration (when the first and second switches 3,4 are open); or a short to B+ configuration (first switch 3 is open, second switch 4 is closed); or a short to ground configuration (first switch 3 is closed, second switch 4 is open). As can be seen from this arrangement, the input signal has one of three configurations, thereby providing a choice of three commands for a single electric wire 6.

By providing a second input terminal 8 on the ECU 1 which is connected to a similar single electric wire 9 and switch 10,11 arrangement, the ECU can be arranged to monitor the input signals at each input terminal 2,8 thereby providing a choice of up to nine commands. For example, whilst the input terminal 2 has an input signal indicating an open Circuit configuration, input terminal 8 may have an input signal indicating any one of three configurations, and so on to provide a total choice of nine commands.

The present invention will now be described with reference to Figure 2, which for the sake of simplicity shows only an arrangement for three commands. In the arrangement shown in Figure 2, an ECU 20 comprises a tristate buffer 21 having a sense line 22 and an enable line 23; a Schmitt trigger 24; and two flipflops 25,26 having Q outputs (Q1 and Q2 respectively). The D-inputs of the flip-flops 25,26 are connected to the output of the Schmitt trigger 24, and the clock inputs of the flip-flops are connected to the sense line 22, with the clock input to flip-flop 26 being inverted by an inverter 27. Square wave pulse signals are provided to the sense line 22 and the enable line 23 by any suitable means well known in the art (not shown). The ECU 20 has an input terminal 28.The Schmitt trigger 24 gives more precise switching signals and helps to filter out any unwanted or transient signals.

The electric switching circuit shown in Figure 2 also includes a two-way switch 29, which is connectable to ground (first switch), or is connectable (second switch) to a line 30 at a voltage level of B+, or is connectable to neither. Connected between the input terminal 28 and ground is a capacitor 31, with a resistor 32 connected between the input terminal and the two-way switch 29.

In this arrangement a sense signal which is a slow square wave signal (Figure 3A) of approximately 10Hz is transmitted to the input of the tristate buffer 21 on the sense line 22.

For ease of understanding, the sense signal is taken to have an upper voltage Jevel of 1 and a lower voltage level of 0. An enable signal (Figure 3B) is transmitted to the tristate buffer 21 on the enable line 23. The pulse length TE of the enable signal is shorter than the pulse length Ts of the sense signal, and a pulse of the enable signal is transmitted at each edge of the sense signal. If the two-way switch 29 is connected to neither ground nor line 30, the input signal at input terminal 28 follows the sense signal as shown in Figure 3C. In this configuration, when the sense signal is at voltage level 1, the clock input to flip-flop 25 is at voltage level 1, and the clock input to flip-flop 26 is at voltage level 0. The D-inputs to both flip-flops 25,26 are at voltage level 1.

As a consequence, output Q1 is at voltage level 1 and output Q2 is at voltage level 0.

Similarly, when the sense signal is at voltage level 0, the D-inputs to both flip-flops 25,26 and the clock input to flip-flop 25 are all at voltage level 0, and the clock input to flip-flop 26 is at voltage level 1. The output 0, therefore remains at voltage level 1, and output Q2 remains at voltage level 0.

If the two-way switch 29 is connected to line 30 at B+, the input signal at the input terminal 28 will be predominently high, but will go low when the enable signal goes high and when the sense signal goes low. The input signal will stay low whilst the enable signal is high, during which time the capacitor 31 charges through the resistor 32 At the end of the high of the enable signal the tristate buffer 21 is disabled, the capacitor 31 discharges, and the input signal returns to high as shown in Figure 3D. In this configuration, the outputs Q1,Q2 of the flip-flops 25,26 both remain at voltage level 1.

Similarly, if the two-way switch 29 is connected to ground, the input signal at the input terminal 28 remains predominently low, but goes high when the enable signal and the sense signal both go high, during which time the capacitor 31 is charged. When the enable signal goes low, the tristate buffer 21 is disabled, the capacitor 31 discharges, and the input signal returns to low as shown in Figure 3E. In this configuration, the outputs Qr,Q2 of the flip-flops 25,26 both remain at voltage level 0.

By sensing the voltage levels of the outputs 01,Q2 an indication of the position of the twoway switch 29 can be determined. Where output Q, is at voltage level 1 and output Q2 is at voltage level 0, an open circuit at the two-way switch 29 is indicated. Where both outputs Q1,Q2 are at voltage level 1, this indicates that the two-way switch 29 is connected to line 30 at B+. Where both outputs Q"Q2 are at voltage level 0, the two-way switch 29 is connected to ground. Remaining circuitry (not shown, but which is well known to those skilled in the art) in the ECU 20 monitors the voltage levels of the outputs Qa,Q2 and actuates electric apparatus (not shown) in accordance with the voltage levels monitored at the outputs Q1,Q2.

.By varying the value of the resistor 32 and/or the capacitor 31 and/or the values of Ts and TE, the response of the electric switching circuit can be varied to meet the required needs.

In an further embodiment, the electric switching circuit shown in Figure 2 can be modified by replacing the flip-flops 25,26, the tristate buffer 21, and the Schmitt trigger 24 by a programmable means (not shown) such as a microprocessor. The programmable means generates the sense and enable signals and monitors the input signal at the input terminal 28. From this information, the programmable means then generates the voltage levels at the outputs Q1 and 02. The voltage waveforms are substantially the same as those shown in Figure 3. The operation of the programmable means is in accordance with the flow diagram shown in Figure 4.

In the flow diagram shown in Figure 4, the program starts at a step 40. The program then proceeds to a decision point 41 where the voltage level of the sense signal is monitored. If the voltage level is 1, the program proceeds via a step 42 (where the sense signal is reset to voltage level 0) to a decision point 43 where the voltage level of the input signal is monitored. If the voltage level of the input signal is 0, the program proceeds to a step 44 where the voltage level at the output Q2 is set at 0. If the voltage level of the input signal is at 1, the program proceeds to a step 45 where the voltage level at the output Q2 is set at 1.If at decision point 41 the voltage level of the sense signal is at 1, the program proceeds to a step 46 where the sense signal is reset to voltage level 0, and then to a decision point 47 where the voltage level of the input signal is monitored. If the voltage level of the input signal is at 0, the program proceeds to a step 48 where the voltage level of the output Q1 is set at 0. If the voltage level of the input signal is at 1, the program proceeds to step 49 where the voltage level of the output Q, is set at 1.

From step 44 or step 45 or step 48 or step 49 the program proceeds to a step 50 where the enable signal is set at voltage level 1, and then to a decision point 51 where the enable signal is monitored for a predetermined period of time (the time of a pulse length TE as detailed above). The program then proceeds to a step 52 where the enable signal is reset to voltage level 0, and then to a decision point 53 where the sense signal is monitored for a predetermined period of time (the time of a pulse length Ts as detailed above), at the end of which the program returns to decision point 41.

It will be apparent that the voltage levels at the outputs Q1 and Q2 are, in this case, exactly the same as those in the arrangement shown in Figure 2 for the same configuration of the two-way switch 29.

The present invention has several advantages over the previously known arrangements. Apart from providing an electric switching circuit with reduced resistors and electric wires for increased switch commands, the present invention provides control over parasytic resistance; control over quiescent currents; and inherent protection against input transients (which can, amongst other factors, be generated by the debounce function of the plungers of the switches). Further, where the present invention is used in association with the cental door locking system of a motor vehicle, it is no longer necessary to provide a continuous current through the circuitry associated with the system as the present invention can operate using a pulsed input.

Claims

1. An electric switching circuit comprising an electronic control unit having an input terminal, the electronic control unit being connected to electric apparatus to be actuated; a first switch connected between the input terminal and a line at a first predetermined voltage level; and a second switch connected between the input terminal and a line at a second predetermined voltage level which is different from the first predetermined voltage level, the electronic control unit monitoring an input signal at the input terminal to determine if the first switch is closed, or if the second switch is closed, or if neither switch is closed, and actuating the electric apparatus in accordance with the monitored voltage level.

2. An electric switching circuit according to Claim 1, wherein the first predetermined voltage is ground.

3. An electric switching circuit according to Claim 2, wherein the electric switching circuit includes a resistor connected between the input terminal and each switch, and a capacitor connected between the input terminal and ground.

4. An electric switching circuit according to Claim 3, wherein the electronic control unit comprises a tristate buffer having a sense input, an enable input, and an output connected to the input terminal; a Schmitt trigger having an input connected to the input terminal; two flip-flops having D-inputs connected to the output of the Scmitt trigger, clock inputs connects to the sense input of the tristate buffer, and Q-outputs; an inverter connected between one of the clock inputs and the sense input; and circuitry which monitors the voltage level of the Q-outputs of each flip-flop and actuates the electric apparatus in accordance with the voltage levels monitored.

5. An electric switching circuit according to Claim 3, wherein the electronic control unit comprises a programmable means which monitors the input signal at the input terminal and produces two output signals having one or the other of two voltage levels, the output signals being dependent on the input signal monitored, and circuitry which monitors the voltage levels of the output signals and actuates the electric apparatus in accordance with the voltage levels monitored.

6. An electric switching circuit substantially as hereinbefore described with reference to and as shown in Figure 1 of the accompanying drawings.

7. An electric switching circuit substantially as hereinbefore described with reference to and as shown in Figures 2 and 3 of the accompanying drawings.

8. An electric switching circuit substantially as hereinbefore described with reference to and as shown in Figure 4 of the accompanying drawings.