GB2281667A

GB2281667A - Fuel injector driver control circuit

Info

Publication number: GB2281667A
Application number: GB9417275A
Authority: GB
Inventors: Werner Fischer; Viktor Kahr
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1993-09-04
Filing date: 1994-08-26
Publication date: 1995-03-08
Anticipated expiration: 2014-08-26
Also published as: FR2709594A1; FR2709594B1; GB9417275D0; JPH0786030A; GB2281667B; DE4329981A1

Description

2281667 DRIVE CONTROL OF AN ELECTROMAGNETIC LOAD The present invention

relates to control means for and a method of controlling an electromagnetic load.

A control means and a method for such a purpose is described in, for example, DE-OS 29 05 900 (OS-A-4 327 692), which concerns control of, in particular, electromagnetic injection valves in an internal combustion engine.

In such control means the inductive load is fed from a voltage source by way of a transistor connected in series, which is drivable by a drive control. A desired rapid current decay during switching off of the transistor can be achieved by a Zener diode connected in parallel with the transistor or a correspondingly operated transistor with a Zener voltage, which is higher than the operating voltage at the instant of switching-off. it is a disadvantage, however, that the quenching voltage is dependent on the battery voltage. Since the switching-off time depends on the quenching voltage, different switching-off times result, which is disadvantageous in particular for control of the fuel quantity.

Moreover, the quenching voltage cannot be as small as desired, as the switching means may otherwise be switched through in the case of increased battery voltage.

There thus remains a need to be able to preset a defined quenching voltage in the drive control of an electromagnetic load.

2 According to a first aspect of the present invention there is provided control means for an electromagnetic load, comprising switching means connectible in series with such load, actuating means for actuating the switching means, quenching means and means for so driving the switching means during a switching-off operation thereof that in use a presettable voltage is present across the load during that operation.

According to a second aspect of the invention there is provided a method of controlling an electromagnetic load by way of switching means connectible in series with such load, actuating means for actuating the switching means and quenching means, the method comprising the step of so driving the switching means during a switching-off operation thereof that in use a presettable voltage is present across the load during that operation.

In control means embodying and a method exemplifying the invention the current quenching takes place by a constant quenching voltage, which is independent of battery voltage, across the electromagnetic load. Moreover, any desired value of quenching voltage can be selected.

An embodiment of the control means and example of the method of the present invention will now be more particularly described with reference to the accompanying drawings, in which:

Fig. 1 is a schematic block diagram of control means embodying the invention; Fig. 2 is a set of diagrams showing signals, plotted against time, in the control means; Fig. 3 is a schematic block diagram showing a first form of circuit arrangement in the control means; and Fig. 4 is a schematic block diagram showing a second form of circuit arrangement in the control means.

Referring now to the drawings there is shown in Fig. 1 a control device for a load 100, in particular an inductive load, which is connected in series with switching means 110 between ground and battery voltage Ubat The terminal which lies at battery voltage U bat is connected by way of a point 101 with a current source 120. A point 102 between the load and the switching means is similarly connected with the current source 120.

The switching means 110 is preferably a field effect transistor. The source terminal S in that case is preferably connected with ground and the drain terminal D by way of the point 102 with the load 100. The gate terminal G of the switching means is acted on by current from a control unit 130 supplied by way of a connecting line 115. In addition, the current source 120 is connected with the connecting line 115 at a point 122. The current source 120 acts by a current i on the gate G by way of this line.

The control device also includes control equipment 130, essentially consisting of a first current source 132 and a second current source 134. Alternatively, voltage sources can also be used in place of the current sources. These two current sources are connected with the connecting line by way of the common point 133.

When the first current source 132 is activated, a current, which charges the gate G to a preset voltage, flows by way of the connecting line 115, in which in turn leads to switching-through by the switching means 110. In this case, the load is acted on by voltage and thereby by current when the first current source 132 is active.

When the second current source 134 is activated, a current similarly flows by way of the connecting line 115, which draws the gate to ground potential. This has the effect that the switching means 110 opens and the load is separated irom ground.

The activation of the first current source 132 and the second current source 134 takes place in dependence on different signals from different sensors 145 and 140. These sensors detect different operating parameters such as, inter alia, vehicle accelerator pedal setting or rotational speed of an intermal combustion engine.

The operation of this device will now be explained by reference to Fig. 2 which shows temporal courses of individual voltage values and current values.

The gate voltage U 9 is entered as a function of time in the top diagram of Fig. 2, the drain vol tage U d is entered in the centre diagram and the current L through the load 100 is entered in the bottom diagram. The drain voltage U d corresponds to the potential at the point 102. The drain voltage lies above the voltage U m across the load by the battery voltage U bat The gate voltage U 9 corresponds to the potential at the gate of the switching means 110.

The first current source 132 is active up to the instant T 0 This means that the switching means is in its closed state and the maximum possible current I L flows through the load 100. At the instant tO, the first current source 132 is de-activated and the second current source 134 is activated. This means that the gate voltage falls as a function of time. The drain voltage Ud and the current k at first remain at their values.

At the instant tl, the gate voltage has fallen to the Miller p] ateau. From this instant tl onward, the resistance at the field effect transistor 110 rises. Thus, the drain voltage Ud similarly rises from the instant tl onward. The drain voltage U d rises until the quenching voltage UmS which falls across the load, has reached a preset value U z. At the same time, the current IL reduces.

At the instant t2, the voltage U m across the load is equal to the preset quenching voltage U z, From this instant onward, the current source 120 supplies a current to the gate of the switching means 110. This current has the-effect that the switching means no longer increases its resistance. This, in turn, has the effect that the drain voltage U d or the quenching voltage U. does not rise any further, but remains at a constant value. The energy stored in the load 110 is thus reduced by way of the switching means 110. During the quenching, the quenching voltage across the load U. is kept at the constant value U z, At the instant U, the current IL through the load has fallen so far that the quenching voltage U z can no longer be maintained.

The voltage across the load thereupon falls to 0 and the voltage across the drain falls to the battery voltage U bat' Furthermore, the gate is completely discharged by way of the current source 134 and the switching means 110 opens.

During the current quenching, the switching means operates not as a switch, but as a variable resistor. The load 100 is so switched off or the switching means 110 is so controlled that the voltage U.

dropping across the load 100 is constant. Since the switching-off time of the load is determined by the voltage U m dropping across the load, a constant switching-off time results for a constant voltage U M.

A defined switching-off time of the load can be achieved by the setting of a defined voltage Um across the load.

One form of the current source 120 is illustrated in more detail in Fig. 3. The point 101 is connected with the base of a transistor 250 by way of a resistor 230 and a point 235. The collector of the transistor 250 in turn is connected with the point 122. The point 102 is connected by way of the anode of a diode 210.

The cathode of the diode 210 is connected with the cathode of a Zener diode 220. The anode of the Zener diode 220 is connected with a point 245, from where it is connected by way of a resistor 240 with the point 235 and also directly with the emitter of the transistor 250.

The transistor 250, the resistors 230 and 240, the diode 210 and the Zener diode 220 function as a voltage-dependent current source. As soon as the voltage Um present across the load exceeds the Zener voltage U z of the Zener diode 220, a current flows from point 102 to point 245 and by way of the resistor 240. This is the case at the instant t2 according to Fig. 2. The voltage drop arising therefrom across the resistor 240 in turn has the effect that the transistor 250 switches through and a corresponding current flows to the junction 122. The voltage across the load during the switching-off operation can be set by suitable choice of the Zener diode.

The Zener diode 220 here operates as quenching equipment. The drive control of the switching means takes place in dependence on the current flowing through the quenching equipment. This means that the current source supplies no current as long as the voltage dropping across the load 100 is smaller than the Zener voltage U z of the Zener diode. When the voltage dropping across the load exceeds the Zener voltage, the current source supplies a current. This current supplied by the current source has the effect that the gate voltage U 9 remains at the attained value until the voltage dropping across the load falls below the Zener voltage.

Another form of current source, with a so-called current mirror, is shown in Fig. 4 The point 101 is connected with the collector of a transistor 300 by wzy of a point 301". The collector of the transistor 300 is connected with the base of the transistor 300 by way of a junction 303. The point 303 is at the same potential as the base of a further transistor 310. The emitter of the transistor 310 and the emitter of the transistor 300 are both is connected with the point 302, which in turn is connected with the anode of a Zener diode 220. The cathode of the Zener diode 220 is connected with the point 102, which lies at drain voltage. The collector of the transistor 310 is in turn connected with the point 122 of the connecting line.

The current source does not operate as long as the voltage U.

across the load 100 is smaller than the Zener voltage of the Zener diode 220. As soon as the Zener voltage is exceeded, a current flows from the point 302 by way of the transistor 300 to the point 301. This current causes a current in the transistor 310 from point 302 to point 122. The current in turn has the effect that the gate voltage does not fall any further. The voltage U m dropping across the load exceeds the Zener voltage of the Zener diode 220 at the instant t2.

Claims

1 Control means for an electromagnetic load, comprising switching means, connectible in series with such load, actuating means for actuating the switching means, quenching means and means for so driving the switching means during a switching-off operation thereof that in use a presettable voltage is present across the load during that operation.

2. Control means as claimed in claim 1, wherein the load is operable by vol tage f rom a battery and said presettable voltage is independent of the battery voltage.

3. Control means as claimed in claim 1 or claim 2, the means for driving comprising voltage-dependent current supply means.

4. Control means as claimed in claim 3, the supply means comprising a current mirror.

5. Control means as claimed in claim 3 or claim 4, the supply means comprising a Zener diode, a further diode and at least one resistive impedance which are connected in series and connectible in parallel with the load. c 6. Control means as claimed in claim 5, the means for driving E being arranged to drive the switching means starting from voltage drop across the at least one impedance.

9 7. Control means substantially as hereinbefore described with reference to the accompanying drawings.

8. A method of controlling an electromagnetic load by way of switching means connectible in. series with such load, actuating means for actuating the switching means and quenching means, the method comprising the step of so driving the switching means during a switchingoff operation thereof that in use a presettable voltage is present across the load during that operation.

9. A method as cl aimed in cl aim 8 and substanti a] I y as hereinbefore described with reference to the accompanying drawings.