Such an electrical component may be, for example, an injector for fuel injection into an internal combustion engine or another reactive component.

BACKGROUND Injectors which control the injection of fuel into internal combustion engines, for example diesel engines or directly injected petrol engines, are well known to the skilled person. Such an injector, which is connected to a fuel line and a fuel return line, consists essentially of a nozzle and a valve in which a coil in the form of an electromagnet can control the valve. The coil acts on an armature part which is fixed in the valve so that an electrical signal can control the valve. The valve, which opens and closes the fuel return line, is normally open so that the fuel can flow through the injector and back through the fuel return line without any pressure being built up. When the valve is closed, the entire fuel pressure will act on the nozzle which opens so that fuel can be injected into the cylinder. When the valve is opened again, the nozzle shuts off the fuel injection. Such an injector with a control is described in inter alia US 6076508.

An injection operation is brought about by a suitable control signal being sent to the coil which closes the valve. The control signal then holds the valve closed during the holding operation for as long as the

injection operation is to continue. Then, when the control signal is turned off, the valve is opened again. As more force is required to close the valve than is required to hold it closed, the amplitude of the control signal varies with time during an injection operation. The coil draws more current during the closing operation than during the holding operation. In order to close the valve rapidly and to overcome the force which holds the valve open, the control signal must on the one hand deliver a high current and on the other hand have a short rise time during the closing operation.

In order to comply with new, more stringent environmental requirements which demand reduced emissions and also to reduce fuel consumption, the injection operation of modern engines must be controlled more accurately than previously. This means that the valve and thus the electromagnet must be controlled more rapidly and precisely than previously.

In order to control an electromagnet rapidly, it is necessary for the drive to be capable of delivering a high current with as short a rise time as possible.

The problem with driving an electromagnet using a high current and a short rise time, that is to say with a steep flank, is that the drive signal generates great electromagnetic interference in the form of high- frequency radio interference. This interference can on the one hand disrupt the control electronics of the vehicle and moreover additional equipment installed in the vehicle, such as telephone, radio, communication radio etc. If the interference is strong, other vehicles or apparatus in the vicinity of the vehicle may also be affected.

DISCLOSURE OF THE INVENTION The object of the invention is therefore to produce an arrangement for driving an electrical component, for

example an injector, in a way which generates as little electromagnetic radiation as possible, to produce a system comprising an electrical component, for example an injector, which is driven in a way which generates as little electromagnetic radiation as possible, and to produce a method for driving an electrical component, for example an injector, in a way which generates as little electromagnetic radiation as possible.

The solution according to the invention for achieving this object is described in the characterizing part of patent claim 1 with regard to the arrangement, in the characterizing part of patent claim 5 with regard to the system and in the characterizing part of patent claim 10 with regard to the method. The other patent claims contain advantageous improvements and developments of the arrangement according to the invention (claims 2 to 4), the system according to the invention (claims 6 to 9) and the method according to the invention (claim 11).

By virtue of a first design of the arrangement according to the invention, an arrangement is provided for driving an electrical component by means of a balanced, symmetrical drive signal consisting of a first signal and a second signal, where the second signal is an inverted image of the first signal. This considerably reduces the radio interference generated.

In an advantageous first development of the arrangement according to the invention, the arrangement comprises means for, from an incoming control signal, creating a balanced, symmetrical output signal consisting of a first signal and a second signal, where the second signal is an inverted image of the first signal. The advantage of this is that the existing control signal can be used as an input signal for the arrangement.

In an advantageous second development of the arrangement according to the invention, the arrangement is adapted so as to deliver a drive signal with a rise time shorter than 10 microseconds/ampere. The purpose of this is for the drive signal to be capable of driving the electrical component sufficiently rapidly.

In an advantageous third development of the arrangement according to the invention, the arrangement is adapted so as to drive at least one injector for fuel injection into an engine.

By virtue of a first design of the system according to the invention, a system is provided, which drives an electrical component by means of a balanced, symmetrical drive signal consisting of a first signal and a second signal, where the second signal is an inverted image of the first signal. This considerably reduces the radio interference generated from the system.

In an advantageous first development of the system according to the invention, the system comprises means which create a balanced, symmetrical output signal from an incoming control signal. The advantage of this is that the existing control signal can be used as an input signal for the system.

In an advantageous second development of the system according to the invention, the electrical component included is capacitive or inductive. The advantage of this is that the system can comprise reactive components.

In an advantageous design of the second development of the system according to the invention, the electrical component included is a coil in an injector. The advantage of this is that radio interference generated by a fuel-injection system can be reduced considerably.

In an advantageous third development of the system according to the invention, the electrical component is electrically separated from the earth potential in the system. The advantage of this is that earth loops in the system can be avoided.

A method according to the invention for driving an electrical component comprises the step of driving the electrical component by means of two drive signals, where one drive signal is an inverted image of the other drive signal. The advantage of this method is that the electromagnetic radiation generated when an electrical component is driven can be reduced considerably.

In an advantageous development of the method according to the invention, the method comprises the step of, from an incoming control signal, creating two output signals, where one output signal is an inverted image of the other output signal. The advantage of this is that the existing control signal can be used as an input signal for the control unit which drives the electrical component.

BRIEF DESCRIPTION OF FIGURES The invention will be described in greater detail below with reference to illustrative embodiments shown in the accompanying drawings, in which FIG 1 shows a known fuel-injection system, and FIG 2 shows such a system according to the invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS The illustrative embodiments of the invention with developments described below are to be regarded only as examples and are not in any way to limit the protective scope of the patent claims.

In the examples of the invention described below, an electrical component can be any component which

generates interference when it is driven. Preferably, this means components which are to a greater or lesser extent reactive, that is to say which contain coils and/or capacitors, and which are driven by a relatively high current and/or signals with a short rise time, for example relays, contactors, solenoid valves, high- voltage lamps, piezo-components etc. In these examples, an injector for fuel injection into an internal combustion engine will be used as an example of such an electrical component.

An injector 6 for fuel injection into an engine 4 is normally connected to a control unit 5 by a two-pole cable 2,3 according to Fig. 1, which shows a known fuel-injection system 1. The positive pole 2 is used for the drive signal D, and the other pole 3 is connected to chassis earth. As an asymmetrical drive signal drives the injector 6, part of the signal will couple capacitively to the engine 4 via, for example, the parasitic capacitance cp 9 with a current icp. This gives rise to a common-mode current icM, which flows. through the engine 4 back to the control unit 5, for example through an earth connection 8. This current path gives rise to an undesirable earth loop. This earth loop, together with the common-mode current iCM, leads to the system generating electromagnetic interference, referred to here as radio interference.

The amplitude and the frequency content of the radio interference radiated, that is to say the electromagnetic interference, depend on many factors.

They are affected by inter alia the amplitude, shape and rise time of the drive signal, by its periodicity, by the parasitic capacitance between the injector and the engine block, by the length of the cables between the control unit and the injector, by the length of the earth loop, by the resistance of the earth connection etc.

One known way of seeking to limit this radio interference is to connect an earth connection 8 directly from the engine block to the control unit.

This may partly limit the interference in lower frequency bands, typically below 30 MHz, but high frequencies are not affected.

Another known way of limiting radio interference which is generated when an electrical component is driven is to screen the cable to the electrical component. In this case, the cable which connects the control unit to the injector would then be screened. Screening which is correctly carried out would partly limit the interference generated, but part of the signal would still couple to the engine block, and, because not only the cable functions as an antenna, screening of the cabling would not reduce the interference sufficiently.

Moreover, a connection with screen would require new, expensive connectors and injectors and furthermore expensive manufacture.

A first illustrative embodiment of the system according to the invention is shown in Fig. 2. A fuel-injection system 11 is shown, comprising a control unit 15 connected by a two-pole cable 12,13 to an injector 6 for fuel injection into an engine 4. The positive pole 12 is used for the positive drive signal D+, and the negative pole 13 is used for the negative drive signal D-. The control unit 15 comprises a control module 19 and a drive module 17, the drive module 17 containing two drive stages 18a and 18b. The control unit 15 is advantageously integrated into an existing engine control unit, although it is also possible for the control unit to consist of a separate unit.

The drive module 17 delivers two drive signals D+ and D-. This means that the injector 6 is driven by a balanced, symmetrical drive signal consisting of D+ and D-, D-being an inverted image of D+. As the drive

signal is symmetrical, a common-mode current icm will not arise, that is to say icM=0, and icp=0 and thus no signal is coupled through the parasitic capacitance cp 9. This means that, on the whole, no radio interference is generated.

A symmetrical drive signal can be produced in various ways. The input signal for the drive module 17 can, as in the example, be created in the control module 19 which is integrated into the control unit 15. This can take place by, for example, the input signal S creating two output signals S+ and S-by dividing S into two signals, where one signal is inverted. It is also possible to generate the two output signals S+ and S- directly in the control system, for example using a signal processor. The output signals S+ and S-are used as input signals for the drive stages 18a and 18b.

In order to minimize the interference as much as possible, it is advantageous for both the absolute value and the time characteristic of S+ and S-to be as alike as possible. For various reasons, it is difficult to avoid small differences in the signals, but the interference is reduced considerably even if the signals differ slightly in absolute value.

In order for it to be possible for the drive signals D+ and D-to drive the injector 6 optimally, it is important for the system to be adapted for rapid pulses. There must therefore not be any components in the signal chain which low-pass filter the signal too much, that is to say limit the rise time of the drive signal. For a typical drive signal, the voltage is, for example, 28 V, the maximum current is, for example, 8 A, and the rise time is, for example, a few microseconds.

In order for it to be possible to control an injector even more rapidly and precisely, the injector can

comprise two electric coils, one which opens the valve and one which closes the valve. It is then possible to control both the opening operation and the closing operation in an injection operation with great accuracy. With such an injector, where both higher currents and shorter rise times will be used, it is more important still to have a great reduction of radio interference, because the interference level increases with higher currents and more rapid operations.

In an advantageous development of the system according to the invention according to Fig. 2, the system therefore comprises a control system with two drive modules (17 in Fig. 2) per injector (6 in Fig. 2).

Another advantage of a system according to the invention is that the earth of the control electronics does not have to be coupled together with the engine block but can be electrically separated from the engine. It is a requirement in, for example, marine applications that components are electrically separated from earth, the purpose of this being to avoid galvanic corrosion.

In a first illustrative embodiment of the method according to the invention, the method comprises the step of driving an injector 6 by means of two drive signals, where one drive signal D-is an inverted image of the other drive signal D+. D+ is a signal with positive amplitude and a given time-dependence, and D- is a similar signal with negative amplitude and the same time-dependence. The drive signals D+ and D-are the signals from the drive stages 18a and 18b which drive the injector 6.

In a development of the method, the method comprises the step of an input signal S for the control unit creating two output signals S+ and S-, where the output signal S+ is an image of the input signal S and the

output signal S-is an inverted image of the input signal S. The output signals S+ and S-are used as input signals for the drive stages 18a and 18b.

The output signals S+ and S-can be produced in various ways. They can, as in the example, be created in the control module 19 which is integrated into the control unit 15. This can take place by, for example, the input signal S creating S+ and S-by dividing S into two signals, where one signal is inverted. It is also possible to generate the two signals S+ and S-directly in the control system, for example using a signal processor.

The invention is not to be regarded as being limited to the illustrative embodiments described above, but a number of further variants and modifications are conceivable within the scope of the following patent claims. The system and the method can also be used for, for example, systems which are not vehicle-based where it is desired to reduce radiated radio interference, where components which are at least partly reactive are driven by an asymmetrical drive signal, for example for contactors or other electrical components.