DE102011003737A1 - Method for operating final state transistor for controlling injector in combustion engine, involves providing voltage for switching final state transistor by bootstrap-switching part with bootstrap-condenser - Google Patents

Abstract

The method involves providing a voltage for switching a final state transistor (10) by a bootstrap-switching part (150) with a bootstrap-condenser (151). Another voltage is applied as charging voltage for the bootstrap-condenser. The latter voltage serves as the bootstrap-switching part in the combustion engine for supplying other components. An independent claim is also included for a circuit for operating a final state transistor for controlling an injector in a combustion engine.

Description

The present invention relates to a method for operating an output stage transistor for driving an injector in an internal combustion engine, a corresponding circuit and an engine control unit.

State of the art

In internal combustion engines, a number of final stage transistors (FET) are usually used as switches in the prior art for the purpose of driving an injector, for example a solenoid or piezoinjector. Usually this is a so-called high-side switch for connecting the injector to the on-board voltage, a so-called low-side switch for connecting the injector to ground and a so-called booster switch for connecting the injector to the so-called booster voltage, which for fast switching of the injector is used. In principle, such a circuit is in 1 of the DE 100 07 691 B4 disclosed.

The control of the transistors, as used in diesel common rail (CR) or gasoline direct injection power amplifiers (BDE), is relatively expensive. For switching through a bootstrap principle is used, in which a bootstrap capacitor is charged by means of a charge pump (charge pump) to a voltage which is about 8.5 V above the source voltage of the transistor.

Capacitive charge-pump circuits are known which generate a higher voltage. This voltage is used to recharge the bootstrap capacitors. The bootstrap principle requires clocked operation in these output stages, since otherwise the bootstrap capacitor discharges inadmissibly during activation, which leads to destruction of the output stage. In particular, the holding phase is critical, sometimes even switching off the power amplifier is necessary. For this cycle operation complex hardware and software functions are to be provided in the control unit.

It is desirable to simplify the driving of the final stage transistors.

Disclosure of the invention

According to the invention, a method for operating an output stage transistor for driving an injector in an internal combustion engine having the features of patent claim 1 is proposed. A circuit according to the invention is designed so that it can be operated according to the invention. An inventive engine control unit has a circuit according to the invention. Advantageous embodiments are the subject of the dependent claims and the following description.

Advantages of the invention

The invention provides a particularly simple way to switch power transistors by means of a bootstrap principle. In particular, in a BDE or CR engine control unit voltages are present anyway, which are suitable for charging a bootstrap capacitor. Moreover, these voltages are essentially permanently available, using the example of the booster voltage, so that no clocked operation is necessary any more. The circuit and control effort required for a cycle operation in the prior art can be saved. Furthermore, can be dispensed with the charge pump. Overall, there is a cost savings. The invention also allows a permanent turn on in the hold phase. It comes to an overall improvement of the power level or power amplifier. The circuit is simpler and intrinsically safe, d. H. Failure does not result in damage or destruction of components.

The invention provides a simplified, clearer circuit topology. The failure rate is reduced as hardware and software components are eliminated. In particular, the complex software solution for safe control in the prior art is no longer needed. The circuit according to the invention has only a very low power loss, since the connection of the bootstrap capacitor with the supply voltage can be made very high impedance. The Schaldung is very easy to dimension, since essentially only leakage, Umladeströme and leakage currents must be compensated.

The emergency function is improved because no central driver supply voltage is needed anymore.

When using the booster voltage as the supply voltage, the conduction paths remain short, as this is present at the booster switch. The booster voltage is in a common rail injection system in a car or truck, for example, to the 50 V, which is well above the on-board voltage of conventional 12-14 V or 24 V-28 V and therefore as a supply voltage for a bootstrap capacitor easily enough.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained not only in the respectively specified Combination, but also in other combinations or alone, without departing from the scope of the present invention.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described in detail below with reference to the drawing.

Brief description of the drawings

1 shows a known circuit for controlling an injector of an internal combustion engine.

2 shows a preferred embodiment of a circuit according to the invention for controlling an injector of an internal combustion engine.

In 1 a known circuit for controlling an injector of an internal combustion engine is shown like a circuit diagram and a total of 100 designated. The circuit in 1 is used to operate an output stage transistor 10 for driving an injector 20 in an internal combustion engine. The final stage transistor 10 is here as a MOSFET, here specifically designed as a self-locking n-channel MOSFET, and connected as a high-side switch. At the injector 20 it may, for example, be a solenoid or piezo injector for a BDE or CR engine. To drive the injector, the MOSFET 10 switched low impedance and so the injector connected to the on-board voltage UBatt. This is done by applying a voltage at the gate G, which is about 8.5 V more positive than at the source S.

For this purpose, the circuit has 100 via a bootstrap circuit part 150 that by a charge pump 170 is fed.

The bootstrap circuit part 150 essentially has a bootstrap capacitor 151 and a circuit arrangement 152 , The charge pump 170 is conventionally designed and provides an output voltage VLSS, which in the present example is approximately 8.5 V, around the bootstrap capacitor 151 charge.

A circuit arrangement 171 , For example, a push-pull output stage, is periodically switched between the switching states and charges a pump capacitor 172 over a diode 173 with the supply voltage on. The switching state of the push-pull output stage 171 changed, are the supply voltage and the voltage at the pump capacitor 172 in series and charge an output capacitor 175 over a diode 174 to almost twice the supply voltage. The bootstrap capacitor 151 is when the switch is closed 153 over a diode 176 with the voltage of the output capacitor 175 provided.

To turn on the power transistor 10 become the switch 153 opened and the high-side switch of the circuit 152 switched on. During power-up, the bootstrap capacitor becomes 151 slowly via a gate-source resistor 154 discharged. The final stage transistor 10 may therefore remain switched on only as long as a sufficiently high voltage at the bootstrap capacitor 151 pending.

In 2 is a preferred embodiment of a circuit according to the invention for controlling the injector 20 schematics shown and total with 200 designated. Elements of the circuit in 2 that made them look 1 correspond, are provided with the same reference numerals.

The circuit 200 is different from the circuit 100 essentially by charging the bootstrap capacitor 151 no charge pump, but an already existing voltage is used. In principle any voltage which is sufficiently above the source voltage of the transistor to be switched in order to switch it can be used as the permanent charging voltage. Accordingly, in the case of the MOSFETs described here, voltages which are at least one turn-on voltage above the source voltage (= UBatt) are suitable.

In the context of the invention it has been recognized that such voltages are often already generated in engine control units and used for other purposes. In the embodiment according to 2 For example, it will charge the bootstrap capacitor 151 The so-called booster voltage U _Boost used, which is normally used to quickly open the injector 20 serves and of a so-called booster capacitor 270 is delivered. The booster capacitor 270 is, for example, charged by a DC / DC converter to about 48 V.

By saving the charge pump and simplifying the control, d. H. Elimination of clocking, the circuit is much easier and cheaper. Only a few passive components, such. As resistors, diodes, etc. should be supplemented to optimize the circuit by means of the booster voltage.

The bootstrap capacitor 151 off circuit 200 is when the power amplifier transistor is turned off 10 over the closed switch 153 loaded. When the power amplifier transistor is switched on 10 , open switch 153 and through-connected high-side switch 152 becomes the bootstrap capacitor 151 continue from the booster voltage of the capacitor 270 provided. The circuit breaker 10 can stay on permanently.

Although the invention has been described using the example of a high-side switch for connecting the injector to the on-board voltage, it is in principle suitable for switching any power transistors for driving an injector, in particular also for the low-side switch for connecting the injector to ground and the booster switch for connecting the injector to the booster voltage. The injector itself is not part of a circuit according to the invention.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10007691 B4 [0002]

Claims (10)

Method for operating an output stage transistor ( 10 ) for driving an injector ( 20 ) in an internal combustion engine, wherein a first voltage for switching the output stage transistor ( 10 ) from a bootstrap circuit part ( 151 ) with a bootstrap capacitor ( 151 ), wherein as charge voltage for the bootstrap capacitor ( 151 ) a second voltage (U _Boost ) is used, which is also used to supply other components ( 20 ) as the bootstrap circuit part ( 150 ) is used in the internal combustion engine. Method according to claim 1, wherein for switching the output stage transistor ( 10 ) from the bootstrap circuit part ( 151 ) provided first voltage permanently to the output stage transistor ( 10 ) is created. Method according to claim 1 or 2, wherein as the second voltage a booster voltage (U _boost ) for the injector ( 20 ) is used. Method according to one of the preceding claims, wherein the second voltage (U _Boost ) of a capacitor ( 270 ) which is charged by means of a boost converter or a DC / DC converter. Method according to one of the preceding claims, wherein the second voltage (U _Boost ) is not from a charge pump ( 170 ) is produced. Method according to one of the preceding claims, wherein as the output stage transistor ( 10 ), a self-blocking n-channel MOSFET is used and the first voltage is the gate-source voltage. Circuit ( 200 ) for operating an output stage transistor ( 10 ) for driving an injector ( 20 ) in an internal combustion engine, comprising a bootstrap circuit part ( 150 ) with a bootstrap capacitor ( 151 ) for generating a first voltage for switching the output stage transistor ( 10 ) and a charging circuit ( 270 ) for generating a second voltage (U _Boost ) for charging the bootstrap capacitor ( 151 ), the charging circuit also being used to supply other components ( 20 ) as the bootstrap circuit part ( 150 ) is used in the internal combustion engine. Circuit ( 200 ) according to claim 7, wherein the charging circuit ( 270 ) for generating a booster voltage (U _boost ) for the injector ( 20 ) serves. Circuit ( 200 ) according to claim 7 or 8, wherein the output stage transistor ( 10 ) is a self-blocking n-channel MOSFET. Engine control unit having a circuit ( 200 ) according to claim 7, 8 or 9.

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