EP0653693A2 - Apparatus for controlling the voltage drop across an appliance - Google Patents

Abstract

A device for controlling the voltage drop across an appliance, particularly an electromagnetic appliance, is described. The appliance and a controlling element are connected in series between earth and supply voltage. First means provide an actual current which corresponds to the voltage present across the appliance. Second means define a nominal current. Control means define a quantity to be applied to the controlling element in dependence on a comparison of the actual current with the nominal current. <IMAGE>

Description

State of the art

The invention relates to a device for controlling a voltage drop across a consumer according to the preamble of the independent claim.

Devices for regulating a voltage are known in which the difference between a target voltage and the measured voltage is fed to a controller. This controller forms a manipulated variable to act upon an actuator.

The controllers used usually include operational amplifiers and capacitors. The operational amplifiers in particular require a very high outlay on components and application. Conventional controllers must be set so that they work stably.

Object of the invention

The invention is based on the object of providing a voltage regulator in a device of the type mentioned at the outset, which is constructed as simply as possible. This object is achieved by the features characterized in the independent claim.

Advantages of the invention

The device according to the invention has the advantage that the voltage regulator has only very few components that are easy to integrate. Furthermore, the voltage regulator works stably and does not tend to vibrate. In particular, the controller does not need to be specially designed. The dynamics of the controller are determined by just a few components and are therefore easy to control.

Advantageous and expedient refinements and developments of the invention are characterized in the subclaims.

drawing

The invention is explained below with reference to the embodiment shown in the drawing. The figure shows a schematic representation of the circuit arrangement.

Description of the embodiments

The exemplary embodiment described is a device for regulating the voltage at a consumer, in particular at an electromagnetic consumer. It is particularly advantageous to use the device according to the invention in connection with internal combustion engines, in particular when metering fuel into a combustion chamber of the internal combustion engine. For this purpose, a solenoid valve can then be used in a particularly advantageous manner to control the metering of fuel into the internal combustion engine.

In this case, especially with small loads, it is necessary for the smallest injection quantities to be metered as precisely as possible. For this, it is again necessary that the point in time at which the armature of the energized solenoid valve reaches an end position is known. This point in time is usually referred to as the "Begin of Injection Period" (BIP). This point in time is obtained by evaluating the time profile of the solenoid valve current. The time course of the current is evaluated at a constant voltage to determine whether this course has a kink or a significant change in the difference quotient of the current.

It is usually provided that the voltage applied to the solenoid valve is adjusted to a constant value by means of a voltage regulator. It is particularly advantageous if the device described below is used to determine a variable that characterizes the start of injection and / or the end of injection. In this case, the consumer is a solenoid valve for determining the amount of fuel injected into an internal combustion engine. The device is used to regulate the voltage at the solenoid valve in order to be able to determine the point in time at which the armature of the solenoid valve reaches its end position.

In Figure 1, essential elements of a device for controlling a solenoid-controlled fuel metering device are shown schematically. A connection of a consumer 100, in particular an electromagnetic consumer, is connected to a voltage supply device (Ubat). The second connection of the consumer 100 is connected to ground via a switching means 110 and a sensor 145. The sensor 145 is connected to an evaluation circuit 140. The switching means 110 is preferably implemented as a field effect transistor.

Voltage current transformers 421 and 422 tap the potential values present at the connections of the consumer 100. The voltage current transformers 421 and 422 apply a current I _H and I _{L to} a block 400. Furthermore, block 400 is connected to a reference voltage V _CC via a current source 450. An output of block 400 is connected to the gate of field effect transistor 110 via a gate resistor 423.

Mit K ist ein Verstärkungsfaktor bezeichnet
The block 40 compares the currents I _H and I _L with the target current I _target and specifies an actuation current I _G for applying the switching means 110, preferably according to the following formula:

${\text{I.}}_{\text{G}}{\text{= K * (I}}_{\text{Should}}{\text{+ I}}_{\text{L}}{\text{- I}}_{\text{H}}\text{)}$

K is a gain factor

In particular, block 400 is shown in more detail in FIG. Elements already described in FIG. 1 are identified in FIG. 2 with corresponding reference symbols.

Ohmic resistors are used as voltage current transformers in the exemplary embodiment shown. The voltage current transformers act on the block 400, which essentially comprise a first current mirror 410 and a second current mirror 420. The voltage current transformers apply currents to the first current mirror 410. The first current mirror 410 is in turn connected to a second current mirror 420. This is connected to the gate of field-effect transistor 110 via a gate resistor 423.

A current mirror is usually understood to mean the interconnection of two semiconductor elements in such a way that a current through one semiconductor element results in a corresponding or proportional current through the other semiconductor element. If two transistors are used for a current mirror circuit, the two switching paths of the transistors form two current paths.

In the first current mirror 410, a transistor 440 serves as the second current path and a transistor 445 as the first current path. The potentials at the two connections of the consumer 100 are tapped via the two resistors 421 and 422. The first resistor 421 is connected via a node 449 to the collector of the transistor 440 of the second current path of the first current mirror. The second resistor 422 is connected via a node 448 to the collector of the transistor 445 of the first current path of the first current mirror.

The base of transistor 440 and the base of transistor 445 are connected via point 446. Point 446 is also connected to point 448.

In the second current mirror 420, a transistor 430 forms the first current path. The collector of transistor 430 is connected to point 449 via point 438. A transistor 435 forms the second current path. The base of transistor 430 is connected to the base of transistor 435 and point 436. This point 436 is connected to point 438. The collector-emitter current of transistor 430 is impressed on transistor 435.

The second current path is connected to a reference voltage V _CC via a current source 450. The collector of transistor 435 is connected via node 439 to current source 450, to gate resistor 423 and thus to the gate of field effect transistor 110.

This device now works as a voltage regulator as follows. The potential values at the consumer 100 are converted into currents by the resistors 421 and 422. The first current mirror 410 forms the difference between the two current values. This actual current is a measure of the voltage drop across the consumer.

This actual current is applied to the first current path of the second current mirror 420. This current is mirrored and compared with the target current supplied by the current source 450. This setpoint current supplied by the current source 450 serves as the setpoint. The gate of the field effect transistor is acted upon by the differential current between the target current and the actual current.

The desired current is selected such that a current flows through the second path of the current mirror 420 in the steady state, which corresponds to the desired value supplied by the current source 450. If these two currents are the same, that is to say the voltage drop across the consumer 100 corresponds to the target voltage, then no gate current flows and the switching means remains in its position.

If the voltage drop across the consumer is too high, a correspondingly higher current flows through the current mirror, which in turn causes the gate to discharge and the switching means to be blocked. This causes the voltage at consumer 100 to drop. The same applies if the voltage at the consumer is too low. In this case, too little current flows through the current mirror and the gate is charged via the gate current. Accordingly, the field effect transistor becomes conductive or enables a stronger current flow through the consumer.

Essentially, the procedure is as follows. The voltage to be regulated at the consumer 100 is converted into a current by the voltage current transformers 421 and 422 and the current mirror 410. The current mirror 420 regulates the voltage drop across the consumer to the target current. This is done by mirroring the current supplied by the first current mirror 410 and subtracting it from the desired current at node 439. This differential current is used to control the field effect transistor. This means that the current changes the gate charge and thus the state of the field effect transistor. The voltage regulation has settled when the current established in the second current path is equal to the current supplied by the current source.

Only very small currents are required to influence the gate charge and thus the state of the field effect transistor. The second current mirror is used to adapt the I current to this current level.

As an alternative, it would also be conceivable for the actual current to be compared directly with the target current. In this case, the differential current would be fed to the second current mirror as an input variable.

The current provided by the current source 450 corresponds to the voltage drop across the consumer. The voltage at the consumer can be influenced directly by changing the current value. There is a fixed, preferably proportional relationship between the current supplied by the current source 450 and the voltage drop across the consumer. Therefore, the current source 450 allows a variable setpoint for the voltage drop across the consumer.

The second current mirror essentially works as a controller with proportional behavior. Due to the capacitances between the gate and source or between the gate and drain of the field effect transistor 110, there is also an integral behavior of the current control.

The dynamics of the controller are essentially determined by the current source and the capacitances of the field effect transistor 110. The dynamics can therefore be influenced very easily. Since no operational amplifiers are used, there are no stability problems, which means that the controller does not tend to vibrate.

By using the current mirror, the component expenditure is reduced considerably compared to an implementation with operational amplifiers. Furthermore, the application effort for the controller is reduced since the control parameters do not have to be set.

The circuit shown in the figure, in particular the current mirrors 410 and 420, can be easily integrated. All measuring voltages are immediately converted into currents. This has the advantage that there are no high voltages at the input of the integrated circuit. A high common mode rejection is possible due to the voltage current transformer.

Based on the current flowing through the solenoid valve 100, the evaluation circuit determines the point in time at which the armature of the energized solenoid valve reaches an end position. The time course of the current is evaluated at a constant voltage to determine whether this course has a kink or a significant change in the difference quotient of the current. During the evaluation of the current or during the determination of the switching time, the voltage at the solenoid valve is regulated to a constant value by means of the device described.

Claims (6)

Device for regulating a voltage drop across a consumer, in which the consumer and an actuator are connected in series between ground and supply voltage, characterized by first means, which provide an actual current, which is a measure of the voltage applied to the consumer, with a second means for specifying a setpoint current, with regulating means which, depending on a comparison of the actual current with the setpoint current, specify a variable for acting on the actuator. Device according to Claim 1, characterized in that the first means comprise at least one current mirror which provides a current which corresponds to the voltage drop across the consumer. Device according to claim 1 or 2, characterized in that the control means comprise at least one current mirror. Device according to one of the preceding claims, characterized in that the difference between the current and the desired current is applied to the actuator. Device according to one of the preceding claims, characterized in that a field effect transistor serves as the actuator. Device according to one of the preceding claims, characterized in that the consumer is a solenoid valve for determining the amount of fuel injected into an internal combustion engine and the device is used to determine a variable characterizing the start of injection and / or the end of injection.

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