EP1005051B1 - Method for driving an electromagnetic consumer - Google Patents

Description

State of the art

The invention relates to a method for controlling an electromagnetic consumer according to the preambles of the independent claim.

A method for controlling an electromagnetic consumer is known from DE-OS 44 20 282. There, a device for driving a consumer is described, which comprises a movable element. The consumer is a solenoid valve for controlling the fuel metering in an internal combustion engine. Within a time window, a switching time is detected at which the movable element reaches a certain position. This is done by evaluating the time course of a quantity corresponding to the current flowing through the load. During the time window in which the current is evaluated, it is provided that the voltage applied to the consumer is regulated or controlled to a constant value.

In the cold start phase, the supply lines to the load are low-impedance, so that the currents at a constant voltage reach a higher level than in normal operation. If a current monitoring is provided, which shuts off the power amplifier from a certain threshold value of the current, this can lead to the output stage being switched off by the current monitoring.

This is particularly problematic if, during the time window in which the switching time is detected, the consumer is connected to the supply voltage. Depending on the duration of the time window, the current flowing through the consumer increases to different levels.

Object of the invention

The invention is based on the object, in a method for controlling an electromagnetic load of the type mentioned, the duration of the time window within which the switching time is detected to specify suitable. The time window should be sufficiently large so that the switching time can be detected. On the other hand, the time window should be so small that it does not lead to an increase in current to impermissible values and thus to a shutdown of the power amplifier.

Advantages of the invention

By the procedure according to the invention according to claim 1 current shutdowns of the output stage are avoided during the detection of the switching time. The time window within which the switching time is detected, is set such that on the one hand, a detection of the switching time possible and on the other hand the current does not rise to impermissibly high values.

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

drawing

The invention will be explained below with reference to the embodiments shown in the drawing. FIG. 1 shows a schematic representation of the output stage, FIG. 2 shows various signals applied over time, and FIG. 3 shows a flow chart for clarifying the procedure according to the invention.

Description of the embodiments

The invention will be described below using the example of a consumer. The consumer is in particular a solenoid valve for controlling the fuel metering in an internal combustion engine. The consumer comprises a movable element, which is usually referred to as a valve needle in a solenoid valve.

FIG. 1 shows a device based on a block diagram. A consumer 100 is connected to a first terminal with a supply voltage Ubat, the second terminal of the consumer 100 is connected to the first terminal of a switching means 110 in connection. The second terminal of the switching means 110 is in communication with the first terminal of a current measuring means 120. The second terminal of the current measuring means is in contact with ground.

The terminals of the consumer 100 and the terminals of the current measuring means 120 act upon a control unit 130 with signals, which in turn supply the switching means 110 with a drive signal A.

In the illustrated embodiment, the load 100, the switching means 110, and the current measuring means 120 are connected in series in this order. This order is chosen only as an example. The three elements can also be arranged in a different order. Thus, the switching means can also be arranged between the supply voltage and the load. Furthermore, the current measuring means 120 can be arranged between the switching means 110 and the load 100 or between the load 100 and the supply voltage. Furthermore, it is possible that further switching means, in particular a between the load 100 and the supply voltage, are provided.

The switching means 110 is preferably realized as a transistor, in particular as a field-effect transistor. The current measuring means 120 is preferably designed as an ohmic resistor. In the consumer 100 is preferably the coil of a solenoid valve that is used for the metering of fuel.

In the sub-figure 2a, the current I flowing through the load 100, and preferably detected by the current measuring means 120, is plotted against time. FIG. 2 a shows a metering or an injection process. At time t1, the control of the consumer 100 begins.

At this time t1, the current I rises steeply. At time t2, a first value S1 is reached. To this Time opens the switching means. If the current drops by a certain value, the switching means 110 closes and the current rises again to the value S1. The value S1 is also referred to as pull-in current.

The period between the time t1 and the time t2 is referred to as free current run-up. At this the regulation follows the attraction current.

At time t3, a time window within which the switching means 110 is constantly in its closed state begins. This has the consequence that the current increases. At the time tBIP the movable element reaches its new end position due to the magnetic force. This results in a change in the inductance of the consumer. This causes a change in current increase. At time t4, the time window ends.

From the time t4 is regulated to a second value S2 for the current. This value is also called a holding current. The control of the consumer ends at time t5, in which the switching means 110 is opened and the current drops to 0 until the time t6.

The current profile is shown only schematically and can take other courses in other types of solenoid valves or other driving method. In particular, the behavior during the achievement of the new end position at time tBIP can be different. It is essential that at the switching time tBIP the current waveform has a kink and / or a discontinuity. Usually, this kink is detected by a current evaluation.

The problem now is that during the period t3 to t4, the switching means 110 is constantly closed. With a small ohmic resistance of the consumer 100, the current therefore increases very strongly in this period. This may cause a maximum current value to be exceeded and shut down the final stage, i. the switching means 110 is permanently opened.

The times t3 and t4 define a time window within which the switching time is detected. It is provided that within the time window, the switching means 110 is in its closed state. By evaluating the current profile within the time window, the switching time tBIP is detected. During the time window, which is defined by the times t3 and t4, the load 100 is supplied with the supply voltage Ubat and the time profile of the current is evaluated to determine the switching time. Due to the fact that the load is applied to the load in the time window, the control in the time window is simplified substantially, a voltage control is not required.

$$\mathrm{t}4\mathrm{=}\mathrm{TBIP}\mathrm{+}\mathrm{B}\mathrm{/}\mathrm{2}$$

The limits for the time window t3 and t4 are preferably predefined on the basis of the switching time tBIP of the preceding drive and the width B of the time window. The calculation is preferably carried out according to the formula. $$\mathrm{t}\mathrm{3}\mathrm{=}\mathrm{TBIP}\mathrm{-}\mathrm{B}\mathrm{/}\mathrm{2}$$

$$\mathrm{t}4\mathrm{=}\mathrm{TBIP}\mathrm{+}\mathrm{B}\mathrm{/}\mathrm{2}$$

The width B of the time window is, as described in Figure 3, given.

According to the invention, by specifying the time window, i. the time interval between the times t3 and t4, the current increase during the time window limited. This is done in particular at the start of the internal combustion engine.

In subfigure 2b, the time profile of the duration of the time window is plotted with a solid line. The maximum value IB of the current I, which is detected shortly before the time t4, is plotted with a dashed line. Furthermore, the threshold SW is plotted with a double line. The conditions in normal undisturbed operation are shown.

At time 0 i. At start-up of the engine, a minimum value BMIN is determined for the duration of the time window, i. specified in the distance between t3 and t4. The maximum value IB of the current is clearly below the threshold value SW. This has the consequence that in the next injection, a larger value is given for the time window. This means that the duration B of the time window increases over the time several stages until a maximum value BMAX is reached. The value BMIN is selected so that, even under unfavorable conditions, the maximum current IB is not greater than the threshold value SW.

Simultaneously with the increase of the duration B of the time window, the maximum value IB of the current also increases. The maximum value does not reach the threshold SW. Threshold SW is chosen to be slightly less than the maximum current value at which the current monitor responds.

It can also be seen from FIG. 2b that the threshold value SW is not constant, but depends on the battery voltage Ubat applied to the load is, is given. As can be seen in FIG. 2b, this value rises slowly during the starting process.

In Figure 3, the procedure of the invention is explained with reference to a flow chart. Preferably, the procedure according to the invention is carried out only once after the start of the internal combustion engine. That is, after the engine is started, the program starts in step 300.

In the subsequent step 310, the value B for the time window is set to the minimum value BMIN. The subsequent query 320 checks whether the maximum value of the current IB is greater than the threshold value SW. If this is not the case, i. the maximum value IB of the current is smaller than the threshold value SW, then in step 330 the time window B is increased by the value X.

The maximum value IB of the current corresponds to the current value which is present at the time t4. If this can not be detected with difficulty or only with difficulty, a current value immediately prior to time t4 can be used as maximum value IB. The maximum value IB of the current corresponds to the largest current value measured in the time window. The maximum value IB of the current I is preferably detected immediately before the end of the time window (t4).

The subsequent query 340 checks whether the width B of the time window is greater than the maximum value BMAX. If so, the program ends in step 350.

If this is not the case, the query 320 is repeated. In normal operation, the program steps 320, 330 and 340 are run through several times until the width B of the time window has reached the maximum value BMAX. If this is the case, the procedure ends.

If the query 320 recognizes that the maximum value IB of the current is greater than the threshold value SW, the width B of the window is reduced by the value Y in step 360. The subsequent query 370 checks if the width B is less than or equal to the minimum value BMIN. If this is not the case, the query 320 is performed again. If this is the case, the width B is set to the minimum value BMIN in step 380, and the query 320 is performed again.

This means that if the maximum value of the current IB is greater than the threshold value SW, the width of the window B is reduced by the value Y until the maximum value IB of the current is smaller than the threshold value. It is preferably provided that the lower value BMIN is not undershot.

According to the invention, starting from a start value (BMIN), the time duration of the time window is increased if the current is smaller than the threshold value. The time duration of the time window is increased until a maximum value (BMAX) for the time duration is reached. The time duration of the time window is reduced if the current is greater than the threshold value.

Claims (3)

1. Method for driving an electromagnetic load (100), that comprises a moveable element, in particular a solenoid valve for controlling the fuel metering to an internal combustion engine, a switching time (BIP) being determined within a time window (t3, t4), at which time the moveable element reaches a specific position, characterized in that the duration (B) of the time window (t3, t4) can be predetermined such that the current (IB), which flows through the load (100) during the time window (t3, t4), does not exceed a threshold value (SW), the duration (B) of the time window being extended, starting from a start value (BMIN), if the current (IB) is smaller than the threshold value (SW), and the duration (B) of the time window being shortened if the current (IB) is greater than the threshold value (SW).
2. Method according to Claim 1, characterized in that, over the duration (B), a supply voltage (Ubat) is applied to the load (100), and the time profile of the current is evaluated for the purpose of determining the switching time (BIP).
3. Method according to one of the preceding claims, characterized in that the current is detected directly before the end of the time window (t3, t4).

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