WO1998020400A2 - Circuit arrangement for adapting the current of a valve driver to the current required for actuating the valve - Google Patents

Abstract

The invention concerns a circuit arrangement for adapting the current of a valve driver to the current required for actuating the valve, the valve being actuated electromechanically as a result of current acting upon a valve coil. In order to actuate the valve, there is provided a plurality of valve coils which can be acted upon by current either individually or in groups.

Description

Circuit arrangement for adapting the current of a valve driver to the current required to actuate the valve

The invention relates to a circuit arrangement for adapting the current of a valve driver to the current required to actuate the valve, the valve being actuated electromagnetically by supplying current to a valve coil.

Such a circuit arrangement is known to the applicant, in which valves of a blocking-slotted brake system are switched electromagnetically in a motor vehicle. The switching is carried out by means of transistors which, when switched on, allow current to flow through a valve coil. Since this application is a safety-relevant function, the transistor and valve coil must be designed so that the valve can be switched even under unfavorable conditions. The product of the number of turns and the current is essential for the power available to actuate the valve. Unfavorable conditions can, for example, be that the vehicle electrical system voltage has dropped. Furthermore, unfavorable conditions can be that the valve coil has heated up and, as a result, its ohmic resistance is correspondingly high. An interpretation of the system in such a way that a reliable function is possible even under such unfavorable conditions, but requires that under normal conditions a comparatively large one Electricity flows. The design must be such that a certain minimum current flows even under these unfavorable conditions. The current through the valve coil leads to a power loss in the collector-emitter section of the switched transistor due to the resistance in this section. This power loss is comparatively large under normal conditions if the system is designed in such a way that reliable operation is ensured even under unfavorable conditions.

The present invention is therefore based on the object of solving problems associated with the occurrence of power loss.

These problems are in particular the dissipation of the heat loss. In order to ensure sufficient heat transfer and heat dissipation, the degree of integration of the semiconductor elements on a chip is limited.

According to the invention, this object is achieved by providing a plurality of valve coils for actuating the valve, which can be supplied with current individually or in groups.

As a result, the power which is consumed when the valve is actuated can advantageously be adapted to the power which is required to actuate the valve. This means that savings can be made with regard to the measures of heat dissipation. Overall, this results in the possibility of providing higher integration of the components on a chip.

The invention can be used particularly advantageously in a motor vehicle. As a result, fluctuations in the vehicle electrical system voltage can be compensated for, as Changes in the valve coils as a result of temperature changes that can occur especially in the motor vehicle and there in particular in the valves of anti-lock brake systems.

In the circuit arrangement according to claim 2, a minimum current is set which is required to actuate the valve. Furthermore, all valve coils are initially supplied with current, a measurement of the current is then used to infer the flowing current, this value of the current is compared to the minimum current and the current through one or more valve coils is switched off depending on the extent to which the value of the flowing Current exceeds the minimum current.

This shows that a reliable and quick response of the valve is guaranteed. If one applies current to the valve coils one after the other, it becomes clear that a statement as to whether the total current flowing is sufficient for the actuation of the valve can only be made when a static value of the current has been established. This problem is advantageously avoided by designing the circuit arrangement according to claim 2. By initially applying current to all valve coils, a reliable function of the valve is ensured, the valve responding immediately without a time delay. If it turns out that the flowing current exceeds the minimum current so far that the function of the valve is also possible with a current application of fewer valve coils, then one or more valve coils are switched off accordingly. The larger current only flows for a comparatively short time. Since the valve coils can be switched off very quickly, it is possible to do without particularly complex measures for dissipating the heat loss. At the same time, a safe and quick response of the valve is guaranteed. accomplishes.

In the circuit arrangement according to claim 3, a conclusion is drawn from a measurement of the current of the flowing current, this value of the current is compared with the minimum current and - if not all valve coils are supplied with current - at least individual valve coils are supplied with current if the value of the flowing current falls below the minimum current.

In this way it can advantageously be achieved that there is always enough energy available to actuate the valve. When the current-carrying valve heats up due to the flowing current, the heating increases the ohmic resistance of the valve coil. This simultaneously reduces the current flow through this valve coil. If this current has decreased to a certain value in the direction of the minimum current, then at least one further valve coil can be supplied with current in order to provide sufficient energy for the continuous operation of the valve.

The circuit arrangement according to claim 4 has two valve coils, the windings of which are wound on the same winding support.

This enables a particularly simple assessment of whether the connection of both valve coils is necessary. This also limits the number of semiconductor switches required. Furthermore, such a valve coil arrangement is easy to manufacture.

In the embodiment of the circuit arrangement according to claim 5, a conclusion is drawn from a measurement of the current through one of the valve coils on the flowing current, the measurement of the current in the valve coil taking place at a Current application for actuating the valve is switched on first or last switched off.

With such a measurement, it is easily possible to limit the effort for the measurement by only measuring the current through one of the valve coils. Due to the appropriately proposed selection of the valve coil, the value of the flowing current is also always known.

In the circuit arrangement according to claim 6, the valve coils are switched on and off by means of semiconductor switches such as transistors.

This enables the switches to be integrated into valve driver stages on one chip.

In the circuit arrangement according to claim 7, several calf conductor switches are integrated on one chip.

The reduction in power loss has a particularly advantageous effect here, since the integration density on the chip can thereby be increased. For example, a larger number of valve driver stages, that is to say a plurality of semiconductor switches, can take place on one chip. Smaller and cheaper housings can also be used. The routing within the circuit housing and the routing on the circuit board are also simplified. This affects, for example, the size of the pads on the chip, the cross-section and the number of bonding wires, and the cross-section of the circuit pins.

An embodiment of the invention is shown in more detail in the drawing. It shows in detail:

1: the current conditions in a valve coil for actuating a valve, 2: a circuit arrangement according to the prior art,

3: a circuit arrangement according to the present invention,

4: an embodiment of a circuit arrangement and

5 - 7: the current conditions in the circuit arrangement according to the present invention.

Fig. 1 shows the current conditions in a valve coil for actuating a valve. Curves 1, 2 and 3 have in common that the current only rises to its maximum value after a certain time delay after the semiconductor switch has been switched. This is due to the fact that the inductance of the valve coil counteracts a current rise in the start-up phase.

Reference number 4 shows a dashed line, which represents the minimum current that must flow in order to enable actuation of the valve.

Curve 3 thus shows the current profile under the most unfavorable conditions that usually occur. The current after the start-up time is just above the minimum current 4. The value of the ohmic resistance of the valve coil and other resistance values such as, for example, along the switching path of the semiconductor switch must be coordinated so that the current 3 is still above the worst case Minimum current 4 is.

Curve 1 shows the current that can be set as a maximum in the design according to curve 3. This can happen, for example, if the vehicle electrical system voltage assumes equally large values and the valve coil is comparatively cold, so that its ohmic resistance is correspondingly low.

It can be seen that in a design to enable a current profile according to curve 3 in the worst case, under the conditions under which a current profile occurs according to curve 1, considerable power losses must be dissipated.

In addition to these extreme cases according to curve 1 and curve 3, an average value according to curve 2 is often established under normal conditions. Here, too, a considerable portion of the power loss has to be dissipated.

So it can happen that a multiple of the required current flows.

Fig. 2 shows a circuit arrangement which is already known to the applicant. The valve coil 5 of the valve is switched on and off via the transistor 6. The maximum current flowing through the valve coil 5 and the transistor 6 in the switched-on state is dependent on the operating voltage Vcc, on the ohmic resistance s _pu i _{e5 of} the valve coil winding and on the on-state resistance R _{KE6 of} the transistor 6 between the collector and emitter in the switched-on state.

The valve coil 5 is dimensioned in terms of its magnetic properties, the winding wire cross-section and the number of turns in such a way that at the lowest available operating voltage Vcc a sufficiently large current flows through the valve to ensure the valve function. Since the operating voltage, which essentially corresponds to the vehicle electrical system voltage, and the ohmic resistance ^R _Spu i _e5 are subject to very large fluctuations curve curves corresponding to curves 1 to 3 of FIG. 1. The fluctuations in the ohmic resistance ^R _coil5 are essentially based on the change in resistance with temperature.

3 shows a circuit arrangement according to the present invention. Instead of the valve coil 5 of FIG. 2, two valve coils 7 and 9 are provided in FIG. 3. These two valve coils 7 and 9 also each have n turns, as does the valve coil 5, but their ohmic resistance Rs _pu i _e7 ^{and R} s _pu i _{e9 are} each twice as great as the ohmic resistance Rs _pu i _{e5 of} the valve coil 5.

The two windings of the valve coils 7 and 9 are advantageously identical. These two windings can be bifilar wound on a winding body or on two separate winding bodies located one behind the other.

The two valve coils 7 and 9 are switched by separate driver transistors 8 and 10. These driver transistors 8 and 10 can be switched on and off individually.

When integrated on an IC chip, the two transistors 8 and 10 take up the same area as the transistor 6 according to the circuit _{example in} FIG. 2. As a result, the on- _resistance R _KE8 ^{and R} _{KEIO of} each of these transistors 8 and 10 is twice as large like the on _resistance R _{KE6 of} the transistor 6.

Due to the double resistance Rs _pu i _e7 ^and d

^R s _pu i _{e9 of} the windings of the valve coils 7 and 9 with respect to the ohmic resistance Rs _pu i _{e5 of} the valve coil 5, the current in the individual windings of the two valve coils 7 and 9 is half the current in the winding of the valve coil 5. If both valve coils 7 and 9 are energized, the force acting on the valve is just as great as in the circuit example in FIG. 2. The product n * I is also essential here. The number of turns of all valve coils 5, 7 and 9 are the same. Half the current flows in the valve coils 7 and 9 in each case compared to the valve coil 5. When the two valve coils 7 and 9 are connected in parallel, the valve has the same force on the valve as in the circuit arrangement according to FIG. 2.

In order to ensure a safe and fast response of the valve, current is first applied to both valve coils 7 and 9 by switching both driver transistors 8 and 10 through. In the embodiment according to FIG. 3, the further sequence is particularly simple because both valve coils are identical. It is checked in the next step whether the current flow exceeds twice the value of the minimum current 4 according to FIG. 1. In this case, reliable functioning of the valve is ensured even if one of the two valve coils 7 or 9 is switched off. The transistor 8 is switched off, for example, by means of a corresponding control circuit. After a decay phase in which the current through the valve coil 7 drops to "0", only current flows through the valve coil 9. This current is greater than the minimum current 4 according to FIG. 1. The current is advantageously measured in order to switch on the second valve coil 7 again when the current drops below the minimum current 4.

In the driver stage in the circuit arrangement according to FIG. 2, the power loss P _{2 was} :

P ₂ = (Vcc / (R _{coil 5} + R _KE 6)) ² * ^R _KE 6

The power loss P ₃ in the driver stage is at 3 with the valve coil 9 switched on:

P ₃ = (VCC / (R _S coil9 + KE10)) * ^R KE10

Since R _REIO is twice as large as R _RE6 ^an d ^R s _pu i _e9 is twice as large as R _Spule5 ri ^st power dissipation in the circuit arrangement of Fig. 3 with respect to the circuit of Fig. 2 is reduced to half, when only one the valve coils 7 and 9 is switched on.

The current can be measured in a manner known per se. If necessary, the current can be measured in one of the two windings. Advantageously, this is the winding that is energized in each case when the valve is actuated, since the current can then be measured continuously, and thus the other valve coil can also be switched on again when the current drops. For reasons of redundancy, it can also be useful to measure the current in both windings. The measurement method here is the measurement of the voltage drop via an ohmic shunt, the current level measurement of the current in the driver transistor or a brief redirection of the current via an external resistor, combined with a measurement of the voltage drop. The last-mentioned method is explained, for example, in the patent application ....

4 shows the configuration of a circuit arrangement in which the current measurement in the circuit of the valve coil 9 takes place by means of the shunt resistor 11. Identical components for the circuit arrangement according to FIG. 3 are provided with the same reference symbols.

The valve driver stage is switched on and off by means of the signal ON switched off. The driver transistor 10 is switched directly by means of this signal.

A reference voltage is applied to one input 13 of the comparator 12. The voltage which is to be measured by means of the shunt resistor 11 is applied to the other input 14 of the comparator 12 in order to determine the current. The reference voltage is designed so that the voltage drop across the shunt resistor 11 corresponds to a current in the branch of the valve coil 9 which corresponds to the minimum current 4 according to FIG. 1. When transistor 10 is switched on, no current initially flows, so that the voltage at input 14 of comparator 12 is lower than the reference voltage that is present at input 13 of comparator 12. The output signal of the comparator 12 therefore has the value "1".

This output signal, like the signal "ON", is fed to an AND gate 15. Immediately after switching on, the output signal of this AND gate 15 is also at "1". This output signal is fed to transistor 8, which is therefore also switched on.

As a result, both valve coils 7 and 9 are initially supplied with current when switched on.

If the current now rises accordingly, the voltage drop across the shunt resistor 11 exceeds the reference voltage. The output signal of the comparator 12 then goes to "0". The output signal of the AND gate 15 also goes to "0". The transistor 8 then switches off. As a result, the valve coil 7 is no longer energized.

If the current through the valve coil 9 falls below the minimum current 4 according to FIG. 1, the voltage drop across the shunt resistor 11 is less than the reference voltage. The The output signal of the comparator 12 then goes back to "1" and, as a result, also the output signal of the AND gate 15. The transistor 8 is then switched on again, so that both valve coils 7 and 9 are then supplied with current again.

The device is switched off by setting the ON signal to "0". The transistor 10 switches off immediately. Since the ON signal is also fed to an input of the AND gate 15, its output signal also goes to "0", so that the transistor 8 also switches off.

In Figures 5 to 7, the minimum current for safe actuation of the valve is identified by the reference number 4.

FIG. 5 shows a curve 16 which shows the valve current through the valve coil 5 in the circuit arrangement according to FIG. 2. Furthermore, FIG. 5 shows a curve 17 which shows the total current through both valve coils 7 and 9 in the circuit arrangement according to FIG. 3 or FIG. 4. It can be clearly seen that the total current is reduced and thus the power loss that has to be dissipated is lower.

6 further shows a curve 18 which corresponds to the current profile through the valve coil 9. This valve coil is not switched off to reduce power loss.

FIG. 7 shows a curve 19 which corresponds to the current profile if the valve coil 7 would not be switched off. Curve 20 shows the current profile through the valve coil 7 with a shutdown of this valve coil 7 to reduce the power loss.

Claims

claims 1. Circuit arrangement for adapting the current of a valve driver to the required current (4) for actuating the valve, the valve being actuated electromagnetically by a valve coil (5, 7, 9) being acted on by current, characterized in that for actuating the Valve several valve coils (7, 9) are provided, which can be supplied with current individually or in groups (8, 10). 2. Circuit arrangement according to claim 1, characterized in that a minimum current (4) is set which is required to actuate the valve, that first all valve coils (7, 9) are supplied with current that from a measurement of the current on the flowing Current is closed (11), that this value of the current is compared with the minimum current (4) and that the current is switched off by one or more valve coils (7, 9) depending on the extent to which the value of the flowing current exceeds the minimum current (4th ) exceeds. 3. Circuit arrangement according to claim 1 or 2, characterized in that it is concluded from a measurement of the current (11) on the flowing current, that this value of the current is compared with the minimum current (4) and that - if not all valve coils (7 , 9) are supplied with current - at least individual valve coils (7, 9) are supplied with current if the value of the flowing current falls below the minimum current (4). 4. Circuit arrangement according to one of claims 1 to 3, characterized in that two valve coils (7, 9) are present, the windings of which are wound on the same winding support. Circuit arrangement according to one of Claims 1 to 4, characterized in that the current flowing from a measurement of the current (11) through one of the valve coils (9) is inferred, the current (11) being measured in the valve coil (9) which is switched on or switched off last when a current is applied to actuate the valve. Circuit arrangement according to one of Claims 1 to 5, characterized in that the valve coils (7, 9) are switched on and off by means of semiconductor switches (8, 10) such as transistors. Circuit arrangement according to Claim 6, characterized in that a plurality of semiconductor switches (8, 10) are integrated on one chip.