DE3546513A1 - Method and circuit for operating a gas inlet or exhaust valve - Google Patents

Abstract

The invention discloses a circuit for operating a gas inlet or exhaust valve which is held in its open and closed positions electromagnetically. In order to control the current flow (which is required while the valve is being held) through a coil which is provided with a freewheeling device, it is provided that the switching-on current be monitored directly while, during disconnection and when the freewheeling device is operating, the decay current is not measured but is simulated.

Description

The invention relates to a method for operating a gas shuttle valve.

It is known from DE-OS 30 24 109, a gas exchange valve to be provided for an internal combustion engine by a spring system is pressed into its opening and closing position and in the respective positions by exciting an electric magnets is held.

The current control necessary for the electromagnet is due to the high holding forces to be applied of the magnet has a relatively high current. It is ever but especially the catch current is relatively high, while after capturing the gas exchange valves even with smaller ones Streams can be kept.

The object of the invention is to provide a method with which a control of the magnets with high efficiency and for simple, yet functionally reliable measures is made possible.

The object is achieved by claim 1.

From DE-OS 28 28 678 is a circuit for an electro known magnetic consumer with a freewheel, the one high inrush current and then a clocked current is supplied with a lower effective current.

However, the difficulty arises that the Grenzwer te between which the current has to swing back and forth must be monitored during the clock phase. For energy reasons  the current should not exceed a certain upper threshold step, but on the other hand, he must not be under one know threshold value drop so the stops to be applied forces are ensured by the electromagnet.

However, it is expensive, both the top and the lower threshold through a separate evaluation watch. According to the invention, the structure is simplified that only the upper threshold directly during the clock phase is detected and also monitored while then going out from the upper threshold the drop when the utility is switched off voltage, i.e. the current that occurs via the freewheel, is not monitored directly measured, but is simulated. As soon as this simulated current fell to a lower value len, which is considered the lower threshold, becomes the supply voltage switched on again and accordingly the increase measured.

A major advantage is that the measuring resistor, above which the voltage drop due to the current flow through the electromagnetic control elements for gas exchange valve is measured, not within the freewheeling circuit needs to be attached, since it only switches on current, but not the freewheeling current. The switch on electricity can be at any other location of the electricity supplier range, for example directly against mass, who measured the while the freewheeling current is only simulated. By the method of the invention thus makes it possible to use the ohm resistance from the relatively sensitive area of the electromagnetic consumer and in to bring the proximity of the ground connection. This is one easier measurement possible, and some filters for loading sides of the interference voltage influence are superfluous.  

In the following the invention will be explained with reference to the drawing tert. Show it:

Figure 1 shows a circuit structure according to the invention. and

Fig. 2 is a current flow diagram for explaining the invention.

In Fig. 1, the structure of a circuit for the inventive method is shown. The gas exchange valves, which are not shown, are held in their opening or closing positions by means of an electromagnet ( 10 ), the electromagnet ( 10 ) is assigned a freewheel ( 12 ), which here is the simplest case in the form of a diode ( 12 ) is shown. The positive supply voltage is labeled ( 14 ), the ground connection for the circuit is labeled ( 16 ). The parallel connection of the electrical coil ( 10 ) and diode ( 12 ), the cathode of which is at the positive terminal and the anode of which is at the negative terminal, is connected to a circuit which is divided into two branches ( 18 ) and ( 20 ). The branch ( 18 ) connects the side of the coil ( 10 ) facing away from the positive voltage ( 14 ) via the collector-emitter path of a transistor ( 22 ) via a shunt ( 40 ) to the ground connection ( 16 ), the branch ( 20 ) is in parallel and connects the same connection of the coil ( 10 ) via a thyristor ( 30 ) and the shunt ( 40 ) to the ground connection ( 16 ).

The collector ( 26 ) of the transistor ( 22 ) is connected to the coil, the emitter ( 28 ) leads via the shunt ( 40 ) to the ground connection ( 16 ). The connection of the two branches in point ( 38 ) shortly before the ground connection ( 16 ) is placed on the shunt, an ohmic resistor ( 40 ) to ground ( 16 ), which will be discussed later.

The thyristor ( 30 ) with its anode ( 34 ) is in the branch ( 20 )

The two inputs ( 44 ) and ( 46 ) of the control element ( 42 ) grip the voltage across the ohmic resistor ( 40 ). Furthermore, the control element ( 42 ), as shown with the indicated bus line ( 52 ), receives information that allows the control of transistor ( 22 ) and thyristor ( 30 ) depending on other motor parameters.

The method according to the invention will be explained below with reference to the current profile through the coil ( 10 ) shown in FIG. 2.

If the gas exchange valves, as is open in DE-OS 30 24 109, are to be kept in their open and closed position by the electric magnets ( 10 ), a relatively high trapping current is necessary for capturing the gas exchange valves. Accordingly, by switching on the voltage, the current rises to a value I _max , in which a pulse is passed to the gate ( 36 ) of the thyristor ( 30 ) via the control element ( 42 ) at the output ( 48 ), as a result of which the thyristor ignites and the Inrush current increases. The increase in the current, that is to say the current current value, can be determined by the control unit ( 42 ) by querying the voltage drop across the ohmic resistor ( 40 ) through the inputs ( 44 ) and ( 46 ).

The ohmic resistance ( 40 ) has a relatively low value, the value must be just sufficient to produce a measurable voltage drop at all. Values on the order of 0.1 to 0.01 ohms are quite sufficient. This allows the losses caused by the ohmic resistance ( 40 ) to be restricted.

At time t ₀ , the value rose to a current value I _max . The control unit can work time-controlled, ie it switches off at time t ₀ , it can also work with current measurement, ie it switches off when the threshold value I _{max is reached} . At time t ₀ or when the current is reached, a safe catching of the armature is guaranteed, the control device can now switch off.

For this it is necessary that the current profile from the positive pole 14 to the ground connection 16 is interrupted, this must be done in that the thyristor 30 is deleted again. Simply by simply wiring a low-cost thyristor 30, however, deletion is not possible; the current flowing through the thyristor 30 must be switched off briefly since the thyristor 30 does not extinguish until it is de-energized.

For this purpose, the transistor 22 is provided, the base 24 of which is controlled via the output 50 of the switching element 52 , so that the path from the collector 26 to the emitter 28 is switched through and the current flows accordingly via the transistor 22 . Since the resistance of the transistor 22 in the open state was less than the resistance of the thyristor 30 with a series resistor 54 , the current flows essentially through the transistor 22 and the thyristor 30 clears. Immediately afterwards, the transistor 22 can be blocked by appropriately removing the drive signal at the base 24 , a further current flow from the positive connection 14 to the ground connection 16 is no longer possible.

The circuit could of course also be constructed in that the thyristor 30 was omitted and only one transistor 22 controls the current flow from the electromagnetic consumer 10 with freewheel 12 to the ground connection 16 . For this purpose, however, a relatively large power transistor 22 must be provided, since currents in sizes up to 30 to 50 amperes are to be controlled. Such power transistors are relatively voluminous and also extremely expensive for series use.

The invention takes advantage of the fact that a thyristor is a relatively inexpensive component and is nevertheless suitable for controlling, especially for switching on large currents and voltages. The transistor 22 , as is now provided, only has to take over the full current for a very short time, and a short-term peak load on a transistor can exceed the maximum permissible continuous load many times over without the transistor taking damage.

Since the switching surge of the transistor 22 only has to last until the thyristor 30 is extinguished again, the transistor 22 can be significantly undersized for the maximum current strengths, it is sufficient if the transistor 22 is set up to very many lower continuous current values.

With the interruption of the current, the current flow through the coil does not abruptly collapse, rather the current gradually drops via the freewheel 12 , as shown in FIG. 2 in the period between T 0 and T ₁₁ .

It is of course possible to detect this current flow through the coil 10 by means of a suitable measuring instrument and accordingly, when a lower threshold value is reached, to switch the current on again, so that in the holding phase of the armature of the gas exchange valve it is ensured that the armature at the core of the Electromagnet 10 sticks. However, this is relatively expensive since interference voltages are captured when the current flow is queried through the coil, which make the measurement result uncertain. In addition, the fluctuations in the supply voltage are included as measurement errors.

A key point of the invention is that the current query does not take place in the electromagnetic consumer 10 , or in the circuit that flows through the electromagnetic consumer 10 , but by the ohmic resistor 40 , which is on one side directly at the ground terminal 16 and is accordingly prone to failure.

However, since this ohmic resistor 40 does not detect the falling current, the drop in current, the drop characteristic of which is known due to the operating parameters, is simulated in the control unit 42 . The accuracy achieved in this way is sufficient to ensure safe operation of the circuit and the electromagnetic consumer 10 .

Now the simulated current drop has reached a lower value I ₂ , which is shown in FIG. 2 at time t ₁₁ , the current flow through the magnet 10 is switched on again. This can either be done in that the transistor 22 opens by controlling the base 24 via the control unit 42 and thus the current can flow from the positive pole 14 to the ground terminal 16 . So that the current rises again to a point in time t ₁₂, there it reaches the threshold value I ₁, which is predetermined in the control unit 42 , the transistor 22 is blocked, and the current falls again simulated to its lower threshold value I ₂ which it reaches at time t ₂₁ . The current is switched on again, reaches its upper value I ₁ at the time t ₂₂, then the transistor 22 blocks again, and the fall phase is again simulated.

In this way, there is a clocked power supply to the electromagnet 10 , the currents being chosen to be relatively low in order to save energy. Due to the free-wheel circuit, only an energy surge between switching on and off is necessary; the subsequent drop phase of the current takes place via the free-wheel 12 and does not require any external power supply.

The current values I ₁ and I ₂, between which the current flowing through the circuit in the holding phase, which closes the catching phase, moves, is of the order of magnitude about 10 to 20% of the maximum current I _max , which must be expended during the catching phase .

Accordingly, it is easily possible to control these significantly lower currents in the order of 3 to 5 amps via the transistor 22 .

Alternatively, it is of course possible to also allow this current to flow through the firing of the thyristor 30 by a corresponding signal at the output 48 of the switching device 42 to the gate 36 ; in this case, the transistor 22 serves only for this purpose, similarly to switching off the capture current to delete the thyristor each time it reaches a current flow of the order I ₁ .

The switch-on time, which was set to the zero point of the coordinate system in FIG. 2, is supplied to the control device 42 via the bus line 52 . Likewise, the control unit 42 receives the information of the switch-off via the bus line 52 , the switch-off process not being the subject of this invention. As disclosed in DE-OS 28 28 678, thereby interrupting the freewheel 12 is notwen dig, to achieve an abrupt switching off, as by the freewheel 12 otherwise even when disabling the power supply, a decrease in current flow to take place with the usual drop rate would.

The other parameters, in particular the threshold values I _max , I ₁ and I ₂ , do not have to be supplied to the control unit 42 ; these values can be specified in the control unit 42 itself. Alternatively, it is also possible to determine these threshold values depending on other operating parameters via the bus line 52 .

Likewise, the fall rate, which is used to simulate the falling current course, is anchored in the control unit 42 itself.

If several gas exchange valves are operated with the circuit according to the invention in a multi-cylinder engine, this circuit is particularly advantageous insofar as all ohmic resistors 40 can be connected to a common ground point 16 , so that interference which finds its way into the control unit 42 is kept as low as possible will. Circuit tolerances that result from the construction of identical circuits due to the scatter in the values of the components are also optimally suppressed in this way.

Claims (1)

A method of operating a gas exchange valve of an internal combustion engine, with an electromagnet influencing the movement of the gas exchange valve, characterized in that the electromagnet has a free-wheeling circuit, in the hal tephasen the gas exchange valve is supplied with current in a clocked manner, the current is measured in the clock cycle during the current supply and at If a limit value is exceeded, the switch-off phase is simulated during the switch-off phases and the current is switched on again after a lower threshold value of the simulated curve has been reached.