DE3508187A1 - VALVE CONTROL - Google Patents

Abstract

The current is regulated by the exciting winding (28) of a valve that can be electromagnetically actuated in response to a signal voltage (UG) used as a command variable. To this purpose, the signal voltage (UG) and a return voltage (Ud) are supplied to an integrating regulator (10). The regulator (10) commands a pulse width modulator (20). The latter commands a switching transistor (24) which is in series with the exciting winding (28). A diode (32) is connected parallel to the exciting winding (28). Return means create a return voltage (Ud) which is proportional to the modulated current (IL) through the exciting winding (28), even during the cutoff period, during which the switching transistor (24) is shut off.

Description

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Patent registration

Oelsch limited partnership, __ Jahnstraße 68-7 ?,

Valve control circuit

, p The invention relates to a valve control circuit to regulate the electric current through the excitation winding an electromagnetically actuated valve in accordance with one that is used as a guide Signal voltage.

Such a valve control circuit is about

the current in the excitation winding a valve e.g. in a hydraulic circuit more or less open depending on the signal voltage. To the ",. Actuation of the valve must be relatively high Currents are controlled. With a simple proportional control requires large and complex electronic components. Also occurs large power dissipation.

The invention is based on the object of a Provide valve control circuit in which with relatively small components while avoiding a undesirably high power dissipation of the average

,. r Current through an exciter winding controlling a valve. -

over ^a

is proportional to one that serves as a reference variable Signal voltage is made.

According to the invention, this object is achieved by:

(a) an integrating electrical controller the signal voltage and a feedback

b voltage are switched on,

(b) a pulse width modulator controlled by the output voltage of the regulator,

(c) a switching transistor that

(c.) in series with the excitation winding a supply voltage and

(c ") from the pulse width modulator up and

is controllable and

(d) one connected in parallel to the field winding Diode through which, when the switching transistor is blocked, the collapse of the Magnetic field induced in the excitation winding Electricity flows and

(e) feedback means for generating the feedback voltage proportional to the modulated current

through the excitation winding.

So it is the current through the excitation winding by a pulse width modulator via a switching transistor controlled. Such a pulse width control has the advantage that on the switching transistor either (in the blocked state) the current or (in the conductive State) the voltage is zero. When the switching transistor is conductive, a current flows through the excitation winding and the switching transistor in the current

₆ 3508137

circuit of the supply voltage. This stream builds up slowly due to the inductance of the field winding up, so it rises. When the switching transistor is blocked, the current continues to flow in the via the Closed circuit diode. This current sets the stored in the magnetic field of the excitation winding Energy turns into Joule heat and decreases over time. Rise and fall are at appropriate Dimensioning of the circuit elements approximately linear, the current by one of the pulse width modulation dependent DC mean value fluctuates. The feedback means are designed in such a way that they correspond to the modulated current through the field winding provide at least approximately the corresponding feedback voltage. This is supported by the integrating controller compared with the signal voltage. When the DC mean value of the feedback voltage corresponds to the signal voltage remains the output signal of the integrating controller and thus the pulse width modulation remains unchanged.

Refinements of the invention are the subject of Subclaims.

An embodiment of the invention is as follows explained in more detail with reference to the accompanying drawings:

Fig. 1 shows a Venti1 control circuit for OQ regulation of the electric current through

the excitation winding of an electromagnetic actuatable valve.

Fig. 2 shows waveforms in the Venti 1 control circuit of Fig.l occur.

The valve control circuit contains an integrating electrical controller 10. This consists practically of an operational amplifier 12, whose Output to the inverting input via a Capacitor 14 is connected. At the inverting input of the operational amplifier 12 is via a Resistor 16 a signal voltage U "from a (not shown) encoder applied. This signal voltage Up serves as a reference variable. It is also connected to the inverting input of the operational amplifier 12 with the opposite sign still has a feedback voltage. The feedback voltage is efert of return means 18 in a manner still to be described.

The output of the controller 10 controls a pulse width modulator 20. The pulse width modulator 20 controls, in turn, a switching transistor via a transistor 22 and a Hi Ifsspeising voltage U 24

In the circuit of a supply voltage U are in

Series a first ohmic resistor 26, the switching transistor 24 and an excitation winding 28.

A current through the field winding is a (not shown) valve proportionally adjustable. The ohmic resistance of the field winding 28 is represented by a resistor 30. A diode 32 is connected in parallel with the excitation winding 28. The forward direction of the diode 32 is such that the current flows through the diode 32 can, which after blocking the switching transistor 24 is induced by the collapse of the magnetic field in the excitation winding 28. At senior Switching transistor 24 flows through the exciter winding

8 3508137

treatment 28 a current I. in the direction of accordingly indicated arrow, i.e. from top to bottom in Fig.l. The parallel diode 32 is for this direction of current locked. When the switching transistor 24 blocks, the circuit of the supply voltage U

interrupted. The collapsing magnetic field of the excitation coil 28 continues to induce a current in Direction of arrow I, which is now in that of the excitation winding 28, the resistor 30 and the diode 32 formed, closed circuit flows. With a suitable dimensioning, this current increases Components from approximately linear.

In terms of quantity, the following results:
15th

According to the law of induction is

^u ■ ^L ■ & ^m ·

During the switch-on time t. (see Fig. 2, line 1), during which the switching transistor 24 is conductive is, applies approximately

^U a ^{= L} - ^ ^R L ¹ LO
a

whereby

L is the inductance of the excitation coil 28,
ΔΙ is the total change in the current in the

Excitation coil 28 during the switch-on time t

(see Fig. 2, line 2),
I is the mean current in the excitation coil 28

during the switch-on time t. and

a

R is the ohmic resistance (30) of the

Excitation coil 28 is.

It is assumed that

^U Rl - i ^U a ⁽³

and

\ -ΐ ¹ LO ⁽⁴⁾

is, where
10

U _{1 is} the voltage drop across resistor 26 κ ι

is.

During the switch-off time t, i.e. the time (cf.

the end

2), during which the switching transistor 24 is blocked is is approximate

LA ¹ L + R. I _n -0, (5)

t ^LL
the end

if RI _{1n is} assumed to be large compared to the voltage drop across diode 32, ie

P ₁ . I _L0 ^ 0.7V. (6). From equations (2) and (5) it follows

U i (1 + t ^) R. L _n (7). ^a a ^{L LU}

If you set
30th

Sn _n ⁺ toff - ^{1 (8)}

(see Fig. 2), so we approx

ο. τ - ül ¹ ^ i "
LO R _L 'T "

ίο

It is

= K (9)

the pulse width modulation factor. So it will

¹ LO ■ ^K · Üf ⁽¹⁰⁾ ·

The mean current through the excitation coil 28 is proportional to the pulse width modulation factor K.

To this current on one of the signal voltage U
To regulate proportional value, the current must be measured and fed back to the controller 10 via suitable feedback means 18. A measurement of the current via the voltage drop across the field winding itself has the disadvantage that two additional lines then have to be led to the field winding, which is difficult with commercially available components. The voltage drop across the resistor 26 cannot directly serve as a measure of the current through the field winding, because a current flows through the resistor 26 only during the switch-on time.

It therefore becomes the voltage drop across the resistor 26 via lines 34 and 36 to a peak rectifier 38 switched. This charges a capacitor 40. The time constant of this combination of peak rectifier 38 and capacitor 40 is small compared to the switch-on time t. . The voltage U at the capacitor 40 therefore follows during the switch-on time t. practically instantly dem Voltage drop U across resistor 26. That's in

R I

the third and fourth lines of Fig.2.

The voltage fails during the switch-off time t

drop U _D , at the resistor 26 away. The condensate

K I

Sator 42 then discharges through the resistor 42. It should be noted that the negative feedback both inputs of the operational amplifier 12 are always kept practically at the same potential. Suitable dimensioning of the components ensures that the voltage U, across the capacitor 40 during the switch-off time t a b falls to the same extent as the current I. through the field winding 28. A feedback voltage is produced in this way, which in its course corresponds to the course of the current through the excitation winding follows.

In terms of quantity, this results in the following: During the switch-off time is

Aq = C Δ U (U)

whereby

Δς is the change in charge in capacitor 40

during the switch-off time, 25th

C is the capacitance of the capacitor 40 and

Δ U, the change .der on the capacitor 40 falling voltage during the switch-off time t (see Fig. 2, line

ä U S

4).
The change in charge / ■ q is the discharge current i times

Switch-off time t. So there is

from ^b

i. t -CAU, (12). from d

It's U again. small compared to the mean capacitor voltage U,. It then becomes the discharge current

It follows

U - R. C. ^ -ü (14).
!O

If we write equation (5) in the form

I = i 4_k (15)

^{L0 R} L Sus

so you can see that you can adapt the course of lh to the course of I: namely, one chooses

RC = i (16),

^R L

Then it will be

(17),

do ¹ LO

i.e. the voltage U, across the capacitor 40 changes in relation to its mean value during the Switch-off time t to the same extent as the Current I through the field winding 28 in the ratio changed to its mean value. A signal curve for the voltage U i on the capacitor is therefore obtained 40, which is also demolished during the switch-off time Signal curve of the current through the field winding is equivalent to. This voltage is applied to the controller 10 as a feedback voltage.

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Claims (3)

Claims (λJ valve control circuit for regulating the electrical current (I.) through the excitation winding (28) of an electromagnetically actuated valve according to a signal voltage (U) serving as a reference variable, characterized by: (a) an integrating electrical controller (10) to which the signal voltage (U) and a feedback voltage (U,) is applied are, „ _N (b) one of the output voltage of the regulator (10) controlled pulse width modulator (20), (c) a switching transistor (24) of the
25th (c,) in series with the excitation winding (28) at ε
1i egt and (28) at a supply voltage (U) _ (c ₉ ) from the pulse width modulator (20) is open and controllable and (d) one connected in parallel to the field winding (28) Diode (32), via which at locked switching transistor (24) if by the collapse of the magnetic field j induced in the excitation winding (28) Electricity flows, and (e) return means (18) for generating the Feedback voltage proportional to the modulus regulated current through the field winding (28). 2. Venti1 control circuit according to claim 1, characterized jQ that the return means (18) (a) contain a first ohmic resistor (26), the one between the switching transistor (24) and the ungrounded terminal of one _lt - supply voltage (U) in series with the Switching transistor (24) is arranged, as (b) a peak rectifier (38) to which the voltage (U _R -,) falling across the ohmic resistor (26) is applied, (c) a capacitor (40) connected to and from the peak rectifier (38) this is chargeable, and (D) a second ohmic resistor (42), via which the capacitor voltage as Feedback voltage (U,) to the controller (10) is switched to. 3. Valve control circuit according to claim 2, characterized characterized in that the capacitor (40) and the second ohmic resistor (42) generated time constant (RC) equal to the comparison ratio of the inductance (L) of the excitation winding (28) to the ohmic resistance (R) of the is formed by the excitation winding (28) and diode (32).