CA1307816C

CA1307816C - Energization of an electromagnet

Info

Publication number: CA1307816C
Application number: CA000524543A
Authority: CA
Inventors: Josef Buchl
Original assignee: Audi AG
Current assignee: Audi AG
Priority date: 1985-12-05
Filing date: 1986-12-04
Publication date: 1992-09-22
Anticipated expiration: 2009-09-22
Also published as: DE3683276D1; ES2029225T3; EP0229880A1; EP0229880B1; JPH0451042B2; DE3543017C1; JPS62169406A

Abstract

ABSTRACT OF THE DISCLOSURE

A circuit and a method for periodically energiz-ing an electromagnet of the kind useful for driving a gas exchange valve in an internal combustion engine by measur-ing either the increase in energizing current or the decay of the holding current during an energization cycle to determine the instant at which energization must commence for the next following cycle to assure flawless engagement of the armature of the electromagnet with the stator in this next cycle.

Description

~L307~6 The invention relates generally to the energization of an electromagnet and, more particularly, to the energization of an electromagnet of the kind useful in driving and retaining a gas exchange valve of an internal combustion engine in its terminal positions.

It is well known that an electromagnet requires significantly higher current le~els for attracting the armature into engagement with its stator or pole piece than it requires for subsequently maintaining the engagement. It would, therefore, be possible to reduce the energy consumption of an electromagnet during each operating cycle ~y initially driving it at the high current level required for attracting the armature into engagement with the stator and by thereafter reducing the current to a level sufficient 15 to maintain the engagement.

The invention is directed, inter_alia, to an electromagnetic operation in which an ~lectromagnet cyclically repeats its operation of attracting and maintaining its armature in engagement with its stator, each operating cycle consisting of a high current level phase followed by a phase of reduced current level.

Electromagnetically controlling the driving of gas exchange valves of internal combustion engines moved between their open and closed positions by spring bias is one possible field of advantageous application of the :~ :
::: ::

`:

~:
,c, : ::
':

:. .

0~
pre~ent lnvention. Such a system has been generally dis-closed in west German Patent Specification DE-OS 30 2~ 109.
One of the problems encountered in operating a gas exchange valve in the manner referred to resides in the fact that the instant at which energization of the electromagnet has -to commence must be chosen in such a manner that even at slowly increasing current the armature is a~tracted into engagement with the stator at a predetermined time. This, however, is affected by such variables as changes in temperature and supply voltage, current distribution, or changes occurring generally during the course o~ engine operation. '~hese variables cannot be neglected since on the one hand the voltage supply of an automotive vehicle i5 subject to considerable variations and, on the other hand, the temperature o~ an internal combustion engine during its initial start~up operation is markedly different from its normal operating temperature. One way of operating electromagnetically controlled gas exchan~e valves in a manner assuring proper engine performance would be to drive its electromagnets at high but energy consuming currents levels.
Circuits accommodating the attraction and reten-tion phases during energiæation cycles of electromagnets are generally known and have been found to be useful in reducing the energy that would otherwise be required or properly drivin~ such electromagnets. Such a reduction in energy requirements is oE particular advantage in automo-tive vehicles where solenoids have of late found applica-tion for controlling the movement of gas exchange valves.
A driver circuit for energizing an electroma~net of this kind is generally disclosed in west German Patent D~-A 35 07 103. The circuit purports to provide for reli-able switchin~ between an attracting or energizing phase and a subse~uent retention or holding phase during an operating cycle o~ an electromagnet. Assured attraction of the armature o~ the electromagnet against its stator is said to be attainable by monitoring the current in the coil of the solenoid, for instance by measuring the maximum current level. During the energization or at-traction phase the current is measured by a comparator. A similar arrangement of current level monitoring of means of a comparator is the general sub~ect of west German Patent Specification DE-A 29 32 859.

s The devices of the prior art may function satisfactorily under certain static operating conditions. They fail, however, to take into consideration the dynamics of autumotive engine operation.
For instance, variations in the rate of current level increases as a result of temperature-induced changes ln the inductance of the solenoid coil, would prevent, or at least mitigate against, an assured attraction of the solenoid armature against the stator.

It is, of course, well-known that proper operation of an internal combustion engine requires flawless operation of its gas exchange valves. That is to say, fuel intake and exhaust valves must move between their open and closed positions in phase with the movement of the piston. Movement of the valves out of phase with the piston, or no movement at all, would result in faulty or no running of the engine, and may ha~e a serlously adverse effect on fuel consumption.

The present invention provides for circuitry which permits proper operation of an electromagnet for driving a gas exchange valve.

The invention also provides circuitry for eneryizing an electromagnet in a manner which comp~nsates for changes in its inductance.

The invention further provides circuitry which determines the instant at which energization of an electromagnet must commence to move the armature into engagement with the stator at a predeterm~ned time.

, .
L, ~3~7~6 The invention again provides an energization circuit for an electromagnetic gas exchange valve actuator whlch determines the instant at which energization must commence to assure proper valve functioning changes in the inductance of the electromagnet notwithstanding.

The invention also provides circuitry for commencing energization of an electromagnet at an instant depending on the rate of current increase during the previous operating cycle of the electromagnet.

The invention further provides for circuitry responsive to the operational pàrameters of an internal combustion engine for determining the rate of energization of an electromagnet used for driving a gas exchange valve.

The invention also provides an ene~gization circuit for an electromagnet used for driving a gas exchange valve which is responsive to changes in vol-tage levels or operating temperature for determining the instant at which energization commences.

The invention again provides a method of energizing an electromagnet used for controlling the movement of a gas exchange valve in a manner compensating for changes in operating conditions and current levels.

Thus according to the present invention there is provided apparatus for periodically energizing an electromagnet, each period lncluding a phase for driving the armature of the electromagnet to engage the stator at a predetermined time and a phase for maintaining said engagement, comprising: means actuable at a predetermined instant during each period for selectively connecting said electromagnet to a source of energizing current;
means ior measuring changes in the energizing current ~lowing in said elec-tromagnet during at least a portion of said period;
means for deriving ~rom said change in current a value _ 4 _ ;.

.

13~316 representative oE said instant for a subse~lent period and means responsive to said deriving means for actuating said connecting means. Suitably said measuring means comprises current level detection means having an input connected to resistance means between said electromagnet and said source of current. Desirably said measuring means further comprises an output member connected to switch means between said electromagnet and said source of current. Preferably said switch means comprises a transistor hav~ng its base connected to said output member of said measuring lo circuit.

In one embodiment of the present invention said measuring means comprises first timing means for defining the length of sald portion of said period. Suitably said measuring means comprises storage means for storing a value representative of the current level in the electroma~net at the end of said portion. Desirably said apparatus further comprises second timing means connected to said storage means for generating a signal derived from said stored current level value for actuating said connecting means.
Preferably said second timlng means is connected to logic circuit means, said logic circuit means controlling the actuatlon of said connecting means. Desirably said logic circult means is connected to said measuri~g means for controlling said output member thereof. Preferably said logic circuit is connected to said first timing means for controlling the actuation thereof~

The present invention also provides a method of periodically energizing an electromagnet~ each period comprising a phase for driving the armature of said electromagnet to engage said stator at a predetermined time and a phase for maintaining said engageme~t, comprising the steps of: connecting said electromagnet to a source of energizing current at least during a predetermined portion of said period; measuring the change ln current at least during a part of said portion; and deriving from sald change a value representatiYe of the instant at which said electromagnet is to be connected to said source of energlzlng .

~3~7~6 current in a subsequent period to cause engagement of the armature with the stator at said predetermined tlme. Suitably said measuring step commences at the beginning of said portion.
Preferably said measuring commences with said driving phase.
Desirably said measuring step is undertaken for a predetermined period to measure the level of current extant in said electromagnet at the end of said period. Suitably a value representative of said extant current level i~ stored in storage means. Deslrably said value determines the instant at which said electromagnet is connected to said source of energizing current in a subsequent period.

In one embodiment of the invention said measuring step is undertaken for a period sufficient for the current to decay to a predetermined level. Suitably a~value representative of said level is storsd in storage means for determining the instant at which said electromagnet is connected to said source of energizing current in a subsequent period.

The invention accordingly comprises a mechanism and system possessing the construction, com~ination of ~lements and arrangements of parts whlch are exemplified in the detailed disclosure.

The invention provides novel circuitry for periodically energizing an electromagnet in cycles including an energization phase and a subseguent holding phase, comprising means for monitoring current levels in the electromagnat at least during a portion of the e~ergization phase and means responsive to a predetermined current level for adjusting the instant at which energization of the electromagnet must commence in a subsequent - energization cycle. Means may be provided for monitoring the rate of change in the current level during a predetermined interval during the energization phase. In accordance with the invention the monitoring interval may commence simultaneously with the flow of energizing current. In accordance with the - 5a -:

, ' ~

.

~o~

invention means may also be provided for monltoring the rate of current increase up to a predetermined threshold level.
Advantageously, the circuit in accordance with the invention comprises logic circuit means ~or controlling the flow of current S through the electromagnet in response to external control signals, level detecting means for monitoring the level of current flowing in the electromagnet, a first variable timing member for providing an input signal to the logic circuit means for defining the instant at which the flow of energizing current commences, and a second timing member operatively connected with the level detecting means for monitoring the rate of change of the current level. In accordance with the invention the second timing member defines a predetermined interval at the end of which the level detecting means is actuated to transfer a current value stored therein to a storage means. Alternatlvely, the second timing member may comprise means for monitoring the time required for reaching the threshold value and for transferring this value to a storage means. Furthermore, means may be provided for adjusting the interval generated by the first timing member in response to the value stored within the storage means.

The present invention will be further illustrated by way of an illustrative embodiment when read in connection with the accompanying drawings, in which:

FIG. l is a diagram of a circuit in accordance wlth the invention for energ1zing an electromagnet;
:
FIG. 2 is a graphical representation of ' - 5b -.

.. . ..

electrical signals generated by the clrcuit of FIG. 1;
FIG. 8 i~ a diagram of a circui.t o.f an alternate embodime~t of the invention; and FIG. 4 is a ~raphical representation of electrical signals yenerated by the circuit of FIG. 3.
DESCRIPTION OF THE ~ D~D '~y~DI-MENTS
FIG. 1 shows an electromagnet or solenoid 10 with a freewheeling or feedback circuit 24 connected in paral-lel thereto. A diode 12 is connected in the freewheeling circuit 24 to control the direction o~ current ~low there-in. ~ne side of the solenoid 10 is connected to the posi-tive terminal 14 of a voltage supply . The other side o~
the ~olenoid 10 is connected, by way of a line 22, to ground 16. A bias resistor 20 and a switch, shown as a transistor 18, are connected in series between the sole-noid 10 and ground 16. The purpose of the resistor 20 is to provide a signal representative o~ a predetermined level of current in the solenoid 10. This signal is applied to a first input terminal of a measuring circuit or level detector A by way of a line 26 connected to the junction o~ the transistor 18 and the resistor 20. The level detector A may be of a kind well known in the art and i~ deemed not to require further description. A first output 28 o~ the level detector A is connected to the base of the transistor 18. A second input 30 of the level detector A i5 connected to the output of a logic circuit B
which at times applies to the level detector A a pulse controlling the instant at which energization of the solenoid 10 must commence to assure engagement of the ar~nature with the stator o~ the electromagnet at the proper time.
The logic circuit B in turn is connected by a line 40 to a first timing circuit ~ which clocks an interval at the expiration of which the transistor 18 must be rendered conductive by the pulse applied to its base by the level detector A. To start its timing function the timing circuit E responds to a pulse S1 supplied from an external source (not shown) along line 42.

~lL310r7~

A second o~tp~t of the level d~tector A is connected to a storage register C along line 32. The register C ~urnishes signals representative of its contents to the first timing circuit ~ by way of a line 34, as well as to a se~ond timing circuit D along li.ne 36.
The second timing circuit D i~ also connected to the logic circuit B by a line 38.
The instant at which energization of the elec-tromagnet 10 must commence is determined as follows:
The pulse S1 is fed to the timing circuit E. The pulse S1 i9 shown at 2c in FIG. 2. The timing member E
responds to the leading edge of the pulse 2c to start its timing function and furnishes a pulse shown in FIG. 2 at 2g. The trailing edge of the pulse 2g determines the time t1 at which logic circuit B applies a pulse to the level detector A to render the transistor 18 conductive. Once the transistor 18 conducts, energizing current begins to flow through the solenoid 10 as shown by curve 2a. The energizing current i~creases until time to at which inst~nt the armature strikes the stator to be retained by it. The energi2ation phase is thus safely termi~ated.
Striking of the stator by the armature is usually accom-panied by a current drop of short duration as shown by the slight break in curve 2a, owing to the change in the inductance o~ the solenoid coil,.
In accordance with the invention, the flow of current in the solenoid is monitored during the energi-zation phase, and any drop in voltage is detected by the level detector A. At the same time as the energization phase commences the second timing member D is aotuated as shown by curve 2e of FIG. 2. At the instant of the trailing edge of pulse 2e a signal of the current level --W1 in FIG 1-- then present in the level detector A is ~ed to, and stored in, the register C.
Thereafter, at time to, a signal 2d i5 applied to an input gate of the lo~ic circuit B. Signals S1 and S2 are present during the holding phase of the cycle. Short-ly be~-ore termination of the holding phase, the signal S

~3~
is turned off, and the logic circuit ~ swltches from a phase of prov.iding the electromagnet with cyclical holding current pulses ~lowiny in the freewheeling or feedback circuit 2~ to a phase oP con~tant current which at the termination of signal S2 drops to O to deenergize the electromagnet for the release of the armature.
In accordance with the invention the timing circuit E reads the current value stored in register C
before a new energization cycle is commenced, for the interval 2g set by the timing circuit E is derived from the current value stored in register C.
If, ~or instance because o~ higher operating temperatures or a lower supply voltage, the inc~ease in current is slower as shown for instance by curve 2b than that shown by curve 2a, the voltage is monitored during an interval 2f starting at tim~ t2 and set by the second timing circuit D. In the example shown it will have reached value W2 --which is lower than W1-~ at the end of the interval set by the second timing circuit D.
OThe interval set by the first timing circuit E for the succeeding energization cycle is a function f W2. The pulse will be shorter since the energization commences earlier.
For this reason and as shown at 2h in FIG. 2, the first timing circuit E releases its W2 derived pulse upon receipt of pulse S1 depicted by curve 2c. The pulse ?h is markedly shorter than pulse 2g of the previous energi-zation cycle. Hence, the energization current of the new cycle begins to flow at the earlier instant tz.
As previously mentioned, the present invention may advanta~eously be applied to the control of gas exchange valves of internal combustion engines.
Therefore, each second of operation entails several energization cycles. However, the paramet~rs affecting the slope or profile of the energizing current flow change comparatively slowly. Thus, i~ may not always be necessary to make adjustments in response to abrupt changes in engine operation. The invention does, however, . .
; -8-: ~ ' ` - ~ 3iD7~1G
provide simple means responding to significant changes in operating conditions for making appropriate adjustments, and ~or assuring flawless opening and closing o the valves at a very low energy consumption level.
FIG. 3 depicts an alternative embodiment of the invention. The circuit of this embodiment differs from the one of Fig. 1 in that the bias resistor 20' is connected in the ~reewheeling circuit 24' rather than hetween the transistor 18 and ground 16. In all other respects the circuit arrangement is substantially the same as that o~ FIG. 1. Therefore, the reference characters are those o~ FIG. 1, but they have been primed.
Curve ~a in FIG. ~ depict~ a curr~nt profile comprising an energising phase and a holding phase substantially identical to that of curve 2a, except that in this case evaluation or monitoring of the profile commences when the energizin~ current is turned of f .
Instead o~ monitoring th~ rise in current during a predetermined interval as in the previous embodime~t, the circuit of FIG. 3 measures the interval required for the current in the feedback circuit 24' to decay from the peak energi~ation level W1' to a lower level W2'. The interval is represented as pulse ge. The length oE the pulse 4e is in this case detected by the second timing circuit D' and is stored in the register C'. It will subse~uently determine the timing interval ~f the first ~iming circuit E' shown as curve 4g'. To be ahle to measure the current in the freewheeling circuit 24' the bias resistor 20' must, of course, be connected in the ~eedback circuit 24'.
Energization o~ the electromagnet 10' commences with a pulse S1 shown by curve 4c. The pulse S1 also starts the timing circuit E'. Curve 4g depicts the interval set by the timing circuit E' under conditions of a relatively teep current increase.
However, where the current increases at a relatively slow rate as shown by curve 4b, the drop in current from W1' ~o W2' re~uires a commensurately longer _g_ , 78~6 interval. Thus, a value is stored in the register C' which corresponds to the pulse shown at 4f. Thi.s value controls the subsequent energization cycle by causing the timing circuit to yenerate a signal as shown at 4h. Hence, the instant at which the transistor 18' begins to conduct occurs earlier than in the previous energization cycle.

Those skilled in the art will appreciate that the measuring of current as described in connection with the embodiment of FIG. 1 may al50 take place at the trailing flank of the energizing current curve, and that the measurin~
of current described in connection with the embodiment of FIG. 4 could also be done in the leading flank of the energizing current curve.

; 15 : ~ ~

:: :::

:~ ~

,~. ~

~ ~.. .. . .

Claims

1. Apparatus for periodically energizing an electro-magnet, each period including a phase for driving the armature of the electromagnet to engage the stator at a predetermined time and a phase for maintaining said engagement, comprising:
means actuable at a predetermined instant during each period for selectively connecting said electromagnet to a source of energizing current ;
means for measuring changes in the energizing current flowing in said electromagnet during at least a portion of said period;
means for deriving from said change in current a value representative of said instant for a subsequent period; and means responsive to said deriving means for actuating said connecting means.

2. The apparatus of claim 1, wherein said measuring means comprises current level detection means having an input connected to resistance means between said electromagnet and said source of current.

3. The apparatus of claim 2, wherein said measuring means further comprises an output member connected to switch means between said electromagnet and said source of current.

4. The apparatus of claim 3, wherein said switch means comprises a transistor having its base connected to said output member of said measuring circuit.

5 The apparatus of claim 3, wherein said measuring means comprises first timing means for defining the length of said portion of said period.

6. The apparatus of claim 5, wherein said measuring means comprises storage means for storing a value representa-tive of the current level in the electromagnet at the end of said portion.

7. The apparatus of claim 6, further comprising second timing means connected to said storage means for generating a signal derived from said stored current level value for actuating said connecting means.

8. The apparatus of claim 7, wherein said second timing means is connected to logic circuit means, said logic circuit means controlling the actuation of said connecting means.

9. The apparatus of claim 8, wherein said logic circuit means is connected to said measuring means for controlling said output member thereof.

10. The apparatus of claim 9, wherein said logic circuit is connected to said first timing means for controlling the actuation thereof.

11. A method of periodically energizing an electro-magnet, each period comprising a phase for driving the armature of said electromagnet to engage said stator at a predetermined time and a phase for maintaining said engagement, comprising the steps of:
connecting said electromagnet to a source of energizing current at least during a predetermined portion of said period;
measuring the change in current at least during a part of said portion; and deriving from said change a value representative of the instant at which said electromagnet is to be connected to said source of energizing current in a subsequent period to cause engagement of the armature with the stator at said predetermined time.

12. The method of claim 11, wherein said measuring step commences at the beginning of said portion.

13. The method of claim 12, wherein said measuringcommences with said driving phase.

14. The method of step 13, wherein said measuring step is undertaken for a predetermined period to measure the level of current extant in said electromagnet at the end of said period.

15. The method of claim 13, wherein said measuring step is undertaken for a period sufficient for the energizing current to reach a predetermined level.

16. The method of claim 14, wherein a value repre-sentative of said extant current level is stored in storage means.

17. The method of claim 16, wherein said value deter-mines the instant at which said electromagnet is connected to said source of energizing current in a subsequent period..

18. The method of claim 11, wherein said measuring step commences with said maintaining phase.

19. The method of claim 18, wherein said measuring step is undertaken for a period sufficient for the current to decay to a predetermined level.

20. The method of claim 19, wherein a value represen-tative of said level is stored in storage means for determin-ing the instant at which said electromagnet is connected to said source of energizing current in a subsequent period.