Patent Publication Number: US-6657846-B1

Title: Electromagnetic injection valve

Description:
FIELD OF THE INVENTION 
     The present invention relates to an electromagnetic injection valve having a double coil, in which a first and a second magnetic coil having the same characteristics are arranged on the same magnetic circuit, with one end of each magnetic coil being connected to the same supply voltage and the other end connected to a first and a second switching means, respectively, of an electronic drive circuit, and a holding circuit controllable by the drive circuit being parallel-connected to the first magnetic coil. 
     BACKGROUND INFORMATION 
     A conventional electromagnetic injection valve is described in Unexamined German Patent Application No. 2 306 007. In the conventional electromagnetic injection valve, two or more magnetic coils on the same magnetic circuit and an electronic drive mechanism functionally adapted to this arrangement are used to open and close the shutoff element of the injection valve by generating an electromagnetic attraction force opening the shutoff element from its closed state via a first excitation, generating an electromagnetic attraction force holding the shutoff element in its open state once it has been opened through a second excitation, and finally generating an opposite magnetic flux through a third excitation, thereby extinguishing the induced magnetic flux and closing the shutoff element from its open state. 
     As a general rule, the current increase in an electromagnetic injection valve, and thus also the force increase in an armature, is largely determined by the inductance and resistance of the valve coil and supply voltage Ubatt of the coil. The inductance is derived from the number of coil windings and the design of the magnetic circuit. In motor vehicles, the supply voltage is limited to 12 volts. Today&#39;s turn-on time requirements for an electromagnetic injection valve used in a motor vehicle have led, in single valve coils, to very high currents that cannot be achieved with present switching transistors and existing line resistance values. 
     Up to now, the fast increase in current and force needed in the injection valve at turn-on has been achieved with a higher voltage from a booster capacitor that is charged by a d.c.-d.c. converter or by recharging. The d.c.-d.c. converter is needed in magnetic circuits with high eddy-current losses because recharging with the valve inductance is too inefficient in this case. In addition, recharging with the valve would lead to excessively long booster capacitor charging times. The recharging current excites the magnetic circuit, thus reducing protection against leakage and unwanted valve opening. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a reliable electromagnetically operated injection valve with the shortest possible turn-on and turn-off times and simple circuitry. 
     In an electromagnetic injection valve according to the present invention, the object is achieved by winding the two magnetic coils in opposite directions so that their forces cancel each other out if the same excitation current flows through them, and by the drive circuit controlling the switching means during one complete open-hold-close cycle of the valve so that 
     during a first phase, an initial charging action occurs while the valve is closed, with both switching means being closed while the holding circuit is inactive, and the current flowing through the two magnetic coils rising at a relatively slow rate; 
     during a second phase, which is a valve opening phase, the current flowing through the second magnetic coil is quickly turned off as the second switching means opens, while the first switching means remains closed and the holding circuit remains inactive; 
     during a third phase, which is a holding phase, the holding circuit is activated, causing the current flowing through the first magnetic coil to drop to a holding current intensity; and 
     during a fourth phase, which is a closing phase, the valve is closed by at least deactivating the holding circuit and opening the first switching means. 
     The canceling action of the double coil transforms the actual valve activation, i.e., the valve opening action, into a turn-off action in one of the two coils in the second phase. The rapid current drop is then determined by dimensioning the extinction voltage. Rapid force rising times can therefore be achieved without increasing the supply voltage. The injection valve can be controlled by a conventional switching output stage or by a current-regulated switching output stage. Reversing the differential current at turn-off also makes it possible to shorten the closing action. One important advantage of the present invention is therefore the ability to simplify and reduce the cost of the output stage. No booster capacitor or d.c.-d.c. converter is needed in the control unit. As a result, it is also possible to easily integrate the output stage into the control unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a block diagram of a circuit of an electromagnetic injection valve having a double coil in conjunction with output stages of a drive circuit. 
     FIG. 2A shows a signal variation over time of control pulse A 2  for the second switching means shown in FIG.  1 . 
     FIG. 2B shows a signal variation over time of control pulse A 1  for the first switching means shown in FIG.  1 . 
     FIG. 2C shows a signal variation over time of control pulse A 1 / 1  for the holding circuit shown in FIG.  1 . 
     FIG. 2D shows a signal variation over time of a differential current of the currents flowing through the first magnetic coil and the second magnetic coil shown in FIG.  1 . 
     FIG. 2E shows a signal variation over time of individual currents flowing through the first magnetic coil and the second magnetic coil shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     In the circuit illustrated in FIG. 1, reference number  1  designates an equivalent circuit of an electromagnetic injection valve having a double coil. The magnetic circuit of injection valve  1  thus includes two magnetic coils SP 1  and SP 2  wound in opposite directions. Both magnetic coils SP 1 , SP 2  have the same characteristics, i.e., number of windings, inductance L, and winding resistance R cu , and their forces cancel each other out if the same current ISP 1 , ISP 2  flows through them due to the opposite winding directions. One end of each magnetic coil SP 1  and SP 2  is connected to the same supply voltage, e.g., Ubatt=12 volts in motor vehicles. A first switching means S 1 , which is represented symbolically as a single controllable switch, is connected in series to first magnetic coil SP 1 , assigned to a current-regulated switching output stage  2 , and opened and closed by a control pulse A 1 / 2  from switching output stage  2 . The circuit of first magnetic coil SP 1  also includes a current measuring element which, in FIG. 1, is a resistor R sens  that is connected in series to switching means S 1 . The with the voltage drop at resistor R sens  is proportional to current ISP 1  in the circuit of first magnetic coil SP 1  flowing through resistor R sens . 
     A first extinction means, e.g., in the form of a Zener diode ZD 1  with a Zener voltage U ZD1 , is connected in parallel to first switching means S 1  and current measuring element R sens . Alternatively, an RC extinction arrangement may be provided. First extinction means ZD 1  is used to quickly turn off current ISP 1  flowing through first magnetic coil SP 1 , as explained in greater detail below. In addition, a holding circuit composed of a switching means S 1 / 1  that can be opened and closed by a control pulse A 1 / 1  from current-regulated switching output stage  2  and a diode, is connected in parallel to first magnetic coil SP 1  and used to hold the injection valve in its open state while first switching means S 1  is open, as explained in greater detail below. 
     Also connected in series to second magnetic coil SP 2  is a second switching means S 2  that can be opened and closed by a control pulse A 2  and is parallel-connected to a second extinction means in the form of a Zener diode ZD 2 . Second switching means S 2  is operated by an unregulated single switching output stage  3 . Zener diode ZD 2 , which is connected in parallel to second switching means S 2  and used as a second extinction means, is used to quickly turn off current ISP 2  flowing through second magnetic coil SP 2 , as explained below. 
     As an alternative to the circuit embodiment illustrated in FIG. 1, it is also possible to operate double-coil injection valve  1  in other embodiments having two single switching output stages and no current regulation. In this case, however, the current drop in the holding phase described below is not possible. 
     The function and operation of the circuit according to the present invention described above and illustrated in FIG. 1 for the electromagnetic double-coil injection valve are explained below on the basis of the signal timing diagram shown in FIG.  2 . FIGS. 2A-2E show the variations over time of: control pulse A 2  for the second switching means (FIG.  2 A); control pulse A 1 / 2  for first switching means S 1  (FIG.  2 B); control pulse A 1 / 1  for the holding circuit (FIG.  2 C); differential current Id=ISP 1 −ISP 2  of the currents flowing through first and second magnetic coils SP 1  and SP 2  (FIG.  2 D); and individual currents ISP 1 , ISP 2  flowing through first and second magnetic coils SP 1  and SP 2 , over one complete open-hold-close cycle divided into four phases—Phase 1, Phase 2, Phase 3, and Phase 4—from a time t 0  to a time t 6 . The description below follows a sequence from Phase 1 to Phase 4. 
     Charging, Phase 1; t 0 -t 1 : 
     At time t 0 , both switching means S 1 , S 2  are or have been turned on; A 2  and A 1 / 2  are on (FIGS. 2 a  and  2 B). Currents ISP 1 , ISP 2  rise at a relatively slow rate (FIG.  2 E). Maximum current I 0 -ON=Ubatt/R cu  is lower at Ubatt=12 volts than I 0 -OFF at turn-off in Phase 2. Both coils SP 1 , SP 2 , i.e., both switching means S 1 , S 2 , must therefore be turned on relatively early prior to the actual opening of valve  1 . The current during this phase can be controlled by selecting a suitable closing time prior to Phase 2 (opening time t 1 ). An alternative is to regulate the current in both coils SP 1 , SP 2 . Time constant Tau−L/R cu  indicates the rate of current rise at time t 0 . The identical characteristics and opposite winding directions of both magnetic coils SP 1 , SP 2  yield differential current Id=ISP 1 −ISP 2 =0 (FIG.  2 D). 
     Valve Opening, Phase 2; t 1 -t 3 : 
     At the start at time t 1 , current ISP 2  is quickly turned off by the extinction action of second Zener diode ZD 2  as S 2  is opened by single switching output stage  3  due to A 2 =OFF (FIG.  2 A). The current gradient during turn-off at time t 1  is determined by I O -OFF=U ZD2 /R cu  and Tau=L/R cu . With a correspondingly high extinction voltage U ZD2  of Zener diode ZD 2 , this current gradient is much higher than at turn-on. Current ISP 1  flowing through magnetic coil SP 1  remains at inrush current level I O -ON. Alternatively, this can also be accomplished by current regulation (see FIG.  2 E). The force increase in the valve is proportional to the square of differential current Id=ISP 1 −ISP 2  and therefore very fast (short turn-on time). 
     Holding phase 3 with open valve; t 3 -t 5 : 
     During the holding phase, differential current Id (FIG. 2D) is reduced to the holding current level at magnetic coil SP 1  by current-regulated switching output stage  2 , which includes current regulator  4 , and regulated between Id−Hmax and Id−Hmin by the current regulating arrangement. S 1  is turned off by control pulse A 1 / 2  with current extinction by first Zener diode ZD 1 . In this case as well, a correspondingly high Zener voltage U ZD1  accelerates extinction and thus the turn-off action of current ISP 1 . To maintain the holding current level, the holding circuit, i.e., switching means S 1 / 1 , is closed by control pulse A 1 / 1  (FIG.  2 C), and S 1  is intermittently opened and closed (FIG.  2 B). Holding current ISP 1 -H is regulated between ISP 1 -Hmax and ISP 1 -Hmin during Phase 3. 
     Valve Closing; Phase 4, t 5 -t 6 : 
     To close the valve, either only current ISP 1  flowing through magnetic coil SP 1  is turned off or, to support the closing action with even shorter turn-off times, current ISP 1  flowing through coil SP 1  is turned off by simultaneously briefly turning on current ISP 2  flowing through magnetic coil SP 2 , which is not illustrated in FIGS. 2A-2E. Doing so reverses differential current Id and thus the force. 
     FIGS. 2A-2E also shows, in Phases 2, 3, and 4, the high negative current gradients that can be achieved with the features according to the present invention, with these gradients symbolized by time constants Tau shown in the figures. 
     The double magnetic coil with a canceling effect according to the present invention transforms the actual turn-on action of the electromagnetic injection valve, i.e., opening the valve during Phase 2, into a turn-off action in one of the two magnetic coils. The rapid current drop is determined by the extinction voltage. Rapid force increase times can thus be achieved without actions that increase the supply voltage. The electromagnetic injection valve can be controlled with either a conventional switching output stage or, as in the embodiment described above, with a current-regulated switching output stage. Reversing differential current Id at turn-off in Phase 4 also makes it possible to shorten the closing action. 
     Therefore, one important advantage of the present invention is the ability to simplify the output stage. No booster capacitor or d.c.-d.c. converter has to be provided in the control unit. This makes it easier to integrate the output stage into the control unit.