WO2005093239A1

WO2005093239A1 - Method and device for controlling the fuel supply in a motor

Info

Publication number: WO2005093239A1
Application number: PCT/FI2004/050033
Authority: WO
Inventors: Antero SALOJÄRVI
Original assignee: Mitron Oy
Priority date: 2004-03-29
Filing date: 2004-03-29
Publication date: 2005-10-06

Abstract

The invention relates to a method for controlling a solenoid (S) to be used in the fuel supply of an engine. In the fuel injection step (t1-t8), the current to be supplied to the solenoid (S) is controlled to set and maintain the solenoid (S) in a pulling state. For generating the current to be supplied to the solenoid (S), at least one power source (2) is used, in parallel with which a capacitor (C1) is connected to level out the load on the power source (2) in the injection step. In the method, the intensity of current to be used for setting the solenoid at the pulling stage is also increased by means of an auxiliary capacitor (C2) which is charged with energy from the power source (2) before the beginning of the injection step. The invention also relates to a device (1) in which the method is applied.

Description

METHOD AND DEVICE FOR CONTROLLING THE FUEL SUPPLY IN A MOTOR

The present invention relates to a method for controlling a solenoid used in the fuel supply of an engine, wherein the current supplied to the solenoids at the stage of fuel injection is controlled to set the solenoid in a pulling state and to keep it in the pulling state, and in the generation of the current supplied to the solenoid, at least one power source is used, in parallel with which a capacitor is coupled to level out the loading of the power source in the injection step. The invention also relates to a device for controlling a solenoid used in the fuel injection of an engine, which device comprises means for controlling the current supplied to the solenoids to set the solenoid in a pulling state and to keep it in the pulling state during the stage of fuel injection, and at least one power source to generate the current supplied to the solenoid, and . a capacitor is coupled in parallel with the power source to level out the loading of the power source in the injection step.

Fuel injectors used for supplying fuel must be capable of injecting a precisely determined quantity of fuel into the cylinders of a combustion engine, such as a diesel engine or a petrol engine. Each fuel injector supplies the fuel into the cylinder via an inlet valve in the cylinder. The injection operation normally takes substantially as long as the inlet valve is open. In practice, however, the valve opens with a short delay, wherein this delay must be taken into account in the fuel injection. To provide a feeding operation as accurate as possible, the delay should be as precisely the same as possible each time the valve opens. Normally, in modern engines, valves are opened and closed by solenoids which are controlled by an electric current. Thus, the electric current to be supplied to the solenoid generates a magnetic field in the solenoid, which magnetic field, in turn, causes a movement of the solenoid plunger. This plunger is coupled to the valve, wherein the valve is opened by the movement of the plunger. In a corresponding manner, by disconnecting the input of current to the solenoid, the magnetic field in the solenoid is reduced almost to zero, wherein a means, such as a spring, coupled to the plunger and causing a counterforce, causes the return of the plunger to its initial position and the closing of the valve.

Arrangements have been developed to cause a response as quick as possible in the solenoid. This is implemented by supplying, -at the beginning of the fuel injection step, a relatively high intensity of current to the solenoid and by maintaining the intensity of current at this first level for some time. After this, the intensity of current is allowed to drop to a second, lower level. At the end of the injection step, the current supply to the solenoid is disconnected. However, the intensity of current on the first or the second level is not constant but it varies slightly. A problem in such arrangements is, among other things, the fact that the intensity of current should be increased to the first level as quickly as possible so that the delay in the opening of the valve would be as short as possible and substantially equal in each injection step. Attempts have been made to solve this problem in the current supply by using boosters which can momentarily generate a high intensity of current. Typically, such a booster is implemented with a capacitor which is charged before the beginning of the input stage, and during the input stage, the charge of this capacitor is used to reduce the time of intensifying the current supplied to the solenoid.

US patent 6,031 ,707 discloses an arrangement in which a capacitor is used to intensify the current supply to the solenoid. In this arrangement, a reference waveform is generated which corresponds to the target waveform for the current to be supplied to the solenoid. The current to be supplied from the power source to the solenoid is modulated by means of the charge in the capacitor in such a way that when the input current is lower than the target current, the capacitor is used in the current input. In other cases, the power is supplied from the power source. However, such an arrangement necessitates the use of a relatively large capacitor as well as a high voltage of about 120 to 140 V for charging the capacitor. The capacitor must be capable of charging a charge which is more than double the energy required by one solenoid in one injection step. It is an aim of the present invention to provide an improved method and device for use in controlling the fuel injection in an engine. The invention is based on the idea of using at least one auxiliary capacitor for intensifying the current supply. This auxiliary capacitor is charged partly by the energy trapped in the solenoid after the injection step. Neither armature of the auxiliary capacitor is coupled to the ground potential but it, in a way, floats in relation to the ground potential. As a result, the voltage on the contacts of the auxiliary capacitor can be connected in series with the voltage of the power supply used for supplying the solenoid, thereby increasing the voltage on the solenoid. As a result, it is possible to increase the rate of intensifying the current in the solenoid. To put it more precisely, the method according to the present invention is primarily characterized in that the intensity of current used for setting the solenoid in the pulling state is further increased with an auxiliary capacitor which is charged by energy supplied from the power source before the beginning of the injection .step- The device according to the invention is primarily characterized in that the device also comprises an auxiliary capacitor which is arranged to be used, in addition to the power source, to increase the intensity of current used for setting the solenoid in a pulling state, and means for charging the auxiliary capacitor with energy supplied from the power source before the beginning of the injection step.

Considerable advantages are achieved by the present invention when compared to methods and devices of prior art. When using the method according to the invention, a faster increase in the intensity of current is achieved when the solenoid is turned on, i.e. when the valve is opened. The device according to the invention has a simpler structure than most control devices of prior art, because the device of the invention does not require a separate power source or a booster to provide a higher voltage to the solenoid, nor a separate control from a microcontroller or a corresponding control block. In the arrangement according to the invention, the auxiliary capacitor is charged after each current impulse, wherein a higher voltage can be supplied to the solenoid during the whole pulling stage of the solenoid. Moreover, the arrangement according to the invention does not require the use of a relatively large capacitor. Furthermore, the arrangement according to the invention utilizes the energy trapped in the solenoid during the injection step for charging the auxiliary capacitor for the next injection step.

In the following, the invention will be described in more detail with reference to the appended drawings, in which

Fig. 1 shows the coupling of a device according to an advantageous embodiment of the invention,

Fig. 2a shows the operation of the coupling of Fig. 1 when the current supplied to the solenoid is intensified during the pulling stage of the solenoid,

Fig. 2b ■ shows the operation of the coupling of Fig. 1 when the current supplied to the solenoid is decreased at the pulling and holding stages of the solenoid, ^:

Fig. 2c shows the operation of the coupling of Fig. 1 when the current supplied to the solenoid is intensified at the holding stage of the solenoid,

Fig. 2d shows the operation of the coupling of Fig. 1 at the end of the injection step,

Fig. 3a shows the intensity of the current flowing through the solenoid during the injection step, and

Fig. 3b shows the voltage in the positive terminal of the solenoid during the injection step.

The control of the injection in a combustion engine (not shown in the appended drawings) can be described by means of different steps. In this description, the injection operation will be described by using the following terms: The injection step refers to the time when fuel is to be injected into the cylinder, i.e., the inlet valve of said cylinder is to be kept open. The injection step can be further divided into stages relevant for the operation of the solenoid, preferably into the pulling stage and the holding stage. At the pulling stage, the solenoid plunger is to be pulled into a position in which the inlet valve of the cylinder is open. At the holding stage, the solenoid plunger is to be kept in this position. Further, it is possible to use the term rest stage, in which the solenoid plunger is in a rest position. However, the timing of the rest stage is outside the injection step. It is obvious that in practical combustion engines which typically comprise several cylinders, some of the functions in the control device 1 are shared and some are cylinder-specific. However, in the substantial elements, the operation of each cylinder- specific part is the same; therefore, in the following, we shall primarily focus on describing the operation of the device in the control of the inilet valve of a single cylinder.

Figure 1 shows the diagram of connection of a device 1 used for controlling the fuel injection according to one advantageous embodiment of the invention. The device 1 comprises a power source 2 which is used to generate the operating voltage required for the operation of the device 1. In parallel with the power source, a first charging capacitor C1 is coupled to be used e.g. for generating the current for coupling the solenoid at the beginning of the injection step. In the diagram of connection of Fig. 1 , it can be seen that the device 1 has two supply circuits for the solenoid S. The first supply circuit comprises a first switch T1 as well as diodes D1 and D3 coupled in the forward direction. Accordingly, the second supply circuit comprises diodes D4 and D5, a second switch T2 and an auxiliary capacitor C2. Furthermore, a diode D3 is coupled between the first and second supply circuits. Furthermore, between the cathode of the diode D1 and the ground potential, a diode D2 is coupled in the reverse direction. The cathode of the diode D1 of the first supply circuit and the cathode of the diode D4 of the second supply circuit are connected to the first terminal S.1 of the solenoid S (= to the positive terminal, with the polarity markings of voltages in Fig. 1). A third switch T3 and a diode D6 are coupled to the second terminal S.2 of the solenoid S. The second terminal of the third switch is coupled to the ground potential via a measuring resistance R1. The solenoid S, the third switch T3, the diode D6, the measuring resistance R1 as well as the measuring line 5 are valve-specific (solenoid-specific); that is, the device 1 comprises a separate block 4 for each solenoid. For the sake of clarity, however, only one such block 4 is shown in the drawings.

The operation of the device 1 is controlled by a control block 3. Preferably, data 6 about the position of the crankshaft in the engine is transmitted to the control block to determine the position of the pistons at each time, for timing the solenoids. Furthermore, the solenoid-specific measuring line 5 can be used to transmit measurement data from each solenoid S to the control block, to be used for measuring the current flowing through the solenoid S, as will be presented hereinbelow. The control block 3 may comprise a conversion block 7, in which the measuring signal in analog form can be processed, primarily for diagnostic purposes.

The switches T1 , T2, T3 used in the device 1 are preferably FET transistors, such as MOSFET transistors.

We shall now describe the operation of the device according to Fig. 1. The time markings refer to Figs. 3a and 3b which show some graph representations for the voltage of the first terminal of the solenoid (Fig. 3b) and for the current flowing through the solenoid (Fig. 3a). When the control block 3 determines that the injection step is about to start (moment of time t^, the plunger of the solenoid S (not shown) is set in the pulling state, i.e. in the position in which the inlet valve of the cylinder (not shown) is open. In other words, this is the beginning of the pulling stage of the solenoid. To achieve this, the control block 3 connects all the three switches T1 , T2, T3; in other words, the switches T1 , T2, T3 are in a low-impedance (conductive) state. The current is thus allowed to flow through the switches T1 , T2, T3. This situation is illustrated in Fig. 2a. Arrow N1 shows the path and direction of the current in this situation. Thus, the solenoid is supplied with a voltage formed by the sum of the voltage V from the power source 2 and the voltage from the auxiliary capacitor C2. The power source 2 has been used to charge the first capacitor C1 to level out variations in the voltage from the power source, particularly at the beginning of the pulling stage of the solenoid when the current is rapidly intensified. Thus, it can be thought that the solenoid is supplied with a voltage equalling the sum of the voltages of the capacitors C1 and C2, subtracted by the threshold voltage on the diode D3, the voltage on the measuring resistance R1 and the voltage losses of the conductors. In the first injection step after starting the engine, there is no charge in the auxiliary capacitor C2 yet, so the voltage in the first terminal S.1 of the solenoid is slightly lower than the output voltage V of the power source 2. In all other injection steps after the starting of the engine, the charge of the auxiliary capacitor produces, between the poles of the auxiliary capacitor C2, a voltage which is in the same order as the operating voltage V formed by the power source 2. The grounds for this will be presented in the description hereinbelow. Consequently, the voltage supplied to the solenoid at the beginning of the injection step is about double the operating voltage V. As a result, the intensity of current of the solenoid can be increased faster than in arrangements of prior art.

After a given time, the intensity of current has reached its maximum value l_max, after which (moment of time t₂) the control block 3 disconnects the first switch T1 and the second switch T2 (Fig. 2b). The third switch T3 is still maintained in the conductive state. At this stage, no operating voltage is supplied to the solenoid S, wherein the solenoid S starts to discharge the energy trapped in it, and the current flowing through the solenoid starts to reduce. The flow of current is indicated by arrow N2 in Fig. 2b. The voltage on the solenoid S is determined by the threshold voltage of the diode D2 in the forward direction, the voltage on the measuring resistance R1, as well as the voltage losses on the path of the flow of current. The auxiliary capacitor C2 is charged by the voltage V of the power source 2 via the diodes D5 and D4. At this stage, the first terminal S.1 of the solenoid S has a slightly lower voltage than the ground potential (i.e., the threshold voltage of the diode D2 in the forward direction). The auxiliary capacitor C2 is charged by a voltage which is approximately the operating voltage V from the power source 2, added with the voltage on the diode D2 and subtracted by the voltage on the diodes D4 and D5 (arrow N3), i.e., in practice, a voltage close to the operating voltage V.

When the current flowing through the solenoid S has reduced to a given value, the intensifying of the current is started again (moment of time t₃). This is effected by the control block 3 connecting the first switch T1 and the second switch T2. Thus, the operation is similar to that presented in the description of the operation of Fig. 2a. The maximum current (moment of time t₄) is in the same order of magnitude, but the rate of increasing remains, however, slightly lower than in the first situation of coupling the current. This is because the energy trapped in the solenoid S cannot be conducted to the auxiliary capacitor C2 at this stage yet. The current control is coupled as a feedback, wherein the maximum and minimum values are determined by the hysteresis of the coupling.

The above-presented steps of Figs. 2a and 2b are repeated, until the pulling stage of the solenoid S is terminated and the holding stage of the solenoid S is started. This means that the solenoid plunger is kept in the pulled position, for which purpose a lower intensity of current will be sufficient than at the pulling stage. In the device 1 according to an advantageous embodiment of the invention, this is implemented by allowing the intensity of current to drop to a lower level until, at a moment of time t₅, the first switch T1 is connected and the second switch T2 is left disconnected (i.e., in the non-conducting state). Thus, the current flows to the solenoid directly via the first switch T1 and the diode D1. Thus, the first terminal S.1 of the solenoid has a voltage whose magnitude is slightly (approximately for the threshold voltage of the diode D1 in the forward direction) smaller than the operating voltage V. This situation is illustrated by the switch diagram of Fig. 2c, in which the flow of current is indicated with arrow N4. The second switch T2 is in the non-conducting state, wherein the auxiliary capacitor C2 is also charged at this stage (arrow N5), but the charge now accumulating will not be used until the next pulling stage. Next, at a moment of time t₆, the reduction of the current is started by disconnecting the first switch T1 , wherein the operation is similar to that shown in Fig. 2b. At a moment of time t₇, the intensifying of the current is started by connecting the first switch T1 again. These stages are repeated until the end of the injection step.

At the end of the injection step, at a moment of time t₈, the third switch T3 is also disconnected, as well as the first switch T1 , if it was in the connected state at that time. Now, the situation is similar to that shown in Fig. 2d. Thus, the energy trapped in the solenoid S is conducted via the diode D6 to the auxiliary capacitor C2 (arrow N6) which thus receives a small initial charge to be used in the next injection step, to increase the pulling current of the solenoid further. Consequently, at the beginning of the next injection step, the voltage of the first terminal S.1 of the solenoid is slightly greater than double the operating voltage V, which is due, for example, to this trapping of the energy of the solenoid in the auxiliary capacitor C2.

Figures 3a and 3b show, in a reduced manner by means of graphs, the input voltage of the solenoid S, provided by the device 1 according to the invention, as well as the current flowing through the solenoid S. In the figures, the reference P1 indicates time intervals in which the operation of the device corresponds to the situation of Fig. 2a. The reference P12 indicates time intervals in which the operation of the device corresponds to the situation of Fig. 2b. The reference P3, in turn, indicates time intervals in which the operation of the device corresponds to the situation of Fig. 2c. However, it will be obvious that the graphic representations of Figs. 3a and 3b are only some non-restricting examples, whereas other kinds of variations in the voltage and current may also occur in the devices in practice.

The control of the switches T1, T2, T3 can be implemented, on one hand, by determining the moments of time t-i — 1₈, wherein the time measurements are taken and the operation of the switches is controlled in the control block 3, accordingly. On the other hand, the switches can also be controlled by measuring the current flowing through the solenoid and by determining different threshold values for the intensity of current. In this case, the switches are controlled when the intensity of current exceeds or drops below the threshold value used in each situation. Examples of such threshold values are indicated with the references ki, k₂, k₃ and k₄ in Fig. 3a. For measuring the current, for example the measuring resistance R1 is used, wherein in the control block 3, the voltage on the measuring resistance is measured (« the voltage difference between the terminal R1.1 of the measuring resistance and the ground potential). When the magnitude of the measuring resistance R1 is known, the current can be calculated on the basis of the voltage and the resistance value.

As already stated above in this description, the moment t, of starting the injection step can be advantageously determined by means of a sensor (not shown) arranged in connection with the engine, for example in the crankshaft.

Consequently, in the device 1 according to the invention, there is no need for a separate input voltage to the auxiliary capacitor C2 used for boosting the current, wherein the coupling has been simplified. Because the auxiliary capacitor has been arranged to be, in a way, floating in relation to the ground potential, it is possible to have significantly higher voltage values for the voltage to be supplied to the solenoid than the operating voltage from the power source. This accelerates the rate of current increase, wherein the opening of the inlet valve is faster and controlled.

It will be obvious that the present invention is not limited solely to the above-presented embodiments but it can be modified within the scope of the appended claims.

Claims

Claims:

1. A method for controlling a solenoid (S) used in the fuel supply of an engine, in which the current to be supplied to the solenoid in the fuel injection step fa — 1₈) is controlled to set and maintain the solenoid (S) in a pulling state, and for generating the current to be supplied to the solenoid (S), at least one power source (2) is used, in parallel with which a capacitor (C1) has been connected to level out the load on the power source (2) in the fuel injection step, characterized in that the intensity of current to be used for setting the solenoid in the pulling state is also increased by an auxiliary capacitor (C1 ) which is charged with energy supplied from the power source (2) before the beginning of the injection step.

2. The method according to claim 1 , characterized in that said auxiliary capacitor (C2) is also charged with energy trapped in the solenoid at the end of the injection step, to be used at the beginning of the next injection step for increasing the current to be supplied to the solenoid.

3. The method according to claim 1 or 2, characterized in that to increase the intensity of current at the beginning of the injection step, said auxiliary capacitor (C2) is connected in series with the power source (2), and the voltage generated in the serial connection of the power source (2) and the auxiliary capacitor (C2) is supplied to the solenoid.

4. The method according to claim 1 , 2 or 3, characterized in that to keep the solenoid (S) in the pulling state, the intensity of current is reduced in relation to the intensity of current used for setting in the pulling stage, wherein said auxiliary capacitor (C2) is left unconnected in series with the power source (2), and the voltage from the power source (2) is supplied to the solenoid (2).

5. A device (1) for controlling a solenoid (S) to be used in the fuel injection of an engine, which device comprises means (T1 , T3) for controlling the current to be supplied to the solenoids (S) for setting and maintaining the solenoid in a pulling state for the time of the fuel injection step (t-i — _β), and at least one power source (2) for generating the current to be supplied to the solenoid (S), and a capacitor (C1) is connected in series with the power source to level out the load on the power source (2) in the injection step, characterized in that the device also comprises an auxiliary capacitor (C2) which is arranged to be used, in addition to the power source (2), to increase the intensity of current used for setting the solenoid in the pulling state, and means (2, D4) for charging the auxiliary capacitor (2) with energy from the power source (2) before the beginning of the injection step.

6. The device (1) according to claim 5, characterized in that the device (1) also comprises means (D4, D6) for also charging said auxiliary capacitor (C2) with energy trapped in the solenoid (S) at the end of the injection step, to be used at the beginning of the next injection step, to intensify the current to be supplied to the solenoid.

7. The device (1) according to claim 5 or 6, characterized in that it comprises means (T2, D3) for connecting said auxiliary capacitor (C2) in series with the power source (2) to increase the intensity of current at the beginning of the injection step, wherein the voltage generated in the serial connection of the power source and the auxiliary capacitor (C2) is arranged to be supplied to the solenoid.

8. The device (1) according to claim 5, 6 or 7, characterized in that it comprises a first switch (T1) and a third switch (T3) for supplying energy from the power source to the solenoid (S), and a second switch (T2) for connecting energy trapped in said auxiliary capacitor (C2) to the solenoid (S).

9. The device (1) according to any of the claims 5 to 8, characterized in that it comprises measuring means (5, 7) for measuring the current flowing through the solenoid, wherein measurement data is arranged to be used in the control of the current to be conducted to the solenoid (S).

10. The device (1) according to any of the claims 5 to 9, characterized in that said auxiliary capacitor (C2) is left unconnected to the ground potential, wherein said capacitor (C2) can be connected in series with the power source (2).