METHOD AND DEVICE FOR CONTROLLING A MULTI-VALVE

Description

State of the art

[0001] The invention relates to a method for controlling a quantity control valve of a high-pressure pump according to the preamble of claim 1. The invention further relates to a computer program, an electrical storage medium and a control and regulating device.

[0002] DE 101 48 218 A1 describes a method for operating a fuel injection system using a quantity control valve. The known quantity control valve is implemented as a solenoid valve electromagnetically actuated by a solenoid coil, with a solenoid armature and associated travel limit stops. Such quantity control valves are known on the market, which are closed when the solenoid coil is de-energized. In this case, to open the quantity control valve, the solenoid coil is controlled with a constant voltage or a pulsed voltage (pulse width modulation - "PWM"), causing the current in the solenoid coil to increase in a characteristic manner. After the voltage is switched off, the current again drops in a characteristic manner, causing the quantity control valve to close. Solenoid valves are also known that are open when the coil is energized.These solenoid valves operate in a similar way, with the solenoid valve opening when the voltage is switched off and the current drops as a characteristic.

[0003] To prevent the armature of the normally closed valve shown in DE 101 48 218 A1 from striking the stop at full speed during the opening movement of the flow control valve, which could lead to significant noise, the electromagnetic actuating device is energized again in a pulsed manner shortly before the end of the opening movement. This current pulse exerts a braking force on the armature before it even contacts the stop. The braking force reduces the speed, thereby reducing the impact noise.

[0004] In modern direct-injection engine systems with demand-controlled fuel delivery, a high-pressure pump is used to generate the necessary fuel pressure. The high-pressure pump is operated in a quantity-controlled manner; for this purpose, the pump's delivery rate can be set from 0 to 100% via a quantity control valve (MSV). The control of this quantity control valve is particularly important because, due to the high engine speed and the associated high control frequency, the MSV's switching process must take place very quickly and despite high magnetic forces, without the stroke-to-stroke fluctuations and thus the delivery rate fluctuations becoming excessive. This would lead to poor rail pressure quality. On the other hand, at low engine speeds, very high demands are placed on the noise emission of the high-pressure pump.For this reason, numerous control concepts have been developed to reduce the dynamic response and thus the acoustic level. This involves slowing down both the initial and final movement of the switching magnet.

[0005] DE 10 2009 046 825 A1 describes a control concept for a quantity control valve, which is also referred to as "Current Soft Stop" (CSS).

[0006] Normally, the quantity control valve is held closed beyond top dead center by the pressure in the delivery chamber of the high-pressure pump. When the delivery chamber pressure drops, the quantity control valve falls back to its original, de-energized open position under spring force and without braking. With the CSS process, the quantity control valve is supplied with a holding current beyond top dead center so that the MSV does not drop out immediately. Only after the pressure in the delivery chamber has reduced is the current reduced in a characteristic manner so that the quantity control valve drops out during this low current supply and falls back to the de-energized open position. The mutual induction and the current through the quantity control valve slow down the movement and the stop is reached much more slowly and therefore quieter. The holding current should be known as precisely as possible so that the currents for holding and starting the movement can be set as precisely as possible.The current supply must end before the following bottom dead center so that the next conveying process is not disturbed.

[0007] The problem is that if the flow is too low, the CSS process only produces slight acoustic improvements, while excessively high flows can result in no improvement or even a deterioration in the acoustics and an increase in rail pressure. This is because, if the flow is too high, the flow control valve remains closed and does not open.

[0008] Since the variation between individual units must be taken into account when setting the current, the effect would be limited under these conditions, as the current is usually set in such a way that the flow control valve opens reliably. This means that a current that is too low would be selected. At this low current, only a slight acoustic improvement might result.

[0009] WO 2010 / 066663 A1 discloses a method that uses an adoption process that can be used to determine a deviation of an actual pressure in the fuel rail from a target pressure. The current supply disclosed therein in connection with the adaptation ends after top dead center and well before bottom dead center of the high-pressure pump. The current supply to the electromagnetic actuating device is reduced to such an extent that the quantity control valve no longer closes, resulting in a pressure drop or even a pressure collapse in the fuel rail.

[0010] Furthermore, DE 10 2008 054 702 A1 discloses a solenoid valve which is designed as a normally open solenoid valve. Current is supplied to the coil in a phase which begins approximately midway between bottom dead center and top dead center and ends at top dead center. The adaptation method disclosed therein provides for the aforementioned current in the coil to be reduced in order to detect or not detect a drop in pressure over the course of a plurality of successive reductions. The aim is to at least partially reduce the emission of audible noise which occurs when the solenoid valve closes during operation of the internal combustion engine. The coil of the solenoid valve is energized according to a desired value for the current in the coil in order to close it and supply fuel to the high-pressure pump.When the solenoid valve closes, the setpoint value for the current in the coil is reduced from a predetermined first current setpoint value to a predetermined second current setpoint value in such a way that the emission of audible sound which occurs when the solenoid valve closes during operation of the internal combustion engine is at least partially reduced. Disclosure of the invention

[0011] The invention relates to a quantity control valve with an electromagnetic actuating device which, when actuated with a first actuation value for the holding current, assumes a closed state and the actuation with a second actuation value enables the quantity control valve to assume an open state.

[0012] By determining a limiting holding current at which the quantity control valve remains in its closed state at the bottom dead center of the high-pressure pump, a significantly improved control is possible, with the acoustic behavior being significantly improved.

[0013] Since the characteristics of the quantity control valve vary from model to model, the impact noise can be effectively reduced if model characteristics, such as the limit holding current, are taken into account during the current supply.

[0014] This limit holding current is determined by setting a control value for the holding current in one step, at which the quantity control valve opens when the pressure has dropped, and the current supply to the quantity control valve is extended beyond the bottom dead center of the high-pressure pump, whereby no pressure increase occurs in the fuel rail, and the holding current is successively incremented from delivery to delivery and the current supply is extended beyond the bottom dead center of the high-pressure pump with each delivery, whereby if the quantity control valve remains closed during a delivery stroke that begins after the bottom dead center of the high-pressure pump and a pressure increase occurs, a current value before the last increment is used as the limit holding current, whereby the limit holding current is determined based on the control signal at which the pressure increase occurs,by using the current value before a last increment as the limit holding current.

[0015] Through the control and adaptation according to the invention, the current level, or the current supply to the quantity control valve pre-controlled by a PWM signal, is adapted to the specimen tolerances in such a way that the CSS method for acoustic improvement functions optimally.

[0016] It is particularly advantageous if the limiting holding current is determined based on a fuel pressure signal. Since the fuel pressure signal is evaluated, no additional sensors are required. Furthermore, this signal is available with sufficient accuracy.

[0017] A pressure increase can be easily detected by extending the current supply to the quantity control valve beyond the bottom dead center.

[0018] Embodiments of the invention are explained in more detail below with reference to the accompanying drawings. The drawings show: Figure 1 a schematic representation of a fuel injection system of an internal combustion engine with a high-pressure pump and a quantity control valve; Figure 2 a schematic representation of the relationship between the control signal and the state of the quantity control valve; Figure 3 a second schematic representation of the time course of the control signal and the time course of the state of the quantity control valve; Figure 4 a flow chart to illustrate the procedure according to the invention.

[0019] A fuel injection system contributes to Figure 1The fuel pump 12 is designated overall by reference numeral 10. It comprises an electric fuel pump 12, which pumps fuel from a fuel tank 14 to a high-pressure pump 16. The high-pressure pump 16 compresses the fuel to a very high pressure and pumps it further into a fuel rail 18. Connected to this rail are several injectors 20, which inject the fuel into their associated combustion chambers. The pressure in the fuel rail 18 is detected by a pressure sensor 22.

[0020] The high-pressure pump 16 is a piston pump with a delivery piston 24, which can be set into a reciprocating motion (double arrow 26) by a camshaft (not shown). The delivery piston 24 defines a delivery chamber 28, which can be connected to the outlet of the electric fuel pump 12 via a quantity control valve 30. The delivery chamber 28 can also be connected to the fuel rail 18 via an outlet valve 32.

[0021] The quantity control valve 30 comprises, for example, an electromagnetic actuator 34, which, when energized, operates against the force of a spring 36. In the form of the exemplary embodiment, the quantity control valve 30 is open when de-energized; when energized, it functions as a normal inlet check valve.

[0022] The high pressure pump 16 and the quantity control valve 30 operate as follows (see Figure 2 ): In Figure 2 At the top, a stroke of the piston 34 and below it a control signal are plotted over time. The control signal is designated by the reference symbol "A". The value of the control signal is between a first control value, which is Figure 2 marked with "0" and a second control value, which is Figure 2 is designated "1". For example, the first control value corresponds to the de-energized state of the electromagnetic

[0023] Actuating device 34, and the second value corresponds to the energized state. The following assumes this embodiment.

[0024] In addition, the high-pressure pump 16 is shown schematically in various operating states. During a suction stroke (left illustration in Figure 2 ) the solenoid coil 44 is de-energized, whereby the actuating plunger 48 is pressed by the spring 36 against the valve element 38 and moves this into its open position. In this way, fuel can flow from the electric fuel pump 12 into the delivery chamber 28. After reaching the bottom dead center UT, the delivery stroke of the delivery piston 24 begins. This is shown in Figure 2shown in the middle. The solenoid coil 44 remains de-energized, as a result of which the quantity control valve 30 remains forcibly open. The fuel is ejected from the delivery piston 24 via the open quantity control valve 30 to the electric fuel pump 12. The outlet valve 32 remains closed. Fuel is not delivered into the fuel rail 18. At a time t1, the solenoid coil 44 is energized, as a result of which the actuating plunger 48 is pulled away from the valve element 38. It should be noted at this point that the current flow curve of the solenoid coil 44 is only shown schematically in Figure 2. It should be noted that the actual coil current is not constant, but due to mutual induction effects, may under certain circumstances simulate the course of typical transient processes. With a pulse-width modulated control voltage, the coil current is also wave-like or spike-shaped.

[0025] By varying the time t1, the amount of fuel delivered by the high-pressure pump 16 to the fuel rail 18 is influenced. The time t1 is controlled by a control and regulating device 54 ( Figure 1 ) is set so that the actual pressure in the fuel rail 18 corresponds as closely as possible to the desired pressure. For this purpose, signals supplied by the pressure sensor 22 are processed in the control and regulating device 54.

[0026] Due to the pressure in the delivery chamber 28, the valve element 38 rests against the valve seat 42, thus closing the quantity control valve 30. Pressure can now build up in the delivery chamber 28, which opens the outlet valve 32 and leads to delivery into the fuel rail 18. This is Figure 2 shown on the far right. Shortly after reaching top dead center (TDC) of the delivery piston 24, the current supply to the solenoid coil 44 is terminated, causing the quantity control valve 30 to return to its forced open position.

[0027] When the current supply to the solenoid coil 44 is terminated, the actuating plunger 48 is moved toward a first stop 50. To reduce the impact speed at the first stop 50, a temporarily falling signal waveform 56 is generated, which reduces the movement speed of the actuating plunger 48 before it hits the first stop 50. During a second falling signal waveform 58, the control signal is brought to the first control value. This second falling signal waveform 58 can be provided, for example, by a rapid quenching of the coil current of the electromagnetic actuating device 34.

[0028] Figure 3shows an exemplary time profile 100 of the control signal designated "A" and the time profile 102 of the state of the quantity control valve 30 designated "Z". At time t1, the value of the control signal is increased from the second control value 64 to the first control value 66. As a result, the quantity control valve 30 transitions from the open state 60 to the closed state 62 and closes at time 104. During a holding phase 106, the quantity control valve 30 remains closed. Due to the pressure in the delivery chamber 28, which keeps the quantity control valve 30 closed, the control signal can assume the second control value 64 during a period 108, i.e., be de-energized, for example. In a further variant of the method, the holding current can also be maintained during the period 108 by applying the first control value. Before reaching the top dead center 120 of the delivery piston 24 orBefore the outlet valve 32 opens 122, the value of the control signal is raised again to the first control value 66. Starting at time 82, a new control occurs. In order to significantly reduce noise emissions, according to the invention, the value of the control signal is specified at the time at which the pressure in the delivery chamber 28 has dropped to such an extent that it no longer holds the quantity control valve 30 in the closed state 62, starting from a limiting holding current.

[0029] The limit holding current is the holding current at which the flow control valve remains closed after a previous current supply. If a current higher than the limit holding current is selected, the flow control valve remains closed. If a lower current is selected, the flow control valve opens.

[0030] To detect whether the current currently being delivered is above or below the holding current limit, the current is extended beyond the bottom dead center of the high-pressure pump. If the flow control valve is still energized because the current is above the holding current limit, the high-pressure pump is fully discharged. This full discharge can be easily detected by the rail pressure sensor due to the pressure increase in the rail. If the holding current limit is exceeded, no discharge occurs and no pressure increase occurs.

[0031] In the method according to the invention, starting from a current level at which the flow control valve reliably opens, the extended flow is gradually increased from delivery to delivery until a pressure increase is detected. This determines the limiting holding current associated with the currently available flow control valve under the respective boundary conditions.

[0032] Alternatively, it can also be provided that the extended flow, starting from a flow level at which the quantity control valve remains closed, is successively reduced from delivery to delivery until a pressure drop is detected.

[0033] An embodiment of the procedure according to the invention is illustrated by way of example with reference to Figure 4 described.

[0034] The adaptation process starts in a first step 300. The subsequent query 305 checks whether the activation conditions for the adaptation are met.

[0035] The activation conditions should ensure the most consistent boundary conditions possible for the adaptation process. Therefore, adaptation is only performed within a specific engine speed, vehicle speed, battery voltage, rail pressure, load, and temperature range, preferably while the engine is idling, but also during steady, slow-speed driving. The target rail pressure must also not change.

[0036] In the subsequent step 310, a starting value for the holding current is set. Furthermore, the current supply is extended beyond the bottom dead center of the high-pressure pump. This ensures that the quantity control valve, with appropriate current supply, remains closed until the next delivery stroke, which begins after the bottom dead center. If the quantity control valve is supplied with a current value above the limit holding current, it remains closed and pressure builds up. If the quantity control valve is supplied with a current value below the limit holding current, the quantity control valve can open when the pressure has dropped. Preferably, the starting value is specified so that the quantity control valve opens when the pressure has dropped.

[0037] In step 315, the current value is incremented by a specific value. In the subsequent step 320, the rail pressure in the high-pressure area downstream of the high-pressure pump is measured.

[0038] The subsequent query 325 checks whether the rail pressure has increased. For this purpose, it checks, for example, whether the rail pressure gradient is greater than a threshold value. Or, it checks whether the rail pressure has increased by more than a threshold value since the last measurement.

[0039] If this is not the case, i.e., there is no pressure increase, the current value is incremented by a specific value in step 315. If a rail pressure increase is detected in step 325, step 330 follows.

[0040] The adaptation ends in step 330. The current value, or the current value before the last increment, is used as the limit holding current. Alternatively, a value calculated from the two values, in particular the average of these two values, can also be used as the limit holding current.

[0041] In step 335, the parameters for the CSS current supply are determined based on the limit holding current. Furthermore, the current supply duration is reset to the normal value.

[0042] The method ends in the subsequent step 340.

[0043] This limit holding current is then used for the correct CSS control by calculating or correcting the current supply of the CSS process depending on this detected limit holding current.

[0044] The holding current before the CSS phase, which corresponds to the period before the discharge chamber pressure drops, is selected with a suitable increase compared to the determined limit holding current so that the quantity control valve is reliably held closed. The current value for the desired drop to the open position of the quantity control valve is selected, for example, with a current that is reduced by a suitable amount compared to the determined limit holding current. This is intended, on the one hand, to ensure that the quantity control valve is reliably held until the start of movement is initiated and, on the other hand, to achieve the maximum braking effect of the current during the movement of the quantity control valve. During this phase, the current is selected just below the holding current required for the particular specimen.

[0045] The characterization of the respective quantity control valve specimen obtained with the adaptation method can be used not only to improve the CSS method. An additional application within the context of normal control would be to determine the limiting holding current to reduce the effective current level and power loss.

Claims

1. Method for actuating a quantity control valve (30) of a high-pressure pump which delivers compressed fuel to a fuel rail (18) and a pressure in the fuel rail (18) is detected by a pressure sensor (22), wherein the quantity control valve (30) has an electromagnetic operating device (34) and the quantity control valve (30), with energizing actuation with a first actuation value (66) for the holding current, assumes a closed state (62) and actuation with a second actuation value (64) enables the quantity control valve (30) to assume an open state (60), wherein a borderline holding current of the quantity control valve (30), at which the quantity control valve (30) remains in its closed state, is determined by an adaptation method, characterized in that this borderline holding current is determined in that, in a step (310), an actuation value for the holding current, at which the quantity control valve (30) opens, is set when the pressure has dropped, and the energization of the quantity control valve (30) is extended beyond the bottom dead centre of the high-pressure pump, there being no increase in pressure in the fuel rail (18), and the holding current is gradually incremented from delivery to delivery, and the energization is extended beyond the bottom dead centre of the high-pressure pump with each delivery, wherein, when the quantity control valve (30) remains closed during a delivery stroke which starts after the bottom dead centre of the high-pressure pump and there is an increase in pressure, a current value before the last increment is used as the borderline holding current, the borderline holding current being determined on the basis of the actuation signal with which the increase in pressure takes place.

2. Method according to Claim 1, characterized in that the actuation value which is applied to the quantity control valve (30) after the top dead centre is specified on the basis of the borderline holding current.

3. Method according to either of Claims 1 and 2, characterized in that the adaptation is carried out during idling of the internal combustion engine.

4. Open-loop and / or closed-loop control device (54) for a fuel injection system (10), characterized in that it comprises means for carrying out a method according to any of Claims 1 to 3.

5. Computer program, characterized in that it is programmed to carry out a method according to any of Claims 1 to 3 when it is programmed on an open-loop and / or closed-loop control device (54) according to Claim 4.

6. Electrical storage medium for an open-loop and / or closed-loop control device (54) of a fuel injection system (10), characterized in that a computer program according to Claim 5 is stored on it.