EP1224392A1

EP1224392A1 - Method and device for controlling fuel metering in an internal combustion machine

Info

Publication number: EP1224392A1
Application number: EP00982995A
Authority: EP
Inventors: Anja Melsheimer; Ole See; Roger Potschin; Marcus Parche
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1999-10-16
Filing date: 2000-10-12
Publication date: 2002-07-24
Anticipated expiration: 2020-10-12
Also published as: WO2001029408A1; EP1224392B1; JP2003512563A; DE50011077D1

Abstract

The invention relates to a method and a device for controlling fuel metering in an internal combustion engine. A valve (110) is used to control the flow of fuel to said internal combustion engine. The valve (110) is controlled by an adjusting element (105) in such a way that when said valve (110) is located in a first position the flow of fuel is stopped and when the valve is located in a second position fuel is released. In certain operational modes, the adjusting element (105) is controlled in such a way that the valve adopts at least one intermediate position.

Description

Method and device for controlling the fuel metering in an internal combustion engine

State of the art

The invention relates to a method and a device for controlling the fuel metering in an internal combustion engine.

Methods and devices for controlling the fuel metering in an internal combustion engine are known. A valve that controls the fuel flow into the internal combustion engine is often used to control the fuel metering. In a first position of the valve, this prevents the fuel flow. In a second position, the valve completely releases the fuel flow.

Furthermore, piezo actuators are known with which such valves can be controlled.

In the case of a pump-nozzle unit (PDE), the injection pump and the injection nozzle form a structural unit. This is driven by the engine camshaft. Every pump-nozzle unit has a fast-switching valve that controls the start and end of injection. When the valve is open, the PDE feeds fuel back into the inlet. If the valve closes, the PDE measures fuel in the corresponding engine cylinder. The closing time of the valve determines the start of injection, the closing duration, ie the duration of the closed state of the valve, determines the injection quantity.

A so-called pump-line-nozzle (PLD) system is designed in a similar manner. Like the PDE, the pump line nozzle has one injection pump per engine cylinder, which is driven by a shaft of the engine, for example the camshaft. The injection timing and the injection quantity are controlled with a valve. The pump and the nozzle are connected to each other via a short line.

Object of the invention

The object of the invention is to achieve a fuel metering that is as accurate as possible in a method and a device for controlling the fuel metering in an internal combustion engine. This object is achieved by the features characterized in the independent claims.

Advantages of the invention

A very precise fuel injection can be achieved with the procedure according to the invention. Advantageous and expedient refinements and developments of the invention are characterized in the subclaims.

drawing

The invention is explained below with reference to the embodiments shown in the drawing. Figures 1 and 2 show two configurations of a pump-nozzle Unit and Figures 3 and 4 different signals plotted over time.

Description of exemplary embodiments

A pump-nozzle unit is shown schematically in FIG. The main elements are described below. The pump-nozzle unit 100 essentially comprises an actuating element 105 which, via a connection 102, which is shown in broken lines, influences a valve 110 such that it assumes at least a first closed and a second open position. The valve 110 is arranged between a fuel inlet 115, which can also be referred to as a low-pressure region, and a line 120. The low pressure region essentially contains a fuel reservoir, which is also referred to as a tank, from which the fuel reaches the valve 110 via a filter and a fuel feed pump.

The line 120 connects an element space 130, in which a pump piston 135, which is moved by a drive unit 140, is movably arranged with an injection nozzle 150. The drive unit 140 is preferably driven directly or via a rocker arm by the camshaft of the internal combustion engine. The injection nozzle 150 essentially includes a nozzle spring 152 and a nozzle needle 154. The control element 105 is acted upon by control signals 160 with control signals. Magnetic actuators and particularly advantageously piezo actuators are usually used as control elements.

If the valve 110 is in its closed state and the pump piston 135 moves in such a way that the element space 130 is reduced, the pressure in the line 120 and thus in the injection nozzle increases. From a - H -

the pressure of the nozzle needle 154 is moved against the spring force of the nozzle spring 152 and opens the injection opening 156, so that fuel enters the combustion chamber of the internal combustion engine. If the valve 110 is in its open position, no pressure build-up is possible and no fuel injection takes place.

By opening and closing the valve 110, the high-pressure area, which is formed by the element space, the line 120 and the fuel-filled area of the injection nozzle, can be connected to the low-pressure area. From the time valve 110 is closed, pressure build-up begins in the high pressure region and fuel injection begins. When valve 110 opens, the pressure in line 120 decreases and the injection ends. This means that the opening and closing times of the valve 110 determine the start of injection, the end of injection and thus the duration of the injection.

The control element 105 is controlled by a control unit 160 depending on the operating state of the internal combustion engine, which is detected by various sensors, in such a way that the valve opens or closes at the desired time and thus the injection begins and ends at the desired time.

FIG. 2 shows a second embodiment of a pump-nozzle unit. This differs essentially from the embodiment in FIG. 1 in that the valve 110 connects the element space 130 directly to the fuel inlet 115. It is common to both embodiments that the valve 110 connects the high-pressure region to the low-pressure region. The valve 110 is usually actuated in such a way that it assumes either its open or its closed position. This type of control is problematic because when the valve is opened, the pressure in the high pressure area is reduced very quickly to the pressure in the low pressure area. This leads, for example, to the nozzle needle moving very quickly into its closed position. When actuated again, the pressure in the high pressure area must be built up again. This is particularly problematic when the injection is divided into at least two partial injections. For example, it can be provided that a pre-injection takes place before the main injection. In order to have a positive effect on the behavior of the internal combustion engine, the two partial injections, for example the pre-injection and the main injection, must follow one another at a certain distance. Due to the complete reduction in pressure when the valve is opened, not all intervals can be realized, since a minimum time is required for the pressure to build up.

Furthermore, it is impossible or very difficult to influence the pressure in the high-pressure chamber in such systems. Such an influence is particularly difficult in the breaks between two injections.

According to the invention it is therefore provided that the actuating element is actuated in such a way that the valve opens and closes at least one intermediate position in addition to its two end positions. This is particularly easy to implement if a piezo actuator is used as the control element. In such a piezo actuator, the position or the extent of the piezo actuator is directly proportional to the voltage applied to the piezo actuator. This makes it possible for the control element to have different positions. sitions can take. This enables the valve 110 to be brought into defined positions.

Various signals are plotted over time t in FIG. In the first partial figure 3a, the voltage U, which is present at the piezo actuator 105, is plotted. The partial figure 3b shows the state of the valve 110 over the time t. The partial figure 3c shows the state of the nozzle needle 154 depending on the time t. The partial figure 3d shows the course of the pressure P in the nozzle needle or in the high pressure area.

At time tl, the control of the pump-nozzle unit begins. This means that from time t1 to time 2, control unit 160 specifies such a signal that valve 110 closes. This is achieved in that the voltage at the piezo actuator 105 increases from a minimum value, which is preferably zero, to a second value. In the illustrated embodiment, this increase is linear. The increase in the voltage on the piezo actuator 105 causes the valve 110 to slowly move from its open to its closed position. The nozzle needle shows no reaction yet, it remains in its closed position. The pressure in the high pressure area rises slowly.

In the period between the times t2 and t3, the piezo actuator 105 is activated in such a way that the valve 110 remains in its closed position, ie the voltage U at the piezo actuator remains at its high value. As a result, valve 110 remains in its closed position. The pressure P in the high pressure range continues to rise. At time t3 or shortly before time t3, the pressure P reaches such a value that the nozzle needle slowly lifts off its valve seat and releases the fuel injection. This leads to a brief drop in pressure. From time t3, the voltage is reduced to an intermediate value up to time t4, as a result of which valve 110 moves in the direction of a first intermediate position. As a result, the pressure P in the element space drops and the nozzle needle moves in its closing direction.

In the period between times t4 and t5, valve 110 is held in the first intermediate position. This is achieved in that the voltage U on the piezo actuator is kept at its intermediate value. This causes valve 110 to also be in its first intermediate position. The pressure P in the element space slowly decreases and the nozzle needle reaches its closed position and remains in its closed position.

If the opening cross-section of the valve is too large in this phase, this is the case, for example, if the valve opens fully in this period, there is a so-called over-relief and the pressure in the high-pressure area drops below the vapor pressure.

The voltage and thus the position of the valve and / or the time period between the times t4 and t5 is chosen so that there is no over-relief. This ensures that defined conditions are present at the start of the next injection. Scattering of the fuel quantity can thereby be significantly reduced with the same activation duration.

The control valve 110 is closed again between the times t5 and t6, ie the voltage at the piezo actuator 105 rises again to its maximum value. As a result, the valve 110 changes to its closed state. The pressure P in the pressure area begins to rise again. In the period between times t6 to t7, valve 110 is held in its closed position. Ie the voltage at the piezo actuator remains at its maximum value. Valve 110 remains in its closed position. As a result, the pressure P rises sharply in the high pressure range. A certain time after the time t6, the value of the pressure has reached such a value that the nozzle needle 154 begins to move and shortly thereafter reaches the fully open state.

In the particularly advantageous embodiment, which is shown in FIG. 3, the voltage U on the piezo actuator is reduced by a small value between times t7 and t8 after the nozzle needle has reached the open position. As a result, valve 110 is not fully open. This means that valve 110 is held in a second intermediate position which is only slightly different from the closed position. This means that a small amount of liquid can escape. The cross section is particularly advantageously selected such that there is no further increase in pressure. This means that the pressure remains almost constant during the period t7 to t8, i.e. that there is a pressure plateau.

In a simplified embodiment, the maximum value of the voltage can be predetermined in the period t7 to t8, as in the period between t6 and t7, the valve 110 remaining in its closed position during this period. This enables higher pressure values to be achieved.

In the period between times t8 and t9, the voltage is reduced to a third intermediate value. This means that the valve 110 moves to a third intermediate position. As a result, the pressure P drops and that at a certain pressure the nozzle needle changes into its closed state. It is particularly advantageous if the value of this voltage can be specified as a function of the operating state. It can thereby be achieved that the pressure reduction rate, ie the pressure change within a certain time, can be predetermined depending on the operating state of the internal combustion engine.

The valve 110 is held in the third intermediate position between the times t9 and t10.

From the time t10, the piezo actuator is activated such that the valve 110 opens, i.e. the voltage is reduced to its initial value. As a result, the valve moves to its fully open position. The pressure P drops to the pressure value in the low pressure range and the nozzle needle remains in its closed position.

The control described includes a main injection as a second partial injection and a pre-injection as a first partial injection. This is a remote pilot injection without a so-called over-relief during the injection break. This is achieved in that the valve is controlled between the two partial injections in such a way that it remains in a first intermediate position.

As an alternative, it can also be provided that an attached pre-injection takes place, in which the pre-injection passes directly into the main injection.

Furthermore, the invention provides that the pressure in the high-pressure region is preferably limited during the main injection. It is particularly advantageous if ! 0 -

in the partial load range, i.e. a large injection pressure is selected at low speeds and / or with small injected fuel quantities, i.e. that during an injection in the partial load range in the period t7 to tδ the valve remains in its completely closed position. At high speeds and / or large injection quantities, a limitation of the injection pressure is selected, i.e. that in the period t7 to t8 the valve is in the second intermediate position. This can reduce mechanical loads on the pump and the drive.

The valve is activated during the injection in such a way that it remains in a second intermediate position. The intermediate position or the required voltage on the piezo actuator is preferably specified as a function of the load state, in particular as a function of the rotational speed and / or a variable characterizing the fuel quantity to be injected. This results in improved mixture preparation and thus reduced emissions.

The pressure reduction rate can be set by specifying the first or the third intermediate position of the valve. This setting is preferably made depending on the operating state of the internal combustion engine. This can take place both at the end of the pre-injection and at the end of the main injection.

It is particularly advantageous if there is a rapid reduction in pressure at full load, ie at high speed and / or a large amount of fuel injected, that is to say that the voltage is reduced to a small value or to the minimum value, as a result of which the valve quickly moves into its open position. In contrast, a lower pressure reduction rate is specified for partial load, ie for partial load t8 to tlO set a higher voltage, ie the valve remains in its closed position.

This means that the valve 110 is activated at the end of the injection such that it remains in a third intermediate position. The intermediate position or the voltage with which the piezo actuator is acted on is preferably set as a function of a desired pressure reduction rate.

Because the pressure reduction can be controlled while the valve is opening, the noises, which are preferably generated by the pump, can be significantly reduced.

It is particularly advantageous if further partial injections take place, i.e. that several pre-injections are provided, or that the main injection is divided into several partial injections. It is also particularly advantageous if at least one post-injection takes place, which takes place after the main injection.

The time intervals t4 to t5 or t7 to t8 and t9 to t10 are preferably specified as a function of the speed, the start of injection and / or other operating parameters.

Further variants of the control profile for the piezo actuator are shown in FIG. 4.

FIG. 4a shows a conventional control without an intermediate position, ie the voltage is raised to its maximum value for the pre-injection and then lowered to the minimum value. For the main injection, the voltage is increased again to the maximum value and reduced to the minimum value at the end of the main injection. The course of an attached pre-injection is shown in sub-figure 4b. That is, at the beginning of the pre-injection, the voltage is raised to an intermediate value and then conducted at the maximum value at the beginning of the main injection. The intermediate value is only slightly below the maximum value. At the end of the injection, the voltage is reset to the minimum value.

A corresponding control with a post-injection is shown in sub-figure 4c. This differs essentially from the control according to FIG. 3 in that the main injection does not cause a reduction in the period between times 7 and t8, but only a flexible pressure reduction rate is set. A short time after the main injection there is a further control to achieve the post-injection.

The procedure according to the invention is not limited to use in pump-nozzle units. It can also be used in other injection systems that use a valve to control high pressure pressure. In particular, the procedure according to the invention is suitable for controlling a pump-line nozzle system or a common rail system.

Claims

Expectations

1. A method for controlling the fuel metering in an internal combustion engine, with a valve for controlling the fuel flow in the internal combustion engine, the valve being controlled by means of an actuating element in such a way that it prevents the fuel flow in a first position and that it controls the fuel flow in a second position fully released, characterized in that in certain operating states the actuating element is controlled such that the valve occupies at least one intermediate position.

2. The method according to claim 1, characterized in that the valve is controlled between two partial injections such that it remains in a first intermediate position.

3. The method according to claim 1 or 2, characterized in that the valve is controlled during an injection such that it remains in a second intermediate position.

4. The method according to claim 1 or 2, characterized in that the valve at the end of an injection so- is controlled so that it remains in a third intermediate position.

5. The method according to any one of claims 1 to 4, characterized in that the intermediate position is set depending on a desired pressure reduction rate.

6. The method according to any one of the preceding claims, characterized in that the intermediate position is set depending on at least one variable characterizing the operating state of the internal combustion engine.

7. The method according to any one of the preceding claims, characterized in that the actuating element is designed as a piezo actuator.

8. Device for controlling the fuel metering in an internal combustion engine, with a valve for controlling the fuel flow into the internal combustion engine, the valve being controlled by means of an actuating element in such a way that it prevents the fuel flow in a first position and that it controls the fuel flow in a second position fully released, characterized in that means are provided which control the actuating element in certain operating states such that the valve assumes at least one intermediate position.