EP2569526B1 - Method for providing a rail pressure sufficient for restarting a common rail internal combustion engine - Google Patents

Description

The present invention relates to a method for providing a sufficient pressure in a common rail for restarting a common rail internal combustion engine.

State of the art

Modern internal combustion engines are often equipped with a so-called start / stop automatic. In such an automatic start / stop system, it is provided that, depending on certain conditions, the internal combustion engine is automatically switched off. This usually happens when the vehicle comes to a standstill. As soon as the driver wants to continue and this by the operation of a control element, such as the gas or clutch pedal indicates, the internal combustion engine starts automatically. This is referred to as restarting in the context of this invention.

If, in the case of an internal combustion engine equipped with such automatic start / stop control, the rail pressure is reduced when the internal combustion engine is switched off, then the restart of the internal combustion engine may be considerably delayed. Furthermore, the hydraulic components are heavily loaded. The DE 10 2008 007 668 A1 discloses, therefore, to leave the rail pressure after idling at the idle target pressure to accelerate the restart. In such start / stop systems, it is envisaged to maintain the idling pressure of about 300 bar, which is set before stopping the engine, as long as possible while the engine is at a standstill. The goal is that when restarting or Restart the rail pressure safely above the pressure at which the injection release takes place (usually approx. 120 bar). As a result, can be injected immediately when restarting without pressure before the rail would have to be built and lost start time. This can be used particularly advantageously in systems in which the injector has no leakage gaps.

However, the injectors used in practice more or less large leaks may be present that lead to an undesirably rapid pressure reduction at standstill. This is especially true for older injectors in which slight damage to the sealing seat of the valve may have been caused by particles in the fuel, which in turn lead to undesirable (sweat) leakage and undesirably rapid pressure reduction at standstill. US 2001/042535 A1 and DE 102 004 006 523 A1 describe a method according to the preamble of claim 1.

It is therefore desirable, in particular for leakage-laden injectors, to have a pressure required for restarting during start / stop operation available.

Disclosure of the invention

According to the invention, a method with the features of claim 1 is proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

Advantages of the invention

The invention makes use of the knowledge that in a start / stop operation, a sufficient rail pressure can be maintained over a longer time, when the rail pressure is increased shortly before the engine stoppage to a first target pressure. This is expediently carried out by separating the rail pressure regulating circuit and operating it in a specific controlled mode. This controlled mode is characterized, for example, by the fact that in the case of a suction unit mounted in front of the high pressure pump metering unit it is brought to its fully open state and that in the presence of a high pressure side pressure control valve this is brought into its fully closed state. Alternatively, these control interventions can be triggered, for example, even when the rail pressure control loop is closed, by significantly raising the rail pressure setpoint beyond the control pressure. As a result, during the remaining running time of the engine until the engine is stopped, the high-pressure pump is set to full delivery, so that the amount of fuel delivered by the pump into the rail causes an additional build-up of pressure in the rail. Thus, the rail pressure at the beginning of engine standstill (stop phase) is considerably higher than the control pressure (eg idling setpoint pressure). As a result, the time period within which the rail pressure remains above the injection release pressure is significantly extended, and thus the probability that additional time is required for the pressure build-up in the rail when restarting or restarting, especially for system instances with leakage significantly reduced. It is a very fast restart of the engine in start / stop operation possible. In addition, the hydraulic components are significantly less stressed by the reduced pressure reduction / build-up cycle. The time interval within which the rail pressure is above the re-start injection enable pressure significantly increases, and substantially, by the amount of time the rail pressure now takes to decay from the overboost back to the desired idle pressure.

The invention develops particular advantages in high-pressure injectors opening. If the switching valves of the injectors, which may be responsible for the sweat leakage, are designed to open inwards, any existing sweat-leakage gaps on the seat may be reduced or completely closed by the increased closing force of the valve at a higher rail pressure.

The pressure increase advantageously begins after the last injection has taken place before the engine is switched off. This is a particularly convenient time to maintain the functionality of the internal combustion engine before stopping and to have as much time for the pressure build-up after stopping.

If the pressure curve at standstill shows that there is no appreciable leakage, the pressure increase can be reduced or completely suppressed. From the pressure curve at standstill can be concluded that the height of the leakage. Depending on this, the height of the setpoint increase can be adjusted in the variant with increased rail pressure setpoint. In the case of a purely controlled intervention, it is also possible, depending on the height of the leakage, to prevent a further increase in pressure when a certain limit pressure is reached, e.g. by closing the metering unit in front of the pump or by setting a defined, depending on the target value of the pressure to be reached current value at a high pressure side mounted pressure control valve.

An arithmetic unit according to the invention, e.g. a control unit of a motor vehicle is, in particular programmatically, adapted to control a common rail internal combustion engine according to a method according to the invention.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described in detail below with reference to the drawing.

Brief description of the drawings

FIG. 1

schematically shows a common rail system, by means of which a preferred embodiment of a method according to the invention will be described.

FIG. 2

shows a rail pressure / time diagram obtainable according to a preferred embodiment of the invention.

Embodiment (s) of the invention

A typical common rail system is based on FIG. 1 illustrated in which an injection system, as it can be based on the present invention is shown. FIG. 1 shows a schematic diagram of a common rail fuel injection system 100 for an internal combustion engine 116, such as a diesel engine. In a partially cut shown, cooled with cooling water 114 cylinder 124 of the engine 116, a piston 126 is movably arranged. An injector 109 for injecting fuel into the cylinder is mounted on the cylinder 124.

The fuel injection system includes a fuel tank 101 that is shown in a nearly full condition. Within the fuel tank 101, a prefeed pump 103 is arranged, which sucks fuel from the tank 101 through a pre-filter 102 and transported at low pressure of 1 bar to a maximum of 10 bar through a fuel line 105 to a fuel filter 104. From the fuel filter 104, a further low-pressure line 105 'leads to a high-pressure pump 106 which compresses the supplied fuel to a high pressure which, depending on the system, is typically between 100 bar and 2000 bar. The high-pressure pump 106 has a metering unit (ZME) 113 for adjusting an amount of fuel. The high-pressure pump 106 feeds the compressed fuel into a high-pressure line 107 and a rail 108 connected thereto, the so-called common rail. From the rail 108, another high-pressure line 107 'leads to the injector 109.

A system of return lines 110 allows the return of excess fuel from the fuel filter 104, the high pressure pump 106, the metering unit 113, the injector 109, and the rail 108 into the fuel tank 101. There is a pressure regulating valve (DRV) between the rail 108 and the return line 110. 112 switched by changing the from the rail 108 in the return line 110 flowing fuel quantity can control the prevailing in the rail 108 high pressure, the so-called. Rail pressure, to a constant value.

The entire common-rail injection system 100 is controlled by a controller 111 which is connected via electrical lines 128 and the like. with the prefeed pump 103, the high-pressure pump 106, the metering unit 113, the injector 109, a pressure sensor 134 on the rail 108, the pressure control valve 112 and temperature sensors 132, 122 connected to the engine 116 and to the fuel supply line 105. The control unit is connected via a bus system 136 with further control devices, not shown, by means of which it can resort to further data, such as the ambient temperature, the driving speed or the engine speed. Furthermore, an automatic start / stop (control) 150 is provided, which supplies a signal S. This start / stop control is designed such that it switches off the internal combustion engine under certain conditions. For example, the engine is turned off when the start / stop control detects that the vehicle is stationary. If the start / stop control detects that the driver wants to continue, the start / stop control starts the internal combustion engine and allows it to continue.

In FIG. 2 a preferred embodiment of the method according to the invention is explained with reference to a rail pressure / time diagram 200. In the diagram 200, different courses of the rail pressure p are plotted against the time t. In the diagram, the injection release pressure, ie the pressure to be at least provided for a successful injection, is indicated by p ₀ . This is about 120 bar in conventional systems.

A rail pressure curve according to the prior art is designated by 201. Usually the engine is idling before parking. In this operating state until time t ₀ , a control pressure value of usually 250 bar to 300 bar is maintained in the rail 108. In the present example, a control pressure value p _R of 300 bar is assumed for this purpose.

At time t ₀ , the stop request takes place and the last injection takes place before the engine stops. The stoppage becomes the Time t ₁ reached. Based on this, the rail pressure decreases depending on the size of any existing leakage until it drops below the injection release pressure at a time t ₂ , so that from this point on no direct restarting is possible. Rather, the rail pressure would now have to be increased (not shown) for restarting, which requires a certain amount of time and thus leads to a loss of comfort and, moreover, loads the hydraulic systems of the internal combustion engine.

In an embodiment of the invention, as shown by the graph 202, the rail pressure in the rail 108 is now increased after the stop request at time t ₀ first. The increase can be made in particular by the high-pressure pump 106 set to full delivery, the metering unit 113 is fully opened and the pressure control valve 112 is completely closed. In this way, the rail pressure is increased up to the time t ₁ to a first set pressure p ₁ from here about 700 bar. Starting from this pressure p ₁ , the rail pressure subsequently decreases again, but only reaches the injection release pressure at a time t ₃ , so that the time interval available for restarting is already extended by t ₃ -t ₂ in this way.

According to the invention, the increase of the rail pressure can be controlled or regulated. If, for example, it is desired that at least one second setpoint pressure p _{2 still} prevail after a predefinable period of time T, in this case the time interval T after a first stop request, ie, in this case, at time t ₄ , the rail pressure p (t ₄ ) and compared with the second setpoint pressure p ₂ . From the difference p ₂ -p (t ₄ ) and the target pressure p ₁ in this first stop request, a newly presettable target pressure p ₁ 'can be determined according to p ₁ ' = p ₁ + (p ₂ -p ( t ₄ )), which serves as a target pressure for subsequent pressure increasing operations. In this way, in subsequent pressure increasing operations after the lapse of the period T nor the desired desired pressure p ₂ can be provided.

Although the pressure decrease of the rail pressure curves 202 and 203 usually runs differently (for example, in the case of injectors opening at the high pressure side, the pressure decrease becomes flatter with increasing output pressure, so that the respective Final pressure is reached at a comparatively later point in time), the second desired pressure p ₂ can nevertheless be provided with sufficient accuracy-possibly by repeatedly carrying out the method just described-after the time T has elapsed.

With the method according to the invention, a rail pressure sufficient for restarting the internal combustion engine during start / stop operation can thus be maintained for longer periods and thus provided, in particular, at points in time which have already fallen below the injection release pressure in the prior art. In both embodiments according to 202 or 203, it can be provided that the increase in the rail pressure p is terminated when an upper threshold value (not shown) is reached, so that a permissible maximum pressure is not exceeded.

Claims (8)

1. Method for providing a rail pressure (p) sufficient for restarting a common rail internal combustion engine (100), wherein the internal combustion engine (100) is operated in a start/stop operating mode in which the internal combustion engine is deactivated in response to a stop request (t₀) and is restarted in response to a subsequent start request, wherein after a stop request (t₀) and before the stationary state (t₁) of the internal computer engine the rail pressure (p) is increased to a first setpoint pressure (p₁, p₁') by feeding in fuel above a control pressure value (p_R), characterized in that a predefinable time period (T) after the stop request (t₀) an actual pressure (p(t₄)) is determined and is compared with a predefinable second setpoint pressure (p₂), and the first setpoint pressure (p₁') is predefined again as a sum of the preceding first setpoint pressure (p₁) and the difference (Δp=p(t₄)-p₂) between the second setpoint pressure (p₂) and the actual pressure (p(t₄)).
2. Method according to Claim 1, wherein the control pressure value (p_R) is an idling setpoint pressure value.
3. Method according to Claim 1 or 2, wherein the rail pressure (p) is increased after the last injection (t₀) before the stationary state (t₁) of the internal combustion engine has taken place.
4. Method according to one of the preceding claims, wherein the control pressure value (p_R) is approximately 250 - 300 bar.
5. Method according to one of the preceding claims, wherein the fuel is fed in by means of a high pressure pump (106), and the high pressure pump (106) is set to full delivery in order to increase the rail pressure (p).
6. Method according to one of the preceding claims, wherein, in order to increase the rail pressure (p), a suction-side metering unit (113) is completely opened and/or a high-pressure-side pressure control valve (112) is completely closed.
7. Method according to one of the preceding claims, wherein the increasing of the rail pressure (p) is ended when an upper threshold value is reached.
8. Computing unit (111) which is configured to carry out a method according to one of the preceding claims.

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