JP2007046609A - Engine control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for achieving smooth transfer from a first mode in which cylinders in a part of a variable displacement engine are stopped to a second mode in which these cylinders are started without worsening emission matter characteristic by a simple and inexpensive configuration in the variable displacement engine. <P>SOLUTION: An intake valve is operated to suck air into at least one stopped cylinder so as to raise temperature of the cylinder in at least one stopped cylinder prior to reintroduction of fuel for restarting the stopped cylinder when switching between the first mode for stopping at least one cylinder by closing its intake valve and an exhaust valve and the second mode for starting the stopped cylinder. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control method of an internal combustion engine (engine) having a cylinder that can be selectively stopped, and more specifically, smooth transition between a cylinder stop mode and a subsequent cylinder restart mode. Related to the control method.

  Recent advances in engine development have led to the manufacture of variable displacement engines (VDEs). VDEs are internal combustion engines (engines) that can selectively stop cylinders when power output does not require full use of the engine. This reduces the work capacity of the engine and is therefore referred to as a variable capacity engine.

  The VDE concept can be applied to both spark ignition engines and compression ignition engines, and brings about an increase in fuel economy especially when the vehicle travels on a highway or the like. Many different cylinder configurations can be implemented depending on the torque demand and the available hardware. For example, there are 4 cylinder, 6 cylinder, 8 cylinder, 10 cylinder and 12 cylinder engines with as many stop cylinders as possible.

  There may be appreciable differences in noise and performance when switching between full and partial stop modes, which leads to driver dissatisfaction. Therefore, it is desirable to switch between operating modes so that the driver cannot recognize as much as possible. In addition to this, it is highly desirable to reduce emissions as much as possible.

  These problems are particularly important in compression ignition engines. Diesel engines are known for their loud noise, which has been greatly improved in recent years through the use of pilot injection. Diesel engines also raise the temperature in the combustion chamber to reduce emissions when fuel is introduced for combustion.

  When the cylinder is stopped in the diesel VDE, combustion is not performed in the cylinder, so that the temperature of the cylinder decreases. When the cylinder is restarted, the combustion chamber temperature is decreasing, so the emissions increase and the noise level also increases. In general, when the cylinder is cold started, the levels of hydrocarbons and CO emissions increase during the first few cycles of engine use.

In Patent Document 1, the same problem is addressed by heating the stopped cylinder using a glow plug that is normally used when starting the engine. This solution is very low heating when the glow plug is designed to create a hot spot just to promote local combustion rather than heating the entire cylinder. It only provides the ability. Modern thin glow plugs have a lower heating capacity and wattage, making this solution less feasible. In addition to these obvious problems, the solution proposed in Patent Document 1 requires not only useless electrical energy to heat the glow plug, but also requires an additional control device.
International Publication No. 99/0049193 Pamphlet

  To alleviate at least some of these disadvantages, the present invention provides a first mode in which at least one cylinder of an engine having a plurality of cylinders is stopped by closing an intake valve and an exhaust valve and a stopped cylinder. A method of controlling an engine for switching between a second mode to be started, the cylinder being stopped in order to raise the temperature of the cylinder before fuel is introduced to start the stopped cylinder Provided is a control method for an engine that performs mode switching by circulating the engine while operating an intake valve so as to allow air to enter.

  Preferably, the number of cylinders allowed to introduce air and not allowed to introduce fuel is set depending on the input from the engine torque demand pedal.

  Furthermore, it is preferable to operate both the intake valve and the exhaust valve of the cylinder prior to the reintroduction of fuel when the mode is switched from the first mode to the second mode.

  During times when air is allowed into the stop cylinder and fuel is not allowed, additional fuel can be supplied to the other working cylinders of the engine to increase the supply torque in response to driver demand.

  Preferably, during the reintroduction of fuel into the cylinder to be restarted, the amount of injected fuel is gradually increased until it matches the amount of fuel supplied to the other working cylinders.

  A further advantage is provided when the rate of increase of the injected fuel quantity is set depending on the input from the engine torque demand pedal.

  This method can be further improved when the additional fuel supplied to the other cylinders, i.e. the working cylinders, gradually decreases as the amount of fuel injected into the cylinders that have been stopped increases.

  The present invention provides a method of operating a conventional diesel engine as shown in FIG. The latest normal compression ignition engine 10 is controlled by an engine control unit (ECU) 12. Diesel engines are usually operated with the throttle wide open, and the engine output is determined by the fuel supplied to the engine for combustion. When a certain torque level is required, the driver depresses the torque request pedal, ie the accelerator pedal 14. The ECU 12 receives a signal from the request pedal position sensor, and controls the fuel supply device 16 to inject more fuel into the engine 10.

  In order to function as a variable displacement engine, the engine 10 must be capable of stopping at least one of its cylinders.

  The development of the variable displacement concept has led to closing the intake and exhaust valves of the cylinders that can be stopped simultaneously with interrupting the fuel supply. By closing the valve, the air remaining in the cylinder is repeatedly compressed and expanded without the loss associated with sucking and pumping air through the intake manifold and exhaust manifold, respectively. Closing the valve is performed by a valve drive controller represented in block 18 of FIG.

  When the valve is forced to remain closed, new air does not enter or exit through the valve. This causes the cylinder to operate as an air spring with much of the energy released during expansion and stored in the compressed air during compression. All of the energy lost during this cycle is transferred as heat into the cylinder wall. However, as the pressure increases during compression, on each upward stroke, a small amount of air is lost due to leakage through the piston ring. Long-term operation in the stop mode results in an equilibrium level such that the pressure in the cylinder oscillates around atmospheric pressure during the engine's circulating motion. As the air in the cylinder is reduced, the heat generated during compression is greatly reduced.

  Once combustion is stopped, there is no need to warm the cylinder, so heat loss in the cylinder is not a problem. But not at restart. Restart is often required when the torque needs to be increased. Elements other than the demand pedal 14 may be relevant, but the need for restart is usually determined by the driver's input to the demand pedal 14. The level of torque demand can vary depending on the situation. For example, a cylinder stop can be expected to occur when traveling on a highway. A slight increase in torque on the highway requires a torque increase, but a greater torque increase is required when it is desired to quickly and safely pass another vehicle.

  The required output difference can be accommodated to some extent by the number of cylinders restarted due to torque demand. For example, when a 12-cylinder engine is operated in a 4-cylinder mode during steady running and the driver pushes the accelerator pedal, it can be changed to a 6-cylinder, 8-cylinder, 10-cylinder, or full 12-cylinder mode.

  When the temperature of the cylinder to be restarted is excessively lowered, a problem resulting from the restart of the cylinder occurs. Injecting fuel into a low temperature cylinder is disadvantageous with respect to noise, smoke, carbon dioxide and hydrocarbon emissions. These effects become more significant as the number of low temperature cylinders restarted increases.

  Ideally, the transition between the stop operation and the operation operation of any cylinder should be as seamless as possible. A preferred embodiment of the present invention operates to control the engine to generate as much heat as possible in the stopped cylinder prior to cylinder restart. Such control continues until the cylinder that has been stopped becomes indistinguishable from the cylinder that has not been stopped.

  Input from the accelerator pedal 14 can be determined by both pedal position and pedal position change rate. When a torque increase request is indicated, the ECU 12 sends a control signal to the valve drive controller 18 to cause the intake valve to resume normal operation and allow air to enter the cylinder. This control may be performed for all the stopped cylinders, but may be performed for some of the stopped cylinders according to the torque request and the cylinder temperature (for example, as the torque request increases). The number of cylinders having a period during which only intake is performed is reduced, or the number of cylinders having a period during which only intake is performed is decreased as the cylinder temperature is increased, or both are performed). Valve stop mechanisms are well known to those skilled in the art and need not be discussed at length here. Specifically, the stop can be accomplished mechanically, electrically, hydraulically, or electrohydraulic.

  By opening the cylinder to the intake port every four strokes, the volume of air in the cylinder can be maintained to the extent that useful heat can be transferred from the air to the surroundings during the compression stroke. High compression forces some of the air through the piston ring. The passage of the air through the piston ring will occur twice in four strokes, since the exhaust valve does not open and the intake valve reopens the intake port twice.

  If it is too complex to have a valve stop that can stop the intake and exhaust valves of the engine independently, stopping and restarting all the valves together can also be efficient. Although it may decrease, it will be possible to generate heat by compressing air. The reason for the low efficiency is that the exhaust stroke pushes out the remaining heated air without passing through the piston ring.

  In order to further increase the in-cylinder temperature, a small amount of fuel may be moderately introduced to burn it and generate heat. Preferably, in the cylinder to be restarted until the cylinder to be restarted is at a normal operating temperature and the amount of fuel injected into the cylinder is equal to the amount of fuel supplied to other cylinders that have not been stopped. The fuel injected into the engine is gradually increased while the engine continues to circulate.

  In order to implement this method, the exhaust valve must be restarted with the intake valve for the cylinder into which a small amount of fuel is introduced in order to be able to remove the combustion gases. Since most of the heat in this mode of operation comes from combustion rather than compression alone, the efficiency loss is not as great when compared to previous methods with only the intake valve operating without fuel.

  A temperature sensor in the stop cylinder may determine the period of the engine that increases the fuel supply level to the stop cylinder. Similarly, as described above, the rate of fuel supply increase may depend on the torque demand by the accelerator pedal 14. It is important that the rate of change is not so high that the fuel supply changes stepwise. Such step changes do not solve start-up problems such as noise, smoke and emissions, which will be perceptible to the driver. Therefore, it is desirable that the reintroduction of fuel is as gradual as possible, but this also has the disadvantage of making the driver feel unresponsive.

  To solve this problem, it is desirable to increase the fuel supply to the working cylinder (rather than the cylinder to be restarted) in order to supply more torque to quickly satisfy the torque demand.

  FIG. 2 shows the sequence of events when the request pedal is depressed while the engine is operating with some cylinders stopped. In FIG. 2, the torque demand is represented by a dashed line. Immediately after the step increase in torque demand, the fuel supply amount to the working cylinder increases as shown by the dotted line. This results in a subsequent increase in torque output, as indicated by the dashed line.

  Region 1 in the figure defines a period in which the intake valve is normally operated without supplying fuel in the stopped cylinder (the exhaust valve may or may not function in hardware or control). . In the region 2, as shown by the solid line, the fuel is reintroduced into the stopped cylinder. Extra fuel further increases torque output. As the amount of fuel injected into the stopped cylinder continues to increase, the stopped cylinder begins to produce substantial work and contributes to torque output. At that point, the fuel supply to the working cylinder (dotted line) reaches a maximum value and then begins to decline. Eventually, the fuel supply level to all cylinders will match the level required to produce the torque output indicated by the accelerator pedal position.

  Significantly, when the torque output reacts immediately and continues to meet the torque demand from the driver, the fuel supply speed in the stopped cylinder increases from zero to a constant level across all cylinders. There is no sudden step change in fuel supply. The absence of a step change when the stop cylinder warms can prevent exhausting excessive smoke from the exhaust pipe of the car and prevent the driver from feeling a sudden change in noise. The change in state can be made slowly so that it cannot be perceived, and importantly, the emissions can be kept at a level manageable by the aftertreatment device in the exhaust system downstream of the engine.

  Noise changes are one of the problems we are currently trying to deal with. Studies have shown that a small amount of pilot injection preceding the main injection has a significant effect on the compression ignition engine sound at a low cost in terms of fuel economy. With this in mind, it is desirable to supply a small amount of pilot injection prior to the main fuel injection when the first fuel is introduced at cylinder restart. Since engine noise is determined by the amount and timing of pilot injection, when the amount of fuel supplied to the stop cylinder increases, the timing and amount of pilot injection should be kept constant while the amount of main injection is increased. Thus, the cylinders that have been stopped can approach the fuel supply of the working cylinders with no appreciable noise change.

  Also, the amount and timing of pilot injection can be modified as a function of crank angle, combustion chamber temperature, pedal demand, or input data from an NVH (noise, vibration and harshness) sensor.

  This can be further improved by gradually changing the timing and / or amount of pilot injection to the other cylinders before and after the reintroduction of fuel to the stopped cylinder. This would allow the ECU to gradually change the overall engine sound to hide any detectable changes caused by starting the stopped cylinder.

  The objective is to ensure that emissions are kept low throughout the engine operation, but intentionally operating at an excessively rich air / fuel ratio in a cylinder where the operating temperature needs to be raised There is a possibility. Such operation produces extra unwanted emissions in the short term, but in some conditions increases the rate of temperature recovery, and the emissions released from the stopped cylinder during restart of the stopped cylinder This can lead to a reduction in the total amount of things.

It is a block diagram showing the operation | movement of the normal variable displacement engine which can apply this invention. 3 is a time chart showing fuel input timings of a stopped cylinder and an operating cylinder according to a preferred embodiment of the present invention.

Explanation of symbols

10 engine
12 ECU
14 Request pedal
16 Fuel supply system
18 Valve drive controller
20 Exhaust system

Claims (14)

In an engine control method having a plurality of cylinders,
A method of switching between a first mode in which at least one cylinder is stopped by closing its intake valve and exhaust valve and a second mode in which the stopped cylinder that has been stopped is started,
At the time of mode switching from the first mode to the second mode, in order to increase the temperature of the stopped cylinder in at least one of the stopped cylinders before reintroducing the fuel for restarting the stopped cylinder, A control method for operating the intake valve so as to enable intake to the stop cylinder.   2. The control method according to claim 1, wherein, at the time of the mode switching, the number of cylinders that can be inhaled only before reintroduction of fuel is set according to an engine state.   3. The control method according to claim 2, wherein, at the time of the mode switching, the number of cylinders that can only be inhaled prior to reintroduction of fuel is set based on at least one of a torque demand for the engine and a cylinder temperature.   The control method according to any one of claims 1 to 3, wherein both the intake valve and the exhaust valve are operated prior to fuel re-introduction when the mode is switched.   4. The fuel cell according to claim 1, wherein a small amount of fuel is introduced into at least one of the stopped cylinders as compared with the operated cylinder in order to increase the temperature of the stopped cylinder when the mode is switched. The control method described in 1.   When the mode is switched, prior to reintroduction of fuel, only the intake valve is operated for cylinders that are only capable of intake, while both the intake valve and exhaust valve are operated for cylinders that are introduced with a small amount of fuel. The control method according to claim 5.   The control method according to any one of claims 1 to 6, wherein additional fuel is supplied to the working cylinder during a time period during which the supply of air to the stopped cylinder is enabled when the mode is switched.   The control according to claim 7, wherein during the reintroduction of fuel for restarting the stopped cylinder, the amount of fuel supplied to the stopped cylinder is gradually increased until it matches the amount of fuel supplied to other operating cylinders. Method.   The control method according to claim 7 or 8, wherein when the mode switching is based on a torque request, an increase rate of the fuel amount supplied to the working cylinder is made faster than an increase rate of the fuel amount supplied to the stop cylinder. .   10. The control method according to claim 7, wherein during the reintroduction of fuel for restarting the stopped cylinder, fuel injection to the stopped cylinder is executed by a plurality of injections whose timing and amount are controlled.   The control method according to claim 7, wherein the fuel injection amount and the fuel injection timing to the stop cylinder are set according to a torque request for the engine.   The control method according to any one of claims 7 to 11, wherein the fuel injection amount and fuel injection timing to the stopped cylinder are set based on a crank angle, a combustion chamber temperature, and an input from an NVH sensor.   The control method according to any one of claims 7 to 12, wherein the additional fuel supplied to the other operating cylinder is decreased as the amount of fuel injected into the stopped cylinder increases.   A computer program for controlling an engine of a vehicle, which is stored in a computer and causes the computer to execute the control method according to any one of claims 1 to 13.

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