METHOD FOR OPERATING AN ENGINE ARRANGEMENT
A method is provided for operating an internal combustion engine having at least one cylinder, said engine operating according to a four stokes cycle. The engine includes at least one controlled intake port to control communication of the combustion chamber with an intake line. The intake port is controlled to achieve a main open phase mainly during the intake stroke. The intake port is controlled to achieve an auxiliary open phase during the power stroke in view of heating the engine at cold start.
Latest RENAULT TRUCKS Patents:
- Gas flow regulating for cleaning a particular filter
- Method and internal combustion engine arrangement for regenerating an exhaust after-treatment device
- Valve actuation mechanism and automotive vehicle equipped with such a valve actuation mechanism
- Control method for an automated gearbox of an automotive vehicle, system for controlling such a gearbox and automotive vehicle equipped with such a system
- METHOD AND INTERNAL COMBUSTION ENGINE ARRANGEMENT FOR REGENERATING AN EXHAUST AFTER-TREATMENT DEVICE
The invention relates to the field of methods for operating an engine arrangement comprising a four stroke internal combustion engine.
Four stroke internal combustion engines (ICEs) are well known. In a reciprocating piston design, they have at least one cylinder or several cylinders in each cylinder, a piston, which is connected to a crankshaft, is displaced between a top dead center position and a bottom dead center position, thereby defining in the cylinder a variable volume combustion chamber. When such an engine is operating according to a four strokes cycle, the four strokes are usually theoretically defined as the periods of times between two immediately consecutive dead center positions of the piston. These strokes are the intake stroke, the compression stroke, the power stroke, and the exhaust stroke. Such engines also comprise at least one controlled intake port and at least one controlled exhaust port to control communication of the combustion chamber respectively with an intake line and with an exhaust line of the engine arrangement. The opening and closing of the intake and exhaust ports are usually performed through a corresponding poppet valve. The intake port is controlled to achieve a main open phase mainly during the intake stroke and the exhaust port is controlled to achieve a main open phase mainly during the exhaust stroke. It is of course well known that these main intake and exhaust opening phases may start before or after the theoretical beginning and/or end before or after the theoretical end of the corresponding stroke.
It is also known that either the intake port or the exhaust port can be controlled to achieve auxiliary opening phases to modify the basic operation of the engine. For example, engine braking can be enhanced by providing that the exhaust port is opened at the end of the compression stroke. Also, it is known to control a brief opening of the intake port, during the exhaust stroke, or at least an early opening of the intake port at the end of the exhaust stroke, to achieve so-called internal exhaust gas recirculation.
Many ways of optimizing four strokes internal combustion engines have been suggested already to enhance their performance in view of often theoretically opposing requisites, and in particular in view of minimizing consumption of fuel and production of harmful emissions. One area of interest for engine arrangement designers is the temperature management of the engine. Indeed, the engine cannot always operate at its optimum temperature. One critical aspect is the operation of the engine at start, before it has reached its optimal temperature. It is then desirable to attain as quickly as possible that optimal temperature. Another critical aspect has also appeared more recently with the presence in the engine arrangement of various exhaust after-treatment systems such as three-way catalysts, particle filters or selective catalytic reduction systems. Such systems often require that the exhaust gases passing through them are comprised within a well defined temperature range, either for their optimum functioning or, in the case of particulate filters, for their regeneration. In such cases, it is sometimes critical to enhance the temperature of the exhaust gases.
Another way to optimize the functioning of four stroke ICEs is to achieve exhaust gas recirculation (EGR). Depending on how and when EGR is performed, various results can be achieved, but a very frequent reason to use of EGR, especially in Diesel engines, is to lower the temperature of the combustion process in order to limit the production of nitrogen oxides (NOx).
Document U.S. Pat. No. 6,347,619 discloses a way to achieve EGR in a wide variety of engine operating conditions. The aim of the system disclosed in this document is to capture exhaust gases at a relatively high pressure. The system disclosed provides EGR in a turbocharged diesel engine by adding a separate EGR manifold and a secondary exhaust valve for each combustion chamber that permits flow of exhaust gases from the combustion chamber to the EGR manifold. The secondary exhaust valve is opened during the expansion stroke of the engine cycle, after the combustion process has been completed, while the pressure in the combustion chamber is still greater than the pressure in the intake manifold. Therefore, this system requires an additional manifold, an additional set of ports and an additional system for controlling the additional ports, and would therefore be quite costly.
It is desirable to provide a new method of operating a four stroke ICE arrangement giving the possibility, at a minimal cost, to ensure an enhanced thermal management of the engine and of the exhaust gases.
The invention, according to an aspect thereof, therefore provides for a method for operating an engine arrangement comprising a four strokes internal combustion engine, characterized in that said method includes the routine of controlling the intake port to achieve an auxiliary open phase during the power stroke.
On
Each cylinder 14 is equipped with at least one intake port 16 and at least one exhaust port 18. As in many modern engines, the engine on
In the case of a multi-cylinder engine, the intake line is preferably equipped with an intake manifold 21 through which it is connected to each of the intake ports 16. The intake manifold 21 has preferably separate intake ducts for each individual intake port 16, or at least preferably an individual intake duct 25 for each cylinder. Similarly, the exhaust line is preferably equipped with an exhaust manifold 23 having individual exhaust ducts for each exhaust port or at least for each cylinder.
In the example shown, the engine 12 is a turbocharged engine which comprises a turbo compressor 24 having its turbine 26 located on the exhaust line 22 and its compressor 28 located on the intake line 20. Also, the engine arrangement may be equipped, as represented on
The engine 12 is for example a compression ignition engine, known as a Diesel engine, but the invention could also be carried out with a spark ignited engine. Also, the engine 12 may be of the direct injection type, where fuel is injected directly in the cylinder. In such a case, only air is admitted through the intake line into the cylinders, but the invention could also be carried out with an engine of the indirect injection type where the injection is performed for example in the intake line or in a pre-combustion chamber:
On
According to the invention, the method additionally includes the routine of controlling the intake port to achieve an auxiliary open phase during the power stroke, said stroke occurring between 0 to 180 degrees of crankshaft revolution. Preferably the auxiliary open phase is controlled to start after the end of the combustion process. In most engine operating conditions, at least for a diesel direct injection engine, the auxiliary open phase can therefore start between 30 and 70 degrees of crankshaft revolution after the top dead center position initiating the power stroke. In the example shown, it starts at approximately 50 degrees of crankshaft revolution after the top dead center position initiating the power stroke. Despite being started after the end of the combustion process, one can therefore note that the auxiliary open phase starts quite early in the power stroke, before the piston has gone halfway down to its bottom dead center position. At that point in time, the pressure within the cylinder is still quite high, typically more than 10 bars, and in some cases superior to 50 bars, which is much higher than the pressure in the intake line, even in the case of a turbocharged engine. As a consequence, the opening of the intake port results in a flow of gases from the cylinder to the intake line, as evidenced by the negative values of the mass flow rate through the intake port represented on
Nevertheless, at that point in time corresponding to the start of auxiliary open phase of the intake valve, the temperature of the gases in the combustion chamber are still very high, especially if compared to the temperature of exhaust gases which are expelled to the exhaust line in the exhaust strokes. One reason for this is that these gases have only undergone a very partial expansion, because the piston has yet only traveled less than 20 to 40% of its displacement towards the bottom dead center, and therefore they have undergone only a very partial corresponding temperature drop. Another reason is that, during this very short period of time between the end of the combustion and the start of the auxiliary open phase, very little heat has been transferred from the gases to the cylinder parts.
As a result, the gases which are expelled to the intake line are at a very high temperature. Such gases can be up to 1500 C hotter than exhaust gases expelled at the end of the exhaust stroke.
Of course, opening of one of the ports of the cylinder so early in the power stroke is detrimental to the amount of work which can be retrieved by the piston, which has adverse consequences on the engine output and on its efficiency.
Therefore, the auxiliary open phase of the intake valve should be short in time. The duration of the auxiliary open phase is preferably within 15 to 50 degrees. In other words, the auxiliary open phase preferably ends between 50 and 120 degrees of crankshaft revolution after the top dead center position initiating the power stroke. In the example shown on
Also, it can be noticed on
As a result of this auxiliary opening phase, a certain quantity of combustion products is expelled directly to the intake line. More particularly, in the configuration of the engine arrangement of
It is to be mentioned that, although not represented on the example of
In any case, the combustion products which have been expelled to the intake line, the so-called direct high temperature EGR gases, are for the most part re-admitted in the cylinder at the following main open phase of the intake port(s), together with fresh air. As a result, the gases which are admitted in the cylinder for the next combustion process are a mixture of fresh air and of combustion products which have been expelled to the intake line directly through the intake port in the auxiliary open phase. The temperature of such a mixture is of course higher than the temperature of the fresh air typically provided through the intake line. The increase of temperature is of course dependent on the proportion between the fresh air and the combustion products which are present in the mixture. This proportion can be varied by varying the duration of the auxiliary open phase of the intake valve, and/or by varying the degree of opening of the intake port.
Of course, during this following main open phase of the intake port(s), it could be provided that indirect EGR gases, which have been re-circulated through the EGR conduit 30, are also admitted in the cylinder, together with some fresh air and with direct high temperature EGR gases. Such an option would enable to adjust the temperature of the mixture for a given ratio of EGR gases compared to fresh air.
When the routine of having an auxiliary open phase of the intake valve is carried out for a cylinder during a certain number of consecutive cycles of the cylinder, it can be seen on
Of course, as stated above, practicing the method of according to the invention with the auxiliary open phase will bring a penalty in terms of engine efficiency, so that this method may only be desirable on specific instances. In most cases, the method will be desirable only where, at specific times, additional heat generation in the engine would be desirable, for example at engine cold-starting or when it is desired to regenerate a particulate filter, or for accurately controlling operating conditions of after-treatment systems. Therefore, the invention will be preferable used in connection with an engine arrangement where the intake port control means are capable of controlling the corresponding intake ports with or without the routine of controlling the intake port to achieve an auxiliary open phase during the power stroke, depending on the instant engine operating conditions. Of course, if the engine is of a camless type, having for example electronically piloted electric or electro-hydraulic valve actuators, it will be easy for the skilled man in the art to develop a proper electronic control unit capable of controlling the ports with or without the routine. If the engine is equipped with cam driven valves, there are numerous known devices which can achieve at least two control laws for a same valve. Such devices are already implemented to selectively drive the exhaust valves according to at least two controls laws, depending on whether or not it is desired to provide one or several additional open phases of the exhaust port during the compression stroke for enhancing the engine braking. Examples of such devices are described in documents U.S. Pat. No. 5,193,497 and U.S. Pat. No. 5,890,469. The skilled man in the art can rely on the disclosure of these documents to devise a corresponding system for controlling the intake valves of an engine arrangement which is to be controlled according to the invention.
The method according to the invention will advantageously be performed in view of heating up the engine arrangement, especially at cold start. The method can also be performed in view of heating up an exhaust after-treatment system. Preferably, it will be performed at low engine loads.
Claims
1. Method for operating an internal combustion engine having at least one cylinder in which a piston connected to a crankshaft is displaced between a top dead center position and a bottom dead center position, thereby defining in the cylinder a variable volume combustion chamber, the engine operating according to a four stokes cycle including an intake stroke, a compression stroke, a power stroke, and an exhaust stroke, wherein the engine comprises at least one controlled intake port and at least one controlled exhaust port to control communication of the combustion chamber respectively with an intake line and with an exhaust line, comprising
- controlling the intake port to achieve a main open phase mainly during the intake stroke,
- controlling the exhaust port to achieve a main open phase mainly during the exhaust stroke, and
- controlling the intake port to achieve an auxiliary open phase during the power stroke.
2. Method according to claim 1, wherein the auxiliary open phase starts and ends during the power stroke.
3. Method according to claim 1, wherein the auxiliary open phase starts. between 30 and 70 degrees of crankshaft revolution after the top dead center position initiating the power stroke.
4. Method according to claim 1, wherein the auxiliary open phase ends between 50 and 120 degrees of crankshaft revolution after the top dead center position initiating the power stroke.
5. Method according to claim 1, wherein the auxiliary open phase lasts between 15 and 50 degrees of crankshaft revolution.
6. Method according to claim 1, wherein the engine is a compression ignition engine.
7. Method according to claim 1, wherein the intake port is controlled through an intake valve
8. Method according to claim 1, wherein the intake valve is controlled through a variable valve control system.
9. Method according to claim 1, wherein the routine of controlling the intake port to achieve an auxiliary open phase during the power stroke is performed in view of heating up the engine arrangement.
10. Method according to claim 1, wherein the routine of controlling the intake port to achieve an auxiliary open phase during the power stroke is performed in view of heating the engine at cold start.
11. Method according to claim 1, wherein the routine of controlling the intake port to achieve an auxiliary open phase during the power stroke is performed in view of heating up an exhaust after-treatment system.
12. Method according to claim 1, wherein the routine of controlling the intake port to achieve an auxiliary open phase during the power stroke is performed at low engine loads.
13. Method according to claim 1, wherein the engine is a multi-cylinder engine, in that the intake line comprise an intake manifold having at least one distinct intake duct per cylinder so that, during the routine of controlling the intake port to achieve an auxiliary open phase during the power stroke for one cylinder, post combustion gases are expelled through the intake port into the corresponding intake duct of the cylinder.
Type: Application
Filed: Jun 2, 2009
Publication Date: Mar 22, 2012
Applicant: RENAULT TRUCKS (Saint Priest)
Inventors: Nicolas Auffret (Compertrix), Romain Le Forestier (Lyon)
Application Number: 13/320,412
International Classification: F01L 1/34 (20060101); F01L 1/00 (20060101);