Internal-combustion engine control method and engine using same

The present invention relates to a method of controlling an internal-combustion engine comprising at least one cylinder (10) with at least one burnt gas exhaust means (12) including an exhaust valve (16) whose opening/closing is controlled by control means (22) and an exhaust pipe (14) connected to an exhaust line (18, 20), at least two intake means (26, 28) comprising each a valve (32, 36) whose opening/closing is controlled by a dedicated actuating means (46, 48) and a pipe (30, 34). The method, during low load or medium load running of the engine:

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an internal-combustion engine control method and to an engine using such a method.

2. Description of the Prior Art

There are known engines wherein opening/closing of the intake valve(s) is controlled by variable-timing control means. In this type of timing, the conventional camshaft is replaced by an actuating means dedicated to each valve, such as an electromagnetic or hydraulic or electrohydraulic or pneumatic or electropneumatic actuator, which acts directly or indirectly upon the valve rod. This allows changing the opening angles and times of the intake valves, as well as their lift laws or their opening frequency, while allowing multi-opening during a single running cycle of this engine. On the other hand, opening/closing of the exhaust valve(s) is controlled by any conventional timing means, such as a camshaft driven in rotation by a belt (or a timing chain) connected to the engine crankshaft. This engine type with two timing architectures is more commonly known as “half camless”.

Similarly, there are engines known as “full camless” that comprise no camshaft, whether for the intake valves or for the exhaust valves. In this case, the engine comprises an actuating means dedicated to each valve, such as an electromagnetic or hydraulic or electrohydraulic or pneumatic or electropneumatic actuator, which acts directly or indirectly upon the valve rod of the intake and exhaust valves.

In both engine types it is possible for example to have, for low and medium loads, a specific combustion such as a combustion with controlled auto-ignition (CAI) or a combustion with homogeneous charge compression ignition (HCCI) through phasing of the intake and exhaust valves allowing opening/closing of these valves with re-introduction or retention of burnt gases in the combustion chamber, as described in French Patent 2,760,487 filed by the assignee on combustion with controlled auto-ignition.

In the case of a half camless engine, considering that the exhaust valves are controlled by a camshaft, it is difficult to obtain such a combustion over a significant engine running range because the lift laws of these exhaust valves are difficult to modify during operation or they can only be modified over a very limited range.

For a full camless engine, the aforementioned drawback can be solved but to the detriment of an excessive production cost for this engine with installation of an actuator for each intake and exhaust valve, associated with a very sophisticated control of these actuators.

Furthermore, in the case of high engine loads, actuating the exhaust valves is difficult considering the stresses imposed by the high back pressures at the exhaust.

The present invention aims to overcome the aforementioned drawbacks by means of a method allowing a half camless engine to run like a full camless engine for low and medium loads.

SUMMARY OF THE INVENTION

The present invention thus relates to a method of controlling an internal-combustion engine comprising at least one cylinder with at least one burnt gas exhaust means including an exhaust valve whose opening/closing is controlled by control means and an exhaust pipe connected to an exhaust line, with at least two intake means comprising each a valve whose opening/closing is controlled by a dedicated actuating means and a pipe, during low load or medium load running of the engine: controlling the closed position of the exhaust valve; and

controlling one of the intake valves so as to operate it as a burnt gas discharge valve.

The method can discharge the burnt gases into the exhaust line via a conduit.

The method can also shut off the mouth of the pipe comprising the discharge valve.

The invention also relates to an internal-combustion engine with at least one cylinder provided with at least one burnt gas exhaust means including an exhaust valve whose opening/closing is controlled by control means and an exhaust pipe, an exhaust line and at least two intake means comprising each a pipe and a valve whose opening/closing is controlled by a dedicated actuating means, comprising means for controlling the exhaust valve control means and means for controlling one of the valves of the intake means in order to change the opening law thereof so that it acts as a burnt gas discharge valve.

This engine can comprise a conduit connecting the pipe of the intake means comprising the discharge valve to the exhaust line.

The pipe of the intake means comprising the discharge valve can carry a means for shutting off the mouth of the pipe.

The exhaust valve control means comprises disconnecting means allowing the control means to be activated or deactivated.

The invention can relate to a use of the method for a combustion with controlled auto-ignition of the engine.

Advantageously, the invention can be used for multi-time engine running or for running of the engine with engine braking.

Another use of the method can concern running an engine under cold start conditions to reduce emissions.

DETAILED DESCRIPTION OF THE INVENTION

The description hereafter gives an example of an embodiment of the invention applicable to a diesel type internal-combustion engine, which may be supercharged, but it is also applicable to any other type of internal-combustion engine, notably of spark ignition type.

In the sole FIGURE, the internal-combustion engine comprises at least one cylinder10, (four cylinders are illustrated), including a combustion chamber in which combustion of a fuel mixture takes place.

This cylinder comprises at least one burnt gas exhaust means12, (two are illustrated), including an exhaust pipe14and a shut-off means such as an exhaust valve16. Exhaust pipes14open into an exhaust line with an exhaust manifold18connected to a tailpipe20allowing discharge of the burnt gases from the combustion chambers and may be to pollution treatment thereof. Opening and closing of exhaust valves16is controlled by any known means such as a camshaft22, driven in rotational synchronism with the crankshaft by a timing belt or chain (not shown). This camshaft carries means24for disconnecting the opening of the exhaust valves such as, for example, those allowing disengagement from the timing belt (or chain). These disconnecting means allow stopping rotation of the camshaft and thus to make it inactive on the exhaust valves so that they remain in closed position.

Other means can be used such as, for example, hydraulic disconnection of the cam actuation, more commonly known as valve opening deactivation.

This cylinder also comprises at least two intake means26,28, one28being used as a burnt gas discharge means when the engine runs under low or medium load conditions, as explained in detail in the description below.

Intake means26, referred to as conventional intake means, comprises an intake pipe30associated with a shut-off means such as an intake valve32.

Intake means28, referred to as intake/discharge means, comprises an intake/discharge pipe34and an intake/discharge valve36. Intake/discharge34carries a shutter38, preferably with a bistable position (fully open or fully closed), located upstream from mouth40of this pipe and allowing control of any fluid circulation in the pipe from and towards this mouth. A conduit42starts at intake/discharge pipe34between intake/discharge valve36and shutter38, and it opens onto exhaust manifold18or, in the example shown, on tailpipe20. This conduit carries a valve44, preferably of variable opening type, arranged between the origin of conduit42and its junction with tailpipe20, which allows controlling of the fluid circulation in this conduit. Opening and closing of each intake valve32and intake/discharge valve36is controlled by a dedicated actuating means,46and48respectively, allowing achieving a totally variable timing or, at least, allowing phasing of these valves and their opening/closing times to be varied. It is therefore possible to use electromagnetic actuators or hydraulic, electrohydraulic, pneumatic or electropneumatic actuators that act upon the valve rod they control. For simplification reasons, electromagnetic actuators will be mentioned in the description hereafter for control of the intake and intake/discharge valves.

Of course, without departing from the scope of the invention, the openings of intake30and intake/discharge valves40can be connected to a single intake manifold (not shown) so as to take advantage of the various operational elements of the engine, such as intake air filtration or engine supercharging.

This engine also comprises a processing unit50, referred to as engine calculator, that contains mappings or data tables allowing evaluation, according to engine parameters such as the engine speed, its load or the intake and exhaust pressures, the power that has to be generated by this engine to meet the driver's throttle control and, consequently, to manage the desired running conditions of this engine, from low loads to medium loads or from high loads to very high loads.

More precisely, this engine calculator allows, according to these running conditions, to control the lift laws of intake32and intake/discharge valves36by means of a control line52acting upon electromagnetic actuators46and48, to activate or deactivate exhaust camshaft22by acting by means of a control line54upon disconnecting means24, to control full opening or full closing of shutters38by means of a line56and to control valve44through a line58.

Thus, when the engine runs in a conventional mode, generally with high to very high loads, it works as a half camless engine while using camshaft22for exhaust valves16and electromagnetic actuators46and48for intake32and intake/discharge valves36.

More precisely, through line54acting upon disconnecting means24, engine calculator50makes (or leaves) camshaft22, which conventionally controls opening and closing of the exhaust valves during the engine exhaust phase, operational. This engine calculator also controls actuators46and48through line52so that the opening/closing timing of intake32and intake/discharge valves36is achieved conventionally with valve36working as an intake valve. Similarly, engine calculator50controls through line56shutters38so as to have them in a configuration of full opening of mouth40of intake/discharge pipe34. Finally, this engine calculator acts upon valve44in cases where it is necessary to re-inject burnt gases to the intake, an operation that is better known to those skilled in the art as EGR (Exhaust Gas Recirculation).

In this configuration, intake/discharge means28is used as an air intake means and conduit42with its valve44can be used as an EGR line, for mixing part of the burnt gases circulating in the exhaust line with the intake air to achieve an air/hot gas mixture promoting combustion of the fuel mixture in the combustion chamber of each cylinder and reducing emissions.

Thus, the air admitted through pipes30and34, may be with a proportion of burnt gases through line42, enters the combustion chamber of cylinder10, then a combustion occurs after injection of a fuel and compression of the fuel mixture. The burnt gases resulting from this combustion are then conventionally discharged from the combustion chamber when exhaust valves16open under the action of camshaft22.

During low load (or up to medium load) running and during engine idle speed, the engine calculator controls the various engine devices (disconnecting means24, electromagnetic actuators, shutters38and valve44) to change from running conditions with a half camless engine to running conditions with a full camless engine where only actuators46and48are used. This has the advantage of reducing the fuel consumption and emissions, and it can also increase the engine braking capacity.

Engine calculator50therefore deactivates camshaft22through disconnecting means24by uncoupling it from the timing belt or chain that drives it in rotation. In this case, exhaust valves16remain constantly closed (another solution would consist in maintaining the camshaft in rotation and in deactivating opening of the valves by means of a hydraulic control). Simultaneously, the engine calculator controls closing of the mouth of intake/discharge pipe34through fully closed positioning of shutter38, as shown by the solid lines in the FIGURE, so as to shut off any circulation towards this mouth40, and it opens valve44in order to allow fluid circulation in conduit42.

In this configuration, the engine only runs with valves32and36. Intake valve32allows air to be fed into the combustion chamber for pipe30and intake/discharge valve36is used as discharge (or exhaust) valve for the burnt gases resulting from the combustion of the fuel mixture in the combustion chamber of the cylinder. These burnt gases are discharged through this valve, then they circulate in the portion of pipe28shut off by shutter38, then in conduit42prior to being eventually sent into tailpipe20, that is in the opposite direction to that of the conventional mode when this conduit is used as an EGR conduit.

Thus, by means of this full camless configuration of the engine, all the intake and exhaust valve phasing possibilities allowing opening/closing of these valves with re-introduction or retention of burnt gases in the combustion chamber can be considered. This allows, in the case of controlled auto-ignition (CAI) or homogeneous charge compression ignition (HCCI) combustion, to intake again and to retain the burnt gases in the combustion chamber so as to compress them thereafter.

Advantageously, it is also possible to use the method according to the invention to operate an engine according to a multi-time mode, or to achieve engine braking for this engine.

Running of this engine according to the two-stroke cycle can be obtained for example by doubling the opening frequency of valves32and36with suitable opening laws. This has the advantage of reducing the indicated power produced upon each engine cycle and thus allows increasing the load zone where running under CAI or HCCI conditions can be obtained.

To achieve engine braking, the opening lift laws of valves32and36are designed for the gas mixture allowed into the combustion chamber to be compressed up to the Bottom Dead Centre. From this configuration, valve36just has to be opened at compression end to lose the energy that was used for compression of the gas mixture, which results in a negative gas compression work that will act as an engine brake.

Using the method according to the invention upon engine cold starting can also be considered.

It is thus possible, with dedicated valve opening laws, to reduce emissions by increasing the proportion of residual burnt gas retained and, consequently, by raising the temperature of the feedstock confined and compressed in the combustion chamber.

The present invention is not limited to the embodiment example described above and it encompasses any variant and equivalent.