WO2000079107A1

WO2000079107A1 - Method for controlling an internal combustion engine in order to obtain an engine braking effect

Info

Publication number: WO2000079107A1
Application number: PCT/FR2000/001667
Authority: WO
Inventors: Alain Fernandez
Original assignee: Renault
Priority date: 1999-06-18
Filing date: 2000-06-16
Publication date: 2000-12-28
Also published as: FR2795133A1; FR2795133B1

Abstract

The invention relates to a method for controlling a four-stroke internal combustion engine, comprising the following steps: creation of a compression phase (PC) during the upward stroke of the piston from a start moment (T1) to an end moment (T2), whereby the closure of all of the valves is controlled during said compression phase, and creation of an expansion/admission phase (PD/A) during which the opening of at least one valve is controlled from the end moment (T2) of the compression phase (Pc) until the moment when the valve is closed (T3).

Description

"Method of controlling a combustion engine with a view to obtaining an engine brake effect"

The present invention relates to a combustion engine, in particular a heat engine of a motor vehicle.

The invention relates more particularly to a method of controlling a four-stroke combustion engine with a view to obtaining an engine brake effect.

The invention relates more particularly to a combustion engine, the intake and exhaust valves of each cylinder of which are each individually controlled by means of an actuator, in particular an electromagnetic actuator, each actuator of a valve being connected to an electronic engine control unit. Such a combustion engine without camshafts, also called "camless" engine, offers great possibilities for the individualized control of the intake and exhaust valves independently of the general distribution diagram (s) of the engine. The invention aims to propose a method for controlling such an engine without camshafts with a view to obtaining an engine brake effect which is applicable over a wide range of speeds.

To this end, the invention provides a method of controlling such a four-stroke combustion engine, of the type in which a piston describes a movement back and forth in the cylinder comprising a downward stroke of the piston from top dead center towards the bottom dead center and an upward stroke of the piston from bottom dead center to the top dead center, characterized in that it consists in positioning, during the upward stroke of the piston, from an instant of start until an instant of end, a so-called compression phase during which the closure of all the valves and to set up a so-called expansion / intake phase during which the opening of at least one valve is controlled, from the moment of the end of the compression phase and until the moment of closing of the valve. Thanks to such a method, it is possible to obtain an engine brake effect even at substantially high speeds. According to other characteristics of the invention:

- the duration of the compression phase is a function of the intensity of the desired engine brake effect; - the valve closing time is either symmetrical with the time when the compression phase begins with respect to the bottom dead center, or coincides with the time when the compression phase begins;

- the instant of end of the compression phase takes place in the vicinity of the top dead center;

- the end of the compression phase takes place before the high point;

- the valve closing instant takes place near the bottom dead center; - the valve closes immediately before bottom dead center; the valve open during the expansion / intake phase is the exhaust valve; the valve open during the expansion / intake phase is the intake valve;

- from the moment of the end of the compression phase, we start by opening the exhaust valve, then we open the intake valve, then we close this exhaust valve, and at the instant of closing the valve we close the intake valve.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

- Figure 1 is a partial schematic sectional view of a part of an internal combustion engine with valves without camshafts and controlled according to a method according to the teachings of the invention;

- Figure 2 is a diagram illustrating a distribution law spanning two strokes of the piston;

- Figure 3 is a valve control diagram according to a first embodiment of the invention;

- Figure 4 is a valve control diagram according to a second embodiment of the invention.

FIG. 1 shows a cylinder 1 0 of a four-stroke internal combustion engine, the upper part of which forms a combustion chamber 12 delimited by a movable piston 14 and by a cylinder head 1 5.

The cylinder 10 is supplied with air / fuel mixture by an intake circuit 16 which opens into the combustion chamber 12 through an intake valve 18 whose movements are controlled by a linear electromagnetic actuator 1 1 in order to d '' shut off or not the communication between the intake circuit 16 and the combustion chamber 12. An exhaust circuit 17 is provided for the evacuation of the burnt gases out of the combustion chamber 12 through a valve exhaust 19 also controlled by an electromagnetic linear actuator 13.

The intake 18 and exhaust 1 9 valves are controlled by an electronic control unit (not shown) which controls the actuators 1 1 and 13, and which also controls the injection of fuel, here indirect, by means an injector 20, as well as the ignition by means of a spark plug (not shown). The electronic control unit notably includes means for storing one or more engine operating maps.

The electronic control unit receives signals representative of operating parameters such as engine speed, atmospheric pressure, pressure in each cylinder, flow of intake and / or exhaust gases, instantaneous torque supplied, etc.

According to the principle of the four-stroke cycle of a combustion engine, it takes place in two rotations of the crankshaft and in four piston strokes, the four cycle times being the intake, compression, combustion and l 'exhaust.

Considering the simplified representation of the cylinder of Figure 1, comprising by way of example an intake valve 18 and an exhaust valve 1 9, during intake, the intake valve 18 is open and the piston go down. The increase in the volume of the cylinder creates a vacuum which causes the suction of the air / fuel mixture.

During compression, the intake 18 and exhaust 19 valves are closed and the piston 14 rises and compresses the mixture in the combustion chamber 12. A few degrees of angle of rotation before the piston reaches top dead center TDC of its upward stroke, ignition is triggered or occurs. During the explosion, combustion then expansion, the piston

14 is pushed down its stroke under the action of the gases, that is to say that it is in a downward stroke from the top dead center TDC to the bottom dead center PMB.

A few degrees of angle of rotation before the bottom dead center PMB, the exhaust valve 19 opens. The piston 14 then begins an upward stroke during which it pushes the burnt gases towards the exhaust circuit 17 at through the exhaust valve 1 9. This is the exhaust time.

In the vicinity of the top dead center TDC the exhaust valve 1 9 is closed and the intake valve 1 8 is open. We then begin a new cycle.

During transient deceleration phases, that is to say when the driver takes his foot off the accelerator, it is desirable to obtain an engine brake effect, in particular for reasons of driving pleasure. The intensity of the desired engine brake effect depends on the operating point.

During a transient deceleration phase, the electronic control unit cuts off the fuel supply to the engine. We are then free to control the operation of the cylinder 10 at our convenience because there is no more fuel admitted into the cylinder 10. We therefore seek to optimize the distribution laws of the valves to obtain an engine brake effect.

At this stage in the operation of the engine, it is possible to decide to implement the method according to the invention by modifying the normal operation of the engine, with the aim of obtaining an engine brake effect.

We then pass from a distribution law spanning four strokes of the piston 14 to a distribution law spanning two strokes of the piston 14. The diagram in FIG. 2 illustrates this principle.

During the upward stroke of the piston 14, a so-called compression phase P _c is put in place during which all the valves are closed.

At the end of the compression phase P _c and during the downward stroke of the piston 14, a so-called expansion / admission phase P _{D / A} is put in place during which at least one valve is opened. The compression phase P _c is adapted to the intensity of the desired engine brake. It is characterized by a duration D, a start instant T, and an end instant T ₂ .

During this compression phase P _c all the valves remain closed. At the end instant T _2, at least one valve is opened.

As soon as the valve opens, marking the end of the compression phase P _c , the expansion / intake phase P _{D / A} begins. It includes firstly the expansion of the compressed gases then, beyond the top TDC dead center, the admission of the gases by the descent of the piston 14. This expansion / admission phase P _{D / A is} spread during the downward stroke of piston 14 until the valve closes. The closing time T ₃ of the valve is chosen so as not to modify the compression work. That is to say that it corresponds either, in a first case, exactly to the start time T of the compression phase P _c (Ta≈T,), or, in a second case, to a symmetrical time of the start time T ₁ relative to the bottom dead center PMB as shown in FIG. 2.

In the second case there is an intermediate phase P ,, between the closing time T ₃ of the valve and the start time T of the compression phase P _c , during which the valves are closed. But this has no effect on the work taken from the crankshaft, since the energy consumed during the end of the down stroke is restored at the start of the up stroke of the piston 14.

We will now explain a first embodiment, illustrated in FIG. 3, for implementing the method according to the invention.

With the fuel supply cut off, the exhaust valve is kept in the closed position 1 9 during the fourth stroke of the piston 14 corresponding to the "escape time". Thus, during the upward stroke of the piston 14, the exhaust gases are compressed which brakes the piston 14. A few degrees of angle of rotation before the top dead center TDC, the opening OE of the exhaust valve is controlled 19, as can be seen in the diagram in FIG. 3. This allows the exhaust gases to relax in the exhaust circuit 17. The piston is in a downward stroke. The FE closure of the exhaust valve 1 9 is ordered at an appropriate time, in particular as a function of the engine speed. At the same time, the opening OA of the intake valve 18 is controlled in order to fill the combustion chamber 12 with fresh air.

A few degrees of angle of rotation before the bottom dead center PMB, the closing of the intake valve 18 is controlled. All the valves are therefore closed. During the upward stroke the fresh air is compressed by the piston 14 which brakes it.

At the end of the upstroke, a cycle has been completed and either continuing on the same principle to maintain the engine brake effect, or resuming a normal engine operating cycle by restoring the power supply. in fuel.

The opening OA of the intake valve 18 makes it possible to replace, in the combustion chamber 12, the exhaust gases with fresh air. However, compressing fresh air consumes more energy than compressing exhaust gases. Consequently, the admission of fresh air makes it possible to obtain a greater engine brake effect than with exhaust gases. Furthermore, this “air pump” type of operation makes it possible to “drain” the exhaust line of all the residual burnt gases.

In variants of this first embodiment, it is possible to control the opening OE of the exhaust valve 19 after the top dead center TDC, and / or order the closing FA of the intake valve 19 after the dead center low PMB.

According to a second simplified embodiment, shown diagrammatically in FIG. 2, one can dispense with admitting fresh air into the combustion chamber 12. In this case, one does not act on the intake valve 18, q which remains closed all the time of the so-called engine brake phase, but only on the exhaust valve 19. The FE valve of the exhaust valve 19 is closed a few degrees of angle of rotation before the bottom dead center PMB .

In this configuration, during each upward stroke, the piston 14 compresses the gases coming from the exhaust circuit 17, and at each downward stroke it sucks up the same gases.

In a variant of this second embodiment, it is possible to control the closing FE of the exhaust valve 19 after the bottom dead center PMB.

According to a third embodiment, one acts in a similar manner to the second embodiment but by controlling the intake valve 1 8 in place of the exhaust valve 19.

In this third embodiment, the exhaust valve 1 9 remains closed all the time of the so-called engine brake phase and the piston 14 compresses and re-aspirates air from the intake circuit at each stroke.

1 6. It is noted that the method according to the invention makes it possible to dose the engine brake effect by controlling the compression phase P _c by variations in the instants of opening and closing of the valves. Keeping a valve open during the downward stroke of the piston 14 prevents the "vacuum pump" phenomenon which would occur if all of the valves were closed during this stroke. This phenomenon would be detrimental to the operation of the engine, since it would lead to the suction of oil in the cylinders.

The principles implemented within the framework of the method according to the invention, which have been explained by considering a single cylinder itself comprising a single intake valve and a single exhaust valve, of course apply to an engine with several cylinders each of which comprises, where appropriate, several intake and several exhaust valves and each of which is individually controlled by the electronic control unit by means of an individual actuator associated with each valve.

Claims

CLAIMS 1. Method for controlling a four-stroke combustion engine, of the type comprising an air intake circuit (16) or an air / fuel mixture and an exhaust circuit (17) of burnt gases which communicate with a combustion chamber (12) of at least one cylinder (10) of the engine, of the type in which the communications of the intake (16) and exhaust (17) circuits with the chamber (12) are capable of '' each be closed respectively by at least one valve, respectively intake (18) and exhaust (19), with opening controlled by an actuator, in particular by an electromagnetic actuator, connected to an electronic control unit, of the type in which a piston (14) describes a movement back and forth in the cylinder (10) comprising a downward stroke of the piston (14) from top dead center (TDC) to bottom dead center (PMB) and an upward stroke of the piston ( 14) from bottom dead center (BDC) to top dead center (TDC), in order to e obtaining an engine brake effect, characterized in that it consists in setting up, during the upward stroke of the piston (14), from a start time (T.,) until an end instant (T ₂ ), a so-called compression phase (P _c ) during which the closure of all the valves is controlled and a so-called expansion / admission phase (P _{D / A} ) in place during which one controls the opening of at least one valve, from the end instant (T ₂ ) of the compression phase (P _c ) and until a closing instant (T ₃ ) of the valve, and in that the duration (D) of the compression phase (P _c ) is a function of the intensity of the desired engine brake effect.

2. Method according to the preceding claim, characterized in that the closing instant (T ₃ ) of the valve is either symmetrical with the start instant (T.,) of the phase of compression (P _c ) with respect to the bottom dead center (PMB), or confused with the start time (T,) of the compression phase (P _c ).

3. Method according to any one of the preceding claims, characterized in that the end instant (T ₂ ) of the compression phase (P _c ) takes place in the vicinity of the top dead center (TDC).

4. Method according to claim 3, characterized in that the end instant (T ₂ ) of the compression phase (P _c ) takes place before the top dead center (TDC).

5. Method according to any one of the preceding claims, characterized in that the closing instant (T ₃ ) of the valve takes place in the vicinity of the bottom dead center (PMB).

6. Method according to claim 4, characterized in that the closing instant (T ₃ ) of the valve takes place before the bottom dead center (PMB).

7. Method according to any one of the preceding claims, characterized in that the valve open during the expansion / intake phase (P _{D / A} ) is the exhaust valve (1 9).

8. Method according to any one of claims 1 to 6, characterized in that the valve open during the expansion / intake phase (P _{D / A} ) is the intake valve (18).

9. Method according to any one of resells ications 1 to 6, characterized in that q ue, from the instant of end (T ₂ ) of the compression phase (P _c ) one begins by opening the exhaust valve ( 1 9) then the intake valve is opened (18) then this exhaust valve (1 9) is closed, and at the instant of closing (T ₃ ) of the valve the intake valve is closed (18 ).