WO2008037870A1 - Method and device for controlling an inlet valve during its opening and upon the piston's way down - Google Patents

Abstract

The invention relates to a method for controlling an inlet valve (13) capable of displacement between an opening position and a closing position, and associated with a cylinder (10) comprising a piston (7) capable of displacement between a lower position and an upper position in an alternating cycle, said method comprising, in a nominal operation mode, the step of controlling the inlet valve for beginning the opening when the piston slides towards its higher position, and the method comprising, in a palliative operation mode, the step of controlling the inlet valve for beginning the opening when the piston slides towards its lower position. The invention also relates to a device for controlling an inlet valve.

Description

 Method and device for controlling an intake valve at opening when the piston is lowered

The present invention relates to a method and a device for controlling an intake valve of a heat engine, such as those used to move motor vehicles.

BACKGROUND OF THE INVENTION A heat engine generally comprises cylinders each defining a combustion chamber closed on one side by a cylinder head and on the other side by a movable piston which slides between a high position (top dead center). and a low position (bottom dead center) and which is connected by a connecting rod to a crankshaft. A fuel combustion chamber supply duct and a flue gas exhaust duct are provided in the cylinder head and are respectively equipped with an intake valve and an exhaust valve movable between a position of opening and a closing position. The valves are usually moved between their two positions by means of a camshaft.

The operating cycle of such an engine comprises four times calibrated by convention on the movements of the piston, namely a time of admission of the fuel into the combustion chamber, a compression time of the fuel in the cylinder, a time of combustion of the gases after the explosion, and a time of escape of the burned gases. The piston slides to the down position during the intake and expansion times and to the up position during the compression and exhaust times. During the admission time, the intake valve is in the open position and the piston which moves from its high position to its lower position sucks the fuel through the passage left by the valve

COPY OF CONRRAMATIOM intake in the open position. The intake valve was opened during the previous exhaust time, a little before the end of it (advance at the opening of the intake) and is closed at the beginning of the compression time (delay to the closing of the admission). During the compression time and most of the combustion time, the intake valve and the exhaust valve are in the closed position. The exhaust valve is opened at the end of the combustion time (advance at the opening of the exhaust) and is kept open all the exhaust time to allow the burnt gases to be evacuated from the combustion chamber by the piston sliding to its high position. The exhaust valve is closed at the beginning of the following admission time (exhaust closing delay).

There is now a new valve displacement technology employing electromagnetic actuators. An electromagnetic actuator comprises a movable actuating member of the valve and two electromagnets which extend on either side of a pallet integral with the movable member and which are controlled to alternately attract the pallet so as to allow the moving the valve between its open position and its closed position. A lubricant is brought between the moving parts to facilitate movement. A disadvantage of this type of actuator ¹ is that it consumes a relatively large energy when the ambient temperature is low because the electromagnets are required to provide sufficient health an effort to overcome the friction which are important due to the high viscosity of the lubricant at low temperature and which oppose the movement of the valve.

This problem occurs especially at the intake valve at the start of the engine when there has not yet been combustion, or a sufficient number of combustions, to raise the temperature of the cylinder in question. One could imagine sizing the electromagnets according to the effort to provide the start of the engine at low temperatures. This would, however, result in an increase in the weight and bulk of the actuator.

OBJECT OF THE INVENTION

An object of the invention is to provide a means for optimizing, at relatively low temperatures, the starting of such engines.

SUMMARY OF THE INVENTION

For this purpose, there is provided, according to the invention, a method of controlling a movable inlet valve between an open position and a closed position and associated with a cylinder equipped with a movable piston between a low position. and a reciprocating high position, comprising, in a nominal mode of operation, the step of controlling the inlet valve to begin opening as the piston slides to its up position, the method comprising, when of a palliative operating mode, the step of controlling the inlet valve to start the opening while the piston slides to its lower position.

Thus, the opening of the valve is facilitated by the depression created in the cylinder by the piston down to its lower position. The force required to move the intake valve is therefore relatively small and the movement of the intake valve from its closed position to its open position is relatively fast.

Advantageously, the valve being associated with a lubricant having a viscosity inversely proportional to an ambient temperature, the method comprises the step of detecting a parameter representative of the viscosity of the lubricant and of controlling the intake valve. according to the palliative operating mode as long as the parameter has a value lower than a predetermined threshold.

The transition from the palliative operating mode to the normal operating mode with advance of the opening of the admission can then be achieved automatically.

Advantageously, the parameter is an ambient temperature and / or the parameter is a characteristic of a kinematic of the valve. The implementation of the method of the invention is then relatively simple.

The invention also relates to a device for controlling an inlet valve movable between an open position and a closed position and associated with a cylinder equipped with a piston movable between a low position and a position. high in an alternating cycle, the device comprising an electromagnetic actuator associated with a management unit incorporating a control program arranged for: in a nominal operating mode, controlling the intake valve to start the opening while the The piston slides to its high position and, in a palliative mode of operation, controls the inlet valve to begin opening while the piston is sliding down. Other characteristics and advantages of the invention will emerge on reading the following description of a particular non-limiting embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made to the appended drawings, among which:

FIG. 1 is a schematic perspective view of a heat engine according to the invention, FIG. 2 is a partial schematic cross-sectional view of this motor,

FIG. 3 is a diagrammatic sectional view showing the actuator of the intake valve; FIG. 4 is a diagram showing the displacement of the intake valve as a function of time.

DETAILED DESCRIPTION OF THE INVENTION With reference to the figures, the heat engine according to the invention comprises a block 10 defining four cylinders 1, 2, 3, 4 in line. The cylinders 1 and 4 frame the cylinders 2 and 3. Each cylinder 1, 2, 3, 4 defines a chamber 5 closed on one side by a cylinder head 6 and on the other side by a piston 7 movable to slide in the cylinder 1, 2, 3, 4 between a high position (top dead center) and a low position (bottom dead center) and connected by a connecting rod 8 to a crankshaft 9 pivotally mounted in the block 10.

In each combustion chamber 5, open an intake duct 11 and an exhaust duct 12 which are formed in the cylinder head 6. The intake duct 11 and the exhaust duct 12 are respectively equipped with a gas valve. 'admission. 13 and an exhaust valve 14 moved between two open and closed positions by electromagnetic actuators 15, 16 respectively. In a manner known in itself, each actuator 15, 16 comprises a body 17 in which are mounted two electromagnets 18.1, 18.2 between ^'which is mounted a magnetic blade 19 integral with one end of an actuating rod 20 having one end opposed arranged to bear on a valve stem. The electromagnets are controlled via a control unit 28, 29 in a manner known per se by means of non-represented servocontrol means, for example from a setpoint current and a speed of displacement of the rod. actuation obtained by derivatization tion of a position signal provided by a rod position sensor 21. The sensor 21 may alternatively be a position, speed, and / or acceleration sensor of the actuating rod 20, these three parameters being moreover deductible from each other by derivation or integration. These parameters are representative of the transition time of the valve 13, that is to say the conditions of passage from the open position to the closed position of this valve, and are each as such a characteristic of a kinematic of the valve 13. The transition time of the valve 13 increases with the viscosity of the lubricant.

The actuator also comprises, in known manner, elastic displacement means comprising in a manner known per se a spring 22 interposed between one face of the actuator body and a shoulder of the actuating rod ¹ to remind the pallet 19 in the open position of the valve and a spring 23 interposed between a face of the cylinder head and a shoulder of the valve stem to return the valve in the closed position.

In a manner known per se, a lubricant is used to lubricate the friction areas of the rod 20 and the body 17, the valve stem and the cylinder head 6. Such a lubricant generally has a viscosity increasing when the temperature decreases.

A spark plug 25 is mounted on the cylinder head 6 to open into the combustion chamber 5. The spark plug 17 is connected to an ignition circuit known per se and not shown here.

An injector 26 of a fuel supply device is also mounted on the cylinder head 6.

A room temperature sensor 27 is mounted in the vicinity of the motor. The engine further comprises a management unit (or ECU, "Engine Control Unit"). This management unit, represented with the reference 30, is connected in particular to the injectors 18, to the control units 28, 29 of the electromagnetic actuators 15, 16, and to the ignition circuit for controlling them. The management unit 30 is also connected to the detector 19 and the sensors 21. The management unit 30, itself known, comprises a calculation module 22, for example a processor 31 associated with a memory 32 containing programs executed by the microprocessor 31.

In a manner known per se, the operating cycle of each of the cylinders is a four-stroke cycle comprising an admission phase (or time), a compression phase, a relaxation phase and an exhaust phase. Each phase represents a quarter cycle of operation, a half-turn of crankshaft 9.

Thus, with reference to FIG. 4, the phases of movement of the piston of each cylinder over a cycle of 720 ° of the crankshaft are referenced ADM for admission, COMP for compression, DET for expansion and ECH for exhaust and each represent a half crankshaft tower. "A" indicates ignition and "I" fuel injection. In known manner, the pistons are at the top dead center ("TDC") at the end of the compression and exhaust phases, and at the bottom dead center at the end of the intake and expansion phases.

In FIG. 4, the curve shows the displacement of the actuating member 24 of the actuator 15 (constituted by the actuating rod 20 and the pallet 19), as detected by the sensor 21. The beginning and the end of the movement, in the zone marked "play catch", correspond to the displacement of the actuating member 24 alone respectively before it comes into contact with the valve stem and after it has lost contact with the tail valve. This displacement alone of the organ of tioning is the result of the existence of a game, called a distribution set, between the actuating rod 20 in extreme high position and the valve in the closed position. In normal operating mode, for each cylinder 1, 2, 3, 4:

the intake valve 13 is controlled to open during the exhaust phase while the piston moves from the bottom dead center to the top dead center (it is referred to as an advance at the opening of the intake) and is controlled to close at the beginning of the compression phase as the piston starts moving from the bottom dead center to the top dead center (we are talking about a delay in closing the intake), - the exhaust valve 14 is controlled to open at the end of the relaxation phase while the piston moves from the top dead center to the bottom dead center (we speak of an advance at the opening of the exhaust) and to close at the beginning of the intake phase while the piston moves from the top dead center to the bottom dead center (we are talking about a delay in closing the exhaust),

- The spark plug 17 is controlled to generate a spark at the end of the compression phase, - the injector 18 is controlled to inject fuel during the exhaust phase.

The actuation of the intake valve is then controlled according to a nominal operating mode.

There is a palliative mode of operation in which, for each cylinder 1, 2, 3, 4, the intake valve is controlled to open during the intake phase when the piston initiates its movement from the top dead center to the point low death (there is no longer any advance at the opening of the admission but a delay in the opening of the admission) and is ordered to close sea during the compression phase as the piston moves from the bottom dead center to the top dead center. It will be noted in FIG. 4 that the opening electromagnet of the valve is excited at the end of the exhaust phase so that the catch of the distribution clearance takes place during the exhaust phase and the effective opening valve starts during the intake phase.

When the motor starts, the control unit checks whether the ambient temperature is above or below a predetermined threshold. This threshold corresponds for example to the temperature below which the viscosity of the lubricant used for the lubrication of the valve and the actuating rod is such that the force required to move the valve would cause excessive consumption of the actuator in nominal operating mode.

If the detected temperature is below the threshold, the unit of. management controls the actuator so as to steer the intake valve in palliative operation mode. The depression caused by the descent of the piston then facilitates the opening of the intake valve.

When the detected temperature exceeds the threshold (FIG. 4 shows the case where a combustion was sufficient to raise the temperature detected by the detector 27 above the threshold), the management unit controls the control module 28 of FIG. the actuator 15 so as to drive the intake valve in nominal operating mode. Of course, the invention is not limited to the embodiment described and variants may be provided without departing from the scope of the invention as defined by the claims.

In particular, any parameter representative of the viscosity of the lubricant can be used to determine to undermine the desirability of a transition to a palliative operating mode and for example a kinematic characteristic of the valve, such as the acceleration thereof deduced from the information supplied by the sensor 21. The function of the detector 27 can advantageously be filled by the oil temperature sensor which most engines are equipped with today, which allows to reuse the information of this existing sensor rather than add an additional detector. In this case, it is interesting to use both the detector information 27

(constituted, therefore, by this engine temperature sensor) and the position sensor 21, speed, and / or acceleration of the actuating rod 20. For this purpose, the step of detecting a parameter representative of the viscosity of the The lubricant of the process according to the invention starts with the measurement of the lubricant temperature by the detector 27. In the case where the temperature of the lubricant is higher than a predetermined threshold (corresponding to an acceptable fluidity of the lubricant), the valves are controlled. intake in the nominal mode. Conversely, in the case where the temperature of the lubricant is below said predetermined threshold, the inlet valves are firstly controlled according to the palliative mode, and a characteristic parameter of a kinematics of the valve 13 is then measured. such as the position, speed, and / or acceleration of the actuating rod 20.

The measurement of this parameter then takes over the initial measurement of the temperature:

when this parameter is below a predetermined threshold, thus indicating a significant transition time of the valve 13, the fluidity of the lubricant is considered insufficient and the initial temperature measurement is confirmed, the intake valves continuing to be ordered according to the palliative mode;

when this parameter is above said threshold, indicating a shortened transition time, the fluidity of the lubricant is considered acceptable and the valves are then controlled according to the nominal mode.

This embodiment is particularly advantageous for taking advantage of an existing temperature sensor, while avoiding the defects related to the fact that these sensors are generally far from the valve actuators, they are for example arranged in the housing of engine oil. In fact, when the engine has only been running a few moments, the oil temperature sensor may indicate a temperature below the predetermined threshold while locally, at the valve actuators, the small amount of oil required is a higher temperature and therefore has an acceptable fluidity.

Claims

1. A method of controlling an intake valve (13) movable between an open position and a closed position and associated with a cylinder (10) equipped with a piston (7) movable between a low position and a reciprocating high position comprising, in a nominal mode of operation, the step of controlling the intake valve to begin opening while the piston is sliding toward its up position, characterized in that the In a palliative mode of operation, the method comprises the step of controlling the inlet valve to begin the opening while the piston is sliding towards its lower position. The method of claim 1, wherein, the valve (13) being associated with a lubricant having a viscosity inversely proportional to an ambient temperature, the method comprises the step of detecting a parameter representative of the viscosity of the lubricant and controlling the intake valve according to the palliative operating mode as long as the parameter has a value lower than a predetermined threshold. The method of claim 2, wherein the parameter is an ambient temperature. The method of claim 2, wherein the parameter is a characteristic of a kinematics of the valve (13). 5. Control device of an intake valve (13) movable between an open position and a closed position and associated with a cylinder (10) equipped with a piston (7) movable between a low position and a high position according to an alternating cycle, comprising an electromagnetic actuator (15) associated with a management unit (21, 28) incorporating a control program arranged for: - in a nominal operating mode, control the inlet valve to begin opening while the piston is sliding to its up position, and, - During a palliative operating mode, control the inlet valve to start the opening while the piston slides to its lower position. 6. Device according to claim 5, wherein the management unit (21) is connected to a detector (27) of a parameter representative of a viscosity of a lubricant associated with the valve. 7. Device according to claim 6, wherein the detector is a detector (27) of ambient temperature. 8. Device according to claim 5, wherein the detector is a sensor (21) of a position of an actuator movably mounted in the actuator to act on the valve.