FR2781011A1 - Control of operation of turbo-charged IC, by controlling timing of opening inlet valves before exhaust valves are fully closed - Google Patents

Abstract

The method of control, of the operation of the direct injection spark ignition engine, is effected when the pressure of air in the inlet chamber (P2) is greater than the pressure in the exhaust chamber (P3). It is achieved by the overlap of the valves, by opening the inlet valves before the outlet valves close by allowing the start of the injection when the exhaust valves are almost closed, in order to ensure that the fuel does not short cut directly to the exhaust.

Description

The present invention relates to the field of motors with

  4-stroke internal combustion, supercharged.

  Supercharging can be achieved by a turbo-compressor or by

  a driven compressor such as a screw compressor for example.

  Supercharged engines allow reductions in

  consumption at the price, however, of sophisticated technology.

  In known manner, turbo-compressed engines recover part of the energy lost in the exhaust gases by means of a turbine placed in the flow of burnt gases. This energy is used positively, to compress the intake air, which increases the air filling and therefore increases the engine performance. A

  centrifugal compressor coupled to the turbine can be used for this purpose.

  US Patent 4,909,035 illustrates an engine of this type.

  The turbo-compression does lead to an increase in the efficiency of the engine since the power supplied to the compressor is recovered on

the energy of the exhaust gases.

  Turbo-compression is the most widely used type of supercharging, especially on medium and large engines

  displacement. These engines have good yields.

  However, a first problem lies in the response time during an acceleration. In addition, a lack of boost pressure at low revs is often found. Furthermore, an exhaust turbine necessarily generates a backpressure unfavorable to engine operation. This changes the exhaust thermal with, for example,

  unfavorable effects on the time of activation of the catalytic converter.

  The driven compressors as described for example in application EP 249718 generate a good boost pressure at low speed with an almost zero response time. In addition, their implementation is easy. The conventionally known drawbacks of mechanical compressors are poor efficiency, especially at high speed, a cost

  important, the generation of noise.

  Furthermore, it is known that in supercharged engines with positive ignition and indirect injection (that is to say in the intake circuit and not in the combustion chamber), any crossing of the valves is harmful to the operation of the engine. . Indeed, a crossing of the valves means a simultaneous opening of the intake and exhaust valves, opening during which a part of the fuel can be directly short-circuited to the exhaust, without having been burned if the intake pressure is greater than that of the exhaust. This generates

overconsumption and pollution.

  We have therefore sought to avoid this crossing, to "uncross" the valves, that is to say to open the intake only when the exhaust is closed. This leads to high levels of residual gases in the combustion chambers, especially at low speed, full load, which

  promotes the appearance of rattling on spark ignition engines.

  To avoid rattling, one solution is to set the engine to "advance" upon ignition which leads to a loss of engine performance. In addition, the uncrossing of the valves implying that residual gases occupy the entire dead cylinder volume, the latter can not be used as useful volume for performance. The air filling of the

cylinder is therefore not optimal.

  The objectives of the present invention are in particular to - reduce the rate of residual gases and simultaneously increase the filling in a positive-ignition, supercharged ignition engine. - to avoid any risk of fuel being discharged directly into the exhaust line. The field of application of the invention is therefore preferably that of supercharged engines, and more precisely in the operating zones where the air pressure at the intake (P2) is greater than the

  pressure (P3) prevailing in the exhaust manifold (s).

  The present invention relates to a method for controlling the operation of a supercharged spark ignition engine and with direct injection of petrol into the combustion chamber (s) when the air pressure in the circuit d admission is greater than

exhaust pressure.

  According to one embodiment of the invention, the method consists in carrying out a crossing of the valves and in controlling the start of the injection to the quasi-closing of at least one of the exhaust valves which

  prevents fuel short-circuiting.

  In accordance with one embodiment of the invention, the

  supercharging can be achieved through a turbo-compressor.

  According to another embodiment of the invention, overeating

  is performed by a driven mechanical compressor.

  Preferably, a mechanical type variable distribution is used such as, for example, a camshaft phase shifter, for

  cross the valves.

  Without departing from the scope of the invention, an electro-hydraulic or electromagnetic means can be used to cross the valves. This type of distribution makes it possible to adapt the operation

  engine with turbocharging characteristics.

  Advantageously, the invention is implemented for the

  operation at high load and low engine speed when a turbo

compressor is used.

  In the case where a mechanical compressor is used, the process is then implemented for operation at high load, whatever the

engine speed.

  Other characteristics, details, advantages of the invention

  will appear better on reading the description which follows, made as

  illustrative and in no way limitative with reference to the attached plates, in which: - Figure 1 is a cylinder pressure-volume diagram obtained according to the prior art; - Figure 2 is a curve giving the lifting of the valves according to the prior art; - Figure 3 is a cylinder pressure-volume diagram obtained according to the invention; and - Figure 4 is a curve showing the valve lift according to

The invention.

  Figures 1 and 2 therefore relate to the prior art.

  Figure 1 shows the classic diagram of the pressure in a cylinder as a function of the cylinder volume, for the different times of an engine cycle. The 4 times are respectively referenced: (1) intake, (2) compression, (3) rebound and (4) exhaust. The pressure P2 at

  the intake here is greater than the exhaust pressure P3.

  Figure 2 shows the corresponding lift of the exhaust (curve E) and intake (curve A) valves. It is noted that the opening of the intake coincides approximately with the closing of the exhaust, this in particular in order to avoid the short-circuiting of gas.

  unburnt at the exhaust as indicated at the beginning of the description.

  Figure 3 illustrates the implementation of the invention. The expansion (3) and compression (4) phases are unchanged with respect to the art

  anterior, as well as the exhaust.

  However, the end of the exhaust (4) and the start of the intake (1) are modified. This is due to the crossing of the valves associated with a start

  injection control at the end of the exhaust.

  Figure 4 illustrates this implementation: when the exhaust (curve E ') is not yet finished, the intake (curve A') begins; furthermore, injection I does not start until the valve (s)

are closed.

  The crossing of the valves can be operated by delaying the exhaust and / or by advancing the intake with respect to the known operation. According to the invention, that is to say when the intake pressure is higher than the exhaust pressure, the residual gases are swept towards the exhaust during the crossing phase. Furthermore, no fuel is discharged directly to the exhaust since the start of the injection is only carried out at the end of the crossing phase, that is to say after the exhaust is closed. The crossing of the valves according to the invention may be permanent, but it will preferably be carried out within the framework of a distribution.

  variable, on certain operating zones.

  The variable distribution can be mechanical: it will then be

  for example obtained by means of a camshaft phase shifter.

  Without departing from the scope of the invention, the distribution may be

  fully variable: electrohydraulic or electro-

  magnetic can then be used.

Claims (5)

  1) Method for controlling the operation of a supercharged spark ignition engine with direct injection of petrol into the combustion chamber (s) when the air pressure in the intake circuit (P2) is higher than the exhaust pressure (P3), characterized in that it consists in crossing the valves and in controlling the start of the injection to the quasi-closing of at least one of the exhaust valves to avoid fuel short-circuiting The exhaust.   2) control method according to claim 1, characterized in that   the supercharging is carried out by a turbo-compressor.   3) control method according to claim 1, characterized in that   the supercharging is carried out by a driven mechanical compressor.   4) control method according to any one of claims   above, characterized in that a variable distribution of   mechanical type for crossing valves.   ) Control method according to claim 4, characterized in that   a camshaft phase shifter is used.   6) control method according to any one of claims 1 to   3, characterized in that a variable distribution of the electrohydraulic or electromagnetic type is used to cross the valves. 7) A control method according to claim 2, characterized in that it is implemented for operation at high load and low engine speed. 8) A control method according to claim 3, characterized in that it is implemented for high load operation, whatever the engine speed.