EP0182826A1

EP0182826A1 - Four-stroke combustion engine with a device for conveying gases from an exhaust gas pipe back into the combustion chamber

Info

Publication number: EP0182826A1
Application number: EP85902472A
Authority: EP
Inventors: Peter SCHÜLE
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-05-29
Filing date: 1985-05-25
Publication date: 1986-06-04
Also published as: WO1985005654A1; DE3419963A1

Abstract

Moteur de combustion à quatre temps avec au moins une chambre de combustion, des organes de régulation pour l'admission et l'échappement et avec un dispositif pour ramener des gaz d'une conduite de gaz d'échappement à la chambre de combustion, caractérisés par le fait qu'est prévue une installation pour l'ouverture temporaire de l'organe de régulation de l'échappement (14, 42) qui ouvre l'organe de régulation de l'échappement pendant le laps de temps suivant l'ouverture de l'organe de régulation de l'admission (10) et précédant l'allumage. Une construction simple et efficace est possible.Four-stroke combustion engine with at least one combustion chamber, regulating members for intake and exhaust and with a device for bringing gases from an exhaust gas line to the combustion chamber, characterized by the fact that provision is made for an installation for the temporary opening of the exhaust regulator (14, 42) which opens the exhaust regulator during the period of time following the opening of the admission control member (10) and preceding the ignition. Simple and efficient construction is possible.

Description

Four-stroke engine with a device for returning gases from an exhaust pipe into the combustion chamber

The invention relates to a four-stroke internal combustion engine with at least one combustion chamber, control organs for the inlet and outlet of grass, such as valves or slides, and with a device for returning gases from an exhaust pipe into the combustion chamber. In the book "Paths to high-performance four-stroke engine" by Ludwig Apfelbeσk, Motorbuch-Verlag Stuttgart 1983, it is stated on page 28 that due to an overlap of the opening times between the intake valve and the exhaust valve, the transition between the exhaust process and the intake process is fresh gas, the got into the exhaust pipe, can be pushed back into the cylinder by vibrations. Such a mode of operation appears to function at best in a narrow speed range, and in addition, such a mode of operation would presuppose that a higher harmonic of the exhaust system, which generally works on the fundamental frequency for optimum sound absorption, is exploited. With a higher harmonic, however, the amplitude of the vibrations is small and the effect is therefore limited. Such a return of fresh gas into the combustion chamber prevents unburned fuel from escaping through the exhaust, but the degree of filling of the combustion chamber cannot be increased.

It is also known to lay a pipe from the exhaust system to the intake line of the engine, through which a certain proportion of exhaust gases get into the combustion chamber through the intake control element during the intake process. The purpose of this is that the peak temperature in the combustion chamber is reduced in order to reduce the amount of nitrogen oxides formed. This is because the carbon dioxide contained in exhaust gases has a relatively high specific heat capacity and therefore causes the combustion temperatures to decrease. Such exhaust gas recirculation is structurally complex. The arrangement is suitable for reducing the nitrogen oxides, but is not suitable if an overload is to be achieved. The invention is based on the object, starting from the four-stroke engine described above, to provide a possibility which can be implemented in a structurally simple manner and which makes it possible to bring fresh gas or exhaust gases which have optionally come into the exhaust line back into the combustion chamber.

This object is achieved according to the invention in that a device for briefly opening the exhaust control member is provided, which opens an exhaust control member in the period after the opening of the intake control member and before the ignition.

The invention thus provides that the exhaust control element, hereinafter simply called the exhaust valve, after it has been closed at a later point in time after the completion of the exhaust process, in the end section of which the intake valve (more precisely the intake control element may have already been opened) is opened again before igniting the combustible gas mixture. If there are several exhaust control members, they do not have to be opened and / or closed at the same time. In particular, the exhaust control element used for gas recirculation can already be closed before the end of the exhaust process. The advantage of the invention is that the period of reopening can be selected so that during this period there is a relatively high pressure in the exhaust pipe of the combustion chamber, which returns the gases in the exhaust pipe in the immediate vicinity of the combustion chamber back into the combustion chamber. This can be done by choosing the appropriate time space in which the outlet valve is opened again, this described gas recirculation can possibly be carried out effectively within a large speed range. It is also advantageous that the fundamental or a low harmonic, for example the second or third harmonic, can be used when using vibrations of the exhaust system if there is a longer period of time between the end of the exhaust process and the reopening of the exhaust control member. With such fundamental or harmonics, the amplitudes of the vibrations are relatively large and the gas recirculation is therefore particularly effective. This makes it possible to bring about a pressure increase in the combustion chamber through the gas recirculation. In addition, a high pressure in the exhaust pipe enables the exhaust valve to be opened again at a point in time when the fresh gases drawn in are already compressed after the intake process has been completed.

Another advantage of the invention is that the length of time that the outlet valve is opened again, and thereby the amount of the returned gases, can be precisely determined in a simple manner.

In the case of engines with a very large speed range, according to one embodiment of the invention, the period in which the exhaust valve is opened again can be controlled as a function of the speed, so that optimum gas return is achieved in each case.

In the book cited at the beginning it is stated that in two-stroke racing engines a considerable overload is achieved in that a certain amount during the flushing process Fresh gas quantity first reaches the specially designed exhaust system and is then returned to the cylinder by a pressure wave. However, this information does not help the person skilled in the art, who is concerned with the improvement of four-stroke engines, and does not lead him to the invention, because the gas exchange process on the two-stroke engine is fundamentally different from that of the four-stroke engine. The intake process does not take place directly with the two-stroke engine, but the intake takes place via the crankcase during the overflow cycle into the combustion chamber. The overflow process takes place with the exhaust slot open. This means that the exhaust process begins before the overflow and ends after the overflow, which means that fresh gas can be returned. In the four-stroke engine, however, the exhaust and intake processes take place at different times, which means that the entire intake process cannot take place during exhaust.

The invention can be applied to such engines that are designed for high performance, particularly those that work with an overlap between the opening times of the intake valve and exhaust valve in the transition area between the exhaust process and the intake process. The overlap in the opening times of the intake and exhaust control members is known to be used in high-performance engines to accelerate the fresh gas column in front of the intake control member so that the combustion chamber can be filled quickly. Due to the high flow velocity in the intake pipe, after the exhaust control element is closed, overloading in the combustion chamber can also be achieved. Accordingly, in one embodiment of the invention, the exhaust control member is opened again with the intake control member still open. According to In a further embodiment of the invention, the maximum opening of the exhaust control member is also while the intake control member is still open; in another embodiment, however, the intake control member is already closed again at the maximum opening of the exhaust control member. Finally, the beginning of the reopening of the exhaust control member can be set so that the intake control member is already closed at this time. In the described embodiments, it is generally to be expected that fresh gas, generally a gasoline vapor-air mixture or fresh air in combustion chamber injection, will also reach the exhaust line at the beginning of the intake. When the exhaust control member is opened again, all or part of this fresh gas is returned to the combustion chamber. Depending on the duration of the opening of the exhaust control member, exhaust gas can also be returned. It can thus be prevented that unburned fuel can escape to the outside through the exhaust and, if desired, the combustion temperature can also be reduced by the recycled proportions of exhaust gas. In the embodiment in which the exhaust valve is opened again when the intake valve is already closed or is about to close, the pressure wave passing the exhaust valve from the exhaust pipe can cause an overload in the combustion chamber, thereby increasing the performance of the engine can be increased.

The invention can also be used in those engines in which there is no overlap between the opening times of the intake and exhaust control members, that is to say in conventional commercial engines. In such a case, no fresh gas can get into the exhaust pipe, and therefore at opening the exhaust control element again only delivers exhaust gas back into the combustion chamber, so that the generation of excessive amounts of nitrogen oxides is prevented. It is particularly advantageous here in the invention that the amount of exhaust gas recirculated can be determined very precisely by suitable control of the exhaust valve.

The exhaust control member, in the event that it is a valve controlled by a camshaft, can be controlled in a simple manner in the manner according to the invention in that the camshaft has a further nooke for the exhaust valve which, in addition to the nooke controlling the exhaust process, has the desired Has angular distance.

The invention is also applicable to engines in which no valves are provided, but in which slides are provided. The piston of the engine can also act as such a slide.

Instead of opening the exhaust valve again, it is also possible to open a further control element (valve, slide) which is provided in addition to the intake valve and exhaust valve and which is connected to the exhaust pipe. It also appears possible, in those cases in which four valves are provided per cylinder of the four-stroke engine, namely two intake valves and two exhaust valves, to open only one of the two exhaust valves during the reopening process according to the invention, or to close the two exhaust valves again in a different time sequence to open.

If the invention applies to existing engine systems, in particular also to motor vehicles with a four-stroke engine, To be realized, it may be appropriate to provide changes to the exhaust system for optimal tuning, especially with regard to the resonance frequencies of the exhaust systems. However, the fact that in the invention, the period at which the exhaust valve opens again can be in a relatively wide range, it seems possible that changes to the exhaust system can be made redundant, at least in some cases, by this period of reopening of the exhaust valve is placed appropriately.

Further features and advantages of the invention result from the following description of exemplary embodiments of the invention with reference to the drawing, which shows details essential to the invention, and from the claims. The individual features can be implemented individually or in any combination in any combination in one embodiment of the invention. Show it:

Fig. 1: a longitudinal section through a cylinder

Four-stroke internal combustion engine of a first exemplary embodiment, partially broken off, a camshaft controlling the exhaust valve having two cams,

2 shows a longitudinal section, partially broken off, through the cylinder of a second embodiment of a four-stroke engine, in which two valves and a slide are provided,

Fig. 3: schematically shows a timing diagram for the actuation of the intake and exhaust control members. In Fig. 1, a piston 4 is slidably guided in a cylinder 2, which drives a crankshaft, also not shown, in a known manner via a connecting rod, not shown. An intake valve 10 actuated by a first camshaft 8 is arranged in a cylinder head 6, and an exhaust valve 14 actuated by a second camshaft 1 is also provided. The valves 10 and 14 control the connection between an inlet duct 16 and an outlet duct 18 and the combustion chamber 20 of the engine. The first camshaft 8 has a cam 22 associated with the intake valve 10, and the second camshaft 12 has a cam 24 associated with the exhaust valve 14. The camshafts are coupled to the crankshaft. The ends of the valves facing away from the valve plates 26 are held in contact with the cams controlling them by springs 28. From the direction of rotation shown in the camshafts 8 and 12 in the counterclockwise direction and the position of the cams 22 and 24 and from the fact that the piston 4 is in its uppermost position, it can be seen that the exhaust process has just ended and that the exhaust valve 14 is straight is still open while the inlet valve 10 has already opened somewhat. The engine shown in Fig. 1 thus operates with an overlap of the opening times of the intake and exhaust valves. As far as the motor according to FIG. 1 has been described so far, it belongs to the prior art. The engine 1 differs from known engines in that the camshaft 12 has a further cam 30 assigned to the exhaust valve 14. Through the further cam 30, the outlet valve 14, after it has initially been completely closed starting from the position shown in FIG. 1, and after the inlet valve 10 has been completely opened, whereby the piston 4 has also moved downward, opened again. As a result, there is the possibility that fresh gas, that is to say a combustible fuel-air mixture which has entered the outlet channel 18 directly from the inlet channel 16, is conveyed back into the combustion chamber 20 by a pressure wave generated by the exhaust system. The maximum opening of the outlet valve 14 caused by the further cam 30 occurs at a time when the inlet valve 10 has almost closed again. The pressure wave originating from the exhaust system therefore causes the fuel that has not yet burned to be returned to the combustion chamber 20, as well as a pressure increase and thus an overload. This means that the fuel is used well and the performance is increased.

Because the rotational position of the first camshaft 8 is changed relative to the second camshaft 12, the engine 1 can be modified such that the opening does not overlap when the charge is changed. In such a case, fuel-free exhaust gas is returned to the combustion chamber 20 when the exhaust valve 14 is opened by the further cam 30.

The further cam 30 is lower than the cam 24 and more pointed than this. Therefore, the maximum opening of the exhaust valve caused by the further cam 30 is smaller than the opening caused by the cam 24, and also the exhaust valve 14 remains open for a shorter time when opened by the further cam 30 than when it is opened by the cam 24 is opened. By suitable arrangement and design of the further cam 30, the timing of the opening of the exhaust valve 14 again and the duration of the opening can be adapted to the respective requirements.

The engine 31 shown in section through a cylinder in Fig. 2, like the engine of Fig. 1, has a conventional camshaft 8 controlling the intake valve, and in contrast to Fig. 1 and in accordance with the prior art, has a conventional camshaft 34 with only a single cam 35 for controlling the exhaust valve 14. The engine 31 according to FIG. 2 differs from known engines in that the exhaust port 18 of the cylinder head 6, which leads into an exhaust pipe 38, is connected to a bore 42 in the cylinder 44 by a branch 40 of the exhaust pipe 38. The bore 42 is fully open in its bottom dead center in the position of the piston 4 shown, but is covered when the piston 4 moves upward. The piston 4 thus forms a slide which closes or releases the bore 42. In the exemplary embodiment, the outlet valve 14 is closed and the inlet valve 10 is in the process of being closed; the suction process is therefore nearing its end. Through the released bore 42, a pressure wave delivered by the exhaust system enters the combustion chamber 20 and introduces exhaust gases and thus carbon dioxide into the combustion chamber 20. Depending on the embodiment and position of the valve timing, unburned fuel contained in the exhaust pipe 38 can also be returned to the combustion chamber 20 through the branch 40.

With the upward movement of the piston 4 during the now following compression stroke, the bore 42 is through the Piston 4 closed. The ignition then takes place by means of a spark plug and the piston 4 is moved downward again by the gases which expand as a result of its heating in the interior of the combustion chamber 20 and thereby does mechanical work. As soon as the piston 4 clears the bore 42, exhaust gases are already exiting through the branch 40 into the exhaust pipe 38. After passing through the bottom dead center, the piston 4 moves up again and then opens the exhaust valve 14 at a suitable time so that the combustion gases can be removed from the combustion chamber 20 as far as possible.

Fig. 3 shows in a diagram, which contains the crankshaft position in degrees in the horizontal axis, the time course of the opening of the intake valve and the exhaust valve of the engine 1 according to Fig. 1 when changing the gas, i.e. during the exhaust process and the subsequent intake process. Curve a shows the opening of the exhaust valve 14 during the normal exhaust process. The outlet valve 14 opens quickly (rising edge of curve a), then remains open for some time (horizontal section of curve a) and then closes again quickly (falling edge of curve a). During the closing process of the exhaust valve 14, the intake valve 10 opens (curve b). There is therefore an overlap of tax times. During the closing process of inlet valve 10 (falling flank of curve b, outlet valve 14, controlled by further cam 30, opens again briefly (curve c). The maximum opening according to curve c is lower than in curve a, and the Maximum opening is only achieved during a very short period of time, therefore curve c does not have a horizontally extending section simplified. In reality there are no jumps in speed and acceleration of the valve lift curves and these therefore run with rounded transitions between the different curve parts.

In the example of motor 1 according to FIG. 1, the following timing is provided:

Opening the exhaust valve: 60 ° of the crankshaft in front of the lower one

Dead center (UT),

Closing the exhaust valve 14: 40 ° after top dead center

(OT),

Opening the intake valve 10: 40º before TDC,

Closing the inlet valve 10: 50 ° after UT, opening the outlet valve 14 again (curve c): 30 ° after

UT,

Closing the exhaust valve 14: 80 ° after UT.

Claims

1. Four-stroke internal combustion engine with at least one combustion chamber, control members for the inlet and outlet and with a device for returning gases from an exhaust pipe into the combustion chamber, characterized in that a device for briefly opening an outlet control member (14, 42) is provided which opens the exhaust control element in the period after the opening of the intake control element (10) and before the ignition.

2. Engine according to claim 1, characterized in that the outlet control member (14) is opened while the inlet control member (10) is still open.

3. Engine according to claim 2, characterized in that the maximum of the opening of the exhaust control member (14) is present when the intake control member (10) is still open.

4. Engine according to claim 2, characterized in that the maximum of the opening of the outlet control member (14, 42) is present when the inlet control member (10) is already closed.

5. Engine according to one of the preceding claims, characterized in that on a camshaft controlling the exhaust control member (12) a further cam (30) associated with the exhaust control member (14) is arranged.

6. Engine according to one of claims 1 to 4, characterized in that a with an exhaust duct (18) of the engine in connection exhaust pipe (38) with a closable by a slide, in the combustion chamber (20) leading opening (42) in Connection is.

7. Motor according to claim 6, characterized in that the piston (4) forms the slide.

8. Engine according to one of the preceding claims, characterized in that the period in which the exhaust control member is opened again is controlled as a function of speed.