EP0628701B1 - Sealing arrangement for internal combustion engine valve stem - Google Patents

Description

The present invention relates to the field of internal combustion engines having at least one cylinder and each combustion chamber of which is supplied with a fuel mixture under pressure via an intake pipe which is itself closed, on the combustion chamber side, by a valve, the movement of each valve being controlled by a cam.

More precisely, the invention provides a sealing device for the valve stem, intended to prevent fuel from leaking from the intake channel to the housing containing the cam (s).

We try to avoid such leaks because they contribute in particular to the fouling of the cam box and to a deterioration of the oil contained in the cam box.

It is known to seal the valve stems by means of a seal surrounding the valve stem and arranged for example on a member for guiding the valve stem (see US-A-3,120,221).

The seals thus used may wear out, be damaged by the very movement of the valve, temperatures, so that their sealing function is no longer (or is poorly) fulfilled after a certain period of operation. .

The present invention in particular provides a solution to the aforementioned sealing problem.

Indeed, the subject of the present invention is a sealing device intended to prevent the leaks defined above.

The sealing device according to the invention can replace or add to a conventional sealing device.

The sealing device according to the invention is based on the use of a back pressure.

It is known to use additional pressure or pressure to assist the movement of the valve itself. For example, documents US 1,361,109 or FR 2,641,336 disclose devices for assisting the movement of a valve by virtue of a pressure difference between two volumes.

In a different way, the back pressure used according to the present invention essentially has a sealing function between two volumes. According to the present invention, the displacement of each valve is achieved by means of a cam or equivalent means. The two functions, displacement and sealing, do not interfere in any way between them since the displacement is obtained by mechanical means while the sealing is carried out by essentially pneumatic means of a different physical nature.

The system according to the present invention is simple, easy to implement, and therefore reliable.

It does not require any particularly significant transformation of the classic essential elements of the intake system: the valve (the valve seat), the valve stem, the intake duct, the cams, the cam box are in no way modified. ; their respective functions, proven and known for a long time, therefore remain unchanged.

The present invention aims in particular to improve one of the functions linked to the injection of fuel into the combustion chamber.

To do this, the present invention relates to a sealing device for a valve stem controlled by a cam contained in a camshaft housing of an internal combustion engine having at least one cylinder.

According to the invention, the sealing device comprises a pipe connecting on the one hand an inlet pipe for the fuel mixture into a combustion chamber, closed by a valve, and on the other hand a camshaft housing , and a non-return valve placed in said pipe in order to separate said pipe into two volumes, the first volume being connected to the housing and constituting a pressurized capacity having a pressure P1 greater than or equal to the pressure P2 prevailing in the pipeline. intake and in the second volume, said device being intended to prevent fuel leaks from the intake pipe to the camshaft housing.

According to one embodiment of the invention, the second volume is connected to a pump housing of a cylinder of the internal combustion engine.

According to another embodiment of the invention, the second volume is connected to a compressor external to the cylinder.

According to a particular embodiment of the invention, the intake pipe is supplied with compressed air and it comprises a pneumatic fuel injector so that said valve acts as a pneumatic injector to spray said fuel into the combustion chamber.

• La figure 1 représente schématiquement une partie d'un moteur comportant un dispositif d'étanchéité selon un mode de réalisation de l'invention ; et
• La figure 2 représente schématiquement une partie d'un moteur comportant un dispositif d'étanchéité selon un autre mode de revendication de l'invention.

The invention will be better understood, other details and improvements will appear better on reading the description which follows, given by way of illustration and in no way limiting, with reference to the appended drawings in which:

• FIG. 1 schematically represents a part of an engine comprising a sealing device according to an embodiment of the invention; and
• FIG. 2 schematically represents a part of an engine comprising a sealing device according to another mode of claim of the invention.

In FIG. 1, the reference 1 indicates the combustion chamber, the intake channel bears the reference 2, a cam is referenced 3, the cam box is referenced 4; the valve 5 comprises, on the combustion chamber side 1, a tulip 51 closing the intake orifice 6 and resting on a seat (not referenced); the valve 5 also comprises a rod (or tail) 52 extending the tulip 51 and guided in translation by a guide or equivalent means 7; an elastic return element 8 pushes the valve 5 against the cam 3, which tends to bring the tulip 51 back onto its seat, that is to say to close the orifice 6. The cam 3 on the contrary pushes the valve 5 into the other direction, tending to open port 6.

A sealing element 9 such as a seal can be provided for example at the level of the return element 8 in order to ensure a first seal between the intake channel 2 and the cam box 4. The fluid under pressure circulating in channel 2 may for example comprise a mixture of air and fuel; the fuel can be caused to accumulate along the stem of the valve 52, to infiltrate beyond the sealing element 9.

In known manner, the element 9 is particularly effective in preventing leaks in the direction of camshaft 4 towards the conduit 2 but is however very ineffective in preventing leaks in the direction of conduit 2 towards the camshaft 9. This last function is the one for which efficiency is sought according to the invention.

On the strength of this observation, the present invention therefore proposes another sealing device, which, as has already been said, can be substitute or add for example to a known sealing device 9.

The sealing device according to the invention notably comprises a pipe 10 connecting the intake pipe 2 to the cam box 4. A non-return valve 11 or any other means intended to allow the fluid to pass under the effect of a given pressure difference and to prevent this passage when the pressure difference is less than the given pressure difference, is further placed in line 10.

The valve 11 therefore makes it possible to separate the pipe 10 into two volumes: the first volume 12 in connection with the cam box 4, the second volume 13 communicating with the intake pipe 2. In the first volume 12 there is a pressure P1 while that in the second volume 13 there is a pressure P2. The valve 11 opens when the pressure P2 is greater than the pressure P1, thus making the volume 12 play the role of a pressure storage capacity.

It should be noted that according to the embodiment of FIG. 1, the volume 12 is in fact almost nonexistent, so that the pressure P1 is the pressure in the cam box 4.

FIG. 2 illustrates an embodiment in which the volume 12 appears clearly.

The embodiments of FIGS. 1 and 2 differ in particular in the place where the conduit 10 opens:

In FIG. 1, the duct 10 opens out towards the combustion chamber 1 near the intake orifice 6, while in FIG. 2 the tapping is more upstream.

Line 2 can convey, for example, a fluid having the pressure of the pump housing, a pressure which of course varies during each engine cycle.

The non-return valve 11 therefore makes it possible to store in the volume 12 and in the space 4 the maximum pressure P1 obtained during each cycle. This pressure will oppose, in particular at the level of the stem 52 of the valve 5, the pressure P2 which prevails near the inlet orifice 6 and which is necessarily less than or at most equal to P1.

The valve 5 can be used to carry out a pneumatic injection of fuel into the combustion chamber 1, from compressed air taken, for example, from the pump housing of a two-stroke engine.

Without departing from the scope of the invention, the compressed air can be supplied by a compressor external to the cylinder.

A fuel introduction member (not visible in the figures) can be provided; it can open into the intake pipe 2, so that the valve then performs a pneumatic fuel injection function in the combustion chamber.

Claims (4)

1. Sealing device for a valve rod controlled by a cam contained in a cam shaft housing of an internal combustion engine having at least one cylinder, characterised in that it has a pipe (10) linking a passage (2) for feeding a carburetted mixture into a combustion chamber (1), closed off by a valve (5), on the one hand, and a cam shaft housing (4) on the other, the device having in addition a non-return valve (11) positioned in the said pipe (10) in order to divide the said pipe (10) into two volumes (12, 13), the first volume (12) being linked to the housing (4) and forming a capacity under pressure having a pressure P1 greater than or equal to the pressure P2 prevailing in the inlet passage (2) and in the second volume (13), the said device being designed to prevent fuel leakage from the inlet passage (2) to the cam shaft housing (4).
2. Sealing device as claimed in claim 1, characterised in that the second volume (13) is linked to a crankcase of a cylinder of the internal combustion engine.
3. Sealing device as claimed in claim 1, characterised in that the second volume (13) is linked to a compressor external to the cylinder.
4. Device as claimed in any one of the preceding claims, characterised in that the inlet channel (2) is supplied with compressed air and has a pneumatic fuel injector so that the said valve (5) acts as a pneumatic injector for spraying the said fuel into the combustion chamber (1).

Images