DE2063651A1 - Pistons, in particular for internal combustion engines - Google Patents

Description

Pistons in particular for internal combustion engines The invention relates to a piston, in particular for internal combustion engines, with on the Circumference of the piston skirt machined from oil drag grooves existing sawtooth-like profiled surface roughness.

During the working stroke of the piston in an internal combustion engine flows a tiny amount of combustion gas past at least the upper compression rings. Since the compression rings in the following cycle again with the hot upper cylinder section, in which the combustion took place before come into contact is the lubrication the upper compression rings pose a complicated problem. On the one hand, the ring assembly should prevent lubricant from entering the combustion chamber; on the other hand must that the uppermost compression ring there is enough lubricant available that this - despite the high operating temperature - is still adequately lubricated. Sufficient Lubricated means: the top ring must not have burn marks or tiny scuff marks get and its wear should - just like the wear of the cylinder and piston - stay within the smallest limits. Sufficient lubrication in the area of the ring belt is primarily due to the formation and adhesion of a hydrodynamic lubricating film - even with a sparse supply of lubricant - between the piston skirt and the cylinder liner influenced.

This creates a hydrodynamic lubricating film between the piston skirt and cylinder liner has been used for several years in particular the piston skirt with a machined minimum surface roughness, whose Depending on the type of engine, surface roughness is generally not less than 2 to 6 μm. Such a surface roughness on the one hand favors the running behavior of the Piston through the formation of a lubricating film with the help of the stored in the surface roughness Lubricant and on the other hand limits the wear between the piston skirt and Cylinder liner.

For this purpose it is known to have one on the circumference of the piston skirt Surface roughness in the form of so-called oil drag grooves that form a semicircular, Have curved or sawtooth-shaped, angularly symmetrical profile, to be applied by machining. When the piston runs in, the height of the profile is increased because of the greater wear initially heavily worn. Although this wear and tear with increasing contact percentage of the Profile is limited, the seizure sensitivity of the piston increases as a result the surface roughness, which has been reduced by wear, only requires relatively little lubricant can hold in the oil drills. This makes the training one on the whole Circumference of the piston skirt hydrodynamic lubricating film during upward and downward gear of the piston is not always ensured.

It should also be taken into account that in an internal combustion engine the lubricant thrown off by the crankshaft as a result of its direction of rotation almost exclusively on the cylinder liner in the area of the counter-pressure side of the Piston arrives. This leads to the fact that in the ring parry on the counter-pressure side, in particular an excess of lubricant in the area of the compression ring on the piston skirt is offered and therefore the lubricating film in this area is thicker than on the Pressure side of the piston is formed. The print side, however, is a comparative one much higher surface pressure due to the thicker hydrodynamic lubricating film on the counterpressure side is additionally increased when the counterpressure side is exposed. One can therefore often observe that as a result of the inadequate supply of lubricant on the pressure side, in particular on the compression ring on the piston bottom side, burn marks, more or less large seizure marks and above-average wear occur The different thickness of the film on pressure and counter pressure side also means that the oil control ring on the downward gear of the piston The lubricant does not completely adhere to the cylinder liner in the area of the counter-pressure side can eliminate. The remaining lubricant then cokes and the resulting lubricant Oil coke accumulates in a disadvantageous way between the piston and the compression ring, so that the formation of a hydrodynamic lubricating film is disturbed and the wear is increased not insignificantly.

The difficulty with a two-stroke engine is that it is relatively minor from the fuel mixture between the piston skirt and the lubricant To hold on to the cylinder barrel and to convey it up into the ring belt of the piston A hydrodynamic lubricating film builds up on the circumference of the piston skirt can.

The invention has now set itself the task of the aforementioned State of the art to eliminate deficiencies and in particular the sawtooth-like profiled surface roughness of the piston skirt forming oil drag grooves so to make that when the internal combustion engine is operating a uniformly thick Lubricant film is present between the piston and the cylinder liner, so that both The same hydrodynamic pressure development is always the same on the pressure side as on the counter pressure side is guaranteed in the lubricating film and there is no longer any superfluous lubricant in can get into the combustion chamber. Furthermore, the lubricant consumption should continue be lowered without that on the pressure side of the piston Lubricant minimum is undershot.

This object is achieved according to the invention in such a way that the oil drag grooves different flank angles and an obtuse profile angle with one approaching zero have going rounding radius.

The smaller flank angle of the oil drag grooves has expediently a size of 0.5 to 10 °, preferably 1 to 5 °, in particular 2 to 3 °, while the profile angle 100 to 170 °, preferably 130 to 1700, in particular 150 to 170 °, is large and the radius of curvature of the groove base is 0 to 0.1 mm, preferably 0 to 0.05 mm, in particular 0 to 0.01 mm.

In the context of the further development of the invention, the depth is of the oil slugs 1 to 20 Jun, preferably 2 to 15 µm, especially 6 to 12 Ma.

By the inventively designed on the piston skirt attached The Abbot's curve, which shows the change in the contact percentage, runs along the oil drag grooves represents the sawtooth-like profiled surface roughness due to wear, straight from 0 to 100 o / o That means that after a relatively small amount of wear the profile points have a sufficiently large contact area without doing so the roughness of the surface roughness would have been markedly reduced. As a result remains in the oil drag grooves after the piston has run in for training an evenly thick lubricant film required on the circumference of the piston saved. These advantages become more apparent the sharper the groove base the oil drag pills is executed.

Another embodiment of the invention is that the smaller Flank angle of the oil drag grooves on a piston.

for four-stroke internal combustion engines points to the end of the piston skirt, whereby the lubricant is conveyed in the direction of the crankshaft space.

In the case of a piston for a two-stroke internal combustion engine the smaller flank angle of the oil drag grooves directed towards the piston crown, so that the lubricant is pumped up in the direction of the ring belt.

In the oil drag pills according to the invention remains even when standing Internal combustion engine stored such an amount of lubricant that when Starting immediately, a hydrodynamic lubricating film can build up again.

A preferred development of the invention is that on the counter-pressure side of the piston the smaller flank angle of the oil drag grooves to Piston skirt end and on the pressure side to the piston crown. That way will achieved that on the counter-pressure side, where the amount of lubricant is greater than on the pressure side is, the lubricant down into the crankshaft space and on the pressure side is conveyed up into the ring belt. Doing this will be an even thick lubricant film achieved while reducing lubricant consumption.

The invention is illustrated by way of example in the drawings and is explained in more detail below.

1 shows a cylinder 1 with a Connecting rod 3 connected piston 2 for a four-stroke internal combustion engine. According to FIG. 1 a, which shows an enlarged section from FIG. 1, is the piston skirt provided with the oil drag grooves 4 designed according to the invention, the smaller ones Flank angle directed towards the end of the piston skirt and its groove base sharp-edged is trained.

2 shows a connecting rod 3 arranged in a cylinder 1 and connected to it Piston 2 for a two-stroke internal combustion engine. According to Fig. 2a, an enlarged Excerpt from Fig0 2 represents the piston skirt with the inventively designed Oil drag grooves 4 are provided, the smaller flank angle of which is directed towards the piston head and the bottom of the groove is sharp-edged.

3 shows a connecting rod 3 arranged in a cylinder 1 and connected to it Piston 2 for a four-stroke internal combustion engine O According to FIGS. 3a and 3b, each representing a section from Fig0 3 is the smaller flank angle of the oil drag grooves 4 directed on the counter-pressure side to the end of the piston skirt, while the smaller flank angle of the oil drag grooves 4 on the pressure side to the piston crown The bottom of the grooves of the oil drag grooves is sharp-edged.

Claims

Claims (8)

PATENT CLAIMS 1) pistons, especially for internal combustion engines, with machined on the circumference of the piston skirt, one profiled like a sawtooth Oil drag grooves which form surface roughness, characterized in that the Oil drag grooves have different flank angles and an obtuse profile angle have a radius of curvature that approaches zero. 2) piston for internal combustion engines according to claim 1, characterized characterized in that the smaller flank angle of the oil drag grooves is 0.5 to 10 °, is preferably 1 to 5 °, in particular 2 to 30, large. 3) pistons for internal combustion engines according to claims 1 and 2, characterized in that the profile angle of the oil drag grooves 100 to 1700, preferably 130 to 1700, in particular 150 to 170 °, is large. 4) piston for internal combustion engines according to claims 1 to 3, characterized in that the radius of curvature of the oil drag grooves is 0 to 0.1 mm, preferably 0 to 0.05 mm, in particular 0 to 0.01 mm. 5) pistons for internal combustion engines according to claims 1 to 4, characterized in that the surface roughness of the profile is 1 to 20 µm, preferably 2 to 15 µm, in particular 6 to 12 µm. 6) pistons for combustion engines according to claims 1 to 5, characterized in that the smaller flank angle of the oil tow prillon a piston for a four-stroke internal combustion engine directed towards the end of the piston skirt is. 7) piston for internal combustion engines according to claims 1 to 5, characterized in that the smaller flank angle of the oil drag grooves at a piston for a: two-stroke internal combustion engine directed towards the piston crown is. 8) piston for internal combustion engines according to claims 1 to 7, characterized in that the smaller one on the counter-pressure side of the piston skirt Flank angle of the oil drag grooves to the end of the piston skirt and on the pressure side to the Piston crown is directed 0