DE102006015265A1 - Internal combustion engine`s e.g. diesel engine, piston, for commercial vehicle, has piston shaft and piston head, whose part such as cap, dome or cavity is controlled in reversibly adjustable manner after installing piston into engine - Google Patents

Abstract

The piston (1) has a piston shaft and a piston head (3), where a part such as a cap (13), a dome (10) or a cavity of the head is controlled in a reversibly adjustable manner after installing the piston into an internal combustion engine. The head or the part of the head is adjustable between two end positions. The dome is adjustable with respect to a piston bowl (9). The cavity is filled with an alloy (15) with low melting point. An independent claim is also included for a method for changing a compression ratio in a combustion chamber of a cylinder of an internal combustion engine.

Description

The Invention relates to a piston for an internal combustion engine, especially for a diesel fuel-powered internal combustion engine, according to the generic term of claim 1, an internal combustion engine according to the preamble of claim 19, and a method for changing a compression ratio in a combustion chamber of a cylinder powered by a diesel fuel Internal combustion engine according to the preamble of claim 21.

at Diesel engines is in the starting phase, i. when the engine is cold, a particular minimum compaction ratio required in particular at big Cold the To achieve compression temperature suitable for auto-ignition of the Diesel fuel-air mixture is required. After the start of the Engine and especially after warm-up would be a considerable lower compression ratio sufficient and also of preference, because the high compression ratio in the Combustion chamber not only higher Peak temperatures and thus to higher pollutant emissions (NOx, Soot), but also to a lower ignition delay and thus to a poorer mixture preparation. These problems could be avoided by a variable compression ratio.

From the EP 0 640 176 B1 Already a method and an apparatus for varying the compression or compression ratio of a gasoline engine are known in which a part of a cylinder block of the internal combustion engine with respect to the crankcase can be tilted, which is structurally very complicated and makes in each case an external intervention required ,

outgoing It is the object of the invention to provide a piston, an internal combustion engine and a method of the aforementioned Art to improve that the internal combustion engine in the starting phase with a higher one compression ratio can work as in a subsequent phase of operation.

These Task is inventively characterized solved, that at least a part of the piston crown of the cylinder in the Internal combustion engine built-in piston relative to his Piston shaft controlled reversibly adjustable. In this way can be a top dead center of the piston from the piston head and from Cylinder limited combustion chamber volume to be reduced in the starting phase, about the compression ratio to increase and the at the start to auto-ignition the diesel fuel necessary compression temperature to achieve. After the start phase, the combustion chamber volume can be increased again, by the lower compression ratio a significant reduction the peak temperatures and thus the NOx emissions and the soot content to achieve in the exhaust. Due to the larger combustion chamber volume results also a larger ignition delay and thus a more homogeneous mixture preparation, which in turn for a better Implementation of the fuel ensures, so that the slightly lower thermal efficiency Compensated during operation due to the lower combustion temperatures or even overcompensated becomes. As a result, the specific fuel consumption through the change the compression ratio not or even positively influenced.

A preferred embodiment of the invention provides that the piston crown a rigidly connected to the piston skirt part and a respect comprises piston member adjustable part. It is advantageous Piston bottom to optimize combustion with a piston recess and a arranged in the piston recess dome, with respect to is adjustable to the piston recess in the axial direction of the piston, so that in the starting phase of the engine, the piston combustion chamber side a larger volume repressed as in the subsequent Operating phase of the engine.

The Adjustment of the piston crown or part of it in relation to the piston stem is preferably automatically, that is without an external control intervention, what it is for a number of different ways gives.

A first preferred embodiment of the invention provides the different Exploiting the temperature of the piston before starting or in the operating phase, to an automatic Adjustment of the piston crown as a function of the temperature too cause. For this purpose, preferably a cavity between the in relation the piston skirt adjustable part of the piston crown and the rigid part of the piston crown connected to the piston skirt with a substance, in particular a low melting point alloy filled, the in a change their state of matter of liquid it expands too tight, giving it a larger volume in the cold solid state as in the warm liquid Condition takes.

The substance is expediently arranged in the interior of a pressure vessel inserted into the piston and acts on the piston head adjustable in relation to the piston skirt via an actuator, such as, for example, a plunger immersed in the pressure vessel. In order to achieve that the adjustable part of the piston head is moved with the plunger downwards when it moves into the pressure vessel during heating of the piston, a spring may be provided which the adjustable part of the piston crown presses against the plunger.

A second preferred embodiment of the invention provides the different pressures in the combustion chamber before take-off or in the operating phase, by the piston crown depending on a on the Piston bottom exerted compressive force automatic adjusted. To the adjustable with respect to the piston skirt part of the To move the piston crown before starting in the direction of the combustion chamber is included preferably between the adjustable part of the piston crown and the part of the piston crown rigidly connected to the piston skirt Arranged spring which presses the two parts apart. Around to prevent the adjustable part of the piston crown already moved into its under end position by the compression before the first ignition, are means for throttling the speed of relative movement the two parts provided, which expediently has an upper cavity in the adjustable part of the piston crown and a lower cavity below the adjustable part of the piston crown and the cavities connecting the throttle opening and one in the cavities included incompressible fluid.

alternative However, the adjustable part of the piston head can also be adjusted by external action be, for example by mechanical or hydraulic means, the be activated before and after the start of the internal combustion engine, to extend the adjustable part of the piston crown or again collect.

there provides a further advantageous embodiment of the invention, that with respect to the piston skirt adjustable part of the piston head a Includes membrane, which includes a cavity over at least extends a part of the piston crown and by supplying a pressurized fluid into the cavity with respect to the rigidly connected to the piston skirt Part of the piston crown can be raised axially to enter in the starting phase higher compression ratio to create. This Ausgestal device is especially for pistons suitable with wide and flat piston recesses, as in commercial vehicles be used.

in the Following is the invention with reference to some in the drawing illustrated embodiments explained in more detail. It demonstrate:

1 a longitudinal section through a piston according to the invention of an internal combustion engine whose piston crown has a piston recess and an adjustable dome;

2 a longitudinal section along the line II-II of 1 ;

3 a perspective sectional view of a portion of the piston with lowered dome;

4 a perspective sectional view corresponding 3 but with raised dome;

5 an exploded perspective view of parts of the piston;

6 an enlarged sectional view of parts of the piston in the region of the dome;

7 a longitudinal section through a further piston according to the invention, whose piston crown has a piston recess and an adjustable dome;

8th a longitudinal section along the line VIII-VIII of 7 ;

9 a perspective sectional view of a part of the piston 7 and 8th with raised dome;

10 a perspective sectional view corresponding 9 but with lowered dome;

11 an exploded perspective view of parts of the piston;

12 an enlarged sectional view of parts of the piston in the region of the dome;

13 a longitudinal section through a part of another piston according to the invention, whose piston crown has a piston recess and an adjustable dome;

14 a longitudinal section through a part of yet another piston according to the invention, whose piston crown has a piston recess and an adjustable dome;

15 a perspective sectional view of a part of the piston 14 with raised dome;

16 a perspective sectional view corresponding 15 , but with lowered dome.

The pistons shown in the drawing 1 are all intended for installation in a cylinder (not shown) of a diesel engine. The pistons 1 consist in a known manner substantially from one to the leadership of the piston 1 serving in the cylinder piston skirt 2 , a piston bottom 3 , which defines a combustion chamber with the cylinder, one between the piston skirt 2 and the piston crown 2 arranged, with several annular grooves 4 for receiving piston rings provided Kolbenringzo ne 5 , as well as two pin hubs 6 for receiving a piston pin 7 that the piston 1 with a connecting rod 8th the engine connects.

The piston bottom 3 has a piston or combustion bowl in all pistons 9 on, causing the combustion chamber partially in the piston 1 is shifted into it. The piston recess 9 is from an undercut turbulence ring 11 surrounded and has a dome in its center 10 on, whose axial position along a piston axis 12 is adjustable between two end positions. This allows a distance between a top or a vertex of the dome 10 and a flat top of the rigid with the piston skirt 2 connected turbulence ring 11 change.

The adjustability of the cathedral 10 is exploited to the volume of the piston 1 and with this the volume of the piston 1 and to change the cylinder or its cylinder head limited combustion chamber, which can be set in the combustion chamber, a variable compression with different high compression ratios. This can be exploited to set a high compression ratio in the combustion chamber in diesel engines in the starting phase and in particular in a compression phase before the first ignition of the diesel fuel-air mixture, thereby ensuring a fast and reliable ignition of the mixture even at very low ambient temperatures, and This compression ratio in a subsequent phase of operation, that is with the engine running, lower again, whereby the peak temperature in the combustion chamber and thus the NOx and soot content of the exhaust gas can be lowered and the overall efficiency of the engine can be increased.

In the in the 1 to 6 illustrated piston 1 the adjustment of the dome takes place 10 automatically depending on the temperature of the piston 1 , where the dome 10 at relatively low temperatures, ie temperatures below about 100 ° C, with respect to the bottom of the piston bowl 9 is raised to reduce the volume of the combustion chamber and thus increase the compression ratio, as in 4 while at the higher operating temperatures of the engine relative to the bottom of the piston bowl 9 is raised to reduce the compression ratio, as in 3 shown.

In the piston shown in these figures 1 becomes the dome 10 from an axially movable in the piston crown 3 used hat 13 educated. For axial adjustment of the hat 13 is below the pressure vessel 14 arranged, which is an alloy 15 having a low melting point, the volume of which is greater in the cold solid state than in the warm liquid state, wherein the volume change between these states is about 2%.

How best in the 5 and 6 illustrated, includes the pressure vessel 14 a bowl-shaped top 16 and a bowl-shaped base, both made of deep-drawn or cold extruded steel, and forming the pressure vessel 14 be laser welded along their complementary peripheral edges before a defined amount of the alloy 15 in the liquid state in the pressure vessel 14 is filled. The pressure vessel 14 further includes one in a central bore 18 of the top 16 inserted and welded with this guide bushing 19 for a ceramic pestle 20 after filling the alloy 15 is mounted, with its lower end through the socket 19 inside the pressure vessel 14 protrudes. Over the top, from the pressure vessel 14 protruding end of the plunger 20 Be a PTFE gasket 21 and a retaining ring 22 pushed. The at its outer circumference with an undercut 23 provided retaining ring 22 is done by laser welding to the pressure vessel 14 connected to the seal 21 not to damage. In the event that it should be cheaper, the alloy 15 only after a complete assembly of the pressure vessel 14 must fill in the shell 16 or in the lower part 17 of the pressure vessel 14 still be provided a vent.

At the bottom of the hat made of ceramic 13 is a compression spring 24 fastened by several integral retaining clips 25 with the hat 13 is connected, as in 5 shown, and this down against the pressure vessel 14 suppressed. The feather 24 has a central passage opening 26 for the upper front end of the retaining ring 22 on, out of the radial slots 27 extend, which is a bending of the spring 24 adjacent to the passage opening 26 allow. The hat 13 is at its outer periphery with a circumferential. groove 29 provided, in which a piston ring 28 is used.

To assemble the piston 1 First, the fully assembled pressure vessel 14 with the pestle 20 from above into a recess 30 in the bottom of the piston recess 9 pressed in and with the piston 1 welded. Subsequently, the pressure vessel 14 above the melting point of the alloy 15 heated, so that the plunger 20 in the pressure vessel 14 dips. Last is the hat 13 with the return spring 24 and the piston ring 28 from above into the recess 30 pressed, with the edge of the passage opening 26 when striking against the retaining ring 22 is bent back first and then over the upper front end of the retaining ring 22 in the undercut 23 slips and locks in place.

When the engine is cold, the solidified alloy decreases 15 inside the pressure vessel 14 you largest volume, causing them the plunger 20 through the socket 19 through a distance from the pressure vessel 14 pushed out to the top. This is the hat 14 from the abutting against its underside ram 20 against the force of the spring 24 in the in 4 shown first upper end position moves, so that the combustion chamber at top dead center of the piston 1 has a minimum volume and thus a high compression ratio is achieved. When the piston 1 and therefore the alloy 15 when the engine is warming up above the melting point of the alloy 15 warmed up, this becomes fluid, taking up a smaller volume, so that the plunger 20 in the pressure vessel 14 is withdrawn. Because the hat 13 from the compression spring 24 against the pressure vessel 14 Pressing, he will be axially down in his in 4 dargestell te second lower end position moves, so that the volume of the combustion chamber compared to the cold state is increased. The leadership of the hat 13 gets off the piston 1 accepted.

In the in the 7 to 12 illustrated piston 1 the adjustment of the dome takes place 10 also automatically, but depending on the on the piston crown 3 applied pressure and with a certain time delay. The cathedral 10 There is pressed by the prevailing in the operation of the engine in the combustion chamber high pressures in its lower end position to reduce the compression ratio, as in 10 shown, while it is at unpressurized combustion chamber before starting the engine with respect to the bottom of the piston recess 9 is raised to reduce the volume of the combustion chamber and thus increase the compression ratio, as in 9 shown.

In the piston shown in these figures 1 becomes the dome 10 also from a hat 13 formed in an upwardly open receptacle 31 is axially movable. How best in 12 shown, the hat is made 13 there from a shell 32 and one rigid with the top 32 connected lower part 33 and is by a circumferential PTFE seal 34 opposite the cylindrical peripheral wall of the receptacle 31 sealed. Between the lower part 33 and the bottom of the receptacle 31 are a compression spring 34 and above it a retaining clip 35 used, of which the former the hat 13 inside the receptacle 31 pushes up and the latter on the one hand, the upward movement of the hat 13 limited and on the other hand prevents the hat 13 by the inertial forces acting on the movement of the piston from the receptacle 31 solves. The lower part 33 and the top 32 of the hat 13 enclose an upper fluid chamber 36 passing through a throttle bore 37 in a wall 38 of the lower part 33 can be filled with an incompressible fluid (not shown). The hat 13 is so in the receptacle 31 inserted that between the lower part 33 and the bottom of the receptacle 31 a lower fluid chamber 39 is limited by the throttle bore 37 with the upper fluid chamber 36 communicates and their volume depending on the axial position of the hat 13 in the receptacle 31 varied.

If the top of the hat 13 when the engine is not loaded by a compressive force, the hat will 13 through the compression spring 34 pressed upwards into its upper end position, as in 9 represented, whereupon the incompressible fluid due to its gravitational force in the lower chamber 39 collects. Once the engine is started and the top of the hat 13 acting force due to the pressure in the combustion chamber, the force of the spring 34 exceeds, the hat will 13 pressed down to its lower end position, as in 10 shown, and the fluid from the lower fluid chamber 39 displaced, passing through the throttle bore 37 in the upper fluid chamber 36 flows. After switching off the engine will be the hat 13 by the force of the spring 34 raised again, with the incompressible fluid through the throttle bore 37 back to the lower chamber 39 flows. Because the force of the spring 34 is much lower than the force exerted by the pressure in the combustion chamber, the downward movement of the hat 13 significantly faster than its upward movement. The speed is adjusted by changing one or more of the spring force, bore diameter, and fluid viscosity parameters so that the hat 13 remains in the upper end position until the engine is successfully started, and then moves quickly down to ensure optimum combustion chamber volume during operation. The speed of the upward movement due to the spring force is less crucial, since the cooling of the engine takes time.

For mounting the piston 1 First, the compression spring 34 and the retaining clip 35 with the bottom of the receptacle 31 welded and the upper fluid chamber 36 filled with a predetermined amount of the fluid. After the PTFE seal 34 from above on the lower part 33 has been pushed, the shell becomes 32 on the lower part 33 pressed and welded with this. Then the hat 13 in the receptacle 31 used and for the displacement of the fluid in the upper fluid chamber 36 pressurized from above. This is the retaining clip 35 bent down until it fits into recesses of the base 33 engages and pre-assembly of the hat 13 in the receptacle 31 finished. The hat 13 is then by the force of the spring 34 pressed by itself in its upper end position. Subsequently, the preassembled, the hat 13 containing receptacle 31 from the top into one in the bottom of the piston recess 9 recessed recess 40 pressed.

In contrast to the previously described pistons 1 have the in the 13 to 16 illustrated piston 1 a Cathedral 10 on, which is not automatically adjusted, but is adjustable by external action. The in 13 illustrated piston 1 has for this purpose a mechanical adjusting unit, one on the piston pin 7 guided, in the axial direction of the piston 1 slidable and on the underside of the cathedral einwir kenden cam 41 includes the dome 10 during operation of the motor against the force of a spring 42 pushes in its upper end position and is retracted when turning off the engine down, whereupon the spring 42 the dome 10 pushes down. The displacement of the cam 41 can be done hydraulically, for example, by the after starting the engine in an oil gallery 44 of the connecting rod 8th adjacent oil pressure, and possibly using hydraulic elements, the seal to the combustion chamber back over one or more around the dome circumferential seals 43 he follows.

In the in the 14 to 16 illustrated piston 1 includes the piston crown 3 a cast-in flexible membrane 45 located below the cathedral 10 by prior Alfinierung or another suitable coating not with the existing cast aluminum piston crown 3 connects, allowing them in this area, for example, by supplying a pressurized fluid into the cavity 46 before starting the engine in the axial direction of the piston 1 can be raised. The pressurized fluid may, as before, be engine oil which, prior to starting the engine, is supplied by suitable hydraulic elements through an oil passage in the connecting rod 8th between the piston crown 3 and the membrane 45 is pressed to raise the latter, as in 14 shown on the left. Such a configuration is especially for pistons 1 with wider and shallower hollows 9 as well as with less undercut in the turbulence ring 11 suitable as used for commercial vehicles.

1

piston

2

piston shaft

3

piston crown

4

ring grooves

5

Piston ring zone

6

pin bosses

7

piston pin

8th

pleuel

9

piston bowl

10

cathedral

11

Vortex ring

12

longitudinal axis

13

cap

14

pressure vessel

15

alloy

16

top pressure vessel

17

lower part pressure vessel

18

Through opening

19

guide bush

20

tappet

21

poetry

22

retaining ring

23

undercut

24

compression spring

25

retaining clip

26

Passage opening spring

27

radial Slot spring

28

piston ring

29

groove

30

recess piston crown

31

receptacle

32

top cap

33

lower part cap

34

compression spring

35

retaining clip

36

upper fluid chamber

37

throttle bore

38

wall lower part

39

lower fluid chamber

40

recess piston crown

41

cam

42

Return spring

43

poetry

44

oil passage

45

membrane

46

cavity

Claims (24)

Piston for an internal combustion engine, having a piston skirt and a piston crown, characterized in that at least one part ( 10 . 13 . 46 ) of the piston crown ( 3 ) after installation of the piston ( 1 ) in the internal combustion engine with respect to the piston skirt ( 2 ) controlled reversibly adjustable. Piston according to claim 1, characterized in that the piston crown ( 3 ) or the part ( 10 . 13 . 46 ) of the piston crown ( 3 ) is adjustable between two end positions, in which the piston ( 1 ) displaces different volumes. Piston according to claim 1 or 2, characterized in that the piston head ( 3 ) one rigidly with the piston skirt ( 2 ) and one related to the piston skirt ( 2 ) adjustable part ( 10 . 13 . 46 ). Piston according to one of the preceding claims, characterized in that the piston head ( 3 ) a piston recess ( 9 ) and one in the piston recess ( 9 ) arranged cathedral ( 10 ), and that the dome ( 10 ) in relation to the piston recess ( 9 ) is adjustable. Piston according to one of the preceding claims, characterized in that the piston crown ( 3 ) or the part ( 10 . 13 . 46 ) of the piston crown ( 3 ) automatically adjusted during operation of the internal combustion engine. Piston according to one of the preceding claims, characterized in that the piston crown ( 3 ) or the part ( 10 . 13 . 46 ) of the piston crown ( 3 ) as a function of the temperature of the piston ( 1 ) automatically adjusted. Piston according to claim 6, characterized in that a cavity between the adjustable with respect to the piston skirt part ( 13 ) of the piston crown ( 3 ) and the rigid with piston skirt ( 2 ) connected part of the piston crown ( 3 ) with a substance ( 15 ) is filled, which expands from liquid to solid when changing their state of aggregation. Piston according to claim 7, characterized in that the cavity with the substance ( 15 ) is sealed pressure-tight. Piston according to claim 7 or 8, characterized in that the cavity in the interior of a pressure vessel ( 14 ) is arranged. Piston according to claim 8 or 9, characterized in that one in the cavity or pressure vessel ( 14 ) immersing actuator ( 20 ) on the relative to the piston shaft ( 2 ) adjustable part ( 13 ) of the piston crown ( 3 ) acts. Piston according to claim 9 or 10, characterized by a spring ( 24 ), which the adjustable part ( 13 ) of the piston crown ( 3 ) against the pressure vessel ( 14 ) presses. Piston according to one of the preceding claims, characterized in that the piston crown ( 3 ) or a part of the piston crown ( 13 ) depending on a on the piston head ( 3 ) exerted pressure force automatically adjusted. Piston according to claim 12, characterized in that between the relative to the piston shaft ( 2 ) adjustable part ( 10 . 13 . 46 ) of the piston crown ( 3 ) and the rigid with piston skirt ( 2 ) connected part of the piston crown a compression spring ( 34 ) is arranged, which is compressed during operation of the internal combustion engine by the pressure in the combustion chamber. Piston according to claim 13, characterized by means for throttling the speed of the relative movement of the two parts when the compression spring is compressed ( 34 ). Piston according to claim 14, characterized in that the means comprise an upper cavity ( 36 ) in the adjustable part ( 10 . 13 . 46 ) of the piston crown ( 3 ) and a lower cavity ( 39 ) below the adjustable part ( 10 . 13 . 46 ) of the piston crown ( 3 ), one of the cavities ( 36 . 39 ) connecting throttle opening ( 37 ) and one in the cavities ( 36 . 39 ) comprise incompressible fluid. Piston according to one of the preceding claims, characterized in that the piston crown or a part ( 10 ) of the piston crown ( 3 ) is adjustable from the outside. Piston according to claim 16, characterized in that the piston crown or the part of the piston crown ( 10 ) is mechanically or hydraulically adjustable. Piston according to one of the preceding claims, characterized in that in relation to the piston skirt ( 2 ) adjustable part of the piston crown ( 3 ) a membrane ( 45 ) enclosing a cavity ( 46 ) at least partially over the rigid with piston skirt ( 2 ) connected part of the piston crown ( 3 ) and by supplying a pressurized fluid into the cavity ( 45 ) is adjustable. Internal combustion engine, having at least one cylinder, characterized by a reciprocating piston in the cylinder ( 1 ) according to one of the preceding claims. Internal combustion engine according to claim 19, characterized in that the adjustment of the piston crown ( 3 ) or part ( 10 . 13 . 46 ) of the piston crown ( 3 ) a change in volume from the piston crown ( 3 ) and limited by the cylinder combustion chamber causes. Method for changing a compression ratio in a combustion chamber of a cylinder of a diesel-fueled internal combustion engine, in which a piston can be moved back and forth, characterized in that a top dead center of the piston ( 1 ) from the piston ( 1 ) and controlled by the cylinder volume of the combustion chamber is controlled controlled during a starting phase of the internal combustion engine. Method according to claim 21, characterized that the volume of the combustion chamber during a compression phase the internal combustion engine before a first ignition of the diesel fuel reduced in the combustion chamber and after the first ignition of the diesel fuel is enlarged again. Method according to claim 21 or 22, characterized that the volume of the combustion chamber is changed without external intervention. Method according to one of claims 21 to 23, characterized by a temperature of the piston ( 1 ) or the pressure in the combustion chamber dependent change of a piston volume is changed.