WO2008148425A1

WO2008148425A1 - Composite piston for internal combustion engines having a completely closed cooling channel

Info

Publication number: WO2008148425A1
Application number: PCT/EP2007/055581
Authority: WO
Inventors: Matthias Prussak
Original assignee: Cdp Bharat Forge Gmbh
Priority date: 2007-06-06
Filing date: 2007-06-06
Publication date: 2008-12-11

Abstract

The invention relates to a piston for internal combustion engines, comprising a compact interior component (1) forming the interior of the piston shaft and the piston head, and a sleeve-shaped exterior component (2) forming the exterior contour of the piston head, having a combustion cavity and a piston ring carrier, and the piston shaft, having a contact surface and a piston rod stud bore. The interior component (1) has at least one radial rib (5) of a dimension (D), which substantially corresponds to the inner diameter of the exterior component (2). The components (1) and (2) form a fluid- and gas-tight hollow space (3) suitable for receiving coolants, and the interior component (1) is supported in the axial and radial direction by the flange (5) and via one or more shoulders (6, 7) in the region of the combustion space cavity in the axially opposite direction on the interior contour of the exterior component (2). In the method for the production of a piston for internal combustion engines, a compact interior component (1) forming the interior of the piston shaft and the piston head is introduced into a sleeve-shaped exterior component (2) forming the exterior contour of the piston head, having a combustion cavity and a piston ring carrier, and the piston shaft, having a contact surface and a piston rod stud bore, wherein the interior component (1) has at least one radial rib (5) of a dimension (D) substantially corresponding to the inner diameter of the exterior component (2), and wherein the components (1) and (2) form a hollow space (3). The exterior component (1) is then joined to the exterior contour of the interior component (2) in the axial and radial direction via the flange contour (5) and, in the axially opposite direction, via one or more shoulders (6, 7) in the region of the combustion cavity such that the hollow space (3) is sealed in a fluid- and gas-tight manner.

Description

Composite piston for internal combustion engines with fully closed cooling channel

The invention relates to a composite piston for internal combustion engines with completely closed Kuhlkanal and a method for its preparation.

State of the art

The ever-increasing demands of the legislator regarding reduction of pollutant emissions in internal combustion engines and reduction of specific fuel consumption on the one hand and the trend towards high engine specific performance on the other hand are forcing engine and engine component manufacturers to constantly improve their products. In the case of combustion engines, it is clear that compliance with the required standards (exhaust gas quantity and purity, soot particles, oil losses) can only be achieved by higher operating pressures and higher physical factors

Combustion temperatures can be realized ("clean combustion").

The high temperatures and operating pressures require a piston manufacturer design technical measures, such as the creation of Kuhlkanalen to dissipate the heat of combustion, the creation of rigid piston designs to Oleintritt- and gas outlet in / from the combustion chamber by combustion of the piston between the piston ( Bearing and shank area) and piston upper part (so-called. Brennmuldenbereich) relative to the cylinder inner wall is formed to prevent, as well as a stable lubrication between shaft and cylinder upright.

Equally important, however, is the right material design in view of the ever-tougher operating conditions. Cast materials are increasingly reaching their limits, especially when it comes to the lifetime in the range of elevated temperatures (fatigue strength). However, it was up to now almost entirely reserved for casting technology to reliably represent the design requirements (undercuts, hollow contours).

Blacksmith materials, on the other hand, have indisputable advantages over the cast materials with regard to the properties that can be achieved, in particular fatigue strength at elevated temperatures. For the design degrees of freedom compared to the casting are limited, especially with regard to the formation of the undercut Kuhlkanals.

A solution approach to overcome these limitations are, for example, one-piece forged pistons with open Kuhlkanal, so-called. Monothermic piston. However, the circumferentially open connection between the piston skirt area and the piston head reduces the flexural rigidity of the piston, especially when the load acts at an angle on the piston at certain connecting rod positions. Also, with one-piece forged pistons, the choice of the piston material is limited insofar as that the material for the entire component must always meet the highest possible loads and thus contributes to higher costs. From a production point of view is disadvantageous that the undercut contour no optimal manufacturing technology in terms of

Lifetime properties allowed. Finally, the structural height of the piston is greater than in two-part, built solutions, as a minimum height for the axial gap of the cooling channel can not be fallen below in order to make the Kuhlkanal the mechanical processing accessible.

So far, pistons with open cooling ducts have been considered sufficient and reliable, in the future pistons with closed cooling ducts will have to be used, mainly for reasons of higher bending stiffness required. Closed Kuhlkanal means in this context not only a purely mechanical closing ("Zudeckein") of an open Kuhlkanals with a spring plate but also the assumption of forces in the direct power flow through mechanical and constructive connection of the piston lower part (combustion trough / piston head) circumferentially bearing and shirt area (Piston shaft).

A one-piece forged piston design with a closed coolant channel is known from EP 1 611 975 A1. In this case, in a piston blank with flange formed on the piston head in the radial direction, a closed coolant channel is formed by circumferential "closing" of the flange and wearing of the piston head against the piston shaft. As a result, in contrast to the piston with an open coolant channel, a closed connection between the shaft region and the piston head can be achieved and the flexural rigidity of the piston can be increased. Furthermore, a very compact construction height is possible because the inner contour of the cooling channel is easily accessible due to the selected production technology of a processing. Again, however, the material for the entire component must always meet the highest of all possible loads, which leads to higher material costs. The manufacturing costs are further increased, since the radial flange must be trimmed by a special bending technology circumferentially against the shaft and thus is not classified as "schmiedefreundlich".

Thus, while one-piece pistons with closed coolant channel can be produced by forging technology, this is only possible possible under high material and manufacturing costs. This is why increasingly built or assembled pistons are moving into the focus of the developers. On the one hand, one would like to make use of the material-technical advantages of the forged component and, on the other hand, be able to depict undercut contours or closed cavities by skillful joining methods.

The built piston also has the advantage that the designer can combine different materials adapted to the respective tasks. Thus, particularly in the area of the piston head, high-temperature steel grades are preferably used, whereas aluminum is also used as a material in the shaft area for reasons of weight.

An example of a built-up piston is described in WO 00/53913 A1, in which the piston head and the piston shaft are screwed axially by means of expansion screws. The optimal materials for piston head and piston skirt can be combined depending on the main load and undercut contours or closed cavities (cooling channel) can be realized relatively easily. The now possible closed connection between the shaft area and piston head increases the bending stiffness of the piston. However, the screw height increases the height of the piston and compared to one-piece solutions, an additional installation effort is necessary. The expansion bolts as a link also represent a weak point, especially when the system is subjected to cyclic loads (in this case thermally and mechanically) constantly alternating strains. Also, the free choice of materials for the individual components is already limited again, because due to the selected connection technology, the thermal expansion properties of the components may not differ too much. Another built solution are the so-called monostable pistons, which are described in US 4,581,893. Here, the piston head and the piston skirt are circumferentially friction welded to achieve the closed offer to increase the flexural rigidity and at the same time form a closed cooling channel. Since the cooling channel inside can be processed before welding, a compact overall height is possible. However, an additional installation effort is also necessary here, since the friction welding technology requires compliance with very narrow process window. This is where the

Friction welds also a certain risk, since on the one hand represent weak points in terms of strength and on the other hand, the introduction of residual scale in the cooling channel can never be definitely excluded. Also, the free choice of materials for the individual components is already limited again, since due to the selected connection technology, the weldability of the components must be given.

Presentation of the invention

It is therefore an object of the invention to overcome the disadvantages of the prior art and to develop a built-up piston which has a high flexural rigidity and durability as well as effective cooling to withstand the increasing pressures and temperatures of combustion. It is also an object of the invention to develop a method for producing such a piston, which is both simpler and cheaper to carry out compared to existing methods.

These objects are achieved by a piston having the features of claim 1 and a method having the features of claim 7. Further advantageous embodiments will be apparent from the respective dependent claims. A piston according to the invention for internal combustion engines has a compact inner component, which forms the interior of the piston bearing and the piston head, and a sleeve-shaped outer component, which forms the outer contour of the piston head with Brennmulde and Ringträgerbereich and the piston shaft with tread and Pleuelbolzenbohrung. The interior of the piston skirt is in this case that structure which serves for the construction of the connecting rod bore on the connecting rod side and serves to form one or more cooling channels on the combustion chamber side. The inner component of the piston has at least one radial rib with a dimension (D) that substantially corresponds to the inner diameter of the outer component. Essentially, this means that the specified dimensions are identical except for technologically determined tolerances or joining gaps. The dimension of the at least one radial rib is to be understood here as the distance between the respective outermost points of the rib (s) at the point at which the inner diameter of the outer component is measured. The inner and outer components form a liquid or gas-tight cavity, which is suitable for receiving cooling media. This cavity represents the closed cooling channel, wherein the shape of the cooling channel can be freely adapted to the requirements by known processing methods. The inner component is supported on the inner contour of the outer component via the at least one rib in the axial and radial direction and via one or more shoulders in the region of the combustion trough in the axially opposite direction. By this construction, a two-piece built piston is obtained, which withstands no force, form or material connections (such as screws, rivets, welds, etc.) of the two components the high requirements in terms of pressure and temperature and their fluctuations in the combustion chamber. By correspondingly shaping the inner contour of the outer component and / or the outer contour of the inner component The cooling channel can be optimally adapted to the requirements and the overall height can be kept low.

Preferably, the at least one radial rib is formed as a circumferential flange contour whose dimension is given by its outer diameter.

Although the at least one radial rib or the flange may have a symmetry corresponding to the mechanical and thermal requirements, it is preferred that the at least one radial rib or the flange of the piston according to the invention is rotationally symmetrical. This form provides optimal support for most applications and thus power and heat transfer between the outer and inner components.

In a preferred embodiment of the piston according to the invention, at least one additional cavity is formed between the upper side of the inner component and the inner contour of the outer component, which can be used for additional cooling of the piston head. In particular, one or more additional cavities lying directly under the combustion trough are advantageous, since usually the highest temperatures in the combustion trough arise during the combustion and therefore an efficient cooling is of particular importance with regard to material life.

According to a further preferred embodiment of the piston according to the invention, the inner component and the outer component consist of different materials. The materials may be selected depending on the load case, strength or weight ratio and other required properties.

Furthermore, it is advantageous that defined tolerances are present in the piston according to the invention between the shoulder or shoulders. So can a defined Axial displacement to compensate for thermal expansion differences or by targeted movement to achieve a shaker effect in the cooling medium.

An inventive method for producing a piston for internal combustion engines comprises first inserting a compact inner component, which will form the interior of the piston skirt and the piston head, into a sleeve-shaped outer component, which the outer contour of the piston head with Brennmulde and Ringträgerbereich and the piston shaft with tread and Pleuelbolzenbohrung will form, wherein the inner component has at least one radial rib with a dimension D, which corresponds substantially to the inner diameter of the outer component, and form the inner and outer components already in the initial state before the subsequent joining a cavity. The following step is the joining of the outer component in the axial and radial direction via the at least one radial rib and in the axially opposite direction via one or more shoulders in the region of the combustion trough on the outer contour of the inner component, so that the cavity liquid or gas tight is closed. By this method, in comparison to known methods simpler and more economical way a two-piece piston can be provided, which has both a high bending stiffness and has optimal thermal conduction properties. Due to the high bending stiffness, the game can be between

Keep the piston running surface and cylinder liner in the optimum range and thus reduce the friction between them. Together with the good heat conduction properties, it is thus possible to produce a piston with a long service life. In addition, a lower overall height is possible because no separate fixing elements such as screws are necessary and no minimum dimension for a treatment of the cooling cavity (cooling channel) must be observed. Finally, there are no elaborate or narrow process parameter window having process steps for the formation of a said Characteristics possessing piston necessary. Dangers of scale or similar foreign bodies remaining in the cooling cavity due to processing are avoided.

It is preferred for certain applications that the joining of the outer component to the inner component is performed such that no axial displacement between inner component and outer component is possible. This is particularly advantageous for applications in which a particularly high flexural rigidity is required, which absorbs both thermal and mechanical loads. Although the mechanical loads that occur in the axial direction, for example, due to particularly high mass or other mechanical forces are generally higher than the thermal loads that occur in the radial direction, so also thermal loads in the radial direction can be cleanly absorbed and derived ,

According to an alternative embodiment of the method according to the invention, the joining of the outer component to the inner component is carried out such that an axial displacement between inner component and outer component is possible to compensate for thermally induced expansion differences. It can be so targeted tolerances between the two components are introduced, for example, between the shoulder (s) of the inner component and the combustion chamber trough corresponding inner contour of the outer component.

The joining is preferably a defined circumferential bending, flanging, folding, pressing or clamping process. These joining methods are inexpensive to carry out and easily achieve the necessary joining forces. Depending on the desired properties of the finished piston may be advantageous that the joining takes place in the cold, semi-warm or warm state. In this way, an optimal joining process and thus an optimal mechanical and thermal connection of the piston components can be ensured in function of the selected materials of the respective components.

It is particularly advantageous that targeted biases are introduced in the radial, tangential and / or axial direction during joining. The bias voltages can specifically increase the strength of the connection between the components and improve the mechanical power transmission and the thermal conductivity of the piston. Thus, the life of the piston can be positively influenced.

In the method according to the invention, additional joining elements that are positive, positive or material fit can preferably be used, thereby reinforcing the bond between the inner and outer components.

In an advantageous embodiment of the method, the annular grooves are introduced into the outer component and / or the Pleuelbolzenbohrung in the inner and outer components after joining. In this way, damage to the grooves or holes during joining are avoided.

It is particularly preferred that the inner component is drilled prior to joining and the outer component is pressed by the joining in the bore of the inner component, so that additional force or positive connection is formed. Brief description of the drawings

In the following, embodiments of the piston according to the invention and the method according to the invention will be described with reference to the attached drawings, in which

Fig. 1 is a sectional view of a first embodiment of the invention showing in the left half a piston according to the invention before joining and in the right half after joining, wherein no connecting rod hole was drilled prior to joining; and

Fig. 2 is a sectional view similar to Fig. 1, in which the connecting rod hole was drilled prior to joining.

Ways to carry out the invention

In Fig. 1 is a sectional view of a first embodiment of a composite piston in which the left half of the figure shows the initial state of the piston before joining and the right half of the figure shows the joined state of the piston. FIG. 1 also illustrates a first embodiment of the method according to the invention for producing a piston for internal combustion engines, in which no connecting rod bore is introduced before the joining step. As can be seen from the left half of the figure, in the initial state, before joining, the inner component 1 of the piston is inserted into the outer component 2, the inner diameter D of the flange 5 of the inner component 1 substantially corresponding to the inner diameter of the outer component 2. In essence, it is to be interpreted here that the diameter D of the flange 5 is equal to the inner diameter of the outer component 2, except for manufacturing-related tolerances or specifically introduced clearance. The diameter D must also be chosen so that a easy insertion of the inner to the outer component is possible.

The inner component 1 has at its combustion chamber end end a circumferential shoulder 6 and a central shoulder 7, which face the inner contour of the combustion bowl of the outer component 2. Between the flange 5 and the shoulder 6 of the inner component 1 and the inner contour of the outer component 2, a circumferential cavity 3 is formed, which is adapted to receive a Kuhlmittels such. Ol, will serve. In addition, between the shoulders 6, 7 and the inner contour of the combustion bowl a further cavity 4 is formed, in which also Kuhlfluid can circulate. The cavities 3, 4 are supplied by Kuhlfluid not shown here channels in the inner component 1.

As shown in the right half of Figure 1, the Schäftwandung of the outer component 2 are pressed around the flange 5 of the inner component 1 and simultaneously the inner contour of the combustion bowl of the outer component 2 against the shoulders by the joints, here a clamping operation with a known device 6, 7 of the inner component 1 printed. Thus, both an axial and radial adhesion between the inner and outer components is achieved and the cavities 3, 4 closed gas and liquid-tight.

In the above-described embodiment of the inventive method, the annular grooves and Pleuelbolzenbohrung are introduced only after the joints, so that in particular the annular grooves can not be damaged by the joints.

According to a second embodiment of the method according to the invention, the connecting rod bore 8 is introduced into the inner component 1 before the joints. In the following Fugevorgang then the shaft wall of the outer component 2 in the in pressed in the inner component 1 Pleuelbolzenbohrung. The pushing in can however also be carried out by a special procedure, eg by means of a punch. In this way, an additional support is provided by the depressed into the connecting rod bore 8 bore flanges 9 of the outer component 2 and increases the mechanical strength of the positive and / or non-positive connection of the piston components 1 and 2.

Claims

claims

A piston for internal combustion engines with a compact inner component (1), which forms the interior of the piston skirt and the piston head, and a sleeve-shaped outer component (2), which forms the outer contour of the piston head with the combustion recess and ring carrier region and the piston shaft with the running surface and connecting rod bore, characterized in that the inner component (1) has at least one radial rib (5) with a dimension (D) which substantially corresponds to the inner diameter of the outer component (2), wherein the components (1) and (2) have a liquid or forming a gastight cavity (3) suitable for receiving cooling media, and the inner component (1) projecting over the flange (5) in the axial and radial directions and via one or more shoulders (6, 7) in the region of the combustion trough the axially opposite direction on the inner contour of the outer component (2) is supported.

2. Piston according to claim 1, wherein the at least one radial rib is formed as a circumferential flange contour whose dimension is given by its outer diameter.

3. Piston according to claim 1 or 2, characterized in that the at least one radial rib or the flange (5) is rotationally symmetrical.

4. Piston according to claim 1, 2 or 3, characterized in that at least one additional cavity (4) between the top of the inner component and the inner contour of the outer component (2) is formed, which is used for additional cooling of the piston head.

5. Piston according to one of the preceding claims, characterized in that the components (1) and (2) consist of different materials.

6. Piston according to one of the preceding claims, characterized in that between the or the shoulders (6, 7) defined tolerances are present.

7. A method of manufacturing a piston for internal combustion engines, comprising the steps of:

Inserting a compact inner component (1), which forms the interior of the piston skirt and the piston head, into a sleeve-shaped outer component (2), which forms the outer contour of the piston head with combustion recess and ring carrier region and the piston shaft with contact surface and connecting rod bore, wherein the inner component ( 1) at least one radial rib

(5) having a dimension (D) substantially equal to the inner diameter of the outer component

(2) and the components (1) and (2) form a cavity (3),

Joining the outer component (1) in the axial and radial direction via the at least one rib (5) and in the axially opposite direction via one or more shoulders (6, 7) in the region of the combustion trough on the outer contour of the inner component (2), so that the cavity (3) is liquid-tight or gas-tight.

8. The method of claim 7, wherein the at least one radial rib is formed as a circumferential flange contour whose dimension is given by its outer diameter.

9. The method of claim 7 or 8, wherein the joining of the outer component (2) on the inner component (1) is performed such that no axial displacement between inner component and outer component is possible.

10. The method of claim 7 or 8, wherein the joining of the outer component (2) on the inner component (1) is performed such that an axial displacement between the inner component and outer component is possible to compensate for thermally induced expansion differences.

11. The method according to any one of claims 7 to 10, wherein the joining is a defined circumferential bending, flanging, FaIt-, pressing or clamping operation.

12. The method according to any one of claims 7 to 11, wherein the joining takes place in the cold, semi-warm or warm state.

13. The method according to any one of claims 7 to 12, wherein the joining targeted bias voltages are introduced in the radial, tangential and / or axial direction.

14. The method according to any one of claims 7 to 13, wherein additional force, form or material-locking joining elements are used.

15. The method according to any one of claims 7 to 14, wherein the annular grooves in the outer component (2) and / or the Pleuelbolzenbohrung in the inner and outer components (1) and (2) are introduced prior to joining.

16. The method of claim 15, wherein the inner component (1) is drilled prior to joining and the outer component (2) is pressed by the joining in the bore of the inner component (1), so that additional force or positive engagement is formed.