Thrust washer

Abstract

A thrust washer for an internal combustion engine may include a metal base having a contact surface and a slip surface. The contact surface may be in operative communication with an engine block. The slip surface may define at least one ramp section, at least one flat horizontal section, and at least one oil channel. The ramp section and the flat horizontal section may be connected via an asymptotic curved surface. The ramp section may be positioned asymptotically towards the flat horizontal section.

Claims

1. A thrust washer for an internal combustion engine comprising: a metal base having a contact surface and a slip surface, the contact surface in operative communication with an engine block, and the slip surface defining at least one ramp section, at least one flat horizontal section, and at least one oil channel; and wherein the at least one ramp section extends asymptotically towards the at least one flat horizontal section and is connected thereto such that a transition between the at least one ramp section and the at least one flat horizontal section defines an asymptotic curved surface.

2. The trust washer of claim 1, wherein the contact surface defines a uniform flat profile without interruption.

3. The thrust washer of claim 1, wherein the metal base has a semi-circumferential shape.

4. The thrust washer of claim 1, wherein the metal base has an inner circumferential surface and an outer circumferential surface interposed between the contact surface and the slip surface.

5. The thrust washer of claim 1, wherein the slip surface has a uniform surface profile free of points of inflection and vertices in the transition between the at least one ramp section and the at least one flat horizontal section.

6. The thrust washer of claim 1, wherein the asymptotic curved surface defines a constant curve that is smoothly concordant connecting the at least one ramp section to the at least one flat horizontal section.

7. The thrust washer of claim 1, wherein the at least one ramp section extends between the at least one oil channel and the at least one flat horizontal section, and wherein the at least one ramp section defines the asymptotic curved surface where the at least one ramp section starts at the at least one oil channel with an inclination of an asymptotic curve and continues asymptotically towards the at least one flat horizontal section.

8. An internal combustion engine comprising: at least one thrust washer including a metal base having a contact surface and a slip surface, the contact surface in operative communication with an engine block, and the slip surface defining at least one ramp section, at least one flat horizontal section, and at least one oil channel; wherein the at least one ramp section extends asymptotically towards the at least one flat horizontal section and is connected thereto via an asymptotic curved surface, and wherein the asymptotic curved surface defines a constant curve between the at least one ramp section and the at least one flat horizontal section.

9. The internal combustion engine of claim 8, wherein the constant curve of the asymptotic curved surface is smoothly concordant without points of inflection and vertices.

10. The internal combustion engine of claim 9, wherein the contact surface has a uniform flat profile without interruption.

11. The internal combustion engine of claim 8, wherein the at least one ramp section extends between the at least one oil channel and the at least one flat horizontal section, and wherein the at least one ramp section defines the asymptotic curved surface where the at least one ramp section starts at the at least one oil channel with an inclination of an asymptotic curve and continues asymptotically towards the at least one flat horizontal section.

12. A thrust washer for an internal combustion engine comprising: a semi-circumferential shaped base having a contact surface, a slip surface opposite of the contact surface, an inner circumferential surface, and an outer circumferential surface; and wherein the slip surface defines a uniform surface profile including at least one ramp section and at least one flat section connected via a transition surface having an asymptotic curved profile.

13. The thrust washer as set forth in claim 12, wherein the slip surface further includes at least one oil channel.

14. The thrust washer of claim 13, wherein the at least one ramp section is disposed between the at least one oil channel and the at least one flat horizontal section, and wherein the at least one ramp section extends asymptotically from the at least one oil channel towards the at least one flat horizontal section.

15. The thrust washer as set forth in claim 12, wherein the base is composed of a metal.

16. The thrust washer of claim 12, wherein the asymptotic curved profile of the transition surface defines a constant curve that is smoothly concordant without points of inflection and vertices.

17. An internal combustion engine comprising: a cylinder block; at least one cylinder positioned within the cylinder block; at least one cylinder head positioned above the at least one cylinder; a crankshaft in operative communication with the at least one cylinder, wherein the crankshaft is mounted in the cylinder block via at least one bearing; a first thrust washer arranged adjacent to an upper portion of the at least one bearing and a second thrust washer arranged adjacent to a lower portion of the at least one bearing; the first thrust washer and the second thrust washer each including a semi-circumferential shaped base having a contact surface lying against the cylinder block, a slip surface opposite of the contact surface, an inner circumferential surface, and an outer circumferential surface; the slip surface having a uniform surface profile; and wherein the slip surface includes at least one oil channel, at least one flat horizontal section, and at least one ramp section extending between the at least one oil channel and the at least one flat horizontal section defining an asymptotic curved profile, and is in indirect contact with an axial facing surface of the crankshaft.

18. The internal combustion engine of claim 17, wherein a distance between the slip surface and the axial facing surface of the crankshaft is at least three times greater than a surface roughness of the slip surface.

19. The internal combustion engine of claim 17, wherein the asymptotic curved profile of the at least one ramp section defines a constant curve that is smoothly concordant without points of inflection and vertices.

20. The internal combustion engine of claim 19, wherein the contact surface has a uniform flat profile without interruption.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) This invention will be described more particularly below on the basis of an embodiment illustrated in the drawings. The drawings show:

(2) FIG. 1-a perspective view of a thrust washer together with all its constituent parts;

(3) FIG. 2-a front view of the thrust washer according to this invention;

(4) FIG. 3-a detailed view of a cross-section B-B in FIG. 2;

(5) FIG. 4-a comparative graph of the hydrodynamic pressure generated by thrust washers according to the state of the art and according to this invention;

(6) FIG. 5-a comparative graph of the hydrodynamic pressure generated by thrust washers according to the state of the art and according to this invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(7) This invention relates to a thrust washer 1 for internal combustion engines provided with a metal base comprising at least one slip surface 3 having a uniform surface profile without points of inflection or vertices.

(8) As already mentioned in the state of the art, thrust washers 1 are components which help mount the crankshaft in the block of an internal combustion engine, and are responsible for withstanding the axial loads generated by the gearing or gear change system.

(9) As may be seen in FIG. 1, thrust washer 1 is provided with a metal base, substantially of semi-circumferential shape, and comprises two surfaces. Contact surface 2 is associated with the engine block, and there is no relative movement between washer 1 and the block, while slip surface 3 remains in contact with the crankshaft, generating a relative movement between washer 1 and the crankshaft. Depending upon the applied load, the relative movement places a high load on the contact between slip surface 3 and the crankshaft, while slip surface 3 is responsible for supporting the axial load generated. In addition to this, thrust washer 1 also comprises a diameter for association with the bearing, and at least one oil channel 6.

(10) In order for washer 1 to support the loads generated an oil film must be formed between slip surface 3 of washer 1 and the crankshaft. This oil film must maintain a thickness and is produced by means of a phenomenon known as hydrodynamic support. This hydrodynamic support depends on two factorsthe shape of the surface and the rotation speed of the crankshaft.

(11) Washer 1 is said to maintain hydrodynamic support when there is no metal-to-metal contact, that is there is a distance between the surfaces, this distance being the thickness of the oil film.

(12) In order to have sufficient hydrodynamic support, a specific rotation speed has to be ensured, and the best surface possible for this condition also has to be guaranteed. As the rotation speed varies according to the speed of the vehicle, the surface of the slip surface has to be altered so as to achieve sufficient support to support high loads and axial forces.

(13) In this respect this invention provides a preferred configuration for thrust washer 1 in FIGS. 2 and 3, comprising a surface profile of slip surface 3 incorporating at least one ramp section 4, at least one flat horizontal section 5 and at least one oil channel 6, ramp section 4 and flat horizontal section 5 being connected by means of an asymptotic curve.

(14) Ramp section 4 starts with the inclination of the curve and tends asymptotically towards flat horizontal section 5. This means that ramp section 4 and flat horizontal section 5 are connected through a constant curve which is smoothly concordant, eliminating possible points of inflection or vertices in the connection.

(15) As explained previously in the state of the art, the presence of points of inflection or vertices in the connection between ramp section 4 and flat horizontal section 5 results in a change in the behaviour of the oil pressure, giving rise to instability in the hydrodynamic support of washer 1.

(16) Thus this invention provides a thrust washer 1 which ensures more uniform hydrodynamic support, cancelling out the transitional effects produced by points of inflection or vertices.

(17) This more uniform hydrodynamic support means that there is no metal-to-metal contact between slip surface 3 and the crankshaft, ensuring a distance between the surfaces or an oil film thickness at least three times the surface roughness.

(18) Furthermore washer 1 according to this invention is less influenced by the dimensional tolerance of the surface. The tolerance in the angle of the straight ramp represented in the state of the art affects the result of hydrodynamic support and load support. Change in the tolerance in washer 1 according to this invention has less effect on these properties.

(19) Viewing FIG. 4, the influence of the surface profile of slip surface 3 in relation to the angular position of that surface 3 in connection with the oil pressure maintained on that surface can be seen. In addition to this FIG. 5 shows the profile of slip surface 3 produced in accordance with the angular position of surface 3.

(20) State of the art 1 shows a surface profile for a convex washer, while state of the art 2 shows the surface profile for a ramp-and-pad washer provided with a straight ramp.

(21) Examining FIGS. 4 and 5, it will be concluded that the surface profile of slip surface 3 provided by this invention gives rise to a smaller oil pressure, but with greater hydrodynamic support and a thicker oil film.

(22) In view of the above, thrust washer 1 according to this invention offers an increase in the maximum supported load, increased wear resistance and, as a consequence, excellent performance.

(23) Although a preferred embodiment has been described, it should be understood that the scope of this invention covers other possible variations, being limited only by the content of the appended claims, including possible equivalents therein.