FR2847314A1 - Automobile engine crankshaft comprises crank arm delimited by lateral faces and axial cylindrical sections delimited by convex machined surface delimiting annular connection zone and comprising stress discharge groove - Google Patents

Abstract

The crankshaft (10) comprises a radially extending crank arm (20) delimited axially by lateral faces (26) perpendicular to the rotational axis and cylindrical sections (12,14) extending axially from one lateral face. Theses cylindrical sections are delimited by a convex machined surface (34) which delimits, with the lateral face, an annular connection zone (30). The machined convex surface comprises a discharge groove (40) for mechanical stresses which are exerted in the connection zone adjacent to the groove.

Description

"Crankshaft of an internal combustion engine, especially of a vehicle

  automobile "The present invention relates to an engine crankshaft

  internal combustion, especially of a motor vehicle.

  Crankshafts are mechanical parts in the form of shafts which transform the reciprocating rectilinear movement of the piston-rod assembly

  of an internal combustion engine, in one rotation.

  Each type of crankshaft is dimensioned as accurately as possible in order to optimize the performance and size of the associated engine, and its shape and dimensions depend on the number of cylinders, the number of bearings, the stroke, the layout.

  cylinders and ignition order.

  The crankshaft is one of the most stressed parts of the engine, these torsional, bending, and torsional vibration stresses also involve fatigue resistance problems, as well as significant manufacturing constraints,

  particular for dimensional and geometric tolerances.

  The crankshafts can be made in several parts but they are most often made in one piece by forging or molding, and then undergo different operations

  including precise machining operations.

  The invention relates more particularly to a crankshaft of an internal combustion engine, in particular of a motor vehicle, comprising on the one hand crank arms extending generally radially and delimited axially by lateral faces generally perpendicular to the axis of rotation of the crankshaft and, on the other hand, cylindrical sections each of which extends axially from at least one lateral face of a crank arm and is delimited by a machined convex cylindrical surface which defines, with said lateral face

an annular connection zone.

  The cylindrical sections are either crank pins which the crankshaft comprises for the rotational mounting of a connecting rod, or journals which the crankshaft comprises for its mounting

rotating.

  When such a crankshaft is produced in a single piece, the annular zones of connection between the convex cylindrical surfaces s of the cylindrical sections, such as crankpins or trunnions, and the lateral faces of the crank arms have toroidal fillets so to allow among other things a machining of these convex cylindrical surfaces,

  without interference with the lateral faces of the arms.

  In addition, it has been determined that these connection zones and more particularly the zone around the machining toroidal leaves, is one of the zones of the crankshaft in which the

  mechanical stresses are the highest.

  The reliability and quality of the crankshaft therefore depend in part on the good fatigue life of the crankshaft in these

connection areas.

  An internal combustion engine crankshaft comprising a part from a forge in one piece and constituted by a cylindrical section, here a crank pin, secured to two crank arms, is for example described in the document.

EP-A-0679229.

  In this document, the crankshaft comprises, in the vicinity of the connection zones of the convex cylindrical surface of the crankpin with the lateral faces of the crank arms, on the one hand, machining toroidal fillets and, on the other hand, discharge chamfers which are made in the crank arms so as to reduce the mechanical stresses

  exercising in these crank arms.

  However, these discharge chamfers formed in the arms are distant from the connection zone with the convex cylindrical surface of the crankpin, or more precisely from the machining fillets in which the mechanical stresses are the highest and, therefore, they do not only slightly reduce

constraints in these areas.

  In addition, it is particularly difficult to be able to optimize the shape and positioning of these discharge chamfers because of their realization in the lateral faces of the

  crank arm, in areas difficult to access.

  The invention therefore aims to remedy the aforementioned drawbacks and to generally improve the reliability of a

  combustion engine crankshaft.

  To this end, the invention provides a crankshaft of the type described above, characterized in that the convex cylindrical surface machined of at least one section comprises at least one notch for relieving the mechanical stresses which are exerted

  in the connection area adjacent to the notch.

  Preferably, the position of the discharge notch is determined by calculation as a function of the parameters of the crankshaft and of the engine, as well as the maximum stresses exerted

in the connection area.

  Thanks to the relief notches according to the invention, the level of stress exerted in the areas of connection of the cylindrical sections is significantly reduced, that is to say of the crankpins and of the pins, which allows for the same resistance to fatigue d 'a crankshaft, to reduce the diameters of the cylindrical sections. Advantageously, this reduction in the diameter of the crankpins and / or of the trunnions is reflected on the one hand, by a reduction in friction which contributes to the improvement of engine performance and, on the other hand, by a reduction in the weight of the crankshaft and inertial efforts, which contributes to

  improving engine acoustics.

  According to other characteristics of the invention - the machined convex cylindrical surface of a section comprises at least one stress relief notch associated with each of the connection zones of the section with a side face of a crank arm; each discharge notch extends generally in a radial plane of the section; - The discharge notch is axially symmetrical with respect to the radial plane of the section; - the generator of the discharge notch is rectilinear - the generator of the discharge notch is circular, so as to constitute a radial groove; - The stress relief notch is treated in a physico-chemical manner, so as to reinforce the resistance to fatigue of the crankshaft; - The section is a crank pin that includes the crankshaft for the rotational mounting of a connecting rod; - The section is a journal that includes the crankshaft for its rotational mounting; - The stress relief notch extends angularly on either side of a plane, called the plane of maximum stresses. Other characteristics and advantages of the invention

  will appear on reading the following detailed description for the

  understanding of which reference will be made to the appended drawings in which: - Figure 1 is a side view of a crankshaft of an internal combustion engine with four cylinders; - Figure 2 is an axial sectional view along the plane 2-2 of Figure 1 which illustrates the relief notches of the mechanical stresses produced according to the invention, at the axial ends of a crankpin; - Figure 3 is a cross-sectional view along the plane 3 of Figure 1 of a portion of a cylindrical section which illustrates an alternative embodiment of a notch for relieving mechanical stress; - Figure 4 is a view similar to that of Figure 3, which illustrates another alternative embodiment of a notch

  discharge of mechanical stress.

  In the following description, we will use arbitrarily

  an orientation back and forth along the axis of rotation X-X of the crankshaft which corresponds to an orientation from left to right

considering figure 1.

  In Figure 1, the crankshaft 10 is more specifically a crankshaft for a four-cylinder engine which has five journals 12 which are located in the axis of the crankshaft and which allow the shaft to rest on bearings (not shown)

  by means of which it is rotatably mounted in a housing.

  The crankshaft 10 also comprises four eccentric crank pins 14 of axis Y-Y parallel to the axis of rotation of the crankshaft and

  on each of which is articulated a connecting rod (not shown).

  Trunnions 12 and crank pins 14 are therefore connected to each other by crank arms 20 still sometimes

called elbows.

  The crankshaft 10 also comprises four counterweights 22 in order to ensure the balance of the masses of the crankshaft relative to its axis of rotation with the four crank pins 14 and the eight arms

  which offset them from the axis of rotation of the crankshaft.

  Thus each crank pin 14 extends axially between two crank arms 20, as does each pin 12 which extends either between two arms 20 or between an arm 20 and a rear end section 13 of the crankshaft or a base 15

of the front end section 11.

  The crankshaft 10 is here of the type produced in one piece from a forge or foundry so that the connection zones 30 of the crank pins 14 and the pins 12 with the respective side faces 26 of the crank arms 20 include annular cylindrical fillets 32 to allow the machining of the convex cylindrical surfaces 34 of the crankpins 14

and pins 12.

  This crankshaft 10 comprises a cylindrical section of front axial end 11 and a cylindrical section of rear axial end 13 which are coaxial with the axis of rotation X-X of the crankshaft. The front section 11 is provided here to be mounted in the engine on the flywheel side, while the rear section 13 is provided here to be mounted in the engine on the distribution side, that is to say that the rear section 13 is designed to carry the drive pinion of the engine camshafts

(not shown).

  The front section 11 here advantageously forms a pin for centering the crankshaft 10 in a complementary hole that

  includes the flywheel (not shown).

  The crankshaft 10 also has at its front axial end 11, axially set back towards the rear relative to the front section, a base 15 which has the shape of a crown

cylindrical annular.

  This base 15 is designed to be in axial support, by its front transverse face, against the rear transverse face of the flywheel, so as to allow the flywheel to be fixed.

  to the crankshaft 10, for example by screwing.

  FIG. 2 is a view in axial section of a cylindrical section, such as a crank pin 14 or a journal 12 of the crankshaft, the machined convex cylindrical surface 34 of which comprises, in accordance with the invention, at least one relief notch 40 mechanical stresses exerted in the area of

  connection 30 adjacent to notch 40.

  According to a first embodiment, the machined convex cylindrical surface 34 of the cylindrical section, here a crank pin 14, comprises a stress relief notch 40 associated with each of the two connection zones 30 of the crank pin 14 with the lateral faces 26 of the two arms of

crank 20 adjacent.

  The connection zones 30 are here constituted more precisely by machining leaves 32, having in axial section a generally circular shape and around the periphery of which

  distribute the maximum mechanical stresses.

  Thanks to the relief notches 40, the mechanical stresses are distributed between the machining leaves 32 as before but also in the convex cylindrical surface, more

  precisely around the notches 40.

  The mechanical stresses are thus better distributed and the

  connection area 30 is less stressed.

  Parameters such as the length of the notch (1), the radial depth (e), the axial distance (d) between the notch 40 and the toroidal leave 32 for its axial positioning on the convex cylindrical surface 34, as well as the shape or profile of the notch are obtained by calculation and directly function of other

  parameters such as engine type.

  Preferably, each discharge notch 40 extends generally in a radial plane to the convex cylindrical surface

  34 and symmetrically on either side of this plane.

  As illustrated in Figures 3 and 4, the shape of the notch 40

  may be different depending on the application.

  Thus, FIG. 3 illustrates an alternative embodiment according to which the generator of the stress relief notch 40 is rectilinear, while FIG. 4 illustrates another variant according to which the generator is circular so as to

  constitute an angular section of a radial groove.

  Alternatively, the relief notches 40 are grooves

cylindrical annulars.

  Of course, for better fatigue resistance, the stress relief notches 40 can advantageously undergo treatments, such as physico-chemical treatments, in particular with a view to strengthening them, as well as

  the crankshaft in general.

  As will be understood, the stress relief notches 40 can be made indifferently in the

  crank pins 14 and / or pins 12 of crankshaft 10.

  In the case of a crank arm comprising axially on either side two sections, for example a crank pin and a journal, and for which relief notches 40 are produced in the crank pins 14, the maximum stress plane is a plane passing through the axis of the crankpin and forming an angle (a) with the plane passing through the respective axes of the two sections, the value of this angle (a) being a function of the type of engine. In the case of a crank arm comprising axially on either side two sections, for example a crank pin and a journal, and for which relief cuts 40 are made in the journals 12, the maximum stress plane is a plane passing through the axis of the journal and forming an angle (/ 3) with the plane passing through the respective axes of the two sections, the value of this angle (, 8) being a function of the type of engine. Depending on the type of crankshaft, the angle (, /) may be different

of angle (a).

  Of course, the invention applies to any type of crankshaft 10, whatever the engine, for example an in-line or V-cylinder engine.

Claims (10)

  1. Crankshaft (10) of an internal combustion engine, in particular of a motor vehicle, comprising on the one hand crank arms (20) extending generally radially and delimited axially by lateral faces (26) generally perpendicular to the axis of rotation of the crankshaft (10) and, on the other hand, of the cylindrical sections (12, 14) each of which extends axially from at least one lateral face (26) of a crank arm (20) and is delimited by a machined convex cylindrical surface (34) which defines, with said lateral face (26), an annular connection zone (30), characterized in that the machined convex cylindrical surface (34) of at least one section ( 12, 14) comprises at least one relief notch (40) for the mechanical stresses which are exerted in the connection zone (30) adjacent to the notch (40).   2. Crankshaft (10) according to claim 1, characterized in that the machined convex cylindrical surface (34) of a section (12, 14) comprises at least one relief notch (40) of the stresses associated with each of the zones of connection (30) of the section (12, 14) with a lateral face (26) of an arm crank (20).   3. Crankshaft (10) according to claim 1 or 2, characterized in that each discharge notch (40) extends   generally in a radial plane of the section (12, 14).   4. Crankshaft (10) according to claim 3, characterized in that the discharge notch (40) is axially symmetrical by   relative to the radial plane of the section (12, 14).   5. Crankshaft (10) according to claims 3 or 4,   characterized in that the generator of the discharge notch (40) is straight.   6. Crankshaft (10) according to claims 3 or 4,   characterized in that the generator of the discharge notch (40)   is circular, so as to constitute a radial groove.   7. Crankshaft (10) according to any one of   previous claims, characterized in that the notch of   stress relief (40) is treated in a physico-chemical manner, so as to reinforce the fatigue strength of the crankshaft. 8. Crankshaft (10) according to any one of   previous claims, characterized in that the section is   a crankpin (14) that includes the crankshaft for mounting to rotation of a connecting rod.   9. Crankshaft (10) according to any one of   previous claims, characterized in that the section is   a journal (12) that includes the crankshaft for its rotational mounting. 10. Crankshaft (10) according to any one of   previous claims, characterized in that the notch of   stress relief (40) extends angularly on both sides and   on the other side of a plane, said plane of maximum stresses.