FR2610987A1 - CAME FOR CONTROLLING A LOAD CHANGE VALVE OF AN ALTERNATIVE PISTON MACHINE - Google Patents

Abstract

THE INVENTION RELATES TO A CAM USED FOR THE CONTROL OF A LOAD CHANGE VALVE OF A MACHINE WITH ALTERNATIVE PISTONS. IN THIS CAM WHICH INCLUDES A RISING SIDE 5, A SENDING SIDE 9 AND A POINT ZONE WITH A SLIDING SURFACE TRUNCON 7 CONNECTED BY JUNCTIONS 6, 8 TO THE SAID SIDES, THIS SECTION 7 MAKES A DIFFERENT SS ANGLE OF 90 WITH A GENERATOR 10 FROM THE ANGLE ENCLOSED BY A RIGHT PASSING JUNCTION 6 AND THE CAM ROTATION AXIS 2 AND A RIGHT PASSING THROUGH JUNCTION B AND AXIS 2, AND THE DISTANCE BETWEEN JUNCTION 6 AND AXIS 2 IS GREATER THAN THE DISTANCE BETWEEN JUNCTION 8 AND AXIS 2. APPLICATION ESPECIALLY TO INTERNAL COMBUSTION ENGINES.

Description

The invention relates to a cam used for controlling the change of

  load in a reciprocating piston machine, via an actuating member

  having a sliding surface having a predetermined contour

  mined, and having a rising edge, a descending flank and

  a pointed zone, which has a surface segment of sliding

  which reduces to a minimum value the acceleration, which appears, of the valve on a predetermined rotation angle of the cam and is connected to the rising edge, at a first junction, and is prolonged by the downward flank at

level of a second junction.

  Figures 4 and 5 of the German patent application

  published under No. 375,652 represent what is called an "enlarged cam", in which the tip area of the cam

  is in the form of a sliding surface element

  (circle of rest) which is inserted between a steep rising flank and a sloping downward flank and which is concentric with the base circle of the cam. It is thus necessary to realize the rising of a

  valve over a relatively long stroke of

  te and therefore obtain a performance coefficient relative to

elevated.

  But precisely the flat area of the tip of the cam produces a deleterious effect and this especially when the

  internal combustion engine operates in ranges of over-

  speeds (for example as a result of a driving error as well

  that in the case of a switching fault or a function

  motor brake). In these operating states

  the forces produced by the masses of

  Valve control valves become

  these valve springs acting against the forces

  previous, so that an actuating member of a valve

  eg a pusher, a rocker arm, actuated by the cam, already begins to move away from the descending side of the cam, during the sliding on this side and follows a trajectory of

  ballistic flight. If this actuating member of the valve

  against the cam again after this phase of flight, this is

  fectue in a constant stroke zone of the cam (circle

  of rest), which gives rise to extremely

  tense, which can lead to damage to

  of the valve and have a triggering effect.

oscillation.

  This is why the invention aims to create

  a cam of the type indicated above, the use of which

  to guarantee a high degree of security against damage

  ments, conditioned by overspeeds,

  valves and in addition a high degree of efficiency.

  This problem is solved according to the invention

  thanks to the fact that the section of the sliding surface

  intersects at an angle other than 90, an imaginary bisector

  the angle formed by a straight line passing through the first junction and the axis of rotation of the cam, and another line

  passing through the second junction and the axis of rotation of the

  me, and that the distance between the first junction and the axis of

  rotation of the cam is greater than the distance between the

  conde junction and the axis of rotation of the cam.

  When the actuating member of the valve meets the sliding surface of the cam after the phase

  all control elements of the valve are

  awarded because of their elasticity. During this process of

  compression, the cam continues to rotate on a rotational angle

  determined. The arrangement according to the invention of the cam

  or section of the sliding surface, on which the

  the actuating cam may be applied during override

  speeds, during this compression phase, the stroke of the cam is continuously reduced so that a part of the impact energy is absorbed by the cam,

  that is to say that the shock of the actuating member of the sou-

  Pope is amortized. The elastic control elements of the

  pope therefore undergo reduced compression and are

  therefore subject to a lower stress.

  The damping action during the impact has the effect that a new elastic deflection during the

  next flight phase occurs only to a reduced degree.

  Since the cam has a slip surface section which minimizes the acceleration of the valve, thereby obtaining an extension of the curve

  the valve lift, here too it is possible to obtain

  of valves on long lengths of colrses and thus obtain high degrees of efficiency, without

  to increase the maximum stroke of the valve for this purpose.

  The regularity of the junctions connecting the-

  said section of sliding surface to both sides of the

  cam prevents the occurrence of abrupt changes in

ration in these locations.

  Other features and advantages of the pre-

  invention will be apparent from the description given hereinafter

  reference is made to the accompanying drawings, in which: - Figure 1 shows a cross section of a cam according to the invention;

  FIG. 2 represents, in the form of a dia-

  gram hN = f (<), or hv = f (4), the valve lift (hN stroke of the cam) predetermined by the cam geometry, and the

  valve lift hv, which is actually obtained, as a function of

  angle of rotation C of the cam; and

  FIG. 3 represents, in the form of a dia-

  gram hN = f (C), the acceleration hN of the valve, predetermined

  born by the geometry of the cam, depending on the angle M of

rotation of the cam.

  FIG. 1 shows a control cam 3, which rotates in the direction of the arrow 1 about a fixed axis 2, of a not shown pressure change valve and having a base circle of radius rG. At the base circle 4 is connected a rising edge 5 of the cam which extends, at a junction 6, by a section 7 of sliding surface, which is bent so that the acceleration obtained from the valve during the course of this section 7

  is zero (see also Figure 3). At this section 7 of

  sliding face is connected, at the location 8, a falling edge 9 of the cam which is ultimately extended by the base circle 4 of the cam.

  The section 7 of sliding surface is inclined

  born in the direction of the downward flank 9, in which case it intersects the bisector 10 of the angle formed by the two straight lines 11 and 12 (straight line 11 passing through the axis 2 and the junction 6, straight line 12 passing through the axis 2 and the junction 8), at an acute angle f (r corresponds to the angle between the tangent 13 at point 14, at which the section 7 of the sliding surface intersects

  the bisector 10 of the angle). Junction 6 therefore forms

  the tip of this asymmetrical cam 3.

  In order to avoid sudden variations in

  celeration at the two junctions 6 and 8, the latter

have a regular outline.

  Figure 2 shows, in the form of a dia-

  gram 15, the relation between the stroke hN of the cam and the

  <cam rotation, as a characterization of the set value hN, predetermined by the geometry of the cam, for the lifting of the valve and further represents the relationship between the actual lifting hV of the valve and the angle (of rotation of the cam, in which case to simplify, we did not represent the zone, in which the base circle 4 of

  the cam 3 ends, since then the race of the sou-

  Pope is nil. The different zones 5, 7 and 9 of the sliding surface are characterized on the diagram by the

  same reference numerals as in Figure 1.

  In the case of the possible appearance of

  speeds, an actuating member of the valve actuated by

  the cam according to the invention can deviate from the vertical flank

  both of the cam already during the course of this flank and following

  a ballistic flight path (a line of dashes

  16), which means that then the actual lifting hv of the sou-

  pape is greater than the set value hN predetermined by the geometry of the cam. After this flight phase, the actuating member of the valve can be applied again on

  the cam, inside the section 7 of the sliding surface

  ment. Due to the action of forces due to the masses,

  control elements of the valve, such as, for example, the

  evening, the pusher tail, the rocker arm and the valve stem, are deformed so that during this time interval, the actual lifting hV of the valve is less than

  the set value hN (zone 22, in which the curve

  dashes are located below the curve of the race

  of the cam). But since the meeting of the leverage

  the valve is carried out in a section in the

  which the stroke hN of the cam decreases according to a function li-

  (no acceleration of the valve), the shock of this

  is damped, and therefore also after the new elastic deflection of the compressed valve control elements, a new spacing of the actuating lever of the valve relative to the sliding surface of the cam

  only occurs in a weakened way.

  The associated variation of the hN acceleration of the

  valve, predetermined by the geometry of the cam, is

  shown in the diagram 17 reproduced in FIG. 3: hN = f ().

  Here also the designations of the zones correspond to those of FIG. 1. Section 7 does not have to be necessarily arranged in the form of a zone with zero acceleration, since an extension of the length of the lift stroke of the valve is also still obtained, in the case of a

  variation of acceleration according to curve 18

  a dashed line in Figure 3, by

  also occur in the case of a negative acceleration, which

  still appears to a small degree. It suffices that one is satisfied

  the condition that respectively in the zones

  to the left and to the right of the point 6 of the cam, the sum of all the areas delimited between the curve hN = f (C) and the abscissa axis 21 and situated below this

  axis of the abscissae (negative acceleration) is equal to

  me such surfaces located above the x-axis 21 (positive accelerations). Naturally, an acceleration that still appears to a small degree in zone 7 presupposes

  in the diagram of variation of the lifting of the sou-

  pape hN = f (ô) (Figure 2), in zone 7, a curve shape

  minimum convex curvature (dashed line 18 on the

  gure 2), that is to say that the sliding surface of the cam (FIG. 1) is a little more strongly curved in section 7, but the associated representation has not been given on the

  Figure 1, to keep the clarity of the drawing.

Claims (2)

  1. Cam used to control the change   load in a reciprocating piston machine, through the   an actuator having a sliding surface having a predetermined contour, and having a   rising edge (5), a falling edge (9) and an area   te, which has a sliding surface section (7) which reduces to a minimum value the acceleration, which appears, of the valve at a predetermined rotation angle of the cam and is connected to the rising edge (5), at the a first junction (6), and is extended by the falling edge (9) at a second junction (8), characterized in that the section (7) of the sliding surface intersects at an angle   () different from 90, an imaginary bisector (10) of the   gle formed by a straight line (11) passing through the first junction (6) and the axis (2) of rotation of the cam, and another straight line   (12) passing through the second junction (8) and the rotational axis (2)   of the cam, and that the distance between the first junction (6) and the axis (2) of rotation of the cam is greater than the   distance between the second junction (8) and the rotational axis (2). the cam.   2. Cam according to claim 1, characterized   in that the two junctions (6, 8) have a regular shape.