US2567690A

US2567690A - Cam for operating valves of internal-combustion engines

Info

Publication number: US2567690A
Application number: US57873A
Authority: US
Inventors: John L H Bishop; John H Weaving
Original assignee: Austin Motor Co Ltd
Current assignee: Austin Motor Co Ltd
Priority date: 1947-11-08
Filing date: 1948-11-02
Publication date: 1951-09-11
Anticipated expiration: 1968-09-11

Description

p 1951 J. H. BISHOP ET AL 2,567,690

CAM FOR OPERATING VALVES OF INTERNAL-COMBUSTION ENGINES Filed Nov. 2, 1948 2 Sheets-Sheet 1 Y I l "I JIQ "if. 7 Z

.S Q Z M INVENTORS JOHN LESLIE HUNTHOLD BISHOP JOHN' HAROLD WEAVING ATTORNEY Sept, 11, 1951 J. L. H. BISHOP ET AL CAM FOR OPERATING VALVES OF INTERNAL-COMBUSTION ENGINES Filed Nov. 2, 1948 2 Sheets-Sheet 2 I a e I 6 0 50 032" 26 J2 I H 2. I my 5.

I X Z INVENTORS JOHN LESLIE HUNTHOLD BISHOP JOHN HAROLD WEAVING ATTORNEY PatentedSept. 11, 1951 oAM 110 .QPERATING vALve s -OF INTERNAL-.GOMBUSEIONLENGINES F'J-bhnL. HfBishopfilorthfifd,Birrningliatm,"and

JohniHfWeaving-gMoseley, 'BirniinghamfEngland, assign'orstto'lThe AustiniMotor iGompany -I'Limited,1:Northfield, Birmingham,l'England rampand -thus avoid the obvious disadvantages of a longramp. In'an ordinary eam it is quite usual toarrange curves-=50-that theifirst small -"parts'of :the lift, which is "from the -clearance "circle to the hese oirtle, "for taking up -tappet z'clearance, "takes theiform of: a constant eccen- I tricity ramp on the opening side and a similar 'zra'mp :on "the "closing side, "the two *slopes bein'g,

ihowever, :often :made unequal. "The slope "of :the ceopening tramp :determines :the velocity' at :which the valve will'ibe lifted off its "seat an'd' the irclosing ramp its seating velocity; the slope also :determines the actual :opening period Of the -1va1lves. :It :will :therefore be apparent that -a :-"slope I of Y less inclination improves the :valve seating conditions but wouldi'have the disadvantage of increasing the openin :period and causing the Waive i110 sopen itoo f-soon.

It is quite :common ithat an 'opening ramp smay havesar'lengthiofsapproximately?30 degrees f the :camshait rotation, rthe :first 2 degrees 'ro'f lift "being :efiected "by an :eccentric firadiu's to .za'ccelerate athe -.tappet xfrom :zero jvelooityxtoithe ,tconstant velocity-20f the remainder of the ramp.

\ *Inaa :ramp designed iin raccorldanoe with Ithe present invention,:afterYefiecting-LtabDut the firsti2 idegrees :.of; lift :hy can :eccentri'c :radius :to impart a-melocity to the 'tappet cof approximately ihfllf that produced :Lby w the usual-'constantzeccentricity r-amp,sthe :next I'or -amain :part "of :th'e' ramp, isay 226 "degrees :of t'camshaft notation, is represented uby'ztheiiull L period :of -:a negative "sine :cur-ve combined' withian fiascen'ding =straight line curve, the combined tcurve ending :preferably in a straight dine :curvetof approximately .6 degrees of namesha'ft v rotation, and "the inclination of :this lat :ter straight line acur-ve is xlpreferably"arranged to tbe approximately ihalf that of the :usual :contstant eccentricity ramp.

:3 Claims. ((31:123-90) The-invention isexplained by-referenoe to the accompanying "drawings *of which F-igure 1' is a somewh-atdiagrammatic viewdf a "cam *df -convention'a1 form. v i

Figures -2, 3' and =4 illustrate, respectively, '-the lift= curve; velocity curve and accelerationcurve "of an-opening ramp of the conventional or '-'usual for-ms.

Figures 5, "6 and '7 "illustrate, respectively, the lift curve, velocity curve and acceleration curve "of an opening ramp "designed in accordance with the invention.

Figure 8=isa somewhat diagrammatic detail Wiew to illustrate a specialform' of spring loaded tappet used with the cam;

Referring first to 'Figure ljA indicates the 'usual base circle'o'f' the cam' shownby a'chain line; and B theusual clearancecircle- Ihe part' of'the cam-surface between C and Dis theopening 'ranip during which the tappet is lifted from tlie clearance circle" B i to the base circle A, to takeup 'valve'clearance. The-part of thecam surfacelietWeen -Ean'd F -is the 'clo'singramp.

"Referring to Figure 2, which illustrates the lift curveof an openingramp of conventional form, the lift is measured along the vertical ordinate y and the angle of rotation 0f the cam is 'measured along the horizontal ordinates #It will be seen that, for the first 2'degrees; the'ltappet is lifted with increasing velocity-while between 2 degrees and 30 degrees it is lifted at constant velocity.

Referring to Figure 3, which is the -v'eloeiiiy -"curve"--the velocity is measured along the vertieal ordinate 1/. It 1 will he seen 'that between i O a'n'd Z degrees'the velocity increases -constaritly, and that between 2 degrees and -30 '-degrees the "velocity remains constant. r Referring to Figure 4 in which aeceleration is me asured' alongthe 'verticalprdinate 'y,iit'-will be seen that, between 0 and? degrees, the acceleraztion first rises instantly ".to maximum "value and then remains-constant, and 'that-at-Z degrees it -falls instantly to zero value. Between "2 'de-" grees and-"30 degrees it remains at zero'valu'e.

"The sudden changes in velocity 'andiacceleration are objectionable "andtend to noisy operation.

Referring to :ZEigure '5 which. illustrates the lift "curve of :a ramp designed according to this imvention it willibe seen that between :0 degrees and 2 degrees the tappet is lifted for a very short distance at increasing velocity, and that between 2 degrees and 26 degrees it rises in accordance with a full negative sine curve plotted on an ascending straight line G, H. Between 26 degrees and 32 degrees the shape of the ramp is represented by line H, J. The valve clearance is arranged so that the valve is lifted from its seat at some point on the line H, J The velocity of the valve on opening will be in accordance with degrees and 32 degrees the velocity remains.

constant to the end of the ramp.

Referring lastly to Figure 7, which is the second derivative of the lift curve it will be seen that, at degrees, the acceleration rises instantly to a maximum but only to a relatively small value, that it remains constant between 0 degrees and 2 degrees and falls instantly at 2 degrees to zero value. Between 2 degrees and 26 degrees the acceleration curve varies in accordance with a full positive sine wave. Between 26 degrees and 32 degrees it remains constant at zero acceleration to the end of the ramp F.

'It will be seen, by reference to Figures 5 and 6, that there are no violent changes in the curves, and that in Figure '7 the curve makes no violent change except the small sudden change at the beginning of the ramp.

Referring to the sine curve combined with an ascending straight line curve shown in Figure 5,. it is the slope of the straight line curve which determines the actual total lift of the tappet over the full period of the sine curve. By suitable choice of the slope of the ascending straight line curve, it can be arranged that, at the end of the period of the sine curve, the actual lift could be the same amount as that obtained with a common constant eccentricity ramp, and yet ending with a much less velocity.

' The closing ramp may have the same features as the opening ramp but in the reverse order.

In a ramp designed as above described it will be apparent that, provided the tappet is maintained in contact with the ramp, the motion of the tappet is harmonic. Furthermore the. main part of the velocity curve will be a full negative co-sine curve and the main part of the acceleration curve will be a full period positive sine curve.

Referring to the lift curve of Figure 5, for the first half of the period of the negative sine curve, the tappet will be subjected to a positive acceleration and for the second half of the period of the negative sine curve, the tappet will be subjected to a negative acceleration.

For this reason it will be necessary to keep the tappet in contact with the cam while traversing the ramps. A form of tappet which may be used for such purpose is shown in Figure 8 in which M indicates the cam. The tappet is formed in two parts, an upper part N, which bears upwardly against the valve stem P, and enters at its lower end, as a sliding fit, in a bore Q formed in from the top of a lower part R of the tappet. A light coil spring S is inserted 4 between the lower end of the part N and the bottom of the bore Q. A collar 1?. is formed on the upper end of the part N and the normal distance between such collar and the top of the part R is the valve clearance. As the tappet traverses the opening ramp it presses up the part R against the force of the spring S, while the valve remains closed until the gap is taken up.

Having fully described our invention, what we claim and desire to secure by Letters Patent is:

1. An operating mechanism comprising a movable member, an element actuated by said movable member, and a rotary cam having a peripheral surface adapted to engage said member,

' said surface having a lifting portion and a circular portion of smaller radius than the base circle of said cam whereby clearance is provided between said member and element, a ramp portion connecting said lifting portion and said circular portion, the contour of the major part of said ramp portion being represented by a lift curve consisting of two functions in series, the first function consisting of a negative sine curve combined with an ascending straight line, whereby said member is accelerated from a predetermined velocity to a positive maximum velocity with the acceleration represented by a positive one half period sine curve and is decelerated from said maximum positive velocity to another predetermined constant velocity with the acceleration represented by a negative one half period sine curve, and the second function consisting of a straight line curve tangent to the end of said negative sine curve whereby said member is moved at a minimum constant velocity with zero acceleration prior to contact with said lifting portion.

2. An operating mechanism comprising a movable member, an element actuated by said mov able member, and a rotary cam having a peripheral surface adapted to engage said member, said surface having a lifting portion and a circular portion, a ramp portion connecting said lifting portion and said circular portion, the contour of the major part of said ramp portion being represented by a lift curve consisting of two functions in series, the first function consisting of a negative sine curve combined with an ascending straight line, whereby said member is accelerated from a predetermined velocity to a positive maximum velocity with the acceleration represented by a positive one half period sine curve and is decelerated from said maximum positive velocity to another predetermined constant velocity with the acceleration represented by a negative one half period sine curve, and the second function consisting of a straight line curve tangent to the end of said negative sine curve whereby said member is moved at a minimum constant velocity with zero acceleration prior to contact with said lifting portion.

3. An operating mechanism comprising a movable member, an element actuated by said movable member, and a rotary cam having a peripheral surface adapted to engage and move said member, said surface having a lifting portion and a circular portion, a ramp portion connecting said lifting portion and said circular portion, the contour of the major part of said ramp portion being represented by a lift curve consisting of a negative sine curve combined with an ascending straight line whereby said member is accelerated from a predetermined velocity to a positive maximum velocity with the acceleration represented by a positive one half period sine curve and is decelerated from said maximum positive velocity to another predetermined constant velocity with the acceleration represented by a negative one half period sine curve.

JOHN L. H. BISHOP. JOHN H. WEAVING.

I REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,175,687 Biskigt Mar. 14, 1916 1,254,840 Nacker Jan. 29, 1918 1,336,447 Suffa Apr. 13, 1920 6 Number Name Date 1,365,735 Sherbondy Jan. 18, 1921 1,543,483 Hutt June 23, 1925 1,583,335 Borschelr May 4, 1926 1,635,304 Baster July 12, 1927 1,705,803 Brush Mar. 19, 1929 OTHER REFERENCES Cam Design Analysis, Shorter Product Engineering, May 1940, page 223.

Cams, Elementary & Advances, Furman, 1921 by John Wiley & Sons, page 88, Sect. VI.