US 2179354 A
Description (OCR text may contain errors)
P. L. SCOTT Nov. 7, 1939.
Filed Aug. 7. i935 DEGREES fkyfizar I 1% /z' J. 500624 Y Jffar'nqys.
Patented Nov. 7, 1939 PATENT OFFICE PUMP Philip Lane Scott, Chicago, 11]., assignor to Super Diesel Tractor Corpora corporation of New York tion, La Porte, Ind., a
Application August, 7, 1935, Serial No. 35,108
This invention relate's to fluid pumps and particularly liquidfuel pumps of the typeused in internal combustion engines for delivering liquid fuel to an atomizing valve, although it is not 5 limited to pumps of this type. One object of my invention is to provide a simple means of changing the delivery characteristic or flow rate of the pump without altering the shape of the driving cam.
in Other objects 'willappear from time .to time throughout the specification and claim.
The invention is illustrated more or less diagrammatically in the accompanying drawing wherein:
15 Figure 1 is a vertical section through a cam driven fuel pump; 7
Figure 2 is a plan view of the adjusting structure including a partial section along 2-2 of Figure 1 of the pump housing; 3 Figure 3 is a graph showing a certain pump delivery characteristic; and
Figure 4 is a graph showing another pump delivery characteristic.
Like numerals refer to like parts throughout.
25 As shown in the drawing, I is a pump base supporting a cam shaft 2 carrying a series of cams, one of which is shown 3. 4 is a pump body adjustably mounted on the base I and locked in any desired position bythe cap screws 5, 5 3 which are inserted through the slots 5a, 5a. Mounted within the pump body'is a slider 6, adapted to slide within the bore 1. Uponthe lower end of the slider is a roller 8, mounted upon a pin 9. Within the body 4 is a barrel II] 35 screwthreaded into the body. Within the barrel ID is a plunger I I adapted to reciprocate therein. The plunger and slider are spring returned by means of the spring I2 acting on the washer I3 and in turn on the hardened button' It positioned m within the slider 6. I5 is a suction valve assembly screwthreaded into the body 4 and leading in to the pump chamber I 6. I1 is adischarge valve assembly screwthreaded into the body 4.
' Figures 3 and 4 show pump discharge rates. gr, The abscissae represent degrees rotation of the cam shaft and the ordinates represent the percentage of discharge occurring. during the preceding selectedmumber of degrees of cam shaft rotation, each of these degree intervals of rota- ;0 tion being conveniently chosen, as say each five degrees, all such intervals being equal.
plunger pumps the rate of discharge varies from zero to a maximum and again to zero during each 55 delivery period. The discharge obviously is zero body which carries the cam showing the condition existing when the axis of at the beginning and end and occurs at varying rates during equal time intervals in the pump-: ing stroke, reaching a maximum at various positions in the stroke depending upon the type of drive used. In cam driven pumps this variation 5 in rate of discharge, or pmnp delivery characteristic can be controlled to a considerable extent by the shape of the cam.
When such pumps are used for feeding fuel to I the atomiaerv of a Diesel engine, this variation in in the rate of discharge becomes highly important, since it has a pronounced eflect upon combustion. Certain type of combustion chambers, for example, operate most satisfactorily with relatively low initial rates of discharge and with the peak obtained well along in the stroke. Other cham bers operate bestwhen the initial rates rise rapidly and the peak is reached relatively early in the stroke. Pressure and temperature conditions also require different pump delivery characteristics. It istherefore highly desirable in commercial pumps to arrange to provide for con siderable variation in the discharge character'- istics.
Such changes in delivery characteristic have heretofore been accomplished by changing the cam or by using only a portion of the drive face of the cam for actual delivery and changinggthe mechanism which determines the portion of the cam face to be used, thereby obtainingthe result by using different portions of the driving face. Both these methods are expensive and cumber- I some. themechanism which'is the subject of this iiiivention the desired result is easily and 'quickly accomplished by setting the axis of the slider and roller (the cam follower) off center from the center line of the cam 'sha It is easily demonstrated that the amount of t is offset caus'esa marked change in the position of the peak rate of discharge with respect to th total discharge period. -Figures Sand 4 are graphs showing two distinct delivery characteristics obtained by merely shifting the axisof the pump followenFigure 3 the pump body is shifted away fromthe axis of the cam shaft in the direction of rotation of the cam, the condition shown in Figure 1. In this case it will be noted that the maximum rate of discharge occurs early in the, stroke, which as explained is desirable for certain engines. To move It is well known that for all reciprocating ward the axis of the camshaft against the direc- 2 I an s tion of the rotation of the cam. Thus, this peak rate of discharge may be moved along the degree base line, as shown in the graph, by merely shifting the pump body back and forth. The con- 5 structionwhich makes this possible is simply to' provide some slots in the body section of the pump and some cap screws or bolts to lock the body when the desired position is reached.
The movement of the pump body above described will produce varying positions of the plunger and cam follower assembly. As the body is moved to the right, as shown in Figure 1, the plunger and cam follower will move downward somewhat toward the cam shaft, acting under the influence of. the spring i2. This occurs without materially changing the stroke, although there may be a slight tendency to increase the stroke. With the plunger and pump body moved to the right, the plunger merely reciprocates approximately the same amount, but in a different portion of the barrel. In general this does not appreciably affect the operation of the pump.
The use and operation of the invention are as follows:
The operation of such pumps generally'when used on Diesel engines is too well known to need detailed description. A source of oil supply is connected to the inlet valve assembly i5, whereby oil is admitted on the suction stroke of the pump into the chamber i6 and then, upon the discharge stroke, expelled from the chamber it through the discharge valve assembly ii to the atomizing valve in the engine. The cam and cam follower are conventional structures. The particular cam 85 shown has a flat driving face and a long circular eccentric return or suction face. The novelty of the device consists in' the ability to shift the pump body with respect to the cam shaft to obtain varying delivery characteristics as already de- 40 scribed. Assuming the pump to be placed in operation on an engine and a particular delivery rate to be found unsuited to the specific engine construction and conditions, it is merely necessary to loosen the cap screws I and shift the pump to right or to the left as the particular requirements of the engine indicate is desirable. The body may be locked in an approximate position and the engine again operated and if improvement is noted the pump may be shifted further in the same direction and this process repeated until the optimum is passed and 'a decrease in performance is observed. The body may be then shifted backward to the point determined as giving the best operation.
Such changes of delivery characteristic are. of exceptional importance when changes in fuel are made, even though other engine conditions remain the same. It is therefore highly desirable to be able to vary delivery characteristic in an installed pump without expensive or complicated changes orreplacements.
It is of course obvious that this principle may be applied to a wide variety of pump construction and it is in no wise limited to the particular form shown.
A variety of locking devices may be employed, and the shifting of the body may be accomplished by sorewthreadeddevices such as are used to position electric motors. A calibrated scale may be attached to identify various body positions as best for certain purposes.
I claim: I
In a pump, a base member, a pump driving cam shaft supported in said member, a cam on said shaft, 9. pump body provided with inlet and outlet valves, a plunger reciprocally mounted in said body, a follower positioned to actuate said plunger and to be acted upon directly by the cam, and means for movably mounting said body upon said base for movement at right angles to the axis of the cam shaft, to adjust the axial distance between the center line of the cam shaft and the center line of the follower.
' Him LANE SCOTT.