US2915014A

US2915014A - Fuel injection pumps

Info

Publication number: US2915014A
Application number: US567395A
Authority: US
Inventors: John N Morris
Original assignee: SU Carburetter Co Ltd
Current assignee: SU Carburetter Co Ltd
Priority date: 1955-02-24
Filing date: 1956-02-23
Publication date: 1959-12-01
Anticipated expiration: 1976-12-01

Description

Dec. 1, 1959 J. N. MORRIS 2,915,014

FUEL INJECTION PUMPS Filed Feb. 23, 1956 FIG. I. f

INVENTOR. JOHN NEVILLE MORRIS.

m u4mj nam i ATTORNEYS.

United States Patent v FUEL INJECTION PUlVlPS John N. Morris, Birmingham, England, assignor to The S.U. Carburetter Co. Ltd.', Birmingham, England, a British company i I ApplicationFehruary 23, 1956, Serial No. 567,395

- Claims priority, application Great Britain liebruary24, 195'5 8 Claims. (Cl. 103-38) This invention relates to a fuel injection pump for internal combustion engines. More particularly, it is directed to a pump of the type having adjustable means controlling the delivery of one or more pump members, and a displaceable pressure responsive member for controlling the adjustable means disposed in' a housing and forming with said housing a first and asecond pressure 7 chamber on respective sides of said displaceable member.

In order to supply the liquid fuel to spark-ignition engines of the type employed in automatic vehicles or certain stationary installations, the fuel injection pump must be capable of responding rapidly to sudden changes in the position of the engine accelerator control. Fuel injection pumps have been employed for some time in connection with aircraft engines; however, since the speed with which they follow the movement of the throttle is not too important the emphasis has been placed upon steady-state metering accuracy. The present invention is ,directed to a construction ofan injection pump which isparticularly adapted for use where rapid accommodation to sudden changes in fuel demand is required. For convenience in explanation, the invention will be described with reference to one specific type of injection pump; however, as will appear from the description, the invention is applicable to other pumps of the general character outlined in the introductory paragraph above.

In accordance with the invention a fuel injection pump having such basic elements as above enumerated is further provided with means for supplying a-substantially unrestricted flow of fluid under pressure to thefirst pressure chamber, a servovalve-controlled passage interconnecting the first and second pressure chambers, a servo-valve therefor, and a restricted passage for venting the second pressure chamber. The opening in the valve-open positon of the servo-valve is chosen relative to the size of the restricted passage so as to permit a rapid build-up of fluid pressure in the second pressure chamber when the servo-valve is in its wide open position.- This enables the pump to shift rapidly in a first direction. In orderto enable the pump to shift rapidly in the reverse direction, an auxiliary venting means for the second pressure chamber is provided. This includes a ventpassage of a size related to the restricted passage and to the size of the second pressure chamber such as to decrease rapidly the pressure in the second pressure chamber 'whenunrestricted. The servo-valve is operatively associated with the last mentioned vent passage for restricting the flow of fluid therethrough except when in the servo-valve-closed position.

As a further feature of the invention the functions of the restricted passage and of the auxiliary vent passage inay be combined in a single passage controlled by the servo-valve. Now, however, the servo-valve is ar ranged to cause restricted flow through the passage during normal steady-state operation and unrestricted flow when the servo-valve is in its valve-closed position.

' A better understanding of the invention will be had 2,915,014 Patented Dec. 1, 1959 from a reading of the following detailed description with reference tothe accompanying drawings in which:

Fig. 1 is an elevational view partly in section showing a fuel injection pump embodying the present invention;

Fig. 2 is a fragmentary elevational viewvshowing the servo-valve and the bifurcated lever for coupling the input signal thereto; and 1 p v r Fig. 3 is a sectional view taken on line 33 in Fig. 2.

Referring now to the drawings, the fuel injection pump is providedwith a cast housing 10 having a capsule pressure chamber 12 and an operating chamber 14. A drive shaft 16 passes through the chamber 14 and has its upper end, which is not shown in the drawing, operatively connected to a distributing valve arrangementfor sequentially connecting the pump cylinders, one of which is shown at 18, to the fuel supply and to the injection nozzles for the engine. The other end of the drive shaft is arranged to be driven by the engine in a suitable manner. The cylinder 18 along with a suitable number of further cylinders, not shown, are positionedin the I form of a circle in a cylinder block 20. Each of the cylinders is provided with a pump member in the form of a plunger 22 of which two are visible in the drawing. The jplungers 22 bear against a wobble-plate 24 which is mounted upon acombined skew shaft and servo-piston unit 26,. The unit 26 is slidably mounted upon the shaft 16 and keyed thereby by a key 28 for driven rotation therewith. The unit 26 is provided with a cylindrical apron 30 making a sliding fit in the cylindrical portion 32 of the housing .10. The apron 30 along with the web portion 34 of the unit 26 forms a displaceable pressure. responsive member within the aforementioned cylindrical portion 32 The wobble-plate 24 has its peripheral region provided with abearing surface which engages a complementary surfacein the housing 10. This surface may be generally spherical in nature. As the com-. bined skew shaft and servo-piston unit 26 moves longitudinally along the drive shaft 16 the'skew portion 'of the unit 26 will displace the center of the wobble-plate 24 thereby increasing or decreasing its tilt or inclination. In: a known manner rotation of the skew shaft will cause the wobble-plate to reciprocate the pump members 2'2. Asshown in the drawing, the stroke of the pump members will be a maximumwhen the unit 26 occupies its extreme upward position and will be a minimum when the unit 26 occupies its extreme lowermost position.

Provision is made for connecting a source of fiuiduuder pressure to the housing 10 through the large port 36 for establishing a substantially unrestricted flow thereof. The pressure fluid might conveniently bethe lubricating oil employed in the'engine. The fluid will fill up the portion of the chamber 14.above the unit 26 (afirst; pressure chamber and pass into a servo-valvecontrolled pas sage 38 formed in the drive shaft 16 by way of the ports 40. It is noted that theports 40 are located at a point on the drive shaft 16 above theupper limit of movement of the servo-piston unit 26 ;A further group of comparatively large ports 42 are located inthe walls of the drive shaft 16 in communication with the passage 38 in the lower portion of the chamber 1,4.ata point well below the'lower limit of travel of the servoepiston unit 26. A servo-valve in the form of a cylindrical sleeve mem ber 44 is mounted for :sliding movement longitudinally uponthe drive shaft 16. -As shown in the drawing, the valve 44 isprovidedpwith a land area 46 which cooperates with the portsfl42 toprovide a variable obstruction ther-er,

- for dependent upon the relative positionv of the servo:

valve. As long as-the ports 42, are not completelyv obstructed or closedthe pressurefluid will leave the passage,

50 formed in the walls thereof. This fluid will now commence to fill up the portion of the chamber 14 located below the servo-piston 26 (a second pressure chamber).

A vent passage 52 is formed within the drive shaft 16 and communicates through a lateral passage 54' with the exterior of the housing 10. The other end of the passage 52 communicates with a plurality of vent port and passage means 56 and 58 which are located in the shaft 16 within the lower portion of chamber 14. The vent port and passage means 56 is located with respect to the servo-valve such that the lower portion 60 thereof completely obstructs the port means 56 for all positions of the servovalve except that position wherein the land area 46 completely obstructs or closes off the ports 42, i.e. for all positions other than the servo-valve-closed position. The reason for this will be described below. The other vent port and passage means 58 is located at a point which is always unobstructed by the servo-valve and forms with the passages 52 and 54 a permanent restricted passage for venting the aforementioned second pressure chambet in the lower portion of chamber 14. The ports 42 as well as the clearance or groove 48 and ports 50 in the servo-valve should be of such size and proportionthat the opening in the valve-open position of the servo-valve relative to the size of the restricted passage 58 will permit a rapid build-up of pressure in the second pressure chamber below the servo-piston 26.

A helical compression spring 62 surrounds the drive shaft 16 and is disposed between the web 34 of the servopiston 26 and the upper face of the servo-valve 44. This serves as a feedback coupling between the servo-piston and the servo-valve. A thrust race 64 is provided between the spring 62 and the upper face of the valve 44. The spring 62 urges the valve 44 downwardly against the bifurcated ends 66 of an articulable link or see-saw lever 68 which straddles the drive shaft 16. As seen in Figs. 2 and 3 the ends 66 of the lever 68 are provided with tapered bearing surfaces 70 engaging V-notches 72 formed in the lower edge of the servo-valve 44. This prevents rotation of the servo-valve and at the same time applies the controlling force thereto. The other end of the lever 68 is acted upon by a thrust pin 74 which in turn is engaged by a second thrust pin 76 fixed to one face of a pressure responsive device 78 situated in the chamber 12. The device 78 may take the form of asealed multicapsule stack. The chamber 12 is provided with a port 80 for connection with the air induction manifold of the engine. The opposite face of the device 78 is positioned centrally by an adjustable abutment pin 82.

So long as the operating conditions of the engine remain unchanged (i.e., while the induction manifold pressure applied to the capsule unit in the chamber 12 remains constant), the mechanism described above is in a stable state. This arises from the circumstance that, under the conjoint influences of the control spring 62 and the load transmitted by the

linkwork

68, 74 and 76 from the capsuleunit 78, the servo-valve 44 assumes a position in which its land area 46 so regulates the efflux of'fiuid through the outlet ports 42 that, in conjunction with the restricted provision for escape of fluid from the second pressure chamber, the differential fluid pressure acting on the servo-piston unit 26 exactly balances the load exerted by the control spring 62. Consequently, any given load exerted upon the servo-valve 44 by the capsule unit 78 and its associated linkwork is necessarily exactly counterbalanced by the load exerted by'the control spring 62, and, therefore, corresponds to a particular length of that spring and hence a definite position of the combined skew shaft and servo-piston'unit 26. Thus, any given value of the induction manifold pressure results in a corresponding. stroke being performed by the fuelpumping plungers 22.

Letit be assumed that the pump is in a stable fuelmetering condition with a relatively low pressure obtaining in the chamber 12; which, of course, corresponds i to the engine either idling or being on light load (that is to say, when the throttle valve admitting air into the induction manifold is partially shut). :If now the throttle is abruptly opened, the induction manifold pressure rises very rapidly, for example to atmospheric pressure or to some pressure intermediate. between the low pressure previously existing and atmospheric pressure. The capsule unit 78 has a relatively low elasticity and, therefore, this sudden increase in its ambient pressure not only has the effect of diminishing momentarily the thrust exerted by the capsule unit on its associated linkwork, but also enables the capsule unit to undergo a substantial contraction. This permits the servo-valve 44 momentarily to slide under the influence of the control spring 62, it being borne in mind that at the instant of opening the throttle and consequently applying the sudden increase in pressure to the capsule unit 78 the pump was operating at a relatively small stroke; that is to say, the control spring 62 was substantially compressed and exerting a relatively large load upon the servo-valve.

The momentary downward displacement of the servovalve 44 brings about a momentary large increase in the effective opening of the associated outlet ports 42, and thus permits high-pressure fluid from the passage 38 in the drive shaft 16 to flow through these portsat' a high rate into the relatively lower-pressure region constituted by the second pressure chamber. This momentary high flowof fluid temporarily raises the fluid pressure behind the servo-piston unit 26 to such a value that, acting on the rear face of the servo-piston and thereby assisting the control spring, the latter is enabled to expand and rapidly move the servo-piston unit. A condition of stability is eventually established, with the control spring '62 now more distended and the servo-piston unit 26 having moved to a position corresponding to a greater stroke of the fuel-pumping plungers 22. The load exerted by the control spring on the servo-valve eventually exactly counterbalanccs the new load exerted by the capsule unit 78.

It will be appreciated from the foregoing description that the provision of outlet ports 42 in the drive shaft which are of substantial depth and peripheral extent, taken in conjunction with the relatively low spring rate of'the capsule unit 78, permits the stroke-varying mechanism to respond very rapidly to an abrupt increase in the'induction manifold pressure.

Now consider the operation of the device when the throttle is suddenly closed or partially closed from a formerly open position. For this purpose assume, initially, that the port means 56 has been omitted. The Concomitant sudden reduction in the induction manifold pressure causes the capsule unit 78 momentarily to distend, it being free to do so since at the instant of the change of pressure in the induction manifold the control spring was relatively distended, corresponding to a substantial displacement of the servo-piston unit towards the full-stroke position. The control spring 62 was, therefore, at the instant under consideration, exerting a relatively small load upon the servo-valve. Now the sudden distension of the capsule unit momentarily causes the servo-valve to be moved by the lever 68 against the control spring 62, and this movement results in the valve completely closing the outlet ports 42 in the drive shaft, thus precluding temporarily any further flow of oil from one side of the servo-piston unit to the other. Under the action of the high-pressure fluid on its front face, the servo-piston unit now proceeds to move towards the position at which the amplitude of the wobble-plate 24 is diminished, forcing the fluid out of the second pressure chamber by way of the restricted vent passage referred to earlier. This the servo-piston unit is free to do since the fluid behind it is momentarily no longer being replenished as it is normally by the passage of fluid past the \land area 46 on the servo-valve 44. The rate at which this movement of the servo-piston unit takes place is, however, limited by the necessarily relatively srnall size of the vent passage by which fluid can escapefrom the second pressure chamber. The vent passage has to be relatively small in order to limit the amount of fluid supplied by way of the relatively large port 36 to the front face of the servo-piston unit. In consequence the response of the mechanism to a sudden closure of the throttle is very sluggish and a considerable interval of time may elapse before the mechanism has readjusted itself to the new pressure obtaining in the induction manifold. During this interval the fuel delivered to the engine is excessive, and misfiring and temporarily excessive fuel consumption result.

Now consider the effect of the port means 56 which, under normal steady metering conditions (i.e. when the land area 46 of theservo-valve 44 is very close to its shut off position with respect to the associated ports 42), are just covered by the valve 44 and are thus inoperative as a leakage or vent path. During the momentary phase when the capsule unit 78 is substantially expanded temporarily, and consequently the valve 44 has been moved against the spring 62 and has shut off the associated ports 42, the vent port and passage means 56 becomes exposed and thus said means 56 incombination with

passages

52 and 54 serves as an additional or auxiliary venting means for second chamber, 14 which auxiliary means is in parallel with the permanently opened passage of relatively small size previously mentioned, for the fluid to escape from the lower portion of chamber 14 to the exterior of the housing 10.

As will be appreciated from the above description, the effect of theprovision of the auxiliary venting passage is momentarily to increase the rate of fluid venting or spillage from the low pressure side of the servo-piston unit 26, thus increasing the speed at which the servopis-ton unit 26 can move in the downward direction to diminish the amplitude of the wobble-plate 24 and the stroke of the pump plungers 22. This facility is provided for a brief interval of time following upon a sudden decrease in the air induction manifold pressure.

As an alternative to employing the restricted vent passage including port means 58 and

passages

52 and 54, the port means 56 may be utilized. This is brought about as seen in Fig. 3 by arranging for the V-notches 72 in the valve 44 to cyclically uncover the port means 56 as the drive shaft 16 is rotated; It is to be understood that in steady-state operation of the pump, the valve 44 will assume a position almost closing the ports 42. For this position of the valve 44 the notches 72 and the port means 56 can be proportioned to provide the necessary restricted venting. This will not interfere with the increased rate of venting provided by the port means 56 when they are completely uncovered due to the valve 44 moving to its extreme upper position. As a further alternative a small orifice may be provided in the wall of housing communicating with the second pressure chamber therein. This may augment or replace port means 58.

The invention has been described with reference to a specific embodiment thereof. Nevertheless, it is intended to encompass the numerous changes and modifications which will appear obvious to those skilled in the art to which it appertains, and which come within the scope of the appended claims.

What I claim is:

1. A fuel injection pump for internal combustion engines having adjustable means controlling the stroke of at least one pump member, a housing, and a displaceable pressure responsive member coupled to said adjustable means for controlling said adjustable means and disposed in said housing and forming with said housing a first and a second pressure chamber on respective sides of said member, comprising in combination therewith, means communicating withsaid first chamber for supplying a substantially unrestricted flow of fluid under 6 pressure thereto, a servo-valve-controlled passage inter connecting directly said two chambers, a movable servovalve in valving cooperation with said controlled passage wherein movement of said valve regulates progressively the amount of' fluid interconnection between said chambers, a feedback coupling between said pressure responsive member and said servo-valve, a restricted passage communicating with said second chamber forventing fluid therefrom to the exterior of said chambers, the amount of fluid interconnection provided by said servo-valve and controlled passage being related'in size to the size of said restricted passage for permitting a rapid build-up of pressure in said second chamber when said servo-valve moves to its valving position with respect to said controlled passage corresponding to a full interconnection between said chambers, and auxiliary venting means communicating with said second chamber and including a vent passage of a size related to the size of said restricted passage and to the size of said second chamber for rapidly decreasing the pressure in said second chamber when unobstructed, said servo-valve also being in valving cooperation with said auxiliary venting means for obstructing the flow of fluid therethrough from said second chamber for all valving positions of said servo-valve except when said servo-valve is in its valving position corresponding to fully obstructing said controlled passage, whereby said displaceable member is rapidly actuated to either of its extreme positions responsive to movement of said servo-valve to its corresponding extreme position.

2. A fuel injection pump for internal combustion engines having a plurality of pumping plungers of variable stroke, an adjustable wobble-plate coupled thereto for actuating said plungers, a rotatable drive shaft, a combined skew shaft and servo-piston unit keyed to and longitudinally slidable on said drive shaft, said unit being coupled to said wobble-plate for altering the amplitude of the motion thereof, and a housing for said combined skew shaft and servo-piston unit forming with said unit a first and a second pressure chamber on respective sides of said unit, comprising in combination therewith, means communicating with said first chamber for supplying a substantially unrestricted flow of fluid under pressure thereto, a servo-valve-controlled passage having first and second ports in saidfirst and second chambers respectively for interconnecting said two chambers, a movable servo-valve in valving cooperation with said second port wherein movement of said valve regulates progressively the amount of opening of said second port, a feedback coupling between said servo-piston unit and said servovalve, a restricted passage communicating with said second chamber for venting fluid therefrom to the exterior of said pump, the amount of-opening of said second port being related in size to the size of said restricted passage for permitting a rapid build-up of pressure in said second chamber when said servo-valve moves to its valving position corresponding to said second port being fully opened, and auxiliary venting means communicating with said second chamber and including a vent passage of a size related to the size of said restricted passage and to the size of said second chamber for rapidly decreasing the pressure in said second chamber when unobstructed, said servo-valve also being in valving cooperation with said auxiliary venting means for obstructing the flow of fluid therethrough from said second chamber except when saidservo-valve is in its valving position corresponding to said second port being fully closed, whereby said servo-piston unit is rapidly actuated to either of its extreme positions responsive to movement of the servovalve to its corresponding extreme position.

3. A fuel injection pump for internal combustion engines having apluralityof pumping plungers of variable stroke, an adjustable wobble-plate coupled thereto for actuating said plungers, a rotatable drive shaft, a combined skew shaft and servo-piston unit keyed to and longitudinally sl-idable on said drive shaft, said unit being coupled to said wobble-plate for altering the amplitude of the motion thereof, anda housing for said combined skew shaft and servo-piston .unit forming with said unit a first and a second pressure chamber on respective sides of said unit, comprising in combination therewith, means communicating with said first chamber for supplying a substantially unrestricted flow of fluid under pressure thereto, a passage formed Within said drive shaft and extending beyond the limits of movement of said servo-piston unit on both sides thereof, one or more ports formed in the Wall of said drive shaft on each side of said servo'piston unit for establishing direct hydraulic communication between said passage and said first and second chambers, respectively, a servo-valve slidably mounted on said drive shaft within said second chamber for operative valving cooperation with the drive shaft ports therein, a feedback coupling between said servo-piston unit and said servo-valve, a permanently open and restricted passage communicating with said second chamber for venting thereof, the size of the drive shaft ports in the second chamber being related to the size of said restricted passage for permitting a rapid build-up of pressure in said second chamber when the servo-valve is in its wide open valving position with respect to said drive shaft ports, and auxiliary venting means communicating with said second chamber and including a vent passage of a size related to the size of said restricted passage and to the size of said second chamber for rapidly decreasing the pressure in said second chamber when unobstructed, said servo-valve also being in valving cooperation with said auxiliary venting means for obstructing the flow of fluid therethrough from said second chamber except when said servo-valve is in closed valving position with respect to said drive shaft ports of said second chamber, whereby said servo-piston unit is rapidly actuated to either of its limiting positions responsive to movement of the servo-valve to its corresponding extreme position.

4. A fuel injection pump according to claim 3, wherein said auxiliary venting means comprises a second passage within said drive shaft communicating at one end with the exterior of said housing and at the other end with further port means in the wall of said shaft which further port means is located within said second chamber with respect to said servovalve such that said servovalvecompletely obstructs said further port means for all valving positions of said servo-valve except for the aforesaid servo-valve-closed position.

5. A fuel injection pump for internal combustion engines having a plurality of pumping plungers of variable stroke, an adjustable wobble-plate coupled thereto for actuating said plungers, a rotatable drive shaft, a combined skew shaft and servo-piston unit keyed to and longitudinally slidable on said drive shaft, said unit being coupled to said wobble-plate for altering the amplitude of the motion thereof, and a housing for said combined skew shaft and servo-piston unit forming with said unit a first and a second pressure chamber on respective sides of said unit, comprising in combination therewith, means communicating with said first chamber for supplying a substantially unrestricted flow of fluid under pressure thereto, a passage formed within said drive shaft and extending beyond the limits of movement of said servopiston unit on both sides thereof, the wall of said shaft being apertured within said first chamber for establishing communication between said first chamber and said passage, first port means formed in the wall of said drive shaft within said second chamber for establishing communication between said passage and said second chamber, a servo-valve in the form of a sleeve member slidably mounted on said drive shaft within said second chamber and secured against rotation, said sleeve member having an internal land and groove arrangement for valving cooperation with said first port means, movement of said sleeve member longitudinally in opposite direction on said shaft functioning respectively progressively to close and open said first port means, said first port means being substantially completely closed when said sleeve member is at one end of its travel, a feedback coupling between said servo-piston unit and said sleeve member, an auxiliary passage formed in said drive shaft communicating at one end with the exterior of said housing and at the other end with second port means in the wall of said shaft disposed within said second chamber, an auxiliary valving surface internally formed on said sleeve member and arranged to cooperate with said second port means, said auxiliary valving surface being formed with interruptions circumferentially disposed therein, which interruptions intermittently coincide with said second port means as said drive shaft is rotated for intermittently opening said second port means, said second port means being normally sealed by said auxiliary valving surface except for said intermittent interruption as long as said sleeve member is away from said one end of its travel, and said second port means being fully open when said sleeve member is at said one end of its travel, said second port means and said interruptions in the auxiliary valving surface of said sleeve member being related to the size of said first port means and to the size of said second chamber so as to permit a rapid build-up of pressure in said second chamber when the sleeve member moves to substantially fully open said first port means and to permit a rapid decrease in the pressure in said second chamber when the sleeve member is at said one end of its travel, and means coupled to said sleeve member for controlling the position thereof whereby said servo-piston unit is rapidly actuated to either limiting position responsive to movement of the sleeve member to its corresponding extreme position.

6. A fuel injection pump according to claim 5, wherein the interruptions formed in the surface of said auxiliary valving surface comprise at least one notch formed in one edge of the sleeve member, and wherein said means for controlling the position of the sleeve member comprises an articulable link engaging said notch for exerting pressure upon said sleeve member in a longitudinal direction and for simultaneously restraining said sleeve member from rotating.

7. A fuel injection pump for an internal combustion engine of the spark-ignition type having an engine accelerator control, said pump being capable of rapid accommodation to sudden substantial changes in the position of the engine accelerator control, comprising in combination, a plurality of individual pump members for supplying fuel to the cylinders of said engine, adjustable means coupled to said pump members for controlling the delivery thereof, a displaceable pressure responsive member cooperating with said adjustable means for controlling said adjustable means with movement in one direction causing increased fuel delivery and movement in the opposite direction causing decreased fuel delivery, a housing, said displaceable member being disposed in said housing and forming with said housing a first and a second pressure chamber on respective sides of said member, means communicating with said first chamber for supplying a substantially unrestricted fiow of fluid under pressure thereto, a servo-valve-controlled passage hydraulically and directly interconnecting said two chambers, a movable servo-valve in valving cooperation with said valve-controlled passage wherein the movement of said servo-valve regulates progressively the amount of hydraulic interconnection between said two chambers, a feedback coupling between said pressure responsive member and said servo-valve, a restricted passage communicating with said second chamber for venting thereof, the amount of fluid interconnection provided by said servovalve and said valve controlled passage being related in size to the size of said restricted passage for permitting a rapid build-up of pressure in said second chamber when said servo-valve is in its valving position corresponding to movement of said displaceable member rapidly in one of said two directions, auxiliary venting means communicating with said second chamber and including a vent pasage of a size related to the size of said restricted passage and to the size of said second chamber for rapidly decreasing the pressure in said second chamber when unobstructed for moving said displaceable member rapidly in the other of said two directions, said servo-valve also being in valving cooperation with said auxiliary venting means for obstructing the flow of fluid therethrough from said second chamber except when said servo-valve is in a valving position corresponding to obstructing the interconnection between said first and second chambers, and means for coupling said servovalve to said engine accelerator control for actuating said servo-valve to its open valving or its closed valving positions responsive to sudden substantial changes in the position of said accelerator control in opposite directions respectively, whereby sudden substantial changes in opposite directions in the position of the engine accelerator control will be accompanied by correspondingly rapid increases and decreases, respectively, in the quantity of fuel delivered.

8. A fuel injection pump for internal combustion engines having a plurality of pumping plungers of variable stroke, an adjustable wobble-plate coupled thereto for actuating said plungers, a rotatable drive shaft, a combined skew shaft and servo-piston unit keyed to and longitudinally slidable on said drive shaft, said unit being coupled to said wobble-plate for altering the amplitude of the motion thereof, and a housing for said combined skew shaft and servo-piston unitforming with said unit a first and a second pressure chamber on respective sides of said unit, comprising in combination therewith means communicating with said first chamber for supplying a substantially unrestricted fiow of fluid under pressure thereto, a passage formed within said drive shaft and extending beyond the limits of movement of said servopiston unit on both sides thereof, the wall of said shaft being apertured within said first chamber for establishing communication between said first chamber and said passage, first port means formed in the wall of said drive shaft within said second chamber for establishing communication between said passage and said second chamber, a servo-valve in the form of a sleeve member slidably mounted on said drive shaft within said second chamber and secured against rotation, said sleeve member having an internal land and groove arrangement for valving cooperation with said first port means, movement of said sleeve member longitudinally in opposite direction on said shaft functioning respectively progressively to close and open said first port means, said first port means being substantially completely closed when said sleeve member is at one end of its travel, a feedback coupling between said servo-piston unit and said sleeve member, an auxiliary passage formed in said drive shaft communicating at one end with the exterior of said housing and at the other end with second port means in the wall of said shaft disposed within said second chamber, an auxiliary valving surface internally formed on said sleeve member and arranged to cooperate with said second port means, said second port means normally being sealed by said auxiliary valving surface except when said sleeve member is away from said one end of its travel, and said second port means being fully open when said sleeve member is at said one end of its travel, the size of said second port means being related to the size of said first port means and to the size of said second chamber so as to permit a rapid build-up of pressure in said second chamber when said sleeve member moves to a valving position substantially fully opening said first port means and to permit a rapid decrease in the pressure in said second chamher when said sleeve member is at said one end of its travel, and means coupled to said sleeve member for controlling the position thereof whereby said servo-piston unit is rapidly actuated to either limiting position responsive to movements of the sleeve member to its corresponding extreme position.

References Cited in the file of this patent UNITED STATES PATENTS 2,439,498 Wallace Apr. 13, 1948 2,448,347 Beeh Aug. 31, 1948 2,611,318 Wahlmark Sept. 23, 1952 2,624,326 Fiser Jan. 6, 1953 2,667,840 High Feb. 2, 1954 2,672,816 Friedlander Mar. 23, 1954