US3771917A

US3771917A - Fuel injection system

Info

Publication number: US3771917A
Application number: US00158759A
Authority: US
Inventors: P Davies
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1971-07-01
Filing date: 1971-07-01
Publication date: 1973-11-13
Anticipated expiration: 1990-11-13

Abstract

An emission control in which a fuel injection pump has a delivery valve providing a ratio of retraction volume to delivered fuel of between 1 and 1.5, and a low speed fuel stop that increases pump fuel flow over the normal maximum, at low r.p.m.''s, to compensate for the lower delivery at this period resulting from the retardation of injection.

Description

United States Patent 1 1 3,771,917

Davies NOV. 13, 1973 Inventor: PaulDavles, Maldon England Burman, Fuel Injection and Controls for Internal [73] Assignee: Ford Motor Company, Dearborn, cmbustion Engines 1962 Mich.

Primary Examiner-Carlton R. Croyle Flledl J y 1971 Assistant Examiner-Richard Sher US. Cl.'.... 417/289, 123/139 DE, 123/139 DP,

123/140 R, 417/293, 417/499 [51] Int. Cl. F04b 49/00, F02d 1/04 [58] Field of Search 123/140 R, 139 DP, 123/139 DE; 417/293, 289, 499

[56] References Cited UNITED STATES PATENTS 3,146,715 9/1964 Knudson 123/140 R Attorney-Keith L. Zerschling et al.

[57] ABSTRACT An emission control in which a fuel injection pump has a delivery valve providing a ratio of retraction volume to delivered fuel of between 1 and 1.5, and a low speed fuel stop that increases pump fuel flow over the normal maximum, at low r.p.m.s, to compensate for the lower delivery at this period resulting from the retardation of injection.

5 Claims, 3 Drawing Figures Max/mum Fue/ P IEnnuv 13 1915 3.771317 saw 2 or 3 PA (/4. 0A V/[S PATENTEnnov 13 :915

SHEET 30F 3 INVENTOR.

PA (/L 0/! W55 BY ATTOR/VAKS FUEL INJECTION SYSTEM This invention relates to diesel engines and particularly to fuel injection pumps in diesel engines.

A type of fuel injection pump in widespread commercial use comprises a camshaft which actuates a plurality of reciprocating plungers which each supply fuel to an associate combustion chamber through an unloading or retraction type delivery valve, a high pressure line, and an injector. Delivered volume of fuel is controlled by a control rod connected to simultaneously rotate the plungers relative to respective spill ports.

This type of pump is referred to below as a pump of the kind specified.

lt is known that a significant reduction in the smoke emissions of a diesel engine can-be achieved by retarding the timing of the pump relative to the engine crankshaft at low r.p.m. This retardation is usually carried out by an arrangement of centrifugal fly-weights which produce an angular displacement in the coupling connecting the pump to the engine in accordance with engine speed. A typical centrifugal coupling device of this kind produces an angular displacement of about 8 of crankshaft rotation at 800 r.p.m. which decreases to zero in approximately linear manner at about 2000 r.p.m.

Unfortunately this device is an expensive addition to a diesel engine. It is the object of the present invention to effectively'retard the pump at low r.p.m. in' a diesel engine having a pump of the kind specified without using a centrifugal coupling.

We have found that, without alteringthe timing of the pump relative to the engine, a retardation of delivery of fuel through the injectors is produced by increasing the ratio of unloading volume of the delivery valves to delivered volume of the pump from about 0.6 as used in a normal engine of this kind, to between 1 to 1.5. That is, by reducing the residual pressure to a very low level lower than is conventional, it therefore takes longer to buildup to previous injection pressure level. Moreover the effect of increasing the unloading volume is relatively small at high r.p.m. (i.e. above about 2000 r.p.m.) and increase with decreasing r.p.m. in the low speed range of the pump so that the desired effect of retarding delivery only at low r.p.m. can be achieved, although an advance of the static timing of the pump may be necessary to avoid distributing the timing of delivery at high engine speeds.

The proposed increase in the unloading volume of the pump has the undesired effect of decreasing the volume of fuel delivered per cycle of the pump. There is a negligible decrease in the high speed range, but the delivered volume compared to the required column falls off approximately linearly with decreasing r.p.m. in the low speed range. This undesired effect is compensated, however, by arranging for the control rod of the pump to be displaced at low r.p.m. to restore the delivered volume of the pump to that of a pump with normal unloading volume. I

According to the invention a diesel engine having a fuel pump of the kind specified has the following features:

a. the ratio of unloading volume of the delivery valves to maximum delivered volume of the pump is between 1 and 1.5 so that the delivery valve produces an effective retardation of the time of the delivery of fuel relative to the engine crankshaft at low r.p.m. and a reduction in delivered volume at low r.p.m. relative to the delivered volume at high r.p.m.; and

b. means operable at low r.p.m. to increase the delivered volume and thereby restore the delivered volume at low r.p.m. to a design value.

In a preferred embodiment the means for restoring delivered volume of fuel is a spring loaded stop for limiting the maximum power position of the rack. The spring rate is chosen so that the stop can only be displaced to increase fuel flow at low r.p.m.

The invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 shows a fuel injection pump, delivery valve, high pressure line and injector of a diesel engine embodying the invention;

FIG. 2 is a diagram showing the arrangement for actuation of the control rod of the pump;

FIG. 3 is a graph showing fuel delivered per cycle, smoke emission and torque against engine speed.

The drawings show a conventional fuel injection pump of the kind specified which is modified in accordance with the invention in only two important respects described in detail below. Accordingly the construction and operation of the pump will not be described in detail.

The pump includes a camshaft 10 driven from the crankshaft of a diesel engine and a plurality of reciprocating plungers 11, one for each cylinder of the engine. The plunger 11 pumps fuel from a fuel gallery 12 through an unloading delivery valve 13, a high pressure line 15 and an injector 15 into an associated combustion chamber of the engine. The volume of fuel delivered per cycle is varied by linear movement of a control rod 16. The control rod 16 rotates the plunger 11 to vary the point in the injection stroke of the plunger at which a spill port 17 is uncovered by a helix 18. The helix 18 is connected by an internal bore 19 in the plunger to the space above the plunger.

The delivery valve 13 is a non-return valve loaded by a spring 20 and is guided in a bore 21 in a valve holder 22 by flutes 30. A small collar 23 forms a piston working in the bore 21. The volume swept by the collar 23 in moving between the position in which the delivery valve is seated (as shown') and the position in which the collar clears the valve seat and the delivery valve is fully open is called the unloading volume of the valve. Conventionally an unloading valve is used to provide a rapid drop in pressure in the high pressure line at the completion of injection to assist rapid closure of the injector and to prevent after dribbling of fuel. This drop in pressure occurs because as the collar 23, is drawn into bore 2l, the volume withdrawn corresponding approximately to the unloading volume permits an expansion of the'fuel in the high pressure line thereby depleting the residual pressure. The ratio of unloading volume to fuel per cycle at maximum power is about 0.6 in conventional engines. This ratio is sometimes as high as 0.9 but the effect of the high unloading volume is then offset'by the use of a flat on the collar so that the effective unloading volume is less than the swept volume of the collar because fuel slips past the collar through the flat.

The ratio of unloading volume to delivered volume of fuel at maximum power in an engine embodying the invention is between 1 and 1.5 and preferably about 1.25. This high unloading volume produces a significant delay in the onset of injection because it takes longer for the plunger to restore pressure in the depleted high pressure line before the injector will open. The preferred ratio of 1.25 is estimated to produce a delay of about 6 of crank rotation at 800 r.p.m. which diminishes with increasing r.p.m. to a negligible delay at about 2000 r.p.m.

The increased unloading volume delays onset of injection but has little effect on the timing of completion of the injection of fuel so that there is a reduction in the delivered volume of fuel.

Referring now to FIG. 3, curves I (dashed) show the variation of delivered volume of fuel, smoke emission, and torque with engine speed for a conventional diesel engine operating at full power. Curves II (chain dotted) show the effect of increasing the unloading volume of the delivery valves from 35 mm to 70 mm. The corresponding reduction in delivered volume of fuel and its variation with r.p.m. is clearly apparent from these curves. Thus the desired effect of delaying injection at low r.p.m. has been achieved at the expense of reduced fuel delivery. In order to restore the delivered volume of fuel to its optimum or design value'in the low speed range of the engine, we provide a spring loaded fuel stop 24 shown schematically in FIG. 2.

The control rod 16 of FIG. 1 is subject to the force of a governor spring 25 connected between the control rod 16 and a throttle control 27 and to the force applied by a governor 28. The governor spring 25 acts in a direction to force the control rod 16 against a fuel stop 24 for maximum fuel delivery. The governor exerts a force in the opposite direction which increases with increasing r.p.m. The load on the fuel stop at full throttle thus decreases with rising engine speed. A fuel stop spring 29 biases the fuel stop to a preset position correct for high speed operation of the engine. The preload of the fuel stop spring and its spring rate are chosen so that the governor spring begins to overcome the fuel stop spring when the engine speed falls below about 2,000 r.p.m. and is gradually deflected as engine speed falls to provide the required increase in delivered volume of fuel at low r.p.m..

Curves III in FIG. 3 (dotted lines) show the behaviour of the engine with increased unloading volume and spring loaded fuel stop. The fuel curve has been restored approximately to its normal level and the torque curve is approximately the same as for the unmodified engine. The smoke curve however shows a significant reduction relative to the unmodified engine. This reduction in smoke is attributable to the retardation of injection at low r.p.m. produced hydraulically by the increase in unloading volume of the delivery valves.

For purposes of comparison equivalent curves IV are shown in FIG. 3 for the same engine without the increased unloading volume and with a fixed fuel stop but fitted with an automatic advance unit in the form of a coupling between the engine and the pump in which fly weights produce varying angular displacement of the pump camshaft relative to the engine crankshaft in accordance with engine speed.

The invention thus provides a reduction in smoke that is comparable to that which can be achieved using an automatic advance unit.

The effectiveness of the spring loaded fuel stop in correcting the fuel delivery curve depends on the characteristics of the particular pump. In general, the spring loaded fuel stop will provide a first order correction. Further second order corrections may be provided by a variable rate spring or by providing a flat or bleed passage in the collar of the delivery valves. Such second order correction of the fuel delivery curve is best made by measuring the fuel delivery curve of the pump for a variety of different combinations of fuel stop spring arrangements or modified fuel delivery valves until the desired shape of fuel delivery curve is achieved.

I claim:

1. Fuel injection control means for use with a fuel in jection pumping means having a drive shaft, a pump plunger reciprocatable by said shaft for pumping fuel through a chamber into a high pressure discharge line, a helix type port connected to the chamber and connectable at times to a spill port to spill fuel from the chamber upon' reciprocation of the plunger, a retrac tion type delivery valve movable in said discharge line to alternately open the discharge line or close and subsequently be withdrawn from said line to reduce the residual pressure therein, and movable means to adjust the position of the helix type port relative to the spill port to vary the fuel delivery volume, the control means comprising a fuel flow control rod movable in opposite directions to increase or decrease fuel flow, an operator controlled lever for moving the control rod, and means interconnecting the lever and rod, the means including a first spring biasing the rod towards a maximum fuel flow position, a speed responsive means operably connected to the rod and operable above a predetermined speed to oppose the first spring and move the rod in a fuel flow decreasing direction, and a second spring biasing the rod in a fuel flow decreasing direction, the force of the first spring being such that.

below the predetermined speed the first spring overcomes the second spring to position the rod for maximum fuel flow, the second spring in combination with the speed responsive means at the predetermined speed moving the rod to a lower than maximum fuel flow position.

2. A control means as in claim 1, including a second movable lever between the second spring and rod, first stop means engageable by the second lever during movement of the second lever and rod in a fuel flow decreasing direction to limit the fuel flow decreasing biasing force of the second spring.

3. A control means as in claim 1, including a second movable lever connected to the second spring between the second spring and rod, and stop means in the path of movement of the second lever for limiting its movement thereby controlling movement of the rod.

4. A control means as in claim 3, the stop means including a first stop in the path of movement of the second lever in one direction by the second spring to limit the movement of the control rod by the second lever in a fuel flow decreasing direction, and second stop means in the path of movement of the second lever in the other direction by the control rod to limit the maximum fuel flow.

5. A control means as in claim 1, wherein the'ratio of retraction volume of the delivery valve to maximum delivered volume at full power is between 1 and 1.5.

Claims

1. Fuel injection control means for use with a fuel injection pumping means having a drive shaft, a pump plunger reciprocatable by said shaft for pumping fuel through a chamber into a high pressure discharge line, a helix type port connected to the chamber and connectabLe at times to a spill port to spill fuel from the chamber upon reciprocation of the plunger, a retraction type delivery valve movable in said discharge line to alternately open the discharge line or close and subsequently be withdrawn from said line to reduce the residual pressure therein, and movable means to adjust the position of the helix type port relative to the spill port to vary the fuel delivery volume, the control means comprising a fuel flow control rod movable in opposite directions to increase or decrease fuel flow, an operator controlled lever for moving the control rod, and means interconnecting the lever and rod, the means including a first spring biasing the rod towards a maximum fuel flow position, a speed responsive means operably connected to the rod and operable above a predetermined speed to oppose the first spring and move the rod in a fuel flow decreasing direction, and a second spring biasing the rod in a fuel flow decreasing direction, the force of the first spring being such that below the predetermined speed the first spring overcomes the second spring to position the rod for maximum fuel flow, the second spring in combination with the speed responsive means at the predetermined speed moving the rod to a lower than maximum fuel flow position.

5. A control means as in claim 1, wherein the ratio of retraction volume of the delivery valve to maximum delivered volume at full power is between 1 and 1.5.