Abstract:
In a fuel injection pump, an engine drives a rotary plunger having an axially extending bore connected to a compression chamber, plural fuel inlet ports alignable with an inlet passage for introducing fuel to the compression chamber, fuel distribution ports for distributing the compressed fuel through the bore to each one of the fuel delivery passages and plural spill ports. A spill-port timing control unit is provided comprising a stator core, a coil wound on thereon, a magnetized ring having a spill groove, and a spring for resiliently maintaining the ring in a reference angular position with respect to the stator core. The magnetized ring is mounted on the plunger so that it can rotate from the reference angular position to an angularly displaced position in proportion to the magnetic flux of the coil to align the spill groove of the ring with each spill port of the plunger to create a passageway through which the compressed fuel is allowed to escape at the termination of fuel injection.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to fuel injection pumps of the distribution type wherein a plunger having a spill port is driven by the output shaft of a Diesel engine to determine the end timing of injected fuel, and more specifically to a fuel injection pump having a compact spill-port timing control unit. 
     The spill-port timing control unit of known distribution type fuel injection pumps for Diesel engines comprises a spill ring movably mounted on the rotary plunger of the pump and a centrifugal governor that axially moves the ring to bring its spill port into alignment with a spill port of the plunger to allow compressed fuel to escape through the aligned ports to the outside at the end of fuel injection. Another type of spill-port timing unit which has been developed to replace the governor type unit comprises a rotary or linear solenoid having a moving part which is linked to the spill ring by a mechanical means such as levers. This resulted in a relatively complicated mechanism and takes up a substantial amount of space in the fuel pump housing, and as a result the injection pump became bulky. It has therefore been desired to develop a spill-port timing control unit that is easy to manufacture and compact in design without sacrificing the required degree of sensitivity to a control signal applied to the solenoid. 
     SUMMARY OF THE INVENTION 
     It is therefore a primary object of the invention to provide a spill-port timing control unit for distribution type fuel injection pumps which takes up as small a space as possible in the injection pump. 
     A fuel injection pump includes a rotary plunger driven about its axis by an internal combustion engine, the plunger having a plurality of angularly spaced apart spill ports through which pressurized fuel is allowed to escape to the outside of the plunger. The spill-port timing control unit of the invention comprises a stator core, a coil wound on the core adapted to be energized by a current supplied thereto, a magnetized spill ring having a spill groove, and a spring for resiliently maintaining the ring in a reference angular position with respect to the stator core. The magnetized ring is mounted on the plunger so that it can rotate from the reference angular position in proportion to the magnetic flux of the coil to align the spill groove of the ring with each one of the spill ports of the plunger to create a passageway for the escaping fuel. 
     Preferably, the spill ring is axially movably mounted on the plunger, and its spill groove is part-helically formed on the inner wall of the ring. The ring is provided with a cam for axially displacing it in proportion to the angle of its rotation, whereby the angular displacement of the ring with respect to the reference angular position is greater than the angular displacement of the spill groove of the ring with respect to the spill port of the plunger. This spill ring structure is particularly useful to obtain accurate information on the angular position of the spill ring for precision fuel control, and can be advantageously adapted in a fuel injection pump of the type having an inner cam ring mounted in an angularly adjustable position and a pair of fuel compression pistons which reciprocate in a compression chamber in camming contact with the inner walls of the cam ring. The inner cam ring is adjustably rotated by means of a known timing mechanism to determine the start timing of fuel injection. 
     In a further preferred form of the invention, the rotary solenoid is mounted on the inner cam ring so that the spill ring rotates with the cam ring to compensate its angular position with respect to the injection start timing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be described in further detail with reference to the accompanying drawings, in which: 
     FIG. 1 is an axial cross-sectional view of a fuel injection pump according to a first embodiment of the invention; 
     FIG. 2 is a cross-sectional view taken along the lines 2--2 of FIG. 1; 
     FIG. 3 is an end view of an alternative form of the magnetized spill ring; 
     FIG. 4 is a schematic illustration of a fuel injection control circuit; 
     FIG. 5 is a flowchart describing the operation of the control circuit of FIG. 4; 
     FIG. 6 is an axial cross-sectional view of a fuel injection pump according to a second embodiment of the invention; 
     FIG. 7 is a partially broken, side view of the spill ring of the second embodiment; 
     FIG. 8 is a cross-sectional view taken along lines 8--8 of FIG. 7; and 
     FIG. 9 is an illustration of a developed form of the spill ring of FIG. 7 useful for describing the second embodiment. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, there is shown a fuel injection pump of the distribution type constructed according to a first embodiment of the invention. Illustrated at 1 is a rotary shaft which is coupled to the output shaft of an internal combustion engine. The shaft 1, when driven by the engine, drives a vane type feed pump 2 to feed fuel under pressure controlled by a regulating valve 3 into the pump housing 4. A toothed wheel of a ferromagnetic material 1a is mounted on the shaft 1. A Hall generator 1b secured to the pump housing 4 in proximity to the periphery of the wheel 1a measures the rotational speed of the shaft 1 by generating pulses in response to variations in magnetic field intensity. A face cam 5 having a plurality of camming surfaces each for an engine cylinder is axially slidably coupled by a known coupling means 5a to the drive shaft 1 for rotation therewith while keeping a camming contact with a roller 6 which is mounted within a roller ring 6a in an angularly adjustable position with respect to the face cam 5. Therefore, the face cam 5 rotates with the engine shaft and reciprocates in synchronism with the stroke movements of engine pistons. To the face cam 5 is fixedly coupled a plunger 7 extending horizontally to define a compression chamber 8 at the forward end thereof where it is formed with a plurality of axially extending, circumferentially spaced apart inlet ports 7a (only one being shown) corresponding in number to engine cylinders. Each of the ports 7a comes into alignment with a fuel passage 9 (having a fuel shutoff valve 10 therein) to admit fuel into the chamber 8 when the plunger 7 is moved to an appropriate angular and axial position. When the plunger 7 is moved forwards the fuel is compressed in the chamber 8 and then allowed to escape through an axially extending bore 7d and through a distribution port 7b to a delivery passage 11, the fuel being passed through a delivery valve 12 to a fuel injector, not shown. The axial bore 7d terminates in a plurality of radially extending spill ports 7c associated respectively with engine cylinders. As hydraulically operated timimg arrangement 13 of a known structure, located below the face cam 5, is actuated by a well known timing control valve, not shown, to adjust the angular position of the roller 6 with respect to the face cam 5 to control the start timing of fuel injection. 
     Illustrated at 14 is a spill-port timing control unit, or rotary solenoid 14 constructed according to the present invention. The rotary solenoid 14 includes a magnetized rotor or spill ring 15 rotatably mounted on the rear end portion of plunger 7 having the spill port 7c, a stator core 16 having a circular opening 17 for accommodating the rotor 15, and a pair of coils 18 wound on the upper and lower parts of the stator core. 
     As illustrated clearly in FIG. 2, the spill ring 15 is formed with an axially extending spill groove 15a on the inner wall thereof. As shown in FIG. 3, the spill ring 15 may alternatively comprise a magnetized outer cylinder 40 and a ferromagnetic inner cylinder 41 having an axial spill port 42. 
     The spill groove 15a comes into alignment with each spill port 7c of the plunger 7 to allow the compressed fuel to escape through the aligned spill ports into the pump housing 4 to terminate the fuel injection. 
     The coils 18 are connected in circuit through a line 22 to a control unit 30 (FIG. 4) to be energized by a control signal supplied therefrom. The spill ring 15 comprises a pair of magnets N and S which equally divide it along its axial length. The plunger 7 preferably comprises a permalloy or any other ferromagnetic material so that when the coils are not energized it can allow as many magnetic flux lines as possible to pass therethrough to make the spill ring 15 less subject to disturbances in flux density and stably balanced in a predetermined angular position against the force of a spiral spring 21 that couples the spill ring 15 to the stator core 16. 
     When the coils 18 are energized, the spill ring 15 is caused to rotate from the reference position under the flux-induced thrust until it balances against the spring 21. The angular displacement of the spill ring 15 is thus proportional to the current supplied to the coils 18. It is seen therefore that the time of alignment between each one of the radial spill ports 7c and the spill groove 15a is adjustably controlled and the amount of fuel injected is determined. 
     A ferromagnetic needle pointer 24 is attached to the spill ring 15. This pointer extends upwards to a Hall generator or angular position sensor 25 that detects the angular position of the spill ring 15 and provides an r position signal to the control unit 30 through a line 26. 
     The control unit 30 also receives engine speed signal (N) from the Hall generator 1b through a line 27 and other engine parameter signals from known sensors 28 such as engine&#39;s operating temperature (THW) and intake air temperature (THA) and an engine load signal (A) from a variable resistor 29 operatively coupled to the accelerator pedal. The control unit 30 preferably comprises a microcomputer including a microprocessor, a read-only memory and a random access memory and an input/output port through which input and output signals are passed. The microcomputer is programmed as shown in the flowchart of FIG. 5 to process on the input signals to compute an optimum fuel injection time and provide a corresponding signal to the coils 18 through line 22 to adjust the angular displacement of the spill ring 15 with respect to the spill ports 7c. More specifically, the program includes a main routine in which the microprocessor starts execution at step 101 by initializing the various counter and registers and goes to a step 102 to read the input data mentioned above. At step 103, trimming values f(THA) and f(THW) are derived as a function of the intake air temperature THA and engine temperature THW. The microprocessor returns to step 102 to repeat this process to constantly update the derived trimming values. In response to a pulse from the engine speed sensor 1b, the main routine is interrupted and an interrupt routine is initiated. The interrupt routine starts at step 104 in which a basic timing datum (To) for spill port alignment is derived from a map stored in the read only memory as a function of engine speed value N and acceleration angle A. This timing datum is trimmed with the trimming values at step 105 and the trimmed datum is converted at step 106 into a current signal for application to the coils 18. 
     Therefore, the invention allows a spill control solenoid structure that is easy to manufacture and compact in size. 
     The rotary solenoid can also be employed in a fuel injection pump of the type as shown at 64 in FIG. 6 wherein an inner cam ring and a pair of cam-engaging pistons are employed for effecting fuel compression at the rear end of a fuel distribution plunger without reciprocating it. 
     In FIG. 6, the solenoid 64 is supported in an angularly adjustable position by means of a yoke 50 which is rotatable about the axis of the drive shaft 1 by the hydraulically operated timimg arrangement 63. The yoke 50 is integrally formed with an inner cam ring 52 having an inner wall contoured to provide a plurality of inwardly facing camming faces that correspond in number to engine cylinders. A fuel distribution plunger 57 extends through the yoke 50 and is coupled with the drive shaft 51 for rotation therewith. A pair of radially reciprocable pistons 53a and 53b are mounted in a cylinder 54 which is formed at the rear end portion of the plunger 57 in communication with a bore 57d that extends axially to the forward end of plunger 57. The pistons 53a and 53b are provided with cam followers 55a and 55b respectively which are brought into camming contact with the inwardly facing camming surfaces of the cam ring 52 to reciprocate at fuel injection timing. 
     The plunger 57 is provided with radially extending fuel induction ports 57a each of which aligns with a fuel intake port, not shown, provided in the pump housing 58, fuel distribution ports 57b near the forward end thereof and spill ports 57c intermediate the ports 57a and ports 57b, the number of ports in each set corresponding to the number of engine cylinders. 
     Fuel supplied to one of induction ports 57a is led to the chamber 54 and compressed by the reciprocating pistons 53a and 53b, the compressed fuel being fed to the forward end of the plunger 57 when the pistons move radially outwards and delivered through one of the distribution ports 57b. The latter comes into alignment with an associated one of fuel delivery passages 59 to inject the compressed fuel to an engine cylinder. This timing is determined by the angular position of the yoke 50 and hence the fuel distribution ports 57b with respect to the fuel delivery passages 59 under the control of the timing means 63. 
     Since the rotary solenoid 64 is mounted in an angularly adjustable position, the reference position of the spill ring 57 is also rotatable with the inner cam ring 52 and hence with the variable injection start timing. The benefit of this arrangement is that the amount of fuel injected is not affected by the injection start timing adjustment. With this start timing correction, the fuel injection quantity is solely determined by the injection end timing and hence by the signal supplied from the control unit 30. 
     While the solenoid 64 may be of the identical construction to the solenoid 14 of the previous embodiment, this solenoid is not satisfactory for certain applications which require high precision control on the angular position of the spill ring. More specifically, in the FIG. 1 embodiment the angular displacement of the spill ring 15 that is required to vary the fuel injection quantity from a mininum to a maximum value is represented by the difference between the angular displacement of the spill ring 15 set for a minimum quantity and that for a maximum quantity. Because of the axially straight spill groove 15b, this difference is small compared with either of these angular displacements. If use is made of a fuel injection pump capable of fuel injection under a pressure of 500 kg/cm 2 , for example, the amount of fuel injected per piston stroke typically varies in a range from a minimum of 7 mm 3  to a maximum of 40 mm 3 , which range roughly corresponds to an angular displacement of 5 degrees. If this range is to be divided into 50 units of resolution, the spill ring 15 will be required to have a unit angular displacement as small as 0.1 degrees. This would require a costly, high precision position detector. 
     To this end, the invention provides a rotary solenoid 64 which includes a rotary spill ring 65 of a structure differing from the spill ring 15 of the previous embodiment in that a part-helical spill groove 65a is provided on the inner wall thereof and a cam 65b is formed at the forward end thereof as clearly shown in FIGS. 7 and 8. The spill ring 65 is maintained in a home position by a spiral spring 66 which provides a biasing action both in angular and axial directions. A cam pin 70 is stationarily mounted in the housing 58 in camming contact with the cam portion 65b of the spill ring 65. The spill ring 65 rotates with respect to the stator core 67 in response to the current supplied to coils 68 from the control unit 30 in the same manner as in the previous embodiment. A ring position needle 69 extends from the spill ring 65 to a position detector 71 to detect the angular displacement of ring 65 with respect to a reference point. 
     The operation of the rotary solenoid 65 will be better understood with reference to FIG. 9 in which the inner wall of the spill ring 65 is shown in developed form in relation to spill ports 57c of the rotary plunger 57. 
     The spill ring shown at A in FIG. 9 is positioned so that its cam portion 65b is located on the right side of the cam pin 70 to provide a minimum amount of fuel injection, while the spill ring shown at B in FIG. 9 is in a position rotated clockwise relative to the cam pin 70 for maximum amount of fuel injected. With the spill ring 65 located as shown at A, FIG. 9, it is assumed that fuel injection occurs, so that fuel injection will terminate when the spill ring 65 has rotated counterclockwise by an angle θ1 at which the spill port 57c coincides with the spill port 65b. In response to a current supplied to the coils 67, the spill ring 65 is rotated counterclockwise from the position A by an angle Δθ and is simultaneously displaced axially rearwards against the spring 66 by a maximum distance L due to the camming action. The spill port 57c is now positioned close to the forward end of the spill ring 65. If fuel injection occurs with the spill ring 65 in the position B, then the amount of injected fuel is proportional to an angle θ2. It is appreciated therefore that by rotating the spill ring 65 by appropriately choosing the angle of skew of spill port 65a and the amount of axial displacement L, the apparatus as taught by the invention allows a high resolution between minimum and maximum amounts of fuel injection. As a result, the position needle 69 swings through a larger angle than is available for the position needle 24 of the previous embodiment.