Abstract:
A fuel supply control device is disclosed wherein, as pressure of fuel from a fuel injection pump increases, a piston responsive to fuel pressure temporarily reduces or shuts off initial flow of fuel from the pump to a fuel injector through a series of fuel passageways. A second piston may be provided in a passageway to control movement of the first piston such that when the engine operates under relatively low loads at low speed, the second piston causes the first piston to restrict fuel flow. When the engine operates at relatively high speeds and high loads, the second piston cooperates with the first piston to feed fuel to the injector at high pressure.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a fuel injection device for use with a diesel engine, and more particularly to a fuel supply control device for use with a fuel injection pump of the diesel engine. 
     Conventional fuel injection pumps control the amount of fuel injected into the engine as a function of engine load. Characteristic of such pumps are; relatively high initial fuel injection rates, causing production of NO x  -rich exhaust gas at high noise levels. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a fuel supply control device for use with a fuel injection pump to reduce NO x  component in exhaust gas as well as noise by using a reduced initial fuel injection rate for a relatively large part of the piston stroke. 
     A fuel supply control device, for use with a fuel injection pump of a diesel engine, according to this invention serves to reduce the initial fuel injection rate from the pump when the initial fuel injection rate is relatively large and then recovers the injection rate later in the piston stroke, thereby reducing the NO x  component in exhaust gas, and noise. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features, and advantages of this invention will be apparent from the following description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings in which the same reference numerals designate corresponding elements or parts throughout the drawings and in which: 
     FIG. 1 is a diagramatic view showing a fuel supply system in which a fuel supply control device according to this invention is incorporated; 
     FIG. 2 is a cross-sectional view of the fuel injection pump used in the system of FIG. 1; 
     FIG. 3 is a cross-sectional view of the preferred embodiment of the fuel supply control device according to this invention; 
     FIG. 4 shows a part of a modification of the device of FIG. 3 in cross-section; 
     FIG. 5 is a view, similar to FIG. 4, of a part of a second modification of the device of FIG. 3; 
     FIG. 6 is a modification of the invention including integral formation of a fuel supply control device and an injector; 
     FIG. 7 is a graph showing the injection rate characteristics of the system of FIG. 1 with the fuel supply control device removed; and 
     FIG. 8 is a graph, similar to FIG. 7, of the system of FIG. 1 incorporating the fuel supply control device according to this invention being provided. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, there is shown a fuel supply system, generally designated by reference numeral 10, in which a fuel supply control device according to this invention is incorporated. Fuel is fed at a constant flow rate from a fuel tank 12 by an electromagnetic fuel pump 14 through a pipe 16 to a fuel filter 18 and thence through a pipe 20 to a fuel injection pump 22 of well-known design which acts to control the amount of fuel supplied through a pipe 24 to one of plural fuel supply control devices 26 according to this invention, in such a manner that the amount of fuel fed from pump 22 increases with engine load. Injection pump 22 has a relatively large initial injection rate. Fuel from control device 26, which will be described hereinafter in more detail, is fed through a pipe 28 to an injector 30 from which fuel is injected into the diesel engine (not shown). Combustion occurs when pressure of fuel from control device 26 increases beyond a predetermined value to operate injector 30. The remaining fuel not used by injector 30 returns through pipes 32 and 34 to tank 12. Remaining fuel not used by fuel injection pump 22 also returns to tank through filter 18, a pipe 36 and pipe 34. 
     FIG. 2 is a detailed illustration of fuel injection pump 22. A pump housing 201 is provided with a fuel inlet 202 which introduces fuel from pipe 20 to a fuel passageway 203. A pre-compressor vane pump 204 is driven by a drive shaft 205 which in turn is driven by the engine crankshaft (not shown). A regulating valve 202a regulates pressure of fuel fed from pump 204 to a chamber 216. Drive shaft 205 has a gear 206 attached thereto. A cam disc 207 is mounted for axially sliding movement relative to shaft 205 and is rotatable together with gear 206. Cam disc 207 regulates the phases of the fuel injection timing. Toward this end, the flange surface of cam disc 207 has the same number of symmetrically-arranged cams 208 as the engine has cylinders (not shown). The cam surfaces can be brought into contact with rollers 209 rotatably supported within a cylindrical member 210. The member 210 is supported coaxially with drive shaft 205 and rotates about the shaft axis relative to cam disc 207 by an angle corresponding to the pressure of fuel within the housing by way of a connecting rod 211 of a timing device 212 of well-known design. A plunger 213 is secured at one end to cam disc 207 and its free end is axially-movably received in a cylinder 214. A fuel inlet passageway 215 conducts fuel from chamber 216 to an intake port 217 provided in cylinder 214. The plunger 213 is provided with the same number of grooves 218 as the engine has cylinders and each groove is sequentially communicable with inlet port 217 as the plunger rotates. Plunger 213 is also provided with an axially-extending fuel delivery passage 219 formed therewithin which communicates through grooves 218 with a high-pressure chamber 220 formed by cylinder 214 and the plunger. A distributor port 221 is formed in the outer surface of plunger 213, and communicates with fuel delivery passageway 219. The distributor port 221 can sequentially align with each of the same number of output passages 222 as the engine has cylinders. Each output passage 222 communicates through the corresponding cutoff valve 223 and outlet 224 to the corresponding fuel supply control device 26. Cut-off valves 223 prevent output of fuel at pressures that are not significantly greater than the pressure within housing 216. Thus, when a cut-off port 224 provided in plunger 213 slides out of a control sleeve 226, fuel pressure in the plunger decreases so that no fuel is delivered through the cut-off valve 223. This control sleeve 226 is operated by movement of the accelerator (not shown) transmitted through a lever 227, a spring 228, and a link mechanism 229: when the accelerator is depressed, i.e. when the spring 228 is pulled to the left, the link mechanism 229 rotate counterclockwise about a pivot 230, thereby blocking the cut-off port 225 with the control sleeve 226, thereby increasing the fuel pressure at the distributor port 221 and therefore increasing the amount of fuel supplied to any of the control devices 26. A centrifugal governor 231 is provided on a governor shaft 232. When the pump speed increases, the rotational speed of the drive gear 206 connected to shaft 205 increases, which causes the rotational speed of a gear 233 meshing with the gear 206. As the vanes of the governor 231 swing out, a sleeve 234 fitted slidably over the shaft 232 slides to the right in FIG. 2, thereby turning the link mechanism 229 clockwise about pivot 230 which opens cutoff port 225. This reduces the supply of fuel to device 26, thereby maintaining the rotational speed of the engine, and therefore feed pump 204, at a substantially constant value. 
     In FIG. 2, in order to show the lines of the vane pump 204 shown in solid lines in the side view, the cross-section of the vane pump 204 is shown at 204&#39; rotated through 90 degrees. Similarly, to simplify matters, the starter timer 212 is shown rotated through 90 degrees. 
     Fuel entering the fuel injection pump 22 is precompressed by vane pump 204 and is then fed through chamber 216 and passage 215 to intake port 217. Plunger 213 is rotated by shaft 205 and is reciprocated by cam disc 207, and fuel enters high pressure chamber 220 through intake groove 218 when one of the grooves aligns with inlet port 217. In high-pressure chamber 220, the fuel is compressed by the action of cam disc 207 and therefore plunger 213, and fed to distributor port 221. Fuel is then forced under pressure by way of one of output passages 222 aligning with port 221 and corresponding delivery valve 223, through outlet 224 to control valve 26 (in FIG. 1). 
     However, in this injection pump, since cam disc 207 and plunger 213 are designed to have a predetermined profile, it is impossible to alter the profile of the cam disc and the plunger shape according to changes in the engine&#39;s operating conditions, in order to satisfy the injection requirements at low engine loads as well as at high loads. Thus the injection quantity is normally set on the high side, so that if this type of mechanism were used by being directly connected to injector 30, the fuel injection rate (quantity of fuel injected/period of injection) would be too large at the beginning of the piston stroke. The fuel injection rate at the start of the injection would rise abruptly, the quantity of NO x  exhaust gases would be large, and noise levels would also be high--all of which, however, can be rectified by provision of the fuel supply control device 26 according to this invention. 
     FIG. 3 is a cross-sectional view of the preferred embodiment of the fuel supply conrol device 26. Device 26 may take the form of a switching valve having a fuel passageway 261 formed generally transversely to a bore 262. Passageway 21 communicates through a fuel inlet 263 by way of pipe 24 with pump 22. At either end of bore 262, stops 264 and 264a are formed. Stops 264, 264a also serve as oil seals at either end of the bore. A piston 265 reciprocates in the bore 262 between oilseals 264, 264a. Fuel passageways 266a and 266b of pre-determined cross-sectional area are formed through piston 265, and when either passage is aligned with the fuel passageway 261, fuel is supplied to injector 30 through fuel output 263a and pipe 28. 
     Chambers 267a and 267b are formed between each of stops 264 and 264a and piston 265. Chamber 267a is supplied with fuel under pressure by an actuation passage 268 communicating with passage 261. Chamber 267b is supplied with substantially constant reference pressure such as fuel under pressure from pump chamber 216 through a passage 269. In FIG. 3, pressure actuation chamber 267a and chamber 267b contain springs 270a and 270b respectively. Spring 270b is stronger than spring 270a to the degree that when fuel pressure in chamber 267a is at its lowest value, passageways 261 and 266a are aligned. 
     In operation, the fuel pressure begins to rise due to working of the fuel pump 22 (in FIG. 1), and the pressure within pump chamber 216 rises with the passage of fuel through actuation passageway 268. In this manner, a pressure difference is gradually created between fuel pressure actuation chamber 267a and base-pressure chamber 267b, and piston 265 moves downward against the resistance of spring 270b. As a result, the area of coincidence of the fuel passageways 261 and 266a is decreased, but shortly after fuel starts being injected from injector 30, the connection between fuel passageways 261 and 266a is broken. The fuel passageways 261 and 266a are isolated from one another, but as plunger 213 continues its compression stroke, the fuel pressure in fuel passageway 261 and, hence, the fuel pressure actuation chamber 267a, increases. Eventually, the fuel passageway 266a is brought into alignment with fuel passageway 261, and fuel injection from injector 30 is immediately recommenced. 
     In the decompression stroke of plunger 213, cut-off port 225 opens to chamber 216, and therefore, at this time the fuel pressure difference between fuel pressure actuation chamber 267a and base pressure chamber 267b equalizes and piston 265 is moved upwards in response to the spring constants and lengths of springs 270a, 270b The function of stops 264a and 264b is to determine the limiting positions of piston 265 and therefore the fuel passageways 266a and 266b. 
     FIG. 4 shows a modification of the present invention, showing a cutoff shaft 273 or piston provided within a bore 271 intersecting actuation passageway 268 similar to the one of FIG. 3 in order to suspend the function of control device 26 according to the state of the engine operation. The remaining structure of the device is the same as that of the device of FIG. 3. When the engine is lightly loaded at a low speed, an electromagnetic valve (not shown) switches off to lift cutoff shaft 273, and actuation passageway 268 then communicates with the fuel pressure actuation chamber 267a (FIG. 3) by passageway 272, causing a two-stage fuel injection similar to the injection described in the structure of FIG. 3. During all other engine operating conditions the electromagnetic valve is then switched on, lowering cutoff shaft 273; fuel passageway 268 is thus closed so that fuel cannot enter fuel pressure actuation chamber 267a, causing fuel to flow unhindered through control device 26 to injector 30. In FIG. 4, a passageway 273a communicates with pump chamber 216 of FIG. 2, and a stop 274 installed on the bottom of bore 271 is provided with a spring 274a biasing cutoff shaft 273 upwards. Reference pressure such as fuel pressure on the intake side of pump 26 or atmospheric pressure is admitted to the space below piston 273 through a passageway 269a. 
     In FIG. 5, a modification of the piston shown in FIG. 3 is illustrated. In this modification, fuel passageways 266a and 266b are formed as annular grooves in the outer surface of piston 265 so that they can each communicate with fuel passageway 261. 
     In FIG. 6, a further modification of the present invention includes integral formation of a fuel supply control device 26 and an injector 30. Control device 26 includes a bore 280 in which is movably disposed a piston 281 which is normally urged by a biasing means 282 to the right in FIG. 6 against an inlet 283 of the control device. The control device includes two branch passageways 284a and 284b in its body, both communicating with the inlet 283 through a passageway 285. Branch passageway 284a communicates through an annular groove 286a provided on piston 281 with a passageway 287a provided in device 26, whereas branch 284b is normally blocked by piston land 281b so that it cannot communicate with a passage 287b provided in the device. If piston 281 moves to the left passage 284a is at first blocked by piston land 281a and then branches 284a, 284b are simultaneously connected through annular grooves 286b and 286b with passageways 287a, 287b, respectively. Injector 30 includes an upper part 301 integral with the device 26 and an intermediate member 302 cooperating to form a cavity 303 which communicates with atmosphere through a passage 304 provided in the body through bore 280. Disposed in the cavity 303 is a seat 305 which is normally biased downward by a spring 306 disposed between the upper end of the cavity and the seat member. Seat member 305 has a rod 307 screwed thereinto that extends movably through a bore 308 within intermediate member 302. A lower; member 309 includes a bore 309a in which a needle valve 310 is vertically movably received. The needle valve is securely connected to the lower end of the rod 307 and has a tapered portion 311 ending in a needle 312 which protrudes through a nozzle 313 in lower member 309. A groove 312a is formed on the needle 312. The upper part 301, the intermediate member 302, and the lower member 309 have the passageways 287a, 287b; 315a, 315b; and 316a, 316b. respectively, extending therethrough. The passageways 287a, 315a, and 316a form a fuel passageway leading to the cavity 314 and the passageways 287b, 315b and 316b forms another fuel passageway leading to the cavity 314. The upper part 301, the intermediate member 302, and the lower member 309 are sealingly held together, in the serial order mentioned and arranged so that the fuel passageways mentioned above are aligned as described, by a jacket 317 in the form of a radially-symmetrical shell. One end of the jacket 317 is threaded on the inside to match threads provided on the lower portion of the upper part 301. The other end has a flange 319 which serves to restrain a shoulder 309b formed on the lower member 309. 
     During initial injection, fuel entering inlet 283 from passageway 24 (FIG. 1) flows through passageway 285, branch passageway 284a, and groove 286a. As pressure of fuel increases, piston 281 moves to left against return spring 282. Communication between branch passageway 284a and passageway 287a is then blocked by land 281a so that fuel pressure at inlet 283 abruptly increases. Thus, at the moment when passages 284a and 284b communicate with passages 287a and 287b, a large amount of fuel is forced through the pair of passageways constituted by the passageways 287a, 315a, 316a and 287b, 315b, 316b, so that needle valve 310 is lifted, thereby causing fuel to be injected through nozzle 313 outward into the engine cylinder. 
     FIGS. 7 and 8 show the injection patterns of the system without and with device 26, respectively. 
     While this invention has been described and shown with respect to a preferred embodiment and modifications thereof, various changes and modifications thereof could be made by those skilled in the art without departing from the spirit and scope of this invention.