This invention relates, generally, to combustion timing adjustment mechanisms for internal combustion engines and, more particularly, to hydraulically-actuated timing adjustment mechanisms for diesel engines.
Fuel delivery and spark timing in a conventional internal combustion engine is generally specified in rotational degrees of the crankshaft either before or after the top dead center position of a connecting rod journal of the crankshaft and its associated piston at the end of the compression stroke. In a fuel injection type of internal combustion engine, the combustion characteristics are, in part, determined by the injection timing. In a typical prior art four-stroke-cycle engine, fuel injection is initiated between approximately 35 degrees and 5 degrees before top dead center (BTDC). When the timing is advanced (closer to 35 degrees BTDC), more time is allotted for the combustion process, which results in more complete combustion of the injected fuel, greater fuel efficiency and a reduction in unburned hydrocarbon emissions. However, advanced timing produces significantly higher combustion pressures, as well as significantly higher combustion temperatures, which result in increased nitrogen oxide (NO2) emissions, except at low engine loads when relatively little fuel is being burned. In addition, because of the increased combustion pressures, advanced timing may make an engine much more difficult to start. On the other hand, when the timing is retarded (closer to 5 degrees BTDC), the NO2 emissions are reduced because most combustion occurs after the piston reaches top dead center. However, because less time is allocated for the combustion process, the emission of unburned hydrocarbons is increased.
The timing that is selected for normal operation of an internal combustion engine is generally a compromise that produces acceptably low quantities of both hydrocarbon and NO2 emissions.
U.S. Pat. No. 3,951,117 and U.S. Pat. No. 4,134,549, both of which issued to Julius P. Perr, disclose a fuel supply system including means for varying the timing of the initiation of injection of the fuel, and the timing may be varied through an infinite number of steps. The injectors disclosed in the above patent and application operate such that injection is terminated when a moving member moves past and opens a spill port. This method of terminating injection has the disadvantages that injection pressure is lost as soon as the spill port is opened, and that the time of termination of injection cannot easily be adjusted.
U.S. Pat. No. 4,142,498 to James T. Hammond discloses a manually-adjustable timing advance mechanism for internal combustion engines, including a driven shaft having cams thereon for actuating a fuel pump for internal combustion engines, a driving shaft adapted to be driven by an engine proportionally to engine speed, the shafts having aligned, splined ends in close adjacency with the lead of the splines on the ends being dissimilar. A splined coupling interconnects the ends and is axially movable thereon and rotatable with the shafts. A collar rotatably receives the coupling and restrains the coupling against axial movement. An adjusting mechanism including a manually and selectively operable actuator is provided for axially adjusting the position of the collar and for holding the collar in a desired position of adjustment. By reason of the dissimilar lead between the splines, movement of the collar, and thus the coupling, will change the angular relationship between the two shafts so that precise timing can be achieved without disassembling the mechanism.
U.S. Pat. No. 4,249,499, also issued to Julius P. Pen, discloses an apparatus, for use with an injector, that includes a movable plunger and a cam drive for the plunger. The apparatus includes movable pistons connected between the cam drive and the plunger, the pistons forming a timing chamber therebetween. A volume of timing fluid is fed into the timing chamber and forms a hydraulic link between the pistons, the timing fluid volume determining the length of the link and the time of initiation of injection. The apparatus further includes a pressure release valve for releasing at least a portion of the timing fluid volume when the pressure in the timing chamber is above a predetermined level. In one form of the invention, the timing is adjustable through many steps, and in another form of the invention the timing is adjustable between two steps.
The present invention provides a variable timing apparatus installable on a compression ignition (diesel) internal combustion engine that is equipped with: an engine oil pump that provides pressurized engine oil for pressurized lubrication of moving engine components; a timing drive that, if the engine employs a two-stroke cycle, rotates at the speed of the crankshaft, or, if the engine employs a four-stroke cycle, rotates at half the speed of the crankshaft; a conventional mechanical fuel injection pump with a straight-splined drive, the body of the fuel injection pump being secured to the normal injection pump mount and the straight-splined drive being coupled to the engine's timing drive with a straight-splined coupler. To implement the invention, the straight-spline drive on the injector pump drive shaft is replaced by a left-hand helical splined drive. A hydraulically-actuated link between the engine timing drive and the fuel injection pump drive is provided. The link provides an injection timing advance when pressurized engine oil is supplied to the link after engine startup. The device utilizes two sets of helically-splined connectors. One set comprises right-hand helically-splined connector elements, while the other set comprises left-hand helically-splined connector elements.
The hydraulically-actuated link apparatus includes a tubular extender equipped with front and rear mounting flanges at opposite ends. A front mounting flange of a tubular extender bolts to the normal injection pump mount, whether it be on the engine block, itself, or on a an injection pump drive housing; the injector pump bolts to a rear mounting flange of the tubular extender. The tubular extender houses a slidable coupler that is directly coupled both to the timing drive of the engine and to the injection pump. Typically, the timing drive is either a gear or sprocket that is coupled to the engine crankshaft. On a four-stroke-cycle engine, the timing drive rotates at half the speed of the crankshaft. On a two-stroke-cycle engine, the timing drive rotates at the same speed as the crankshaft. For an engine which rotates in a clockwise direction as viewed from the rear, or output, end thereof, the drive end of the engine timing drive shaft is equipped with a right-hand helical splines. As heretofore stated, the standard straight-splined drive on the injection pump is replaced with a left-hand helically-splined drive. A slidable coupler, having a front socket equipped with right-hand internal helical splines that mate with the right-hand helical splines of the drive end of the timing drive shaft and a rear end socket equipped with left-hand internal helical splines that mate with the left-hand external helical splines of the injection pump drive. The slidable coupler is equipped with an internal wall that separates the right-hand helically-splined portion from the left-hand helically-splined portion. A coil spring, inserted within the slidable coupler between the injection pump drive and the internal wall, urges the slidable coupler to a normally-retarded timing position. At engine startup, when there is little or no oil pressure flowing to the engines bearings, the sliding coupler is in the normally-retarded timing position. When the engine starts and the engine is running at idle speed, oil pressure is sufficient to overcome pressure of the spring within the sliding coupler, thereby moving the sliding coupler axially rearward approximately 1.0 cm. As the sliding coupler travels axially rearward, it rotates approximately 20 degrees in a counterclockwise direction and causes the injection pump drive to rotate an additional 20 degrees in a counterclockwise direction as the coupler slides over it, thereby advancing injection timing by a total of 40 degrees.
The invention will now be described with reference to the attached drawing figures. It should be understood that the drawing figures may not be to scale, and are intended to be merely representative of the invention. Though the invention is illustrated in the context of a Navistar 6.9/7.31 V8 diesel engine equipped with a Stanadyne DB2 fuel injection pump, the invention can be applied to many other compression-ignition (diesel) engines which employ mechanical injection pumps.
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Although only a single embodiment of the hydraulically-actuated timing advance mechanism for compression-ignition (diesel) engines with mechanical fuel injection pumps is shown and described, it will be obvious to those having ordinary skill in the art that changes and modifications may be made thereto without departing from the scope and the spirit of the invention as hereinafter claimed.