Patent Grant
6889663
The invention relates generally to control of compression-ignition engines, and more particularly to cam sensor elimination in four stroke compression-ignition engines having cylinders with large displacement volumes, such as locomotive or marine type engines.
Although various techniques for eliminating cam sensors have been provided in the context of relatively small spark-ignition engines, these type of techniques are believed not to be suited to the unique designs of larger compression-ignition engines, such as diesel engines. For example, the single cylinder displacement for a large sixteen cylinder locomotive diesel engine may be on the order of 11 liters whereas the single cylinder displacement for a typical diesel truck may be on the order of only 2 liters per cylinder. Therefore a single cylinder for a large locomotive engine may easily be more than five times larger than that of a large diesel truck. In addition, a typical truck engine has 6 or 8 cylinders as opposed to 12 or 16 for a typical locomotive engine, thus each cylinder contributes a smaller portion of the total power. This generally translates into very different design constraints since high injection pressure levels (on the order of 10-20 k.p.s.i.) are required in conjunction with much higher volume fuel flow rate ranges (100-1600 mm3/stroke) to effectuate proper combustion in the larger locomotive engine.
Other differences also impact the type of fuel injection system which may be employed on larger compression ignition engines. For example, locomotive engines are typically designed to maintain governor stability e.g., provide a relatively constant speed output to provide a steady power generating source for large fraction motors used to propel the wheels. Also, large locomotive engines encounter radical load changes due to switching of large auxiliary loads such as compressor loads, fan loads, and “hotel” power loads (an alternator for generating 110 V at 60 Hz) for passenger train applications. Driving such loads or turning off such loads can result in load changes on the order of 500 horsepower at any instant.
Another design consideration generally unique to such larger engines is lower engine speeds (RPM) and reduced chamber air movement. Smaller engines typically operate at engine speeds of several thousand RPM's. However, larger locomotive engines typically operate at between 0-1050 RPM. The rate at which the pistons move generally impacts the air intake speed and/or swirl. Lower RPM typically translates into slower air intake. With smaller volume cylinders, sufficient chamber air movement to allow proper atomization of the fuel to air mixture typically occurs during the power stroke. However, larger cylinders typically have much less cylinder air movement which results in a more stagnant trapped air volume. This generally requires a greater fuel injection pressure to be applied to overcome the in-cylinder compression and penetrate the trapped air volume in a sufficiently atomized state, such that entrainment will result in a homogenous and stoichiometric bum of the air/fuel mixture.
In a conventional locomotive engine design, a crank sensor synchronizes an engine governor unit (EGU) to the crank. A cam sensor, however, determines the respective stroke the engine is actually in, that is, without the cam sensor, the EGU would not be able to determine the difference between a compression stroke and an exhaust stroke. Once the cam position is known, the EGU does not typically need additional cam data because by sensing crank teeth information, the EGU is able to maintain the proper cam sense. Presently, one simply cannot start the locomotive engine without the cam sensor.
In view of the above-discussed issues, it would be desirable to provide control techniques that would allow for reliably providing controlled start of the compression-ignition engine of the locomotive even in the absence of the cam sensor since, presently, the cam sensor is a single point failure in the locomotive. Another reliability enhancement resulting from the elimination of the cam sensor would be to eliminate loss of synchronization in the EGU due to noisy cam pulses. It would be further desirable to lower manufacturing costs of the engine since if one could eliminate the cam sensor, one could also eliminate machining done on the cam sensor cover and timing wheel. Further, wiring and circuitry on the EGU that processes the cam sensor signal could be eliminated. Additionally, elimination of the cam sensor would result in a simpler manufacturing process not requiring time consuming and error prone cam sensor gapping actions.
Generally, the present invention fulfills the foregoing needs by providing in one exemplary embodiment a method for controlling start of a compression ignition engine having a plurality of cylinders. Each cylinder includes a respective piston reciprocally movable between respective top and bottom positions along a cylinder longitudinal axis. The method comprises providing a respective fuel delivery assembly for each cylinder. The method further comprises retrieving from memory a set of fuel delivery assembly firing rules and then processing the firing rules so that a firing signal is delivered to each fuel delivery assembly on every crank revolution during a cranking mode of operation. The fuel delivery assembly is arranged to be responsive to any firing signal received during an injection window leading to the top position along the longitudinal axis so as to supply fuel to each cylinder during that injection window. The fuel delivery assembly is further arranged to be insensitive to any firing signal received outside the injection window so that no fuel is delivered to each cylinder outside the injection window.
The present invention further fulfills the foregoing needs by providing in another embodiment a method for controlling start of a compression ignition engine having a plurality of cylinders. Each cylinder includes a respective piston reciprocally movable between respective top and bottom positions along a cylinder longitudinal axis. The method comprises allows for providing a respective fuel delivery assembly for each cylinder. The method further allows for retrieving from memory a set of fuel delivery assembly firing rules. The firing rules are processed so that a firing signal is delivered to each fuel delivery assembly on every other crank revolution relative to an assumed cam position. Reprocessing the firing rules every n engine revolutions so that the firing signal is delivered to each fuel delivery assembly relative to a cam position about 180 degrees relative to the original assumed cam position, n corresponds to a positive integer greater than 1.
The present invention further fulfills the foregoing needs by providing in yet another embodiment a method for controlling start of a compression ignition engine having a plurality of cylinders grouped in at least two sets of cylinders. Each cylinder including a respective piston reciprocally movable between respective top and bottom positions along a cylinder longitudinal axis. The method allows for providing a respective fuel delivery assembly for each cylinder. The method further allows for retrieving from memory a set of fuel delivery assembly firing rules. The method further allows for processing the firing rules so that a firing signal is delivered to each fuel delivery assembly in one of the two sets of cylinders on every other crank revolution relative to an assumed cam position and for processing the firing rules so that a signal is delivered to each fuel delivery assembly in the other of the two sets of cylinders on every other crank revolution relative to a cam position about 180 degrees relative to the assumed cam position.
Before any embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.
Each unitized power assembly 14 further includes a cylinder liner 40 which is insertable into a bored aperture (not shown) in the engine block of the engine 10. The unitized power assembly 14 includes a cylinder jacket or casting for housing the cylinder 28 and associated components. For a typical engine 10, such as may be used in locomotive applications, an exemplary range of injection pressure is between approximately 15-20 k.p.s.i. An exemplary fuel delivery flow volume range is between about 100-1600 mm3/stroke. An exemplary range of per cylinder displacement may be from about 5.5 liters to about 11 liters. It will be appreciated that the present invention is not limited to the above-described exemplary ranges.
The fuel delivery assembly 30 includes a fuel injecting mechanism 42 connected to a high-pressure injection line 44 which fluidly connects to a fuel pressure generating unit 46 such as a fuel pump. This configuration is known as a pump-line-nozzle configuration. The fuel pressure generating unit 46 builds pressure through the actuation of fuel pushrod 48 which is actuated by a lobe on the engine camshaft dedicated to fuel delivery actuation. The fuel delivery assembly 30 includes an electronic signal line 50 for receiving electronic signals from an electronic controller, as will be described later. The electronic signal line 50 provides a control signal to an electronically-controlled valve 52 which forms part of the fuel delivery assembly 30.
The unitized power assembly 14 derives its name from the fact that each cylinder and accompanying components (or power assembly) may be removed from the engine individually to facilitate servicing. Consequently, the entire engine need not be removed or replaced to facilitate repair of the cylinder or any of its associated components. It will be appreciated that the system and techniques of the present invention are not limited to unitized power assemblies.
The above-described actions allow during the cranking mode of operation to fire one or more solenoids in the fuel delivery assembly as if each cylinder TDC corresponds to the compression stroke. This results in firing the cylinder if indeed the cylinder is at TDC of the compression stroke, however, the fuel delivery assembly will not inject fuel if the cylinder is at TDC of the exhaust stroke since in this latter case a fuel pump cam would not be moving upwardly, and thus no fuel flow will develop and the cylinder would not be fired even in the presence of a firing signal. This embodiment enables to start the engine with all cylinders and could be continued indefinitely. In the event that there may be a concern regarding incremental wear on the injector pump valve if it is receiving a firing signal every crank revolution, then the following optional steps may be used to synchronize the engine. It will be appreciated, however, that if incremental wear of the injector valve is not a factor, then the following steps are not necessary.
Step 112 allows for determining whether the engine has reached a predefined engine condition, such as engine RPM ranging from about 200 to about 250 RPM. If the engine has reached the predefined engine RPM, then step 114 allows for processing a new set of firing rules so that a firing signal is delivered to each fuel delivery assembly during every other crank revolution relative to an assumed cam position. If the engine has not reached the predefined engine speed, then the method iteratively continues at step 106. Step 116, reached through connecting node A, allows for monitoring one or more operational engine parameters indicative of the level of performance of the engine, e.g., engine speed, acceleration, etc. As indicated at decision block 118, if the level of engine performance decreases, then step 120 allows for changing the assumed cam position by about 180 degrees, prior to return step 122. Conversely, if the level of engine performance increases, then the method proceeds to return to step 122. This would indicate that the assumed cam position corresponds to the actual cam position. Further engine synchronization would be maintained by sensing a signal indicative of crank teeth position, as would be readily understood by one of ordinary skill in the art.
Step 210 allows for determining whether the engine has reached a predefined engine condition, such as engine RPM ranging from about 200 to about 250 RPM. If the engine has reached the predefined engine RPM, then the method continues at step 212 reached through connecting node B. If the engine has not reached the predefined engine speed, then the method iteratively continues at step 206. Step 212 allows for monitoring one or more operational engine parameters indicative of the level of performance of the engine, e.g., engine speed, acceleration, etc. As indicated at decision block 214, if the level of engine performance decreases, then step 216 allows for changing the assumed cam position by about 180 degrees, prior to return step 220. Conversely, if the level of engine performance increases, then the method proceeds to return step 220.
As suggested above, this last-described embodiment will attempt to fire the engine correctly for n revolutions, then fire incorrectly for n revolutions and could give the operator the impression that the engine is not running properly. It is believed that appropriate training of the operator would avoid that issue. In addition, n should be chosen to allow enough time for the engine to accelerate to the decision speed. Also, the decision speed must be far enough above the cranking speed to assure that the engine has in fact reached this speed by its own power.
In one exemplary implementation n may be equal to one. That is, one would assume a cam position (e.g., either corresponding to a compression stroke or to an exhaust stroke) and would attempt firing the engine based on the assumed position. If the engine does not start, one would change the assumption to the other position and would attempt firing the engine based on this other position. It is contemplated to make use of sensors commonly available in locomotive engines indicative of the probability of correctly making an appropriate firing cycle the first time. That is, to increase the probability that the assumed cam position corresponds to the actual condition of the engine, e.g., whether in a compression stroke or in an exhaust stroke. For example, one could use a manifold pressure sensor to sense manifold pressure characteristic during cranking that would indicate which cycle the engine may be on. It will be appreciated that any other sensor suitable for measuring characteristics indicative of the probability of being in a compression stroke or in an exhaust stroke could be used equally effectively. Another technique that may be used for improving the probability of correctly making an appropriate firing cycle the first time may be for the controller to remember the last firing cycle based on the engine position when it was last running, as may be sensed by an engine position sensor. In practice, this technique may be somewhat difficult to implement since the resolution of typical engine position sensors tends to decrease as the engine coasts to a stop.
It will be appreciated that in this exemplary embodiment, half of the cylinders will receive a firing signal during the firing window and produce power. The other half of the cylinders will receive the signal during the exhaust intake stroke and no fuel will be delivered.
Step 312, reached through connecting node C, allows for determining whether the engine has reached a predefined engine condition, such as engine RPM ranging from about 200 to about 250 RPM. If the engine has not reached the predefined engine speed, then the method iteratively continues at step 308 reached through connecting node D. If the engine has reached the predefined engine RPM, then step 314 allows for monitoring one or more operational engine parameters indicative of the level of performance of the engine, e.g., engine speed, acceleration, etc. As indicated at decision block 316, if the level of engine performance decreases, then step 318 allows for changing the assumed cam position by about 180 degrees, prior to return step 322. Conversely, if the level of engine performance increases, then step 320 allows for continuing to maintain the firing signal relative to the assumed cam position prior to return step 322. It is believed that this last-described technique, may offer some advantages in one exemplary embodiment since it does not require any wiring changes to an existing engine control design and it is further believed that this embodiment better handle dry-injector conditions.
It will be understood that the specific embodiment of the invention shown and described herein is exemplary only. Numerous variations, changes, substitutions and equivalents will now occur to those skilled in the art without departing from the spirit and scope of the present invention. Accordingly, it is intended that all subject matter described herein and shown in the accompanying drawings be regarded as illustrative only and not in a limiting sense and that the scope of the invention be solely determined by the appended claims.
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| Number | Date | Country | |
|---|---|---|---|
| 20050010355 A1 | Jan 2005 | US |
