Patent Grant
7735465
This application claims priority of German patent application no. 10 2006 032 474.9, filed Jul. 13, 2006, the entire content of which is incorporated herein by reference.
A method of the above kind for operating an internal combustion engine is disclosed in United States patent application publication no. US 2006/0157006 A1 (now U.S. Pat. No. 7,325,528) which is incorporated herein by reference and is assigned to the same assignee as the present application.
U.S. Pat. No. 5,901,673 discloses a two-stroke engine wherein fuel is injected into the combustion chamber for each crankshaft revolution in the region of bottom dead center of the piston and the air/fuel mixture, which is formed in the combustion chamber, is ignited in the region of the top dead center of the piston.
United States patent application publication no. US 2006/0157006 A1 (now U.S. Pat. No. 7,325,528) discloses controlling a two-stroke engine in at least one operating state so that the number of combustions is less than the number of revolutions of the crankshaft in the same time interval.
To limit the rpm of an internal combustion engine, U.S. Pat. No. 6,880,525 discloses holding the ignition switch open when exceeding an end rpm in order to suppress an ignition spark over at least one crankshaft revolution. The suppression of the ignition spark is intended to prevent a combustion in the next engine cycle. In this way, a reduction of the rpm can be reached so that the rpm cannot increase uncontrolled beyond a highest rpm.
It has been shown that in internal combustion engines controlled in this manner, a large increase of the rpm from the full load rpm can occur when the load is suddenly reduced. This can, for example, take place in a brushcutter when the filament tears. The sudden uncontrolled increase of the rpm leads to a high load on the component. It has furthermore been shown that the exhaust gas values deteriorate greatly with an uncontrolled increase of the rpm.
It is an object of the invention to provide a method for operating an internal combustion engine wherein an uncontrolled large increase of the rpm from the full load rpm is avoided.
The method of the invention is for operating an internal combustion engine. The engine includes: a cylinder; a piston mounted in the cylinder to undergo a reciprocating movement along a stroke path between top dead center and bottom dead center during the operation of the engine; the cylinder and the piston conjointly delimiting a combustion chamber; a crankcase connected to the cylinder; a crankshaft rotatably mounted in the crankcase; the piston being connected to the crankshaft for imparting rotational movement to the crankshaft; a device for metering fuel to the engine and a device for supplying air to the engine; an ignition unit for igniting an air/fuel mixture in the combustion chamber; and, a control unit controlling the metering of the fuel and the ignition of the mixture in the combustion chamber; the method comprising the step of controlling the engine in at least one operating state so as to cause the number of combustions to be less than the number of engine cycles in the same time interval with the operating state being a high rpm range wherein the rpm (n) of the engine lies above a rated rpm (nV) and below an rpm (nA) in a regulating range.
It has been shown that self ignitions can occur in the full load operation of the internal combustion engine. This means that the mixture, which is present in the combustion chamber, ignites automatically because of the high temperature in the combustion chamber and because of the pressure before the ignition generates an ignition spark. The tendency to self ignition is increased when the load on the engine decreases abruptly and greatly. The reduction of the load effects simultaneously an increase of the rpm. If the rpm moves into the regulating range of the ignition characteristic line, then the control so controls the engine that the rpm is reduced. This can take place via interruptions of the ignition. The interruption of the ignition has, however, no effect for revolutions wherein the mixture ignites automatically so that the rpm at first greatly increases when the load drops away. The engine is only slowly braked because of the masses in the crankcase. It was observed that the engine falls back to an rpm below the regulating range after a certain time.
To avoid the excessive increase of rpm, the internal combustion engine is so controlled in a high rpm range above the rated rpm and below the rpm in the regulating range that the number of combustions is less than the number of engine cycles in the same time interval. The rated rpm is the rpm of the engine at maximum power. It has been shown that by controlling the engine so that the number of combustions is less than the number of engine cycles in the same time interval, the tendency to self ignition can be considerably reduced above the full load rpm. If a combustion takes place for each revolution of the crankshaft, then the occurring combustion is comparatively weak because exhaust gases from the previous engine cycle can still be present in the combustion chamber. Because the engine is so controlled that a combustion does not take place for each engine cycle, the occurring combustions are very intense. If the internal combustion engine is a two-stroke engine, then the very intense combustion in the combustion chamber effects a pressure increase in the crankcase via the transfer channels of the two-stroke engine. This pressure increase effects that, in the following engine cycle, the induction of fresh combustion air or fresh mixture is deteriorated. For the following engine cycle, no mixture quantity is present in the combustion chamber which is sufficient for a self ignition. Because no combustion takes place in this engine cycle, pressure and temperature in the combustion chamber can continue to decrease so that the probability of a self ignition is reduced also for the follow-on combustions. The control of the internal combustion engine in such a manner that the number of combustions is less than the number of engine cycles in the same time interval causes that no self ignitions can occur in the high rpm range.
The same applies when the internal combustion engine is a four-stroke engine. In this case, an engine cycle includes two revolutions of the crankshaft whereas an engine cycle in a two-stroke engine includes one revolution of the crankshaft. For a four-stroke engine, it is achieved that via a very good combustion in the high rpm range, the pressure level in the combustion chamber is increased in the subsequent induction cycle so that no mixture quantity, which is sufficient for a self ignition, can be inducted. In the follow-on engine cycles, pressure and temperature have decreased so far that the probability of self ignition is significantly reduced. Self ignitions can in this way be effectively prevented also for a four-stroke engine.
Because the formation of self ignitions is prevented in the high rpm range, the rpm of the internal combustion engine can be reduced in the regulating range in the usual manner, for example, by interrupting the ignition. An uncontrolled large increase of the rpm can be avoided in that the engine is so controlled in an rpm range below the regulating range that the number of combustions is less than the number of engine cycles in the same time interval.
It has been shown that the formation of self ignitions can be effectively prevented when the engine is so controlled that in the high rpm range at most nine combustions take place for ten engine cycles. Already by preventing individual combustions, for example, by interrupting the ignition, self ignitions can be avoided. It is advantageous to suppress every seventh combustion by corresponding control of the internal combustion engine. It can, however, also be provided that the internal combustion engine is so controlled that a lower number of combustions takes place. Especially, the internal combustion engine is so controlled that, in the high rpm range, a combustion takes place at most every four engine cycles. Advantageously, the internal combustion engine is so controlled that, in the high rpm range, the number of combustions is at a ratio of 1 to 4 to 1 to 10 to the number of engine cycles. Because the combustion chamber is scavenged over three to nine engine cycles after a combustion takes place, it is ensured that also the next combustion is very good and leads to a very high pressure in the combustion chamber which prevents an adequate induction of mixture for a self ignition in the next engine cycle.
Advantageously, the number of combustions in the high rpm range is controlled in accordance with a pregiven regular pattern. Advantageously, a combustion takes place every N revolutions wherein N is a number from 4 to 10. It can also be provided that a combustion is suppressed every N revolutions wherein N is a number from 4 to 10.
It is practical to control the internal combustion engine in the regulating range so that the rpm drops. The control of the internal combustion engine in the regulating range for lowering the rpm advantageously develops after a pregiven number of engine cycles have been run through in the high rpm range. Because a pregiven number of engine cycles were run through in the high rpm range, it is ensured that the engine is subjected to a pregiven pattern of combustions and cycles wherein no combustion takes place. It is ensured that no self ignitions take place so that the internal combustion engine can be so controlled by interrupting the ignition that the rpm falls off. Advantageously, the ignition time point is shifted to a later time point in the regulating range of the internal combustion engine. An ignition time point shift can only have an effect on the rpm of the internal combustion engine when a self ignition has not taken place already in advance of the ignition. The internal combustion engine is practically so controlled in the regulating range that the number of combustions is less than the number of engine cycles in the same time interval. The number of combustions in the regulating range is especially controlled in accordance with a pattern which contains a stochastic component. It can, however, also be provided that the control of the number of combustions in the regulating range corresponds to the control of the number of combustions in the high rpm range.
Advantageously, in engine cycles wherein no combustion should take place, the ignition is interrupted. It can, however, also be provided that the number of combustions is controlled via the metering of fuel. Especially, no fuel is metered in the engine cycles wherein no combustion should take place. It can, however, also be provided that also in engine cycles wherein no combustion should take place, a small quantity of fuel for lubrication of the crankcase is supplied in a two-stroke engine.
The invention will now be described with reference to the drawings wherein:
The internal combustion engine shown in
The two-stroke engine 1 includes at least one transfer channel 12 which connects the crankcase 3 to a combustion chamber 5 in the region of bottom dead center of the piston 7. The combustion chamber 5 is delimited by the cylinder 2 and the piston 7. Two or four transfer channels 12 are provided and are arranged symmetrically with respect to a partitioning center plane centered with respect to the inlet 4. The piston 7 has a piston pocket 30 indicated in phantom outline in
A valve 18 is provided for metering fuel and is especially configured as an electromagnetic valve. The valve 18 can, however, also be integrated into an injection nozzle. The valve 18 is integrated in an ignition module 20. The valve 18 is controlled by a control unit, for example, a central control unit (CPU) which is arranged in the ignition module 20. The ignition module 20 controls the ignition of the spark plug 8 via a line 19. A magnet 21 is mounted on the crankshaft 25 for generating the ignition energy. More specifically, the magnet 21 is mounted on a fan wheel 11 which, in turn, is mounted on the crankshaft so as to rotate therewith.
As shown in
The electromagnetic valve 18 is integrated on the ignition module 20 and is connected via a fuel line 14 to the fuel pump 16 mounted in the fuel tank 13. The fuel pump 16 can be configured as a membrane pump and is driven by the fluctuating crankcase pressure. For this purpose, the fuel pump 16 is connected via a pulse line 22 to the crankcase 3. The fuel pump 16 pumps the fuel from the fuel tank 13 into a fuel store 17 from where it reaches the electromagnetic valve 18. A pressure control valve can be mounted in the fuel store 17 and this valve can be connected via a return line to the fuel tank. A sensor 37 is mounted on the crankshaft 25 to detect the rpm (n). The sensor 37 is connected via a line 38 to the control mounted in the ignition module 20.
As shown in
During operation of the two-stroke engine 1, substantially fuel-free combustion air is drawn by suction in the region of top dead center of the piston 7 from the inlet 4 via the piston window 30 and the transfer channel 12 into the crankcase 3. To lubricate the crankcase 3, the valve 18 conducts a fuel/oil mixture (which is typical for a two-stroke engine) to the combustion air at the start of the induction phase. The fuel/oil mixture is conveyed by the combustion air into the crankcase 3 and the transfer channel 12 is thereafter substantially completely filled with fuel-free air. The fuel/oil mixture and the combustion air are compressed with the downward stroke of the piston 7 in the crankcase 3. As soon as the piston 7 opens the transfer channel 12 toward the combustion chamber 5, first fuel-free air and thereafter a fuel/oil/air mixture flows from the crankcase 3 into the combustion chamber 5.
In the subsequent upward stroke of the piston 7, the mixture is compressed in the combustion chamber 5 and, controlled by the control unit integrated into the ignition module 20, is ignited by the spark plug 8. The ignited mixture expands with the combustion so that the piston 7 is pressed in the direction toward the crankcase 3. The exhaust gases flow through the outlet 6 from the combustion chamber 5 and are scavenged or expelled by the substantially fuel-free air flowing in through the transfer channel 12.
The control of the two-stroke engine 1 controls the time point at which the spark plug 8 generates an ignition spark. The control of the ignition time point ZZP takes place based on the diagram shown in
In
The ignition time point ZZP in the high rpm range 40 and in the regulation range 41 lies between an upper tolerance band 42 and a lower tolerance band 43. The actual position of the ignition time point ZZP between the tolerance bands 42 and 43 can be dependent upon the particular two-stroke engine. The ignition time point ZZP in the high rpm range 40 and in the regulation range 41 can, however, also be dependent on additional factors, for example, on the number of combustions referred to the number of engine cycles.
To avoid an abrupt increase in rpm after the time point t1, the combustions of the two-stroke engine 1 are controlled in the high rpm range as shown in
It can also be provided to control the combustions of the two-stroke engine 1 in the high rpm range 40 as shown in the diagram of
An ignition takes place in the first engine cycle 50. The combustion taking place thereafter in the combustion chamber 5 leads to a very great pressure increase to 40 bar. This very intense combustion causes an intense increase of the crankcase pressure pKGH to over 0.8 bar via the transfer channels 12. Because of this very great pressure increase in the crankcase 3, the pressure pKGH in the crankcase 3 drops only slightly below the ambient pressure in the subsequent engine cycle 51 which is identified in the diagram by “0”. Because of the high pressure pKGH in the crankcase 3, only small amounts of fuel are inducted into the crankcase 3. In the engine cycle 50, a substantial combustion of the fuel in the combustion chamber 5 has taken place. The exhaust gases in the combustion chamber 5 are scavenged only incompletely in the following cycle. In the engine cycle 51, no sufficient quantity of fresh mixture is present in the combustion chamber 5 so that no self ignition can adjust. In the subsequent engine cycle 52, only a small amount of fresh mixture likewise reaches the combustion chamber 5 because the induction of fresh mixture into the crankcase 3 was hindered in the engine cycle 51 because of the high pressure in the crankcase 3. Therefore, no self ignition can take place in engine cycle 52. In the engine cycle 53, the combustion chamber 5 is again scavenged with a fresh mixture. In the engine cycle 53, also no self ignition can take place because the combustion chamber 3 was cooled down by the multiple scavengings and the pressure could also decrease. An ignition of the mixture takes place again in the fifth engine cycle 54. A strong good combustion takes place with a pressure increase to almost 35 bar. The strong combustion results because the mixture present in the combustion chamber 5 is substantially of exhaust gas because of the multiple scavengings of the combustion chamber 5 in the previous engine cycles 51 to 53. The intense pressure increase in the combustion chamber 5 transfers into the crankcase 3 and leads to a great increase of the crankcase pressure pKGH to above 0.8 bar in the crankcase 3. This high pressure in the crankcase 3 hinders the subsequent induction of fresh mixture so that self ignitions are also avoided for the following engine cycles.
In
A flowchart for a method for operating an internal combustion engine is shown in
Because at first a certain number of engine cycles is run through during which the internal combustion engine is so controlled that the number of combustions is less than the number of engine cycles in the same time span, it is ensured that combustions take place still only in the imposed pattern and no self ignitions can take place any more. It can also be provided that in the regulating range 41 too, the internal combustion engine is so controlled that a combustion does not take place in each engine cycle. The number of combustions in the regulating range can then be controlled in accordance with a pattern which contains a stochastic component. However, it can also be provided that the control in the regulating range of the control corresponds to the number of combustions in the high rpm range. In the high rpm range and in the regulating range, the control of the combustions can take place in accordance with the same pattern.
An embodiment of a single cylinder two-stroke engine 31 is shown in
The described method for preventing self ignition and for limiting the rpm of an internal combustion engine is also applicable in a four-stroke engine.
In addition to the described methods for operating an internal combustion engine, all of the methods disclosed in United States patent application publication US 2006/0157006 A1 can be applied.
It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 032 474 | Jul 2006 | DE | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3885720 | Brennan | May 1975 | A |
| 5901673 | Ishikawa | May 1999 | A |
| 6360724 | Suhre et al. | Mar 2002 | B1 |
| 6880525 | Geyer et al. | Apr 2005 | B2 |
| 7325528 | Schieber et al. | Feb 2008 | B2 |
| 20060157006 | Schieber et al. | Jul 2006 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20080011271 A1 | Jan 2008 | US |
