Patent Application
20070289584
The injectors (3a to 3f) are respectively connected by a fuel line (6a to 6f) and a flow limiting valve (8a to 8f) to a common high pressure rail (10), generally called a common rail. The flow limiting valves have a flow rate limited quantity which is chosen for the whole performance range of the engine from a no-load condition to an overload condition such that in normal operation a stop position blocking flow through the flow limiting value is not reached. The flow rate limit is typically ≧30% higher than a quantity of fuel required for rated load operation. The common rail (10) is in turn connected by a line (12) and a high pressure pump (14) to a fuel reservoir (16).
The injectors (3a to 3f) are connected by corresponding signal lines (20a to 20f) to a control unit (22) which controls the opening and closure of the injectors (3a to 3f), e.g., the movement of a nozzle needle relative to a nozzle seat, in a known manner. The amount of fuel injected per injection cycle is controlled by the opening duration of the injector. The control unit (22) is also connected to the high pressure pump (14) by a signal line (24) in order to control operation of the latter. The control unit (22) is furthermore connected to temperature sensors (32a to 32f) by corresponding signal lines (30a to 30f).
As can be seen in
The control system (1) according to a first variant of the disclosure is described in greater detail with reference to the flow chart shown in
It is then determined in block 108 whether the exhaust gas temperatures lie within predetermined limits, wherein the predetermined limits may be absolute limits or may be determined in accordance with a requested map. In the determination it is established whether the absolute value of Tdev established in block 106 is smaller than a first predetermined value. In this way it is determined whether the temperature deviation with respect to the average temperature comes within predetermined limits. The first predetermined value may be a fixed temperature of, for example, 40° C. or a percentage of the average exhaust gas temperature, such as 10%, and thus may change during operation of the engine.
If the exhaust gas temperatures lie outside of the predetermined limits, this indicates a substantial malfunction of the engine and the process control passes to block 110 in which a corresponding malfunction message is issued and, if applicable, operation of the engine is halted. If the exhaust gas temperatures lie within the predetermined limits, the process control passes to block 112. In block 112 it is determined whether the absolute value of Tdev is smaller than a predetermined second value. In this way it is determined whether the temperature deviation with regard to the average temperature lies within second, more-narrow predetermined limits. The predetermined value may be a fixed temperature of, for example 20° C., or a percentage of the average exhaust gas temperature, such as 5%, and thus may change during operation of the engine. If the absolute value of Tdev is smaller than the predetermined value, this shows correct operation of the engine, and the process control passes to block 114. In block 114, N is increased by 1, i.e. N is set to equal N+1.
Next, the process control passes to block 116 where it is determined whether N is greater than the number of combustion chambers. If this is not the case, the process control returns to block 106 in which a temperature deviation Tdev of the exhaust temperature of the next combustion chamber with respect to the average temperature Tavg is in turn determined. If in block 116, however, N is greater than the number of combustion chambers, the process control passes to block 118. If N is greater than the number of combustion chambers, this indicates that the temperature deviation Tavg for each combustion chamber with respect to the average temperature has been determined and has been reacted to accordingly. Block 118 is a time delay block which allows the process to pause for a predetermined period of time before the process passes back to block 102 and a new cycle is implemented.
If it is determined in block 112 that the absolute value of Tdev is smaller than the predetermined value, this indicates that the engine is not running fully optimally, but that the deviation is not so substantial that a malfunction message should be issued, and the process control passes to block 120. In block 120 it is determined whether a maximum change limit for the combustion chamber N has been reached. As will be explained in greater detail below, the control system is able to change the actuation of the injectors (3a-3f) which are normally actuated in accordance with the requested fueling map in order to change the amount of fuel injected by the latter. However, the control system should not be able to change the actuation limitlessly, and so a change limit is defined, for example, as a percentage change to the actuation which would normally be implemented according to the requested fueling map.
If it has been determined in block 120 that the maximum change limit for the combustion chamber N has been reached, the process control passes to block 114 where N is once again increased by 1, and the process control follows the process described above. In decision block 120, when determining whether the maximum change limit for the combustion chamber N has been reached, it is taken into account whether a subsequent change would include a step away from the maximum change limit to the normal actuation according to the requested fueling map, or a step beyond the maximum change limit. In other words, if the maximum change limit for the combustion chamber N has been reached and a subsequently planned change would result in the limit being exceeded, this change is then not permitted, and control passes to block 114.
If the subsequently planned change would result, however, in a step away from the maximum change limit to the normal actuation according to the requested fueling map, the process control then passes to block 122. The process control also passes to block 122 if it has been determined in block 120 that the maximum change limit for the combustion chamber N has not yet been reached. In block 122 the actuation waveform of the injector allocated to the combustion chamber N is changed. The change to the actuation results in longer opening or faster closure of the injector in order to increase or to reduce the quantity of fuel injected into the combustion chamber N. Next, the process control passes back to block 114 in which the value N is increased by 1 and the process control then follows the previously described process sequence.
The process described above is one variant of the disclosure and enables equalization of the exhaust gas temperatures of the different combustion chambers of a combustion engine having a common rail injection system within predetermined limits. It is clear from the above description that the corresponding degree of change to the actuation waveform for the respective injectors is recorded. These recorded values are preferably stored in a permanent memory and can be read out for various purposes, such as for a system check for example. Furthermore, the recorded values may be used as a basis for actuating the individual injectors when an engine is restarted. In this way, during normal operation of the engine it is possible for the engine, when restarted, to be operated from the start with an optimized actuation map. Following maintenance or repair work to the engine, the changed values may be, however, reset to the normal actuation map.
The control system (1) according to a second variant of the disclosure is explained in greater detail with reference to the flow chart shown in
In block 208 it is then determined whether the exhaust gas temperatures lie within predetermined limits, these limits possibly being on the one hand absolute limits and on the other hand being determined in accordance with the requested fueling map. With this determination, it is established whether the absolute value of Tdev determined in block 206 is smaller than a first predetermined value. In this way it is determined whether the temperature deviation with respect to the average temperature lies within the predetermined first limits. The first predetermined value may be a fixed temperature of, for example, 40° C., or a percentage of the average exhaust gas temperature, such as 10%, and thus may change during operation of the engine.
If the exhaust gas temperatures lie outside of the predetermined limits, this indicates a substantial malfunction of the engine, and the process control passes to block 210 in which a corresponding malfunction message is issued, and if applicable, operation of the engine is halted. If, however, the exhaust gas temperatures lie within the predetermined first limits, the process control passes to block 212. In block 212 it is determined whether the absolute value of Tdev is smaller than a second predetermined value which is smaller than the first predetermined value. In this way it is determined whether the temperature deviation with respect to the average temperature lies within second, narrower predetermined limits. The second predetermined value may be a fixed temperature of, for example, 20° C. or a percentage of the average exhaust gas temperature, such as 5%, and thus may change during operation of the engine. If the absolute value of Tdev is smaller than the second predetermined value, the process control passes to block 214. In block 214, N is increased by 1, i.e. N is set to equal N+1.
Next, the process control passes to block 216 where it is determined whether N is greater than the number of combustion chambers. If this is not the case, the process control passes back to block 206 in which a temperature deviation Tdev of the exhaust temperature of the next combustion chamber with respect to the average temperature Tavg is in turn determined. If, however, in block 216 N is greater than the number of combustion chambers, the process control passes to block 218. If N is greater than the number of combustion chambers, this indicates that the temperature deviation for each combustion chamber with respect to the average temperature has been established and has been reacted to accordingly. Block 218 is a time delay block which allows the process to pause for a predetermined period of time before the process passes back to block 202 and a new cycle is begun.
Up to this point, the process sequences of the first and the second variants are the same. If it is determined in block 212 that the absolute value of Tdev is smaller than the second predetermined value, the process control passes to block 220 rather than to block 214. As explained in greater detail below, the control system is able to change the actuation of the injectors (3a-3f), which are normally controlled by means of the requested fueling map, in order to change the quantity of fuel injected by the injectors. However, it may be desired to have the control system not able to change the actuation limitlessly, and thus a maximum number of change steps are defined which respectively have a predetermined value, and for example a percentage change to the actuation with respect to the normally implemented actuation according to the requested fueling map. For example, a change step can include a change of ±0.5% with respect to the “normal” actuation.
In block 220 it is determined whether the number of previously undertaken change steps with regard to the combustion chamber N has reached a predetermined value of, for example, 10. Only the number of change steps away from the “normal” actuation defined by the requested fueling map are taken into account. If, following changes away from the normal actuation map, a change step towards the normal actuation profile is undertaken, the number of change steps away from the normal actuation map is correspondingly corrected. Therefore, the number of change steps indicates how far the actuation of an injector deviates from its normal actuation (for example five increases of +0.5% each, i.e. 2.5% deviation with respect to the normal actuation map). Furthermore, it is also taken into consideration whether the next change would include a step towards the normal actuation or away from it.
If it has been determined in block 220 that the number of changes has reached the maximum number for the combustion chamber N and the subsequently planned change step would exceed the maximum number, the process control passes to block 214. In block 214, N is once again increased by 1 and the process control follows the further process already described above. If, however, the subsequently planned change would result in a step away from the maximum number of changes to the normal actuation defined by the requested fueling map, the process control then passes to block 222. The process control also passes to block 222 if it has been determined in block 220 that the maximum change limit for the combustion chamber N has not yet been reached. In block 222, the actuation of the injector allocated to the combustion chamber N is changed. The change to the actuation results in longer opening or faster closure of the injector in order to increase or to reduce, respectively, the quantity of fuel injected by the injector into the combustion chamber N. Next, the process control passes again to block 214 in which the value N is increased by 1 and the process control then follows the sequence described above.
In another variant of the disclosure, the process may use a small percentage of the nominal requested fueling for the incremental changes of the injection actuation waveform rather than an absolute, fixed amount. In this way, the process can be used for both low and high fueling levels of the engine.
In still another variant of the disclosure, the process may allow for an offset of exhaust gas temperature in cylinders based on cylinder location. Due to the different locations of the exhaust gas temperature measurements, an engine with exactly the same amount of fuel delivered to each cylinder will still have some variation between the exhaust gas temperatures measured for each cylinder. The process can account for this by using a predefined offset for the cylinder exhaust gas temperatures.
The process sequences described represent different variants of the disclosure, without however, being restricted to the described variants. In the process sequences described, a deviation Tdev of the exhaust gas temperature is respectively determined for a single combustion chamber (blocks 106/206). Next, the deviations established are compared with specific threshold values (blocks 112/212) and, if necessary, an adaptation of the actuation waveform of the injector allocated to the respective combustion chamber is implemented (blocks 122/222). After this, the deviation Tdev of the exhaust gas temperature is then respectively established for the next combustion chamber, and the corresponding value is provided for the steps.
Alternatively to this sequential determination of the temperature deviation for each individual combustion chamber and the implementation of the subsequent steps (comparison with specific limit values/if appropriate change to the actuation waveform of an injector, etc.) it is also possible to determine the temperature deviations for all combustion chambers or a group of combustion chambers simultaneously, and to provide the corresponding values simultaneously for the subsequent steps. In other words, instead of sequential processing of the temperature signals, provision is also made for the parallel processing of the same.
The disclosed variants of methods for balancing cylinder-to-cylinder fueling variation in a combustion engine provide improved engine performance and reduction in false alarms with gas temperature monitoring systems. The present disclosed variants have been described above with respect to preferred variants of the disclosure, without being restricted to the specifically described variants. The person skilled in the art will become aware of numerous modifications and amendments which fall within the scope of the present disclosure which is defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102006027591.8 | Jun 2006 | DE | national |
