The present invention relates to a method for controlling valve lift shifting in an internal combustion engine comprising a variable valve lift system whereby the engine can operate selectively in either of at least two valve lift modes, and more particularly to minimizing torque changes when shifting modes in a variable valve lift system of an internal combustion engine.
In an internal combustion engine with a variable valve lift system, in particular a cam profile shifting (CPS) system, for instance as described in U.S. Pat. No. 5,287,830A, switching cam profiles can introduce a change in the output torque of the engine, which can cause discomfort to persons in a vehicle in which the engine is operating. The reason for such a change in the output torque could be that in the amount of air trapped in the cylinders differ from one valve lift mode to another.
Accordingly, the present invention is directed to a method for minimizing a change in engine output torque when shifting modes in a variable valve lift system of an internal combustion engine, the method including comparing an actual fuel supply with a fuel supply threshold value, and at least partly based on the result of the comparison, determining whether a valve lift mode shift should be performed.
Thereby, based on the comparison, it can be determined that if the fuel supply is equal to or below the fuel supply threshold value, a valve lift mode shift is performed. As is closer described below, if the engine fuel supply is above the fuel supply threshold value, it can be determined that a valve lift mode shift is not performed. The fuel supply threshold value should be chosen so that the energy released at individual combustions, regardless of the air supply, is low. Thereby, at, or under the fuel supply threshold value, a difference of the air supply caused by a valve lift mode shift will not cause a noticeable step in the output torque of the engine.
It should be noted that the invention does not exclude the possibility that criteria other than the fuel supply, such as requested transient torque, can be considered when determining whether a valve lift mode shift should be performed.
Preferably, the fuel supply threshold value corresponds to the fuel supply being cut off. Thereby, it is secured that a difference of the air supply caused by a valve lift mode shift will not cause a step in the output torque of the engine.
It will be appreciated that features of the invention are susceptible to being combined in any combination without departing from the scope of the invention as de-fined by the accompanying claims.
By way of example only, embodiments of the present invention will now be de-scribed with reference to the accompanying drawings wherein:
In a low lift mode, shown in
Alternatively, still within the scope of the present invention, the variable valve lift system can be provided in a variety of manners known in the art, for example as described in U.S. Pat. No. 5,950,583A. In particular, the CPS actuator can be provided in alternative manners, and the CPS system can be adapted to assume more than two cam profile modes.
The engine also comprises a variable valve timing (VVT) system 8, which is adapted to adjust the VVT position, i.e. set the camshaft I at desired angular positions in relation to the camshaft wheel 3b. The VVT system comprises a VVT actuator 8a, for example of the type described in U.S. Pat. No. 6,135,077A, at the camshaft wheel 3b. The VVT actuator 8a is adapted to mechanically change the VVT position, and is controllable by the hydraulic system 9. For control of the VVT actuator 8a, the VVT system 8 comprises a VVT actuator control valve 9c in the hydraulic system 9. The VVT actuator control valve 9c is also controllable by the ECU 7, and could be of the same type as the CPS actuator control valve 9b.
Also provided are means (not shown) to establish the engine speed, in a manner known in the art.
As can be seen in
Here reference is made to
Based on the result of the determination 315 regarding the engine fuel supply CF, it is determined whether a valve lift mode shift should be performed. If the engine fuel supply CF is equal to or below the fuel supply threshold value FT, a valve lift mode shift is performed 316. If the engine fuel supply CF is above the fuel supply threshold value FT, it is determined 317 whether the CPS mode should be changed according to an alternative CPS mode shifting strategy. This alternative strategy could be a strategy that takes the VVT position into account for cam profile shifts, as described in the European Patent Application No. 05110938.7, filed by the same applicant on the same day as this application. If it is determined 317 according to the alternative CPS mode shifting strategy that a valve lift mode shift should be performed, a valve lift mode shift is performed 316. However, if it is determined 317 according to the alternative CPS mode shifting strategy that a valve lift mode shift should not be performed, a required CPS mode 311 and a current CPS mode 312 are again determined.
Alternatively, if it is determined 317 according to the alternative CPS mode shifting strategy that a valve lift mode shift should not be performed, simply no cam profile shift is performed. As a further alternative, no consideration for any alternative CPS mode shifting strategy could be made. In such a case, if it is determined 315 that the engine fuel supply CF is above the fuel supply threshold value FT, a required CPS mode 311 and a current CPS mode 312 are again determined, or simply no cam profile shift is performed.
The fuel supply threshold value FT could be predetermined, or it could be determined based on at least one engine operation related parameter, for example the engine speed. Such determinations could be based on predetermined functions or tables mapping the fuel supply threshold value FT to the engine operation related parameter(s). Also, the fuel supply threshold value FT could be calibratable. In a preferred embodiment, the fuel supply threshold value FT is zero, i.e. the fuel supply CF is cut off.
It should be noted that the invention is equally applicable to engines with variable valve lift systems providing more than two valve lift modes.
It should also be noted that the method according to the invention is equally applicable to engines with spark ignition and engines with compression ignition.
Number | Date | Country | Kind |
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05110940.3 | Nov 2005 | EP | regional |