Turbochargers and exhaust gas turbochargers are used widely in series-produced motor vehicles, in order to increase the power of the respective vehicle engines. According to the design which is customary today, exhaust gas turbochargers have a rotor with a compressor wheel and a turbine wheel and a shaft which is arranged between the compressor wheel and the turbine wheel and is rotatably mounted in corresponding rotor bearings on the turbine side and the compressor side. The rotor bearings can generally be sliding bearings or roller bearings with oil lubrication. The bearings are usually supplied with lubricant by means of lubricant, for example engine oil, which is conducted to the individual bearing points via a pressure line, for example. The lubricant has both the object of lubricating the bearings and the function of cooling them. The cooling is highly significant, in particular in the case of the turbine-side bearing, since a significant quantity of heat is conducted into the shaft by the hot turbine wheel.
An operating state which is particularly difficult to cope with for this reason is the rapid shutting down of the internal combustion engine from an operating state with a high load. The supply of lubricant is interrupted when stopping occurs and the conduction of heat away from the shaft is no longer ensured. This results in overheating of the lubricant oil and an associated carbonization of the lubricating oil remaining in the exposed parts of the bearings, as a result of the subsequent heating of the shaft which is caused by the hot turbine. The carbonization of the lubricating oil finally causes the rotor bearings to be covered in soot, which is frequently the cause of turbocharger damage.
The abovementioned critical operating state, that is to say the rapid shutting down of the internal combustion engine from an operating state with a high load, can be found to occur particularly in motor vehicles with what are referred to as a start/stop automatic system, said system automatically switching off the internal combustion engine if, for example, no drive energy is used to propel the motor vehicle (stop condition) when it is stopped at a traffic light. When starting occurs (starting condition), the internal combustion engine is then started and the vehicle accelerates up to the next braking process.
Start/stop devices for motor vehicles are known in which the operating state of the vehicle and of the operator control pedals, for example the accelerator pedal and/or brake pedal, are determined and evaluated in order to switch off and start the internal combustion engine again. Such start/stop devices are suitable particularly for vehicles in short-range traffic or town traffic in order to reduce the fuel consumption and the exhaust gas emissions. They are now found in widespread application both in conventional motor vehicles and in low-energy vehicles, hybrid vehicles and the like.
Combining an internal combustion engine which can be supercharged by a turbocharger with a start/stop automatic system therefore heightens the risk of what is referred to as “hot-soak”, that is to say the destruction or damaging of the turbocharger, that is to say carbonization of the turbocharger, in particular of the lubricating oil which is present in the rotor bearings.
The inventors herein have recognized the issues with the above approaches and offer a method to at least partly address them. A method for operating an internal combustion engine is provided. The method comprises operating at least one turbocharger, operating a start/stop automatic system which automatically switches off the internal combustion engine when a stop condition is met, and automatically starts the internal combustion engine when a starting condition is met, and when the stop condition is met, delaying the automatic switching off of the internal combustion engine by a predefinable delay time (Δt).
In anther embodiment, a method for a turbocharger in an engine comprises pumping oil to a turbine of a turbocharger using an oil pump. The method includes, under a first condition, shutting off the oil pump immediately in response to an automatic stop condition of the engine, and under a second condition, shutting off the oil pump after a time delay in response to the automatic stop condition of the engine.
For example, if a temperature of the turbine is above a threshold, the oil pump may continue to be operated even after an automatic shut down of the engine is indicated.
In one embodiment, the oil pump may be driven by an external motor, in which case the engine may shut down immediately following the automatic stop condition. In another embodiment, the engine shut down may be delayed along with the oil pump shut down. By continuing to operate the oil pump, oil may continue to be pumped to the turbine to provide continued turbine cooling. In this way, carbonization of the turbocharger may be largely avoided, in particular carbonization of the rotor bearings. As a result, a longer service life of the turbocharger may be provided.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.