A METHOD OF CONTROLLING AN EGR ENGINE HAVING A VTG TURBO

CHARGER II

TECHNICAL FIELD

The present invention relates to a method and a system for controlling an engine having a Variable Turbine Geometry (VTG) turbo charger.

BACKGROUND Diesel engines for use in heavy vehicles such as trucks and buses are sometimes provided with a Variable Turbine Geometry (VTG) also termed Variable Geometry Turbocharger or Variable Geometry Turbine (VGT). Such an engine is typically provided with an EGR (Exhaust Gas Recirculation) valve. Other engines for other uses may also be provided with a VTG in combination with EGR. One reason for employing VTG technology and EGR technology is that it facilitates fulfillment of emission requirements for i.a. diesel engines.

In operation one important control object when controlling the VTG and the EGR valve is to generate low emissions. In particular it is important to meet emission requirements. Another important control object when controlling an engine having a VTG in combination with EGR is to optimize engine performance so that the engine generates high power at all times and consumes a minimum of fuel.

There is a constant desire to improve control of engines to optimize performance and at the same time keep fuel consumption to a minimum and not exceed existing emission requirements.

Hence, there exist a need for a method and a system that can provide improved engine performance.

SUMMARY

It is an object of the present invention to provide a method and a system that improves engine performance of an engine having a VTG.

It is another object of the present invention to provide a method and a system that improve the engine performance of an engine having a VTG and EGR.

These object and others are obtained by the method, system and computer program product as set out in the appended claims. Thus, in order to obtain improved performance, the control unit controlling the engine is adapted to controlling a combustion engine with a Variable Geometry Turbine (VTG), such that when determining that a demand for a higher torque exists, the engine is controlled according to a high charger gas pressure mode in which the VTG is closed to generate a higher turbo charger gas. Hereby the demand for a higher torque can be met quicker and the engine response is improved.

In another embodiment the electronic control unit is adapted to detect a demand for a high torque, where upon determination that a condition indicating a demand for a high torque is fulfilled, the electronic control unit (ECU) initiates closing of the VTG to a position providing maximum torque, while at the same time not exceeding any emission requirements. Hereby the engine response is maximized and maximum torque is delivered instantly by the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail by way of non-limiting examples and with reference to the accompanying drawings, in which:

- Fig. 1 is a general partial view of an engine including a turbo charger with VTG and EGR. - Fig. 2 is a flow chart illustrating steps performed in a control procedure when switching between different control modes in accordance with a first embodiment.

- Fig. 3 is a flow chart illustrating steps performed in a control procedure when switching between different control modes in accordance with a second embodiment.

DETAILED DESCRIPTION In Fig.l selected parts of an engine 100 of a motor vehicle 10 is schematically depicted. The engine depicted in Fig. 1 can for example be designed to be part of a truck or any other heavy vehicle such as a bus or the like. The exemplary engine 100 in Fig. 1 is a diesel engine provided with a turbocharger and having five cylinders 105. The turbo charger is a turbo charger having a Variable Turbine Geometry (VTG). The turbo charger comprises a compressor 102 driven by a turbine 103. As stated above the turbine may be of a type having a Variable Turbine Geometry (VTG).

Furthermore the exemplary engine comprises an EGR valve 107. The EGR valve 107 controls the amount of exhaust gas that is re-circulated to the gas inlet of the engine 100.

The engine is controlled by a computer in the form of an electronic control unit (ECU) 106. The ECU 106 is connected to the engine to control the engine. In addition sensors provided in association with the engine provide sensor signals to the ECU 106. Using the sensor signals, the ECU 106 exercises control of the engine using some programmed computer instructions or similar means. Typically, the programmed computer instructions are provided in the form of a computer program product 110 stored on a readable digital storage medium 108, such as memory card, a Read Only Memory (ROM) a Random Access Memory (RAM), an EPROM, an EEPROM or a flash memory.

In Fig. 2 a flow chart illustrating steps performed in a control procedure when switching between different control modes in accordance with a first embodiment is shown. First in a first step 201 the ECU is set to control the engine in accordance with a first, regular, control method. Next, in a second step 203, the ECU checks if a mode switch condition is fulfilled. The mode switch condition is one or more conditions set to predict a torque demand increase in the near future. Conditions used to predict a torque increase can for example be a high fuel injection for a period of time followed by a low fuel injection. Another condition used to predict a torque demand increase can be if the fuel injection rate increases above

some predetermined threshold value. If a torque increase is predicted in step 203, the control procedure proceeds to a third step 205, else the ECU continues to control the engine in the first, regular, control mode.

In step 205, the ECU starts to generate a higher exhaust gas pressure by closing the VTG to a more closed position, while maintaining the same engine speed. As a result of the higher exhaust gas pressure the amount of fuel will have to be increased somewhat to maintain engine speed. The higher the acceptable amount of additional pumping work, the more closed a position the VTG is set to. A more closed VTG position will allow for a higher power to be delivered from the turbine to the turbo compressor of the turbo charger, at least within some range. While in this control mode, the control system can be set to cause an optimisation the charger pressure in relation to the extra fuel required to maintain the higher charger pressure in accordance with some pre-set control strategy.

The EGR is controlled in a closed loop while the VTG can be controlled using mapped values stored in a map or look-up table. The values in the map are then chosen such that charger gas pressure is higher than in the first, regular control mode. To generate the higher charger pressure a higher exhaust gas pressure is needed which will result in a higher pumping work that the engine needs to perform.

Thereupon, in a fourth step 207, the ECU checks if a condition to exit the high exhaust gas pressure mode is met. The condition used to exit the mode can for example be that the amount of fuel injected is higher than a threshold value or that the amount of fuel injected is higher than a threshold value in combination with an amount of excess of air, for example as measured by an inlet air gas mass flow sensor. The mode with high exhaust gas pressure can also be set to be timed out after some predetermined time in the mode. If an exit condition is met the procedure returns to step 201, where the ECU controls the engine in accordance with the first, regular, control mode. If, on the other hand, no exit condition is met, the ECU continues to control the engine in a mode with a higher charger gas pressure.

In Fig. 3 a flow chart illustrating steps performed in a control procedure when switching between different control modes in accordance with a second embodiment is shown. First in

a first step 301 the ECU is set to control the engine in accordance with a first, regular, control mode. Next, in a second step 303, the ECU checks if a mode switch condition is fulfilled. The mode switch condition is set to detect a high torque demand. Conditions used to detect a high torque demand can for example be that the amount of injected fuel is limited by the mass flow of air into the cylinders by more than a predetermined value. Another condition that can be used is to compare the torque demand to the existing torque value. If the difference exceeds some predetermined threshold value the condition in step 303 is determined to be fulfilled. If a high torque demand is detected in step 303, the control procedure proceeds to a third step 305, else the ECU continues to control the engine in the first, regular, control mode.

In the third step 305, the ECU starts to generate a high torque by closing the VTG to a more closed position. Thus, by increasing the turbine speed, a higher charge gas pressure is obtained. Hereby more fuel can be injected to the cylinders resulting in a higher torque. In step 305, the VTG is controlled to a position generating a maximal turbine power. This position is dependent on the current gas mass flow through the turbine. By storing values for different modes of operation in a map or a look-up table in the control system, the control system can be adapted to control to the VTG to the position generating the maximal turbine power for each gas mass flow through the turbine. This is obtained by reading the current gas mass flow and control the VTG to the position corresponding to the highest turbine power for that gas mass flow as given by the value of the map stored by the control system.

Hence, the EGR is controlled in a closed loop while the VTG can be controlled using mapped values stored in a map or look-up table. The values in the map are then chosen such that charger gas pressure is maximized. To generate the maximized charger pressure a higher exhaust gas pressure is needed which will result in a higher pumping work that the engine needs to perform.

Thereupon, in a fourth step 307, the ECU checks if a condition to exit the high torque mode is met. The condition used to exit the mode can for example be that the amount of fuel injected is equal to the demand for fuel. In addition a pre-condition of air excess can be required to exit the high torque mode, or the amount of fuel injected in combination with an

amount of excess of air. If an exit condition is met the procedure returns to step 301, where the ECU controls the engine in accordance with the first, regular, control mode. If, on the other hand, no exit condition is met, the ECU continues to control the engine in a mode with a higher exhaust gas pressure. The higher exhaust gas pressure will then act to support the demand for a high torque.