Patent Application
20140363278
The present disclosure relates to a control system for controlling a turbocharger with a variable geometry turbine.
A variable-geometry turbocharger (VGT) can be used to allow the effective aspect ratio (A/R) of the turbo to be altered as conditions change. In an increasing transient loading condition, transient response is limited by turbocharger lag, as the fuel system response is much quicker. It would be desirable to set the VGT position in order to provide boost to the engine at the highest rate possible, thus maximizing transient response and limiting smoke production.
According to an aspect of the present disclosure, a turbo-charged engine has a variable geometry turbine driving a compressor. An intake manifold receives intake air from the compressor, and an exhaust manifold supplies exhaust to an input of the variable geometry turbine. It was determined that the maximum turbine power can be determined experimentally or by simulation as a function of corrected exhaust flow, where corrected exhaust flow is equal to exhaust flow (gps)×(exhaust temperature (C)+273.15)1/2/exhaust manifold pressure (abs kPa). This can then be calibrated in the engine controller and used in the actuator control. The control system can detect the need for a fuel to air ratio that is above a calibrated point transitioning closer or at the max turbine power set point.
Referring to
A temperature sensor 30 senses the temperature T(man) of the compressed intake air at the intake manifold 12. A pressure sensor 32 senses the pressure P(man) of the compressed intake air at the intake manifold 12. A temperature sensor 34 senses the temperature T(in) of the exhaust at an inlet of the turbine 20. A pressure sensor 36 senses the pressure P(in) of the exhaust at an inlet of the turbine 20. A position sensor 38 senses the position Vp of the vane (not shown) of the variable geometry turbo charger 22. The signals from sensors 30-38 are received by the electronic control unit (ECU) 40. The ECU generates a variable turbine geometry control signal Vc which is communicated to a vane position control input 42 of the turbine 20.
The ECU 40 also receives a requested fueling signal, RF, and a maximum fueling signal, MF. RF is preferably derived from a user input, such as a throttle position or pedal position, or from pedal position translated to a speed command which then results in a fueling commanded by a speed control algorithm (all speed governor) (not shown). MF is preferably derived from existing smoke limiting algorithms (not shown) which are designed to limit the engine's smoke output by only allowing a quantity of fuel to be injected that can be burned without resulting in excessive smoke.
The ECU 40 executes an algorithm 100 represented by
The algorithm starts at step 102 when the engine is started.
In step 104 requested fueling, RF is compared to maximum fueling, MF. If RF is greater than MF, the algorithm proceed to step 106, otherwise the algorithm keeps comparing RF to MF.
In step 106 the sensors 30-36 are read, and then step 108 calculates a corrected turbine mass flow value, FLOW, according to the equation FLOW=min×(T(in))1/2/P(in), where min is estimated mass flow rate of exhaust through the turbine 20. This mass flow rate min is preferably determined by a well known method using the turbine inlet temperature from sensor 34, the turbine inlet pressure from sensor 36 and the fuel rate which is supplied by an engine control (not shown). Alternatively, the turbine mass flow could be determined by using a fresh air measurement plus estimated fueling along with a direct measurement of turbine inlet temperature and pressure. In a system with EGR, this speed density mass flow measurement would be combined with EGR flow measurement. Alternatively, this could also be done with a mass air flow sensor.
In step 110, the corrected value calculated in step 108 is used with a look-up table, such as shown in
Referring now to
Returning to
Thus, this system determines an optimal variable turbine geometry vane position values as a function of sensed parameters. Such parameters include fueling-related parameters, and intake manifold air temperature and pressure
The result is a system which optimizes boost control during a load increasing transient. The system determines the variable geometry turbine set point that provides the maximum turbine power available to the compressor to build boost air. With the onset of a load increase, fuel increases faster than air flow can increase to match. Commanding the variable geometry turbine set point closer to or at the maximum turbine power allows the increase in airflow to better match the increase in fuel flow, provided improved combustion efficiency and reduced smoke.
During steady state conditions the set points for the variable geometry turbine is typically set to achieve emission and torque at the best fuel consumption solution. This variable geometry turbine set point is typically not at the maximum turbine power available.
While the disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description is to be considered as exemplary and not restrictive in character, it being understood that illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected.
It will be noted that alternative embodiments of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations that incorporate one or more of the features of the present disclosure and fall within the spirit and scope of the present invention as defined by the appended claims.
