Abstract:
An electrical booster in an internal combustion engine with an exhaust gas turbocharger is activated so that the electrical booster is connected with the minimum possible power consumption. The connection of the electric booster depends on the power balance, the electric booster being activated when the instantaneously available compressor power of the exhaust gas turbocharger is insufficient to provide the necessary power.

Description:
CLAIM FOR PRIORITY 
   This application is a continuation of International Application No. PCT/DE03/00018 which was filed on Jan. 7, 2003 and published on Jul. 24, 2003 and which claims the benefit of priority to German Application No. 102 02 146.5 filed Jan. 21, 2002. 

   TECHNICAL FIELD OF THE INVENTION 
   The invention relates to a method for controlling an electrically driven compressor in a internal combustion engine with an exhaust gas turbocharger. 
   BACKGROUND OF THE INVENTION 
   To increase the power of internal combustion engines exhaust gas turbochargers are used which compress the inlet air in order to increase the air throughput of the engine. 
   A disadvantage of an exhaust gas turbocharger lies in the fact that a certain of exhaust mass flow is necessary to produce the required turbine power. A further disadvantage of the turbocharger lies in the fact that mechanism first has to be accelerated before the required operating point is reached. These disadvantages of the exhaust gas turbocharger lead to what is known as the “turbo lag”, which manifests itself as a delay in the case of positive jumps in load. 
   To compensate for the turbo lag the use of an electrically driven compressor, an e-booster, in addition to the exhaust gas turbocharger is known. This involves using a compressor turbine which is driven by an electric motor and additionally compresses the air. 
   SUMMARY OF THE INVENTION 
   The invention provides a method for controlling an electrically driven compressor, in which the compressor is connected with minimum power for its electrical operation. 
   In one embodiment of the invention, a turbine model determines the turbine power available at a particular moment. A compressor model determines the compressor power required at a particular time. If the compressor power required is greater than the available turbine power, a pressure to be generated by the electrical compressor is determined in an inverse compressor model. In a charge control the pressure to be generated by the electrically driven compressor is used to determine the power required for the compressor. The electrically driven compressor is activated by a controller corresponding to its required power. In the method in accordance with the invention, the electrically driven compressor is connected if the turbo power of the exhaust gas turbocharger available at that moment is not sufficient. With the method in accordance with the invention, connection is controlled on the basis of a power balance between the exhaust gas turbocharger and the electrically driven compressor. 
   In a preferred embodiment of the invention, charge pressure control is provided which, in the case in which the electrically driven compressor is connected, activates the turbine with maximum power and controls the charge pressure using the electrical compressor power. This charge pressure control ensures that the electrically driven compressor is connected with minimum power in its connected state. At the same time the occurrence of “turbo lag” is prevented. 
   The charge pressure is preferably controlled using a PID regulator for the turbine of the exhaust gas turbocharger and for the electrically driven compressor. 
   Preferably, the charge pressure control determines the required values for the turbine power and for the power of the electrically driven compressor, as well as a signal for whether the electrically driven compressor is connected. 
   The turbine model preferably determines the instantaneously available turbine power depending on the exhaust gas mass flow from the engine, a turbine speed and an exhaust gas temperature. 
   The compressor model preferably determines the required values for the power required at the time by the turbine of the exhaust gas turbocharger and of the electrically driven compressor. These values are determined in the compressor model preferably depending on at the mass air flow, the ambient pressure, the inlet air temperature before the compressor, the maximum compressor power and the current charge pressure. 
   The required value for the mass air flow is used as the value for the air mass flow and the required value for the instantaneous charge pressure as the charge pressure value. 
   Depending on the required pressure value of the electrically driven compressor, the ambient pressure, the mass air flow and the inlet air temperature before the electrically driven compressor, the inverse model for the electrically driven compressor determines the required power value for the electrically driven compressor. Preferably, the inverse model for the electrically driven compressor uses the required value for the mass air flow as the mass air flow value. 
   In addition, an inverse turbine model can be provided which determines the required value for the pressure quotients over the turbine of the exhaust gas turbocharger and the required value for the exhaust gas mass flow. The inverse turbine model determines the required value for the exhaust gas mass flow through the turbine and the required value for the pressure quotient over the turbine depending on the required value for the turbine power, the turbine speed, the exhaust gas temperature before the turbine, the required value for the turbine power and independently of this whether the electrically driven compressor has been connected or not. 
   Preferably, an e-booster is provided as electrically driven compressor which is arranged upstream from the compresser of the exhaust gas turbocharger. Alternately, the e-booster can be arranged downstream from the compressor of the exhaust gas turbocharger. 
   The method in accordance with the invention can be used for any type of register charging in which compression is undertaken by connecting an electrical load. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in greater detail on the basis of the following figures. In the drawings: 
       FIGS. 1A and 1B  shows an overview of register charging with an electrically driven compressor according to two preferred embodiments. 
       FIG. 2  shows a view of the charge pressure regulation. 
       FIG. 3  shows a system overview. 
       FIG. 4  shows a view of the coordination of the charge pressure regulation. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1A  shows a schematic overview diagram of register charging with an e-booster as an electrically driven compressor. The flow path depicted starts with an air filter  10 . Downstream of the air filter  10  an e-booster  12  is provided. Parallel to the e-booster  12  there is a bypass channel  14 , in which a controllable butterfly valve  16  is arranged. So that the electrically driven compressor  12  responds rapidly and provides the required pressure without any lag, this is a small design. To obtain a sufficient air mass flow with a small compressor the bypass channel  14  is provided. 
   Downstream from the e-booster  12  a compressor  18  of an exhaust gas turbocharger is provided. A bypass channel  20  with a controllable butterfly valve  22  is arranged in parallel to the compressor  18 . The bypass channel  20  is opened at times to protect the exhaust gas turbocharger in order to pump air into the circuit at a corresponding pressure quotient via the compressor  18  of the exhaust gas turbocharger.  FIG. 1B  shows an alternative embodiment where the e-booster  12  is arranged downstream of the compressor  18 , rather than upstream as shown in FIG.  1 A. 
   Downstream from the compressor  18  of the exhaust gas turbocharger a charge air cooler  24  is provided. Connected to the charge air cooler  24  are a butterfly valve  26 , and inlet air line  28  and cylinders  30  of the internal combustion engine. 
   Shown schematically further downstream is a turbine  32  of the exhaust gas turbocharger. The diagram shows a wastegate  34  in parallel to the turbine  32  of the exhaust gas turbocharger which controls the air flow through the turbine  32 . A conversion is undertaken downstream in a catalyzer  36  shown schematically. 
     FIG. 3  shows a schematic overview in which the method in accordance with the invention is illustrated by individual model blocks. The exhaust gas mass flow from the engine  40  (FLOW ENG), the turbocharger speed  42  (N TCHA) and the exhaust gas temperature before the turbine  44  (TEG TUR UP) are present as input variables at the turbine model  38 . The turbine model  38  calculates from these variables the maximum turbine power  46  (POW TUR MAX), that is the gross power of the turbine taking account of its efficiency. 
   A compressor model  48  calculates the required value  50  for the pressure at the e-booster (PRS BOOST SP). Similarly the compressor model  48  calculates the required value  52  for the compressor power (POW CHA SP). 
   Input variables for the compressor model  48  are the required value for the mass air flow  54  (MAF KGH SP), the ambient pressure  56  (AMP), the inlet air temperature  58  before the compressor of the exhaust gas turbocharger (TIA CHA UP) and the required value  60  for the charge pressure (PUT SP). The maximum turbine power  46  is also present as an input variable as maximum power (POW CHA MAX) of the compressor of the exhaust gas turbocharger  62  at the compressor model  48 . 
   The inverse model for the e-booster  64  determines the required value for the booster power  66 . The ambient pressure  56  (AMP), the required value for the mass air flow  54  (MAF KGH SP), the inlet air temperature  68  before the e-booster (TIA BOO-ST UP) and the required value for the booster pressure (PRS BOOST SP)  50  are present as input variables at the inverse model for the e-booster. 
   A charge pressure control is shown schematically in  FIG. 3  as block  69  The charge pressure control defines as its output variable the required value for the booster pressure  70  (POW BOOST EL_SP) a flag  72  for the status of the charge pressure control (LV PUT CTL TCHA) and a required value  74  for the turbine power (POW TUR_SP). The charge pressure control  69  possesses as input variable the required value of the booster power  66  from the e-boost inverse model  64 , the required value for the compressor power  52  of the exhaust gas turbocharger from the compressor model  48 , the required value for the charge pressure  60 , the charge pressure  76  (PUT) and the pressure quotient at the e-booster  78  (PQ BOOST). The pressure quotient  78  is the quotient of the pressure after the booster divided by the pressure before it. 
   The output variables of the charge pressure control are available at the inverse model for the turbine  80 . At the inverse turbine model the flag for the status of the charge pressure control  72  (LV_PUT CTL TCHA) and the required value for the turbine power  74  are present as input variable at the inverse turbine model. Further the turbocharger speed  42  and the exhaust gas temperature before the turbine  44  are present at the inverse turbine model  80 . The required value for the exhaust gas mass flow through the turbine  82  and the required value for the pressure quotients over the turbine  84  (PQ EX SP) are calculated as output variables of the inverse turbine model. 
   The e-booster is controlled by the booster control  86 , at which the flag for the status of the charge pressure controls  72  and additionally the required value for the booster power  70  are present. 
     FIG. 2  shows the charge pressure control  69  in detail. Starting from the required value for the charge pressure  60  and the actual value for the charge pressure  76  the difference is formed as required value minus actual value. The deviation of the charge pressure from the required value for the charge pressure  88  (PUT DIF) is processed together with the flag for the status of the charge pressure control  72  (LV_PUT_CTL TCHA) into a factor for the turbine power  90  (FAC_POW_TUR_PUT_CTL). The factor is multiplied by the required value for the turbine power  52 . The product is forwarded as basic value for the required value of the turbine power  92 . 
   The basic value for the required value of the turbine power  92  is present at a coordination block of the charge pressure control  94 . Further the charge pressure control  94  is coordinated depending on the pressure quotients at the booster  78  and the maximum turbine power  46 . The output variable of the coordination of the charge pressure control  94  is the flag for the status of the charge pressure control  72  which assumes the value of 1 if the booster is switched off and assumes the value of 0 when the maximum power of the turbine is required. 
   The power of the booster is controlled in a similar way to determining the basic value for the required value of the turbine power. Depending on the state of the charge pressure control and the control deviation of the charge pressure  88  a factor for the turbine power  100  (FAC POW TUR PUT CTL) is determined and multiplied by the required value for the booster power  102 . The product is forwarded as the required value for the booster power  104  (POW BOOST EL_SP). 
     FIG. 4  shows a possible embodiment for coordination of the charge power control. In the lowest branch the basic value for the required value of the turbine power is compared to the maximum power of the turbine  46 . The comparator  106  generates a 1 if the basic value for the required value of the turbine power is greater than or equal to the maximum turbine power. The output signal of the comparator  106  is present at an S-R flip-flop  108  at the Reset input. The logical AND of the two comparisons is present at the S-input of the flip-flop  108 . The first comparison checks whether the pressure quotient at booster  78  is less than or equal to 1. If this is the case the pressure is not built up by the booster. As the second variable a comparison is made as to whether the charge pressure  88  is less than or equal to 0. The control deviation, as already explained above is formed as the difference between the required value and the actual value, so that a negative control deviation indicates that the actual value is greater than the required value. The status bit  72  (LV PUT CTL TCHA) is generated at the output of the S-R flip-flop  108 .