WO2005071241A1

WO2005071241A1 - Method and device for controlling an electrically driven compressor of an internal combustion engine

Info

Publication number: WO2005071241A1
Application number: PCT/EP2004/053053
Authority: WO
Inventors: Michael STÜRTZ; Markus Teiner
Original assignee: Siemens Aktiengesellschaft
Priority date: 2004-01-23
Filing date: 2004-11-23
Publication date: 2005-08-04
Also published as: DE102004003607B4; DE102004003607A1

Abstract

The invention relates to a device and a method for controlling an electrically driven compressor of an internal combustion engine. The aim of the invention is to create a method and a corresponding device that require less effort to be developed while being more reliable regarding the adjustment of optimally effective operating points of electrical compressors. Said aim is achieved by determining the variables of a requested compressor performance (PL, POW CHA SP) and a required rotational speed (N CHA SP) of the compressor based on a model as a function of a respectively desired boosting level or boost pressure (PUT SP) and a required air mass flow (MAF KGH SP), the selected model being based on a formulation that is causal for the ratio between the respective variables and is based on the physics of the system.

Description

description

Method and device for controlling an electrically driven compressor of an internal combustion engine

The present invention relates to a method and a device for controlling an electrically driven compressor of an internal combustion engine.

According to the prior art, upstream compressors are used to increase the torque of internal combustion engines. A compressor brings about a pre-compression of the supplied fresh air and thus an increase in the cylinder charge, which results in an advantageous increase in performance of the internal combustion engine.

In the design of exhaust gas turbochargers, a compressor is driven by the exhaust gas flow. However, in order to be able to deliver fresh air at all, a sufficient exhaust gas flow must also be available for exhaust gas turbochargers. Especially in the area of low engine speeds, an exhaust gas turbocharger basically has an effect that is far too low due to the low exhaust gas flow.

To cover even the low speed range of an internal combustion engine, the use of an electrically driven charger has therefore been proposed. Known solutions for controlling an electrically driven charger or an e-compressor work with characteristic fields. Various variables from the engine control flow into these characteristic curve fields, the characteristic curve fields having to be created and / or applied in complex tests since they are based essentially on empirical approaches. Since it is hardly possible in principle to determine a characteristic field on the basis of tests for each individual operating point, operating points are generally determined on the basis of approximation methods. This can ensure optimal operation of an electric charger with an internal combustion engine, however, can only be achieved in a very rough approximation.

It is therefore the object of the present invention to provide a method and a corresponding device which are less in terms of their development effort and more reliable in relation to the setting of efficiency-optimal operating points of electrical compressors.

This object is achieved according to the invention by a method in which the sizes of a required compressor output and a required compressor speed are determined on the basis of a model as a function of a desired degree of charging and a required air mass flow. The modeling chosen is based on an approach that is responsible for the ratio of the quantities involved to one another and is based on the physics of the system. A device for implementing such a method also provides a solution to this problem, the device having a computing unit with a model which is connected to means for determining operating variables of the electrically driven compressor from input variables.

In an embodiment of the invention, as an extension of the input parameter set, an ambient pressure and an ambient or intake air temperature are also used as input variables of the model. This maps current climatic conditions to an extent that is sufficient for the operation of a reliably controlled internal combustion engine.

In a preferred embodiment of the invention, only the physics of the compressor and the electric motor driving it itself are used as the basis for a faster and more precise control of the overall system comprising the internal combustion engine, engine control, electric compressor, electric motor and control electronics compared to the known prior art Control strategy for charging the internal combustion engine ^¬ chosen. The corresponding model is then derived from this basis, in particular in the form of closed ^mathematical equations. In a further development, as predefined quality criteria for the model, for example, fast response, boost pressure build-up, etc., depending on the application and / or selection of a specialist in development, can be provided as influencing variables. The concrete modeling of the compressor speed and the compressor output will be discussed in detail below with reference to the drawing. The same applies to the regulation of the electric motor as the drive for the compressor.

In the context of this description, the present invention is illustrated essentially against the background of use in the motor vehicle industry. Applications outside of this sector are, however, expressly not ruled out, since an inventive method and a corresponding device can be used for all internal combustion engines.

In embodiments of the invention, a combination of an inventive controlled or regulated electrical ^¬ rule loader is reacted with an exhaust gas turbocharger. Furthermore, in one embodiment, specifications from an exhaust gas treatment system, for example from a λ probe and / or nitrogen oxide sensors of an exhaust gas tract, are also taken into account in the form of control variables and / or default values.

Further advantages of a method according to the invention and a device for implementing a method according to the invention are described in more detail below with reference to the illustration of exemplary embodiments with reference to the drawing. In schematic representation they show:

FIG. 1: an overview of a device for charging an internal combustion engine with an electrical see loader and a bypass channel with flap;

FIG. 2: a flowchart to illustrate a model according to the invention;

Figure 3 is a diagram showing the method for calculating a target operating point as block A of Figure 2;

FIG. 4: a flowchart to illustrate the modeling of a compressor as block B of FIG. 2;

FIG. 5: a system overview to illustrate an exemplary embodiment.

In the individual representations of the drawing, the same components, components, sizes and process steps are given the same designations throughout.

In a device 1 according to FIG. 1, fresh air is added via a fresh air filter 2 and precompressed via an electric compressor or e-charger or e-charger 3. A bypass 4 lying parallel to the electric charger 3 is closed in the illustrated case by a controllable opening flap. The fresh air flow symbolized by an arrow P subsequently passes an opened throttle 5 and is fed to an internal combustion engine 7 via intake pipes or distributor pipes 6. After the combustion of the fresh gas mixture in the internal combustion engine, the exhaust gases are discharged via an exhaust tract 8 with means for exhaust gas use and / or pollutant sensing, which are not shown, whereby they pass through a catalytic converter 9.

The electric compressor 3 serves to significantly improve the torque of the internal combustion engine 7 by means of a Increased charging of the cylinders with fresh gas, so that the internal combustion engine 7 can provide sufficient torque to a drive train, which is only indicated in FIG. 1, even in a range of low speeds. According to the invention, a method for controlling the electric charger 3 is used, which is based on modeling the physical charger taking into account a desired degree of charging of the internal combustion engine 7 and a charger power required for this. In contrast to methods according to the prior art, a suitable method is used to determine a compressor speed that is currently required for each operating point and a required compressor output as a function of a desired degree of charging and air mass flow. As a result, the application of the method described in detail below essentially only activates the electric charger 3 if an engine power that is currently available is not sufficient for a driving state and / or a request. In the opposite case, deactivation only occurs when the available power of the internal combustion engine 7 is sufficient to correspond to a current driver request.

A major advantage of this approach is therefore that the electric charger 3 is only operated with a minimum required power. Compared to conventional control of an e-charger, this leads to a significantly improved overall system efficiency. The duty cycle and operating point of the charger 3 can be optimized in accordance with various quality criteria, such as, for example, an efficiency, a dynamic behavior or a maximum predetermined duration.

With reference to the figures in FIGS. 2 to 4, a modeling of compressor speed and compressor output is now shown. 2 gives an overview, and FIGS. 3 and 4 show those shown in FIG. 2 Function blocks A, B for determining an operating point of the loader 3 and an interpolation in loader characteristic curve fields are shown in more detail:

The parameters of the compressor at the nominal operating point are calculated from the boundary conditions of ambient pressure AMP, intake and ambient air temperature TIA_ABSV_CHA_UP as well as the desired air mass MAF_KGH_SP and the required boost pressure PUT_SP. These are volume flow VOL_FLOW_CHA_UP_SP, pressure quotient PQ_CHA_SP and air mass flow MAF_CHA_SP. Some

Values such as Volume flow VOL_FLOW_CHA_UP and supercharger speed N_CHA_COR_SP are standardized in the model with a te peratu-dependent factor FAC_TIA.

The pressure upstream of the compressor PRS_CHA_UP_SP is calculated from the ambient pressure AMP and the pressure losses in the air filter IP_PRS_LOSS_AIC which are dependent on the air mass flow. The target pressure after compressor PRS_CHA_DOWN_SP is calculated from the boost pressure PUT_SP and the pressure losses in the charge air cooler IP_PRS_LOSS_ICO, which depend on the air mass flow. The pressure quotient PQ_CHA_SP results from the pressures after and before the compressor.

The density of the air in front of the compressor RHO_CHA_UP can be calculated from the pressure in front of the compressor, the intake air temperature TIA_ABSV_CHA_UP and the general gas constant RA. Using the density, a volume flow VOL_FLOW_CHA_UP can be calculated from the mass flow. The volume flow is standardized with the factor FAC_TIA and from the standardized volume flow VOL_FLOW_CHA_UP_RED_SP and the pressure quotient

PQ__CHA_SP calculates the normalized supercharger speed N_CHA_COR_SP. For the details of this calculation, reference is expressly made to the disclosure of published patent application DE 100 46 322 AI. The normalized supercharger speed N_CHA_COR_SP is normalized back via the factor FAC_TIA in order to obtain the physical speed N CHA SP that is being sought. The compressor performance POW_CHA_SP or P _L can be calculated using the main turbocharger equations:

1 P _L = m _L -Δh _L

Compressor output air mass flow through compressor enthalpy difference η _L compressor efficiency c pL specific heat capacity at constant pressure K adiabatic exponent

The term c _L • - is combined to IP_FAC_POW_CHA_l, due to its course depending on the volume flow and charging speed, it makes sense to store the map as a function of the charger speed and the standardized volume flow related to the charger speed.

The term entered in the map IP_FAC_POW_CHA_2

sets.

With this simplification, the desired compressor capacity can be calculated as the product of the intake air temperature TIA_ABSV_CHA__UP (Tl), air mass flow MAF_CHA_SP and the two defined factors. The abbreviations are tion components CHA and ECHA were both used synonymously in the drawing to designate the electric charger.

By calculating the required compressor power P _L , this can be used as a pilot control in the regulation of the electric motor associated with the electric compressor 3. This results in a faster and more stable control, which also improves the dynamic behavior of the overall system. The control of the electric motor itself is based in a known manner on the specification of a target speed and a required power, from which the torque required in each case results. On the basis of the interfaces defined according to the invention, any electric motors from different manufacturers, each with its own control electronics, can be used as a so-called black box, since their properties can be specified in a clearly defined manner.

There are two fundamentally different approaches when modeling a system: forward modeling and backward modeling or inverse modeling. In the case of forward modeling, actual states to be expected are modeled on the basis of control values. In the case of an inverse model, a desired default value is specified at the output and an input value or input vector is determined on the basis of the model. When using an inverse model, it is possible to check the feasibility of the desired default values at the output by comparing a recalculated input value. FIG. 5 shows an exemplary embodiment in the form of a system overview in which the advantages of reverse modeling are used in order to create a basis for improved control for the electric motor of the compressor 3. The device 1 comprises an inverse E-compressor model 10, a control device 11 for the electric motor of the electric compressor 3 and a control device 12 for driving and monitoring the control of the bypass valve in the bypass 4. The flap in the bypass 4 is opened in the event that the e-charger 3 can no longer make a contribution to an increase in pressure. This is the case from a certain higher speed of the internal combustion engine 7. In this operating state, the electric motor that drives the compressor 3 is then switched off.

In the inverse e-compressor model, a currently required compressor output POW_CHA_SP and a corresponding speed N_CHA_SP of compressor stage 3 are determined on the basis of the desired air mass flow MAF_KGH_SP, the intake air temperature TIA_ABSV_CHA_UP, the boost pressure setpoint PUT_SP and the ambient pressure AMP as input values. These values are now used in the regulation of the electric motor in order to regulate the requested compressor speed. So far, the schematically illustrated method corresponds to that of FIGS. 1 to 4. If, after the control device 11 has been determined, the rotational speed of the internal combustion engine 7 is so high that the electric compressor 3 can no longer increase the pressure, the bypass flap in the bypass path 4 of the electric compressor 3 becomes opened by means of the control device 12 for the bypass flap and the electric motor of the compressor 3 switched off. Bit LV_BYP_ENA, which is shown in FIG. 5, is used for this.

In the case which is not shown graphically and which also has a forward-looking e-compressor model, a compressor output can now be determined on the basis of its maximum operating parameters and the current ambient conditions before the shutdown measure just introduced is initiated. A comparison of the maximum realizable with the actually required values of the compressor 3 can then be shifted towards an engine control. From here, the shutdown measures described above can also be initiated. The example shown is shown for the sake of simplicity without boost pressure control in the compressor 3. A boost pressure control can, however, be arranged in a superimposed manner in the arrangement shown in a manner known to the person skilled in the art.

Claims

claims

1. A method for controlling an electrically driven compressor (3) of an internal combustion engine (7), through which fresh air is compressed, characterized by the fact that the sizes of a required compressor output (P _L , POW_CHA_SP) and a required compressor speed (N_CHA_SP) on the The basis of a model (11) is determined as a function of a desired degree of supercharging or boost pressure (PUT_SP) and a required air mass flow (MAF_KGH_SP), the selected modeling being based on a factor that is responsible for the ratio of the variables involved to one another and on the physics of the system based approach.

2. The method according to claim 1, characterized in that an ambient pressure (AMP) and an ambient or intake air temperature (TIA_ABSV_CHA_UP) are used as input variables of the model (11) as further input variables.

3. The method according to one of the two preceding claims, characterized in that essentially only the physics of the compressor and the electric motor driving it itself is selected as the basis for a control strategy for charging the internal combustion engine (7) for regulating the overall system.

4. The method according to any one of the preceding claims, characterized in that fast response and / or boost pressure build-up are provided as influencing variables in the model as predefined quality criteria depending on the application and / or selection of a specialist.

5. The method according to the preceding claim, characterized in that the method in an internal combustion engine machine (7) with a combination of a regulated electric charger (3) with an exhaust gas turbocharger is used.

6. The method according to any one of the preceding claims, characterized in that specifications of a waste gas treatment system, for example, a λ-probe and / or stick ^¬ oxide sensors of an exhaust gas tract, are taken into account in the form of control variables and / or default values.

7. The method according to any one of the preceding claims, characterized in that a boost pressure control is superimposed on the method.

8. Device for controlling an electrically driven compressor (3) of an internal combustion engine (7), characterized in that the device (1) is designed to carry out a method according to one or more of the preceding claims, by a computing unit with a model (11) It is provided which is connected to means for determining operating variables of the electrically driven compressor (3) from input variables.