DE102016200710A1 - Method and device for operating an engine system with a supercharged combustion engine - Google Patents

Abstract

The invention relates to a method for operating an engine system (1) with a supercharged internal combustion engine (2), wherein the engine system (1) has an exhaust-driven charging device (6) with a compressor (62), comprising the following steps:
- setting (S4) a compression capacity by means of a boost pressure control, wherein the boost pressure control is given a target boost pressure,
Limiting (S3) the desired boost pressure to a maximum allowable boost pressure that depends on a maximum allowable compressor _speed (n _compmax ) of the compressor (62);
- Determining the maximum allowable boost pressure (p2max) using a charge cycle model of the internal combustion engine (2) and a provided compressor map of the exhaust-driven charging device.

Description

Technical area

The invention relates to methods for operating supercharged internal combustion engines, and more particularly to means for limiting a compressor speed of a supercharger for an internal combustion engine.

Technical background

Today's internal combustion engines typically have exhaust-driven superchargers to provide fresh air under a boost pressure. An increase in the boost pressure makes it possible to increase the air supply into the cylinders of the internal combustion engine and thus to increase the power. Exhaust-driven superchargers usually have a turbine in the exhaust system, which is connected via a shaft with a compressor in the air supply system. In the turbine converted exhaust enthalpy is provided as mechanical rotational energy to a compressor, which converts the mechanical energy into a compression of fresh air.

The turbocharger and compressor of a supercharger are subject to high stresses due to centrifugal forces due to the high rotational speeds commonly encountered in such superchargers. In order to avoid damage to the components of the charging device, they must therefore be protected against overspeeding.

Disclosure of the invention

According to the invention a method for operating an engine system with a supercharged internal combustion engine according to claim 1 and a device or an engine system according to the independent claims are provided.

Further embodiments are specified in the dependent claims.

• – Einstellen einer Verdichtungsleistung mithilfe einer Ladedruckregelung, wobei der Ladedruckregelung ein Soll-Ladedruck vorgegeben wird,
• – Begrenzen des Soll-Ladedrucks auf eine maximal zulässigen Soll-Ladedruck, der von einer maximal zulässigen Verdichterdrehzahl des Verdichters abhängt;
• – Bestimmen des maximal zulässigen Soll-Ladedruck mithilfe eines vorgegebenen Ladungswechselmodells des Verbrennungsmotors und eines bereitgestellten Verdichterkennfelds der abgasgetriebenen Aufladeeinrichtung.

According to a first aspect, there is provided a method of operating an engine system with a turbocharged internal combustion engine, the engine system having an exhaust gas driven supercharger with a compressor, comprising the steps of:

• - Setting a compression capacity by means of a boost pressure control, wherein the boost pressure control a target boost pressure is specified,
• Limiting the desired boost pressure to a maximum permissible boost pressure, which depends on a maximum permissible compressor rotational speed of the compressor;
• - Determining the maximum allowable target boost pressure using a given charge cycle model of the engine and a provided compressor map of the exhaust-driven charging device.

Exhaust-driven superchargers usually have a turbine and a compressor, which are rotatably coupled to each other via a shaft. Since very high speeds of rotation of the turbine and the compressor can result due to the usually low moment of inertia with changes in the operating state, the compressor speed must be limited to protect the exhaust gas driven charging device. This can be done by limiting the setpoint boost pressure given to the charge pressure control to a maximum set boost pressure. A procedure to determine the maximum target boost pressure using a map that depends on the engine speed and possibly other variables is inaccurate and requires limiting the compressor speed to a value that is a significant tolerance distance from a maximum still tolerable actually permissible compressor speed. As a result, the maximum available compressor power u.U. not be retrieved.

Furthermore, when using a map with defined nodes, the number of input variables is limited, so that the influence of other quantities, such as e.g. when changes in a camshaft position, a valve lift, an exhaust back pressure, an exhaust gas temperature, a temperature of the ambient air, an ambient pressure and the like, can not be sufficiently considered.

Therefore, the above method provides for calculating the maximum allowable boost pressure appropriately using a calculation model taking into account the physical conditions in the internal combustion engine. The calculation is made by means of a compressor map for the compressor of the supercharger and a charge cycle model for the internal combustion engine. Calculation using the calculation model allows a larger number of factors to be taken into account and allows a much higher accuracy than when using a predefined map. In particular, the use of the charge exchange model has the advantage that the dependence between the boost pressure and the mass flow through the compressor in the determination of the maximum allowable boost pressure can be considered. In particular, in the compressor map can be made of a proven physical description of the compressor behavior. The compressor map can as mathematical model or look-up table.

Furthermore, the charge cycle model may be considered for an operating point that occurs at the maximum allowable compressor speed. On these you can set the target boost pressure up to the maximum permissible compressor speed.

In particular, the charge cycle model for a maximum compressor mass flow and a maximum target charge pressure can be assumed.

It may be provided that the charge exchange model for at least one actual other variable is assumed, if the actual boost pressure deviates from the limited target boost pressure by no more than a predetermined amount.

Furthermore, the at least one other variable may include the pressure of an internal residual gas in the cylinder after an exhaust stroke.

• – einen Massenstrom in den Verbrennungsmotor,
• – eine Abgastemperatur,
• – eine Nockenwellenstellung; und
• – einen Abgasgegendruck.

In particular, the pressure of the internal residual gas may be determined as a function of at least one of the following quantities:

• A mass flow into the internal combustion engine,
• An exhaust gas temperature,
• A camshaft position; and
• - An exhaust back pressure.

It can be provided that the maximum permissible boost pressure is only determined if an actual boost pressure deviates from the last predetermined, possibly limited, target boost pressure by no more than a predetermined amount.

Furthermore, the maximum allowable boost pressure may be determined by combining the charge cycle model with the provided compressor map of the compressor, wherein the compressor map indicates a relationship between a pressure ratio across the compressor, a mass flow through the compressor, and a compressor speed.

It can be provided that the maximum permissible desired charge pressure is determined by means of the combination of the charge exchange model with a compressor characteristic map by an iterative calculation.

• – eine Verdichtungsleistung mithilfe einer Ladedruckregelung einzustellen, wobei der Ladedruckregelung ein Soll-Ladedruck vorgegeben wird,
• – den Soll-Ladedrucks auf eine maximal zulässigen Soll-Ladedruck zu begrenzen, der von einer maximal zulässigen Verdichterdrehzahl des Verdichters abhängt; und
• – den maximal zulässigen Soll-Ladedruck mithilfe eines Ladungswechselmodells des Verbrennungsmotors und eines bereitgestellten Verdichterkennfelds der abgasgetriebenen Aufladeeinrichtung zu bestimmen.

According to a further aspect, an apparatus, in particular an engine control unit, for operating an engine system with a supercharged internal combustion engine, wherein the engine system comprises an exhaust-driven supercharger with a compressor, wherein the apparatus is designed to:

• To set a compression capacity by means of a boost pressure control, the charge pressure control being given a desired charge pressure,
• - Limit the target boost pressure to a maximum allowable boost pressure, which depends on a maximum allowable compressor speed of the compressor; and
• - Determine the maximum allowable boost pressure using a charge cycle model of the engine and a provided compressor map of the exhaust-driven charging device.

Brief description of the drawings

Embodiments are explained below with reference to the accompanying drawings. Show it:

1 a schematic representation of an engine system with an internal combustion engine and a charging device; and

2 a flowchart illustrating a method for setting a maximum allowable boost pressure.

Description of embodiments

1 shows a schematic representation of an engine system 1 with an internal combustion engine 2 , The internal combustion engine may be in the form of a fuel-guided (diesel engine) or air-guided internal combustion engine (gasoline engine).

The internal combustion engine 2 can be a number of cylinders 3 , in the present case four cylinders. The internal combustion engine 2 Air is supplied via an air supply system 4 fed. In the air supply system 4 is still a throttle 7 arranged. Combustion gases during operation of the internal combustion engine 2 arise from the cylinders 3 of the internal combustion engine 2 via an exhaust system 5 dissipated.

It is an exhaust gas driven charging device 6 provided a turbine 61 having. The turbine 61 is in the exhaust system 5 arranged so that the combustion exhaust gas coming from the cylinders 3 during operation of the internal combustion engine 2 is ejected, this drives, whereby the exhaust enthalpy of the combustion exhaust gas is converted into mechanical rotational energy.

The turbine 61 is with a compressor 62 via a coupling wave 63 connected to the turbine 61 provided mechanical energy to the compressor 62 to provide and to use for the compression of fresh air taken from the environment. This sucks the compressor 62 Fresh air from the environment of the engine system 1 and puts these on the output side of the compressor 62 in a boost pressure section 41 available under a boost pressure. Downstream of the boost pressure section 41 closes off the throttle 7 a Saugrohrabschnitt 42 of the air supply system. The suction pipe section 42 is directly with intake valves (not shown) of the cylinder 3 connected.

It may be a loader 64 on or in the turbine 61 be provided, with which the proportion of exhaust gas enthalpy, which is converted into mechanical energy, can be adjusted. The loader 64 may be in the form of a wastegate valve, a VTG actuator or the like.

Usually, the charging device 6 equipped with a speed sensor, with which the speed of the shaft 63 can be detected so that it can be easily limited. To save costs, however, charging devices without a speed sensor are often provided. Nevertheless, the compressor speed of the coupling shaft 63 be effectively limited to damage to the components of the charging device 6 to avoid. The limitation of the compressor speed is usually carried out by limiting the boost pressure to a maximum allowable boost pressure via a boost pressure control.

Furthermore, a control unit 10 provided that operates the engine system. The control unit detects for state variables in the engine system and receives a default size, which may indicate, for example, a driver's desired torque or an accelerator pedal setting. Based on the default size and the operating state of the internal combustion engine 2 then become positioners in the internal combustion engine, such as the loader 64 , a fuel injection (not shown) and the throttle 7 set to a desired drive power of the internal combustion engine 2 provide. In general, a charge pressure is determined from the default size, with the help of the boost pressure control, the setting of the loader actuator 64 and / or the throttle 7 is influenced, adjusted. The setting is based on a regulation that regulates the boost pressure to a target boost pressure. The determination of the desired charge pressure takes place in a manner known per se, based on the default value and other operating state variables of the internal combustion engine 2 , but is limited to a maximum allowable boost pressure to limit the compressor speed.

To describe the behavior of the compressor 62 the exhaust-driven charging device 6 For example, a compressor map is provided which has a relationship between a pressure ratio across the compressor, ie a quotient of an output side pressure p2 corresponding to a boost pressure and an input side pressure p1 substantially equal to an ambient pressure, a compressor mass flow m '. _komp through the compressor 62 and compressor _speeds n _comp provides. Usually in conventional compressor maps a normalized mass flow or a temperature-corrected volume flow is assumed. The compressor speed is usually specify for a reference temperature. When using such a Verduchichterkennfelds this must be considered potentially.

Critical values of the compressor speed are generally taken at high engine torques or high engine speeds, since there are the requirements for a high boost pressure or high delivery volume. In these operating ranges, the throttle valve is usually fully open, so that the output side of the compressor 62 adjusting boost pressure p2 and that by the internal combustion engine 2 flowing mass air flow m ' _{motor are} not independently adjustable.

The relationship between the supercharge pressure P2 and the air flowing through the internal combustion engine mass flow m _'motor at open throttle 7 can be mapped by a charge cycle model. A charge cycle model generally indicates gas mass flows through the engine system in an internal combustion engine. The compressor map may be used to indicate a relationship between the boost pressure p2 and the compressor mass flow m'comp at a given maximum allowable compressor _speed . The charge cycle model can be used to obtain from a boost pressure p2, which corresponds to a maximum permissible boost pressure p2max, an associated mass flow m ' _engine through the internal combustion engine 2 to determine.

Thus, the maximum permissible desired boost pressure p2max can be determined via the compressor _map when specifying a maximum compressor _speed n _compmax . In particular, by specifying a maximum compressor speed and by equating the mass flows, the maximum permissible desired charge pressure p2max can be determined.

The charge cycle model may define a mass flow as a function of a boost pressure p2, a camshaft position, an exhaust temperature, and so on. It applies to the charge exchange model: M ' _motor = f (p2), such as M ' _motor = k1 × (p2 - p _rest ) wherein p _rest corresponds to a pressure of an internal residual gas in one of the cylinders or the cylinders after an exhaust stroke. The pressure of the internal residual gas is also a function of the mass flow m ' _engine in the internal combustion engine 2 , the exhaust temperature, the camshaft position, the exhaust back pressure and the like. k1 corresponds to a function that is essentially of an engine speed n _{engine of} the internal combustion engine 2 depends.

Furthermore, the compressor map is available as the following function f1: p2 / p1 = f1 (m ' _comp , n _comp ) ➔ p2 = f1 (m' _comp , n _comp ) × p1 for the given maximum permissible compressor _speed n _kompmax then: p2max = f1 (k1 × (p2max -p _rest ), n _compmax ) × p1

By combining the above formulas, one obtains a non-linear equation that can be solved iteratively after the maximum allowable boost pressure p2max. The maximum permissible boost pressure p2max is now available to limit the desired boost pressure for the boost pressure control.

The boost pressure used in the above equation corresponds to a maximum allowable boost pressure p2max at the predetermined maximum compressor _speed n _kompmax and the mass flow corresponds to a mass flow at the predetermined maximum compressor speed at the maximum allowable boost pressure p2max.

The calculation of the maximum permissible desired boost pressure p2max can be limited in particular to cycles in which the actual boost pressure is in the vicinity of the desired boost pressure or the maximum permissible boost pressure. In this case, the full charge-exchange model does not have to be calculated, but one can rely on the actual values from the charge-exchange model.

Based on the flowchart of 2 the sequence of the cyclical calculation of the maximum permissible set boost pressure is briefly explained again.

In step S1, it is checked whether the actual boost pressure deviates from the last predetermined, possibly limited, target boost pressure by no more than a predetermined amount. If the difference between the actual charge pressure and the last predetermined possibly limited desired boost pressure is less than predetermined by the predetermined amount (alternative: yes), then the method in step S2 continued. Otherwise (alternative: no) returns to step S1 and omitted a recalculation of the maximum allowable target boost pressure in the current computing cycle.

In step S2, p _{rest of} an internal residual gas in the cylinder is now based on the current pressure p _rest 3 after an exhaust stroke and on the engine speed, the iterative calculation of the maximum allowable boost pressure started.

If the maximum permissible desired charge pressure is present, then the setpoint boost pressure currently specified by the charge pressure control is correspondingly limited in step S3.

Based on the now limited nominal boost pressure, the boost pressure control is now executed in step S4.

Subsequently, it is possible to return to step S1 in order to execute the method cyclically.

Claims (13)

Method for operating an engine system ( 1 ) with a supercharged internal combustion engine ( 2 ), the engine system ( 1 ) an exhaust gas driven charging device ( 6 ) with a compressor ( 62 ), comprising the following steps: - setting ( S4 ) a compression capacity by means of a boost pressure control, wherein the boost pressure control a target boost pressure is specified, - limiting ( S3 ) of the desired charge pressure to a maximum allowable boost pressure, which is determined by a maximum allowable compressor _speed (n _compmax ) of the compressor ( 62 ) depends; Determining the maximum permissible desired boost pressure (p2max) using a charge exchange model of the internal combustion engine ( 2 ) and a provided compressor map of the exhaust gas driven charging device. The method of claim 1, wherein the charge cycle model is considered for an operating point that occurs at the maximum allowable compressor speed. The method of claim 2, wherein the charge cycle model for a maximum compressor mass flow and a maximum target boost pressure is adopted. The method of claim 3, wherein the charge cycle model is adopted for at least one actual other size. Method according to claim 4, wherein the charge exchange model is assumed for at least one actual other variable, if the actual Boost pressure deviates from the limited desired boost pressure by no more than a predetermined amount. The method of claim 4 or 5, wherein the at least one other variable, the pressure of an internal residual gas in a cylinder ( 3 ) of the internal combustion engine ( 2 ) after an exhaust stroke. Method according to claim 6, wherein the pressure of the internal residual gas is determined as a function of at least one of the following variables: - a mass flow into the internal combustion engine ( 2 ), - an exhaust gas temperature, - a camshaft position; and - an exhaust back pressure. Method according to one of claims 1 to 7, wherein the maximum allowable boost pressure is only tuno if an actual boost pressure deviates from the last predetermined possibly limited desired boost pressure by not more than a predetermined amount. The method of claim 1 to 8, wherein the maximum allowable target boost pressure by combining the charge cycle model with the provided compressor map of the compressor ( 62 ), wherein the compressor map indicates a relationship between a pressure ratio across the compressor ( 62 ), a mass flow through the compressor ( 62 ) and a compressor speed (n _comp ). The method of claim 9, wherein the maximum allowable boost pressure (p2max) is determined by means of the combination of the charge cycle model with a compressor map by an iterative calculation. Device, in particular engine control unit ( 10 ), for operating an engine system ( 1 ) with a supercharged internal combustion engine ( 2 ), the engine system ( 1 ) an exhaust gas driven charging device ( 6 ) with a compressor ( 62 ), wherein the device is designed to: - set a compression capacity by means of a boost pressure control, wherein the charge pressure control is given a target boost pressure, - limit the target boost pressure (p2) to a maximum permissible target boost pressure (p2max), the maximum permissible compressor speed of the compressor ( 62 ) depends; The maximum permissible boost pressure (p2max) using a charge exchange model of the internal combustion engine ( 2 ) and a provided compressor map of the exhaust-driven charging device ( 6 ). Computer program adapted to carry out all the steps of a method according to one of Claims 1 to 10. A machine-readable storage medium on which a computer program according to claim 12 is stored.

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