Method for determining the power requirement of an electric exhaust gas turbocharger

Abstract

The present invention relates to a method for determining a power requirement (mechanical target power of the electric drive P). mech,EM,Des ) of an electric exhaust gas turbocharger (eATL) in a turbo hybrid electric vehicle concept (tHEV). The method according to the invention comprises, in one process step, the establishment of a power balance around the electric exhaust gas turbocharger in the form of a differential equation, wherein boundary conditions and a driver request are used as quantities of the differential equation.

Description

[0001] The present invention relates to a method for determining the power requirement of an electric exhaust gas turbocharger (eATL) in a turbo hybrid electric vehicle concept (tHEV).

[0002] In a tHEV (thermoelectric hybrid electric vehicle), an exhaust gas turbocharger is used, which can be driven by an electric motor when needed. The eATL throttles the combustion engine on the exhaust side to enable lambda=1 operation across the entire engine map. This throttling is achieved by increasing the size of the eATL turbine, thus reducing exhaust backpressure. The disadvantages resulting from the larger turbine size are masked by the electric drive of the eATL. The electric drive has sufficient power to compensate for the increased moment of inertia caused by the heavier and larger components, and the reduced responsiveness due to the large turbine wheel. The electrical power consumption is limited by the electrical supply. The tHEV concept incorporates several electrical consumers that must be powered by a limited energy source (battery).These include the drive for the eATL's electric motor, an air conditioning compressor, possibly an electric chassis, and the vehicle's traction motor.

[0003] To maximize the vehicle's drive performance, the energy content of the limited power supply must be optimally distributed among the high-voltage components. To prevent wasted energy potential, the electrical power requirements of the two eATLs must be determined. For this purpose, the digital motor electronics must detect the boundary conditions acting on the eATLs. Detecting such boundary conditions, as well as recording driver input, is a known technology.

[0004] The following is also known from the prior art. Document US 10,393,038 B2 relates to a two-stage air charging system for an internal combustion engine with mixed exhaust gas recirculation, comprising a high-pressure exhaust gas recirculation circuit, a low-pressure exhaust gas recirculation circuit, an air throttle system, a turbocharger system, and an electric air charging system. It also describes a method for controlling the system, which includes monitoring desired operating commands and operating parameters. Based on the monitored target operating commands and operating parameters, feedback control signals are determined.

[0005] Document DE 11 2019 000 085 T5 discloses a charging system capable of actively controlling the rotational speed of a turbine generator. This is achieved using a variety of different parameters to adjust the turbine generator's rotational speed to a target speed.

[0006] Document EP 2 123 882 B1 describes a method in which a rotary motor of an electrically assisted charger is controlled based on different temperature limits.

[0007] Document EP 4 015 807 A1 relates to a method for controlling the boost pressure of an exhaust gas turbocharger, wherein the power required to generate this pressure is provided by a turbine and an assisting electric motor. The power requirement is optimally distributed between the electric motor and the turbine, taking into account the power limits of the individual components and other parameters.

[0008] Document DE 10 2006 000 100 A1 discloses a control device for an internal combustion engine with a turbocharger, which calculates a target turbocharger output based on airflow rate information and compares it with the actual output. The missing output is provided by a support device until the target output is reached.

[0009] Document EP 2 696 052 B1 describes a turbocharger with an electric motor for power assistance between the turbine and compressor. The electric motor is controlled using a continuous instruction value and an acceleration instruction value, with the target power of the electric motor being determined by combining the two instruction values.

[0010] Document DE 10 2018 218 041 A1 discloses a method for controlling an electrically assisted exhaust gas turbocharger, wherein the electrically assisted exhaust gas turbocharger is controlled by means of a first and a second control loop, wherein an actual value of the electrically assisted exhaust gas turbocharger and a modeled value, as well as a first setpoint for the electrically assisted exhaust gas turbocharger are determined, wherein the modeled value corresponds to the actual value reduced by the power of the electric machine, wherein in the first control loop the modeled value is adjusted to the first setpoint and in the second control loop the actual value of the electrically assisted exhaust gas turbocharger is adjusted to the first setpoint or a second actual value is adjusted to a second setpoint.

[0011] Against the background of the prior art described above, the object of the present invention is to determine the power requirement of an electric exhaust gas turbocharger in a tHEV concept in order to enable the most power-optimized energy distribution of the energy supplied from the power source.

[0012] The method according to the invention comprises, in one process step, the establishment of a power balance around the electric exhaust gas turbocharger in the form of a differential equation, wherein boundary conditions and a driver request are used as variables in the differential equation. Boundary conditions are understood to be, in particular, parameters that are independent of the drive system and yet influence it. These include, for example, weather or climatic conditions that are reflected in the ambient pressure or ambient temperature. Similarly, actual states of measurable parameters of the engine control unit, such as an actual boost pressure, an actual oil temperature, or an actual oil pressure, are also considered boundary conditions. The driver request is incorporated in the form of a target value. The target value can, for example, be a target boost pressure or a target mass flow rate on the charging side of the combustion engine of the tHEV concept.Determining a target mass flow rate or a target boost pressure based on the driver's request, which is transmitted by the driver's actuation of the accelerator pedal, is known from the prior art.

[0013] In an advantageous embodiment of the method according to the invention, the power balance comprises compressor power at the electric exhaust gas turbocharger, power loss at the electric exhaust gas turbocharger, acceleration power of the electric exhaust gas turbocharger, mechanical power of the electric drive of the electric exhaust gas turbocharger and / or turbine power.

[0014] The differential equation is given in particular by: PCmpr+PLoss+[±Pacceleration]+[±Pmech,EM]−PTur=0, where, P Cmpr a compressor output at the electric exhaust gas turbocharger, P Loss a power loss at the electric exhaust gas turbocharger, ±P accelerationThe acceleration power of the electric exhaust gas turbocharger and the sign define whether power is being absorbed or delivered, ±P mech,EM a mechanical power of the electric drive of the electric exhaust gas turbocharger and the sign defines whether power is absorbed or delivered and P Tur represents turbine power.

[0015] Preferably, a system of two equations is formed from the differential equation, wherein one equation of the system is the differential equation in the actual state and one equation of the system is the differential equation in the target state, and a turbine power P is determined by the differential equation in the actual state. Tur The value is calculated in the current state, which is then substituted into the differential equation of the target state, and the differential equation in the target state is then used to solve for a mechanical power output of the electric drive P. mech,EMis resolved to determine the target power of the electric drive P mech,EM,Des , which corresponds to the performance requirement.

[0016] The invention and an advantageous embodiment thereof are explained in more detail below with reference to the accompanying figures. They show: Fig. Figure 1 shows an embodiment of a complete implementation of the method according to the invention. Fig. Figure 2 shows the determination of a modeled target speed n Des of the eATL, which is needed to determine the eATL's performance requirements

[0017] Fig. Figure 1 shows an embodiment of a complete implementation of the method according to the invention. In this embodiment, two different branches are initially distinguished: a target branch, shown above in Fig. 1, and an actual branch, below in Fig. 1.

[0018] Both branches can be mathematically represented by a system of two equations, where the equations correspond to a differential equation. Accordingly, one equation of the system is derived from the differential equation in the current state, and the other equation is derived from the differential equation in the desired state. The differential equation is represented as follows: PCmpr+PLoss+[±Pacceleration]+[±Pmech,EM]−PTur=0, where, P Cmpr a compressor output at the electric exhaust gas turbocharger, P Loss a power loss at the electric exhaust gas turbocharger, ±P acceleration The acceleration power of the electric exhaust gas turbocharger and the sign define whether power is being absorbed or delivered, ±P mech,EM a mechanical power of the electric drive of the electric exhaust gas turbocharger and the sign defines whether power is absorbed or delivered and P Turrepresents turbine power.

[0019] The system of equations thus becomes: PCmpr,Act+PLoss,Act+[±Pacceleration,Act]+[±Pmech,EM,Act]−PTur,Act=0, PCmpr,Des+PLoss,Des+[±Pacceleration,Des]+[±Pmech,EM,Des]−PTur,Act=0,

[0020] Equation (I) is the actual equation and equation (II) is the target equation. The indices "Act" and "Des" represent the actual state and the target state, respectively. The actual turbine output is used in the target equation to calculate the target mechanical output of the electric drive P. mech,EM,Des , which represents the performance requirement to be determined, in order to be able to resolve it.

[0021] Equation (I) is accordingly solved for the actual turbine power P Tur,Act resolved and then calculated. The actual compressor output at the eATL P Cmpr,Act The calculation is as follows: PCmpr,Act=m˙Cmpr,Act∗cp,Air∗TbeforeCompressor,Act∗[(pBoost,ActpPreCompressor,Act)κAir−1κAir−1] where c p,Luft , k Luft : Material properties of air ṁ Cmpr,Act Actual mass flow rate through compressor. Determined using a filling model. T VorVerdichter,Act Actual compressor temperature. Approximation with ambient temperature. p Ladedruck,Act Actual boost pressure. Determined via, for example, a pressure sensor. p VorVerdichter,Act Actual pressure before the compressor. Can be determined using the filling model and the ambient pressure.

[0022] The actual acceleration performance of the eATL P acceleration,Act is based on the actual rotational speed n Act and the moment of inertia is determined by the eATL, as shown in the following equation: Pacceleration,Act=12∗JeATL∗ωAct2∗1dT with ωAct=nAct∗2∗π

[0023] Here, dT corresponds to the cycle time of the function on the digital engine control unit (discrete-time calculation) and J eATL corresponds to the moment of inertia of the eATL (total travel time on the shaft).

[0024] The actual power loss at the eATL P Loss,Act is determined based on the actual rotational speed, the actual oil pressure and the actual oil temperature.

[0025] The actual mechanical performance of the eATL P mech,EM,Act , or rather its drive, and thus the actual shaft power of the eATL is calculated from: Pmech.EM,Act=ωAct∗TQAct with ωAct=nAct∗2∗π, where n Act the actual rotational speed of the eATL and TQ Act corresponds to the currently set torque of the eATL.

[0026] The actual turbine output P determined in this way Tur,Act is then substituted into equation (II) as already mentioned and this is compared to the power requirement of the eATL P. mech,EM,Des dissolved.

[0027] The target compressor output at the eATL P Cmpr,Des is determined based on the actual boost pressure from: PCmpr,Des=m˙Cmpr,Des∗cp,Air∗TVorCompressor,Act∗[(pBoostPressure,DespPreCompressor,Des)κAir−1κAir−1] where c p,Luft , k Luft : Material properties of air ṁ Cmpr,Des Target mass flow rate through compressor. Determined via filling model. T VorVerdichter,Act Actual compressor temperature. Approximation with ambient temperature. p Laderuck,Des Target boost pressure. Determined, for example, via a pressure sensor. P VorVerdichter,Des Target pressure before the compressor. Can be determined using the filling model and the ambient pressure.

[0028] The target power loss at the eATL P Loss,Des is determined based on the target speed, the actual oil pressure and the actual oil temperature.

[0029] The target acceleration power of the eATL P acceleration,DesThe target speed and moment of inertia are determined by the eATL. To determine the target speed n Des A rotational speed model is needed. Here, the rotational speed ω is used. Des overdetermined. Paceceleration,Des=ω(t)Des∗JeATL∗ω˙(t)Des(Diff.equation) with ωDes=nDes∗2∗π J eATL corresponds to the moment of inertia of the eATL (total travel time on the shaft).

[0030] There are two approaches to solving the differential equation: a) The eATL uses the maximum usable motor power for acceleration b) the eATL reports the currently usable maximum motor torque available for acceleration.

[0031] Mathematically speaking, this means P(t)∗dt=ω(t)∗JeATL∗dω Pacceleration,Des=12∗JeATL∗(ωDes(t+0)2−ωDes(t−1)2)

[0032] The implementation for determining the target rotational speed n DesIn digital motor technology, in Fig. 2 shown.

[0033] After determining the unknowns from equation (II), the desired power requirement or the mechanical target power of the electric drive of the eATL P can be calculated. mech,EM,Des will be calculated.

[0034] The calculation of the current state according to equation (I) is represented by the upper branch, while the description of the target state according to equation (II) is represented by the lower branch. Fig. 1 is shown. The corresponding results are then used to determine the turbine performance and thus flow into Fig. Enter 1 into the corresponding block of the diagram. The diagram contains further details on how the parameters determined during the calculation can be used. Component protection is particularly noteworthy here, as it defines limit values ​​for the operation of the eATL based on the determined parameters.

Claims

[1] Method for determining the power requirement of an electric exhaust gas turbocharger in a turbo hybrid electric vehicle concept, wherein the method includes setting up a power balance around the electric exhaust gas turbocharger in the form of a differential equation, where boundary conditions and a driver request are used as quantities of the differential equation. [2] Method according to the preceding claim, wherein the power balance comprises compressor power at the electric exhaust gas turbocharger, power loss at the electric exhaust gas turbocharger, acceleration power of the electric exhaust gas turbocharger, mechanical power of the electric drive of the electric exhaust gas turbocharger and / or turbine power. [3] Method according to any of the preceding claims, wherein the differential equation is represented as follows: PCmpr+PLoss+[±Pacceleration]+[±Pmech,EM]−PTur=0, where, P Cmpra compressor output at the electric exhaust gas turbocharger, P Loss a power loss at the electric exhaust gas turbocharger, ±P acceleration The acceleration power of the electric exhaust gas turbocharger and the sign define whether power is being absorbed or delivered, ±P mech,EM a mechanical power of the electric drive of the electric exhaust gas turbocharger and the sign defines whether power is absorbed or delivered and P Tur represents turbine power. [4] A method according to one of the preceding claims, further comprising forming a system of equations, wherein one equation of the system of equations is the differential equation in the actual state and one equation of the system of equations is the differential equation in the target state, and a turbine power P is determined by the differential equation in the actual state. Turcalculated in the current state, which is then substituted into the differential equation of the target state, and the differential equation in the target state is used to find a mechanical power output of the electric drive P. mech,EM is resolved to determine the target power of the electric drive P mech,EM,Des , which corresponds to the performance requirement.

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