METHOD FOR REGULATING AND LIMITING THE SPEED OF A TURBOCHARGER

Description

[0001] The following invention relates to a method for controlling a control variable in the operation of a turbocharger according to the independent method claim. Furthermore, the invention relates to a turbocharger for operating a compressor according to the independent apparatus claim. In addition, the invention relates to a computer program product according to the independent product claim.

[0002] Turbochargers are known to be positioned downstream of the exhaust flow of an internal combustion engine. They convert the thermal and kinetic energy of the exhaust gases into mechanical power. This mechanical power can then be used to drive a compressor, which supplies combustion air to the engine. The faster the engine runs, the faster the turbocharger spins. The faster the turbocharger spins, the more air the compressor forces through, which, in turn, accelerates the turbocharger due to the increasing volume of exhaust gas. However, at a certain speed, the turbocharger reaches a load limit, i.e., its maximum permissible speed, which can lead to mechanical damage, such as excessive friction, and / or thermal damage, such as overheating.

[0003] Modern boost pressure control systems are based on physical models of the air path, such as a compressor model. Adherence to component limits is achieved by limiting the target boost pressure and / or by considering a turbocharger speed modeled via the compressor model. However, in the event of a leak in the compressor's intake system, the modeled fresh air mass flow is underestimated. To compensate for the escaping air, the boost pressure regulator will then increase the load on the exhaust gas turbocharger. This carries the risk of operating the exhaust gas turbocharger beyond its load limit. Therefore, even a minor sealing problem in the intake system (e.g., a missing or defective O-ring) can lead to significant damage to the exhaust gas turbocharger.Directly connecting a turbocharger speed sensor to the control loop is often not straightforward, as this would result in an overdetermined system (one manipulated variable with two control targets). Therefore, established boost pressure control methods cannot be robust under all operating conditions. Either they intervene unnecessarily in a system without leakage (resulting in power loss), or the turbocharger speed is not robustly limited in the event of a leakage (risk of component damage).

[0004] Documents DE 10 2008 044 156 A1, DE 10 2005 012 946 A1 and DE 10 2015 210 226 A1 represent exemplary state of the art.

[0005] It is therefore an object of the present invention to at least partially overcome the disadvantages described above in a method for controlling a variable during the operation of a turbocharger. In particular, it is an object of the present invention to provide a method for controlling a variable during the operation of a turbocharger, especially the speed of a turbocharger, which can be implemented simply, with little effort and with little computing power, in order to drive the turbocharger robustly and safely under all operating conditions and to reliably protect it from exceeding its load limit. Furthermore, it is an object of the invention to provide a suitable turbocharger for operating a compressor. Finally, it is an object of the invention to provide a corresponding computer program.

[0006] The problem according to the invention is solved by a method for controlling and, in particular, limiting the rotational speed of a turbocharger according to the independent method claim. Furthermore, the problem according to the invention is solved by a turbocharger for operating a compressor according to the independent apparatus claim. In addition, the problem according to the invention is solved by a computer program product according to the independent product claim.

[0007] The invention provides a method for controlling and, in particular, limiting the speed of a turbocharger that is in operative connection with a compressor, to solve the problem, comprising the following steps: 1) Providing a target value for the turbocharger speed based on model-based feedforward control for calculating a target boost pressure upstream of the turbocharger, i.e., using model-based feedforward control to calculate a target boost pressure upstream of the turbocharger and converting the target boost pressure upstream of the turbocharger into the target value for the turbocharger speed; 2) Determining an actual value for the turbocharger speed; 3) Controlling a turbocharger actuator (the actuator can be a wastegate or variable vanes in gasoline engines and variable vanes in diesel engines) to compensate for the difference between the target value and the actual value for the turbocharger speed. wherein in step 2) when determining the actual value for the speed of the turbocharger a main signal and a secondary signal are provided, wherein the main signal and the secondary signal are fused to make the actual value for the speed of the turbocharger plausible.

[0008] The signal within the meaning of the invention can be understood as the function that maps the value of the rotational speed as a function of time.

[0009] The invention recognizes that when regulating boost pressure, the turbocharger's load limit, i.e., its maximum permissible speed, is not taken into account, or at least not sufficiently. The model-based feedforward control comprises a mathematical model for calculating a target boost pressure upstream of the turbocharger (or a target boost pressure of the compressor). This mathematical model is based on the well-known Euler turbine equation. The target boost pressure upstream of the turbocharger can be calculated, for example, for a desired turbocharger output.

[0010] The inventive concept lies in using the turbocharger speed, rather than the turbocharger boost pressure, as the controlled variable when controlling a control variable during turbocharger operation. This allows the maximum permissible turbocharger speed to be directly considered, or in other words, incorporated into the control process, for example, as a maximum adjustable setpoint for the turbocharger speed. To obtain the setpoint for the turbocharger speed, the target boost pressure upstream of the turbocharger is calculated using a known model-based feedforward control method and converted into a target value for the turbocharger speed. The target boost pressure is thus considered the input variable. The target value for the turbocharger speed can be calculated using a compressor model.

[0011] The invention presents a new approach for determining the actual value of the turbocharger speed. The core concept lies in validating the modeled actual value of the turbocharger speed by comparing two signals and providing a fused actual value for the turbocharger speed for further use in the controller.

[0012] The primary signal for the turbocharger speed can be derived from the compressor model. A secondary signal for the turbocharger speed can be taken from either a turbine model or a sensor reading. In a system without leakage in the intake tract, these speed signals correlate with each other. In the case of a leak, the primary signal assumes lower values ​​than the secondary signal, because the secondary signal is not affected by the leakage.

[0013] The invention provides a fused speed control in step 2), where the main signal is validated using the auxiliary signal. Advantageously, the invention intervenes in the speed control loop in the event of deviations between the main signal and the auxiliary signal that are attributable to a leakage. In the case of a leakage, the main speed can be increased. The invention thus enables robust prevention of overspeeds, independent of the current operating situation. Simultaneously, the intervention in the control loop is carried out in such a way that feedback effects on the dynamic behavior of the closed loop (particularly with regard to stability and oscillation tendency) are minimized.

[0014] The fused speed is determined as follows: A fused speed signal is generated based on the leakage factor. This can be implemented, for example, using a Kalman filter whose parameters are defined based on the leakage factor. This provides an improved method for controlling the turbocharger speed, which is simple, requires little effort, and demands minimal computing power.

[0015] The fused rotational speed can also be determined as follows: Depending on the main signal, a minimum and a maximum threshold are calculated. By comparing the main signal and the auxiliary signal, a leakage factor is determined, for example, as follows: If the auxiliary signal is smaller than the minimum threshold, a leakage factor of 0 is calculated.

[0016] If the secondary signal is greater than the maximum threshold, a leakage factor of 1 is calculated.

[0017] If the secondary signal lies between the two thresholds, a leakage factor between 0 and 1 is interpolated.

[0018] Furthermore, the invention can provide, in a method for controlling the speed of a turbocharger, that in step 1) when providing the setpoint for the turbocharger speed, a setpoint limit for the turbocharger speed is imposed. Advantageously, a maximum permissible turbocharger speed can be considered as a limit value. By taking the setpoint turbocharger speed into account, it is advantageously possible to cap the pressure-based value with a mechanical limit value, so that the controller can regulate precisely to this limit value when it is reached. This ensures that the limit value represents the torque limit both dynamically and in steady-state conditions.

[0019] Furthermore, the invention can provide, in a method for controlling the speed of a turbocharger, that in step 2) the actual value of the turbocharger speed is detected in the auxiliary signal, i.e., measured and / or sensed. A speed sensor can be provided for this purpose. Thus, the speed control loop can directly consider the actual speed value of the turbocharger. Moreover, the actual speed of the turbocharger can be specifically incorporated into the setpoint limitation. Long-term influences on the turbocharger, such as contamination or wear, which cannot be represented by model-based feedforward control, can also be taken into account by incorporating the actual speed value of the turbocharger into the control.

[0020] Furthermore, in a method for controlling the speed of a turbocharger, the invention provides that in step 2) the actual value for the turbocharger speed is supplied in the auxiliary signal from or via a turbine model. The turbine model can, for example, be map-based and represent the turbine speed as a function of an air mass flow and / or speed ratios before and after the turbine. Using a turbine-model-based calculation of the turbocharger speed, a speed sensor can be dispensed with, as the auxiliary signal is modeled using the turbine model. This also ensures that an auxiliary signal is provided which is not affected by any leaks in the intake line upstream of the compressor.

[0021] Furthermore, the invention can provide, in a method for controlling the speed of a turbocharger, that in step 2) the actual value for the turbocharger speed is provided in the main signal from or via a compressor model, in particular by means of a conversion from a detected actual boost pressure of the compressor or actual boost pressure upstream of the turbocharger. Advantageously, the actual value for the turbocharger speed can be calculated analogously to the setpoint value for the turbocharger speed, preferably using the same conversion or with the same gain factor. The same software and / or hardware can be used for this purpose as in existing control systems.

[0022] Furthermore, the invention can provide, in a method for controlling the speed of a turbocharger, that the same mathematical model, in particular the compressor model, and / or the same parameters are used for the setpoint for the turbocharger speed in step 1) and the actual value for the turbocharger speed in the main signal in step 2). In this way, consistency in the pressure path through the turbocharger can be established.

[0023] According to a further advantage of the invention, in step 1) and / or step 2), at least one thermodynamic quantity can be used or taken into account as a parameter in the operation of the turbocharger, such as a temperature upstream of the compressor, a pressure upstream of the compressor, and / or a mass flow rate of intake air through the compressor. Thus, the actual operating conditions of the turbocharger, which can influence the boost pressure and / or the speed of the turbocharger, can be taken into account.

[0024] Furthermore, the problem according to the invention is solved by a turbocharger for operating a compressor, which can serve to supply combustion air to an internal combustion engine. According to the invention, the turbocharger has a control unit designed to regulate the operation of the turbocharger according to a method that can be implemented as described above. The control unit can be implemented in an engine control unit of the internal combustion engine or as a separate control unit for the turbocharger. The turbocharger according to the invention offers the same advantages that were described above in connection with the method according to the invention. These advantages are fully referenced here.

[0025] Furthermore, the invention provides a computer program product for solving the problem, which can be stored in a memory unit of the control unit described above, and which, when at least partially implemented in a processing unit of the control unit, carries out a method that can proceed as described above. The same advantages described above in connection with the method according to the invention can also be achieved using the computer program product according to the invention. These advantages are also fully referenced here.

[0026] Further measures improving the invention are described in more detail below with reference to the figures and the preferred embodiments of the invention. The features mentioned in the claims and in the description can be essential to the invention individually or in any combination. It should be noted that the figures are for descriptive purposes only and are not intended to limit the invention in any way. They show: Fig. 1 a schematic flowchart of a possible control method according to the invention, in which the speed of a turbocharger is controlled as the controlled variable, Fig. 2 a schematic flowchart of a compressor model, Fig. 3 a schematic representation of a main signal and a secondary signal according to the invention, Fig. 4 a schematic flowchart of a control method according to the invention, in which the speed of the turbocharger is controlled as the controlled variable, Fig. 5 a schematic explanation of a fusion of an actual value for the speed of a turbocharger within the scope of the invention, Fig. 6 a diagram for a control method according to the invention and Fig. 7 a diagram for a known control method.

[0027] In the different figures, identical features of the invention are always provided with the same reference numerals, which is why they are usually only described once.

[0028] The Figure 1The figure schematically shows the principle of a control R of a speed N in the operation of a turbocharger 100 for a compressor 101, in which the speed N as a control variable is derived from a compressor model VM for a boost pressure P of a turbocharger 100.

[0029] The aim of the control R is to ensure that the turbocharger 100 delivers sufficient power at low exhaust gas flows and, at high speeds, does not exceed its load limit, in particular its maximum permissible speed N, under different operating conditions, even with leaks L in the intake system of the compressor 101.

[0030] The Figure 1 schematically shows the sequence of a possible method in accordance with the invention for controlling R and in particular limiting a speed N of a turbocharger 100, which is in operative connection with a compressor 101, comprising the following steps: 1) Providing a setpoint Nsoll for the rotational speed N of the turbocharger 100 based on a model-based feedforward Mp for calculating a target boost pressure Psoll upstream of the turbocharger 100, i.e., using a model-based feedforward Mp for calculating a target boost pressure Psoll upstream of the turbocharger 100 and converting Upn of the target boost pressure Psoll upstream of the turbocharger 100 into the setpoint Nsoll for the rotational speed N of the turbocharger 100, 2) Determining an actual value Nist for the rotational speed N of the turbocharger 100, 3) Controlling an actuator S of the turbocharger 100 to compensate for the difference between the setpoint Nsoll and the actual value Nist for the rotational speed N of the turbocharger 100.

[0031] According to the invention, in step 2) when determining the actual value Nist for the rotational speed N of the turbocharger 100, a main signal HS and a secondary signal NS are provided, wherein the main signal HS and the secondary signal NS are fused, as described in the Figures 4 , 5and 6 to show, in order to validate the actual value Nist for the speed N of the turbocharger 100.

[0032] The invention proposes, firstly, to use the rotational speed N of the turbocharger 100 and not the boost pressure P upstream of the turbocharger 100 as the control variable when controlling a control variable during the operation of a turbocharger 100 (see the Figure 1 and 2 ). The maximum permissible speed Nmax of the turbocharger 100 can be directly taken into account or, in other words, controlled along with it, e.g. as a maximum adjustable target value Nsoll for the speed N of the turbocharger 100 (see the Figure 2 To obtain the target value Ntarget for the speed N of turbocharger 100, the target boost pressure Ptarget upstream of turbocharger 100 is calculated from the known model-based feedforward control Mp and converted into a target value Ntarget for the speed N of turbocharger 100 (an example conversion Upn to a compressor model VM is shown in the Figure 2 (to see).

[0033] Furthermore, within the scope of the invention, an actual value Nist for the rotational speed N of the turbocharger 100 is determined as a fused actual value Nist for the rotational speed N of the turbocharger 100 from two signals HS, NS (see the Figures 4 , 5 and 6 ). As is particularly evident the Figures 4 , 5 and 6 As shown, within the scope of the invention, the actual value Nist modeled in step 2) for the speed N of the turbocharger 100 is validated by comparing two signals HS, NS.

[0034] The main signal HS for the speed N of turbocharger 100 can still be derived from the compressor model VM. A secondary signal NS for the speed N of turbocharger 100 can be taken either from a turbine model TM or a sensor value Nsensor, as shown in the Figures 4 and 5 to suggest.

[0035] As in the Figure 3As shown, these speed signals HS and NS correlate with each other in a system without a leakage L in the intake tract upstream of compressor 101. In the case of a leakage L in the intake tract upstream of compressor 101, the main signal HS assumes smaller values ​​than the secondary signal NS, because the secondary signal NS is not affected by the leakage L.

[0036] In the Figure 3 Three areas 1, 2, 3 are indicated: a permissible area 1 (no leakage s), border area 2 (possible or medium leakage m) and an impermissible area 3 (large leakage l).

[0037] As it is in the Figures 3 and 5As indicated, in permissible range 1, the actual value Nist for the speed N of turbocharger 100 can be set essentially equal to the main signal HS. In limit range 2, the main signal HS can advantageously be increased. In impermissible range 3, the actual value Nist for the speed N of turbocharger 100 can be determined essentially equal to the auxiliary signal NS.

[0038] As it is in the Figure 5 As indicated, the invention intervenes in the speed control loop according to the following in the event of deviations between the main signal HS and the secondary signal NS, which are attributable to a leakage L. Figure 1 a.

[0039] The actual value Nist of the fused rotational speed Nist is, as described in the Figure 5 As shown, it is determined as follows: Depending on the leakage factor LF, a plausible actual value Nist of the fused rotational speed N is mapped.

[0040] As it is Figure 5As indicated, the plausible actual value Nist of the fused rotational speed N can be determined, for example, using a Kalman filter KF, whose parameters are defined depending on the leakage factor LF.

[0041] The actual value Nist of the fused rotational speed Nist can also be further, as described in the Figure 5 As shown, the following applies: Depending on the main signal HS, a minimum threshold SWmin and a maximum threshold SWmax are determined (see the Figure 3 ).

[0042] A leakage factor LF is calculated by comparing the main signal HS and the auxiliary signal NS, for example as follows: If the auxiliary signal NS is smaller than the minimum sleeper height SWmin, a leakage factor of 0 is calculated.

[0043] If the secondary signal NS is greater than the maximum threshold SWmax, a leakage factor of 1 is applied.

[0044] If the secondary signal NS lies between the two threshold values ​​SWmin and SWmax, a leakage factor between 0 and 1 is interpolated.

[0045] The invention enables robust prevention (see the Figure 6 ) of overspeeds Nist>Nmax (cf. the Figure 7 ) regardless of the current operating situation. At the same time, the intervention in the control loop is carried out in such a way that feedback effects on the dynamic behavior of the closed control loop with regard to stability and oscillation tendency are minimized.

[0046] Advantageously, in step 1), when providing the setpoint Nsetpoint for the speed N of turbocharger 100, a setpoint limit for the speed N of turbocharger 100 can be implemented, taking into account the maximum permissible speed Nmax of turbocharger 100 as a limit value. By controlling the speed R of the speed N, it is advantageously possible to cap the pressure-based value of the speed N with a mechanical limit value, so that the controller can regulate precisely to this limit value when it is reached.

[0047] According to the Figure 2Is it conceivable that the same mathematical model, in particular the compressor model VM, and / or the same (thermodynamic) parameters are used for the target value Ntarget for the speed N of turbocharger 100 in step 1) and the actual value Nactual for the speed N of turbocharger 100 in the main signal HS in step 2)? The compressor model VM and the parameters used are determined using the Figure 2 explained.

[0048] As it is Figure 2 As shown, when converting the boost pressure P (Upn) into the boost speed N of the turbocharger 100, the following thermodynamic quantities can be used or considered as parameters in the operation of the turbocharger 100: a pressure PvV upstream of the compressor 101, a mass flow rate dm / dt of intake air through the compressor 101, and a temperature upstream of the TvV upstream of the compressor 101. As shown in the Figure 2As shown, these parameters are incorporated via a characteristic map K for the speed N of the turbocharger 100.

[0049] The Figure 6 Figure 1 shows a control system R according to the invention in the case of a leakage L, where the secondary signal NS was determined via a turbine model TM. It is also conceivable that the rotational speed N can be sensed for the secondary signal NS. According to the Figure 5 It is still conceivable that both possibilities for generating the auxiliary signal NS can be incorporated into the control R within the framework of selection A. Since the controller now uses a fused speed Nist, which is greater than the setpoint Nsoll, the boost pressure control deviation (~300 mbar) is not compensated by the controller.

[0050] The Figure 7 demonstrates a regulation without a fusion of the actual value in accordance with the invention, which is in the Figure 6 was taken into account. In the Figure 7The controller regulates the boost pressure Pist or the speed Nist modeled via compressor to the target speed Nsoll, thereby endangering the turbocharger T beyond the load limit Nist>Nmax.

[0051] The turbocharger 100, which can be operated according to a method, represents a further aspect of the invention in addition to the method. As stated in the Figure 4As shown, the turbocharger 100 according to the invention has a control unit 10 designed to regulate the turbocharger 100 accordingly. It is conceivable that the control unit 10 can be integrated into an engine control unit 10* of an internal combustion engine or be a separate control unit 10 of the turbocharger 100. The control unit 10 includes a storage unit 11 in which a computer program can be stored. If at least partially implemented in a processing unit 12 of the control unit 10, this program executes a process that can proceed as described above.

[0052] The preceding description of the figures describes the present invention solely by way of examples. Naturally, individual features of the embodiments can be freely combined with one another, provided it is technically feasible, without departing from the scope of the invention. Reference symbol list

[0053] 100 turbochargers 101 compressors 10 control units 10*engine control units 11 Storage unit 12 Processing unit 1. Permissible area 2. Borderline area 3. Impermissible area Selection from the measured speed value or the speed value according to the turbine model KKennfeld KFKalman filter Leakage small leakage, medium leakage, large leakage LFLeckage factor MP model-based feedforward control N speed Nset Target value for the speed Nmax Maximum permissible speed Actual value for the speed HS main signal NS secondary signal N sensor measured speed PBoost pressure Ptarget boost pressure Pist Actual boost pressure PvV Pressure before compressor Pref Reference pressure RRegulation Sactuator SWminminimal threshold SWmaxmaximal threshold TvV temperature before the compressor Treff reference temperature dm / dt mass flow Upn conversion of boost pressure to engine speed TM Turbine model VM Compressor model

Claims

1. Method for controlling (R) a speed of a turbocharger (100) which is operatively connected to a compressor (101), comprising the following steps: 1) providing a target value (Nsoll) for the speed (N) of the turbocharger (100) on the basis of a model-based pre-control (Mp) for calculating a target boost pressure (Psoll) upstream of the turbocharger (100), 2) determining an actual value (Nist) for the speed (N) of the turbocharger (100), 3) controlling an actuator (S) of the turbocharger (100) in order to compensate for the difference between the target value (Nsoll) and the actual value (Nist) for the speed (N) of the turbocharger (100), wherein, in step 2), when determining the actual value (Nist) for the speed (N) of the turbocharger (100), a main signal (HS) and a secondary signal (NS) are provided, wherein the main signal (HS) and the secondary signal (NS) are fused in order to make the actual value (Nist) for the speed (N) of the turbocharger (100) plausible, wherein, in step 2), a minimum threshold (SWmin) and a maximum threshold (SWmax) are calculated from the main signal (HS), wherein a leakage factor (LF) is mapped according to the secondary signal (NS), the minimum threshold (SWmin) and the maximum threshold (SWmax), wherein the actual value (Nist) of the fused speed (N) is mapped according to the leakage factor (LF), and wherein, in a system without leakage in the intake path, the main signal (HS) and the secondary signal (NS) correlate with each other.

2. Method according to claim 1, characterized in that the leakage factor (LF) is mapped as 0 when the secondary signal (NS) is less than the minimum threshold (SWmin), or in that the leakage factor is mapped as 1 when the secondary signal (NS) is greater than the maximum threshold (SWmax), or in that the leakage factor (LF) is interpolated between 0 and 1 when the secondary signal (NS) is between the minimum threshold (SWmin) and the maximum threshold (SWmax).

3. Method according to any of the preceding claims, characterized in that the main signal (HS) and the secondary signal (NS) are fused by means of a Kalman filter (KF).

4. Method according to any of the preceding claims, characterized in that, in step 1), when providing the target value (Nsoll) for the speed (N) of the turbocharger (100), a target value limitation for the speed (N) of the turbocharger (100) is implemented.

5. Method according to any of the preceding claims, characterized in that, in step 2), the actual value (Nist) for the speed (N) of the turbocharger (100) is detected in the secondary signal (NS).

6. Method according to any of the preceding claims 1 to 4, characterized in that, in step 2), the actual value (Nist) for the speed (N) of the turbocharger (100) in the secondary signal (NS) is provided from a turbine model (TM).

7. Method according to any of the preceding claims, characterized in that, in step 2), the actual value (Nist) for the speed (N) of the turbocharger (100) in the main signal (HS) is provided from a compressor model (VM), in particular by means of a conversion from a detected actual boost pressure (Pist).

8. Method according to any of the preceding claims, characterized in that the same mathematical model and / or the same parameters is / are used in the operation of the turbocharger (100) for the target value (Nsoll) for the speed (N) of the turbocharger (100) in step 1) and the actual value (Nist) for the speed (N) of the turbocharger (100) in the main signal (HS) in step 2).

9. Method according to any of the preceding claims, characterized in that, in step 1) and / or in step 2), at least one thermodynamic variable is used as a parameter in the operation of the turbocharger (100), such as a temperature (TvV) upstream of the compressor (101), a pressure (PvV) upstream of the compressor (101), and / or a mass flow rate (dm / dt) of intake air through the compressor (101).

10. Turbocharger (100) for operating a compressor (101), comprising a control unit (10) designed to control the operation of the turbocharger (100) according to a method according to any of the preceding claims.

11. Computer program product which can be stored in a memory unit (11) of the control unit (10) according to the preceding claim, and which, when at least partially executed in a computing unit (12) of the control unit (10), carries out a method according to any of the preceding claims 1 to 9.