Turbocharger control with overspeed protection

1. An engine system comprising:

an engine having an intake manifold and an exhaust manifold;

a turbocharger having a compressor and a turbine, the compressor being upstream of the intake manifold, the turbine being downstream of the exhaust manifold, wherein the turbocharger is configured obtain power from airflow exiting the exhaust manifold to drive the compressor to compress air to be provided to the intake manifold;

a wastegate positioned and configured to allow airflow exiting the exhaust manifold to bypass the turbine, the wastegate selectively controllable in a range of opening positions between open and closed;

a plurality of engine airpath sensors associated with the engine; and

a controller configured to perform the following:

estimate turbocharger speed using the engine airpath sensors and a model of the engine air path as a function of measured or estimated boost pressure downstream of the compressor, measured or estimated mass flow into the compressor, measured or estimated compressor inlet temperature, and measured or estimated compressor inlet pressure;

calculate a target turbocharger speed by reference to a target boost pressure; and

control the wastegate to minimize the distance between the target boost pressure and an actual boost pressure, while preventing turbocharger speed from exceeding a predefined maximum speed.

2. The engine system of claim 1 wherein the engine airpath sensors comprise:

a boost pressure sensor configured and positioned to measure the actual boost pressure to provide the measured boost pressure downstream of the compressor; and

wherein the controller is configured such that the engine airpath sensors used to estimate turbocharger speed include the boost pressure sensor.

3. The engine system of claim 1 wherein the controller is further configured to predict future turbocharger speed and calculate commands to the wastegate to avoid overspeed of the turbocharger.

4. The engine system of claim 1 wherein the controller is further configured to estimate turbocharger speed using a compressor model, predict future turbocharger speed and calculate commands to the wastegate to minimize a future difference between actual boost pressure and target boost pressure while avoiding overspeed of the turbocharger.

5. The engine system of claim 1 wherein the controller is configured to estimate turbocharger speed using a compressor model, a measured actual boost pressure, and each of an estimated compressor mass flow, estimated compressor inlet pressure and estimated compressor inlet temperature.

6. The engine system of claim 1 wherein the controller is configured to perform the step of controlling the wastegate to minimize the distance between the target boost pressure and an actual boost pressure, while preventing turbocharger speed from exceeding a predefined maximum speed, by:

calculating a current compressor power;

determining a target acceleration power needed to achieve the target turbocharger speed relative to the estimated turbocharger speed;

determining a turbine power needed to achieve the target acceleration power using the current compressor power; and

determining a wastegate position needed to modify turbine flow to achieve the turbine power.

7. The engine system of claim 1 wherein the controller comprises an upper level controller configured to predict future turbocharger speed within a time horizon, and to calculate feasible future turbocharger energy targets that prevent turbocharger speed exceeding a maximum speed limit, and a low level controller configured to control wastegate position in accordance with turbocharger energy targets computed by the upper level controller.

8. An engine system comprising:

an engine having an intake manifold and an exhaust manifold;

a turbocharger having a compressor and a turbine, the compressor being upstream of the intake manifold, the turbine being downstream of the exhaust manifold, wherein the turbocharger is configured obtain power from airflow exiting the exhaust manifold to drive the compressor to compress air to be provided to the intake manifold, the turbine taking the form of a variable nozzle turbine (VNT) selectively controllable in a range of opening positions between open and closed;

a plurality of engine airpath sensors associated with the engine; and

a controller configured to perform the following:

estimate turbocharger speed using the engine airpath sensors and a model of the engine air path as a function of measured or estimated boost pressure downstream of the compressor, measured or estimated mass flow into the compressor, measured or estimated compressor inlet temperature, and measured or estimated compressor inlet pressure;

calculate a target turbocharger speed by reference to a target boost pressure; and

control the VNT to minimize the distance between the target boost pressure and an actual boost pressure, while preventing turbocharger speed from exceeding a predefined maximum speed.

9. The engine system of claim 8 wherein the engine airpath sensors comprise:

a boost pressure sensor configured and positioned to measure the actual boost pressure to provide the measured boost pressure downstream of the compressor; and

wherein the controller is configured such that the engine airpath sensors used to estimate turbocharger speed include the boost pressure sensor.

10. The engine system of claim 8 wherein the controller is further configured to predict future turbocharger speed and calculate commands to the VNT to avoid overspeed of the turbocharger.

11. The engine system of claim 8 wherein the controller is further configured to estimate turbocharger speed using a compressor model, predict future turbocharger speed and calculate commands to the VNT to minimize a future difference between actual boost pressure and target boost pressure while avoiding overspeed of the turbocharger.

12. The engine system of claim 8 wherein the controller is configured to estimate turbocharger speed using a compressor model, a measured actual boost pressure, and each of an estimated compressor mass flow, estimated compressor inlet pressure and estimated compressor inlet temperature.

13. The engine system of claim 8 wherein the controller is configured to perform the step of controlling the VNT to minimize the distance between the target boost pressure and an actual boost pressure, while preventing turbocharger speed from exceeding a predefined maximum speed by:

calculating a target turbocharger speed using the target boost pressure;

calculating current compressor power;

determining a target acceleration power needed to achieve the target turbocharger speed relative to the estimated turbocharger speed;

determining turbine power needed to achieve the target acceleration power using the calculated current compressor power; and

determining a VNT position needed to achieve the turbine power.

14. The engine system of claim 8 wherein the controller comprises an upper level controller configured to predict future turbocharger speed within a time horizon, and to calculate feasible future turbocharger energy targets that prevent turbocharger speed exceeding a maximum speed limit, and a low level controller configured to control VNT position in accordance with turbocharger energy targets computed by the upper level controller.

15. A method of controlling a turbocharger in an engine system that includes:

an engine having an intake manifold and an exhaust manifold;

a turbocharger having a compressor and a turbine, the compressor being upstream of the intake manifold, the turbine being downstream of the exhaust manifold, wherein the turbocharger is configured obtain power from airflow exiting the exhaust manifold to drive the compressor to compress air to be provided to the intake manifold;

a wastegate positioned and configured to allow airflow exiting the exhaust manifold to bypass the turbine, the wastegate selectively controllable in a range of opening positions between open and closed;

a plurality of engine airpath sensors associated with the engine;

a controller configured to obtain signals from the engine airpath sensors and control at least the wastegate, the method comprising:

the controller estimating turbocharger speed using the engine airpath sensors and a model of the engine air path as a function of measured or estimated boost pressure downstream of the compressor, measured or estimated mass flow into the compressor, measured or estimated compressor inlet temperature, and measured or estimated compressor inlet pressure;

the controller calculating a target turbocharger speed by reference to a target boost pressure; and

the controller issuing command signals to control the wastegate to minimize the distance between the target boost pressure and an actual boost pressure, while preventing turbocharger speed from exceeding a predefined maximum speed.

16. The method of claim 15 wherein the engine airpath sensors comprise:

a boost pressure sensor configured and positioned to measure the actual boost pressure and provide the measured boost pressure downstream of the compressor; and

wherein the step of estimating turbocharger speed includes taking sensor readings from the boost pressure sensor.

17. The method of claim 15 further comprising:

the controller predicting future turbocharger speed; and

the controller calculating commands to the wastegate to avoid overspeed of the turbocharger.

18. The method of claim 15 , further comprising:

the controller predicting future turbocharger speed; and

the controller calculating commands to the wastegate to minimize a future difference between actual boost pressure and target boost pressure while avoiding overspeed of the turbocharger.

19. The method of claim 15 wherein the step of issuing command signals to control the wastegate to minimize the distance between the target boost pressure and an actual boost pressure, while preventing turbocharger speed from exceeding a predefined maximum speed comprises:

determining a target acceleration power needed to achieve the target turbocharger speed relative to the estimated turbocharger speed;

determining a turbine power needed to achieve the target acceleration power; and

determining a wastegate position needed to achieve the determined turbine power.

20. The method of claim 15 wherein the step of the controller issuing command signals to control the wastegate to minimize the distance between the target boost pressure and an actual boost pressure, while preventing turbocharger speed from exceeding a predefined maximum speed, comprises issuing a command to open the wastegate either to prevent turbocharger overspeed or to prevent actual boost pressure from exceeding target boost pressure, or issuing a command to close the wastegate to raise the actual boost pressure when below the target boost pressure.