USE OFPOST COMPRESSORBLEED TO CONTROL TURBOCHARGEROVERSPEEDING

Background

[0001] Turbochargers are added to engines to improve performance. Turbocharger systems are applied to engines in a range of applications including aquatic vehicles, ground vehicles, aircraft, and stationary engines such as generators. Performance parameters enhanced by turbochargers include operator perceived power, actual power, efficiency, and other parameters. Variables associated with turbocharged systems are controlled to enhance their performance. But there is a need to control turbocharged systems to prevent them from being damaged in use and to prevent them from damaging other engine components.

. BRIEF DESCRIPTION OF THE DRAWINGS

[0002J FIG. 1 illustrates a diagram of an engine system, according to one embodiment. [0003] FIG. 2 illustrates a turbocharging system include a diesel particular filter, according to one embodiment of the present subject matter.

[0004] FIG. 3 illustrates a process for controlling turbocharger spool rotation speed, according to one embodiment of the present subject matter.

[0005] FIG. 4 illustrates a process for controlling turbocharger spool rotation speed, according to one embodiment.

[0006] FIG. 5 illustrates a process of sensing turbocharger spool rotation speed and controlling turbocharger spool rotation speed, according to one embodiment.

DETAILED DESCRIPTION

[0007] In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments which may be practiced. These embodiments are described in sufficient detail to enable those

skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the scope of the present invention. The following description of example embodiments is, therefore, not to be taken in a limited sense, and the scope of the present invention is defined by the appended claims.

[0008] While turbocharging systems provide increased power and efficiency, they also add cost and complexity to engine systems. As such, improvements to turbocharging systems should maintain or improve the simplicity of the engine system. Improvements in simplicity can decrease cost, assembly time, etc. To encourage these reductions, the turbocharging systems here use components of an engine system for multiple functions (e.g., to regenerate a particulate filter and to relieve turbocharger boost), in some embodiments. [0009] An ongoing requirement of turbocharged engines is that the turbocharging system be robust and perform well in stressed conditions such as harsh working environments. The turbocharging systems discussed here provide robust systems by providing systems which protect turbochargers from undesired stress.

[0010] One Way turbochargers are damaged is if their spool rotation speed limits are exceeded. Sometimes spool rotation speed limits are specified by a manufacturer, and sometimes they are known based on experienced failures. Spool rotation speed limits often are a function of the turbocharger design. In some instances, a spool rotation speed limit is selected to avoid a vibrational mode.

[0011] When a turbocharger spins too fast, it enters a condition called overspeed. Various embodiments include a control system to control turbocharger spool rotation speed and to reduce occurrences of turbocharger overspeeding. The control system is mounted to the engine system, including the intake and the exhaust, in some examples. Some examples provide an engine system for use by a vehicle builder in building equipment such as semi- truck or construction equipment.

[0012] Turbocharger spool rotation speed can be controlled with vane adjustments in variable nozzle turbines (VNT). Other vane adjustments, such as compressor adjustments, are possible. Variable geometry compressor housings are used in some instances. Configurations

controlling turbocharger spool rotation speed by adjusting one or more of these variables do not reduce turbocharger spool rotation speed enough.

[0013] Turbocharger spool rotation speed can also be controlled by derating an engine. Engine derating adjusts one or more of fuel quantity, timing, combinations thereof, or some other engine variable. Derating schemes reduce available engine power, in some examples. In vehicular applications, drivers should be able to use turbocharged systems without becoming frustrated by operational inconsistencies. An operator using a derated engine, for example a driver driving a vehicle, can notice that derating such as fuel derating is occurring. This user experience is undesirable, and can lead to decreased goodwill, unneeded warranty visits, and other problems. The turbocharging systems discussed here provide for a more consistent driving experience while also protecting one or more turbochargers from damage. [0014] Some systems which combine adjustments to a vane system of a VNT while fuel derating still intrude too heavily upon the driving experience. As such, the present systems and methods include one or more compressor bleed valves to control turbocharger spool rotation speed to within acceptable limits. A compressor bleed valve bleeds gas from the boosted portion of the intake system of an engine. In some applications, air is bled from a conduit connected to the turbocharger compressor outlet.

[0015] Various compressor bleed valves are possible. Valves which provide a variable orifice are possible, as are valves which provide for a fixed orifice size. In some systems, bled air is used as a fresh air supply for a particulate filter regeneration system. A particulate filter, such as a diesel particulate filter (DPF), should be cleaned periodically. Some designs clear particulates by using compressed air to oxidize fuel in combustion to heat a particulate filter during regeneration. Systems have not been demonstrated which use the compressor bleed valve to bleed air to regenerate a diesel particulate filter and to control turbocharger spool rotation speed. In some examples, the compressor bleed valve includes a compressor wastegate, but the present subject matter is not so limited.

[0016] The present subject matter is capable of controlling turbocharger spool rotation using feedback control, such as through mechanical feedback systems, simple electronic feedback systems, or complex electronic feedback systems using controls such as engine controllers. Simple electronic feedback systems, in some examples, include sensors coupled

with simple signal amplifiers or other electronics to amplify a sensor signal and to actuate an electronic actuator coupled to the compressor bleed valve, with such actuation based on that sensor signal. Such simple systems can be inexpensive. Complex systems can include electronic controllers such as engine controllers that receive one or more sensor signals and analyze those signals. Such controllers can optionally access the state of function of the engine in view of predetermined data such as look-up tables, and control an actuator coupled to a compressor bleed valve based on such an assessment.

[0017] The present inventors have recognized that a compressor bleed valve can be used to reduce turbocharger spool rotation speed to below its overspeed limit. The present technology is able to reduce turbocharger spool rotation speed while limiting the impact upon the driving experience. Some of the designs discussed here use only a compressor bleed valve to protect against turbocharger overspeed. Other designs use the compressor bleed valve in combination with one or more of adjusting vanes of a VNT and fuel derating. In some of the examples that derate in combination with using the compressor bleed valve to decrease turbocharger spool rotation speed demonstrate an acceptable decrease in user perceived power losses incurred during a derate event.

[0018J These systems and methods can be applied to various turbocharging configurations, including, but not limited to, configurations using vane adjustments such as VNT control, configurations using a pre-turbine wastegate control, and configurations which do not use pre-turbine wastegates or vane adjustments such as VNTs, or other configurations. The present subject matter applies to single or multi-stage turbocharging systems. Multi-stage turbocharging systems include series configurations, parallel configurations, and combinations thereof. The present designs can be implemented without a pre-turbine wastegate. The turbocharging systems of this disclosure are applicable to gas engines, ethanol engines, diesel engines, biodiesel engines, and other engines which benefit from turbocharging.

[0019] FIG. 1 illustrates a diagram of an engine system 100, according to one embodiment. Engine 102 is coupled to turbocharger 104. This system can include multiple turbochargers. The turbocharger 102 includes a spool, a compressor outlet 106 and a turbine •inlet 108. In some embodiments, the compressor outlet 106 is coupled to an intake system of

the engine 102. Other embodiments include coupling the compressor outlet 106 to another air management device, such as a turbocharger, a supercharger, or another device. The turbine inlet 108 is coupled to an exhaust system of the engine 102. In some examples, the turbine inlet 108 is coupled to an exhaust manifold. In some embodiments, the exhaust system 116 of the engine 102 includes additional components, such as pretreating devices (e.g., those that induce combustion of fuels unburnt in combustion), or another device or devices disposed between the engine and the turbine inlet 108.

[0020] In some examples, a compressor bleed valve 110 is coupled to the intake system of the engine 102 between the compressor outlet 106 and the engine 102. The compressor bleed valve 110 bleeds gas from a pressure controlled area that is at high pressure to another area that is at low pressure (i.e., a pressure lower than the high pressure). The compressor bleed valve 110 is configured to bleed charged air which has been compressed by the turbocharger 104. The compressor bleed valve 110 is coupled to a compressed air conduit 112 extending from the turbocharger compressor outlet 106 to an intake system of the engine 102. The compressor bleed valve 110 is adapted to bleed compressed gas to the atmosphere, or to another system which is at a lower pressure than the pressure controlled area. [0021] Various styles of compressor bleed valve 110 are covered by this application including, but not limited to globe valves, gate valves, butterfly valves, and ball valves, etc. Spring valves, poppet valves, and other configurations are possible. The compressor bleed valve 1 10 is coupled to a valve actuator 114, and is triggered to open by that valve actuator 114, in some examples.

[0022] Actuation schemes for the compressor bleed valve differ among embodiments. Some embodiments use remote feedback. Remote feedback designs include actuation based on instructions from another system, such as an engine controller . Thus, the compressor bleed valve opens whenever instructed to in a remote feedback scheme. A computer signal or a pneumatic signal from another system, such as a controlled engine system, is used to actuate the compressor bleed valve 110 in various examples. Some embodiments include a valve actuator 114 coupled to a circuit controlled by an engine controller which includes a motor such as a rotary motor to open a butterfly valve. Some embodiments include a valve actuator 114 to actuate a stem of a valve. Other actuation mechanisms are possible.

[0023] Some examples use local feedback. Local feedback is based on the pressure in the compressed air conduit 112. In one local feedback scheme, the compressor bleed valve 110 opens when sensed pressure within the compressed air conduit 112 is within a target range. For example, if the compressor bleed valve behaves like a compressor wastegate, the compressor bleed valve senses pressure in the compressed air conduit 112, such as with a diaphragm, and opens itself, such as by using a lever attached to its diaphragm. Some examples actuate the compressor bleed valve 110 using force derived from exposure to pressure in the compressed air conduit 112. Such a compressor wastegate embodiment is tuned to reduce instances of overspeed at a certain operational state (such as at a certain fuel rate and boost pressure).

[0024] In another local feedback scheme, a turbocharger spool rotational speed sensor provides a variable signal to an actuator that is coupled to the compressor bleed valve. That actuator can include a signal processor, such as an amplifier. The compressor bleed valve is opened based on the variable signal, in some examples. Some embodiments use both remote and local feedback.

[0025] In various embodiments, the compressor bleed valve 110 vents to atmosphere. In additional embodiments, the compressor bleed valve 130 vents into another system. In some examples, vented air is monitored, such as with a mass air flow sensor. The mass air flow sensor provides a signal of vented air to a controller, such as an engine controller, in some examples. In additional embodiments, gas which exits the compressed air conduit 112 through the compressor bleed valve 110 is routed into another system of engine 102. An example discussed herein routes bled air to a diesel particulate regeneration system, but the technology is not so limited.

[0026] Various embodiments include a turbocharger controller circuit 118. The turbocharger controller circuit is an electrical device in some examples. Such a device is a machine or is computer-implemented at least in part. In some examples, this is a stand-alone computer. In additional embodiments, this is a software or software-hardware subsystem which is part of an engine controller.

[0027] The technology described herein, including processes and methods of operating devices, can be machine or computer-implemented at least in part. Some examples can

include a computer-readable medium or machine-readable medium encoded with instructions operable to configure an electronic device to perform methods as described in the above examples. An implementation of such methods can include code, such as microcode, assembly language code, a higher-level language code, or the like. Such code can include computer readable instructions for performing various methods. The code can form portions of computer program products. Further, the code can be tangibly stored on one or more volatile or non-volatile computer-readable media during execution or at other times. These computer-readable media can include, but are not limited to, hard disks, removable magnetic disks, removable optical disks (e.g., compact disks and digital video disks), magnetic cassettes, memory cards or sticks, random access memories (RAMs), read only memories (ROMs), and the like.

[0028] Some examples can include a computer-readable medium or machine-readable medium encoded with instructions operable to configure an electronic device to perform as described is these examples. An implementation of such methods can include code, such as microcode, assembly language code, a higher-level language code, or the like. Such code can include computer readable instructions for performing various methods. The code can form portions of computer program products. Further, the code can be tangibly stored on one or more volatile or non-volatile computer-readable media during execution or at other times. These computer-readable media can include, but are not limited to, hard disks, removable magnetic disks, removable optical disks (e.g., compact disks and digital video disks), magnetic cassettes, memory cards or sticks, random access memories (RAMs), read only memories (ROMs), and the like.

[0029] In the illustrated example, the turbocharger controller circuit 118 is configured to determine spool rotation speed of the turbocharger 104. In certain examples, the turbocharger controller circuit 118 instructs the valve actuator 114 to actuate. An actuation signal can include an electrical signal or a pneumatic signal. In some designs, the valve actuator 1 14 actuates based on a turbocharger spool rotation speed signal. For example^ some embodiments include a Hall Effect sensor which determines turbocharger speed and which provides a turbocharger speed signal to actuator 114 which actuates in a linear or nonlinear

non-feedback relationship with turbocharger spool rotational speed. This is just one configuration, and others are possible.

[0030] FIG. 2 illustrates a turbocharging system including a diesel particulate filter (DPF) ₅ according to one embodiment of the present subject matter. The system includes a turbocharger 202 that includes a compressor 204, a turbine 206, and a spool 208 coupling the compressor 202 and the turbine 206 together. The turbocharger 202 is coupled to an engine 210. The engine 210 is in communication with an engine controller 250. The illustrated engine controller 250 includes a fuel rate circuit 212, a state of ignition circuit 214, a pilot 216, and one or more other circuits 218. Any of these systems can be used alone or in combination as inputs on which to base control of the compressor bleed valve 224. [0031] The compressor bleed valve 224 is coupled to the compressed air conduit 220. The compressed air conduit 220 can include intake piping, the intake manifold, or other intake components. The compressor bleed valve 224 is also coupled to a turbine exhaust conduit 222. This can include exhaust system components such as a turbine housing, piping connected to the turbine housing, and other conduit. Also coupled to the turbine exhaust conduit 222 downstream of the turbine outlet 226 is the DPF 228. In some examples, the compressor bleed valve 224 vents to the turbine exhaust conduit 222 between the engine 210 and the DPF 228.

[0032] The DPF 228 can be regenerated through heating. Some examples use a fuel injection system 230 to provide fuel for ignition to regenerate the DPF 228. Gas, such as air, is provided to such combustion at least in part by the compressor bleed valve 224. In some examples, this system uses fuel which is also used by the engine 210, but other fuel sources and fuel types are possible. Some examples include opening the compressor bleed valve 224 into sealed fluid communication with the exhaust system 238 of the engine 210 downstream of a turbine outlet 226 and upstream of a diesel particular filter 228. Some of these examples include feeding ignition of diesel fuel upstream of the DPF 228 using turbocharged air 220 from the compressor bleed valve 224. In some examples the DPF 228 also includes a spark ignition system 232. Some of these examples include a spark plug 232. A DPF sensor 234 is in communication with the DPF 228 and monitors regeneration, in some examples.

Information relating to regeneration can be provided to the engine controller 250, in some examples. The engine controller can control regeneration, as such.

[0033] Gas, such as charged air, that is mixed with fuel from the fuel injection system 230 is monitored by a mass air flow sensor in some embodiments. Some embodiments control the gas flow rate of the compressor bleed valve 224 concurrent to controlling fuel flow rate from the fuel injection system 230 in order to regenerate the DPF 228. In some examples, gas flow through the compressor bleed valve 224 can be limited in order to maintain a constant level of regeneration of the DPF. In additional examples, the gas flow rate through the compressor bleed valve 224 is controlled to prioritize the function of maintaining engine power such that a vehicle operator does not perceive a power reduction.

[0034] The present subject matter is different from an exhaust gas recirculation (EGR) system, in various embodiments. An EGR system takes gas from an exhaust system, which is downstream 238 from an engine 210, and reintroduces that gas into the intake stream 240 of the engine 210. An EGR system can be configured various ways. On configuration is termed a high pressure EGR configuration in which a conduit 221 extends from an exhaust manifold, and upstream of a turbine 206, to the intake system of an engine 210. In these embodiments, the turbocharger is designed such that the exhaust manifold pressure is higher than the intake manifold pressure and the flow direction is from the exhaust manifold into the intake manifold. Low pressure EGR configurations, including the one illustrated, include an EGR valve 236 downstream of the turbine 206. In some examples, the EGR valve 236 opens to allow exhaust to flow from the exhaust stream 238 to the intake stream 240. Various mechanisms are used to ensure that the exhaust pressure in the exhaust stream 238 is higher than the intake stream 240, such as intake throttles, exhaust throttles, and other mechanisms. In some examples, the EGR valve 236 allows gas from the exhaust stream 238 downstream of the DPF 228 to enter the induction stream 240.

[0035] In some examples, a turbocharger speed sensor 242 monitors spool 208 rotational speed. A turbocharger controller circuit 244 monitors data from the turbocharger speed sensor 242 and opens and closes the compressor bleed valve 224 to protect against turbocharger 202 overspeed. The turbocharger controller circuit 244 is illustrated as being a part of the engine controller 250, but the present subject matter is not so limited. A boost

pressure sensor 246 is in communication with the turbocharger controller circuit 244 and can be used to estimate turbocharger spool 208 speed. One or both of the turbocharger speed sensor 242 and the boost pressure sensor 246 can be used in establishing turbocharger spool 208 speed, for example. As mentioned herein, fuel consumption by the engine 210 is also monitored and used to control the opening and closing of the compressor bleed valve 224 in some examples.

[0036] In various examples, the turbocharger speed sensor 242 is a turbocharger spool rotation speed sensor. This sensor is coupled to the turbocharger 202 and configured to . provide the turbocharger spool rotation speed signal. The turbocharger spool rotation speed signal is provided to the turbocharger controller circuit 244. Some examples include a comparator configured to compare the turbocharger spool rotation speed signal to a specified turbocharger spool rotation speed threshold and to provide an overspeed signal to the turbocharger controller circuit 244. In some embodiments, including those which operate independent of an engine controller 250, this configuration could allow for an inexpensive signal producer provided that the turbocharger controller circuit 244 was a simple circuit. A comparison done by the turbocharger controller circuit 244 could include a comparison by a turbocharger controller circuit comparator portion of the turbocharger controller circuit 244. [0037] A turbocharger spool rotation speed threshold can include a rotations per minute (RPM) number. It can also be a variable determined by one or more measurements. For example, the RPM rating can be lower when the turbocharger 202 is measured to be in a certain state (e.g., colder or when the engine speed is below a specified threshold). [0038] Some examples provide a turbocharger spool rotation speed estimation circuit configured to determine an estimated turbocharger spool rotation speed signal. This can include a computer having one or more look-up tables. Such tables can include estimated turbocharger speed based on one or more additional variables, such as a compressor map, mass air flow, throttle position, engine timing, injector duty cycle, measured exhaust gas temperature, measured air-fuel ratio, boost pressure and other variables. In various examples, a comparator is configured to compare the estimated turbocharger spool rotation speed signal to a specified turbocharger spool rotation speed threshold. In some embodiments, the comparator provides an overspeed signal to the turbocharger controller circuit 244. In some

examples, comparison is done by the turbocharger controller circuit 244, which includes an turbocharger controller circuit comparator.

10039] Some embodiments derate fuel delivery to an engine 210 in addition to controlling the bleeding of charged air from the compressed air conduit 220. Various examples include a fuel system coupled to the engine and configured to inject fuel into the intake system of the engine. The fuel rate sensor 212 can monitor the fuel system and deliver a fuel rate signal to a turbocharger controller circuit 244, such as for estimation of turbocharger speed. Some examples include a throttle configured to throttle air to the intake system of the engine 210. Some examples include a throttle positioning sensor configured to provide a throttle position signal. Some examples include an engine power circuit configured to increase fuel injected into the engine based on the throttle position signal. An engine power circuit can be part of the engine controller 250 and can be controlled to achieve derating. Examples are included in which the engine controller 250 is configured to fuel derate the engine based on the spool rotation speed signal.

[0040] In some examples, the engine controller 250 can include a multivariable model predictive controller (MPC). The MPC can include a model of the dynamic process of engine operation, and can provide predictive control signals to the engine subject to constraints in control variables and measured output variables. The model can be a static model, in some examples. In some examples, the model is dynamic. In some instances, one or more models produce one or more output signals y(t) from one or more input signals u(t). A dynamic model typically contains a static model plus information about the time response of the system. Thus, a dynamic model is often of higher fidelity than a static model. [0041] In mathematical terms, a linear dynamic model has the form:

[0042] y(t) = B0*u(t) + Bl*u(t-1) +..+ Bn*u(t-n)+ Al*y(t-1) + ... + Am*y(t-m)

[0043] where B0...Bn, and Al ...Am are constant matrices. In a dynamic model, y(t) which is the output at time t, is based on the current input u(t), one or more past inputs u(t- 1),..., u(t-n), and also on one or more past outputs y(t-l)...y(t-m). [0044] A static model is where the matrices Bl=~.=Bn=0, and

[0045] k\=.. ~Am-Q, are given by the relationship: [0046] y(t) = BO u(t)

[0047] A static model as shown is a simple matrix multiplier. A static model typically has no "memory" of the inputs u(t-l), u(t-2)... or outputs y(t-l)... etc. As a result, a static model can be simpler, but can be less powerful in modeling some dynamic system parameters. [0048] For some turbocharged diesel systems, the system dynamics can be complicated. Several of the interactions can have characteristics known as "non-minimum phase". This is a dynamic response where the output y(t), when exposed to a step in input u(t), will initially move in one direction, and then reverse and migrate towards a steady state in the opposite direction. In some cases, such dynamics can be important for improved operation of the control system.

[0049] In some examples, the MPC can include a multivariable model that models the effect of changes in one or more actuators of the engine (e.g., VNT vane position, compressor bleed valve position, fuel rate, etc.) on each of two or more parameters (e.g. turbocharger speed, air-fuel ratio, boost pressure). In some of these instances, the multivariable controller can control the actuators to produce a desired response in the two or more parameters. Likewise, in some examples, the model may simulate the effects of simultaneous changes in two or more actuators on each of one or more engine parameters, and the multivariable controller can control the actuators to produce a desired response in each of the one or more parameters.

[0050] For example, an illustrative state-space model of a discrete time dynamical system can be represented using equations of the form: [0051] x(t + 1) = Ax(t) + Bu{t)

[0052] y(t) = Cx(t)

[0053] The model predictive algorithm involves solving the problem:

[0054] «(/t) = argmm{J}

[0055] Where the function J is given by,

J = x(t + N ₁ , 1 t) ^τ Px(t + N _y \ t) +

[0056] ",-'r _T

Y ₁ [x(t + k \ t) ⁷ Qx{t + k \ t) + u(t + k) ¹ Ru(t + k)\

A=O

[0057] y _min ≤ y(t + k \ t) ≤ y _ιmκ

10058] u _min ≤ u(t + k) ≤ u _m3X

[0059] x(t I 0 = x(0

[0060] x(t + k + \ \ t) = Ax(t + k \ t) + Bu(t + k)

[0061] y(t + k \ t) = Cx(t + k \ t)

[0062] In some embodiments, this is transformed into a Quadratic Programming (QP) problem and solved with standard or customized tools.

[0063] The variable "y(k)" contains the sensor measurements. In some examples, these include, but are not limited to, turbocharger spool rotational speed, boost pressure, air flow, nitrous oxide emissions (NOx) and particulate matter (PM) emissions, etc. The variables y(k + t \ t) denote the outputs of the system predicted at time "t+k" when the measurements

"y(t)" are available, in some examples. Such variables are used in the model predictive controller to choose the sequence of inputs which yields a "best" (according to performance index J) predicted sequence of outputs.

[0064] The variables "u(k)" are produced by optimizing J and, in some cases, are used for the actuator set points. For the turbocharger problem these include, but are not limited to, the

VNT vane position, compressor bleed valve position, EGR valve position, fuel quantity such as during fuel derate, etc. The variable "x(k)" is a variable representing an internal state of the dynamical state space model of the system. The variable x{t + k j t) indicates the predicted version of the state variable k discrete time steps into the future and is used in the model predictive controller to optimize the future values of the system.

[0065] The variables y _n ,i _n and y _max are constraints and indicate the minimum and maximum values that the system predicted measurements y(k)ax& permitted to attain. These often correspond to limits on the closed-loop behavior in the control system. For example, a limit can be placed on the turbocharger speed such that the speed is not permitted to exceed a certain number of revolutions per minute during a specified time. In some cases, a minimum y _m i _n or maximum y _ma χ constraint is provided. For example, a maximum turbocharger spool rotational speed constraint can be provided, while a minimum turbocharger spool rotational speed constraint can be unnecessary or undesirable.

[0066] The variables u _mm and u _ma χ are also constraints, and indicate the minimum and maximum values that the system actuators ύ(k) are permitted to attain, often corresponding to physical limitations on the actuators. For example, the compressor bleed valve can have a minimum of zero corresponding to a fully closed valve position and a maximum value of one corresponding to the fully open valve position. Like above, in some cases and depending on the circumstances, only a minimum u _m ; _π or maximum u _max constraint can be provided. Also, some or all of the constraints (e.g. y _m i _n , y _ma χ, u _mm , u _max ) can vary in time, depending on the current operating conditions.

[0067] The constant matrices P, Q, R are often positive definite matrices used to set a penalty on the optimization of the respective variables. These are used in practice to "tune" the closed-loop response of the system, in some examples.

[0068] The model predictive controller can be any type of predictive controller. In such cases, the best practice implementation of the an optimal model predictive controller such as described above may be in the form of a fast online implementation of the algorithm. However, those skilled in the art will recognize that the aspects of the fast implementation algorithm should be tailored to each control problem and computing environment. [0069] In some applications, such as automotive applications, the computing power available in practical engine control units (ECUs) is often low in terms of available memory and CPU, at least when compared to the computing power available at stationary locations, such as buildings. In such cases, a model predictive controller such as described above can be in the form of a fast online implementation of an algorithm. Related examples are described in "Constrained Optimal Control of Linear and Hybrid Systems", written by F. Borrelli and published in volume 290 of Lecture Notes in Control and Information Sciences, by Springer, 2003, said examples incorporated herein by reference. In some examples, aspects of a fast implementation algorithm can be tailored to each control problem in view of its computing environment. The engine controller 250 can include other controllers and control processes, including, but not limited to, proportional integral derivative controllers and feed forward controllers. Combinations of controller processes can be used.

[0070] FIG. 3 illustrates a process 300 for controlling turbocharger spool rotation speed, according to one embodiment of the present subject matter. At 300, the process begins. At

302, the process includes turbocharging an engine. At 304, the process includes determining if a turbocharger is spinning at overspeed. At 306, the process includes reducing turbocharger speed by opening a compressor bleed valve if the turbocharger is spinning at overspeed. The process ends at 310.

[0071] FIG. 4 illustrates a process 400 for controlling turbocharger spool rotation speed, according to one embodiment. At 402, the process begins. At 404, the process includes turbocharging an engine with a bleed valve closed. At 406, the process includes sensing turbocharger speed. At 408, the process determines if sensed turbocharger speed in excess of a specified turbocharger speed. If so, at 410, the process opens a compressor bleed valve to relieve pressure to reduce turbocharger speed to the specified turbocharger value. If not, at 412, the process ends.

(0072] FIG. 5 illustrates a process 500 of sensing turbocharger spool rotation speed and controlling turbocharger spool rotation speed, according to one embodiment. This embodiments monitors overspeed at several different times. The embodiment can independently derate an engine, adjust vanes of a VNT, adjust a pre-turbine wastegate and bleed a compressor valve. The process begins at 502. At 504, the process uses normal engine and turbocharger controls to run an engine. At 506, the process determines turbocharger spool rotational speed. The turbocharger spool rotation speed can be determined through a direct sensor measurement of the turbocharger spool rotation speed, such as with a Hall effect sensor. The engine can also estimate turbocharger spool rotational speed. In one example, if no turbocharger spool rotation speed sensor is present, an estimation of turbocharger spool rotation speed can be made. Such an estimation can be based on other measurements. For example, such an estimation can determine turbocharger spool rotational speed based on a compressor map with data from a mass air flow sensor and a boost pressure sensor. In various embodiments, the process only senses or only estimates. In some embodiments, determining turbocharger spool rotation speed includes estimating turbocharger spool rotation speed based on an engine measurement.

[0073] At 508, the process determines whether an overspeed condition exists. If it does not, the process returns to normal engine and turbocharger control at 504. If it does, the process uses turbocharger controls to correct at 510. The process maintains control of the

turbocharger until the overspeed condition is reduced. This can include adjusting VNT, opening a wastegate other than the compressor bleed valve, or both. Some examples include closing variable vanes in a turbine housing of the turbocharger to reduce turbocharger spool rotation speed prior to opening the compressor bleed valve.

[0074] At 512, the process determines whether the adjustments to only the turbocharger controls were sufficient. If they were, the process returns to normal operation at 504. If they were not, the process, at 514, uses engine controls to correct, including fuel derate and compressor bleed valve. These can be engaged sequentially or concurrently. The process maintains control of the turbocharger until the overspeed condition is reduced. Some examples include fuel derating the engine less than required to reduce turbocharger spool rotation speed without opening the compressor bleed valve. Some examples include opening the compressor bleed valve concurrent to closing the variable vanes to reduce turbocharger spool rotation speed. At 516, the process ends.

[0075] The Abstract is provided to comply with 37 C.F.R. § 1.72(b) to allow the reader to quickly ascertain the nature and gist of the technical disclosure. The Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.