US20040144082A1

US20040144082A1 - Controller for controlling oxides of nitrogen (NOx) emissions from a combustion engine

Info

Publication number: US20040144082A1
Application number: US10/353,379
Authority: US
Inventors: Lawrence Mianzo; Ibrahim Haskara
Original assignee: Visteon Global Technologies Inc
Current assignee: Visteon Global Technologies Inc
Priority date: 2003-01-29
Filing date: 2003-01-29
Publication date: 2004-07-29

Abstract

A controller for controlling oxides of nitrogen (NOx) emissions from a combustion engine based on estimating a parameter for the engine. The controller capable of adjusting cylinder temperature based on the estimated parameter for controlling NOx emissions.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to controlling oxides of nitrogen (NOx) emissions from a combustion engine based on estimating a parameter for the engine.

2. Background Art

As emission regulations become increasingly strict, the need for accurate emission control strategies becomes more important. For combustion engines, one important component of the generated emissions comes from the exhaust gases produced during combustion, and particularly from the oxides of nitrogen (NOx) contained in the exhaust gases. The amount of NOx emissions are a function of the cylinder temperature. By controlling the cylinder temperature, such as by controlling exhaust gas residual, NOx production can be controlled.

Past attempts for controlling NOx production have included operations that measure an engine parameter and compare the measured parameter to a predefined target for the measured parameter. Based on a difference between the measured parameter and the predefined target, these systems control the cylinder temperature. One disadvantage with such systems is that the measured parameters are difficult to measure with accuracy. As such, the control strategies that rely on difficult to measure parameters have a difficult time reflecting true conditions of the measured parameters. In addition, even if the inaccuracies in the measurements are forgiven, the predefined targets for the measured parameters can become inaccurate over time from the aging, wearing, and other inconsistencies in the engine.

SUMMARY OF THE INVENTION

The present invention overcomes the above-identified deficiencies with a method for controlling oxides of nitrogen (NO _x) emissions based on estimating at least one parameter for the engine and calculating an emissions control signal based on the estimated parameter.

One aspect of the present invention relates to a method for controlling oxides of nitrogen (NOx) emissions from a combustion engine. The method comprises estimating at least one parameter from the group of cylinder temperature and cylinder fraction, and comparing the estimated parameter to a desired value for the estimated parameter determined by detecting an engine operating point. The comparison of the estimated parameter and the desired value for the estimated parameter is used for calculating an emissions control signal for controlling NOx emissions from the engine. The control signal increases cylinder temperature when the estimated parameter is below the desired value of the at least one parameter and decreases cylinder temperature when the estimated parameter is above the desired value.

Another aspect of the present invention relates to a controller for controlling oxides of nitrogen (NOx) emissions from a combustion engine. The controller comprises an estimator, a detector, a comparator, and a calculator. The estimator is configured for estimating at least one parameter from the group of cylinder temperature and cylinder fraction. The comparator is configured for comparing the estimated parameter to a desired value for the estimated parameter determined by the detector detecting an engine operating point. The calculator is configured for using the comparison of the estimated parameter and the desired value for calculating an emissions control signal for controlling NOx emissions from the engine. The control signal increases cylinder temperature when the estimated parameter is below the desired value of the at least one parameter and decreases cylinder temperature when the estimated parameter is above the desired value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a controller for controlling emissions from a combustion engine, in accordance with one aspect of the present invention; and [0009]
FIG. 2 illustrates an estimator for use in the controller, in accordance with the present invention.[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

FIG. 1 illustrates a [0011] controller 10 for controlling oxides of nitrogen (NO_x) emissions from a combustion engine 14. The controller 10 can be used with any type of combustion engine, such as, a variable valve time engine, a fixed valve timing engine, an engine having internal exhaust gas recirculation, and an engine having external exhaust gas recirculation.
One aspect of the present invention relates to the [0012] controller 10 having an estimator 16 for estimating at least one parameter for the engine 14. The parameter that is estimated is referred to as the estimated parameter 18 and the value determined for the estimated parameter 18 is the estimated value 20. As described below, sometimes there can be more than one estimated parameter 18 and corresponding estimated value 20.
The estimated [0013] parameter 18 is selected for in-cylinder conditions that are predictive of NOx emissions, such as, temperature, fraction, and pressure. Based on one of these estimations, the engine 14 can be controlled to limit the amount of NOx. The estimated value 20 can be used to control the engine 14 for limiting NOx or the estimated value 20 can be use to actually predict NOx and the predicted amount of NOx can be used to control the engine 14.
The [0014] estimator 16 can be any type of computer-readable or programmable medium that is capable of modeling the engine 14 for the purposes of estimating the estimated parameter 18. More particularly, the estimator 16 can model the functioning of at least one of the cylinder temperature, fraction, or pressure.
The [0015] controller 10 further comprises a detector 24 for determining an acceptable value 26 for the estimated value 20. The acceptable value 26 is determined based on the operating conditions of the engine 14. More specifically, the acceptable value 26 can be determined from an algorithm or look-up table that coordinates the acceptable value 26 with the speed 28 and load 30 acting on the engine 14.
The [0016] detector 24 is configured to detect an acceptable value 26 for each estimated value 20. As such, if the estimator 16 determines an estimated value 20 for each of the cylinder temperature, cylinder fraction, and cylinder pressure, the detector can determine an acceptable value 26 for each of the cylinder temperature, cylinder fraction, and cylinder pressure. It can be advantageous to estimate all three of these engine parameters so that the effects of each parameter on the other parameters can be understood and used to improve the accuracy of the estimated values 20.
The [0017] acceptable values 26 correspond with values for temperature, fraction, and pressure that achieve tolerable NOx emissions levels for the given operating point. In other words, NOx emissions are related to one or a combination of in-cylinder parameters for temperature, pressure, and fraction. If anyone or more of these parameters are not at acceptable levels, then desired levels of NOx emissions are not being achieved and engine operating parameters need to be adjusted. There are a number of ways to adjust the engine operating parameters, including controlling exhaust gas residual, spark timing, valve timing, and gas flow. If the estimated values 20 are greater or lower than the acceptable values 26, then the controller 10 can adjust control of the engine 14 so that the estimated values 20 approach the acceptable values 26 and the desired NOx levels are achieved.
For example, if the estimated [0018] parameter 18 is cylinder temperature and the estimated value 20 is greater than the acceptable value 26 for the cylinder temperature, then the engine 14 is not running as desired. The engine 14 needs to be adjust so that when the estimator next determines the estimated value 20 for the cylinder temperature, the estimated value 20 is closer to the acceptable value 26 for the cylinder temperature. Accordingly, more or less exhaust gas can be recirculated to adjust the cylinder temperature as needed.
The [0019] controller 10 still further comprises a comparator 34 to quantify a difference between the estimated values 20 and the acceptable value 26 for use in controlling the engine 14. The comparator 34 determines if the estimated value 20 is greater than or less than the acceptable value 26. The comparator 34 can also compare the estimated values 20 to acceptable ranges instead of a particular acceptable value 26. In either case, the object of the comparator 34 is to quantify the level of control required to adjust the estimated values 20 to values closer to the acceptable values 26 so that the engine 14 can be controlled for limiting NOx emissions.
The [0020] controller 10 still further comprises a calculator 38 for turning the results from the comparator 34 into an emissions control signal 40 for controlling the engine 14. As NOx is best controlled by adjusting combustion conditions in the cylinder, the calculator 38 determines the emissions control signal 40 in a manner that increases cylinder temperature when the estimated values for the estimated parameters are below the acceptable values and that decreases cylinder temperature when the estimated values for the estimated parameters are above the acceptable values.
The [0021] controller 10 can still further comprise an emissions control signal transmitter 44 for adjusting the emissions control signal 50 to a particular engine component that affects the estimated parameter. For example, the engine component can be a valve 46, such as an EGR valve, an intake valve, an exhaust valve, or an exhaust valve on a variable valve timing engine. By controlling a position for the valve, the estimated parameters, i.e., temperature, fraction, and/or pressure, can be adjusted.
The [0022] controller 10 can be used in any type of combustion engine, such as, a variable valve time engine, a fixed valve timing engine, an engine having internal exhaust gas recirculation, and an engine having external exhaust gas recirculation.
With respect to external EGR systems, the [0023] transmitter 44 can be configured for controlling the position of the EGR valve that controls the amount of exhaust gas that is recirculated to the intake port. With respect to internal EGR systems, the transmitter 44 can be configured to control the intake valve timing and the exhaust valve timing. The intake valve timing can be controlled to admit more intake air to the engine and/or the exhaust valve timing can be controlled to allow more exhaust gas to escape from the cylinders. Whether more intake gas is admitted or more exhaust gas is allowed to escape, such control affects the combustion conditions for the purposes of controlling NOx emissions.
FIG. 2 illustrates one configuration of the [0024] estimator 16 that can be implemented in conjunction with the controller 10 for determining the estimated value 20 for the estimated in-cylinder parameter 18. As described below, the estimator 16 includes a cylinder temperature model 50 for estimating temperature, a cylinder fraction model 52 for estimating cylinder fraction, and a cylinder pressure model 54 for estimating cylinder pressure.
The estimated [0025] value 20 for the cylinder temperature is referred to below as T_cyl, the estimated value for the cylinder pressure is referred to below as P_cyl, and the estimated value 20 for the cylinder fraction is referred to below as F_cyl. Based on estimating each of these in-cylinder conditions, the controller 10 can adjust, if necessary, an engine component 46 to achieve tolerable NOx emissions levels. In addition, as described with more detail below, the estimator 16 includes intermediate models 58, 60, 62, 64, 66, and 68 for receiving measurements and performing calculations that are needed for the models 50, 52, and 54.
The [0026] cylinder temperature model 50 for the estimated parameter 18 of cylinder temperature T _cyl 72 is given by the following equations:
{dot over (T)} _cyl=ƒ₁(P _cyl ,F _cyl ,T _cyl) (1)
[0027] $\begin{matrix} {\dot{T}}_{cyl} = \frac{1}{m_{cyl} c_{v}} \cdot [{\dot{Q}}_{w} - P_{cyl} {\dot{V}}_{cyl} + {\dot{m}}_{i n} h_{i n} + {\dot{m}}_{ex} h_{ex} + {\dot{Q}}_{ch} - {\dot{m}}_{cyl} u - m_{cyl} (u_{1} - u_{2}) {\dot{F}}_{{cyl}_{1}}] & (2) \end{matrix}$
{dot over (T)}[0028] _cyl 74 is the cylinder temperature rate of change and obtained from Equation (1) based on a Function f₁applied to a relationship of P_cyl, F_cyl, and T_cyl. From the cylinder temperature rate of change {dot over (T)}_cyl 74, the estimated cylinder temperate T _cyl 72 is known. According to one aspect of the present invention, the relationship shown in Equation (1) can be rewritten as shown in Equation (2) and used for obtaining the cylinder temperature T _cyl 72.
In Equation (2), c[0029] _vis a specific heat of the mixture of air and fuel in the cylinder and obtain as a function of engine operating conditions and thermodynamic properties of working fluid; u is the internal energy of the mixture of air and fuel and obtained as a function of engine operating conditions and thermodynamic properties of working fluid; u₁is the internal energy of the combustion products and obtained as a function of engine operating conditions and thermal properties of working fluid; u₂is the internal energy of the charge product and obtained as a function of engine operating conditions and thermodynamic properties of working fluid; {dot over (Q)}_w 76 is the rate of heat transfer through the cylinder wall and obtained based on Equation (13) and intermediate model 56, as described below, or as a function of a look-up table based on engine operating parameters; h_inis the enthalpy of the flow through the intake valves and obtained from intermediate model 60 as a function of engine operating conditions and thermodynamic properties of working fluid; h_exis the enthalpy of the flow through the exhaust valve and obtained as a function of engine operating conditions and thermodynamic properties of working fluid; {dot over (Q)}_ch 78 is the combustion heat release rate and obtained from Equation (10) and intermediate model 58, as described below, or it can be determined as a function of a look-up table based on engine operating parameters; {dot over (m)}_in 80 is the mass flow rate of air through the intake valves and obtained as a measurement, estimation, or as a function of a look-up table based on engine operating parameters; {dot over (m)}_cyl 82 is the cylinder mass rate of change and obtained from solving Equation (9), as described below; m_cyl 84 is the cylinder mass and obtained from solving Equation (9), as described below; P_cyl 88 is the cylinder pressure and obtained from Equation (6) and model 54, as described below, or as a function of a look-up table based on engine operating parameters; {dot over (V)}_cyl 90 is the cylinder volume rate of change and obtained from intermediate model 62 as a function of engine geometry and crank angle measurements; and {dot over (F)}_cyl 92 is the burn mass fraction rate of change and obtained from Equation (4) and model 52, as described below, or as a function of a look-up table based on engine operating parameters.
The [0030] cylinder fraction model 52 for the estimated parameter 18 of cylinder fraction F _cyl 94 is given by the following equations:
{dot over (F)} _cyl=ƒ₂(P _cyl ,F _cyl ,T _cyl) (3)
m _cyl {dot over (F)} _cyl1 ={dot over (m)} _in F _i⇄cyl +{dot over (m)} _ex F _cyl⇄e −{dot over (m)} _cyl F _cyl+min((m _cyl(1−F _cyl))_SOC,(m _iƒ AFR)_SOC){dot over (x)} _b (4)
{dot over (F)}[0031] _cyl 92 is the cylinder fraction rate of change and obtained from Equation (3) based on a Function f₂applied to a relationship of P_cyl, F_cyl, and T_cyl. From the cylinder fraction rate of change {dot over (F)}_cyl 92, the estimated cylinder fraction F _cyl 94 is known. According to one aspect of the present invention, the relationship shown in Equation (3) can be rewritten as shown in Equation (4) and used for obtaining the cylinder temperature F _cyl 94.
In Equation (4), {dot over (m)}[0032] _in F _i⇄cyl 98 is the mass flow rate of the burned gas across the intake valves and obtained according to Equation (7), as described below, or as a function of a look-up table based on engine operating parameters; {dot over (m)}_exF_cyl⇄e 100 is the mass flow rate of the burn gas across the exhaust valves and obtained according to Equation (8), as described below, or as a function of a look-up table based on engine operating parameters; {dot over (m)}_cyl 82 is the cylinder mass rate of change and obtained from Equation (9), as described below; and the function min(.) evaluates to (m_ifAFR) at the start of combustion (SOC) if the mixture is lean or (m_cyl(1-F_cyl)) at SOC, if the mixture is stoichiometric or rich. The stoichiometric criteria refers to the conditions when a sensor indicates that the chemical composition between the air and fuel has optimal oxygen levels to burn all the air, the rich designation means there is more fuel than the optimal stoichiometric amount of fuel, and the lean designation means that there is less fuel than the optimal stoichiometric amount of fuel. This is done since only the part of the mixture that is stoichiometric will burn completely, i.e., excess fuel is not burned and if the fuel is lean, only the portion of unburned gas in the cylinder stoichiometrically proportional to the fuel will burn.
The [0033] cylinder pressure model 54 for the estimated parameter 18 of cylinder pressure P _cyl 88 is given by the following equations:
{dot over (P)} _cyl=ƒ₃(P _cyl ,F _cyl ,T _cyl) (5)
[0034] $\begin{matrix} {\dot{P}}_{cyl} = [\frac{{\dot{m}}_{cyl}}{m_{cyl}} + \frac{{\dot{T}}_{cyl}}{T_{cyl}} + \frac{R_{1} - R_{2}}{R} {\dot{F}}_{cyl} - \frac{{\dot{V}}_{cyl}}{V_{cyl}}] P_{cyl} & (6) \end{matrix}$
{dot over (P)}[0035] _cyl 102 is the cylinder pressure rate of change and obtained from Equation (5) based on a Function f₃applied to a relationship of P_cyl, F_cyl, and T_cyl. From the cylinder pressure rate of change {dot over (P)}_cyl 102, the estimated cylinder pressure P _cyl 88 is known. According to one aspect of the present invention, the relationship shown in Equation (5) can be rewritten as shown in Equation (6) and used for obtaining the cylinder pressure P_cyl.
In Equation (6), m[0036] _cyl 84 is the cylinder mass and obtained from Equation (6) and intermediate model 64; {dot over (m)}_cyl 82 is the cylinder mass rate of change and obtained from solving Equation (9) and intermediate model 64; T_cyl 74 is the cylinder temperature and obtained from Equation (2), as described below, or as a function of a look-up table based on engine operating parameters; {dot over (T)}_cyl 72 is the cylinder temperature rate of change and obtained from solving Equation (2) and model 50 or as a function of a look-up table based on engine operating parameters; R is a gas constant and obtained on R=F_cylR₁+(1−F_cyl)R₂; R1 is the gas constant for burned gas; R2 is the gas constant for unburned gas; {dot over (F)}_cyl 92 is the burn mass fraction rate of change and obtained from solving Equation (4) and intermediate model 52 or as a function of a look-up table based on engine operating parameters; V_cyl 90 is the cylinder volume and obtained from engine geometry; {dot over (V)}_cylis the cylinder volume rate of change and obtained from intermediate model 62 as a function of the engine geometry and crank angle measurements 106 from intermediate model 60.
As described above, some of the variables relate to additional equations which are now described. [0037]
Equation (7) relates to the mass flow rate of the burned gas across the intake valves and is given by the following equation: [0038]
F _i⇄cyl:=_F _cyl _{iƒ{dot over (m)}} _in _>0 ^F ^_i1 ^{iƒ{dot over (m)}} ^_in ^>0 (7)
[0039] F _i 107 is the intake manifold fraction as determined from intermediate model 60 and F_cylis the cylinder fraction as determined from intermediate model 60.
Equation (8) relates to the mass flow rate of the burned gas across the exhaust valves and is given by the following equation: [0040]
F _cyl⇄e:=_F _cyl _{iƒ{dot over (m)}} _ex _≦0 ^F ^_e ^{iƒ{dot over (m)}} _ex ^>0 (8)
[0041] F _e 109 is the exhaust manifold fraction as determined from intermediate model 60 and F_cylis the cylinder fraction as determined from intermediate model 60.
Equation (9) relates to the mass rate of change from the conservation of mass, assuming the convention that flow rate is positive into the cylinder, and represented according to the following equation: [0042]
{dot over (m)} _cyl ={dot over (m)} _in +{dot over (m)} _ex (9)
wherein {dot over (m)}[0043] _in 80 is the mass of the air flow rate through the intake valves and obtained from intermediate model 60 as a measurement or an estimation; {dot over (m)}_ex 108 is the mass of air flow rate through the exhaust valves and obtained from intermediate model 60 as a measurement or estimation.
Equation (10) refers to the combustion heat release rate {dot over (Q)}[0044] _ch 78 and represented according to the following equation and intermediate model 56: $\begin{matrix} {\dot{Q}}_{ch} = \frac{\partial m_{b}}{\partial t} Q_{LHV} & (10) \end{matrix}$
wherein Q[0045] _LHVis the lower heating value of the fuel and obtained as a function of engine operating parameters and fuel property tables; m_b 110 is the mass of the burned fuel and obtained as the product of the mass fraction burned x_b 112 and the injected fuel m _if 114 as determined by Equation (11), as described below.
Equation (11) relates to the mass of the burned [0046] fuel m _b 110 and represented according to the following equation:
m _b =x _b m _if (11)
wherein: m[0047] _if 114 is the injected fuel and obtained from intermediate model 60 as a measurement or calculation of injected fuel; and x_b 112 is the product of the mass fraction burned and obtained according to Equation (12) and intermediate model 58. Equation (12) is determined according to the following equation: $\begin{matrix} x_{b} = 1 - \exp [- {a (\frac{θ - θ_{0}}{Δ θ})}^{m + 1}] & (12) \end{matrix}$
wherein: 0[0048] ₀ 106 is the crank angle at the start of combustion and measured by intermediate model 60; Δθ is the total combustion duration 118; and a and m are correlation parameters.
Equation (13) refers to the variable rate of heat release through the cylinder wall, {dot over (Q)}[0049] _w 72, and represented according to the following equation and intermediate model 56:
{dot over (Q)} _w =hA(T _cyl −T _wall) (13)
wherein: h is the convective heat transfer coefficient and obtained from heat transfer calculations; a is the surface area for heat transfer and obtained from engine geometry; T[0050] _wallis the cylinder wall temperature and obtained from intermediate model 60 estimating or measuring coolant temperatures 120.
As described above, the equations (1) , (3), and (5) are used for determining the estimated [0051] parameters 18 of temperature, fraction, and pressure to determine the estimated values 20 for temperature T_cyl, 74 fraction F _cyl 94, and pressure P _cyl 88. The models 50, 52, and 54 can include values determined by the other models or the values that are included from the other models can be substituted for with measured parameters, look-up tables, or other algorithms
Each equation (1), (3), and (5) is not necessary for controlling the [0052] engine 14, rather, only one of the estimated values 20 for fraction or temperature is needed for controlling the engine 14. The Equations (1), (2), and (3) can be rewritten, as shown below, to illustrate the interaction of the three equations.
{dot over (T)} _cyl=ƒ₂(P _cyl ,T _cyl ,F _cyl (1)
{dot over (F)} _cyl=ƒ₃(P _cyl ,T _cyl ,F _cyl) (3)
{dot over (P)} _cyl=ƒ₁(P _cyl ,T _cyl ,F _cyl) (5)
In addition, Equations (1), (3), and (5) can include feedback correction functions [0053] g ₁ 122, g ₂ 124, and g ₃ 126 for use in adjusting the estimations according to aging, wearing, and other engine inconsistencies.
{dot over (T)} _cyl=ƒ₁(P _cyl ,T _cyl ,F _cyl)+g ₁(error) (1)
{dot over (F)} _cyl=ƒ₂(P _cyl ,T _cyl ,F _cyl)+g ₂(error) (2)
{dot over (P)} _cyl=ƒ₃(P _cyl ,T _cyl ,F _cyl)+g ₃(error) (3)
The feedback correction functions g[0054] ₁, g₂, and g₃can be any type of correction function. As shown below, the functions g₁, g₂, and g₃are determined from intermediate model 66 and can be a value that is multiplied against the error determined from a difference between an estimated value 20 and a measurement for the estimated value 20. As shown below, the cylinder pressure P_cylis measured and generates the feedback correction functions for g₁, g₂, and g₃.
{dot over (T)} _cyl=ƒ₁(P _cyl ,T _cyl ,F _cyl)+g ₁(P _cyl _— _error)
{dot over (F)} _cyl=ƒ₂(P _cyl ,T _cyl ,F _cyl)+g ₂(P _cyl _— _error)
{dot over (P)} _cyl=ƒ₃(P _cyl ,T _cyl ,F _cyl)+g ₃(P _cyl _— _error)
g ₁(P _cyl _— _error)=k ₁(P _cyl _— _measured −P _cyl _— _estimated)
g ₂(P _cyl _— _error)=k ₂(P _cyl _— _measured −P _cyl _— _estimated)
g ₃(P _cyl _— _error)=k ₃(P _cyl _— _measured −P _cyl _— _estimated)
[0055] P _cyl _— _error 126 is determined by the difference between a measured cylinder pressure P_cyl _— _measuredand the estimated cylinder pressure P_cyl. The P_cyl _— _erroris multiplied by a gain k₁, k₂, or k₃. The gains can be the same or different values.
While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. [0056]

Claims

What is claimed:

1. A method for controlling oxides of nitrogen (NO_x) emissions from a combustion engine, the method comprising,

estimating at least one parameter from the group of cylinder temperature and cylinder fraction;

detecting an engine operating point and determining at least one desired value for the at least one parameter based on the engine operating point;

comparing the estimated parameter to the at least one desired value for the at least one parameter; and

calculating an emissions control signal that increases cylinder temperature when the estimated parameter is below the desired value of the at least one parameter, and that decreases cylinder temperature when the estimated parameter is above the desired value of the at least one parameter.

2. The method of claim 1 further comprising estimating the at least one parameter as a function of estimating cylinder pressure.

3. The method of claim 2 wherein the estimating function for estimating cylinder pressure comprises detecting cylinder pressure and estimating cylinder pressure as a function of the detected cylinder pressure.

4. The method of claim 3 further comprising providing a cylinder pressure model for estimating the cylinder pressure and providing a cylinder temperature model for estimating cylinder temperature and providing a cylinder fraction model for estimating cylinder fraction.

5. The method of claim 4 wherein the emissions control signal is for controlling at least one valve position for controlling an amount of gas flow at a cylinder for controlling cylinder temperature.

6. The method of claim 5 wherein the controlling comprises adjusting an EGR valve position for controlling an amount of exhaust gas flow at the cylinder.

7. The method of claim 5 wherein the controlling comprises adjusting an exhaust valve position for controlling an amount of exhaust gas flow at the cylinder.

8. The method of claim 7 wherein the controlling comprises adjusting an intake valve position for controlling an amount of intake air gas flow at the cylinder.

9. The method of claim 5 wherein detecting the engine operating point comprises measuring engine speed and measuring engine load.

10. The method of claim 9 further comprising determining an acceptable amount of NO_xbased on the engine operating point and estimating an amount of NO_xemissions based on the at least one estimated parameter, wherein the emissions control signal is a function of the acceptable amount of NO_xemissions and the estimated amount of NO_xemissions.

11. A controller for controlling oxides of nitrogen (NO_x) emissions from a combustion engine, the controller comprising,

an estimator configured for estimating at least one parameter from the group of cylinder temperature and cylinder fraction;

a detector configured for detecting an engine operating point and determining at least one desired value for the at least one parameter based on the engine operating point;

a comparator configured for comparing the estimated parameter to the at least one desired value for the at least one parameter; and

a calculator configured for calculating an emissions control signal that increases cylinder temperature when the estimated parameter is below the desired value of the at least one parameter, and that decreases cylinder temperature when the estimated parameter is above the desired value of the at least one parameter.

12. The controller of claim 11 wherein the estimator is further configured for estimating the at least one parameter as a function of cylinder pressure.

13. The controller of claim 12 wherein the estimator is configured for further estimating cylinder pressure as the function comprising detecting cylinder pressure and estimating cylinder pressure as a function of the detected cylinder pressure.

14. The controller of claim 13 wherein the estimator further comprises a cylinder pressure model for estimating the cylinder pressure, a cylinder temperature model for estimating cylinder temperature, and a cylinder fraction model for estimating cylinder fraction.

15. The controller of claim 14 further comprising an emissions control signal transmitter configured for adjusting the emissions control signal for controlling at least one valve position for controlling an amount of gas flow at a cylinder for controlling cylinder temperature.

16. The controller of claim 15 wherein the emissions control signal transmitter is further configured for adjusting the emissions control signal for controlling an EGR valve position for controlling an amount of exhaust gas flow at the cylinder.

17. The controller of claim 15 wherein the emissions control signal transmitter is further configured for adjusting the emissions control signal for controlling an exhaust valve position for controlling an amount of exhaust gas flow at the cylinder.

18. The controller of claim 17 wherein the emissions control signal transmitter is further configured for adjusting the emissions control signal for controlling an intake valve position for controlling an amount of intake air gas flow at the cylinder.

19. The controller of claim 15 wherein the detector is further configured for detecting the engine operating point based on measuring engine speed and measuring engine load.

20. The controller of claim 19 wherein the calculator is further configured for determining an acceptable amount of NO_xbased on the engine operating point and estimating an amount of NO_xemissions based on the at least one estimated parameter, wherein the emissions control signal is a function of the acceptable amount of NO_xemissions and the estimated amount of NO_xemissions.