WO2008100284A2

WO2008100284A2 - Power system

Info

Publication number: WO2008100284A2
Application number: PCT/US2007/017652
Authority: WO
Inventors: James W. Landes; Maarten Verkiel; Charles E. Rose
Original assignee: Caterpillar Inc.
Priority date: 2006-09-29
Filing date: 2007-08-08
Publication date: 2008-08-21
Also published as: WO2008100284A3; DE112007002313T5

Abstract

A method of operating a power system (12) of a machine (10) is provided. The power system (12) may include an engine (14). The method may include selectively supplying power from the engine to one or more other components of the machine. The method may also include, while supplying power from the engine to one or more other components of the machine, in response to a determined temperature of exhaust gas of the engine, increasing the torque and decreasing the speed at which the engine supplies power to increase the temperature of the exhaust gas.

Description

POWER SYSTEM

Technical Field

The present disclosure relates to power systems for machines and, more particularly, to power systems that include an engine.

Background

Many machines have a power system with an engine that provides power for various tasks. For example, many machines have a power system operable to propel the machine. While the engine of such a power system is providing power to other components of the machine to perform one or more tasks, varying operating conditions may cause the temperature of the exhaust gas produced by the engine to vary considerably, sometimes to undesirable levels. For example, when the engine operates under high load, the exhaust gas of the engine may reach undesirably high temperatures. U.S. Patent No. 4,715,012 to Mueller. Jr. ("the '012 patent") shows a tractor control system that reduces load on a tractor's engine in response to high exhaust gas temperatures. The tractor control system disclosed by the '012 patent controls a multiple-range transmission dependent on engine speed and the temperature of exhaust gas of the engine. If engine speed drops, the tractor control system compares the temperature of exhaust gas of the engine to predetermined ranges. The '012 patent discloses that, if the exhaust gas temperature is high, the tractor control system may downshift the multiple-range transmission.

Although the tractor control system of the '012 patent downshifts the multiple-range transmission of the tractor in response to high exhaust gas temperature, certain disadvantages persist. For example, the control system disclosed by the '012 patent does not address the possibility of the exhaust gas having undesirably low temperatures. This may cause undesirably high emission of pollutants in some applications and circumstances because some exhaust-gas- treatment devices require exhaust gas temperatures above certain levels to effectively reduce pollutants in exhaust gas. The power system and methods of the present disclosure solve one or more of the problems set forth above.

Summary of the Invention

One disclosed embodiment relates to a method of operating a power system of a machine. The power system may include an engine. The method may include selectively supplying power from the engine to one or more other components of the machine. The method may also include, while supplying power from the engine to one or more other components of the machine, in response to a determined temperature of exhaust gas of the engine, increasing the torque and decreasing the speed at which the engine supplies power to increase the temperature of the exhaust gas.

Another embodiment relates to a power system for a machine. The power system may include an engine, a multiple-ratio transmission connected to the engine, and power-system controls. The power-system controls may be operable to evaluate the relative importance associated with at least two objectives. The power-system controls may also be operable to control a transmission speed ratio of the multiple-ratio transmission dependent at least partially on the relative importance associated with each of the at least two objectives.

A further embodiment relates to a method of operating a power system of a machine. The power system may include an engine. The method may include selectively supplying power from the engine to one or more other components of the machine. The method may also include, while supplying power from the engine to one or more other components of the machine, in response to a determined temperature of exhaust gas of the engine, increasing parasitic power drain on the engine to increase the temperature of the exhaust gas.

Brief Description of the Drawings

Fig. l is a diagrammatic illustration of one embodiment of a machine that includes a power system according to the present disclosure;

Fig. 2 A is a first portion of a flow chart showing one method of operating a power system according to the present disclosure;

Fig. 2B is a second portion of the flow chart showing one method of operating a power system according to the present disclosure; Fig. 2C is a third portion of the flow chart showing one method of operating a power system according to the present disclosure;

Fig. 2D is a fourth portion of the flow chart showing one method of operating a power system according to the present disclosure;

Fig. 2E is a fifth portion of the flow chart showing one method of operating a power system according to the present disclosure; and

Fig. 3 is a flow chart showing another embodiment of a method of operating a power system according to the present disclosure.

Detailed Description

Fig. 1 illustrates a machine 10 having a power system 12 according to the present disclosure. Power system 12 may include an engine 14, an exhaust system 15, a drive train 18, propulsion devices 20, and power-system controls 22.

Engine 14 may be any type of device operable to produce power by combusting fuel. For example, engine 14 may be a diesel engine, a gasoline engine, a gaseous fuel driven engine, or a gas turbine engine. Engine 14 may include an engine brake 23, a variable-geometry turbocharger (VGT) 24, and engine controls 26. Engine brake 23 may be any type of system operable to selectively cause engine 14 to brake machine 10. For example, engine brake 23 may be a compression-braking system. VGT 24 may include provisions for adjusting the positions, orientations, and/or shapes of one or more of its components to adjust its operation.

Engine controls 26 may be operable to control various aspects of the operation of engine 14, including, but not limited to, fuel delivery, operation of engine brake 23, and operation of VGT 24. In some embodiments, engine controls 26 may include an engine controller 27. Engine controller 27 may include one or more processors (not shown) and one or more memory devices (not shown). Engine controls 26 may also include an exhaust gas temperature sensor (EGT sensor) 29 operable to supply a signal indicative of the temperature of exhaust gas from engine 14. Engine controller 27 may be operatively connected to EGT sensor 29.

Exhaust system 15 may include a turbine unit 28 of VGT 24, an exhaust brake 25, an exhaust-gas-treatment device 30, and various passages connected between engine 14 and the atmosphere. Exhaust brake 25 may be any type of device operable to selectively restrict the flow of exhaust gas from engine 14. Engine controller 27 may be operatively connected to exhaust brake 25 so that it may control when and to what degree exhaust brake 25 restricts the flow of exhaust gas from engine 14. Exhaust-gas-treatment device 30 may be any type of device operable to reduce the amount of one or more undesirable substances in exhaust gas from engine 14. For example, exhaust-gas-treatment device 30 may be a lean NO_x reduction device (e.g. a hydrocarbon based SCR device), a NO_x absorber,, an oxidation catalyst, a particulate trap, or any combination of one or more such devices. Exhaust-gas-treatment device 30 may require exhaust gas temperature above one or more threshold levels to effectively reduce the amount of one or more undesirable substances from exhaust gas. For example, in some embodiments, exhaust-gas-treatment device 30 may require an exhaust temperature above a threshold level, such as about 200 degrees Celsius, to reduce the amount of HC and CO in exhaust gas. Similarly, exhaust-gas-treatment device 30 may require an exhaust gas temperature above another threshold level, such as about 250 degrees Celsius, to reduce NO_x in exhaust gas.

Drive train 18 may include a multiple-ratio transmission 38, various other components for transmitting power from engine 14 to propulsion devices 20, and a drive train retarder 48. Multiple-ratio transmission 38 may include a rotary input member 40, a rotary output member 42, provisions for transmitting power between rotary input member 40 and rotary output member 42, and transmission controls 44. Multiple-ratio transmission 38 may be any type of device operable to transfer power between rotary input member 40 and rotary output member 42 at any of a plurality of transmission speed ratios under the control of transmission controls 44. Within this disclosure, the term "transmission speed ratio" refers to the ratio of the speed of rotary input member 40 to rotary output member 42. Multiple-ratio transmission 38 may have different configurations that provide different sets of available transmission speed ratios. Multiple-ratio transmission 38 may have a finite set of discrete transmission speed ratios that it can provide. Alternatively, multiple-ratio transmission 38 may be able to adjust the transmission speed ratio through a continuous range. In some embodiments, different operating states of multiple-ratio transmission 38 provide different ranges within which it can continuously vary the transmission speed ratio.

Transmission controls 44 may include any components operable to control whether and at what transmission speed ratio multiple-ratio transmission 38 transfers power between rotary input member 40 and rotary output member 42. In some embodiments, transmission controls 44 may include a transmission controller 46 that includes one or more processors (not shown) and one or more memory devices (not shown). Additionally, transmission controls 44 may include various actuators, sensors, valves, and/or other control components operatively connected to transmission controller 46. Drive train retarder 48 may be any type of device operable to mechanically draw power from drive train 18 and convert that power into another form. For example, drive train retarder 48 may be a fluid pump or an electric generator. Propulsion devices 20 may be any type of device operable to apply power to the environment surrounding machine 10 in a manner to propel machine 10. For example, as Fig. 1 shows, propulsion devices 20 may be wheels. Alternatively, propulsion devices 20 may be track units or other types of devices configured to apply power to the ground to propel machine 10. In some embodiments, propulsion devices 20 may be propellers or other types of devices configured to propel machine 10 using fluid.

In addition to drive train 18 and propulsion devices 20, power system 12 may include various other components that derive power from engine 14. For example, power-system 12 may include an electric generator 96, electrical power loads 98 connected to electric generator 98, a hydraulic pump

100, and hydraulic power loads 102 connected to hydraulic pump 100. Hydraulic pump 100 may be a variable-displacement hydraulic pump. Electric generator 96 and hydraulic pump 100 may be drivingly connected to engine 14. Electrical power loads 98 may include various types of components operable to receive electricity from electric generator 98 and use that electricity to perform one or more tasks. Additionally, electrical power loads 98 may include one or more electrical storage devices, such as one or more batteries and/or one or more capacitors. Similarly, hydraulic power loads 102 may include various types of devices operable to receive hydraulic fluid pumped by hydraulic pump 100 and use that hydraulic fluid to perform various tasks. Hydraulic power loads 102 may also include one or more energy storage devices operable to receive hydraulic fluid pumped by hydraulic pump 100 and store energy from that hydraulic fluid. For example, hydraulic power loads 102 may include one or more hydraulic accumulators. Power-system controls 22 may include engine controls 26, transmission controls 44, an operator interface 50, and a master controller 54. Operator interface 50 may include various components configured to transmit operator inputs to other components of machine 10. For example, operator interface 50 may include a throttle 52 and various associated components for communicating operator inputs relating to desired speed and/or acceleration of machine 10 to other components. Additionally, operator interface 50 may include controls 104, 106 for relaying to other components operator inputs relating to desired operation of electrical loads power loads 98 and hydraulic power loads 102.

Master controller 54 may include one or more processors (not shown) and one or more memory devices (not shown). Master controller 54 may be operatively connected to exhaust brake 25, engine controls 26, EGT sensor 29, transmission controls 44, drive train retarder 48, and operator interface 50. Master controller 54 may also be operatively connected to electric generator 96, electrical power loads 98, hydraulic pump 100, and hydraulic power loads 102 so that master controller 54 can control one or more aspects of the operation of these components. Additionally, master controller 54 may be operatively connected to various other sources of information about operating conditions of machine 10, such as other sensors (not shown) and/or other controllers (not shown).

Accordingly, master controller 54 may coordinate control of exhaust brake 25, engine 14, multiple-ratio transmission 38, and drive train retarder 48, electric generator 96, electrical power loads 98, hydraulic pump 100, and hydraulic power loads 102 dependent on inputs from engine controls 26, EGT sensor 29, transmission controls 44, operator interface 50, and other sources of information. Power system 12 is not limited to the configuration shown in Fig. 1. For example, power system 12 may omit one or more of the components shown in Fig. 1, such as one or more of engine brake 23, VGT 24, exhaust brake 25, EGT sensor 29, and drive train retarder 48. Additionally, drive train 18 may connect multiple-ratio transmission 38 to engine 14 and propulsion devices 20 in different manners than Fig. 1 shows. Furthermore, power system 12 may be a "hybrid electric" power system with one or more electric drive motors connected to propulsion devices 20 directly or through some portion of drive train 18. Moreover, power-system controls 22 may have a different configuration than shown in Fig. 1. For example, in some embodiments, one controller may replace two or more of engine controller 27, transmission controller 46, and master controller 54.

Industrial Applicability Power system 12 may have application in any machine that requires power for performing one or more tasks. In some embodiments and/or circumstances, power system 12 may provide power to propel machine 10. Power system 12 may propel machine 10 by operating engine 14 to produce power while multiple-ratio transmission 38 receives power from engine 14 through rotary input member 40 and transmits at least some of that power to rotary output member 42, thereby driving propulsion devices 20. Additionally, when machine 10 is stationary, engine 14 may supply power to various other components of power system 12 to perform various tasks. For example, power system 12 may supply power from engine 14, to electric generator 96 and/or hydraulic pump 100, to electrical power loads 98 and/or hydraulic power loads 102 for various tasks, such as excavating or otherwise moving objects or materials. During such operation, exhaust gas produced by engine 14 may flow through exhaust system 15, including exhaust-gas-treatment device 30, to the atmosphere. While engine 14 supplies power to one or more other components of power system 12, power-system controls 22 may adjust various aspects of the operation of power system 12 dependent upon inputs from the operator of machine 10 and other operating conditions to meet the power needs of machine 10. This may include controlling engine 14 and multiple-ratio transmission 38 to supply propulsion devices 20 with sufficient power to meet the propulsion demands communicated by an operator through throttle 52 while also supplying sufficient power to any other power loads that require power from engine 14. When power system 12 is propelling machine 10, for any given speed of machine 10, the transmission speed ratio of multiple-ratio transmission 38 may dictate the engine speed and, thus, the torque necessary to meet the power needs of machine 10. In many circumstances, power-system controls 22 may meet the power needs of machine 10 with any of multiple possible combinations of engine speed and engine torque. However, each different combination of engine speed and engine torque that meets the power needs of machine 10 may impact other performance objectives differently. For example, meeting the power needs of machine 10 with low engine speed and high engine torque may promote fuel efficiency, but it may also undermine power-system responsiveness (the ability to rapidly increase power output). In addition to fuel efficiency and power-system responsiveness, engine speed and engine torque may, in some circumstances, affect emissions. As mentioned above, the temperature of exhaust gas from engine 14 may need to exceed certain threshold levels for exhaust-gas-treatment device 30 to effectively reduce undesirable substances in the exhaust gas. Generally, increasing engine speed and decreasing engine torque tends to decrease the temperature of exhaust gas from engine 14. Thus, in some circumstances, the combination of engine speed and engine torque used to meet the power needs of machine 10 may affect whether the temperature of the exhaust gas from engine 14 meets the threshold levels required by exhaust-gas-treatment device 30. As a result, power-system controls 22 may advance one or more of the objectives of low emissions, high fuel efficiency, and high power-system responsiveness by controlling engine speed and engine torque in an effective manner. Figs. 2A-2E illustrate one method that power-system controls 22 may execute to maintain low emissions, provide high average fuel efficiency, and provide high power-system responsiveness when needed. Fig. 2A shows a process for selecting one of three general control algorithms 58, 60, 62. Figs 2B and 2C show details of control algorithm 58. Fig. 2D shows details of control algorithm 60. Fig. 2E shows details of control algorithm 62. Control algorithms 58, 60, 62 may favor different objectives.

Control algorithm 58 may favor maintaining a desirable exhaust gas temperature. Control algorithm 60 may favor power-system responsiveness. Control algorithm 62 may favor fuel efficiency.

Accordingly, before advancing to one of control algorithms 58, 60, 62, power-system controls 22 may evaluate the relative importance associated with each of these objectives (step 55). Power-system controls 22 may evaluate the relative importance associated with each of these objectives in a number of different manners, including, but not limited to, determining an ordinal rank of the objectives and weighting the objectives relative to one another. Exhaust gas temperature may have high importance when engine 14 has recently begun producing power and in other circumstances that tend to increase undesirable substances in the exhaust from engine 14. Power-system responsiveness may have high importance in circumstances where the operator of machine 10 has recently frequently demanded large increases in power output. Fuel efficiency may have high importance in most other situations. After evaluating the relative importance associated with each objective, power-system controls 22 may advance to one of control algorithms 58, 60, 62 dependent upon which of the objectives has highest importance (step 56).

As Fig. 2B shows, within control algorithm 58, power-system controls 22 may compare the temperature of exhaust gas from engine 14 to a first reference temperature (step 64). In some embodiments, the first reference temperature may substantially correspond to a threshold exhaust gas temperature necessary for exhaust-gas-treatment device 30 to reduce one or more substances in exhaust gas. For example, the first reference temperature may substantially correspond to an exhaust gas temperature that exhaust-gas-treatment device 30 requires to effectively reduce NO_x in exhaust gas, which may be 250 degrees Celsius. Power-system controls 22 may determine the temperature of the exhaust gas in a number of ways. In embodiments that include EGT sensor 29, the signal from EGT sensor 29 may allow power-system controls 22 to directly determine the temperature of the exhaust gas. Power-system controls 22 may also infer the exhaust gas temperature from various other information, such as engine speed and fuel consumption or various other operating conditions of machine 10. If the determined exhaust gas temperature falls above the first reference temperature, power-system controls 22 may check whether power- system responsiveness or fuel efficiency has the next highest importance after exhaust gas temperature (step 86). If power-system responsiveness has second highest importance, power-system controls 22 may advance to control algorithm 60 (Fig. 2A). If fuel efficiency has second highest importance, power-system controls 22 may advance to control algorithm 62 (Fig. 2A).

However, if the determined exhaust gas temperature falls below the first reference temperature, power-system controls 22 may respond by decreasing engine speed and increasing engine torque to increase the exhaust gas temperature. In circumstances when power system 12 is propelling machine 10, this may also involve decreasing the transmission speed ratio of multiple-ratio transmission 38. Power-system controls 22 may base the magnitude of these changes on various operating conditions, such as how long and how far the determined exhaust gas temperature falls below the first reference temperature. Accordingly, to keep track of how long the determined exhaust gas temperature remains below the first reference temperature, power-system controls 22 may run a timer (step 66).

Additionally, in some embodiments, power-system controls 22 may categorize the determined exhaust gas temperature based on how far it falls below the first reference temperature. To do so, as Fig. 2C shows, power-system controls 22 may compare the determined exhaust gas temperature to a second reference temperature that is below the first reference temperature (step 68). The second reference temperature may also substantially correspond to an exhaust gas temperature that the exhaust-gas-treatment device 30 requires to effectively reduce one or more substances from exhaust gas. For example, the second reference temperature may substantially correspond to an exhaust gas temperature that exhaust-gas-treatment device 30 requires to remove HC and CO from exhaust gas, which may be 200 degrees Celsius. If the determined exhaust gas temperature falls above the second reference temperature, power-system controls 22 may consider the determined exhaust gas temperature in a "low 1" stratum (step 70). If it falls below the second reference temperature, power- system controls 22 may consider the determined exhaust gas temperature in a "low 2" stratum (step 72).

After categorizing the determined exhaust gas temperature, power- system controls 22 may identify target amounts to decrease the decrease the engine speed and increase the engine torque (step 74). In concert with determining target amounts to change engine speed and engine torque, power- system controls 22 may also identify target changes for the operation of various other aspects of the operation of power system 12. For example, when power- system 12 is propelling machine 10, power-system controls 22 may determine an appropriate change in transmission speed ratio to accompany the change in engine speed and torque. Additionally, power-system controls 22 may identify target changes in the operating state of various other aspects of the operation of power system 12 to accommodate the change in engine speed and torque. For example, in some circumstances and/or embodiments, power-system controls 22 may determine a target amount to increase the displacement of hydraulic pump 100. This may facilitate operating engine 14 at lower speed and higher torque by absorbing more torque from engine 14 with hydraulic pump 100 while maintaining the required flow rate of hydraulic fluid. Of course, power-system controls 22 may also identify target changes to other components of power system 12 to adjust the torque load on engine 14.

In some embodiments, power-system controls 22 may identify the target changes based in part on the exhaust gas temperature's stratum and the elapsed run time of the timer. In such embodiments, power-system controls 22 may identify larger target changes when the determined exhaust gas temperature falls in the "low 2" stratum than when it falls in the "low 1" stratum. Additionally, power-system controls 22 may identify larger target changes the longer the timer has run (i.e., the longer the determined exhaust gas temperature has remained below the first reference temperature).

After identifying target changes in engine speed engine torque, and other associated aspects of the operation of machine 10, power-system controls 22 may determine whether the current operating conditions allow the target changes (step 76). Various circumstances may prevent implementing the target changes. For example, inability of engine 14 to produce the target torque at the target speed may prevent implementing the target change in engine speed and torque. Additionally, in some embodiments and/or circumstances, it may not be possible to adjust the operation of power loads on engine 14 to provide reaction torque equal to the target engine torque. If the current conditions allow, power-system controls 22 may implement the target changes (step 78). If not, power-system controls 22 may decrease the engine speed and increase engine torque by the maximum amounts possible (step 80).

Additionally, if power-system controls 22 have to change the engine speed and engine torque by less than the target amounts, power-system controls 22 may use supplemental measures to increase exhaust gas temperature. For example, power-system controls 22 may increase parasitic power drain on engine 14 to increase exhaust gas temperature (step 82). Power-system controls 22 may increase parasitic power drain on engine 14 by adjusting any aspect of operation of engine 14 and/or other components of machine 10 to increase parasitic losses in engine 14 and/or to increase the amount of power other components draw from engine 14. In some embodiments, power-system controls 22 may increase parasitic power drain on engine 14 by causing one or more of exhaust braking, engine braking, and drive train retarding. Power-system controls 22 may cause exhaust braking with exhaust brake 25 and/or by controlling VGT 24 to restrict the flow of exhaust gas through exhaust system 15. Power-system controls 22 may cause engine braking with engine brake 23. Power-system controls 22 may use drive train retarder 48 to provide drive train retarding. Additionally, power-system controls 22 may increase parasitic power drain on engine 14 by causing electric generator 96, hydraulic pump 100, and/or any other power load on engine 14 to draw more power from engine 14. In some circumstances, in order to increase the temperature of the exhaust gas, power-system controls 22 may cause the power loads on engine 14 to draw more power from engine 14 than necessary to meet the current power needs of machine 10. In such circumstances, power-system controls 22 may divert some of the power drawn from engine 14 to one or more energy storage devices for later use by machine 10. For example, power-system controls 22 may cause electric generator 96 to generate more electricity with power from engine 14 and divert some or all of the additional electricity to one or more electrical storage devices of electrical power loads 98 for later use. Similarly, power-system controls 22 may cause hydraulic pump 100 to draw more power from engine 14, and power- system controls 22 may divert some or all of the hydraulic fluid from hydraulic pump 100 to one or more energy storage devices of hydraulic power loads 102. Power-system controls 22 may base the magnitude of the increase in parasitic power drain on engine 14 on how low the determined exhaust gas temperature is and how long the determined exhaust gas temperature has been low. For example, power-system controls 22 may increase the parasitic power drain on engine 14 by a greater magnitude when the determined exhaust gas temperature falls in the "low 2" stratum than when it falls in the "low 1" stratum. Additionally, power-system controls 22 may increase the parasitic power drain on engine 14 by a greater magnitude the longer the timer has run (i.e., the longer the determined exhaust gas temperature has remained below the first reference temperature).

After decreasing the transmission speed ratio, decreasing engine speed, increasing engine torque, and initiating any necessary supplemental increases in parasitic power drain on engine 14, power-system controls 22 may pause for a delay period (step 84). Power-system controls 22 may then reevaluate which control algorithm 58, 60, or 62 to execute (Fig. 2A, steps 55, 56).

If power-system responsiveness has highest importance, power- system controls 22 may advance to control algorithm 60. As Fig. 2D shows, in control algorithm 60, power-system controls 22 may identify a target combination of engine speed and engine torque to maximize power-system responsiveness in the prevailing circumstances (step 88). In some embodiments, power-system controls 22 may do so by referencing empirical data relating to how different combinations of transmission speed ratio, engine speed, and engine torque may affect power-system responsiveness. In concert with determining target engine speed and engine torque, power-system controls 22 may identify appropriate target values of other operating parameters, such as target values for the transmission speed ratio and/or the displacement of hydraulic pump 100. Power-system controls 22 may then implement the target engine speed and engine torque, as well as any other target operating parameters identified (step 90). Power-system controls 22 may then reevaluate which control algorithm 58, 60, or 62 to execute (Fig. 2A, steps 55, 56).

If fuel efficiency has highest importance, power-system controls 22 may advance to control algorithm 62. As Fig. 2E shows, in control algorithm 60, power-system controls 22 may identify a target combination of engine speed and engine torque that maximizes fuel efficiency under the circumstances (step 92). In some embodiments, power-system controls 22 may reference empirical data regarding the fuel efficiency that different combinations of transmission speed ratio, engine speed, and engine torque provide. In concert with determining target engine speed and engine torque, power-system controls 22 may identify appropriate target values of other operating parameters, such as target values for the transmission speed ratio and/or the displacement of hydraulic pump 100. Power-system controls 22 may then implement the target engine speed and engine torque, as well as any other identified target operating parameters (step 94). Subsequently, power-system controls 22 may again evaluate which control algorithm 58, 60, or 62 to execute (Fig. 2A, steps 55, 56).

Methods that power-system controls 22 may execute to control power system 12 are not limited to the examples provided above. Power-system controls 22 may implement different methods of evaluating the relative importance of different objectives for power system 12. In some embodiments, power-system controls 22 may evaluate the importance associated with more or fewer than three different objectives. For example, in addition to exhaust gas temperature, power-system responsiveness, and fuel efficiency, power-system controls 22 may evaluate the importance associated with operating engine 14 in manner such that it discharges relatively low emissions into exhaust system 15. In embodiments where power-system controls 22 evaluate the importance associated with other objectives, power-system controls 22 may execute various control methods for advancing those objectives as their relative importance warrants. Additionally, power-system controls 22 may perform one or more of the actions discussed above in different orders than shown in Figs. 2A-2E. In some embodiments, power-system controls 22 may determine whether the determined exhaust gas temperature is low before determining what importance the exhaust gas temperature has with respect to fuel efficiency and power-system responsiveness. Power-system controls 22 may also identify different combinations of transmission speed ratio, engine speed, and engine torque that would promote desirable exhaust gas temperatures, power-system responsiveness, and fuel efficiency, respectively, before evaluating the relative importance of these objectives and implementing the associated combination.

Power-system controls 22 may also omit one or more of the actions shown in Figs. 2A-2E and/or execute additional actions not shown in Figs. 2A-2E. For example, in some embodiments, a control method may omit the supplemental measure of increasing parasitic power drains on engine 14. Additionally, in some embodiments, power-system controls 22 may forgo determining the importance of maintaining desirable exhaust gas temperatures and adjust operation of power system 12 to increase exhaust gas temperature any time it is low. Furthermore, in addition to the measures discussed above, power- system controls 22 may use other measures to increase exhaust gas temperature when necessary. For example, power-system controls 22 may also deliver fuel to the combustion chambers of engine 14 in a manner to increase exhaust gas temperature. Additionally, power-system controls 22 may take various actions to reduce the exhaust gas temperature if it becomes undesirably high.

Furthermore, power-system controls 22 may perform one or more of the actions discussed above in different manners. For example, rather than using fixed numerical values for the first and second reference temperatures, power-system controls 22 may calculate them dynamically as a function of one or more operating conditions. Alternatively, in some embodiments, power-system controls 22 may forgo categorizing the determined temperature of the exhaust gas and, instead, use the actual determined value of the exhaust gas temperature as a factor in controlling the operating state of power system 12. Additionally, rather than referencing empirical data relating to power-system responsiveness and fuel efficiency when controlling power system 12 to advance these objectives, power- system controls 22 may simply operate according to preset strategies designed to advance these objectives.

Fig. 3 shows another embodiment of a method that power-system controls 22 may implement in controlling power system 12. Initially, power- system controls 22 may evaluate the relative importance of a plurality of objectives based on the current operating conditions of machine 10 (step 108). The plurality of objectives may include, for example, providing a desirable exhaust gas temperature, promoting power-system responsiveness, and promoting fuel efficiency. Power-system controls 22 may determine the relative importance of the plurality of objectives in a number of different ways, including, but not limited to, determining an ordinal rank of the objectives and weighting the importance of the objectives relative to one another.

Subsequently, for each objective, power-system controls 22 may determine an operating strategy that would advance the objective the maximum amount (steps 110, 112, and 114). For example, power-system controls 22 may determine a combination of engine speed and torque that optimize exhaust gas temperature, the combination of engine speed and torque that would optimize power-system responsiveness, and the combination of engine speed and torque that would optimize fuel efficiency. Power-system controls 22 may use various different methods to determine operating strategies that would advance each of the different objectives the maximum amount, hi some embodiments, power- system controls 22 may reference lookup tables that provide information about operating parameter values that advance each of the different objectives the maximum amount under the operating conditions at hand. After determining the relative importance of the different objectives and the operating strategies that would optimize each objective, power-system controls 22 may use this information to determine target operating parameters (step 116). For example, power-system controls 22 may determine a target combination of engine speed and torque based on the relative importance of the exhaust gas temperature, power-system responsiveness, and fuel efficiency and also based on the different combinations of engine speed and torque determined to maximize each of these objectives. Of course, in concert with determining a target combination of engine speed and torque, power-system controls 22 may determine target values for associated operating parameters, such as the transmission speed ratio and the displacement of hydraulic pump 100.

Power-system controls 22 may use the relative importance of the different objectives and information about which control strategies advance each objective the most in various ways to determine target operating parameters such as target engine speed and torque. In embodiments where power-system controls 22 assign weights to the importance of the different objectives, power-system controls 22 may use these weights to determine target operating parameters (such as engine speed and torque) that advance the objectives in proportion to their respective importance under the circumstances at hand. For example, power- system controls 22 may determine a target engine torque by using the weighted importance of the different objectives as weighting factors to calculate a weighted average of the engine torques associated with optimal exhaust gas temperature, optimal power-system responsiveness, and optimal fuel efficiency.

After determining the target operating parameters, power-system controls 22 may implement them (step 118). For example, after a target combination of engine speed, engine torque, and transmission speed-ratio is determined, engine controls 26 and transmission controls 44 working in concert may implement the target engine speed, target engine torque, and target transmission speed ratio. Subsequently, power-system controls 22 may repeat the control method, starting with reevaluating the relative importance of the different objectives (step 108).

Methods that power-controls 22 may execute to control power system 12 are not limited to the examples provided in Fig. 3. As mentioned above, power-system controls 22 may factor in objectives other than exhaust gas temperature, power-system responsiveness, and fuel efficiency, such as the objective of operating power system 12 in a manner to cause engine 14 to discharge low emissions into exhaust system 15. As also mentioned above, power-system controls 22 may control power system 12 based on more or fewer than three objectives. Additionally, power-system controls 22 may perform the actions shown in Fig. 3 in different orders, omit one or more of the actions shown in Fig. 3, and/or execute additional actions not shown in Fig. 3.

The disclosed embodiments may provide a number of performance advantages. Responding to low exhaust gas temperature by decreasing the transmission speed ratio, decreasing the engine speed, and increasing engine torque may help raise the exhaust gas temperature enough to allow exhaust-gas-treatment device 30 to effectively reduce undesirable substances in the exhaust gas from engine 14. Increasing parasitic power drain on engine 14 may further advance this objective. Basing the magnitude of these remedial measures on how low the exhaust gas temperature is and how long it has been low may help raise the exhaust gas temperature sufficiently without unduly compromising other performance objectives. Repeatedly evaluating the relative importance of these and/or other objectives may help power-system controls 22 emphasize the right objectives at the right times. It will be apparent to those skilled in the art that various modifications and variations can be made in the power system and methods without departing from the scope of the disclosure. Other embodiments of the disclosed power system and methods will be apparent to those skilled in the art from consideration of the specification and practice of the power system and methods disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.

Claims

1. A method of operating a power system ( 12) of a machine (10), the power system having an engine (14), the method comprising: selectively supplying power from the engine to one or more other components of the machine; and while supplying power from the engine to one or more other components of the machine, in response to a determined temperature of exhaust gas of the engine, increasing the torque and decreasing the speed at which the engine supplies power to increase the temperature of exhaust gas of the engine.

2. The method of claim 1, further including: directing at least a portion of the exhaust gas of the engine through one or more exhaust-gas-treatment devices (30); and wherein increasing the torque and decreasing the speed at which the engine supplies power to increase the temperature of exhaust gas of the engine in response to a determined temperature of the exhaust gas includes doing so in response to a determined temperature of the exhaust gas being below an exhaust gas temperature necessary for one or more of the one or more exhaust- gas-treatment devices to effectively treat exhaust gas.

3. The method of claim 2, wherein: increasing the torque and decreasing the speed at which the engine supplies power to increase the temperature of exhaust gas of the engine in response to a determined temperature of the exhaust gas being below an exhaust gas temperature necessary for one or more of the one or more exhaust-gas- treatment devices to effectively treat exhaust gas includes increasing the torque and decreasing the speed of the engine by first amounts in response to a determined temperature of the exhaust gas that is between a first reference temperature and a second reference temperature, the second reference temperature being lower than the first reference temperature; and increasing the torque and decreasing the speed of the engine by second amounts, the second amounts being greater than the first amounts, in response to a determined temperature of the exhaust gas that is below the second reference temperature.

4. The method of claim 3, wherein: the first reference temperature substantially corresponds to an exhaust gas temperature necessary for one or more of the one or more exhaust- gas-treatment devices to effectively reduce oxides of nitrogen in exhaust gas; and the second reference temperature substantially corresponds to an exhaust gas temperature necessary for one or more of the one or more exhaust- gas-treatment devices to effectively reduce at least one of hydrocarbons and carbon monoxide in exhaust gas.

5. The method of claim 1 , further including, when supplying power from the engine to one or more other components of the machine, in response to a determined temperature of the exhaust gas being below a reference temperature, increasing parasitic power drains on the engine to increase the temperature of the exhaust gas.

6. The method of claim 1 , further including: evaluating an importance of maintaining the temperature of the exhaust gas at a desirable level relative to at least one other objective; and using the importance associated with the exhaust gas temperature as a factor in determining when to decrease a transmission speed ratio of a multiple-ratio transmission (38) in response to a determined temperature of the exhaust gas.

7. A power system (12) for a machine (10), the power system comprising: an engine (14); a multiple-ratio transmission (38); power-system controls (22) operable to evaluate the relative importance associated with at least two objectives, and control a transmission speed ratio of the multiple-ratio transmission (38) dependent at least partially on the relative importance associated with each of the at least two objectives.

8. The power system of claim 7, wherein: at least one of the objectives includes maintaining exhaust gas from the engine at a desirable temperature; and controlling the transmission speed ratio of the multiple-ratio transmission dependent at least partially on the relative importance associated with each of the at least two objectives includes when maintaining a desirable exhaust gas temperature has highest importance, controlling the transmission speed ratio of the multiple-ratio transmission in a manner that favors maintaining a desirable exhaust gas temperature.

9. The power system of claim 8, wherein: at least one of the objectives includes promoting power-system responsiveness; and controlling the transmission speed ratio of the multiple-ratio transmission dependent at least partially on the relative importance associated with each of the at least two objectives includes when promoting power-system responsiveness has highest importance, controlling the transmission speed ratio of the multiple-ratio transmission in a manner that favors power-system responsiveness.

10. The power system of claim 9, wherein: at least one of the objectives includes promoting fuel efficiency; and controlling the transmission speed ratio of the multiple-ratio transmission dependent at least partially on the relative importance associated with each of the at least two objectives includes when promoting fuel efficiency has highest importance, controlling the transmission speed ratio of the multiple-ratio transmission in a manner that favors fuel efficiency.