Motor/generator transient response system

A transient response system includes a power source operable to generate a power output and a transmission operatively coupled to the power source. The transient response system also includes a generator operatively coupled to the power source and a controller in communication with the generator and at least one of the power source and the transmission. The controller is operable to receive at least one input having a value indicative of a change in load on the power source and operable to cause the generator to remove power from the power output at a rate corresponding to the value of the at least one input.

TECHNICAL FIELD

The present invention relates generally to a transient response system, and more particularly to transient response system having a motor/generator.

BACKGROUND

Work machines, including on-highway trucks and other types of heavy machinery, are used for a variety of tasks. These work machines may include a transmission coupled to an engine such as, for example, a diesel engine, a gasoline engine, or a natural gas engine that provides the power to complete these tasks. The transmission may be a mechanical, hydro-mechanical, hydraulic, or electric transmission that transmits engine power to a traction device. A power load placed on the transmission by the traction device is transmitted to the engine. Power load changes, either requiring additional power or less power, may cause the engine to deviate from a desired operating range. Deviations from the desired speed range may result in poor efficiency, less production, increased wear on the engine, and operator dissatisfaction.

Work machines may include a flywheel to minimize the variations in engine speed caused by a change in the power load. The magnitude of the speed changes may be minimized by increasing the inertia of the flywheel. However, as flywheel inertia increases, responsiveness of the engine decreases. A conventional flywheel may be inefficient at providing a balance between minimizing engine speed fluctuations and allowing the engine to respond quickly to desired power changes. A range of flywheel sizes may be provided for a particular engine application to allow selection of flywheel size based on expected load changes. Unfortunately, this may result in increased parts, tooling, and production cost.

In an attempt to provide a flywheel offering improved response to a wider range of load changes, at least one variable inertial mass flywheel has been proposed. For example, U.S. Pat. No. 5,007,303 (the '303 patent) issued to Okuzumi on Apr. 16, 1991, describes a variable inertial mass flywheel having a main flywheel member coupled to an engine crankshaft and a sub-flywheel member separated from the main flywheel member by electrorheological fluid. The viscosity of an electrorheological fluid is proportional to the intensity of an electric field applied to the fluid. During power load fluctuations, the intensity of the electric field is changed to change the viscosity of the electrorheological fluid. As a result, the change in viscosity increases or decreases friction between the main flywheel and the sub-flywheel. During accelerations or decelerations, the intensity of the field is set low to minimize friction between the main flywheel and the sub-flywheel, thereby creating a low inertia flywheel that may respond quickly. During power load changes of high magnitude, the intensity of the field is set high to increase friction between the main flywheel and the sub-flywheel, thereby creating a high inertia flywheel that may offset the high magnitude changes in power load.

While, the variable inertial mass flywheel of the '303 patent may offer an improved response to a wider range of load changes, as compared to traditional fixed-mass flywheels, the flywheel of the '303 patent may be problematic. For example, the variable inertial mass flywheel may not efficiently use and/or dissipate the energy absorbed by the flywheel.

The present invention is directed to overcoming one or more of the problems set forth above.

SUMMARY OF THE INVENTION

In one aspect, the present disclosure is directed to a transient response system that includes a power source operable to generate a power output and a transmission operatively coupled to the power source. The transient response system also includes a generator operatively coupled to the power source and a controller in communication with the generator and at least one of the power source and the transmission. The controller is operable to receive at least one input having a value indicative of a change in load on the power source and operable to cause the generator to remove power from the power output at a rate corresponding to the value of the at least one input.

In another aspect, the present disclosure is directed to a method of operating a transient response system. The method includes driving a transmission with a power source, the power source operable to produce a power output. The method also includes sensing a load on the power source and identifying a change in the load on the power source. The method further includes controlling a generator to remove power from the power output at a rate corresponding to the value associated with the change in load on the power source.

DETAILED DESCRIPTION

FIG. 1illustrates an exemplary embodiment of a transient response system10for a work machine12having a housing13. The transient response system10is intended for use with an engine16and a transmission14connected to a traction device18of the work machine12. Engine16may be a diesel engine, a gasoline engine, a natural gas engine, or any other engine readily apparent to one skilled in the art. Transmission14may be a mechanical, hydro-mechanical, electric, or any other transmission known in the art.

As illustrated inFIG. 2, the transient response system10may include a motor/generator20, a drive inverter22, a power storage device24, and a control system26. Transient response system10may replace a conventional flywheel of engine16. Alternately, transient response system10may also be used in conjunction with a conventional flywheel.

Motor/generator20may include a motor and a generator in a single unit. Alternatively, the motor and generator may be separated from one another. The motor/generator20may be connected to engine16by a crankshaft28of engine16, or in any other manner known in the art. Motor/generator20may be configured to both drive engine16and be driven by engine16. Motor/generator20may include a conventional starter/generator that is configured to drive engine16when engine16is already running as well as during a starting sequence.

It is also contemplated that the motor/generator may be absent and only a generator (not shown) included in transient response system10. The generator may be connected to engine16by a crankshaft28of engine16, or in any other manner known in the art. The generator may be configured to be driven by engine16to generate power.

Drive inverter22may be connected to motor/generator20via power lines30. Drive inverter22may include various components including insulated gate bipolar transistors (IGBTs), microprocessors, capacitors, memory storage devices, and any other components that may be used for operating motor/generator20. Other components that may be associated with drive inverter22include power supply circuitry, signal conditioning circuitry, and solenoid driver circuitry, among others.

Drive inverter22may direct power, generated by motor/generator20, to power storage device24and to other power consuming devices32via power lines34. Power storage device24may be any device (such as a battery) for storing power. Power consuming devices32may include, for example, one or more of an air conditioning unit, a heating unit, a resistive grid, lights, appliances, personal electronics, pumps, motors, and other electronic engine components and accessories known in the art.

Control system26may be in communication with engine16, transmission14, and drive inverter22via communication lines36,38, and40respectively. Control system26may include a controller42, which may include components such as a memory, a secondary storage device, a processor, and any other component that may be used for running applications. Controller42may contain other components including power supply circuitry, signal conditioning circuitry, solenoid driver circuitry, and other appropriate circuitry known in the art.

A flow chart52illustrated inFIG. 3depicts the operation of the transient response system10. A graph44, illustrated inFIG. 4, depicts a response time comparison of transient response system10and conventional flywheels. These figures will be discussed in the following section to further illustrate the disclosed system and its operation.

INDUSTRIAL APPLICABILITY

The disclosed system may be applicable to any engine that requires dampening of transient power loads applied to the engine to minimize or prevent engine deviations outside of a desired operating range. For purposes of this disclosure, the term “desired operating range” includes those operating conditions that the work machine operator and/or work machine control system wants to achieve and/or maintain such as, for example, engine speed. Deviations from this desired operating range may result in, for example, increased fuel consumption, increased exhaust emissions, increased engine temperatures, decreased machine productivity, operator dissatisfaction, and/or decreased responsiveness.

Deviations from the desired operating range may be experienced when sudden changes in power load experienced by traction device18are transferred by transmission14or other engine powered devices to engine16. Engine16may include various systems (not shown) working in combination with each other to respond to the power load. Such systems may include, for example, fuel delivery systems, air induction systems, control systems, combustion systems, and others known in the art. Each of these systems may have an associated response time lag. The combined response time lags of each system result in a total response time lag of engine16. The response time lag of engine16is a factor that may determine whether power load changes cause deviations from the desired operating range to occur.

Work machine12, as illustrated inFIG. 1, may utilize transient response system10to dampen sudden changes in power load transmitted to engine16from transmission14or other engine powered devices. Transient response system10may determine a change in the power load placed on the engine16and operate motor/generator20to change the power output of engine16in response to the sudden change in power load. While motor/generator20is responding to the change in power load, another power source (not shown) may supply the electrical requirements of work machine12. Transient response system10may enable engine16to respond more quickly to a sudden change in power load than if engine16included only a traditional flywheel. Transient response system10may, therefore, decrease the likelihood of engine16deviating from the desired operating range.

Flow chart52ofFIG. 3depicts the operation of transient response system10. At step54, controller42senses the power load applied to engine16. Controller42may monitor the change in power load that transmission14has transmitted or will transmit to engine16. For example, controller42may sense a change in fluid pressure within a hydraulic transmission or a change in a speed command signal sent to an electric transmission. Sensing the fluid pressure or speed command signal in transmission14may indicate a change in power load before the change is transmitted to engine16. Controller42may also sense an engine speed deviation, which may be an indication that a change in power load has already been transmitted to engine16.

In step56, controller42may determine whether a change in power load has occurred or will occur. If a change in power load has occurred or will occur, control continues to step58where controller42determines whether the change in power load is an increase or a decrease in power load.

If the change in power load is an increase, control continues in step62, where controller42determines the mode in which motor/generator20is currently operating. If motor/generator20is operating in a motoring mode (i.e., adding power to the power output by driving engine16), control commences to step64, where motoring of motor/generator20is increased to add power supplied to the power output of engine16. If motor/generator20is deactivated (i.e., neither absorbing nor adding substantial power with motor/generator20), control commences to step66, where motor/generator20is caused to enter the motoring mode to supply power to the power output of engine16. If motor/generator20is operating in a generating mode (i.e., absorbing power from the power output by driving motor/generator20with engine16), control commences to step68, where the generating function of motor/generator20decreases to reduce the power diverted from the power output of engine16. As a result of each of steps64,66, and68, power may be added to the power output of engine16to offset the increase in power load.

The motoring mode and generating mode of motor/generator20will now be explained in further detail. When in the motoring mode, power from energy storage device24, for example, may be directed to motor/generator20to cause motor/generator20to apply torque to engine crankshaft28, thereby adding power to the power output of engine16. The power directed to motor/generator20may also be supplied by another power source (not shown), such as an auxiliary engine. In the motoring mode, motor/generator20may be used to crank engine16when starting or to add power to crankshaft28when engine16is already running.

In the generating mode motor/generator20may be driven by engine16to generate power for various purposes. When in the generating mode, a portion of the mechanical power output of engine16may be converted by motor/generator20to electrical power. The generated electrical power may be directed to energy storage device24and to other power consuming devices32such as, for example, an air-conditioner, heating unit, resistive grid, lights, appliances, personal electronics, and other accessories. When motor/generator20is in the generating mode, power from the power output of engine16may be diverted from transmission14by motor/generator20.

After steps64,66, or68, control continues to step70, where controller42determines if the actions of steps64,66, or68were sufficient to accommodate the increase in power load. This may be accomplished by monitoring the inputs from the transmission and engine in the same manner as step54described above. If the actions of steps64,66, or68were insufficient, control loops back to step62. If the actions of steps64,66, or68were sufficient, control loops back to step54.

Returning to step58, if controller42determines that the change in power load is a decrease, control continues to step74. During step74, as described above for step62, controller42determines which mode motor/generator20is operating in.

If motor/generator20is operating in a motoring mode, control commences to step76, where motoring of motor/generator20decreases and less power is supplied to the power output of engine16. If motor/generator20is deactivated, control commences to step78, where motor/generator20is caused to enter the generating mode to divert power from transmission14to motor/generator20. If motor/generator20is operating in a generating mode, control commences to step80, where generating by motor/generator20increases to increase the power diverted from transmission14by motor/generator20. As a result of steps76,78, and80, the power output of engine16directed to transmission14prior to the power load decreases, thereby offsetting the decrease in power load.

After steps76,78, or80, control continues to step82, where controller42determines if the actions of steps76,78, or80were sufficient to accommodate the decrease in power load. This may be accomplished by monitoring the inputs from the transmission and engine in the same manner as step54described above. If the actions of steps76,78, or80were insufficient, control loops back to step74. If the actions of steps76,78, or80were sufficient, control loops back to step54.

FIG. 4illustrates the performance of transient response system10relative to conventional flywheels. A curve46represents the response time of transient response system10. A curve48represents the response time a high-inertia flywheel. A curve50represents the response time of a low-inertia flywheel. As illustrated inFIG. 4, transient response system10may cause engine16to deviate less from the desired operating range than a high inertia flywheel. As further illustrated inFIG. 4, transient response system10responds more quickly than a low inertia flywheel. The stability and responsiveness that transient response system10may add to engine16can improve efficiency, production, and life of both engine16and work machine12.