Patent Application
20170284325
The present disclosure relates generally to operation of a machine having a continuously variable transmission (CVT), and more particularly to operation of such a machine where engine speed is proactively controlled in anticipation of transient load changes on the engine.
A continuously variable transmission (CVT) provides a continuous range of transmission ratios between an input shaft and an output shaft. In ground-engaging machines, the use of a CVT is well-known for certain applications, and interest in applying such technology to new environments and machine types exists. A variety of different designs are known, including various pulley systems having variable-diameter pulley wheels, belted systems where a drive belt connects rotating cones, hydrostatic or “hystat” transmissions, certain electric drive machines and still others.
CVT's provide certain desirable properties over manual transmissions and over other types of automatic transmissions. For instance, with a CVT it is often possible to maintain engine speed more or less constant, or vary engine speed within a relatively narrow speed range, while torque applied to a load such as a machine driveline is varied principally by adjustment of the transmission ratio. Such properties enable an engine to be operated much of the time at or close to an optimally efficient engine speed, avoiding swings in speed known to occur in other engines where only a finite number of transmission ratios are available. Commonly owned U.S. Pat. No. 9,097,344 to Hoff et al. is directed to an automatic shift control system for a powertrain. In Hoff et al. a control device selectively varies transmission ratio in response to a shift signal, such as where a speed ratio of a transmission is to be adjusted in anticipation of a load change. While Hoff et al. appears well-suited to its intended applications there is always room for improvement.
In one aspect, a method of operating a machine includes operating an engine of the machine at a lower engine speed, and transferring torque by way of a continuously variable transmission (CVT) from an output shaft of the engine to a drive shaft coupled with ground-engaging elements of the machine. The method further includes receiving data indicative of an expected increase in a load on the engine, and commanding increasing engine speed responsive to the data. The method further includes operating the engine at a higher speed responsive to the commanded increase, and limiting lugging the engine by way of initiating the operating of the engine at the higher engine speed prior to the occurrence of the expected increase in load on the engine.
In another aspect, a machine includes a frame, an engine coupled to the frame, and ground-engaging elements coupled to the frame. The machine further includes a continuously variable transmission (CVT) coupled between the engine and the ground-engaging elements, and an engine speed control system. The engine speed control system includes a monitoring mechanism structured to monitor a machine parameter indicative of one of a plurality of power demands of the machine, a throttle, and an electronic control unit coupled with the monitoring mechanism and with the throttle. The electronic control unit is structured to determine an expected increase in a load on the engine responsive to the data from the monitoring mechanism, and to responsively command an adjustment in a position of the throttle such that an increase in engine speed is initiated prior to occurrence of the expected increase in load on the engine.
In still another aspect, an engine speed control system for a machine having a continuously variable transmission (CVT) includes a plurality of monitoring mechanisms structured to monitor a plurality of different machine parameters indicative of a plurality of different power demands of the machine. The system further includes a throttle structured to couple with an engine of the machine and movable so as to adjust a fueling of the engine to vary engine speed. The system further includes an electronic control unit coupled with the plurality of monitoring mechanisms and with the throttle, and the electronic control unit being structured to receive data from the plurality of monitoring mechanisms indicative of an expected increase in load on the engine. The electronic control unit is further structured to limit lugging the engine by way of commanding an adjustment in a position of the throttle, such that an increased engine speed is produced, responsive to the data, and prior to the occurrence of the expected increase in load.
Referring to
To this end, machine 10 may further include an engine speed control system 40 having an electronic control unit 42, and a plurality of monitoring mechanisms coupled with electronic control unit 42 and structured to monitor a plurality of different machine parameters each indicative of a different one of a plurality of power demands of machine 10. In a practical implementation strategy, system 40 includes a linkage position sensor 44, a bucket tilt sensor 46, a left pedal 48 and a right pedal 50 each positioned within operator cab 15, a pump sensor 54, and a throttle 56. A shifter 52 may be positioned in operator cab 15, also coupled with electronic control unit 42, and structured to enable an operator to shift among a forward gear, a reverse gear, and neutral, or provide for low range and high range shifting in certain embodiments. Each of linkage position sensor 44 and bucket tilt sensor 46 may be structured so as to provide an output state producing a signal, or an output state suitable for interrogation by electronic control unit 42, that is indicative of a position of the monitored element. Thus, linkage position sensor 44 may produce data indicative of a position of linkage 24 relative to frame 12 or to the ground, and bucket tilt sensor 46 may produce data indicative of a position of bucket 26 relative to frame 12 or to linkage 24, or relative to any other reference point. Sensors 44 and 46 may have the form of linear position sensors coupled with actuators 30 and 28, respectively, but could also be rotary potentiometers positioned at pivot locations of linkage 24 and bucket 26 as the case may be. In still other embodiments, sensors 44 and 46 might be optical cameras, or any other suitable monitoring device capable of indicating the state of the monitored parameter of interest. Pump sensor 54 may be coupled with a hydraulic pump 31 of implement system 22 and structured, for example, to monitor an angle of a variable angle swash plate in pump 31 so as to indicate a torque that is requested of pump 31 to provide power to implement system 22. Pump 31 may be driven by way of a geartrain of engine 32.
In a practical implementation strategy, right pedal 50 may include a throttle control pedal, a position of which is indicative of operator requested engine fueling and generally requested engine speed. In a further practical implementation strategy, machine 10 may operate in a so-called throttle locked mode such that engine speed is held steady at least much of the time at an engine speed where operation of engine 32 is optimally fuel efficient. Left pedal 48 can be understood to have a function somewhat analogous to a manual clutch in certain manual transmissions, and has a variable position whereby an operator can modulate torque transferred from CVT 36 to ground-engaging elements 20. In one embodiment, left pedal 48 is depressed to reduce torque transferred to ground engaging elements 20, potentially to zero, and lifts to restore and increase the torque. In the case of a hydrostatic transmission manipulating left pedal 48 could adjust pump displacement, and in the case of an electric drive machine manipulating left pedal 48 could vary electric motor torque, to list some examples. An operator can utilize right pedal 50 and left pedal 48 together to modulate torque applied to ground engaging elements 20. While it is desirable to retain flexibility in operator control over engine speed and propulsion torque, for reasons that will be further apparent from the following description machine 10 is advantageously operated in a fuel economy mode whereby control over throttle position and thus engine speed is handed off to electronic control unit 42 at least some of the time.
In view of the foregoing discussion it will be appreciated that a variety of machine parameters are monitored that can each give an indication of a different power demand of machine 10. For instance, a pump state such as a swash plate angle indicated by sensor 54 can be indicative of a power demand of implement system 22. Torque to ground engaging elements 20 can be indicative of a powertrain propulsion demand. Positions of linkage 24 and bucket 26 can be indicative of present activity being undertaken by implement system 22 such as digging, pushing or lifting. In a practical implementation strategy, a position of linkage 24, potentially a position of bucket 26, and a state of left pedal 48 can be monitored to determine whether machine 10 appears to be positioned and operated in anticipation of an increased power demand such as entering a material pile such as pile 8 to load bucket 26. In
Those skilled in the art will be familiar with a general relationship between engine speed and engine power output. In the case of machine 10, each of the separate power demands such as a power demand for machine propulsion, a power demand for implement actuation and torque, and still others are met by providing a power output from engine 32 that is generally proportional to engine speed. Another way to understand the phenomenon is that a load on engine 32 is generally matched to certain power demands of machine 10 generally, and engine speed controlled to accommodate the engine load requirements. Thus, for relatively higher power demands of machine 10 a relatively higher engine speed may be appropriate, and for relatively lower power demands a relatively lower engine speed may be appropriate. Where fuel consumption is no object, or of less concern, and machine performance is paramount, then fuel economy mode will not be used and an engine speed might be produced that will provide more than enough power output for any given task or operating state of machine 10. There continues to be interest in fuel economy in the industry, however, and thus strategies where fuel consumption can be reduced without unduly sacrificing machine performance are desirable.
To this end, machine 10 and control system 40 may be structured to provide an engine speed that is matched to a maximum one of the power demands of machine 10, and thus avoid overcompensating or otherwise providing ample and extra engine power output for any engine operating state or to achieve any given task. Fuel economy mode according to the present disclosure can be generally understood as providing a desired power output of engine 32, by way of controlled engine speed, that is sufficient to accommodate whatever the highest single power demand is of machine 10 at a given time. Thus, if powertrain power demand is highest at a given time, then an engine speed is commanded that will accommodate that powertrain power demand. If implement torque power demand is highest, then an engine speed is commanded that will accommodate that implement torque power demand. In some instances, performance of machine 10 may be slightly reduced where engine speed is thusly controlled, but with any performance degradation being offset by improvements in fuel economy. This strategy is believed to be particularly applicable to reducing fuel consumption based upon parasitic losses to auxiliary engine-driven components such as pumps, compressors, and the like, as many of such components rotate at a speed that is proportional to engine speed even if the present demands of such components could be satisfied at lower speeds. The present disclosure further reflects the insight that fuel economy can be still further improved without unduly affecting performance where changes in power demand, resulting in an expected increase in load on engine 32, are identified proactively rather than reactively and engine speed adjustment initiated in advance of the occurrence of a change in load on engine 32. As further discussed herein, electronic control unit may be structured by way of one or more computer processors, memory, and suitable programming to operate machine 10 in a fuel economy mode that includes controlling engine speed so as to provide an engine power output that is matched to a maximum one of a plurality of power demands on machine 10, and to proactively control engine speed to provide that engine power output in anticipation of changes in load on engine 10. In a practical implementation strategy, electronic control unit 42 is structured by way of the engine speed control disclosed herein to limit lugging engine 32, and thus reduce degradation of performance of machine 10 such as retarding of ground speed, limiting implement power, and a host of other performance parameters.
Referring also now to
Referring to the drawings generally but in particular now to
At block 450 electronic control unit 42 can be understood more broadly to be determining whether machine movement is suitable for or indicative of expected pile entry. Thus, additions and alternatives could include monitoring machine deceleration, querying whether machine 10 is stopped, turning, in neutral, or still other operations. If at block 450 the operator is commanding acceleration, the logic may advance to block 460 to determine an engine speed matched to an expected increase in power output demand, in other words an expected increase in load on engine 32, that corresponds with pile entry. From block 460 the logic may advance to block 470 to command increased engine speed, and to block 480 to initiate an increase in engine speed prior to occurrence of the expected increase in power output demand. The logic exits at block 490.
The control logic set forth in
As suggested above, during the monitoring of machine parameters, machine 10 may also receive data indicative of an expected increase in a load on engine 32, such as by detecting linkage position and possibly other factors that indicate engine power output demand may need to increase to accommodate operations of machine 10. Responsive to the data indicative of expected increase in load, electronic control unit 32 may command increasing engine speed, and in advance of the occurrence of the expected increase. It has been discovered that proactively increasing engine speed in certain instances can prevent degradations in performance that might otherwise be observed, especially when operating in a fuel economy mode.
Referring also now to
When a machine such as machine 10 enters a material pile, the interaction with the material can result in resistance against forward travel of the machine. To continue to travel forward against the resistance of the material an increased demand for output torque from the CVT may be required, and an increased load on the engine may be needed so long as machine ground speed is to be increased, maintained, or prevented from slowing unduly. Where an engine is attempting to speed up so as to produce increased output power for machine propulsion, energy can be diverted to the increasing of the engine speed instead of applying torque to the CVT. Another way to understand the phenomenon is that engine speed cannot be instantaneously increased to produce more power, and as a result some energy that might otherwise be available for machine propulsion or other purposes is instead used in an attempt to accelerate the engine.
Where engine speed is already controlled to be relatively low, such as for purposes of fuel economy, when a machine experiences an increase in demanded load it may not be possible or practicable to rapidly increase engine speed while also increasing or maintaining propulsion power or powering auxiliary devices. Lugging the engine can occur as a result. In the
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features and advantages will be apparent upon examination of the attached drawings and appended claims.
