Interrelated power delivery controls – including engine control – Transmission control – Transmission controlled by engine
Reexamination Certificate
2000-12-21
2003-04-29
Wright, Dirk (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Transmission controlled by engine
Reexamination Certificate
active
06554742
ABSTRACT:
FIELD OF THE INVENTION
The exemplary embodiment relates to electronically controlled powershift transmissions for large off-road vehicles. More particularly, the exemplary embodiment relates to a system and a method for shifting the transmission of an agricultural or earth moving vehicle by controlling the engagement of a plurality of clutches in accordance with vehicle loading.
BACKGROUND OF THE INVENTION
In the field of transmission systems, a number of transmission configurations and control schemes have been proposed and are presently in use. Such transmissions typically include a collection of intermeshing gears either fixed to transmission shafts or rotating freely on the shafts. Clutches associated with the freely rotating gears may be selectively engaged to establish a series of speed ratios between an engine output shaft and a transmission output shaft to transmit engine torque at a desired speed to driven wheels of the vehicle. Control systems for commanding engagement of the clutches typically include electronic circuitry that responds to operator controls, such as a shift lever, a direction lever and the like in the vehicle cab. The control system sends electronic signals to hydraulic valves that channel pressurized fluid to the clutches. The control systems thus cause the clutches to engage and disengage in predetermined combinations to accelerate, decelerate and drive the vehicle as desired by the operator. Transmissions and control systems of this type are described in U.S. Pat. No. 4,425,620, issued on Jan. 10, 1984 and assigned to Steiger Tractor, Inc., and U.S. Pat. No. 4,967,385, issued on Oct. 30, 1990 and assigned to J.I. Case Company.
Direct shifting between gears is often provided in transmissions such as those described above. This process, called “power shifting”, involves disengaging a first set of one or more clutches (the “off-going clutches”) while substantially simultaneously engaging a second set of one or more clutches (the “on-coming clutches”). Powershift transmissions are particularly useful for a wide variety of off-road vehicles including, but not limited to, large agricultural vehicles and construction vehicles. Large agricultural vehicles include, but are not limited to, tractors, combines, sprayers and bailers. Representative construction vehicles include, but are not limited to, bulldozers, road graders and earth movers.
These powershift transmissions typically include a number of proportionally-engaged clutches. In general, proportional engagement is accomplished by metering hydraulic fluid to the clutches in response to a shift command. The speed at which the clutch is engaged is controlled by the metered amount of hydraulic fluid entering the clutch. Thus, by carefully controlling fluid pressure entering a clutch, clutch engagement is controlled and smooth transmission operation is achieved. While smooth operation is achievable through careful fluid metering and pressure control, this control is not without complications. For example, these transmissions require valves with orifices for regulating pressure. These valves require complicated calibration routines and are prone to failure.
As mentioned, powershift transmissions including proportional clutches typically provide for multiple forward and reverse gear ratios. Shifting between any of the forward or reverse gear ratios, or between neutral and a forward or reverse gear ratio, typically involves engaging various combinations of the proportionally engaged clutches to achieve the desired forward or reverse gear ratio.
During operation, agricultural and construction vehicles experience a wide range of loading conditions. For example, a tractor may be heavily loaded by a fully-engaged implement, partially loaded by partial implement engagement or rolling implement applications, or lightly loaded during transport operations. In addition to variable loading conditions, these vehicles are operated at a wide range of throttle conditions including part-throttle and full-throttle.
To avoid excess wear to a vehicle, vehicle loading must be determined to properly engage clutches within the powershift transmission. This is because the load on the vehicle influences how quickly the shift should be executed. For example, if the vehicle is lightly loaded, a rapid engagement of the desired proportional clutch will cause the vehicle to “lurch” significantly as the shift is completed. Lurching stresses both the internal components of the powershift transmission and also the drive line components of the vehicle. Further, lurching produced by rapid engagement can add to operator fatigue as the vehicle is operated over a prolonged period of time.
A simple solution would be to merely engage the clutch slowly. However, where a vehicle is heavily loaded, a slow engagement of the desired clutch will cause almost instant deceleration of the vehicle, thus producing a significant, momentary “jolt” as an off-going clutch disengages while an on-coming clutch is slowly brought to complete engagement. This condition, similar to the aforementioned rapid engagement under light loading, excessively stresses both the power transmission and the drive line components of the vehicle. Additionally, the speed of the vehicle and/or engine torque may drop significantly during the time interval between the off-going clutch disengaging and the on-coming clutch fully engaging, thus causing the engine torque to drop below the peak point.
Therefore, it is desirable to control the engagement timing of a clutch as a function of vehicle loading. Accordingly, where the vehicle is operating under a no-load condition, the clutch should preferably be engaged later to produce a “smooth” shift, and to prevent lurching. Conversely, where the vehicle is heavily loaded, the clutch should be engaged more quickly than during a no-load condition to avoid sudden deceleration of the vehicle as the shift is executed. Also, clutch engagement should be controlled between the extremes of heavy and light loading.
Significant effort has been expended to resolve the aforementioned powershift transmission problems. The conventional solutions have focussed on controlling the timing of upshift engagement of clutches in power transmissions. While the conventional solutions dramatically decrease wear during upshifts, wear during downshifts remains significant. This excessive wear to both the power transmission and the drive line components of the vehicle has been reduced where upshift control has been replicated to control a downshift of the same gears. For example, the control associated with a shift from fourth gear to fifth gear is replicated to control a shift from fifth gear to fourth gear. While this reduces wear, the wear is still excessive.
For example, one existing solution incorporates a table value used for both upshifting and downshifting. When the shift is commanded, the table is accessed to provide the appropriate clutch engagement timing. The same timing is used for both up-and downshifts between the same gears.
An expanded version of the aforementioned solution provides multiple table values associated with different levels of vehicle loading. Thus, when a shift is commanded, the table is accessed to provide appropriate clutch engagement timing for a specified vehicle load level. However, this is somewhat complicated by the difficulty of adequately ascertaining vehicle loading. While traditional powertrain systems employ a variety of sensors to determine engine and transmission operating conditions, at present it is difficult to directly measure the vehicle loading. Therefore, it is necessary to determine the vehicle loading from known engine operating conditions.
Various methods have been developed to indirectly determine vehicle loading. For example, one method depends upon monitoring a turbocharger employed as part of the vehicle engine. More specifically, the rate of engine exhaust gas flow increases causing the turbocharger to draw in a greater amount of ambient air as the engine rpm increases. The increase in ambient air allows the
Kuczmarski Bradley A.
Lykken Thomas G.
Milender Jeffrey S.
Case Corporation
Trausch A. N.
Wright Dirk
LandOfFree
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