Planetary gear transmission systems or components – Fluid drive or control of planetary gearing – Fluid pump and motor in one of plural paths to or from...
Reexamination Certificate
2001-12-28
2003-07-22
Wright, Dirk (Department: 3681)
Planetary gear transmission systems or components
Fluid drive or control of planetary gearing
Fluid pump and motor in one of plural paths to or from...
Reexamination Certificate
active
06595885
ABSTRACT:
TECHNICAL FIELD
The present invention is directed to a control system and method for a transmission. More particularly, the present invention is directed to a system and method for controlling a torque output of a transmission in a work machine.
BACKGROUND
Work machines, such as, for example, wheel loaders, track loaders, bulldozers, and backhoes, typically use a transmission to translate the rotational speed of an engine shaft into a drive speed. These transmissions are typically operable to provide a series of gear ratios that translate the speed of the engine shaft into different drive speeds. The gear ratios usually include forward and reverse speeds that range from low to high to provide different powers and speeds for the work machine as different operating conditions are encountered.
Some work machines are designed to work in low speed ranges and require precise speed control through the low speed ranges. To achieve this speed control, a split torque transmission may be used to convert the rotational speed of the engine shaft. This type of transmission combines the outputs of a hydrostatic transmission and a mechanical transmission to rotate a drive shaft and move the vehicle.
A split torque transmission may be operated with one or both of the hydrostatic and mechanical transmissions. Typically, the work machine operates on the hydrostatic transmission alone when the machine is operating in the low speed range, such as, for example, when digging or loading operations are performed. The work machine will usually engage the mechanical transmission to supplement the hydrostatic transmission when higher speeds are required. For example, a wheel loader may operate on the hydrostatic transmission when moving at speeds up to two miles per hour. When moving at speeds above two miles per hour, the wheel loader will typically engage the mechanical transmission and operate on a combination of the hydrostatic and mechanical transmissions.
As described in U.S. Pat. No. 5,682,315, a control system for a split torque transmission will rely on several indicators to determine when and how to adjust the transmission to achieve a desired speed. To determine the appropriate transmission settings, the control system may monitor the position of several operator inputs, such as, for example, the position of a speed pedal, a range lever, and a direction lever. In addition, the control system may monitor several operating conditions in the work machine, such as, for example, the engine speed, the mechanical transmission output speed, and the hydrostatic transmission output speed. By monitoring these indicators, the control system will be able to determine when and how to adjust the transmission to achieve the desired speed.
This type of control system may not, however, account for unexpected operating conditions, such as, for example, a severe engine underspeed situation. An engine underspeed situation may occur, for example, when the work machine encounters a heavy load, such as a work pile, when moving at a significant ground speed. Encountering the heavy load will rapidly decrease the groundspeed of the work machine and the operational speed of the engine.
If the transmission is not adjusted to account for the increased output load and to allow the engine to resume an acceptable operating speed, the engine may stall. If the drop in engine speed is rapid enough, the control system may not be able to adjust the transmission quickly enough to prevent the engine from stalling. If the engine stalls, the operator will be forced to restart the engine before resuming work, thereby causing an inconvenient interruption in the work process. This, of course, translates to a loss of machine efficiency.
The transmission control system of the present invention solves one or more of the problems set forth above.
SUMMARY OF THE INVENTION
One aspect of the present invention is directed to a method for controlling a transmission in a work machine. The output of a hydrostatic transmission having a source of pressurized fluid is combined with the output of a mechanical transmission having at least one engaged clutch. An operational speed of an engine is sensed. The engine provides an input to both the hydrostatic transmission and the mechanical transmission. At least one clutch of the mechanical transmission is disengaged and the displacement of the source of pressurized fluid is modified when the operational speed of the engine drops below a stall limit. The disengagement of the at least one clutch and the modification of the displacement of the source of pressurized fluid allow the operational speed of the engine to rise above the stall limit.
In another aspect, the present invention is directed to a control system for a transmission that combines a mechanical transmission having at least one clutch and a hydrostatic transmission having a source of pressurized fluid. The control system includes a sensor configured to sense the operational speed of an engine that provides an input to the transmission. A control is configured to disengage at least one clutch and to modify the displacement of the source of pressurized fluid when the operational speed of the engine drops below a stall limit. The disengagement of at least one clutch and the modification of the displacement of the source of pressurized fluid allows the speed of the engine to increase above the stall limit.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
REFERENCES:
patent: 3722323 (1973-03-01), Welch
patent: 3903756 (1975-09-01), Hamma
patent: 4122732 (1978-10-01), Chana
patent: 4355509 (1982-10-01), Fulkerson et al.
patent: 4462275 (1984-07-01), Mohl et al.
patent: 4875390 (1989-10-01), Hayashi et al.
patent: 4941371 (1990-07-01), Koyama et al.
patent: 5421790 (1995-06-01), Lasoen
patent: 5624339 (1997-04-01), Coutant et al.
patent: 5667452 (1997-09-01), Coutant
patent: 5682315 (1997-10-01), Coutant et al.
patent: 5684694 (1997-11-01), Ishino et al.
patent: 5842144 (1998-11-01), Coutant et al.
patent: 6220966 (2001-04-01), Ara et al.
Caterpillar Inc
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Wright Dirk
LandOfFree
Transmission control system and method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transmission control system and method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transmission control system and method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3057166