Machine element or mechanism – Gearing – With fluid drive
Reexamination Certificate
1999-12-17
2001-07-17
Estremsky, Sherry (Department: 3681)
Machine element or mechanism
Gearing
With fluid drive
C074S720000, C475S076000, C477S038000, C477S041000
Reexamination Certificate
active
06260440
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to a continuously variable transmission, and more specifically to a method and apparatus for shifting ranges in a continuously variable transmission.
BACKGROUND OF THE INVENTION
Many work machines, particularly earth working machines, use a continuously variable transmission to drive traction wheels or tracks of the work machine. Typically, a hydrostatic drive, consisting of a hydraulic pump and a hydraulic motor, provides a continuously variable speed output to the wheels or tracks of the work machine. In particular, the speed output can be continuously varied by controlling the displacements of either the hydraulic pump or the hydraulic motor which comprise the hydrostatic drive system.
In order to operate over a wide range of operating conditions, the output of the continuously variable hydrostatic transmission is transmitted through a mechanical transmission. The mechanical transmission has a number of transmission ranges corresponding to different operating speeds of the work machine. The combination of the continuously variable transmission and the mechanical transmission allows a continuously variable transmission to operate over a wider range of speeds than is possible using the continuously variable transmission alone.
One drawback to using a continuously variable transmission with a number of transmission ranges is that power may not be smoothly transmitted through the transmission due to a range shift from a first gear range to a second gear range. Typically, during the range shift, there is a torque reversal in the continuously variable transmission. When the continuously variable transmission is a hydrostatic transmission, the actuators which control the displacement of a variable displacement hydraulic components have the slowest response time. Thus, during a range shift, the displacement remains relatively constant during the torque reversal. The torque reversal and the relatively constant displacement can cause the work machine to be perceived as non-continuous during the range shift and thus, the range shift may feel objectionable if the shift point is not adjusted for load.
However, it is possible to advantageously choose shift points such that reversal of torque is taken into consideration and the displacement of a controlling variable displacement hydraulic device, either the pump or the motor, remains relatively constant during the shift. However, to choose such advantageous shift points, it is necessary to estimate the volumetric efficiency of the components of the hydrostatic transmission in order to determine which shift points result in the same displacement after the shift as before the shift with no discrete change in output speed.
What is needed therefore is a method and apparatus for adjusting the shift point as a function of load when shifting ranges in a continuously variable transmission which overcomes the above-mentioned drawbacks.
DISCLOSURE OF THE INVENTION
In accordance with a first embodiment of the present invention, there is provided a transmission assembly having a hydrostatic transmission with a variable displacement hydraulic device which controls a motor speed ratio. The transmission assembly further includes a mechanical transmission coupled to the hydrostatic transmission and having a first range and a second range and an output shaft driven at a travel speed ratio. The torque through the hydrostatic transmission reverses when the mechanical transmission shifts from the first range to the second range. A synchronous travel speed ratio is the motor speed ratio which produces the same travel speed ratio in both the first gear range and the second gear range. An equal displacement travel speed ratio is the travel speed ratio at which a displacement of the variable displacement device in the second gear range is the same as the displacement in the first gear range. A travel speed ratio differential is a difference between the synchronous travel speed ratio and the equal displacement travel speed ratio. The shift from the first range to the second range is initiated at a travel speed ratio which varies from the equal displacement travel speed ratio by less than eighty percent of the travel speed ratio differential.
In accordance with a second embodiment of the present invention, there is provided a method of operating a transmission assembly having (i) a hydrostatic transmission with a variable displacement hydraulic device which controls a motor speed ratio, (ii) a mechanical transmission coupled to the hydrostatic transmission and having a first range and a second range, (iii) an output shaft driven at a travel speed ratio, and (iv) a controller. The method includes the steps of storing a synchronous travel speed ratio at which the motor speed ratio produces a single travel speed ratio in both the first gear range and the second gear range and determining an equal displacement travel ratio at which a displacement of the variable displacement device in the second gear range is the same as the displacement of the variable displacement device in the first gear range. The method further includes the steps of calculating a travel speed ratio differential between the synchronous travel speed ratio and the equal displacement travel speed ratio; and initiating a shift from the first range to the second range at a travel speed ratio which varies from the equal displacement travel speed ratio by less than eighty percent of the travel speed ratio differential.
REFERENCES:
patent: 4531431 (1985-07-01), Dreher et al.
patent: 5054599 (1991-10-01), Marcott
patent: 5105922 (1992-04-01), Yant
patent: 5199313 (1993-04-01), Muller
patent: 5270930 (1993-12-01), Ito et al.
patent: 5301783 (1994-04-01), Malloy
patent: 5337871 (1994-08-01), Testerman
patent: 5343994 (1994-09-01), Kyrtsos
patent: 5467854 (1995-11-01), Creger et al.
patent: 5505100 (1996-04-01), Mitchell et al.
patent: 5540051 (1996-07-01), Maruyama et al.
patent: 5551930 (1996-09-01), Creger et al.
patent: 5573473 (1996-11-01), Asayama et al.
patent: 5580332 (1996-12-01), Mitchell et al.
patent: 5636119 (1997-06-01), Coutant et al.
patent: 5684694 (1997-11-01), Ishino et al.
patent: 5842144 (1998-11-01), Coutant et al.
patent: 5980411 (1999-11-01), Wontner
Cronin Michael G.
Kuras Brian D.
Caterpillar Inc.
Estremsky Sherry
Lewis Tisha D.
Morrison John W.
LandOfFree
Method and apparatus for shifting ranges in a continuously... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for shifting ranges in a continuously..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for shifting ranges in a continuously... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2487896