Measuring and testing – Blower – pump – and hydraulic equipment
Reexamination Certificate
2001-11-26
2003-09-30
Williams, Hezron (Department: 2856)
Measuring and testing
Blower, pump, and hydraulic equipment
C073S001350
Reexamination Certificate
active
06626036
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to work vehicles having power shift transmissions. More particularly, it relates to automated methods for calibrating the clutches in the power shift transmissions using removable calibration tools.
BACKGROUND OF THE INVENTION
Power shift transmissions are commonly used in a variety of work vehicles ranging from road graders to agricultural tractors. As the term is generally used in the construction and agricultural equipment industries, a power shift transmission is a transmission that can be shifted from gear ratio to gear ratio without significantly reducing the power output of the transmission during the shift.
In order to do this, the transmissions are arranged with several internal shafts that are each equipped with one or more hydraulic clutches. These clutches are typically multi-plate “wet” clutches that are immersed in hydraulic fluid. To change from gear ratio to gear ratio, one or more clutches are disengaged substantially simultaneously with the engagement of one or more additional and different clutches by introducing fluid into the clutches being engaged at the same time fluid is released from the clutches being disengaged.
Unlike a typical manual mechanical shift transmission in which there is one clutch located outside of the transmission which engages and disengages the engine from the transmission, and wherein manual manipulation of the shift lever causes gears to slide on shafts within the transmission in order to effect the gear change, a power shift transmission connects or disconnects gears by locking them or unlocking them to the corresponding shafts by the engagement and disengagement, respectively, of their corresponding clutches. Generally speaking, in a full power shift transmission all of the gears are always in mesh. What shifts the transmission is the locking and unlocking of particular gears to their corresponding shafts.
One of the benefits of this arrangement is that the time required to disengage the transmission from one gear ratio and engage the transmission in another gear ratio is significantly reduced. A gearshift in a power shift transmission can occur in as little as fifty or one hundred milliseconds.
One danger in this shifting process is that of wear or damage to internal parts. As one set of clutches is disengaged and another set is engaged, at some point all the clutches may be simultaneously engaged. This can cause serious damage to the transmission as gear teeth break, or extreme wear as the clutches are forced to slip with respect to each other. Alternatively, if neither the gears break or the clutches slip, simultaneous engagement in two gear ratios can bring the engine to a sudden and precipitous stop. This is called “four-squaring the transmission”.
The opposite danger is that of being disengaged from any gear ratio for too long. If the power shift transmission is on a tractor pulling a sixteen-bottom plow through a field, for example, and if the gear shifting permits the vehicle to be disengaged from the engine for a half a second or a second, the tractor may stop completely due to the extreme load before the new gear ratio is engaged. Once stopped, it may be necessary to shift down to the lowest gear ratio to start the tractor moving again. This would effectively prevent the tractor from being used in any of the higher gear ratios when a large load is on the tractor.
For this reason, the timing of clutch engagement and disengagement is of critical importance when shifting. To accurately coordinate the engagement and disengagement of the clutches, it is necessary to determine the amount of time between the operator's command to the clutches to engage or disengage and to use this information to “schedule” shifts. By “scheduling” I refer to the process of using the time delay between the time a command is given to an electronic valve controlling fluid flow to a clutch and the time that clutch is actually filled with fluid and begins to engage to determine the proper times of clutch valve energization and de-energization.
Determining the time delay between applying an electrical signal to a clutch valve and the corresponding clutch engagement or disengagement is not a trivial task, nor, for most vehicles can it be measured once and stored in an electronic memory for perpetual use.
As the hydraulic components of the work vehicle wear, the time delay (also known as the “clutch fill time”) can vary, sometimes dramatically. For this reason, it is important that the clutch fill time be periodically re-measured and stored in the electronic circuitry that schedules the transmission shifts. In some applications, such as when small engines are used in demanding applications it may be necessary to determine the clutch fill times of the clutches on an almost continuous basis. In this case, the work vehicle is usually equipped with several clutch fill time sensors that are permanently attached to the electronic circuitry and re-measure the clutch fill times for each clutch as the vehicle actually works in the field. For other vehicles, this continual clutch fill time calibration may not be necessary.
If clutch fill time calibration is only necessary every few weeks or few months, it may be possible to reduce the complexity of the electronic circuitry and reduce the cost of the work vehicle by configuring the electronic circuitry of the work vehicle to automatically interact with a maintenance person or operator and with a removable clutch calibration service tool that are together capable of determining the clutch fill time and saving the clutch fill time in the electronic circuitry.
By providing a removable service tool that need only be connected to the work vehicle electronic circuitry every few months during the calibration process, the cost of the vehicle could be reduced by several hundred dollars. It is an object of this invention to provide such a system and method.
SUMMARY OF THE INVENTION
In accordance with a first embodiment of the invention, a method for calibrating hydraulic clutches in a powershift transmission of a work vehicle is provided which includes the steps of manually connecting a pressure transducer to a first hydraulic fluid conduit extending between a first clutch control valve and a first clutch in the powershift transmission such that the pressure transducer generates an electronic pressure signal indicative of the fluid pressure in the first clutch, manually connecting the pressure transducer to an electronic transmission controller on the vehicle, wherein the electronic transmission controller is configured to drive the pressure transducer and to receive the electronic pressure signal, electronically signaling the first clutch valve to fill the first clutch with hydraulic fluid, electronically monitoring the time required to fill the first clutch, recording a digital value indicative of the time required to fill the first clutch in an electronic memory of the electronic transmission controller, manually disconnecting the first pressure transducer from the first conduit, and manually disconnecting the first pressure transducer from the electronic transmission controller.
The step of manually connecting to a first conduit may include the step of fluidly coupling the first pressure transducer to a quick-connect coupling mounted on the transmission. The pressure transducer may be electrically connected to a first electrical connector such that the transducer and connector together define a removable and replaceable structure and further wherein the step of connecting to the controller includes the step of coupling the first electrical connector to a mating electrical connector on the work vehicle, wherein the mating electrical connector is electrically coupled to the electronic transmission controller. The step of electronically monitoring may include the step of comparing a digital value indicative of a current clutch pressure signal provided by the pressure transducer with a digital value indicative of at least one past clutch pressure signal provided
Johnson Bradley
Milender Jeffrey
Case Corporation
Garber Charles D
Henkel Rebecca L.
Stader John William
Williams Hezron
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