Motor vehicles – Motor as source of power for other machine
Reexamination Certificate
1999-03-04
2001-07-31
Swann, J. J. (Department: 3611)
Motor vehicles
Motor as source of power for other machine
C192S01200R, C192S1030FA
Reexamination Certificate
active
06267189
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a control system for engagement of a power take off (PTO) for an agricultural vehicle such as a tractor. In particular, the present invention relates to a control system for controlling the engagement of a PTO in which the control system continuously determines (i.e., recalculates) a desired acceleration rate of the PTO. Also, the present invention relates to a control system for controlling the engagement of a PTO which provides a clutch with commands to transmit different amounts of torque depending upon the difference between an actual acceleration rate of the PTO and the desired acceleration rate of the PTO, and which provides a command to transmit a low amount of torque when the difference between the actual and desired acceleration rates is large enough to indicate that the clutch is not yet engaged.
BACKGROUND OF THE INVENTION
PTO shafts (or simply “PTOs”) are used on agricultural vehicles such as tractors to provide power for equipment or implements such as combines, mowers and spreaders. As the use of PTOs developed, most tractor manufacturers standardized on 1000 RPM and 540 RPM PTOs. This standardization involved the use of a common size shaft and spline arrangement for each RPM rating. When the shaft sizes were standardized years ago, tractors had relatively low horsepower (e.g., 30 to 50 horsepower). Accordingly, the torque output of a PTO was limited by the horsepower of the tractor. Modern tractors commonly have horsepower ratings in excess of 100 horsepower. However, the shaft sizes for PTOs have not changed due to the need to maintain compatibility with older equipment and maintain the standardization for PTOs. Thus, the torque output of PTOs for many modern tractors is no longer limited by the tractor horsepower. Rather, the torque output is limited by the strength of the PTO and the failure thereof. For very high horsepower tractors (e.g., over 130 horsepower), manufacturers have eliminated the 540 RPM PTO. Due to the gear reduction required to achieve a PTO speed of 540 RPM at engine idle, the very high horsepower tractors can apply a torque to the 540 RPM PTO in excess of that required for the PTO toil. In addition to causing PTO failures, the torque produced by the higher horsepower tractors also can accelerate equipment attached to the respective PTO at a rate which can damage the equipment.
Excessive acceleration of (or application of torques to) a PTO is of particular concern during the process of engagement of the PTO from a standstill or zero angular velocity state to a “lock-up” state, at which the PTO has an angular velocity equaling that of the engine (or, assuming various gear reductions, etc., an angular velocity that is an appropriate fraction or multiple of the angular velocity of the engine). Relevant components associated with this process of engagement of a PTO are shown in
FIGS. 1 and 2
(prior art).
FIG. 1
shows, in simplified form, a conventional (exemplary) arrangement for transmitting power from an engine
2
(of an agricultural vehicle) to a PTO
1
. As shown, PTO
1
is capable of receiving power from engine
2
by way of a PTO clutch
3
. PTO clutch
3
is capable of transmitting power from an input shaft
4
, which receives power from engine
2
, to an output shaft
10
, which is in turn typically coupled to PTO
1
by way of one or more gears (not shown). The amount of power transmitted from engine
2
to PTO
1
depends upon whether PTO clutch
3
is engaged (i.e., whether plates within the clutch have been compressed sufficiently to allow the clutch to transmit torque) and, once the clutch has been engaged, upon the degree of hydraulic fluid pressure applied to the clutch, which determines the amount of torque that the clutch may transmit from input shaft
4
to the PTO via output shaft
10
.
PTO
1
may be coupled, by way of a coupler
15
, to an implement input shaft
5
(supported by an implement attached to the agricultural vehicle). Typically, implement input shaft
5
, which is for receiving power from PTO
1
, is in turn coupled to an implement output shaft
13
for transmitting the power to attached equipment supported by the implement. In certain embodiments, implement input shaft
5
may be coupled to implement output shaft
13
by way of an over-running clutch
6
. Over-running clutch
6
allows implement input shaft
5
(and PTO
1
) to transmit power to implement output shaft
13
but also allows the output shaft to continue to rotate freely when the input shaft no longer is rotating. As shown in
FIG. 2
, an exemplary over-running clutch
6
includes an arrangement in which an output
7
attached to output shaft
13
concentrically surrounds an input
8
attached to input shaft
5
. Input
8
transmits power to output
7
only when spring-actuated locking pins
9
are fully extended into two locking grooves or notches
11
and when input
8
receives power (from PTO
1
) causing the input to rotate in a counter-clockwise direction relative to output
7
, in which case the input is coupled to the output. In other circumstances, such as when locking pins
9
are not fully extended into locking notches
11
(as shown), or when output
7
rotates in a counter-clockwise direction relative to input
8
(e.g., when no power is being transmitted from engine
2
but when output shaft
13
nonetheless is rotating in a counter-clockwise direction), output
7
freely rotates with respect to input
8
and effectively no power is transmitted between the two elements.
As shown in prior art
FIG. 3A
, PTO
1
experiences a rapid change in angular velocity during the PTO engagement process once PTO clutch
3
has been engaged such that power is transmitted from engine
2
to the PTO (e.g., after a time t
1
). In order to control PTO acceleration during this process of engagement of PTO
1
, Case Corporation has developed a PTO clutch control system that monitors the angular velocities of input shaft
4
and output shaft
10
and controls the acceleration of PTO
1
based upon these measured velocities, as described in U.S. Pat. No. 5,494,142 to Kale and incorporated by reference herein. Based upon the monitored speeds of input shaft
4
and output shaft
10
, the clutch control system calculates a desired acceleration for PTO
1
and also repeatedly calculates an actual acceleration of the PTO. The desired acceleration is calculated as the ratio of the angular velocity of input shaft
4
(or a quantity directly related to the engine speed of the agricultural vehicle) to a predetermined amount of time (shown in
FIG. 3A
as the time interval between a time t
3
and a time t
1
), and is only calculated once. That is, only one calculated value of the desired acceleration is utilized by the clutch control system throughout the PTO engagement process. The actual acceleration is calculated as the ratio of the change in angular velocity of output shaft
10
(or a quantity related to the speed of PTO
1
) during a particular time interval (the time between two velocity measurements) divided by the time interval. The predetermined amount of time with respect to the desired acceleration (the time interval between times t
3
and t
1
) is chosen to restrict the desired acceleration to a low enough level so that, if PTO
1
actually accelerated at that rate, no damage to the PTO or to attached equipment would occur. For example, the predetermined amount of time may be 2 seconds. Depending upon whether the desired acceleration exceeds or is less than the actual acceleration at a given time, the clutch control system causes PTO clutch
3
to transmit, respectively, more or the same torque such that the actual acceleration approaches the desired acceleration.
FIG. 3A
shows the time variation during the PTO engagement process of the actual and desired speeds of PTO
1
and the actual speed of engine
2
(or a fraction or multiple thereof, to account for gear reductions or augmentations occurring between engine
2
and PTO
1
), and thereby illustrates a typical PTO acceleration (engageme
Eike Craig R.
Nielsen Bradley A.
Case Corporation
Foley & Lardner
McClellan James S.
Swann J. J.
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