PTO OVERSPEED PROTECTION STRATEGY
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority to U.S. Patent Application 11/701,582, filed
February 2, 2007, the disclosure of which is incorporated by reference in its entirety.
TECHNICAL FIELD
The disclosure generally relates to vehicles with a power take off (PTO) drive,
and specifically to operation of PTO drives of a vehicle
BACKGROUND
Many vehicles are provided with a power take off (PTO) drive. The engines
for these vehicles are typically fuel throttle controlled, preferably electronically, and are
generally connected to an electronic data link of the type defined in, for example, SAE J1922
and/or SAE J1939 protocol. The electronically controlled engine is usually provided with its
own electronic control unit (ECU). An input shaft brake may be incorporated that provides
quicker manual upshifting as is well known in the prior art. It is understood that a data link
or databus complying with SAE J1922, SAE J1939, CAN and/or ISO 11898 protocols, or
similar protocols, carries information indicative of engine torque, engine speed, transmission
output shaft speed, PTO speed, and brake information.
Fully or partially automated transmission systems wherein a microprocessor-
based electronic control unit (ECU) receives input signals indicative of various system
operating conditions and processes same according to logic rules to issue command output
signals to one or more system actuators are known in the prior art, as may be seen by
reference to U.S. Pat. Nos. 4,361,060; 4,593,580; 4,595,986; 4,850,236; 5,435,212;
5,582,069; 5,582,558; 5,620,392; 5,651,292; 5,679,096; 5,682,790 and 5,735,771; the
disclosures of which are incorporated herein by reference in their entirety.
Compound manually shifted mechanical transmissions of the range, splitter
and/or combined range/splitter type are in wide use in heavy-duty vehicles and are well
known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,754,665; 5,272,929;
5,370,013 and 5,390,561, 5,546,823; 5,609,062 and 5,642,643, the disclosures of which are
incorporated herein by reference in their entirety. Typically, such transmissions include a
main section shifted directly or remotely by a manual shift lever and one or more auxiliary
sections connected in series therewith. The auxiliary sections most often were shifted by a
slave actuator, usually pneumatically, hydraulically, mechanically and/or electrically
operated, in response to manual operation of one or more master switches. Shift controls for
such systems may be seen by reference to U.S. Pat. Nos. 4,455,883: 4,550,627; 4,S99,607;
4,920,815; 4,974,468; 5,000,060; 5,272,931; 5,281,902; 5,222,404; and 6,463,823, the
disclosures of which are incorporated herein by reference in their entirety. U.S. Pat. No.
4,527,446, the disclosure of which is incorporated herein by reference in its entirety,
discloses a fully automated, blocked-type transmission wherein the main section is
automatically shifted to main section neutral during each shift.
PTO systems for vehicle drivetrains may be seen by reference to U.S. Pat. Nos.
5,070,982 and 6,497,313, and typically include a PTO synchronizing clutch, or hot-shift
clutch, to synchronize and engage PTO input and output components, such as shafts, gears,
or clutch members. Some systems include a PTO where some components may be damaged
if operated during maximum engine rotational speed. In these applications, when the engine
is operated at an undesirable speed, the PTO clutch may be used for disengaging the PTO
driven device until the engine speed is reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring now to the drawings, illustrative embodiments are shown in detail.
Although the drawings represent some embodiments, the drawings are not necessarily to
scale and certain features may be exaggerated, removed, or partially sectioned to better
illustrate and explain the present invention. Further, the embodiments set forth herein are
not intended to be exhaustive or otherwise limit or restrict the claims to the precise forms
and configurations shown in the drawings and disclosed in the following detailed description.
FIG. 1 is a schematic illustration of an ECU-assisted, non-synchronized
compound mechanical drivetrain system according to an embodiment.
FIG. 2 is a schematic illustration of the structure of the compound mechanical
transmission of FIG. 1.
FIG. 3 is a schematic illustration, in flow chart format, of a control system,
according to an embodiment.
DETAILED DESCRIPTION
FIG. 1 illustrates a computer-assisted (i.e., microprocessor-based, controller-
assisted) vehicular compound mechanical drivetrain system 10. The drivetrain system 10
may be of the type commonly utilized in heavy-duty vehicles, such as the conventional
tractors of tractor/semi-trailer vehicles, and includes an engine, typically a diesel engine, a
master friction clutch contained within a clutch housing, a multiple-speed compound
transmission and a drive axle assembly (not shown).
In the exemplary embodiment illustrated, system 10 includes an engine 12, a
transmission clutch 14, and a transmission 16. The transmission 16 includes an output shaft
20 drivingly coupled to a vehicle drive shaft by a universal joint for driving the drive axle
assembly. The transmission 16 is housed within a transmission housing to which is directly
mounted the shift tower of the shift lever assembly 28. The present system is equally
applicable to remotely mounted shift levers, as are used in cab-over-engine types of vehicles.
In the exemplary embodiment illustrated, the main clutch 14 is a centrifugal
clutch that engages the engine 12 for rotation with the transmission 16 at above about 1200
rotations per minute (RPM). While system 10 is illustrated with a manual shift lever and
centrifugal clutch, this is for illustrative purposes only and not intended to be limiting.
Transmission 16, by way of example, may be of the type well known in the prior art and sold
by the assignee of this application, EATON CORPORATION, under the trademarks "Super-
10" and "Lightning", and may be seen in greater detail by reference to U.S. Pat. Nos.:
4,754,665; 5,370,013; 5,974,354; 5,974,906; and 6,015,366, the disclosures of which are
incorporated herein by reference.
Typically, the shift lever assembly 28 will include a shift finger or the like
(not shown) extending downwardly into a shifting mechanism (not shown), such as a
multiple-rail shift bar housing assembly or a single shift shaft assembly, as is well known in
the prior art and as is illustrated in aforementioned U.S. Pat. Nos. 4,455,883; 4,550,627;
4,920,815 and 5,272.931. Collectively, the main section 16A the shift lever assembly 28
comprisca shifting system
Shifting of transmission 16, comprising non-synchronized main section 16A
coupled in series to auxiliary section 16B, is semi-automatically implemented/assisted by the
vehicular transmission system 10. Main section 16A includes an input shaft 26. which is
operatively coupled to the drive or crank shaft 24 of the vehicle engine 12 by master clutch
14, and output shaft 20 of auxiliary section 16B is operatively coupled, commonly by means
of a drive shaft, to the drive wheels of the vehicle. The auxiliary section 16B is a splitter type,
preferably a combined range-and-splitter type, as illustrated in U.S. Pat. Nos. 4,754,665 and
5,390,561.
The change-gear ratios available from main transmission section 16 are
manually selectable by manually positioning the shift lever 28A according to the shift pattern
prescribed to engage the particular desired gear ratio.
The system may include sensors 30 (for sensing engine rotational speed (ES)),
32 (for sensing input shaft rotational speed (IS)), and 34 (for sensing output shaft rotational
speed (OS)), and providing signals indicative thereof. As is known, with the clutch 14 (i.e.,
no slip) engaged and the transmission engaged in a known gear ratio, ES=IS=OS*GR (see
U.S. Pat. No. 4,361,060). Accordingly, if clutch 14 is engaged, engine speed and input shaft
speed may be considered as equal. Input shaft speed sensor 32 may be eliminated and engine
speed (ES), as sensed by a sensor or over a data link (DL), substituted therefor. As is also
known, the rotational speed (OS) of the output shaft 20 is indicative of vehicle ground speed.
Engine 12 is electronically controlled, including an electronic controller 36
communicating over an electronic data link (DL) operating under an industry standard
protocol such as SAE J-1922, SAE J-1939, ISO 11898 or the like. Throttle position
(operator demand) is a desirable parameter for selecting shifting points and in other control
logic. A separate throttle position sensor (not shown) may be provided or throttle position
(THL) may be sensed from the data link. Gross engine torque (TEG) and base engine
friction torque (TBEF) also are available on the data link.
With reference to FIGS. 1 and 2, the system 10 includes a control unit or ECU
48, such as a microprocessor-based control unit of the type illustrated in U.S. Pat. Nos.
4,595,986; 4,361,056 and 5,335,566, the disclosures of which are incorporated herein by
reference, for receiving input signals 68 and processing same according to predetermined
logic rules to issue command output signals 70 to system actuators, such as the splitter
section actuator 46, the engine controller 36, the range shift actuator and/or a display. A
separate system controller may be utilized, or the engine electronic controller 36,
communicating over an electronic data link DL, may be utilized during shifting, as desired.
In the exemplary embodiment illustrated, the throttle position (operator demand) is
communicated to the ECU 48 via the data link DL and the engine electronic controller 36
while the ECU 48 sends commands to the data link DL and the engine electronic controller
36. Specifically, the ECU 48 is operable to detect the speeds of multiple rotational
components within the system 10 while controlling the speed of these components (such as
the shaft 24 of the vehicle engine 12, the input shaft 26 of the transmission 16, the PTO input
member 152, the PTO output member 154, the PTO output shaft 156, the PTO driven device
160, or the output shaft 20 of the transmission 16).
A sensor (not shown) provides a signal (CL) indicative of clutch-engaged or
disengaged condition. The condition of the clutch also may be determined by comparing
engine 12 speed to input shaft 26 speed if both signals are available. An auxiliary section
actuator 44 including a range shift actuator and a splitter actuator 46 is provided for
operating the range clutch (shown as 130 in FIG. 2) and the splitter section clutch (shown as
88 in FIG. 2) in accordance with command output signals from ECU 48.
As shown in aforementioned U.S. Pat. Nos. 5,651,292 and 5,661,998, the
splitter actuator 46 may be a three-position device, allowing a selectable and maintainable
splitter-section-neutral. Alternatively, a "pseudo" splitter-neutral may be provided by de-
energizing the splitter actuator when the splitter clutch is in an intermediate, non-engaged
position.
The structure of the 10-forward-speed combined range-and-splitter-type
synchronized transmission 16 is schematically illustrated in FIG. 2. Transmissions of this
general type are disclosed in aforementioned U.S. Pat. Nos. 5,000,060; 5,370,013 and
5,390,561.
Transmission 16 includes a non-synchronized main section 16A and an
auxiliary section 16B, both contained within a housing including a forward end wall 16C,
which may be defined by the clutch housing, and a rearward end wall 16D, but (in this
particular embodiment) not an intermediate wall.
Input shaft 26 carries input gear 76 fixed for rotation therewith. The mainshaft
82 carries a splined mainshaft first jaw clutch 84 and a second jaw clutch 86, and the
mainshaft splitter clutch 88. Shift forks (not shown) are provided for axially moving the
clutches 84 and 86 relative to the mainshaft 82 and are controlled by shift lever 28A acting
on the shift assembly 28, as is known. Mainshaft 82 is independently rotatable relative to
input shaft 26 and output shaft 20 and preferably is free for limited radial movement relative
thereto.
The main section 16A includes two substantially identical main section
countershaft assemblies 94, each comprising a main section countershaft 96 carrying
countershaft gears 98, 102, 104 and 106 fixed thereto. Gear pairs 98, 102, 104 and 106 are
constantly meshed with input gear 76. mainshaft gears 108 and 110 and an idler gear (not
shown), which is meshed with reverse mainshaft gear 112, respectively. At least one of the
countershafts 96 is provided for driving a PTO or the like.
The auxiliary section 16B of transmission 16 includes a splitter section 16E
and a range section 16F. Auxiliary section 16B includes two substantially identical auxiliary
countershaft assemblies 114, each including an auxiliary countershaft 116 carrying auxiliary
countershaft gears 118, 120 and 122 for rotation therewith. Auxiliary countershaft gear pairs
118, 120 and 122 are constantly meshed with splitter gear 124, splitter/range gear 126 and
range gear 128, respectively. Splitter clutch 88 is fixed to mainshaft 82 for selectively
clutching either gear 124 or 126 thereto, while synchronized range clutch 130 is fixed to
output shaft 20 for selectively clutching either gear 126 or gear 128 thereto.
The splitter jaw clutch 88 is a double-sided, non-synchronized clutch
assembly which may be selectively positioned in the rightwardmost or leftwardmost
positions for engaging either gear 126 or gear 124, respectively, to the mainshaft 82 or to an
intermediate position wherein neither gear 124 nor gear 126 is clutched to the main shaft.
Splitter jaw clutch 88 is axially positioned by means of a shift fork 132 controlled by a three-
position actuator, such as a piston actuator, which is responsive to a driver selection switch
such as a button or the like on the shift knob, as is known in the prior art and to control
signals from ECU 48 (see U.S. Pat. No. 5,661,998). Two-position synchronized range clutch
assembly 130 is a two-position clutch which may be selectively positioned in either the
rightwardmost or leftwardmost positions thereof for selectively clutching either gear 128 or
126, respectively, to output shaft 20. Clutch assembly 130 is positioned by means of a shift
fork (not shown) operated by means of a two-position piston device. Either piston actuator
may be replaced by a functionally equivalent actuator, such as a ball screw mechanism, ball
ramp mechanism or the like.
By selectively axially positioning both the splitter clutch 88 and the range
clutch 130 in the forward and rearward axial positions thereof, four distinct ratios of
mainshaft rotation to output shaft rotation may be provided. Accordingly, auxiliary
transmission section 16B is a three-layer auxiliary section of the combined range and splitter
type providing four selectable speeds or drive ratios between the input (mainshaft 82) and
output (output shaft 20) thereof. The main section 16A provides a reverse and three
potentially selectable forward speeds. However, one of the selectable main section forward
gear ratios, the low-speed gear ratios associated with mainshaft gear 110, is not utilized in
the high range. Thus, transmission 16 is properly designated as a "(2+1).times.(2.times.2)"
type transmission providing nine or ten selectable forward speeds, depending upon the
desirability and practicality of splitting the low gear ratio.
Preferably, splitter shifting of transmission 16 is accomplished responsive to
initiation by a vehicle operator-actuated splitter button or the like, usually a button located at
a knob of the shift lever 28A, while operation of the range clutch shifting assembly is an
automatic response to movement of the gear shift lever 28A between the central and
rightwardmost legs of the shift pattern, as illustrated in FIG. 2. Alternatively, splitter shifting
may be automated (see e.g., for example, U.S. Pat. No. 5,435,212). Range shift devices of
this general type are known in the prior art and may be seen by way of example in
aforementioned U.S. Pat. Nos. 3,429.202; 4,455,883; 4,561,325, 4,663,725, and 6,463,823.
As best seen in the exemplary embodiment of FIG. 2, an inertia brake 140 is
coupled to one of the countershafts 96 and the housing 16C. The inertia brake 140 may be
used to selectively retard the rotational speed of countershafts 96 and input shaft 26 for a hill
holding function and/or a synchronizing function during shifting.
Inertia brakes are typically relatively low-capacity friction devices operated
automatically. In an embodiment that includes a manually actuated clutch, overtravel of the
clutch pedal may be sensed and used as an input for operation of an inertia brake, such as the
inertia brake 140, to synchronize the gearset to be engaged.
In the embodiment illustrated, one of the countershafts 96 is also coupled to a
PTO 150. The PTO 150 includes a PTO input member 152, a PTO output member 154, a
PTO output shaft 156 having an axis A-A, a PTO engaging device 158, and a PTO driven
device 160. In the embodiment illustrated, the PTO output member 154 is a jaw clutch,
splined to the PTO output shaft 156 and axially moveable by the PTO engaging device 158
relative to the PTO output shaft 156 in order to mesh the PTO output member 154 with the
PTO input member 152, similar to clutches 84 and 86 above. That is, the PTO input member
152 and the PTO output member 154 are selectively engageable and disengagable to provide
torque from system 10 to the PTO 150, as desired. The ECU 48 also includes a PTO output
shaft speed sensor 162 for detecting the speed of the PTO output shaft 156. While the PTO
150 and the inertia brake 140 are illustrated adjacent one another at one end of a countershaft
96, the PTO 150 and the inertia brake 140 may be coupled to the system 10 at other locations.
The ECU 48 preferably monitors parameters of the system 10, or
representative values of these parameters, such as the engine 12 speed sensor 30, the PTO
output shaft speed sensor 162, the countershaft 96 rotational speed. The ECU may also
provide a command for engagement of the PTO output member 154 with the PTO input
member 152, and for actuation of the inertia brake 140. In the embodiment illustrated, the
ECU 48 includes the logic for engaging the PTO 150 for rotation with the system 10, via
engaging device 158, although this logic may be included in other suitable controllers.
FIG. 3 illustrates a flow chart of a method for protecting the PTO 150 and/or
the PTO driven device 160 from overspeed damage. That is, excessive rotational speeds of
the PTO 150 and/or the PTO driven device 160 may result in undesirable damage. In
applications where the engine 12 or other driving device is capable of transmitting an
excessive rotational speed to the PTO 150 and/or the PTO driven device 160, the ECU 48
may operate as illustrated in the exemplary embodiment described below.
An exemplary embodiment of a method of PTO overspeed protection is as
follows. In Step 300, the ECU 48 will detect whether the PTO 150 is engaged by detecting
whether the PTO output shaft 156 is rotating. In Step 310, the ECU will determine if the
PTO 150 rotational speed is greater than a predetermined desired overspeed value. That is,
the ECU 48 will detect whether the engine 12 has reached or is expected to reach a speed
that would result in the PTO being rotated at a speed that is above a desired overspeed value.
In the embodiment illustrated, the desired overspeed value is a speed that is expected to
result in damage to either the PTO 150 or the PTO driven device 160. Collectively, the
portion of the ECU 48 that performs the functions described herein, the PTO engaging
device 158, and the sensors (specifically the engine rotational speed sensor 30 and/or the
PTO output shaft speed sensor 162) described herein comprise a PTO overspeed protection
system.
If the determination of Step 300 is positive, the operation proceeds to Step 310.
If the determination of Step 300 is negative, the operation returns to Step 300.
In Step 310, a speed value representative of the engine speed value is detected.
This speed value may be the rotational speed of any rotational component, including the
shaft 24 of the vehicle engine 12, the input shaft 26 of the transmission 16, the PTO input
member 152, the PTO output member 154, the PTO output shaft 156, the PTO driven device
160, or the output shaft 20 of the transmission 16.
In Step 320, the speed value is maintained below the overspeed value. That is,
the speed value that is monitored, for example, either the PTO input member 152 speed, or
the engine 12 speed, is compared to a value that represents an undesired value. If the speed
value is expected to exceed the overspeed value, the engine 12 rotational speed is reduced by
the ECU 48. In one embodiment, a J1939 data link that controls engine speed is used to
limit fuel to the engine 12 via the engine electronic controller 36 in order to control the
detected speed value. Additionally, the J1939 link may send an engine speed limit command
to the engine electronic controller 36 where the engine electronic controller 36 may prevent
an engine speed above a value of about the overspeed value and the engine speed limit
command will override an operator's manual command for increased engine speed. Further,
the ECU 48 may override any manual input (such as a manual operator demand for throttle
input within the engine electronic controller 36).
Additionally, the ECU 48 may monitor the speed value and reduce the
rotational speed of a PTO component when the speed value is within a predetermined
tolerance of the overspeed value. As an illustrative example, the overspeed value may be
2000 rotations per minute (rpm) and the predetermined tolerance may be 100 rpm, resulting
in the ECU 48 taking actions to reduce the speed value when the speed value increases above
1900 rpm.
In the exemplary embodiments described herein, the ECU 48 is programmed
with a value for engine 12 rotational speed that results in operation of the PTO 150 at or
above a desired maximum operating speed., although the ECU 48 may also monitor the PTO
output shaft speed sensor 162 for an input representative of the rotational speed of the PTO
output shaft 156. Additionally, the ECU 48 may be programmed with differing engine 12
rotational speeds that correlate to differing desired maximum operating speeds, such as a
maximum PTO engaging section speed (to protect members 152, 154, and shaft 156 and
related bearings and seals), and a maximum PTO driven device 160 rotational speed to
protect a selected PTO driven device 160. Further, for driveline systems that may have more
than one PTO driven device 160, the ECU 48 may have an input for determining which PTO
driven device is being rotated and disengage the PTO(s) 150 when a corresponding
undesirable excessive speed is reached.
The overspeed protection method described herein provides the system 10
with an automatic overspeed protection while not relying upon an operator to limit PTO
speed. Additionally, the overspeed protection method prevents the operator from damaging
the PTO due to inattention or misuse that may result from excessive PTO speeds.
Although the steps of the operating the system 10 are listed in a preferred
order, the steps may be performed in differing orders or combined such that one operation
may perform multiple steps. Furthermore, a step or steps may be initiated before another
step or steps are completed, or a step or steps may be initiated and completed after initiation
and before completion of (during the performance of) other steps.
The preceding description has been presented only to illustrate and describe
exemplary embodiments of the methods and systems. It is not intended to be exhaustive or
to limit the invention to any precise form disclosed. It will be understood by those skilled in
the art that various changes may be made and equivalents may be substituted for elements
thereof without departing from the scope of the invention. In addition, many modifications
may be made to adapt a particular situation or material to the teachings of the invention
without departing from the essential scope. Therefore, it is intended that the invention not be
limited to the particular embodiment disclosed as the best mode contemplated for carrying
out this invention, but that the invention will include all embodiments falling within the
scope of the claims. The invention may be practiced otherwise than is specifically explained
and illustrated without departing from its spirit or scope. The scope of the invention is
limited solely by the following claims.
WE CLAIM:
1. A powertrain system (10) comprising:
a multispeed transmission (16) defining a plurality of speed ratios (102/108,
104/110);
a power take off (PTO) (150) having a PTO input member (152) selectively
rotationally engaged with a PTO output member (154);
a detection system (162) for detecting a value representative of a speed of the
PTO output member (154); and
a controller (36) in communication with the detection system (162) and having an
output for overriding a manual input to increase the rotational speed of the PTO output
member (154) above a predetermined overspeed value.
2. The system (10) of claim 1, wherein the controller (36) selectively
communicates a command to reduce the rotational speed of at least a portion of the
PTO (150).
3. The system (10) of claim 1, wherein the detection system (162) detects a
value representative of a rotational speed of at least one of the PTO input member
(152) and the PTO output member (154).
4. The system (10) of claim 1, wherein at least a portion of the PTO input
member (152) is selectively engaged with at least a portion of the PTO output member
(154).
5. The system (10) of claim 4, further comprising a PTO clutch (154,158) for
selectively disengaging the PTO input member (152) with the PTO output member
(154).
6. The system (10) of claim 1, further comprising an output shaft (20) for
transmitting torque from the transmission (16) to drive wheels of a vehicle, wherein
torque transmitted through the PTO (150) cannot be transmitted to the drive wheels.
7. The system (10) of claim 1, further comprising an engine electronic
controller (36) for, at least in part, limiting the speed of an engine (12).
8. A method of operating a drivetrain (10), the drivetrain (10) including a PTO
(150) and a transmission (16) having multiple speed ratios (102/108, 104/110), the
PTO (150) including a PTO output member (154) and a PTO input member (152), the
method comprising:
monitoring a speed value representative of a rotational speed of a PTO component
(160);
comparing the speed value to a preselected PTO overspeed value;
reducing the rotational speed of the PTO component (160) when the speed value
is within a predetermined tolerance of the overspeed value; and
overriding a manual command to increase the rotational speed of the PTO
component above the preselected PTO overspeed value.
9. The method of claim 8, wherein reducing the rotational speed of the PTO
component when the speed value is within a predetermined tolerance of the overspeed
value includes limiting the volumetric flow of fuel to an engine.
10. The method of claim 8, wherein overriding a manual command to increase
the rotational speed of the PTO component above the preselected PTO overspeed
value includes limiting the volumetric flow of fuel to an engine.
11. The method of claim 8, wherein reducing the rotational speed of the PTO
component when the speed value is within a predetermined tolerance of the overspeed
value does not include rotationally disengaging the PTO output member (154) from
the PTO input member (152).
12. The method of claim S, further comprising transmitting torque from the
transmission (16) to drive wheels of a vehicle, wherein torque transmitted through the
PTO (150) cannot be transmitted to the drive wheels.
13. The method of claim 8, wherein reducing the rotational speed of the PTO
component when the speed value is within a predetermined tolerance of the overspeed
value includes stopping at least one of the PTO output member (154) and the PTO
input member (152).
14. The method of claim 8, wherein a PTO clutch (154, 158) will selectively
disengaging the PTO input member (152) and the PTO output member (154), and
wherein maintaining the rotational speed of the PTO component (160) below the
preselected PTO overspeed value does not include rotationally disengaging the PTO
output member (154) from the PTO input member (152).
15. A method of operating a drivetrain (10), the drivetrain (10) including a
multispeed transmission (16), an engine (12), and a main clutch (14) operably
interposed between the engine (12) and the transmission (16), the method comprising:
monitoring a speed value representative of a rotational speed of a PTO component
(160);
comparing the speed value to a preselected PTO overspeed value;
maintaining the rotational speed of the PTO component (160) below the
preselected PTO overspeed value; and
overriding a manual command to increase the rotational speed of the PTO
component (160) above the preselected PTO overspeed value.
16. The method of claim 15, further comprising maintaining the rotational speed
of the PTO component (160) below the preselected PTO overspeed value by, at least
in part, limiting the volumetric flow of fuel to the engine (12).
17. The method of claim 15, wherein a PTO clutch (154, 158) will selectively
disengaging the PTO input member (152) and the PTO output member (154), and
wherein maintaining the rotational speed of the PTO component (160) below the
preselected PTO overspeed value does not include rotationally disengaging the PTO
output member (154) from the PTO input member (152).
18. The method of claim 15, further comprising transmitting torque from the
transmission (16) to drive wheels of a vehicle, wherein torque transmitted through the
PTO (150) cannot be transmitted to the drive wheels.
19. The method of claim 15, wherein overriding a manual command to increase
the rotational speed of the PTO component (160) above the preselected PTO
overspeed value includes limiting the volumetric flow of fuel to an engine (12).
20. The method of claim 15, wherein mamtaining the rotational speed of the
PTO component (160) below the preselected PTO overspeed value includes stopping
one of the PTO output member (154) and the PTO input member (152).

An exemplary embodiment includes a method of operating
a drivetrain. The drivetrain includes a PTO and a
transmission having multiple speed ratios. The PTO
includes a PTO output member and a PTO input member.
The method includes monitoring a speed value
representative of a rotational speed of a PTO
component, comparing the speed value to a preselected
PTO overspeed value, reducing the rotational speed of
the PTO component, and overriding a manual command to
increase the rotational speed of the PTO component
above the preselected PTO overspeed value.