Note: Descriptions are shown in the official language in which they were submitted.
THRESHOLD OPERAT~ON OF A VEHICLE TRANSMISSION
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BACKGROUND OF TE]E INVENTION
This invention relates to a system for controlling
the operation of a vehicle's ~ransmission a~ a threshold
level of the vehicle's engine outputO More specifically,
the invention relates to a system for delaying the operation
of a vehicle's transmission until the engine output speed
has attained a predetermined level.
Many modern day vehicles are fully capable of
utilizing the vehicle engine for providing both auxiliary
~unctions and vehicle drive. Such vehicles can include, as
examples, aerial lift trucks, grade trimmers, fork lif~s,
dozers, trenchers and front end loaders. In the control of
such vehicles, the operator sets engine speed at a
predetermined governed value for powering all functions of
the machine~ Thus, when the bucket of a front end loader is
to be operated, for example, he levers fo~ controlling the
orientation of the bucket are operated and, when the machine
is to be driven in the forward ox reverse direction, the
forwaxd and reverse drive pedals are opera~ed to in turn
operate ~he transmission of the vehicle~ Such an aperation
means that when the vehicle is standing still and the bucket
is being operated as one of the auxiliary functions of the
vehicle, the vehicle's engine is quite likely supplying
excessive horsepower and, thereforer consuming excessive
fuel.
The present invention instead dr~ves the transmis-
sion of the vehicle as a func~ion of engine speed so that a
range of engine speed is provided for powering the auxiliary
functions of the vehicle before the additional power neces-
sary to drive the vehicle is provided. Thus, the present
invention allows the engine to run fast enough for supplying
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the auxiliary functions wi~hout providi.ng transmission output. At higher
engine speeds, the transmission output adapts to engine rpm in a load con-
trol manner; that is, if the engi.ne speed drops because of excess load, the
transmission "downshifts". This "downshift" also occurs as a result of
throttle reduction.
SI~MARY OF: TtIF, INVENTION
These advantages are obtained from the present invention in which
a sensor senses the output of the engine, a controller which is connected
to the sensor controls the transmission output of the vehicle dependent
upon the engine output, and a threshold arrangement is connected to the
controller for preventing transmission output until the engine output has
attained a predetermined level.
More particularly, the present invention provides a system for
controlling a transmission of a vehicle dependent upon engine output, said
engine being adapted to be driven in a first speed range of operation and
also to propel said vehicle by said transmission during a second higher
speed range of operation, the transmission having an input connected to
an output of the engine and having an output, the system comprising: speed
sensing means adapted to sense the output speed of the engine; control
:: 20 means connected to said sensing means and adapted to control said transmis-
sion output solely dependent upon said engine output; and, threshold means
connected to said control means for inhibiting transmission output in the
first range of engine operation until said engine output has attained a
predetermined reference level, and said control means providing propor-
tional control of said transmission relative solely to said engine output
speed once said engine output has attained the predetermined reference
: level.
BRIEF DESCRIPTI ON OF THE DRAWINGS
These and other features and advantages will become apparent :Erom
3Q a detailed consideration of the invention when taken in conj~mction with
the drawings in which:
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Figure l shows one type of machine on which the present system can
be used;
Figure 2 shows the system according to the present invention; and,
Figure 3 is a graph showing swash plate angle of the pump in the
hydrostatic transmission shown in Figure 2 as a function of engine output.
DETAILED DESCRIPTION
In Figure l, front end loader lO comprises bucket ll, operator's
cab 12 and engine 13. Inside operator's cab 12 are the various levers and
pedals for controlling the forward and reverse progress of vehicle lO and
the orientation and work performed by bucket ll. Since vehicle lO is of
ordinary design, the details of it will not be specifi-
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cally shown herein. However, the control system for
propelling vehicle lO is shown in detail in Figure 2.
As shown in Figure 2, vehicle lO has its engine 13
controlled by lever 14 (which alternatively may be a foot
pedal3 connected to engine 13 by shaft 15. Lever 14
controls the amount of fuel supplied to engine 13 and
therefore controls the rotational speed of engine output 160
Output 16 is ~hen connected to hydrostatic transmission 20
in the form of hydraulic pump 21 and hydraulic motor 22
interconnected by hydraulic lines 23 and 24. Hydraulic
motor 22 then has an output shaft 25 connected to the drive
train of the vehicle for propulsion.
The system according to the present invention for
providin~ the operation described herein comprises pulse
pickup unit 30 sensing the speed of rotation of disc 31
affixed to engine output 16 and providing a series of output
pulses the frequency of which is dependent upon this speed.
Typically, disc 31 has a plur~lity of teeth which interact
with a magnetic field established by pulse plckup unit 30 to
induce the pulses which are supplied to frequency-to-voltage
converter 32. Pulse pickup unit 30 ma~ be an SBlOOA
manufactured by Honeywell Inc. Frequency~to-voltage conver-
ter 32 converts the frequency of the pulses received from
pulse pickup unit 30 into a voltage proportional to that
frequency and supplies that voltage to the positive input of
amplifier 33~ The output of ampliier 33 is connected
through resistor 34 to one input of summing junction 36.
The function of summing junction 36 and resistor 34 is
connected to ground through diode 35 and resistor 41. The
other input to summing junction 36 is a reference input
which establishes a threshold level below which output shaft
25 of hydros~atic-transmission 20 will not rotate and above~
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which the revolutions per minute of output shaft 25 isgoverned by the output o~ engine 130 The output from
summing junction 36 is connected to the negative input of
amplifier 33~ Frequency-to-voltage converter 32 and ampli~
fier 33 may be a package manufactured by ~oneywell Inc.
under the number W883A. ~esistor 41 and diode 35 are
included in the feedback circuit of amplifier 33 for
characterizing the output of amplifier 33 as will be
discussed with respect to Figure 3.
The output from amplifier 33 is connected through
forward/reverse switch 37 the output of which is then
connected to valve 38. Yalve 38 may be a V7058A
manufactured by Honeywell Inc. and receives the electrical
signal from forward/reverse switch 37 to provide a hydraulic
output for controlling the swash plate of pump 21 and,
therefore~ the output ~hereof. Forward/reverse switch 37
controls the polarity of the signal supplied to valve 38 for
driving vehicle 10 in a forward or a reverse direction.
As described above~ the reference input to summing
juncti~n ~6 provides a threshold level for operation of
hydrostatic transmission 20. Figure 3 is a graph showing
the operation of hydrostatic transmission ~0 as a unction
of engine output rpm~ The idle point is the lowest setting
of engine 13 providing the lowest output 160 As the engine
is throttled upward, output 16 increases and, as a result,
~he pulses from pulse pickup unit 30 increase in frequency.
This increased frequency results in an increased voltage to
the positive input of amplifier 33. However, the output
from amplifier 33 and forward/reverse switch 37 will not
begin to change until the voltage to the positive input of
amplifier 33 exceeds the input to the negative input termi-
nal which is a function of the reference setting. Once this
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reference setting has been attained by the output from
frequency-to-voltage converter 32, the angle of the swash
plate of pump 21 will follow curve A of Figure 3 for the
forward direction and curve B for the reverse direction.
Curves C and D are provided by the resistor 41 and diode 35
circuit to characterize curves A and B.
It can be seen from Figures 2 and 3 that as the
loading on the machine increases, the output 16 of engine 33
reduces which will proportionally reduce the pump swash
plate angle and reduce the speed of rotation of output shaft
25 from hydrostatic transmission ~0 resulting in a
"downshift". If the forward or reverse progress of vehicle
10 is to be maintained, throttle 14 must be increased to
accommodate the increased load up to the point where engine
13 is at its horsepower limit. When vehicle 10 is at a
standstill during a time when the~auxiliary functions of the
ve~hicle are being utilized, engine speed need only be
operated between the idle and the reference point as shown
in Figure 3 instead of the higher setting at which present
prior art systems are operated. This operation results in
an eficient and economical utilization of engine output.
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