Note: Descriptions are shown in the official language in which they were submitted.
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This is a divisional application of Canadian
application No. 354,890 filed on June 26, 1980.
The invention of the present divisional appli-
cation relates to a control system for controlling a power
transmission device of work vehicles such as wheeled loaders,
in which the driving direction is reversed at short intervals
during operation.
A vehicle operatorhas a number of tasks to per-
form at the same time: steering the vehicle, shifting the
vehicle gearbox, and operating the implement, e.g. lifting and
tipping a bucket.
The purpose of the invention is primarily to make
these tasks easier for the operator of such a vehicle by
automatically controlling the operation of the gearbox.
According to the present invention, there is
provided a control system for controlling a power trans-
mission device arranged between a driving engine and an out-
put drive axle of a vehicle and comprising a torque converter
and a mechanical step gearbox, the gearbox having at least
two drive gears for altering the torque transmitted to the
drive axle, between which gears the shifting sequence can be
controlled automatically dependent on engine parameters such
as load and rotational speed, and having a reversing gear
device for changing the rotational direction of the drive
axle, the reversing of which gear device is controlled by a
directional selector control which is manually actuated by
the vehicle operator. The control system of the invention
is characterized in that it comprises an electrical control
device having drive gear control means and reversing gear
control mean~, which ar~ joined to gear couplings and/or
gear brakes operable by elec~rical control and associated
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with the drive gears or the reversing gear for controlling
the rotational speed and the direction of the drive axle.
A sensor for the rotational speed of the drive axle or the
speed of the vehicle is connected to a comparator which is
operable to compare the actual speed value from the sensor
with a predetermined speed limit value stored in a memory
and, when the actual value is less than the limit value,
to send a go-ahead signal to the drive gear control means.
A forced downshift signal sender is connected to the drive
gear control means and is operable upon manual actuation
by the operator to produce a forced downshift signal which,
if the go-ahead signal is present, causes the drive gear con-
trol means to engage the lowest drive gear. The directional
selector control is connected to the control device to supply
it with a directional command value signal, and when the
command value signal is changed to indicate the opposite
direction, a reverse signal is sent to the reversing gear
control means for changing over the reversing gear and at
the same time to the drive gear control means for inhibiting
the forced downshift function and engaging the next lowest
drive gear.
The electrical control device preferably
includes a microcomputer.
The reversing gear arrangement can either
comprise a separate reversing gear, with the gearbox
comprising a number of drive gears which can be used
independently of the driving direction, or separate sets
of driving gears for forward and reverse. In the latter
case, the gear ratios for reverse driving can be selected
independently of the gears for driving forward.
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First gear is used p;imarily for bucket filling,
and the filling work can be done more quickly with operator-
actuated downshifting than if the gearbox must wait for
an automatically controlled downshift signal. In this
case, it is suitable to block actuation of the forced
downshift signal sender when the vehicle sp~ed is greater
than a certain maximum speed, since downshifting to first
gear would then cause a powerful retardation. This
maximum speed can suitably be selected so as to permit
downshifting only withinthe range of second gear.
A practical arrangement for a vehicle such as
a wheeled loader is to arrange the directional selector
control and the forced downshift signal sender as a multi-
function control next to the steering wheel, so that the
operator can operate the steering wheel, directional
selector control and forced downshift signal sender with
one hand. The operator then has the other hand free to
operate the bucket and to help with the controls to speed
up the reversing if necessary.
Further advantages and features of the invention
will become apparent from the following detailed description
of a preferred embodiment as illustrated by way of example
in the accompanying drawings, in which:
Fig. 1 shows in block diagram form a power
transmission device for a wheeled loader.
Fig. 2 shows in block diagram form a control
device for the gearbox of the power transmission device.
Fig. 3 shows in block diagram form a control
device equipped with a microcomputer.
Fig. 1 shows a driving engine M which drives
a hydrodynamic torqueconverter C, which in turn drives
a mechanical gearbox T which has four driving gears and
one reversing gear, with the aid of which the drive gears
can be used to drive the output axle A, and thus the
vehicle, either forwards or backwards. The shifting in
the gearbox is controlled electrically by means of an
electrical control device 1. A driving direction control
is connected to the control device 1.
Fig. 2 indicates with a dashed rectangle the
electrical control device 1 for controlling the gear~ox
T of the loader. For this purpose, the-control device
has drive gear control means 2 wh~ch are connected, via
a first output 3, with solenoids or the like for
operating couplings or brakes 4 associated with the gear-
box driving gears. The control device 1 also comprises
reversing gear control means S which are connected, via a
second output 6, to solenoids or the like for operating the
couplings and brakes 7 a~sociated with the gearbox reversing
gear.
A first input 8 of the control device 1 is
connected to a sensor 9 for the speed of the loader. The
sensor 9 can, for example, sense the r.p.m. of the output
axle A (Fig. 1). A second input 10 of the control device
is connected t~ a forced downshift signal sender 11,
suitably made as a part of a multifunction control, for
example in the fonm of a ~elector lever 12 located next tothe
~teering wheel. A third input 13 is connected to an indi-
cator 14 for the desired driving direction. Thi8 indicator
14 i8 also suitable included in the multifunction control
constructed as a directional selector lever 12. A fourth
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input 15 is connected to a sensor 16 for the driving direc-
tion of the vehicle. Also sensor 16 can sense the output
axle A and can possibly be combined with sensor 9. A
fifth input 17 in the control ~evice 1 is connected to a
number of sensors 18 for various engine parameters such as
engine r.p.m. and load.
The control device 1 contains a first-comparator
19, in which the directional command value from the 'indi-
cator 14 is compared with the directional actual value from
the sensor 16. When the command signal at input 13 is
changed to the opposite direction to the actual value signal
at input 15, the first comparator 19 sends a reverse signal
on a line 20 to the driving gear control means 2. A line
21 branches off from the line 20 and leads to the reversing
gear means 5.
The actual speed value from the sensor 9 at
input 8 is fed over line 25 to a second comparator 26,
which also has an input connected to a first memory 27
in which a predetermined blocking or limiting speed is
stored, for example 25 km/h. The second comparator 26 is
adapted so that when the speed value in the line 25 is
less than the blocking speed value, it sends a reverse go-
ahead signal via a wire 2~ to the reversing gear control
means 2.
When the driving gear control means 2 receive
the reverse signal on the line 20, theyactuate the down-
~hifting to third gear from fourth gear, if it i~ engaged.
Otherwise, no gear shifting is actuated, i.e. the engaged
gear is maintained.
When the rever~ing gear control means ~ receive
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the reverse signal on line 21, the means send a signal,
via the output 6, to the reversing gear coupling 7 for
shifting the reversing gear, provided that there is a go-
ahead signal in line 2~. If this is not the case then no
reversal of direction takes place. For this purpose, the
reversing gear control means 5 are provided with logic
circuits.
The directional command value signal at input 13
and the directional actual value signal at input 15 are
also compared in a third comparator 29. When the direc-
tional value is 0 and the directional command value is
non-zero, it sends a start signal via line 30 to the driving
gear control means 2.
An engine r.p.m. signal stemming from the sensors
18 at input 17 is ~ent to a fourth comparator 31, which
also has an input connected to a second memory 32 for
a predetermined r.p.m. limit value, e.g. 1000 r.p.m. The
comparator compares the engine r.p.m. with the r.p.m.
limit value, and when the engine r.p.m. exceeds this limit
value the comparator 31 sends a soft-start signal via line
33 to the driving gear control means 2.
The speed actual value signal at input 8 is also
sent to a fifth comparator 34, which has a second input
connected to a third memory 35 for a lower speed limit
value, e.g. 2 km/h. The comparator 34 compares the actual
speed of the vehicle with the limit value stored in the
memory 35 and when the actual speed exceeds this limit
value the comparator 34 sends a ~oft-start 6ignal via a
line 36 to the driving gear control means 2.
The driving gear control means 2 are dispo~ed AO
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that when there is a start signal in the line 30, a shift
signal is sent on output 3 to the drive gear couplings 4
for engaging second gear. This is always the case with a
start signal in direct connection with a reverse signal.
If, h~wever, a soft-start signal occurs in line 33 or 36
silmultaneously with the start signal in line 30 and
without an immediately preceding reverse signal in line
20, the drive gear control means 2 will instead send
a shift signal for engaging third gear. For this purpose
the drive gear control means 2 are provided with logic
circuits.
The forced downshift signal at input 1~ is
sent via a line 37 to the drive gear control means 2. The
actual speed value signal is sent from input 8 of the
control device 1 to a first input of a sixth comparator 38,
while the second input of the comparator 38 is connected
to a f~urth memory 39 for an upper limiting speed, which is
suitably selected to be the same as the upperlimit of the
range of second gear. The comparator 38 compares the vehicle
speed with the upper limiting speed in the memory 39, and
when the vehicle speed is less than the upper limiting speed,
the comparator 38 sends a go-ahead signal on line 40 to the
drive gear control means 2. When they receive both the
forced downshift signal on line 37 and the go-ahead signal
on line 40, they send a downshift signal on output 3 to the
drive gear couplings 4 for downshifting to first gear. If
there is no go-ahead signal in line 40, then no downshift
signal i8 sent.
Input 17, connected tothe sensors 18 for engi'ne
parameter , i~ connected via a line 41 to the drive gear
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control means 2, whereby they receive engine parameter
signals for controlling the automatic up and downshifting
of the gearb~x dependent on the load while driving. It
` is desirable thatthe shift point between the various
driving gears be selected so that the accelerations are
smooth when shifting. For this purpose, the shift point
between two gears should be placed where the torque
curves forthe two gears in question intersect. The torque
can preferably be measured directly by comparison between
the input and output r.p.m. of the torque converter C
(see sensors 18' and 18" in Fig. 1).
Th~s when driving the vehicle in a certain
- direction, the drive gear control means control the
shifting in the gearbox depending on the engine parameter
signals in line 41. If the driver desires to change the
driving direction he flips over the selector lever 12,
whereby the sensor 14 sends a directional command value
signal to input 13, which is opposite to the actual
directional value signal to input 15.
The first comparator 19 now sends a reversing
signal both to the drive gear control means 2 via line 20
and to the reversing gear control means 5 via line 21.
The drive gear control means 2 takes care of the down-
shifting to third gear from fourth gear if fourth is
engaged. The reversing gear control means 5 take care of
the changing of the reversing gear provided a go-ahead
signal is received ~rom the second comparator 26, i.e.
that the vehicle speed is less than 25 km/h. If this i~
not the case, there is fir~t a retardation in third gear
without change-over of the reversing gear until the ~peed
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is reduced to below 25 km/h, whereafter there is a go-ahead
signal in line 28 and the reversing gear control means 5
effect the reversal of the gearbox rotational direction.
Downshifting from fourth to third gear prevents
prolonged retardation in fourth gear, which could result
in overheating in the torque converter. Shifting of the
reversing gear only below 25 km/h prevents excessive
heat generation in the torque converter.
During the retardation process the reversing
signal is maintained in the line 20, whereby the drive gear
control means 2 maintains the driving gear engagement
unchanged. ~hus if third gear or second gear were engaged
when the operator gave the reverse command, third or
second gear, respectively, would remain engaged during
the continued retardation.
When the speed has dropped to 0, this is sensed
by the third comparator 29 by the directional actual value
signal also being 0. The comparator 29 sends a start
signal onthe line 30 to the drive gear control means 2
which couple in the second gear for the start sequence
in the new driving direction.
In an ordinary start without the reversing
sequence, the drive gear control means 2 also receive a
start signal on the line 30 for engaging second gear.
If, however, the engine r.p.m. exceeds 1000 r.p.m. or the
speed of the vehicle exceeds 2 km/h, the drive gear control
means 2 also receive a soft-start signal on line 33 or 36,
respectively, whereby the start i8 effected in third gear
and not in second gear.
If the operator wishes to engage first gear,
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for example to obtain increased force to fil~ the bucket,
he actuates with the selector lever 12 the forced downshift
signal sender 11, whereby a forced downshift signal is sent
via the line 37 to the drive gear control means 2. Providea
that there is a go-ahead signal in the line 40, i.e. that
the vehicle speed is within the working range of second gear,
the drive gear control means 2 effect the downshifting to
first gear. If the speed is too great, it must first ~e
reduced to below the upper limiting speed before downshift-
ing to first gear is effected. After downshifting to firstgear has ~een effected in this ~anner, a time circuit
(not shown here), in the drive gear control means '2 for
example, sees to it that automatic shifting up to second
cannot take place within a certain predetermined time, e.g.
five seconds.
Many functions in the control device indicated
within the dashed line in Fig. 2 can be performed by
a microcomputer. Fig. 3 shows in simplified block diagram
form a control device constructed in this manner. It
contains a data bus 50, to which a microprocessor 51 is
connected. The sensors 9, 16 and 18 for the actual speed,
the actual direction and the engine parameters are joined
via adapters 52 to an enumerator 53 connected to the data
bus 50. The direction selector 12,14 is joined to a
read/write memory 54 connected to the data bus. The forced
downshift -~ignal sender 11 can ~e connected in a corres-
ponding manner ~not shown). The electrically operated
driving and reversing gear co~plings and brakes 4,7 are
joined ~ia an adapter 55 to a program memory 56, connected
to t~e bu~ 50 and corresponding to the drive gear control
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means 2 and the reversing gear control means 5 in Fig. 1.
An output signal from the memory 54 is sent via a line 57
to an input in the enumerator 53.
An additional write/read memory 58 is joined
to an indicator device 59, which shows the operator
desired data, e.g. which gear is engaged at that time.
