Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a method for
controlling the change-over between two and four-wheel drive
modes of a vehicle. The four-wheel drive mode is changed to
the two-wheel drive mode when at least one wheel produces a
locking tendency during braking.
In a control of change-over from a two to a four-
wheel drive mode, conventional practice is to restore the
drive mode from the two-wheel drive mode to the four-wheel
drive mode when there is no tendency for all the wheels to be
locked, after the drive mode has been changed from the four-
wheel drive mode to the two-wheel drive mode.
Some of the operators or drivers may be
accelerating while braking in vehicles equipped with an
automatic transmission. In such a case, in spite of a desire
to restore the drive mode from the two-wheel drive mode to
the four-wheel drive mode, the restoration cannot be achieved
when there is a locking tendency produced in the wheels which
are driven wheels in the two-wheel drive mode.
The present invention provides a method for
controlling the change-over between two-wheel and four-wheel
drive modes of a vehicle comprising the steps of: changing a
four-wheel drive mode to a two-wheel drive mode when at least
one wheel produces a locking tendency during braking; and
changing the two-wheel drive mode to the four-wheel drive
mode when the driving wheels in the two-wheel drive mode have
no locking tendency.
A first feature of the present invention is in that
the two-wheel drive mode is changed to the four-wheel drive
mode when the driving wheels in the two-wheel drive mode have
no locking tendency. With this first feature, it is possible
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to smoothly change over the drive mode to the four-wheel
drive mode, when a driver is accelerating while braking in
the two-wheel drive mode, by changing over to the four-wheel
drive mode, even if the driven wheels in the two-wheel drive
mode are in a locking tendency.
A second feature of the present invention is that
when a driven wheel tends to be locked, the two-wheel drive
mode is maintained until a predetermined time has elapsed
after changing over from the four-wheel drive mode to the
two-wheel drive mode. With the second feature, two-wheel
drive mode is not changed back to the four-wheel drive mode
during an initial stage of changing over from the four-wheel
drive mode to the two-wheel drive mode, when the driven
wheels are in a locking tendency and the driving wheels are
not in a locking tendency.
A third feature of the present invention is that
even if a locking tendency is prod~ced in a driven wheel in
the two-wheel drive mode, the four-wheel drive mode is
maintained until a predetermined time has elapsed after
changing over from the two-wheel drive mode to the four-wheel
drive mode. With the third feature, the four-wheel drive
mode is not changed back to the two-wheel drive mode during
an initial stage of changing over from the two-wheel drive
mode to the four-wheel drive mode, when the driven wheels are
in a locking tendency and the driving wheels are not in a
locking tendency.
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In one aspect, the invention provides a method for
controlling the change-over between two-wheel and four-wheel
drive modes of a vehicle comprising the steps of:
changing a four-wheel drive mode to a two-wheel drive
mode when it is detected that at least one wheel produces a
locking tendency during braking;
changing the two-wheel drive mode to the four-wheel
drive mode when it is detected that the driving wheel~ in
the two-wheel drive mode have no locking tendency;
and maintaining the two-wheel drive mode until a
first predetermined time has elapsed after the change-over
from ~he four-wheel drive mode to the two-wheel drive mode
when it is detected that a driven wheel tends to be
locked even if no locking tendency is detected in the
driving wheels in the two-wheel drive mode.
In preferred embodiments of this aspect, the invention
provides:
The above method, further comprising the step of
maintaining the four-wheel drive mode until a second
predetermined time has elapsed after change-over from the
two-wheel drive mode to the four-wheel drive mode even if a
locking tendency is detected in a driven wheel in the two-
wheel drive mode.
The immediately above method, wherein the vehicle
includes a power transmission system provided with clutch
means for changing over between the two-wheel and four-wheel
drive modes of the vehicle, the method further comprising
starting counting of sa~d first predetermined time from an
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instant when a disengaged state of said clutch means is
detected, and starting counting of said second predetermined
time from an instant when a command is generated for engaging
said clutch means.
In a further aspect, the invention provides a method for
controlling the change-over between two-wheel and four-wheel
: drive modes of a vehicle comprising the steps of:
changing a four-wheel drive mode to a two-wheel drive
mode when it is detected that at least one wheel produces a
locking tendency during braking;
changing the two-wheel drive mode to the four-wheel
drive mode when it is detected that the driving wheels in
the two-wheel drive mode have no locking tendency;
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and maintaining the four-wheel drive mode until a
predetermined time has elapsed after change-over from the
two-wheel drive mode to the four-wheel drive mode even if a
. 20 locking tendency is detected in a driven wheel in the two-
wheel drive mode.
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' In a still further aspect, the invention provides a
. method for controlling the change-over between two-wheel
~: 25 drive modes of a vehicle comprising the steps of:
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changing a four-wheel drive mode to a two-wheel drive
mode when it is detected that at least one wheel produces a
locking tendency during braking;
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:~ changing the two-wheel drive mode to the four-wheel
` drive mode when it is detected that the driving wheels in
the two-wheel drive mode have no locking tendency;
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and wherein the vehicle has an engine mounted at a
front portion thereof and said driving wheels in the two-
wheel drive mode are front wheels, said front wheels being
subjected to anti-lock control independently from each other
and rear wheels of said vehicle being together subjected to
anti-lock control in a collective fashion,
the method further comprising using signals which are
used to carry out the anti-lock control for changing over
between the two-wheel drive mode and the four-wheel drive
mode.
The drawings illustrate one embodiment of the present
invention, wherein:
Fig. 1 is a schematic illustration of a driving system;
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Fig. 2 is a circuit diagram illustrating the
arrangement of an essential portion of a control means; and
Fig. 3 is a timing chart.
The present invention will now be described with
reference to the accompanying drawings, by way of one
embodiment applied in a vehicle in which the front wheels are
driving wheels and the rear wheels are driven wheels in a
two-wheel drive mode. Referring first to Fig. 1, a pair of
front wheels WfR and Wfr and a pair of rear wheels wrQ and
Wrr are suspended respectively on a front portion and a rear
portion of a vehicle body (which is not shown). Brakes Bf~
and Bfr; Br~ and Brr are provided on the front and rear
wheels Wf~ and Wfr; Wr~ and Wrr, respectively. A hydraulic
pressure control circuit 1, to which an anti-lock control
means 2 is added for controlling the brakes BfQ and Bfr on
the front wheels Wf~ and Wfr and the brakes Br~ and Brr on
the rear wheels Wr~ and Wrr with different operation modes
forms a brake device together with brakes BfR, Brf, Br~ and
Brr. The anti-lock control means 2 is, for example, to
separately control the hydraulic braking pressures for the
brake Bf~ on the left front wheels Wfl, the brake Bfr on the
right front wheel Wfr and the brakes BrR and Brr on the rear
wheels wrQ and Wrr. The hydraulic braking pressure is
reduced during anti-lock control.
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The front and rear wheels Wfe, Wfr, Wre and Wrr are
connected through a driving system A to a power unit P. The
driving system A comprises a front differential Df connecting the
front wheels Wfe and Wfr with the power unit P, a rear differential
Dr connecting the rear wheels Wrt and Wrr, and a propeller shaft
3 connecting the power unit P with the rear differential Dr. At
the middle o~ the propeller shaft, there is a dog clutch 4 which
permits changing over between the connection and disconnection
between-the front and rear wheels Wfe, Wfr and wre, Wrr. An
actuator 5, such as a cylinder for driving the dog clutch 4, is
controlled by a control means 6.
Flg. 2 illustrates the arrangement of an essential
portion of the control means 6. A signal indicative of an anti-
lock control state is input from the anti-lock control means 2 to
input terminals 7, 8 and 9. Specifically, when the brake Bfe of
the left front wheel Wfe is being anti-lock controlled, a higher
level signal than normal is input to the input terminal 7, and when
the brake Bfr of the right front wheel Wfr is being anti-lock
controlled, a higher level signal is input to the input terminal
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8. When the brakes ~ and Brr of both rear wheels Wre and Wrr are
being anti-lock controlled, the higher level signal is input to the
input terminal 9. The input terminals 7 and 8 are connected in
- parallel to an OR circuit 10, and the input terminal 9 is connected
to an AND circuit 11.
The OR circuit lO ie connected to an AND circuit 12 which
` i8, in turn, connected to an output terminal 13 to deliver a higher
level signal when the dog clutch 4 is disengaged to change over the
four-wheel drive mode into the two-wheel drive mode. The AND
circuit 12 is also connected to an invertor circuit 14 which is
connected, in an inverted manner, to an input terminal of a timer
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circuit 15. The timer circuit 15 produces a higher level
signal sustained for a given time TA from the moment when the
output from the invertor circuit 14 has been changed from a
lower level into a higher level, i.e., when the output from
the AND circuit 12 has been changed from a higher level into
a lower level to change over the two-wheel drive mode into
the four-wheel drive mode. The output from the timer circuit
15 is input, in an inverted manner, to the AND circuit 11.
A detector 16 (see Fig. 1) is added to the dog clutch 4
for detecting the operated state thereof and produces a
higher level signal when the dog clutch 4 is in a disengaged
state~ The detector 16 is connected to a delay circuit 17
which produces a signal rising with a delay of a given time
TB after the rising of a signal produced from the detector
16. The delay circuit 17 is invertedly connected to the AND
circuit 11. Thus, output from the AND circuit 11 becomes a
higher level, when the rear wheels ~r~ and Wrr are in a
locking tendency, and within a period from a point when the
given time TA has elapsed after changing over of the two-
wheel drive mode into the four-wheel drive mode to a point
when the given time TB has elapsed after the change-over into
the two wheel drive mode has been achieved.
A brake switch 18 is also connected to the AND circuit
12 and produces a lower level signal when a braking operation
has been provided. Therefore, in order that the output from
the AND circuit 12 goes to the lower level, the braking
operation is a necessary condition.
The operation of this embodiment will be described below
with reference to Figs. 3(a~ to 3(c). Fig. 3(a) illustrates
the output from the AND circuit 12. Fig. 3(b) illustrates
the output from the timer circuit 15. Fig. 3(c) illustrates
the output from the delay circuit 17. Until the given time
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TA elap~es after changing over from the two-wheel drive mode
into the four-wheel drive mode, the output from the AND
circuit 11 is at the low level. After the given time TB has
elapsed after changing over from the four-wheel drive mode
into the two-wheel drive mode, the output from the AND
circuit 11 becomes the low level. Therefore, the output from
the AND circuit 11 becomes the hi~h level, only when the rear
wheels WrQ and Wrr show a tendency to be locked, and between
a point A, after a lapse of the given time TA from changing
over from the two-wheel drive mode into the four-wheel drive
mode, and a point s, after a lapse of the given time TB after
changing over from the four-wheel drive mode into the two-
wheel drive mode.
If the breaking occurs when the dog clutch 4 is in an
engaged state to provide the four-wheel drive mode in which
the front wheels Wf~ and Wfr are connected to the rear wheels
Wr~ and Wrr, the output from the AND circuit 12 becomes the
high level in response to the output from the OR circuit 10
becoming the high level, so that the dog clutch 4 is
disengaged to permit changing over from the four-wheel drive
mode into the two-wheel drive mode. In other words, the dog
clutch 4 is disengaged to provide the two-wheel drive mode,
either in a condition where either one of the front wheels Wf~
and Wfr tends to be locked and is anti-lock controlled, or in
a condition where the rear wheels wrQ and Wrr are being anti-
lock controlled.
In changing over into the two-wheel drive mode, the
output from the AND circuit 11 remains at the higher level to
maintain the two-wheel drive mode, until the given time Tg
has elapsed from the point of change-over, when the rear
wheels WrD and Wrr, which are now driven wheels, tend to be
locked. Thus, the drive mode is not immediately returned to
~ the four-wheel drive mode when it has been changed over into
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the two-wheel drive mode in a condition where the rear wheels
wrQ and Wrr are in a locking tendency and the front wheels WfQ
and Wfr are not in a locking tendency in the four-wheel drive
mode.
When at least the front wheels Wf~ and Wfr, which are
driving wheels, have no locking tendency produced in the two-
wheel drive mode, the output from the AND circuit ll is at
the low level after the given time TB has elapsed after
changing over, so that the output from the OR circuit 10 goes
to the low level. In response to this, the output from the
AND circuit 12 goes to the low level, thereby permitting the
dog clutch 4 to be engaged, resulting in the four-wheel drive
mode. When the vehicle is accelerating while the operator of
the vehicle is braking, the drive mode can be rapidly
restored from the two-wheel drive mode to the four-wheel
drive mode.
With this change-over from the two-wheel drive mode to
the four-wheel drive mode, the output from the AND circuit 11
remains at the lower level until the given time TA has
elapsed after the change-over. Accordingly, the drive mode
is not immediately returned to the two-wheel drive mode when
it has been changed over into the four-wheel dive mode in a
~ condition where the rear wheels WrQ and Wrr are in a locking
`; tendency and the front wheels WfQ and Wfr are not in a
locking tendency in the two-wheel drive mode.
As discussed above, according to the first feature of
the present invention, the two-wheel drive mode is changed to
the four-wheel drive mode when the driving wheels have no
locking tendency produced in the two-wheel drive mode.
Therefore, it is possible to smoothly change over the drive
mode to the four-wheel drive mode when the vehicle is
accelerating while the operator of the vehicle is braking
during the two-wheel drive mode.
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According to the second featùre of the present invention,
when the driven wheels tend to be iocked, the two-wheel drive modé `
is maintained until a predetermined time has elapsed after changing
over Prom the four-wheel drive mode to the two-wheel drive mode.
Therefore, the two-wheel drive mode is not changed back to the
four-wheel drive mode during an initial stage of changing over from
the four-wheel drive mode to the two-wheel drive mode, when the
driven wheels are in a locking tendency and the driving wheels are
not in a locking tendency.
According to the third feature of the present invention,
even if a locking tendency is produced in the driven wheels in the
two-wheel drive mode, the four-wheel drive mode is maintained until
a predetermined time has elapsed after changing over from the two-
wheel drive mode to the four-wheel drive mode. Therefore, the
four-wheel drive mode is not changed back to two-wheel drive mode
during an initial stage of changing over from the two-wheel drive
mode to the four-wheel drive mode, when the driven wheels are in
a locking tendency, the driving wheels are not in a locking
tendency.
From the foregoing description of the preferred
embodiment of the invention, it will be apparent that many
` modifications may be made therein. It should be understood that
these embodiments are intended as one example of the invention
` only, and that the invention is not limited thereto. Therefore,
i 25 it should be understood that the appended claims are intended to
cover all modifications that fall within the true spirit and scope
of the invention.
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