Note: Descriptions are shown in the official language in which they were submitted.
~21754S
Description
Multiple Threshold Wheel Slip
Control Arts and Method
,. . _
Technical Field
-
This invention relates generally to wheel slip
control systems for vehicles having differentially
driven wheels in which slip is controlled by
application of a braking force to the slipping wheel,
and, more particularly, to an apparatus and method
having multiple wheel slip threshold levels.
background Art
It is well-known that vehicles having spaced
apart drive wheels or wheel-sets powered by a single
engine through a differential mechanism, are
problematic when one of the differentially driven
wheels or wheel-sets loses traction. Conditions which
give rise to a loss of traction commonly exist in
construction sites and other off-road locations. A
vehicle having one of two differentially driven wheels
or wheel-sets on a slippery surface and the other on a
surface providing good traction is often unable to
move, owing to the fact that the differential directs
full engine power to the wheel having no traction. The
result is a slip condition in which the wheel having no
traction rotates at higher than normal speed and the
wheel having traction remains stationary.
To alleviate such problems, various mechanical
anti-spin devices have been developed and placed in
commercial use. Such mechanical devices have been
proven to have various problems, especially during
cornering of a vehicle. Some devices fail to
accommodate the normal wheel speed differential which
I
~2~7~45
--2--
arises during a turn, causing excessive tire wear owing
to the dragging of the radially outer wheel or
wheel-set.
Other devices drive only the slower wheel in a
turn, making the vehicle hard to steer and applying
excessive torque to the wheel being driven, often
causing failure of the final drive.
An alternative approach involves the provision
of separately actuatable drive wheel brakes. An
operator selectively applies a braking force to the
spinning or slipping wheel, and effects a balancing of
power through the differential mechanism. The
application of the braking force to the slipping wheel
simulates increased traction and results in a more even
distribution of power between the differentially driven
wheels. This approach is commonly used on farm
vehicles
A more sophisticated approach to the just
described system, utilizes electronics to supply the
braking force to the slipping or spinning wheel. An
effective example of this approach is described in US.
Patent 4,344,139, issued to Miller et at. on August 10,
1982, and assigned to the assignee of this invention.
Miller discloses an apparatus for applying a
proportionally varying braking force to the wheel which
loses traction, during a slip control time period. A
slip signal is produced corresponding to any difference
between the rotational velocity of the differentially
driven wheels, and the slip signal is compared with a
predetermined reference signal. In response to the
slip signal exceeding the reference signal, the system
selectively applies a braking force to the faster
turning wheel. The braking force is modulated
proportionally according to the degree of slip
represented by the slip signal.
~2~7S4~
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One problem with the various prior control
systems involves the normal difference in rotational
velocities of the inner and outer vehicle wheels
encountered while cornering. To avoid this problem, a
fully automatic system, such as that described by
Miller, must establish the reference signal at a level
higher than the maximum slip signal that is produced
solely in response to cornering the vehicle. Thus, the
automatic control is inhibited for small values of
wheel slip. Other prior systems have eliminated the
problem completely by providing only manual operation.
These controls rely on the operator to activate the
anti-slip control when he senses the need to do so.
Such Inanely systems necessarily eliminate much of the
lo advantage of an anti-slip control. A further problem
with the fully automatic systems is the inability of
the operator to determine the operational status of the
anti-spin control prior to encountering an actual slip
condition.
The present invention is directed to
overcoming one or more of the problems as set forth
above.
Disclosure of the Invention
In one aspect of the present invention, an
anti-spin apparatus for controllable equalizing the
power delivered through a differential mechanism to at
least two wheels of a vehicle is provided. The vehicle
has a steering mechanism and each of the wheels has a
respective braking mechanism. Means is provided for
producing a slip signal having a value responsive to
the difference in rotational velocity between the
wheels. Means is also provided for producing a test
signal. A processor means receives the slip signal and
test signal, compares the slip signal value with a
~Z3 75~5
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first reference value in response to receiving the slip
signal in the absence of the test signal, and with a
second reference value in response to receiving both
the slip signal and the test signal. A brake control
signal is produced in response to the slip signal value
exceeding the compared reference value, and the braking
mechanisms are controllable operated in response to the
brake control signal.
In a second aspect of the present invention,
means is provided for supplying a steer signal to the
processor means. The steer signal value varies in
response to the position of the steering mechanism.
The processor means controllable negates the effect on
the anti-spin apparatus ox steering the vehicle, in
response to receiving the steer signal in the absence
of the test signal.
In another aspect of the present invention, a
method for controllable equalizing the power delivered
through a differential mechanism to at least two wheels
of a vehicle is provided. The vehicle has a steering
mechanism and each of the wheels has an associated
braking mechanism. A slip signal responsive to a
difference in the rotational velocity between the
wheels is produced. A test signal responsive to the
position of a test switch is also produced. A first
reference value is produced in the absence of receiving
the test signal and a second reference value is
produced in response to receiving the test signal. The
slip signal value is compared with the first reference
value in response to receiving the slip signal in the
absence of the test signal and to the second reference
value in response to receiving both the slip signal and
the test signal. A brake control signal is produced in
response to the slip signal value exceeding the
12~75~5
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compared reference value, and the braking mechanisms
are controllable operated in response to the brake
control signal.
The present invention advantageously compares
the slip signal with multiple reference signals, thus
avoiding problems associated with prior control systems.
Brief Description of the Drawings
For a better understanding of the present
invention, reference may be made to the accompanying
drawings, in which:
Fig. 1 is a diagram of a vehicle drive system
including an anti-slip control in accordance with an
embodiment of the present invention;
Fig. 2 is a block diagram of an embodiment of
the present invention;
Fig. 3 is a functional flow diagram utilized
with the embodiment of Fig. 2; and,
Fig. 4 is a graphical representation utilized
in describing the operation of the embodiment of Fig. 2.
Best Mode For Carrying Outwit Invention
Referring first to Fig. 1, an anti-slip
apparatus embodying certain of the principles of the
present invention is illustrated. It should be
understood that the following detailed description
relates to the best presently known embodiments of the
apparatus. However, the apparatus can assume numerous
other embodiments, as will become apparent to those
skilled in the art, without departing from the appended
claims.
Wheels 100,101 are driven by an engine (not
shown) through an input or drive shaft 104, a
differential mechanism 106, and respective half-axles
108 and 110. A steering mechanism 111 is coupled to
So
--6--
steerable wheels (not shown) of the vehicle. The drive
system is conventional and no further details need be
disclosed for an understanding of the present invention.
The wheels 100,101 are stopped by spring
engaged parking brake pistons, or by hydraulically
engaged service brake pistons, of brake mechanisms
112,114. The brakes are spring biased in the engaged
position and are maintained in the disengaged position
by application of fluid pressure, as disclosed in U S.
Patent No. 3,927,737, issued December 23, 1975 to P. F.
M. Prolonger and assigned to the assignee of this
invention. The service brakes are normally actuated
via a service brake line 137 connected to the service
brake and retarder master cylinders (not shown). The
service brake system is well-known and does not form a
part of this invention. The brakes are also actuated
through the parking brake lines 136,138 as described in
detail below.
Means 115 produces a slip signal having a
value responsive to the difference in rotational
velocity between the wheels 100,101. The slip signal
producing means 115 includes a left wheel speed pick up
in the form of an electromagnetic transducer 116 which
provides pulses in cooperation with a gear-like device
118. The device 118 is mounted on and rotates with the
axle portion 108. Signals from the transducer 116 are
applied to one input of an electronic controller 120,
the details of which are described below. In a similar
manner, right wheel speed signals are provided by a
transducer 122 operated in conjunction with a gear-like
device 124 which rotates with the axle portion 110.
Signals from the transducer 12~ are applied to another
input of the electronic controller 120. Each of the
transducers 116,122 produce respective signals having
values responsive to the rotational speed or velocity
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of the wheels 100,102. Additionally, a drive shaft
speed signal is produced by a transducer 126 in
conjunction with a gear-like device 128 which rotates
with the drive shaft 104. The drive shaft speed
signals are applied to a third input of the electronic
controller 120. Each of the transducers 116,122,126 is
preferably an electromagnetic device which produces a
pulse type, time variable output voltage. Such
transducers are well-known in the art. Louvre, other
lo transducers, such as optical and Hall effect devices,
may be employed as alternatives. Means 127 for
producing a test signal is also connected to an input
of the electronic controller 120. The test signal
producing means 127 is preferably a manual switch 129.
The electronic controller 120 is part of a
processor means 121 for receiving the slip signal and
producing a brake control signal in response to the
slip signal value exceeding a compared reference
value. A means 131 receives the brake control signal
and controllable operates the braking mechanisms
112,114 in response to the received brake control
signal.
A second embodiment of the present invention
includes means 113 for producing a steer signal in
response to the position of the steering mechanism
111. The steer signal is delivered to the controller
120. Means 113 preferably includes a potentiometer 115
controllable connected to the steering mechanism 111.
The output of the potentiometer 115 is a signal having
I a value that varies over a negative to positive voltage
range, in response to the position of the steering
mechanism 111. Other suitable angular position
transducers Jay be substituted for the potentiometer
115 in the means 113, as is well-known in the art.
12~7S45
In both embodiments, the controller 120
operates upon the signal inputs, determines the
existence, magnitude, and location of wheel slip during
a loss of traction situation, and distinguishes between
true wheel slip and a transducer failure. In response
to detecting a true slip condition, the power transfer
between the two differentially driven wheels 1~0,1~2 is
balanced by applying a proportional braking force to
the wheel which loses traction. This is accomplished
by means of locating selection valve 130 and
proportioning valve 132, both of which are included in
the means 131.
The valves 130,132 operate in combination with
a supply 134 of oil or brake fluid under pressure, the
fluid lines from supply 134 running both through and
around the proportioning valve 132 to the solenoid
operated selection valve 130 which directs full
pressure to one of the brake mechanisms 112,114, and
modulated or proportionally controlled pressure to the
other of the brakes 112,114. Note that, owing to the
utilization of spring biased brakes 112,114, brake
pressure is the inverse of fluid pressure and is
applied by relieving the fluid pressure in one of the
two brake lines 136,138, and could be straightforwardly
implemented in the opposite fashion, increasing brake
pressure in direct rather than inverse ratio to the
applied fluid pressure.
Fig. 2 is a block diagram of the preferred
implementation of the anti-spin apparatus described
above. A solid state digital microprocessor 142
performs system control functions. The microprocessor
142 is programmed to establish a plurality of slip
value bands, each band having associated therewith an
applied brake force value expressed in terms of fluid
pressure. The microprocessor 142 is interconnected
~Z175~5
g .
with a band value memory 144 and a timer 146.
Transducers 116,122,126 are connected to the
microprocessor 142 through an input conditioning
circuit 14U. The input circuit 140 provides
appropriately digitized input signals to the
microprocessor 142. Retard brake pressure and service
brake pressure switches 148,150 are likewise connected
through an input conditioning circuit 152 to the
microprocessor 142. The test signal producing means
127 is also connected to the microprocessor 142 through
the input circuit 152. Finally, in the alternative
embodiment, the steer signal producing means 113 is
connected to the microprocessor 142 through the input
circuit 152.
A first output ox the microprocessor 142 is
connected through a pulse-width modulated servo valve
driver 154 to the servo operated proportioning valve
132~ A second output from the microprocessor 142 is
connected to the solenoid driver 133 associated with a
left direction selection valve aye, and a third output
from the microprocessor 142 is connected through the
solenoid driver 136 to a right direction shuttle valve
230b. The pulse width modulated servo valve driver 154
proportionally controls the servo valve 132, in a
manner well know in the auto Therefore, adverting
momentarily to Fig. 1, fluid pressure is modulated via
the proportioning valve 132 to the brake line 136,138
selected by the position of the valve 130.
Referring now to Fig. I a functional
flowchart defining the internal programming for the
microprocessor 142 is shown. From this flowchart, a
programmer of ordinary skill can develop a specific set
of program instructions for a general purpose
microprocessor that defines the necessary slip signal
value bands, timing cycles, and brake fluid pressure
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values necessary for implementation of the instant
invention. It will be appreciated that, while the best
mode of the invention is considered to comprise a
properly programmed microprocessor 142, the result of
which is the creation of novel hardware associations
within the microprocessor 142 and its associated
devices, it is possible to implement the instant
invention utilizing traditional hard wired circuits.
Industrial applicability
The following description refers to Figs. 1,
2, and 4, and to the flowchart depicted in Fig. 3. The
operation of the anti-spin apparatus is first described
according to the embodiment in which the steer signal
producing means 113 is absent from the apparatus The
initial discussion further assumes that the test signal
producing means 127 is in the "non-test" or Normal"
position.
Data delivered by the transducers 116,122 is
sampled in block 164 of Fig. 3. In response to one of
the wheel velocity signals being equal to zero/ control
progresses along the right side of the flow diagram to
block 166. The input shaft speed is determined in
block 166, and is compared in block 168 with the
non-zero wheel velocity. If the ratio of the non-zero
wheel velocity to drive shaft speed is equal to or less
than a constant, for example, 1.5, it is assumed that
the wheel indicating zero speed is actually turning and
that the zero indication is the result of a failed
transducer. In this case, the program returns to the
original starting point and, if desired, an indication
of the apparent transducer failure can be presented to
the operator. The value of the constant selected is
determined according to the year ratio of the
1--
differential mechanism 106. As a matter of convenience
for purposes of this discussion, a differential ratio
of 1:1 is assumed throughout.
If the rotating wheel velocity is greater than
5 1.5 times the drive shaft speed, the program progresses
to blocks aback. If one of the wheel velocities is
not zero, the program progresses to blocks Ahab,
which is an event counter requiring several successive
cycles of the above conditions prior to activation of
the anti-spin apparatus. This delay filters out short
term wheel speed aerations and has been found to be
advantageous for efficient system operation. If the
event counter has not incremented or counted a
sufficient number of cycles, the program progresses to
blocks Ahab which increment the counter. The program
then returns to the original starting point.
Once the event counter Ahab has incremented
a sufficient number of cycles, the program progresses
to block 176. In block 176 a determination is made of
the input switch conditions controlling the service
brake, the retarder, and/or the vehicle speed. It is
additionally advisable to check the condition of brake
fluid pressure at this point.
If both wheel velocities are zero, block 170c
advances the program to blocks 178,180,182,184,
releasing the parking brake 112,114 and resetting the
timer 146. The same result occurs if automatic control
is contra-indicated in block 176.
If block 176 is satisfied, the program
progresses to block 186 to determine whether the slip
control system is activated. If so, the effect is the
same as entering band 5, the most severe slip condition
band, and control passes to block 194. Block 194
increases the wheel brake force by decreasing the wheel
brake hold off pressure by an increment X, for each
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timed interval established by the microprocessor timer
146. If the slip control system is not operative in
block 186, the program progresses to block 188 which
activates the system, and then through blocks 190 and
192 to begin the timing cycle and reduce tune brake hold
off pressure to a value just sufficient to maintain the
brakes in the released position. On the next pass
through the above sequence, a positive result will be
obtained at block 186, and in block 194 the brake hold
off pressure will be decreased by X psi. The control
repeats this sequence at timed intervals until either
the zero speed wheel begins to turn or the brake hold
off pressure is decrement Ed to nearly zero psi. In the
latter case, the brakes are then released completely.
In the former case, the control follows the path from
block 164 to block 196, and continues as described in
the following paragraphs.
Assuming that, in block 164, neither wheel
velocity is found to equal zero, the program branches
to block 196, representing a calculation sub-routine.
Essentially, block 196 determines the location of the
actual slip signal value within one of five slip bands
represented by Table 1. The slip bands are contiguous,
the upper limit of one band being the lower limit of
the next, with the highest slip value being the first
predetermined reference value referred to above. The
first predetermined reference value must be exceeded by
the slip control signal value before anti-slip control
begins. The processor means 121 makes this
determination by comparing the slip signal value with
the first predetermined reference value, and with the
other reference values shown in Table 1.
Since normal cornering of the vehicle produces
an apparent slip condition, with the radially outer
wheels of the vehicle rotating faster than the radially
~2~7S45
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inner wheels, to prevent actuation of the anti-slip
control in response to maneuvering the vehicle while
operating in this mode, the first reference value must
be established higher than the maximum slip signal
value produced by steering the vehicle in a hard
cornering maneuver. This value varies according to the
design of the vehicle. us shown in Table 1! for
purposes of this discussion, a value of 1.7 is
considered to be greater than the maximum slip signal
lo value produced by steering the vehicle.
Continuing through the program of Fig. 3,
program blocks 198,200,202 represent the determination
of which of the wheels is rotating at a higher
velocity, and the disposition of the valve 130 to
direct modulated brake fluid pressure to the highest
velocity wheel and unmodulated brake fluid pressure to
the lower velocity wheel (remembering the inverse
relationship between brake pressure and brake fluid
pressure). The program then advances to block 204 and
determines whether a sufficient slip time period has
elapsed to begin operation of the control system. If
insufficient time has elapsed, program block 206
increments a counter and the program advances to the
starting point. If sufficient time has elapsed, the
program advances to block 208 in which the various
signal conditions which might contra-indicate operation
of the slip control system are considered. If the
conditions are satisfied, the program advances to the
appropriate one of the blocks 210,212,214,216,218, as
determined in block 196. Initially, the vehicle can
enter the slip control mode only via band 5.
Therefore, the slip value must exceed the first
predetermined reference value, for example, 1.7. This
prevents unintentional activation of the control system
35 while steering the vehicle. Once the control mode has
læ~5~5
been entered through band 5, control is exited by
sequencing through the lower bands 4-1, producing a
smooth transition back to the uncontrolled mode.
Assuming that band 5 is entered/ and that a
positive indication is reached in block 186, the brake
force is periodically incremented in block 194 by
reducing the brake pressure by the increment X for
every timing cycle, until the slip signal value causes
entry into another slip band. This is best seen in
lo Fig. 4, where the first step from the hold off pressure
ox 400 psi represents an abrupt reduction in pressure
to 200 psi, followed by three additional incremental
reductions of approximately 33 psi each, increasing the
parking brake force through spring action with each
incremental step.
Next, the slip condition in the example
represented in Fig. 4 enters band 4, in which the slip
has been reduced to the point where the slip signal
value is within the range between 1.5 and 1.7. Blocks
220,222 cause the brake force to be increased by a
smaller increment Y for every timing cycle.
Accordingly, the system approaches the full brake force
condition in a gradual curve, with the brake force
increments becoming smaller toward the full brake force
condition.
As is also represented in Fig. 4, reaching a
lower slip band value and qualifying for successive
entry into slip bands 3,2,1, causes gradually
increasing incremental reductions in brake force until
the system is back to the unbaked condition
represented by application of the full brake fluid
pressure of 400 psi. Preferably, band 3 is the mirror
image of band 4, and causes incremental reductions in
braking force through incremental increases in brake
fluid pressure. Band 2 is the mirror image of band 5,
~2~75q~5
-15-
and causes large incremental reductions in brake
force. Band 1 has no counterpart, and causes still
larger reductions in brake force as represented by the
increment W in the diagram of Fig. 4.
From the foregoing it is apparent that, with
the test signal producing means 127 in the "normal"
mode, the anti-spin apparatus operates to detect
slipping wheel, to apply braking force to the slipping
wheel, and to periodically and incrementally modulate
the brake force either positively or negatively in
accordance with the degree of slip which is detected by
the system. Conditions giving rise to a slip signal
value of 1.7 or less do not cause entry into the slip
control mode, because the first predetermined reference
value is not exceeded. This prevents unintentional
operation of the anti-spin control owing to steering of
the vehicle. However, actual slip that does not exceed
the first predetermined reference value is likewise not
corrected for by the control system.
The utility of the test signal producing means
127 is now described. When the test switch 129 is
moved from the normal" to the "test- position, the
first predetermined reference value is replaced by a
second predetermined reference value. For example as
is shown in Table 1, the reference value required to
enter slip band 5 is reduced from the first value of
1.7 to the second or modified value of 1.25. Band
values 4-1 are likewise reduced. These are the values
stored in the band value memory 144 and utilized in the
calculation of block 196. Therefore, in response to
selecting the "test mode, the processor means 121
receives the slip signal and the test signal and
compares the slip signal with the second predetermined
reference value. Anti-slip control is thus initiated
~217S~S
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in response to a slip signal value less than the slip
signal produced by steering the vehicle. This produces
two important results.
First, the operator can readily determine
whether or not the anti-spin apparatus is functioning
properly by merely steering the vehicle into a hard
turn. If the slip control is operating properly, the
operator can observe the application of the vehicle
brake 112,114 to the radially outer of the
differentially driven wheels 100,101, in response to
the slip signal value produced by steering the vehicle
exceeding the modified threshold value. Thus, it is
relatively easy for the operator to determine the
operability ox the control system prior to encountering
a low traction situation.
Second, when the operator encounters slippery
working conditions in which it is desirable that the
anti-spin control system respond in a rapid fashion, he
can select the "test" position with the test switch
129~ This causes the control system to enter the slip
control mode with the lower slip signal value, making
it more sensitive to low traction conditions, and
enhancing controllability of the vehicle. Since this
mode of operation is selected only under a particular
set of extreme circumstances, the interference with
normal steering functions it minimal and acceptable.
The alternative embodiment of the anti-spin
apparatus, in which the steer signal producing means
113 is included, as shown within the dotted area of
Fig. 3, is a further enhancement of the control
system. In one implementation of this embodiment, the
processor means 121 receives the steer signal and
controllable modifies the slip signal value in response
to the value of the steer signal, in the absence of the
test signal. Assuming that the test switch 129 is in
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the "normal" position, and that neither wheel velocity
is found to be zero in block 164, program control
progresses to block 250, in which a slip value it
calculated as So.
The sign of So is determined in the blocks
252,254,256. If the right wheel is the faster of the
two wheels, the quantity So is positive, and if the
right wheel is not the faster of the two wheels, the
quantity So is negative. So is next delivered to
lo block 262. The inverted steer signal value So is
delivered frown the block 260, and also supplied to the
block 262. The signals So and So are summed and
delivered to the block 196, in which the appropriate
slip band is calculated and control progresses as
described above. As shown in Table 1, the slip band
reference or threshold values utilized by the control
system are much lower as applied to the instant
embodiment of the invention, than the values utilized
in the embodiment having no steer input signal.
For example, assume that the steer signal
producing means 113 supplies a positive signal to block
260 in response to steering the vehicle in a left turn,
and a negative signal in response to steering the
vehicle in a right turn. In response to the vehicle
executing a right turn, the left or radially outer
wheels 100,101 rotate at a higher velocity than do the
right or radially inner wheels. Assulning a no slip
or good traction condition, So is calculated in block
250 and negative So is delivered from block 254 to
block 262. The steer signal polarity is inverted in
block 260 and the signal is delivered as a positive
signal to block 262, effectively canceling the false
slip signal caused by turning the vehicle thus
preventing entry into the control mode.
1217S45
-18-
Dow, given a similar hypothetical situation
but under poor traction conditions, assume that the
left wheel loses traction. The calculated slip signal
So becomes larger/ as does the absolute value of the
negative signal delivered to block 262. Since the
steer signal delivered to block 262 modifies but no
longer cancels the slip signal, the true slip condition
is detected and is delivered to block 196. In response
to this signal exceeding the first predetermined
reference signal, shown in Table 1, band 5 of the
control mode is entered and slip control commences.
Finally, under the same hypothetical
conditions, assume that the left wheel maintains
traction and the right wheel loses traction. The
calculated slip signal So becomes smaller or passes
through zero and becomes larger, as the relative wheel
velocities change. Correspondingly, the negative
signal delivered to block 262 becomes less negative or
goes positive and is modified but no longer canceled by
the steer signal, and the control mode is entered once
the first predetermined reference value is exceeded.
The consequences of other combinations of
wheel slip and steering angle can be readily determined
by applying the above described logic.
In a second implementation of this embodiment,
the processor means 121 accomplishes the same result as
that just described, by continuously modifying the band
threshold values in response to receiving the steer
signal in the absence of the test signal. The first
predetermined reference value is continuously
maintained a predetermined amount greater than the
actual slip signal value produced in response to
steering the vehicle.
Adding the steer signal producing means 113 to
the anti-spin control system accounts for differences
in wheel velocity caused solely by steering the
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vehicle, and prevents such wheel velocity differences
from appearing to the control as an actual slip
condition By negating the effect of steering on
operation of the control, the anti-spin system is made
extremely sensitive to small slip conditions that prior
systems are unable to automatically contend with.
Keeping the above principles in mind, and having the
flexibility of a programmable microprocessor, one
skilled in the art can produce other related methods of
accomplishing this same result.
In the steer signal embodiment, switching the
test signal producing means 127 to the "test" mode
inhibits the action of the steer signal producing means
113 and causes the control to operate on the second
predetermined reference value, as fully described
above. Thus, in each embodiment, the anti-spin control
system can be tested by steering the vehicle in a hard
turn while the test signal producing means 127 is in
the "test" mode. Of course, if the test mode is not
provided in the second embodiment, the control mode
will never be entered solely in response to steering
the vehicle.
It will be appreciated by those skilled in the
art that it is not essential to incorporate all of the
steps represented in the flowchart of Fig. 3 in a given
system/ nor is it necessary to incorporate the steps of
Fig. 3 utilizing a microprocessor.
However, such an implementation is deemed to
be the best mode of practicing the invention owing to
the broad and widespread availability of suitable
microprocessor circuits, the widespread understanding
of programming techniques for such microprocessors, the
cost reduction in such circuitry which has been
realized in recent years, and the flexibility which a
programmable device affords.
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Other aspects, objects, advantages and uses of
this invention can be obtained from a study of the
drawings, the disclosure, and the appended claims.
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TABLE 1
BAND THRESHOLD REFERENCE VALUES
S = SLIP SIGNAL VALUE
NORMAL nest STEER SIGNAL
BAND MODE MODE MODE
.
1 1.0~S~=1.2 1.0<S~=1.1 slyly
2 1.2<S<=1.3 l.l<S~=1.15 l.l<S<=1.15
3 1.3<S<=1.4 1.15<S~=1.2 1.15'S'=1.2
4 1.4<S<=1.7 1.2~-1.25 1.2<S<=1~25
1.7<S 1.25'S 1.25'S
I
