Note: Descriptions are shown in the official language in which they were submitted.
CA 02234974 1998-04-17
Automatic Wheel Chock System
Background of the Invention
1. Cross reference to related applications
Thi~ invention is related to co-pending applications Serial
No. 08/562,957, filed November 27, 1995 and 08/350,132, filed April
11, 1996, both commonly assigned.
2. Field of the Invention
This invention is related to material handling equipment and
in particular to mechanical devices that restrain a vehicle at a
loading dock.
3. Prior Art
Devices that restrain a vehicle against movement away from
loading docks are known and widely used. They range from simple
wheel chocks to complicated mechanical systems. Mechanical vehicle
restraints generally fall into two broad categories, those which
restrain by latching on to an abutment of the vehicle, usually the
ICC bar and, those which engage a wheel.
Examples of the first type are found in a number of commercial
devices such as the Rite-Hite ADL - LDL series and the Serco VR
series of vehicle restraints. These devices are covered by U.S.
Patents, such as 4,264,259; 4,443,150; 5,120,181 and 5,259,718.
Such patents are representative of a variety of devices, wall or
approach mounted, that move hooks or barriers into position to
CA 02234974 l998-04-l7
contact the ICC bar and thus prevent movement away from the loading
dock. Such devices have achieved commercial success and are
generally effective. They however suffer from operational
limitations because of the differences in location and geometry of
the target, i.e. the ICC bar. These limitations include a failure
to engage in some situations, trailer creep and locking up thus
preventing the truck from moving out once the loading operation is
complete.
Examples of the second type (wheel chocks) are found in U.S.
Patents 2,661,505; 3,305,049; 4,207,019; 4,969,792; 5,249,905 and
5,375,965 which show chocking devices which store in the driveway
and move toward the wheel to engage and hold the vehicle. These
patents represent techniques to automatically place a chock in
front of a wheel to prevent a vehicle from moving away from a
loading dock, but most have significant limitations. The device
shown by Willey in US patent 3,305,049 is simple in concept, but
the screw element that is employed is exposed to impact and could
not withstand the lateral and bending forces exerted by the block.
The device shown by Cone in US patent 4,207,019 occupies space
under the rear of the vehicle and could prevent the lowering of a
hydraulic tail gate. The device shown by Warner et al in US patent
S,249,90S provides effective wheel chocking but requires expensive
excavation for installation. Also, proper drainage must be
provided and heating elements may be required in colder climates.
In U.S. Patent 5,375,96S the chock is placed at the end of a
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track and the vehicle drives over it- The chock then moves inward
toward the wheel until contact is made and then the restraining
device is raised to provide a barrier. While eliminating the need
for a trench, the device may be damaged as the vehicle rides over
it both on entering the dock and leaving. Additionally, the
operation requires moving a pair of heavy and complex chock
elements on the approach, at positions spaced from the track which
may damage the approach itself due to repeated travel, the uneven
surface and the presence of obstacles in the path.
Some of these devices have also achieved commercial use but
still have serious technical/operational problems. The advantages
of this class of vehicle restraint however are that positive
engagement with a wheel occurs thus insuring reliability and
minimum trailer creep. Nevertheless, these devices tend to be more
complex than those restraints which engage the ICC bar and, in some
situations require expensive installations such as trenching and
the like. Also, they are susceptible to misposition relative to the
wheel if the vehicle is not aligned on the approach correctly, i.e.
off center or angled.
Additionally, these devices, prior to this invention, approach
the vehicle from the front of the approach and move then toward the
dock face until they engage the vehicle. This causes storage
problems and requires a long run of track or drive member to move
the chock into position.
Thus, one limitation common to most automatic wheel chocking
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devices is that they usually travel through a greater distance and
therefore require a much longer time to engage than devices which
hook on to the ICC bar. The position of the wheels on the rearmost
axle relative to the rear of a vehicle can vary by many feet.
Therefore the chock must be able to travel through a long distance
to ensure that it can engage the wheels of a variety of vehicles.
Usually the chock must overcome a relatively low force to travel
from the stored position to engage the wheel, and then must exert
a significantly higher force against the wheel to secure the
vehicle. Similarly, a high force may-be required to dislodge the
chock from the wheel because it may have become wedged tightly due
to the vehicle being forced away from the loading dock during the
loading operation. Also, a high force may be required to dislodge
the chock from the stored position in winter conditions. The
requirement of high force and fast travel speed through a long
distance can be met by a powerful drive mechanism. However, this
significantly increases the cost of the drive components as well as
the cost of electrical wiring to the drive unit.
As a consequence of these diverse requirements there is a need
in the art for a wheel chock using a variable force drive to move
the device into position and extend and retract the chock that is
less complicated and less expensive than prior devices.
There also exists in the art a need for a wheel chock that is
rugged and can withstand abuses of daily use and environmental
effects of rain, snow and ice.
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SummarY of Invention
In co-pending U.S. Patent Application 08/350,132 an automatic
chock is disclosed which engages the wheel of a transport vehicle
to prevent it from moving away from a loading dock by having a
chock move forward from the loading dock and then swing restraining
elements into position once the proper location relative to a wheel
is determined. The automatic wheel chock is combined with a guide
rail which carries the wheel chock and also acts to guide the
wheels of the transport vehicle to position it relative to the
loading dock. It can be used to engage a single wheel, or as one
of a symmetrically opposite pair to engage a wheel on each side of
the vehicle.
The automatic wheel chock of the present invention is an
improvement over that set forth in the earlier applications. It has
several advantages over existing devices. Because it is stored
against the dock face and approaches the trailer from the rear, it
engages the rear-most set of wheels and is not affected by the
number or position of other axles. It can be easily mounted to an
existing driveway and thus installation does not require the
expense of excavation and concrete construction. Because it is
mounted off to the side of the dock, the driveway is left
unobstructed for easy removal of snow or debris. Also, since it can
rest on the surface of the driveway rather than in a pit, it does
not require a drain. Furthermore, it is easily accessible for
service, and can be easily detached and moved to a new location.
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In the prior applications, the sensing arm was in a fixed
relationship to the chock- In this invention, the sensor arm pivots
and carries a roller that engages the wheel. This arrangement
solves two problems in prior devices. First, mounting a fixed arm
to contact the wheel at a low position, as in the prior devices,
creates a downward vertical force that is greater than the
horizontal force required to rotate the chock. Such a downward
force could induce twisting forces on the pivot pin which could
then increase the force necessary to move the chock. The roller
transfers this vertical force directly into the roadway surface.
Additionally, the roadway will not always be perfectly level
so there will be differences between the wheel height relative to
the rail. For example, if the wheel came to rest in a depression on
the roadway, a fixed sensor would contact the wheel at a higher
point on the wheel. This in turn would cause the carriage to stop
further back relative to the axle of the wheel and the chock would
rotate too soon, potentially interfered by the front of the wheel.
The use of the roller therefore provides a more accurate
methodology of sensing the position of the wheel. This invention is
effective as a restraining chock to engage a wheel closest to the
loading dock face. It will restrain a vehicle having two axles or
more, trucks or semitrailers, irrespective of the number of wheels
on each axle. Thus, as used herein, the phrase " separated axles"
means any combination of two axles on a vehicle. It includes the
two rear axles on a semi-trailer as well as the front steering axle
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and the rear driving axle of a two-axle vehicle. The phrase is used
to describe the initial positioning of the chock in front of one
axle but to the rear of another axle in the context of any pair of
axles on the vehicle.
Another aspect of this invention that is different from the
prior devices is the use of a brake to insure that the chock is
fully retracted prior to moving rearward so that it does not strike
the front of the wheel and prevents the carriage from moving into
the stored position. The brake is automatically released when the
lock assembly contacts the carriage assembly.
These and other aspects of this invention will be described in
greater detail by reference to the attached drawing and the
description of the preferred embodiment that follows.
Brief Description of the Drawing
Figure 1 is a plan view, partially cut-away, of the preferred
embodiment of this invention illustrating the wheel chock in a
retracted position;
Figure 2 is a side view, partially cut-away, illustrating the
wheel chock in a retracted position;
Figure 3 is a detailed view of the chock assembly;
Figure 4 is a detailed view of the sensing roller assembly;
Figure 5A is a detailed view of the components of the carriage
assembly;
Figure 5B is a partial view of the carriage assembly;
Figure 6 is a detailed view of the lock assembly;
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Figure 7 is a detailed view of the latch assembly;
Figure 8 is a detailed view of the brake release tube
assembly;
Figure 9 is a sectional view of the hydraulic cylinder;
Figure 10 is a front view with the vehicle wheel partially
cut-away to reveal the sensor roller;
Figure 11 is a side view, partially cut-away, illustrating the
carriage brake and release mechanism;
Figure 12 is a plan view illustrating the cylinder extending
as the wheel chock moves away from the wall and into engagement
with the wheel;
Figure 13 is a side view illustrating the cylinder extending
with the device partially cut-away to reveal the sensor roller in
contact with the wheel;
Figure 14 is a side view illustrating the chock extended to
engage a wheel;
Figure 15 is a plan view illustrating the chock engaging a
wheel and locked to restrain a vehicle;
Figure 16 is a plan view illustrating the latch re-setting;
Figure 17 is a side view illustrating the latch re-setting;
Figure 18 is a plan view illustrating the chock retracting to
disengage the wheel and the brake being released;
Figure 19 is a side view illustrating the chock retracting to
disengage the wheel with the device partially cut-away to reveal
the sensor roller in contact with the wheel;
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Description of the Preferred Embodiment
Referring first to Figures 1 and 2, a plan view and side view
respectively of a typical loading dock are depicted which has a
driveway surface 1, a dock face 2 and a dock floor 3. Dock bumpers
5 limit the position of the transport vehicle 10 and protect the
dock wall from impact damage. The vehicle 10 is shown for purposes
of illustration with two separated axles each having wheels 11, as
typically found on a semi-trailer. It will be understood that the
utilization of this invention is not in any way restricted by the
wheel/axle configuration of the vehicle to be retained. Thus, the
phrase "separated axles" means any two axles on the vehicle. It
covers the closely spaced axles on the rear of a semi-trailer
equally as separated axles on a two-axle vehicle.
An automatic chocking device is shown with the chock retracted
in the stored position. In Figures 1 and 2 the chocking device is
shown partially cut away to reveal the internal components. Figure
3 illustrates the chock assembly 20 with an arm 21. One end of the
arm 21 has a control arm 24 with a pin 2S, a pivot hole 26, and a
vertical pivot housing 23 which carries a lever assembly 103
comprising an arm 104 and a horizontal pivot housing 105. The
other end has a chock plate 22 which contacts the front of the
wheel of the vehicle 10 and a locking surface 27.
Figure 4 illustrates the sensing roller assembly 107
comprising an axle 108 and a roller 109.
Figure 5A illustrates the carriage assembly 30 for the chock
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assembly 20. A housing 31 is shaped to fit freely around the upper
portion of the guide rail 15 (see Fig. 2), and preferably has low
friction bearing plates 32 fitted into internal recesses of the
housing to reduce the friction when sliding along the track. Two
mounting lugs 33 and 34, attached to the top of the housing, each
have a vertical hole for mounting the chock assembly 20. A flange
35 with a hole 36 extends from the bottom of the housing 31. A
brake wedge 111 protrudes from the front of the housing and has an
angled surface 112. The housing 31 has a guide hole 113 above the
brake wedge 111. A bar 37 has one end attached to the housing and
has at the other end a shaft 38. A collar 39 is attached to the
end of the shaft 38 by means of a pin 40.
Figure 5B is a view of the carriage housing 31 partially cut
away to illustrate a guide bar 114 protruding from the front side
of the housing. The bar 114 carries a plate 115 with a guide hole
116.
Figure 6 illustrates the lock assembly 45. A housing 46 is
shaped to fit freely around the upper portion of the guide rail 15
(see Figs. 2 and 3) and is attached to a bar 50. A locking cam
surface 47 projects rearward from the top the housing and a hole 48
which passes through the lower part of the housing. The housing 46
has low friction bearing plates 49 fitted into internal recesses of
the housing in a manner similar to those in the housing 31 of the
carriage assembly 30. One end of the bar 50 has a plate 51 with a
hole 52 to carry one end of a hydraulic cylinder 70 See Fig. 9).
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The other end has a shaft 53. Also attached to the bar 50 is a
bracket 54, a boss 55 a vertical pin 56 and a horizontal bar 57.
Figure 7 illustrates a latch assembly 60 with a cam plate 61.
The cam plate has an elongated curved cam surface 62 and a shorter
angled cam surface 63. A latch plate 64 is attached to the
elongated cam surface 62.
Figure 8 illustrates a brake release tube assembly 120 with a
tube 121, and release plate 122 with a guide slot 123.
Figure 9 illustrates the double acting hydraulic cylinder
assembly 70 with a cylinder barrel 71 and a threaded mounting bolt
72. A rod assembly 75 has a rod 76 and a piston 77. The ports 78
and 79 are placed in the end of the rod 76 to eliminate external
plumbing which would otherwise be required to both ends of a
conventional cylinder. Fluid is carried to the cylinder from the
ports through hollow passages in the cylinder rod.
When hydraulic fluid is pumped in through the port 78, the
pressure on the piston 77 causes the rod assembly 75 to extend, and
when hydraulic fluid is pumped in through the port 79, the pressure
on the rod side of the piston causes the rod assembly to retract.
The rod assembly can be anchored by a pin 73 ( see Fig. 9) through
the hole in the end of the rod 76 and the cylinder barrel 71 will
then move without any hoses being exposed.
Figure 10 illustrates a front view, i.e. looking in toward the
loading dock, of the guide rail 15. The guide rail is shown
attached to the surface of the driveway by anchor bolts 16 and nuts
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17. Alternately it may be welded to a steel plate which has been
embedded in the concrete of the driveway. The technique of
affixation is not critical to this invention so long as the guide
rail is secured. The wheel 11 is partially cut away to illustrate
the sensing roller assembly 109.
In Figure 11 the chocking device is shown partially cut away
to reveal the components of the carriage brake mechanism. A brake
shoe 125 with a friction surface 126 rests on the angled surface
112 of the brake wedge 111. A brake release adjusting bolt 127
with an internal axial hole îs threaded into the rear of the brake
shoe 125. A release tube assembly 120 is inserted through the
guide hole 113 of the housing 31 and into the front of the brake
shoe 125. The release plate 122 is guided by the bar 114 passing
through the slot 123. A long spring tensioning bolt 128 is inserted
through the brake release adjusting bolt 127, through the release
tube assembly 120, and through the hole 116 in the plate 115. A
brake spring 130 is placed on the spring bolt 128 and compressed by
a nut 131. The nut can be prevented from rotating by a tab
extending to engage the guide bar 114. The tension of the spring
130 holds the brake shoe in contact with the underside of the guide
rail 15. The carriage assembly 30 can be moved forward along the
rail 15 by overcoming the tension of the brake spring 130.
However, when the carriage assembly is forced toward the wall,-the
brake is self-energized by the wedging action of the brake shoe 125
sliding up the sloped surface 112 of the brake wedge 111 and this
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prevents the carriage assembly 30 from moving.
The brake can be released by forcing the release tube assembly
120 against the end of the brake release adjusting bolt 127 and
moving the brake shoe 125 away from the wedge 111. The brake can be
released in one of two ways~ When the lock assembly 45 is moved
fully against the carriage assembly 30 as in Figure 1, the
horizontal bar 57 on the lock assembly 45 will engage the release
plate 122. The release position of the brake relative to the
position of the lock assembly 45 can be varied by turning the brake
release adjusting bolt 127 into and out of the brake shoe 125. The
second release method is by exerting rearward pressure on the
sensing roller 109. This causes the lever 104 to pivot in the
housing 23 of the chock assembly 20. As illustrated in Fig. 12, a
brake release lever 135 pivots on the pin 25. The end of the lever
104 moves the outer end of the brake release lever 135 forward,
causing the inner end of the brake release lever to move rearward
and engage the release plate 122.
The relationship of the components thus far discussed is shown
in Figures 1, 2, 10, 11 and 12. The carriage assembly 30 and the
lock assembly 45 are mounted on the rail 15, as illustrated in Fig.
2. The shaft 53 of the lock assembly 45 fits into the hole 36 in
the flange 35 of the carriage assembly 30 and the shaft 38 fits
into the hole 48 in the lock assembly housing 46. Thus, the
carriage assembly 30 and the lock assembly 45 are provided with
resistance against lateral motion by the rail 15 and are provided
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resistance against twisting motion by engagement with each other.
The lock assembly 45 has freedom of axial motion relative to
carriage assembly 30 limited by the housing 46 of the lock assembly
45 being trapped between two shoulders on the shaft 38 formed by
the bar 37 and the collar 39 (Fig.5A).
The chock assembly 20 is mounted between the lugs 33 and 34
of the carriage assembly 30 and pivots on a pin placed in hole 26.
The sensing roller assembly 107 is carried by horizontal pivot
housing 105. The roller 109 rests on the driveway and is free to
pivot up and down with variations in the driveway surface. The
latch assembly 60 pivots on the pin 56 of the l~ck assembly 45 and
is held by a spring 65 as shown in Figures 2 and 13. The latch
assembly can rotate horizontally to any position about the vertical
axis of the pin 56, but friction produced by the pressure of the
spring 65 causes the latch assembly to maintain its position until
it is moved by an external force. The latch assembly 60 also has
freedom for limited vertical rotation away from the horizontal
plane, but the pressure of the spring 65 forcing the plate 61
against the top of the boss 55 causes the latch assembly to return
to the horizontal plane. Preferably the actuating mechanism is
enclosed by a cover assembly 90 as shown cut away in Figures 1, 2
and 10. The rear of the cover is attached to the carriage assembly
30 and the forward end of the cover is supported by the lock
assembly 45. The cover 90 protects the mechanism from the elements
and also protects personnel from contact with moving parts.
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In operation, when no transport vehicle 10 is at the dock, the
chock 20 is retracted outside of the vertical surface of the guide
rail as shown on Figures 1 and 10. The carriage assembly 30 is
positioned at the rear of the guide rail 15 near the dock wall 2.
When a vehicle 10 being backed up to the dock is not properly
positioned to the dock, the outer rear wheel 11 will be guided by
the vertical surface of the rail 15. That is, the rail 15 tends to
guide the vehicle so that it is pre-positioned relative to the
chock mechanism. When the chock device is actuated, hydraulic fluid
is pumped from a hydraulic power unit (not shown) to the port 78 on
the cylinder rod assembly 75 and this causes the hydraulic cylinder
70 and the lock assembly 45 to be pushed forward away from the dock
wall 2. As the lock assembly moves forward, the end of the cam
surface 62 is deflected by the pin 25 which- causes the latch
assembly 60 to rotate counterclockwise as shown in Figure 12. The
latch assembly is held in the rotated position by the friction of
the spring 65 (see Fig. 13).
As the cylinder 70 extends, the housing 46 of the lock
assembly contacts the collar 39 on the carriage assembly 30 and
causes the carriage assembly to move forward. As the carriage
assembly 30 continues to move forward, away from the loading dock,
the sensing roller 109 contacts the rear of the wheel 11 as shown
in Figures 12 and 13. The small diameter of the roller 109 allows
it to pass under a mud flap or a lowered hydraulic tail gate to
contact the rear of the wheel 11. The vertical freedom of the
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roller assembly allows the roller to contact the driveway and the
wheel 11 with minimal vertical force transferred to the chock
assembly 20. A fixed sensor bar contacting the wheel at such a low
height would generate a vertical force greater than the horizontal
force and might create a twisting force which prevents the chock
assembly from pivoting freely.
As the cylinder 70 continues to extend, the horizontal force
on the roller 109 causes the chock to extend in front of the outer
rear wheel as shown in Figure 14. When the chock is fully extended
the sensing roller 109 is forced against the back of the tire and
the carriage assembly 30 and lock assembly 45 will be prevented
from moving. The hydraulic pressure will increase and will be
sensed by an electrical pressure switch or by a spring sequence
valve (not shown), both of which are well known in the loading dock
industry. The power unit will then direct hydraulic fluid through
the port 79 to the rod side of the cylinder 71 and cause the
cylinder 70 to retract. The lock assembly 45 will then move
rearward toward the dock. The locking surface 47 of the lock
assembly will engage the locking surface 27 of the chock assembly
20 and the chock assembly 20 will be locked in the extended
position as shown on Figure 15.
Figures 14 and 15 illustrate the chock engaging the front of
the wheel 11. As the lock assembly 45 moves rearward towards the
carriage assembly 30, the cam surface 63 of the latch assembly 60
will engage the pin 25. As the cam surface 63 is guided by the pin,
16
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the latch assembly 60 will rotate clockwise to the initial position
as shown in Figure 15.
The horizontal bar 57 on the lock assembly 45 will engage the
brake release plate 122 on release tube 120. The elements are
illustrated in Figure 11. When the brake is released the carriage
assembly 30 will move rearward, toward the dock, and the chock
surface 22 is held firmly against the wheel 11 preventing the
vehicle 10 from moving. The pressure switch will then sense the
increase in pressure and cause the power unit to stop and the
vehicle 10 will be secured.
When the loading operation is completed and the vehicle is to
be released, the hydraulic cylinder 70 is extended. The lock
assembly 4S moves forward and releases the locking surface 27 of
the chock assembly 20 as illustrated in Figure 16. As the lock
assembly moves forward the angled latch plate 64 of the latch
assembly 60 is deflected downward by the lower end of the pin 25
on the chock assembly 20. This is shown in Figure 17 where a
portion of the latch assembly 60 is cut away to show the latch
plate 64 and the pin 25. When the lock assembly moves fully
forward the latch plate 64 will pass under the pin 25 and the
spring 65 will cause the latch assembly to rotate back to the
horizontal plane with the latch plate positioned in front of the
pin 25.
The lock assembly 45 will move the carriage assembly 30
forward until the sensing roller 109 again contacts the rear of the
CA 02234974 1998-04-17
wheel ll and the pressure switch will then cause a valve to shift
and the hydraulic cylinder 70 to retract. The latch bar 64 will
engage the front of the pin 25, preventing the lock assembly 45
from moving closer to the carriage assembly to engage the locking
surface 27 of the chock 20, and also urging the chock assembly 20
to rotate toward the retracted position. The carriage assembly is
prevented from moving toward the wall 2 by the brake engaging the
underside of the rail 15 as shown in Figure 11. The force of the
latch bar 64 against the front of the pin 25 will force the chock
to rotate away from the wheel 11. If the wheel ll is large, as the
chock rotates, the roller 109 may move against the rear of the
wheel. The force on the roller 109 would resist the rotation of the
chock assembly 20. However, force on the roller will also cause
the lever 104 to rotate against the outer end of the brake release
lever 135. The inner end of the brake release lever will engage the
release plate 122 and cause the brake to release and allow the
carriage assembly 30 move until the force on the roller 109 is
reduced. Thus the chock assembly 20 will continue to rotate until
it is fully retracted. As the lock assembly 45 moves closer to the
carriage assembly 30 the horizontal bar 57 on the lock assembly
will engage the brake release plate 122 and allow the entire
mechanism to move to the stored position against the wall 3 as
illustrated in Figure 1.
When the carriage assembly 30 has moved fully rearward along
the rail, a limit switch (not shown) mounted at the end of the rail
18
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15 will sense the carriag~ position and cause the power unit to
stop with the chock in the stored position. If the switch should
malfunction, the pressure. switch will sense the increase in
hydraulic pressure and then cause the power unit to stop.
Modifications of this invention are possible. For example,
while a hydraulic cylinder is shown, the chocking device of this
invention could be powered by other means such as an electric
motor driving a screw, or chain and sprockets. Also, there other
possible configurations of the latch which controls the locking and
release of the chock assemblies. This chocking device could be
used alone, or in pairs to chock the wheels on both sides of the
vehicle.
Iq
