US3105251A - Mobile bridge - Google Patents

Description

Oct. 1, 1963 H. C. STEVENS, JR-. ETAL MOBILE BRIDGE 7 Sheets-Sheet 1 Filed Sept. 12, 1958 INVENTORS. 6. STAT/[1V5 JP.

Oct. 1, 1963 H. c. STEVENS, JR., ETAL 3,105,251

MOBILE BRIDGE Filed Sept. 12, 1958 7 Sheets-Sheet 2 7 I Z. 5 23b 7 74 INVENTORS. HOB 4P0 C. 575/5/1/5 JP.

Oct. 1, 1963 H. c. STEVENS, JR., El'AL MOBILE BRIDGE '7 Sheets-Sheet 3 Filed Sept. 12, 1958 IN VENTORS. #011471? 6. 572/5169" J/F.

MOBILE BRIDGE '7 Sheets-Sheet 4 Filed Sept. 12, 1958 Oct. 1, 1963 H. c. STEVENS, JR., ETAL 1 MOBILE BRIDGE 7 Sheets-Sheet 5 Filed Sept. 12, 1958 I MM M u o T m It mwm a? .3 mm a y i a NV v u m 1 a 0 m ww h m QQ N\ B 2 www Oct. 1, 1963 H. c. STEVENS, JR., EI'AL 3,105,251

MOBILE BRIDGE Filed Sept. 12, 1958 7 Sheets-Sheet 6 W 1 Z .FL. 1i 1 \L gym? ARA/0Z0 msszw United States Patent 3,105,251 MQBILE BRIDGE Howard C. Stevens, .Ir., Muskegon, and Walter Arnold Paulssen, Spring Lake, Mela assignors to Manning,

Maxwell 8; Moore, Inc, Muskegon, Micln, a corporation of New Jersey Filed Sept. 12, 1958, Ser. No. 760,725 4 Claims. (Cl. 1.4-1)

The present invention relates generally to portable bridges and concerns more particularly a folding bridge especially suited for military assault operations.

It is the primary aim of the invention to provide an extremely portable bridge adapted for simple, rapid placement which is capable of reliably carrying heavy loads. It is a collateral object to provide a lightweight bridge which can be towed as a compact, high speed trailer-type vehicle, easily unfolded to its full length and spread to its full width, and thereafter launched into position by a heavy combat vehicle which can immediately cross the newly placed bridge.

With more particularity, it is an object of the invention to provide a lightweight, folding, portable bridge of the above type having a 40 to 60 foot span capable of bearing loads of over 50 tons. In a particular case, a bridge embodying the invention and having a 40 foot span and a 50 ton capacity, weighs only 16,000 pounds and has an overall folded length of just 26 feet.

It is also an object to provide a bridge as characterized above that, when folded and narrowed into towing condition, is sufiiciently compact and maneuverable to move at 40 m.p.h., has the cross-country mobility of a medium tank, crosses bridges including those of its own type, and fords streams and pushes through brush without damage.

It is another object to provide a bridge as described which, when unfolded and spread, can travel over terrain usually traveled by tracked vehicles at speeds up to 15 m.p.h. and, when at its intended site, can be launched into position within one minute without exposing personnel or the operating mechanism of the bridge. It is a collateral object to provide such a bridge that is particularly adapted for being launched by a medium tank or like vehicle without obstructing the vision of the tank driver or the tank commander, and without interfering with the use of the tanks weapons or the ability of the tank to proceed with its normal mission after launching the bridge.

It is an additional object to provide a bridge of the above type which can be quickly converted from towing to launching condition by a small group of men without special tools or equipment. It is an allied object to provide a bridge of the above nature whose unfolding and spreading operations are traction powered so that no power transmitting coupling from another power source is required.

In more detail, it is an object to provide a lightweight hinged section, bridge constructed so that its hinges are not stressed by the heavy loads capable of being borne by the bridge when in use.

Other objects and advantages of the invention will become apparent upon reading the following detailed desoription and upon reference to the drawings in which:

FIGURE 1 is a side elevation of a bridge embodying the invention in transport condition behind a towing vehicle;

FIG. 2 is a rear elevation of the bridge shown in FIG. 1;

FIG. 3 is a fragmentary side elevation of the bridge shown in FIG. 1 partially unfolded and secured to a launching vehicle;

FIG. 4 is a transverse section taken along the line 44 of FIG. 3;

3,165,2'5 l Patented Oct. I, 196i;

FIG. 5 is a horizontal section of the bridge in its fully unfolded and spread condition;

FIG. 6 is a longitudinal section taken approximately on the line 66 of FIG. 5;

FIG. 7 is a fragmentary view partially in section of one of the hinged joints ofthe bridge taken along the line 7-7 of FIG. 9;

FIG. 8 is a fragmentary section taken along the line 8-8 of FIG. 7;'

FIG. 9 is a fragmentary section taken along the lines 9-9 of FIG. 3 and FIG. 7;

FIG. 10 is a fragmentary plan view of the launching hitch for the bridge shown in FIG. 3;

FIG. 11 is a fragmentary longitudinal section taken approximately on the line 11-11 of FIG. 10;

FIG. 12 is a fragmentary longitudinal section taken along the line 1212 of FIG. 10;

FIG. 13 is a schematic diagram showing the hydraulic circuit for the bridge; and

FIGS. 14, 15 and 16 are stop-motion views showing sequential steps during the launching of the bridge.

While the invention will be described in connection with a preferred embodiment, it will be understood that we do not intend to limit the invention to that embodiment. On the contrary, we intend to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

Turning now to FIG. 1, there is shown a bridge 10 embodying the present invention disposed in its' narrowed, folded, transport condition. The bridge is hitched to the rear of a towing vehicle 11 by means of a hitch plate 12 so that the bridge 10 forms a trailer-like vehicle which may be towed at high speeds with the maneuverability common to trailers of this general type.

In keeping with the invention, the bridge 10' may be unfolded and spread from its trailer-like transport condition to its operating condition, in which the bridge is along, low, cantilever structure capable of being launchedand crossed by a heavy vehicle such as a medium tank 13 (see FIGS. 14-16). Briefly, the illustrated bridge is made up of a wheeled undercarriage 21 which supports apair of main trackway members 22a, 22b (see FIG. 2) which have a box-girder form of construction. Each of the main trackway members 22a, 22b supports rear ramps 23a, 2312, respectively, and front ramps 24a, 24b, respec-' tively. A pair of towing and landing arms, of which only the arm 25 is shown, couple the undercarriage 2 1 and the towing hitch 12. It will be understood that the arm 25 underlies the main trackwa'y member 22b and that a similar arm underlies the main trackway member 2221 when the bridge is in its transport, FIG. 1, position.

In carrying out the invention, the main trackway mem 'bers 22a, 22b, are laterally shiftable on the undercarriage 21 and the ramps 23a, 23b, and 24a, 245 are hinged on their respective main trackway members, 'with provision being made for spreading the main trackway members and for unfolding the ramps so that the bridge can be readily converted from its compact transport condition to its operating condition. In the illustrated embodiment, the undercarriage 21 includes a box frame 31 which sup ports a standard axle assembly 32 that carries sets of dual wheels 33, 34. For supporting the members 2211, 22:6 for lateral shifting, these members are provided-With spaced pairs of slide tubes 35a, 3511, respectively, which slidably' fit within sleeves 36 that are fixed to the box frame 31 by strap assemblies 37 (see FIGS. 2 and 4) The tubes 35a, 35b slide freely within the sleeves 36 so that the main trackway members 22a, 221) can be laterally shifted between their transport FIG. 2 positions and their spread FIG. 4 positions.

The undercarriage 21 is disposed near one end of the main trackway members 22a, 22b for a reason which will be brought out below, and to support be longer overhang ing end of these members, the main trackway members are rested on rollers which are 'journaled on the upper edges of the landing arms. That is, the member 22]; rests on a roller 38 that is journaled on the arm 25 along a longitudinal axis so as to facilitate the lateral shifting of the overlying main trackway member. The roller 33 rides in a channel 39 which is secured to the underside of the main trackway member 22b. It will be understood that the main trackway member 22a rides on a roller similar to the roller 38 journaled on its underlying landing arm.

.To lock the main trackway members in their narrow transport position, pins are passed through holes 41, 42 formed on the trackway members and the undercarriage 21 respectively (see FIG. 4). It will be appreciated that when the trackway members are narrowed, these sets of holes move into alinement so that a pin may be easily inserted therethrough.

In order to lock the main trackway members in their spread position and to rigidify the bridge, a plurality of cross braces in the form of gates 45 are provided (see FIGS. 4 and 5). In the illustrated embodiment, the gates 45 are hinged at 46, 47 to the main trackway member 22b and to the ramps 23b, 24b so that when the bridge is narrowed, the gates can be folded to lie flat against the inner sideof the member 2212 and the ramp. When the bridge is spread, the gates are swung across the gap between the main trackway members and between the ramps, and locking rods 48 are passed through complementary portions 49, 50 of a hinge-like lock carried by the trackway member 22a and the ramps 23a, 24a, and the gates 45, respectively.

For the purpose of driving the members 22a, 2212 between their transport and their spread positions, hydraulic motors 5154 are secured within the tubes 35a, 35b (see FIG. 5). The motors 51, 54 are provided with opposed actuator rods 55 which are secured to a common anchor block 56 mounted on the undercarriage frame 31. The motors 52, 53 have similar actuator rods 57 secured to an anchor block 58 carried by the frame 31. The motors 51, 54 are preferably double-acting cylinders so that by properly directing fluid to the motors, the trackway members 22a, 22b can be narrowed or spread. Since the motors act on the common anchor blocks 56', 68, it can be seen that the forces exerted "by the motors tend to cancel out,

during lateral movement of the members 22a, 22b.

Turning next to the structure for hinging the front and rear ramps to the opposite ends of the main trackway members 22a, 22b, as a matter of convenience only the connection at the outer side of the rear ramp 23b and the main tracleway member 22b will be described in detail, and it will be understood that the connection at the inner side of the member 22b and the ramp 23b, as well as the connections between the other ramps and their respective members, are similar. In the illustrated embodiment, the rear ramp 23b is provided with a bifurcated hinge plate 61 which sandwiches a hinge plate 62 secured to the member 22b. The hinge plates extend upwardly above the top cord lines of their respective bridge components and a hinge pin 63 passes through the hinge plates so as to define a hinge axis which lies above the top cords of both the main trackway member 2211 and the rear ramp 23b. The rear ramp 23b swings about the hinge pin 63 from its folded FIG. 1 position to its unfolded FIG. 3 and FIG. 7 positions.

To avoid having the hinge pin 63 bear heavy loads when the bridge is in use, a pressure pin 64 is fixed in the bifurcated plate 61 so that when the bridge is unfolded, the pin 64 lies approximately along the alined top cords of the member 22b and the ramp 2312. As the ramp 23b is unfolded, the pin 64 is brought into abutting contact 'and little strain is imposed upon the undercarriage 21' 4- with the front edge 65 of the plate 62, and the plate 62 is preferably provided with an arcuate relieved portion 66 which receives the pin 64. The pressure pin 64' thus locks the plates 61, 62 against relative vertical movement when the ramp 23b is unfolded.

When a bridge is loaded, it will be understood that the top cord elements of the bridge are subject to compressive forces. In the case of the bridge 1%, an operating load will squeeze the pressure pin 64 between the plates 61, 62, so as to relieve the hinge pin 63 and the actual hinge structure of the relatively high forces involved. In this way, the hinges are protected from damage when the bridge is in use.

To lock the ramp 23b in its unfolded position and to join the lower cord elements of the members 2212 and the ramp 23b, a bifurcated plate 67 is positioned on the member 22b so as to straddle a plate 68 on the ramp 2312 when the ramp is unfolded, and a locking pin 69 is passed through the overlapping plates.

For the purpose of folding and unfolding the ramps, a hydraulically powered elbow linkage is employed. As was the case with the hinge structure described above, the linkages for folding each of the ramps are identical and therefore only the linkage for folding the ramp 23!; will be referred to in detail. In the illustrated embodiment a pair of actuating arms 71 are journaled, one near each end, on a shaft 72 that is secured between plates 73 extending from the end of the main trackway member 22b (see FIGS. 1 and 7). The outer ends of the arms 71 are coupled to the ramp 235 by pairs of links 74, 75, which are rotatably secured to a shaft 76 that extends between the plates 68 on the ramp 23b.

It is important to note that the above described arrangement of the arms 71 and the links 74, permits the elbow linkage formed thereby to be disposed entirely beneath the upper surface of the bridge when the latter is unfolded (see FIGS. 3 and 7 Thus, the upper surface of the bridge, when unfolded, is completely unobstructed, and the operating linkages are completely protected.

Secured to each of the arms 71 and also journaled on the shaft 72 are double sprockets 81, and chains 82 (see FIGS. 1 and 5, not shown in FIGS. 79) are trained about the sprockets 81 and are extended forwardly about idler sprockets $3 journaled on a shaft 84 fixed transversely across the main trackway member 22b. It may now be understood that by driving the chains 82, the sprockets 81 will be rotated so as to swing the arms 71 and, through the links 74, 75', pivot the ramp 23b about its hinge pin 63.

For driving the chains 82, a hydraulic motor b is disposed longitudinally within the member 22b and is provided with an actuating rod 91 which is adapted to be connected to a bar 92 that extends across and is fixed to each of the chains 82 (see FIG. 5). In the illustrated embodiment, the actuating rod 91 of the motor 90b is coupled to the drive bar 92 by alining a hole 93 in the rod 91 with a hole 94 in the bar 92, whereupon a pinv can be passed through the alined holes to couple the motor ill) with the chains 82.

The hydraulically powered elbow linkage described above for swinging the ramp 23b is duplicated at the opposite end of the main trackway member 22b for the purpose of swinging the forward ramp 24b. Thus, a drive bar 95, similar to the bar 92, is found at the front end of the member 2211 and it will be appreciated that moving this bar back and forth is effective to fold and unfold the forward ramp 24b.

It is a feature of the invention that the single motor 9% is effective to operate both the front and rear ramps 23b, 2411. For this purpose, the actuator rod 91 of the motor 9% is proportioned so that when the rod drives one of the bars 92, 95 through its full range of travel, it is automatically positioned to be attached to the other bar so that it may move it through its full range of travel. That is, the motor 991) does not drive the bars 92, 95

simultaneously, but rather first one ramp is unfolded and then the other, with the actuator rod 91 of the motor 90b being proportioned so that the double acting motor 90b need make only one cycle to unfold both the rear and front ramps.

This action can be seen by reference to FIG. 5, wherein the rod 91 is positioned toward the left in that figure so as to be coupled with the bar 95. Actuation of the motor 9% moves the rod 91 and the bar 95 toward the left and thereby swings the front ramp 24b up onto the main trackway member 2212. When the rod 91 has been driven through its full range of travel toward the left and the ramp 24b is fully folded, the hole 93 will lie in aline ment with the hole 94 and the rod can be disengaged from the bar 95 and pinned to the bar 92. The motor 9% is then driven in a reverse direction toward the right, whereupon the rear ramp 23b is folded up onto the member 2211. It will be appreciated that the operation of the motor 9% is virtually identical, except being reversed, during the unfolding operation.

The identically powered linkages for operating the front and rear ramps 24b, 231), are duplicated on the main trackway member 22a for the purpose of folding the associated front and rear ramps 24a, 23a, and a motor 95a is provided for powering these linkages. The operation is identical to that described above in connection with the member 22a and ramps 23a, 24a.

As a feature of the invention, the hydraulic motors 51-54 and 90a, 9811 are driven by rotation of the wheel assemblies 33, 34 so that the bridge is traction powered. That is, power for spreading and unfolding the bridge is derived from towing the trailer-like bridge without an additional power transmitting coupling being required. This is accomplished by driving a pump 100 through differential gearing 151 forming a part of the axle assembly 32 (see FIGS. 5, 6 and 13). Selective operation of the pump 1% is secured by interposing a clutch 102 operated by control lever 193 between the pump and the differential gearing 101. The clutch 102, not shown in detail, may be of any convenient type and in a practical case is of a positive, jaw-type engagement.

The pump 1%, when driven, draws oil from a reservoir. 1124 and distributes it through pressure lines 105 to a set of valves Hid-1&9 which control the various hydraulic motors. Return lines 110 are provided from the valves back to the reservoir 104.

The valves 1426-1139 are preferably manually operated and each has an Off position which prevents fluid from passing therethrough. The valve 1% is effective to admit fluid to either ends of the motors 51, 52 so as to control the lateral shifting of the main trackway member 22a. The valve 157 selectably admits fluid to either end of the motor 93a so as to control the unfolding of the ramps 23a, 24a. Similarly, the valve 108 controls the motor 9% and the valve 16-9 controls themotors 53, 54.

In the preferred embodiment, flow control valves 115 are interposed in the hydraulic lines between the valves 197, 153 and the respective motors 99a, 96b, and the flow control valves are effective to limit the rate at which fluid is exhausted from the motors to a predetermined value. That is, when hydraulic pressure is introduced at one end of the motor, the motor will move only so rapidly as the flow control valves 115 will permit fluid to be exhausted from the opposite end of the motor. In this way, the motors 91hr, 95b restrain. their respective ramps from falling freely when they are overcentered and begin. to move toward a levelposition. It will also be understood that once the ramps are overcentered, their weight will continue to carry them toward their alternate position so that continued operation of the pump 160 is not required through the full range of movement of the motors 90a, 9%.

For the purpose of releasably coupling the bridge to a launching vehicle, a standard hitch 120 is modified by securing thereto a universally mounted cross bar 121 effective to releasably engage the ends of the ramps 23a 23b (see FIGS. 10l2). To universally mount the bar 121 on the hitch 120, a clevis pin 122 is rotatably secured in a hole 123 formed in the forward end of the hitch so as to be swingable about a longitudinal axis, and the bar 121 is pivoted to the pin 122 by a bolt 124 so that the bar may swing about a vertical axis.

For releasably coupling the ends of the ramps 23a, 23b to the cross bar 121, the inner ends of the ramps are provided with hitch plates 126 and 127, respectively. Each of these plates carries an inwardly directed pin 128 which are received in tapered slots 129 at each end of the cross bar 121.

For retaining the pins 128 in the slots 129, locking pins 131 are slidably fitted in the cross bar so as to block withdrawal of the pins 128 from the slots. The locking pins 131 are freely slidable in the cross bar and are retained in position by spring biased latches 132 which are slidably mounted at the top of the cross bar and which pass through apertures 133 formed in the tops of the locking pins. It may be seen that by withdrawing the latches 132 rearwardly against their bias and clear of the openings 133, the locking pins 131 will freely drop downwardly to the dashed line position indicated in FIG. 12. This enables the launching vehicle to back away a few inches and release the bridge 10.

In order to release the latches 132 without the exposure of personnel during the launching operation, a rod 135' is secured to the rear end of each of the latches 132 and a cable 136 is fastened to the approximate center of the rod. When launching the bridge, the cable 136 is run back to the launching vehicle where it can be operated to release the locking pins 131 from a shielded position.

Pursuant to the invention, the landing arms such as the arm 25 are efiective to permit the bridge to be pushed over a ditch only slightly narrower than the total length of the main sections 22a, 22b and their front and rear ramps, combined. To accomplish this, the landing arms are approximately as long as the distance from the undercarriage 21 to the rear of the bridge when the rear ramps 23a, 23b are unfolded, and the arms are bolted to the outer sides of the fnont ends of the front ramps 24a, 24b so as to extend forwardly and upwardly when the bridge is to be launched. The effect of this construction can be seen by reference to FIGS. 14-16. As the launching vehicle 13 approaches a normally impassable ditch 140, the front end of the bridge 10 hangs out over the ditch as the undercarriage 21 approaches the near bank 141. Continued forward movement of the launching vehicle pushes the undercarriage 21 off of the near bank 141 so that the bridge topples forwardly and the landing arms strike the far bank 142 even though the ends of the front ramps 24a, 24b cannot yet reach the far bank.

The launching vehicle 13 continues to push the bridge 10 forwardly and the sloping landing arms act to cam the front end of the bridge 10" up onto the far bank 142. When the forward ends of the front ramps 24a, 24b are solidly placed on the far bank, the bridge is released from the launching vehicle and placement is complete. The vehicle 13 may thereafter proceed across the bridge and perform its normal mission. Since the landing arms 25 are bolted to the outer sides of the front ramps 24a, 24b, they do not interfere with the passage of vehicles over the bridge.

As a further feature of the invention, the bridge is In the illustrated embodiment, theport condition to its spread and unfolded launching condition, it will first be understood that the bridge is transported behind a towing vehicle 11 as is a normal trailer to a point conveniently near the site of the biidges intended installation point. In a military operation, of course, this site would be selected for the security of the towing vehicle and the man working on the bridge.

The first step in the conversion operation is to unfold V the rear ramps 23a, 231), since this will reduce the weight on the roller 38 and the similar roller under the member 22a and minimize the chances of binding when the main trackway sections 22a, 22b are spread. To unfold the rear ramps, the actuator rods of the motors 90a, 96b are pinned to the ramp drive bars, for example, the rod 91 is pinned to the bar 92. The clutch 192 is engaged by operating the lever 103 and the valves 1G7, 193 are opened to direct fluid to the proper end of the motors 90a, 90b. The bridge is then towed by the towing vehicle 11 for a short distance which, in a practical case, involves pulling the bridge at three to four miles per hour for approximately 180 feet, at which time the rear ramps swing overcenter and their weight moves them into unfolded position. The rear ramps are then looked in place by inserting locking pins including the pin 69.

The next step is to spread the main trackway members 22a, 22!). To accomplish this, the valves 167, 168 are closed and the valves 1%, 109 are opened to admit fluid to the proper ends of the motors 5154. The bridge is a then towed at the same slow speed until the members are fully spread, and the cross bracing gates 45 are swung transversely and are locked in place by insertion of the rods 48. a

After spreading the trackway members, the forward ramps are unfolded. This is accomplished by moving the launching vehicle into position and locking the pins 128 in the slots 12.9. The bitch is then disconnected, the landing arms 25 dropped, and the towing vehicle 11 pulled away. Next, the valves 106, 199 are closed and the valves 197, 193 opened to direct fluid to the proper end of the motors 99a, 90b. The actuating rods for the motors need not be repositioned since their movement, to the left in PEG. 5, during the unfolding of the rear ramps positions them accurately for coupling to the drive bars associated with the front ramps. Thus, the rod 91 is unpinned from the bar 92 and is pinned to the bar 95.

The launching vehicle then pushes the bridge slowly for a short distance until the forward ramps swing overcenter and drop into position, whereupon they are pinned and locked.

Finally, the landing arms 25 are bolted to the outer sides of the front ramps 24a, 24b, the clutch 1112 is disengaged, and the curbs 159 are unfolded and locked into position to complete the conversion of the bridge.

It will be noted that conversion of the bridge requires no special tools or equipment and can be accomplished by a small group of men quite rapidly.

While the bridge it) described above is traction powered and is adapted to be towed as a trailer, those skilled in the art will appreciate that the bridge may be readily adapted so as to be self-powered and/or self-propelled.

It will also be observed that an endless track type of undercarriage could readily be substituted for the Wheeled undercarriage 21 illustrated, and it is intended that the term wheeled in the following claims should refer to endless tracks as well as the more conventional wheel assemblies.

Preferably, the main trackway members and the ramps of a bridge'embodying the invention are constructed in box girder form of aluminum for lightness and strength.

We claim as our invention:

1. A portable bridge comprising, in combination, a wheeled undercarriage, a pair of longitudinally extending trackway members spaced side by side on said undercarriage and being slidably mounted thereon for relative lateral movement, means on said undercarriage for laterally moving said trackway members, said undercarriage being disposed near one end of said members, a hitch arm coupled to said undercarriage and extending from the undercarriage to a point spaced outwardly of the opposite end of said members so that the extending members rest on said arm, and friction reducing means disposed between said arm and said members for facilitating the lateral movement of said members.

2. A portable bridge comprising, in combination, a wheeled undercarriage, a pair of longitudinally extending trackway members spaced side by side on said undercarriage and being slidably mounted thereon for relatively lateral movement, means on said undercarriage for laterally moving said trackway members, said undercarriage being disposed near one end of said members, a pair of hitch arms coupled to said undercarriage and extending from the undercarriage to points spaced outwardly of the opposite end of said members each of said arms being disposed beneath one of said trackway members so that the extending members rest. on said arms, and longitudinally journaled rollers disposed between said arms and said members for facilitating the lateral movement of said members.

3. A folding bridge comprising, in combination, a main trackway member, a ramp extending from each end of said trackway member, said ramps being pivoted to said member about transverse axes so that the ramps may be folded up onto the said member, a hydraulic cylinder disposed longitudinally within said member, a folding linkage for each of said ramps, and means for selectively coupling said cylinder to said linkages for folding and unfolding said ramps.

4. A folding bridge comprising, in combination, a wheeled undercarriage, a main trackway member mounted on said undercarriage, a ramp extending from each end of said trackway member, said ramps being pivoted to said member about transverse axes so that the ramps may be folded up onto the said member, a hydraulic motor disposed longitudinally within said member, a hydraulic pump drivingly coupled to the wheels of said undercarriage, said pump being in fluid communication with said motor, a folding linkage for each of said ramps, and means for selectively coupling said motor to said linkages for folding and unfolding said ramps upon movement of the bridge on its undercarriage.

References Cited in the file of this patent UNITED STATES PATENTS 484,086 Cassidy Oct. 11, 1892 1,928,551 Ball Sept. 26, 1933 2,321,677 Higgins June 15, 1943 2,556,175 Frost Tune 12, 1951 2,639,450 Ramer May 26, 1953 2,687,225 Martin Aug. 24, 1954 FOREEGN PATENTS 818,987 France June 28, 1937 859,277 France June 3, 1940 737,573 Germany July 16, 1943 699,321 Great Britain Nov. 4, 1953 1,148,982 France July 1, 1957 779,361 Great Britain July 17, 1957 1,019,339 Germany Nov. 14, 1957

Claims (1)

1. 3. A FOLDING BRIDGE COMPRISING, IN COMBINATION, A MAIN TRACKWAY MEMBER, A RAMP EXTENDING FROM EACH END OF SAID TRACKWAY MEMBER, SAID RAMPS BEING PIVOTED TO SAID MEMBER ABOUT TRANSVERSE AXES SO THAT THE RAMPS MAY BE FOLDED UP ONTO THE SAID MEMBER, A HYDRAULIC CYLINDER DISPOSED LONGITUDINALLY WITHIN SAID MEMBER, A FOLDING LINKAGE FOR EACH OF SAID RAMPS, AND MEANS FOR SELECTIVELY COUPLING SAID CYLINDER TO SAID LINKAGES FOR FOLDING AND UNFOLDING SAID RAMPS.

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