US3912093A

US3912093A - Hoist truck with planetary gear assemblies and load sensor means

Info

Publication number: US3912093A
Application number: US514184A
Authority: US
Inventors: Melvin W Kruschke
Original assignee: PETERSON TRACTOR CO
Current assignee: PETERSON TRACTOR CO
Priority date: 1974-10-11
Filing date: 1974-10-11
Publication date: 1975-10-14
Anticipated expiration: 1992-10-14
Also published as: CA1006868A

Abstract

A field service truck having a boom with two converging beams supporting a hoist pulley and track-mounted pivotal boom supports enabling fore-and-aft movement powered by a travel motor. A boom winch for raising the boom and a hoist winch are journaled around a common shaft carrying planetary gear assemblies. The device also has a sensor for determining when a predetermined tension is exerted on the cable of the boom winch and disabling means for stopping the motors for both winches and the travel motor when the sensor indicates that the predetermined tension has been exceeded, thereby preventing overloading the boom line and related structure.

Description

United States Patent 1191 ASSEIVIBLIES AND LOAD SENSOR lVIEANS Inventor: -Melvin W. Kruschke, Fremont,

Calif.

Assignee: Peterson Tractor Co., San Leandro,

Calif.

Filed: Oct. 11, 1974 Appl. No.: 514,184

US. Cl. 214/75 H; 212/8 R; 212/39 B; 214/86 A; 254/145; 254/184 Int. Cl. B60? 1/46; B66C 23/00; B66D 1/26 Field of Search 214/75 H, 77 R, 86 A; 212/8 R, 8 A, 10, 39 R, 39 B; 254/139, 145,

Kruschke Oct. 14, 1975 [54] HOIST TRUCK WITH PLANETARY GEAR 3,613,918 10 1971 Kruschke 214 75 1-1 3,794,192 2 1974 Monson 214 75 11 Primary ExaminerRobert J. Spar Assistant Examine'rR. B. Johnson Attorney, Agent, or Firm-Owen, Wickersham & Erickson [57] ABSTRACT movement powered by a travel motor. A boom winch for raising the boom and a hoist winch are journaled around a common shaft carrying planetary gear assemblies. The device also has a sensor for determining when a predetermined tension is exerted on the cable of the boom winch and disabling means for stopping the motors for both winches and the travel motor when the sensor indicates that the predetermined tension has been exceeded, thereby preventing overloading the boom line and related structure.

9 Claims, 4 Drawing Figures US. Patent Oct. 14, 1975 Sheet 1 of3 3,912,093

iUI

US Patent 0a. 14, 1975 Sheet 2 of3 3,912,093

U.S. Patent (Set. 14, 1975 Sheet 3 of3 3,912,093

HOIST TRUCK WITH PLANETARY GEAR ASSEMBLIES AND LOAD SENSOR MEANS BACKGROUND OF THE INVENTION This invention relates to a field service truck. It is an improvement over the field service vehicle shown in US. Pat. No. 3,613,918.

The vehicle shown and described in US. Pat. No. 3,613,918 relies 'on a differential for connecting a travel motor that moves the boom back and forth to the hoist winch and the boom winch, so that the boom could be moved fore and aft without substantially changing its height or the height of the load. However, differentials are very expensive and have some disadvantages. Also, the device requires some way of moving the boom laterally, and in US. Pat. No. 3,613,918 this is accomplished by shortening and lengthening one of the beams. This gave rise to complications in the device and was expensive to make and to maintain.

A third problem which occurred was that sometimes operators would try to pick up a loadwith the boom at the wrong angle or by adding parts to the load line, thereby causing excessive loading of the boomline and the boom structure. When an unduly high strain is exerted on the boom line, the boom poles, boom frame, boom supports, travel chains, and boom winch are also subjected to excessive strain. There was no way that unskilled operators could make sure whether a heavy load might be being picked up at an improper boom angle, and sometimes the results were disastrous.

Thus, among the objects of the present invention are the provision of a simpler system for operating the travel motor without having to use a differential, a simpler system of shifting the top of the boom laterally, and the provision of means for automatically preventing overloading of the boom hoist, the boom poles, the I boom frame, the boom support, the travel chains, and the winch mechanisms.

SUMMARY OF THE INVENTION This invention is used in a field service truck having a bed to the rear of its cab and a pair of tracks supported at each side of the bed. The truck also has a boom comprising two converging beams with a hoist pulley at their upper meeting ends, and boom support means pivotally mounted to the lower end of each beam and mounted on the tracks for fore-and-aft movement therealong. The bed also supports, near the cab (l) a boom winch having a cable connected to the upper end of the boom, (2) a boom motor operatively connected to the boom winch, (3) a hoist winch having a cable connected over the hoist pulley and with a hoist fixture thereon, (4) a hoist motor operatively connected to the hoist winch, and (5) a travel motor.

The present invention adds to this combination a common shaft around which the boom winch and hoist winch are journaled for relative rotation. The shaft carries a group of planetary gear assemblies. A first assembly has a first sun gear secured to the common shaft, a first ring gear driven by the hoist motor, and a first planet gear carrier secured to the hoist winch and carrying a first set of planet gears in mesh with the first sun gear and the first ring gear. The second assembly has a second sun gear secured to the common shaft, a second ring gear driven by the boom motor, and a second planet gear carrier secured to the boom winch and carrying a second set of planet gears in mesh with the second sun gear and the second ring gear. A third planetary gear assembly has a third ring gear secured to the common shaft and in driving connection with the travel motor. This third assembly also has a third sun gear mounted on a hollow shaft which is rotatably journaled around the common shaft and a third planet carrier which carries the third set of planet gears in mesh with both the third ring gear and the third sun gear. Secured to the third planet carrier is a sprocket wheel or other suitable drive connection.

A travel shaft assembly is provided comprising twoin-line shafts, one of which is connected to one of the pair of tracks and the other to the other pair of tracks, for causing the respective beams of the boom to move therealong. One of these in-line shafts is operatively connected to the hollow shaft and the other is operatively connected to the common shaft, as by gears and sprockets. This enables operation without any differential, in a manner that will be explained.

In addition, the device includes a sensor which is sensitive to a predetermined tension that may be exerted on the cable of the boom winch, thereby indicating conditions approaching an overload on the boom line and related structures. Then disabling means, as for example a switch, is provided for stopping the winch motors and other motors when the sensor indicates that the predetermined tension has been attained. A manually operable override means may be provided for enabling the operator to operate the motors anyway, if he so desires, as for example to aid in repositioning the hoist.

Other objects and advantages of the invention will appear from the following description of some preferred forms.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a fragmentary view in perspective of a portion of a field service truck embodying the principles of the invention, looking from the rear towards the cab and showing the system of the present invention.

FIG. 2 is a view in elevation and in section, partly diagrammatic in character, showing the common shaft system for the winches and the connection to the various motors concerned. The cables are. omitted.

FIG. 3 is a top plan view of the field service truck of FIG. 1 illustrating in broken lines alternative positions of the boom to show what is meant by a lateral shift thereof.

FIG. 4 is a partly diagrammatic view of the tensionsensing and shutoff means according to the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT A field service truck 10 embodying the principles of the invention is shown in FIG. 3, and a portion thereof is shown enlarged in FIG. 1. The truck 10 has a cab 11 normally occupied by the driver during driving conditions, and to the rear of the cab 11 is a truck bed 12 used for transporting engines, engine parts or other repair parts or assemblies. At each side of the bed 12 is a

vertical side wall

13 or 14, and mounted in each

vertical wall

13 or 14 is a respective track 15 or 16.

In each track 15, 16 is mounted a carriage 17, 18 which is moved fore and aft by the movement of a

chain

19, 20 to which each carriage is attached. To the carriage 17, 18 is pivotally mounted one of the two

legs

21 and 22 of an A-frame boom 23. Other types of booms may be used, although the A-frame type is desirable and gives a superior action, with the open space in between its

legs

21 and 22. This open space enables storage of large equipment on the bed 12, as may be gathered from U.S. Pat. No. 3,613,918. At the upper end 24 of the boom 23 is a suitable sheave 25 over which passes a hoist cable 26 having a hook 27 or other fixture and operated by a hoist winch 28. The boom 23 is swung up and down by a cable 30 which is secured to a fixture 31 (FIG. 3) on the boom and passes over a pulley 32 which is mounted on the cab 11 and from there goes by various pulleys to a boom winch 33.

As shown in FIG. 2, the hoist winch 28 and the boom winch 33 are mounted rotatably around a common shaft 34. This shaft 34 is also used to mount a series of planetary gear assemblies. For example, a first planetary gear assembly 35 comprises a sun gear 36 secured to the shaft 34, a ring gear 37 rotatably journaled around the shaft 34 and a carrier 38 which is rigidly connected to the hoist winch 28 and which carries a set of planetary gears 39 which are in mesh with both the sun gear 36 and the ring gear 37. The ring gear 37 is operated from a hoist motor 40 which may have a drive shaft 41 with a pinion gear 42 geared to an outer set of teeth 43 on the ring gear 37.

. Similarly, a boom motor 45 may have a shaft 46 with a pinion gear 47 on it which is engaged with outer teeth 48 of a ring gear 51 of a second planetary assembly 50. The ring gear 51 is rotatably mounted on the shaft 34, and a sun gear 52 of the second planetary assembly is secured directly to the shaft 34. A carrier 53 is secured to the boom winch 33 and carries a set of planetary gears 54 in engagement with both the ring gear 51 and the sun gear 52.

Also, according to the present invention there is preferably provided a third planetary assembly 55. ln this instance, a ring gear 56 is secured to the common shaft 34, and external teeth of the ring gear 56 are in engagement with a pinion gear 57 secured to a shaft 58 driven by a travel motor 60. A sun gear 61 is mounted on a hollow shaft 62, which is rotatable around the common shaft 34, and a carrier 63 carries a set of planet gears 64 meshed to both the sun gear 61 and the ring gear 56. A travel shaft assembly 65 is provided, preferably comprising a pair of

shafts

66 and 67 that are in line with each other axially and at their outer ends possess gears 68 and 69 for driving the

chains

19 and 20 for moving the boom support means 17 and 18. One travel shaft 66 is connected by drive means to the common shaft 34. This may be done by a sprocket wheel 70 on the first travel shaft 66, a sprocket wheel 7] on the common shaft 34 and a chain 72 meshed with both

sprocket wheels

70 and 71. Similarly, a drive connection is maintained between the carrier 63 and the second travel shaft 67, as by a sprocket wheel 73 on the second travel shaft 67, a sprocket wheel 74 on a hollow shaft 75 that is rigidly joined to the carrier 63, and a chain 76 connecting the sprocket wheels 73 and 74.

Thus, normally the boom motor 45 operates the boom winch 33, and the hoist motor 40 operates the hoist winch 28, and the two are combined with the travel motor 60 through the

planetary assemblies

35, 50 and 55 and the common shaft 34, to regulate the travel so that the boom height can be held or varied as desired during the fore-and-aft travel. In normal conditions, the two

travel shafts

66 and 67 operate simultaneously and at the same speed, and the gear ratios are made accordingly.

However, sometimes it is advisable to shift the lateral position of the hoist hook 27, as shown in FIG. 3, by shifting the lateral position of the top 24 of the boom 23, in order to enable a direct vertical overlying of the hook 27 above a heavy member that is to be picked up by the hoist. In order to do this properly, it is important that this position be exactly regulatable. Accordingly, the present invention provides a side shift motor 80 having a shaft 81 and a pinion gear 82 in engagement with a gear 83 which is secured to the hollow shaft 62 that carries the sun gear 61, and therefore changes the relative rotation of the sprocket wheel 74 attahced to the hollow shaft 75. Thus, it is possible to operate the side shift motor 80 whenever a side shift is desired to be attained. The shaft 67 then rotates at a different speed from the shaft 66, and therefore the chain 20 moves its boom arm 22 at a different speed from the boom arm 21 and the boom 23 therefore performs a sort of twist that moves its upper end 24 and the hook 27 laterally.

As explained so far, the invention accommodates all the operations obtained by US. Pat. No. 3,613,918 and does them in a simpler manner, using machinery which is much easier to build and to assemble. Planetary gears are much less expensive than differentials and are more readily obtainable, as well as being easier to manufacture.

Another feature of the invention is a boom cable tension sensor and overload switch and can best be seen by referring to FlGS. 3 and 4. The cable 30 that connects the boom 23 to the boom winch 33 rides over a pulley wheel 32 mounted on top of the cab 1 1, and then turns approximately a right angle at a second pulley wheel 86. This pulley wheel 86 is carried on one end of an arm 87, the other end of the arm 87 being mounted pivotally to a bracket 88 on a frame member 89 of the truck 10. Thus, as the boom cable 30 is placed under tension from a load secured to the hook 27, there is a tendency to shift the position of the arm 87.

A tension sensor piston 90 is slidably mounted with a cylinder portion 91 of a sensor support member 92 which is secured to the top of the cab l 1. At its exterior end the piston 90 has a follower head 93 which engages the arm 87. To provide fail-safe operation and prevent false actuation of a shut-down system, an indirect system is used for transmission of movement of the arm 87. An interior surface 94 of the piston defines a cavity 95, and a chamber 96 within the member 92 is filled with hydraulic fluid 97, which may be put into it via a check valve 98 mounted in the member 92. The movement of the pistons interior surface 94 exerts pressure against the hydraulic fluid 97 in accordance with the position of the arm 87. A pressure gauge 99 is mounted in the member 92 and communicates with the hydraulic'fluid 97; the gauge 99 is preferably calibrated to indicate the tensile forces developed in the boom cable 30 during lifting operations. To seal the hydraulic fluid 97 within the chamber 96, an elastomeric O-ring 100 is mounted in an annular groove 101 within the cylinder portion 91 of the member 92 adjacent to an end 102 thereof and engages the piston 90.

The hydraulic fluid 97 is used to transmit significant movement of the piston 90 to a switch actuator shaft 103, which is slidably mounted within the member 92 and extends outwardly therefrom through an end wall 104 opposite to the piston end 102. The shaft 103 is axially aligned with the piston 90 and has a flanged head 105 within the chamber 96 and extending into the piston cavity 95, but this head 105 is normally spaced from a piston contact surface 106 at the innermost end of the cavity 95. The surface 106 engages the head 105 only if and when the fluid 97 has leaked out from the interior of the member 92, whether the leakage be due to a seal failure, a' failure in the valve 98, or leakage in the gauge 99 or its fittings. This is a fail-safe feature, as will be explained below.

When the chamber 96 is properly filled with the fluid 97, the contact surface 106 will never engage the head 105 but will be held away from it by the fluid 97, no matter how much pressure is exerted on the piston 90. Instead, inward movement of the piston 90 exerts pressure on the fluid 97, and at times when the load on the boom cable 30 is approaching a danger point, this pressure on the fluid 97 is exerted on the head 105 sufficiently to move the shaft 103 to the right in FIG. 4, overcoming the pressure of a spring 107, which surrounds the portion of the shaft 103 within the chamber 96 and is compressed between the flanged head 105 and an interior end wall 108 of the support member 92, normally urging the shaft 103 toward the piston 90. The shaft 103 is spaced away from the piston 90 even when the boom cable 30 is not under tension, as by a locking ring 109 on the shaft 103 which stops against the end wall 104. Another elastomeric O-ring 110 is seated on an annular groove 111 within the member 92 adjacent to the end wall 104 and engages the shaft 103 to seal the hydraulic fluid 97 within the chamber 96.

An exterior end 112 of the switch actuator shaft 103 engages an electric switch wiper contact 113 so as to move it from connection with a first stationary contact 104 to connection with a second stationary contact 115.

If the fluid 97 should in any way leak out from the member 102, it takes very little tension on the boom cable 30 to compress the spring 107 and push the shaft 103 against the switch contact 113 to move it away from its contact 104 to its contact 105. This is, therefore, a true fail-safe operation.

In normal operation, the hydraulic pressure acting on the shaft 103 is increased by tension on the arm 87, exerted by the cable 30 through the sheave 86, and if and when the tension on the arm 87 increases enough to exceed the tension of the spring 107, then-the shaft 103 moves outwardly and, at a predetermined hydraulic pressure corresponding to a loading on the boom cable 30 that approaches the danger point, the shaft 103 throws the switch arm 113.

The overload control electrical circuit comprises a storage battery 116 having one terminal 117 connected to the truck frame and having another terminal 118 connected inter alia to the wiper contact 113 which passes electrical current through the first contact 114 to the hoist motor 40, the boom motor 45, the travel motor 60 and the side shift motor 80 via corresponding control switches 119, 120, 121, 122. When maximum permissible tension in the boom cable 30 is developed, movement of the arm 87 is communicated through the piston 90 and shaft 103 to the wiper contact 113 which opens the circuit path to the motor 40 and closes a circuit through the contact 114 to an overload indicator 123. A manual override switch 124 bridges the battery terminal 118 to the motor 40 to enable an operator to readjust the orientation of the load and the boom 23 as the particular situation may require to reduce tension to a safe level.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to hem any sense limiting.

I claim:

1. In a field service truck having a bed to the rear of its cab, a pair of tracks supported at each side of said bed, a boom comprising two converging beams with a hoist pulley at their upper meeting ends, and boom support means pivotally mounted to the lower end of each said beam and mounted on the tracks for movement fore and aft therealong, said bed supporting near said cab: a boom winch having cable means connected to the upper end ofsaid boom, a boom motor operatively connected to said boom winch, a hoist winch having cable means connected over said hoist pulley and having a hoist fixture thereon, a hoist motor operatively connected to said hoist winch, and a travel motor, the improvement comprising:

a common shaft around which said boom winch and hoist winch are journaled for relative rotation and carrying first and second planetary gear assemblies, said common shaft being operatively connected to said travel motor,

said first planetary assembly having a first sun gear secured to said common shaft, a first ring gear driven by said hoist motor, and a first planet gear carrier secured to said hoist winch and carrying a first set of planet gears in mesh with said sun gear and said first ring gear,

said second planetary assembly having a second sun gear secured to said common shaft, a second ring gear driven by said boom motor, and a second planet gear carrier secured to said boom winch and carrying a second set of planet gears in mesh with said second sun gear and said second ring gear,

travel shaft means operatively connected to said boom support means for driving them to move them fore and aft on said tracks, and

drive transmitting means joining said common shaft to said travel shaft means.

2. The device of claim 1 wherein the operative connection between said common shaft and said travel motor comprises a third planetary gear assembly having a third ring gear secured to said common shaft and in driving connection with said travel motor, said third assembly also having a third sun gear mounted on a first hollow shaft that is rotatably journaled around said common shaft, and a third planet carrier carrying a third set of planet gears in mesh with said third ring gear and said third sun gear and mounted on a second hollow shaft.

3. The device of claim 2 having in combination the rewith:

a side shift motor operatively connected to said first hollow shaft,

said travel shaft means comprising two-in-line shafts, namely, a first travel shaft operatively connected to one of said pair of tracks and a second travel shaft operatively connected to the other of said pair of tracks,

said first travel shaft being operatively connected to said drive transmitting means, and

second drive transmission means joining said second hollow shaft to said second travel shaft for rotation thereof at the same speed as said first travel shaft except when said side shift motor is operated to move it at a different speed.

4. The device of claim 1 having in combination therewith:

sensing means responsive to tension within said cable means of said boom winch, indicator means connected to said sensing means for indicating the tension within said cable means, and disabling means for stopping all said motors when said sensing means detects a predetermined overload tension.

5. The device of claim 4 having manually operable override means for manually overriding said disabling means.

6 The device of claim 1 having in combination therewith: l

a swinging arm pivotally supported by said truck and supporting a sheave at one end, said boom cable means passing over said sheave and turning a corner there,

a sealed hydraulic cylinder,

a piston in said cylinder and extending out one end thereof, bearing against said arm and moved thereby upon an increase of tension in said boom cable means,

a shaft spaced from said piston in said cylinder and extending out through an opposite end of said cylinder and actuated by the hydraulic pressure as affected by the position of said piston, and

normally closed disabling switch means actuated to a disabling position by said shaft, for stopping all said motors at a predetermined tension of said boom cable means.

7. In a field service truck having a bed to the rear of its cab, a pair of tracks supported at each side of said bed, a boom comprising two converging beams with a hoist pulley at their upper meeting ends, and boom support means pivotally mounted to the lower end of each said beam and mounted on the tracks for movement fore and aft therealong, said bed supporting near said cab: a boom winch having cable means connected to the upper end of said boom, a boom motor operatively connected to said boom winch, a hoist winch having cable means connected over said hoist pulley and having a hoist fixture thereon, a hoist motor operatively connected to said hoist winch, and a travel motor, the improvement comprising:

said first planetary assembly having a first sun gear secured to said common shaft, a first ring gear driven by said hoist motor, and a first planet gear carrier secured to said hoist winch and carrying a first set of planet gears in mesh with said first sun gear and said first ring gear,

travel shaft means operatively connected to said boom support means for driving them to move them fore and aft on said tracks and having a first sprocket wheel secured thereon,

said common shaft having a second sprocket wheel secured thereto in line with said first sprocket, and

chain drive means joining said first and second sprocket wheels.

8. The device of claim 7 having in combination therewith:

a third planetary gear assembly having a third ring gear secured to said common shaft and in driving connection with said travel motor, said third assembly also having a third sun gear mounted on a first hollow shaft that is rotatably journaled around said common shaft, and a third planet carrier mounted on a second hollow shaft and carrying a third set of planet gears in mesh with said third ring gear and said third sun gear, said second hollow shaft having a third sprocket wheel secured thereon,

said first hollow shaft having secured thereto a drive gear,

a side shift motor operatively connected to said drive gear,

said first travel shaft having said first sprocket wheel secured thereto, said second travel shaft having a fourth sprocket wheel secured thereto in line with said third sprocket wheel, and

second chain drive means joining said third and fourth sprockets.

9. The device of claim 1 having in combination therewith:

a swinging arm pivotally supported by said truck and carrying a sheave at one end around which said boom cable means passes,

a sealed hydraulic cylinder supported by said truck near said arm,

a piston in said cylinder and extending out one end thereof and bearing against said arm, for movement thereby upon an increase of tension in said boom cable means,

a shaft having an enlarged end spaced from said piston in said cylinder, said shaft extending out through an opposite end of said cylinder and actuated by the hydraulic pressure as affected by the position of said piston, and

an electrical circuit for said motors,

normally closed switch means in said circuit actuated to a disabling position by said shaft, for stopping all said motors at a predetermined tension of said boom cable means.

Claims

1. In a field service truck having a bed to the rear of its cab, a pair of tracks supported at each side of said bed, a boom comprising two converging beams with a hoist pulley at their upper meeting ends, and boom support means pivotally mounted to the lower end of each said beam and mounted on the tracks for movement fore and aft therealong, said bed supporting near said cab: a boom winch having cable means connected to the upper end of said boom, a boom motor operatively connected to said boom winch, a hoist winch having cable means connected over said hoist pulley and having a hoist fixture thereon, a hoist motor operatively connected to said hoist winch, and a travel motor, the improvement comprising: a common shaft around which said boom winch and hoist winch are journaled for relative rotation and carrying first and second planetary gear assemblies, said common shaft being operatively connected to said travel motor, said first planetary assembly having a first sun gear secured To said common shaft, a first ring gear driven by said hoist motor, and a first planet gear carrier secured to said hoist winch and carrying a first set of planet gears in mesh with said sun gear and said first ring gear, said second planetary assembly having a second sun gear secured to said common shaft, a second ring gear driven by said boom motor, and a second planet gear carrier secured to said boom winch and carrying a second set of planet gears in mesh with said second sun gear and said second ring gear, travel shaft means operatively connected to said boom support means for driving them to move them fore and aft on said tracks, and drive transmitting means joining said common shaft to said travel shaft means.

3. The device of claim 2 having in combination therewith: a side shift motor operatively connected to said first hollow shaft, said travel shaft means comprising two-in-line shafts, namely, a first travel shaft operatively connected to one of said pair of tracks and a second travel shaft operatively connected to the other of said pair of tracks, said first travel shaft being operatively connected to said drive transmitting means, and second drive transmission means joining said second hollow shaft to said second travel shaft for rotation thereof at the same speed as said first travel shaft except when said side shift motor is operated to move it at a different speed.

4. The device of claim 1 having in combination therewith: sensing means responsive to tension within said cable means of said boom winch, indicator means connected to said sensing means for indicating the tension within said cable means, and disabling means for stopping all said motors when said sensing means detects a predetermined overload tension.

6. The device of claim 1 having in combination therewith: a swinging arm pivotally supported by said truck and supporting a sheave at one end, said boom cable means passing over said sheave and turning a corner there, a sealed hydraulic cylinder, a piston in said cylinder and extending out one end thereof, bearing against said arm and moved thereby upon an increase of tension in said boom cable means, a shaft spaced from said piston in said cylinder and extending out through an opposite end of said cylinder and actuated by the hydraulic pressure as affected by the position of said piston, and normally closed disabling switch means actuated to a disabling position by said shaft, for stopping all said motors at a predetermined tension of said boom cable means.

7. In a field service truck having a bed to the rear of its cab, a pair of tracks supported at each side of said bed, a boom comprising two converging beams with a hoist pulley at their upper meeting ends, and boom support means pivotally mounted to the lower end of each said beam and mounted on the tracks for movement fore and aft therealong, said bed supporting near said cab: a boom winch having cable means connected to the upper end of said boom, a boom motor operatively connected to said boom winch, a hoist winch having cable means connected over said hoist pulley and having a hoist fixture thereon, a hoist motor operatively connected to said hoist winch, and a travel motor, the improvement comprising: a common shaft around which said boom winch and hoist winch arE journaled for relative rotation and carrying first and second planetary gear assemblies, said common shaft being operatively connected to said travel motor, said first planetary assembly having a first sun gear secured to said common shaft, a first ring gear driven by said hoist motor, and a first planet gear carrier secured to said hoist winch and carrying a first set of planet gears in mesh with said first sun gear and said first ring gear, said second planetary assembly having a second sun gear secured to said common shaft, a second ring gear driven by said boom motor, and a second planet gear carrier secured to said boom winch and carrying a second set of planet gears in mesh with said second sun gear and said second ring gear, travel shaft means operatively connected to said boom support means for driving them to move them fore and aft on said tracks and having a first sprocket wheel secured thereon, said common shaft having a second sprocket wheel secured thereto in line with said first sprocket, and chain drive means joining said first and second sprocket wheels.

8. The device of claim 7 having in combination therewith: a third planetary gear assembly having a third ring gear secured to said common shaft and in driving connection with said travel motor, said third assembly also having a third sun gear mounted on a first hollow shaft that is rotatably journaled around said common shaft, and a third planet carrier mounted on a second hollow shaft and carrying a third set of planet gears in mesh with said third ring gear and said third sun gear, said second hollow shaft having a third sprocket wheel secured thereon, said first hollow shaft having secured thereto a drive gear, a side shift motor operatively connected to said drive gear, said travel shaft means comprising two-in-line shafts, namely, a first travel shaft operatively connected to one of said pair of tracks and a second travel shaft operatively connected to the other of said pair of tracks, said first travel shaft having said first sprocket wheel secured thereto, said second travel shaft having a fourth sprocket wheel secured thereto in line with said third sprocket wheel, and second chain drive means joining said third and fourth sprockets.

9. The device of claim 1 having in combination therewith: a swinging arm pivotally supported by said truck and carrying a sheave at one end around which said boom cable means passes, a sealed hydraulic cylinder supported by said truck near said arm, a piston in said cylinder and extending out one end thereof and bearing against said arm, for movement thereby upon an increase of tension in said boom cable means, a shaft having an enlarged end spaced from said piston in said cylinder, said shaft extending out through an opposite end of said cylinder and actuated by the hydraulic pressure as affected by the position of said piston, and an electrical circuit for said motors, normally closed switch means in said circuit actuated to a disabling position by said shaft, for stopping all said motors at a predetermined tension of said boom cable means.