US20030066333A1

US20030066333A1 - Chassis straightening bench

Info

Publication number: US20030066333A1
Application number: US09/973,362
Authority: US
Inventors: Robert Thomas; Greg Penner; Daniel McClellan
Original assignee: Delaware Capital Formation Inc
Current assignee: Chief Automotive Technologies Inc; Clove Park Insurance Co
Priority date: 2001-10-09
Filing date: 2001-10-09
Publication date: 2003-04-10

Abstract

A vehicle chassis straightening bench. The bench includes a platform on which a chassis can be secured and have various forces applied to locations on the chassis to assist in repairing collision damage or the like. The bench includes at least one pulling assembly comprising a head movably mounted in a guide. The head is movable by actuation of a double acting hydraulic cylinder. An attachment member is attached to a holder portion of the head and movable thereby. The attachment member can be selectively secured to a portion of a chassis for transmitting force from the hydraulic cylinder to the chassis.

Description

BACKGROUND OF THE INVENTION

The invention relates to an apparatus used to straighten a vehicle chassis such as automobiles, vans, SUVs, trucks, and other vehicles. More specifically, the apparatus is a straightening bench in the form of a lift that includes an elevatable platform on which a chassis may be elevated and anchored. One or more pulling assemblies are provided on the bench to selectively apply pulling forces at selected locations in desired directions to the chassis to help return the chassis to its original shape.

Vehicles are occasionally involved in collisions or otherwise damaged requiring bodywork to return the chassis to its original shape and alignment. The work often includes the use of strategically positioned pulls on the chassis to straighten the chassis. A chassis can be in the form of the frame plus body as would be typically found on a truck or may be a unibody where the frame is part of the body itself. This technique of straightening is well known in the art, but until recently has required large, heavy platforms to support the vehicle and resist the pulling forces applied by pulling tower assemblies. Further, straightening benches utilize high-pressure hydraulic cylinders in the towers to effect operation of the pulling assemblies that apply the selected forces to the chassis. It is not uncommon to find pulling assemblies that utilize hydraulic pressure as high as 10,000 psi and greater which requires heavy duty and expensive multi-stage hydraulic pumps and hydraulic components to operate the pulling assemblies. In order to keep the cost of such benches low, they have traditionally been kept mechanically simple. For example, the hydraulic cylinder that applies the force to a head assembly will simply sit inside a guide tube with the bottom end of the hydraulic cylinder resting on a support in the guide tube, and the free end of the hydraulic cylinder rod is simply butted against the inside surface of the head assembly. This allows the hydraulic cylinder and head assembly to tilt inside the guide tube and relative to each other. Single acting spring return hydraulic cylinders which utilize an internal spring plus the weight of the pulling assembly head to return the cylinder rod to its retracted position are used in such pulling assemblies.

One of the drawbacks of current benches is that, as mentioned, they utilize high-pressure hydraulic fluid to effect various operations including operation of the pulling assembly which includes the guide, moveable head, and an attachment member. High-pressure components are expensive, wear quicker and require additional maintenance. As discussed, some systems have an operating pressure as high as about 10,000 psi. However, one system manufactured by Chief Automotive Systems of Grand Island, Nebr. has an operating pressure of about 5,000 psi. A typical example of such a straightening bench is model S21M produced by and available from Chief Automotive.

High pressure hydraulic systems utilize small diameter hydraulic cylinders to extend the head upwardly within the guide. Such an arrangement allows the cylinder to be received within the interior of the head to provide a simple and compact structure. Another problem with current systems is that the hydraulic cylinder in the guide was not connected to the head and utilized the weight of the head and the return spring in the hydraulic cylinder to return the cylinder rod and the head to their retracted positions. Such an arrangement is slow in operation resulting in some level of inefficiency through lost available work time. Further, such a system limits the versatility of the pulling assembly since it could apply force in only one direction, i.e. through upward movement of the head.

SUMMARY OF THE INVENTION

The present invention involves the provision of a vehicle chassis straightening bench that utilizes a platform with anchors for securing a chassis in position. The bench includes one or more pulling assemblies that are operable to have an attachment member temporarily fixed to the chassis to apply a pulling force to the chassis to assist in straightening the chassis. The pulling assembly is comprised of a driver which includes a head movably mounted in a guide forming a telescoping column. An attachment member can take the form of a chain with a hook that is secured to the head in an adjustable manner and is also directed around a pulley assembly whereby extension of the head relative to the guide will shorten the length of chain beyond the pulley whereby force can be applied to a chassis. The head is driven by an extendable and retractable fluid cylinder, preferably a hydraulic cylinder, which is affixed to both the head and the guide whereby powered extension of the cylinder will positively extend the head and powered retraction of the cylinder will positively retract the head. A pulling force can be applied to an attachment member or other device by the head in either extension or retraction of the column. The pulling assembly can be part of a new bench or can be provided to retrofit existing benches.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of an vehicle chassis straightening bench showing the details of the lift mechanism, pulling assemblies and a truck (shown in broken lines) positioned on the lift platform. [0006]
FIG. 2 is an exploded perspective view of a pulling assembly. [0007]
FIG. 3 is a fragmentary view of the pulling assembly showing internal details thereof. [0008]
FIG. 4 is a side elevation view of a pulling assembly illustrating the assembly equipped for lifting. [0009]
FIG. 5 is a side elevation view of a moveable pulling assembly. [0010]
FIG. 6 is a hydraulic system schematic. [0011]
FIG. 7 is an enlarged elevation view of a pressure gauge. [0012]
FIG. 8 is a side elevation view of a pulling assembly adapted to provide a lifting force. [0013]
FIG. 9 is a side elevation view of a pulling assembly with another alternate embodiment of a lifting device.[0014]
Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. [0015]

DETAILED DESCRIPTION OF THE INVENTION

The [0016] reference numeral 1 designates generally a bench used in straightening a chassis 6 such as a truck, van, sport utility vehicle (SUV), automobile, etc., herein referred to collectively as vehicles. The bench 1 is in the form of a lift that includes a work platform 3 on which the vehicle is placed. The platform 3 is coupled to and supported on a frame 5 that can be utilized in elevating the platform 3 from floor level to a working level, for example 18 inches above the floor, to assist workers in working on a chassis 6. Such platforms and frames are well known in the art, an example of which is the EZ Liner S21M mentioned above. A plurality of anchors 7 are provided for securing the chassis 6 to the platform 3 retaining it against movement during chassis straightening. Such anchors are well known in the art. For safety, the platform 3 may be provided with a locking mechanism (not shown) to prevent the platform from accidentally lowering from its elevated position.
The [0017] bench 1 is also provided with one or more pulling assemblies each designated generally 11, see FIGS. 1 and 2. A plurality of pulling assemblies 11 may be fixed relative to the platform so they are not movable relative thereto or may be mounted in a manner, utilizing a pulling assembly as seen in FIG. 5 for selective movement relative to the platform 3 to change the 5 direction of pull relative to the chassis 6. In general, a pulling assembly 11 comprises a frame member 14 which is attachable to the platform 3 either in a fixed (FIG. 2) or movable manner (FIG. 5). The pulling assembly further includes an extendable and retractable (telescoping) column 15 including an upstanding guide post 16 having movably mounted therein a head 17. The guide 16 may be secured to the frame 14 by welding or bolting and can be provided with a reinforcing gusset 19 to help resist a bending moment on the guide 16 when force is being applied to the chassis 6. As best seen in FIG. 3, a hydraulic cylinder 21 is mounted inside the interior 22 of the guide 16. Preferably the cylinder 21 is mounted in the guide 16 via a cleavis/pin arrangement 24 to facilitate assembly within the guide 16. As best seen in FIGS. 2 and 3, the lower end of the cylinder 21 includes a cleavis 23 mounted to a support 26 via a pin 23P. The support 26 is an elongate member having the lower end abutting and secured to a plate 18 secured in the bottom of the guide 16. Securement of the support 26 to the plate 18, e.g., by welding, allows the cylinder to positively move and apply force to the head 17 in both extension and retraction. Although a cleavis mount is used, the top edge 26E of the support 26 abuts the lower end of the cylinder to prevent pivoting between the cylinder 21 and support 26 thereby providing a rigid actuator column. Such an arrangement allows for the convenient manufacture of the guide 16 by providing the plate 18 at the bottom end thereof forming a support floor. A hole 20 through the guide 16 allows for the removal and insertion of the pin 23P to facilitate assembly and disassembly.
Preferably, the [0018] cylinder 21 is a double acting cylinder, i.e., pressurized fluid is fed to the piston end 21P as well as the rod end 21R in a selective manner allowing it to apply force both in an extension direction and a retraction direction. The cylinder 21 has a movable rod 25 which moves linearly during extension and retraction of the cylinder 21 and is connected to the piston inside the cylinder housing 21H. A link 27 is mounted to the cylinder 21 through a pin mounting arrangement 29 such as a cleavis mount to facilitate assembly. In the illustrated structure, the link 27 includes a collar 28 receiving the free end of the piston rod 25 therein. There is a close fit between the inside surface of the collar and the exterior surface of the rod to prevent lateral pivoting or tilting therebetween while allowing rotation therebetween and forming a rigid connection between the link 27 and cylinder 21. A suitable fastener 28F, such as a castle nut and cotter pin, are used to secure the link to the piston rod. The link 27 and cylinder 21 have their longitudinal axes generally in line with the longitudinal axis of the guide 16. The link 27 is also secured to rod 25 in a rigid manner so as to not move relative thereto except possibly relative rotation.
The [0019] link 27 is also secured to the head 17 through a pin and cleavis arrangement 32 utilizing a pin 32P. However, the link has an upper edge 30 that abuts a portion of the cleavis mount 29 to prevent pivoting therebetween. Thus, the support 26, cylinder 21, link 27 and the head 17 form a rigid actuator column to help maintain alignment of the head 17 within the guide 16 yet can be telescoped to extend and retract the head. Also, even though rigid against flexure laterally of its longitudinal axis, the actuator may have components rotate about the longitudinal axis such as at the connection between the cylinder 21 and link 27. A thru hole 34 is provided in a pulling arm 31 to permit connecting and disconnecting of the pulling arm 31 and link 27. The cylinder 21 may have its rod 25 connected to the support 26 and the housing 21H connected to the link 27 as an alternate arrangement.
It is preferred that the length of the [0020] rod 25 outside of the housing 21H when fully extended be less than about 5 times its diameter and preferably less than about 3½ times its diameter. It is also preferred that the piston in the cylinder have a diameter larger than about 2½ inches. The diameter of the piston in the cylinder is preferably in the range of between about 2½ inches and about 3½ inches.
The [0021] head 17 includes the pulling arm 31 and a holder 33 on the exposed end of the pulling arm. In the illustrated structure, the rod 25 is rigidly secured to the pulling arm 31 portion of the head 17. The pulling arm 31 is tubular and is sized and shaped to fit within the interior 22 of the guide 16 for longitudinal movement therein. Preferably the guide 16 and pulling arm 31 are tubular and in the form of sleeves with generally annular transverse cross sectional shapes. The length of the pulling arm 31 is at least about four times the outside diameter, or transverse dimension in the event the cross-sectional shape is not circular, to help prevent binding throughout movement of the pulling arm 31 within the guide 16. As shown, the pulling arm 31 is movably mounted inside the guide 16. Alternatively, the pulling arm 31 could have a hollow interior receiving therein the guide 16. The holder 33 is configured to releaseably retain an attachment member 35 therein in a manner that the length of the attachment member available for pulling may be adjusted easily.
Preferably, the housing [0022] 21H has an outside diameter slightly less than the inside diameter of the guide 16. The length of the cylinder 21, support 26 and link 27, as well as the length of the pulling arm, are such that the pulling arm does not travel along the outside of the housing 21H when the pulling arm is inside the guide 16.
The [0023] attachment member 35, in the illustrated structure, includes a chain 37 which is preferably of a standard link chain style, FIG. 2. The chain 37 is adjustable in the holder 33 by engaging one or more of the links under catches 39. The chain 37 extends downwardly from the holder 33 longitudinally along the guide 16 on the exterior thereof, wrapping partially around a pulley assembly that includes a pulley 41. The pulley 41 is rotatably mounted on a collar 43 that is selectively movable longitudinally along the guide 16 to adjust the height which the attachment member projects from the guide 16 to the chassis 6. The chain 37 includes a hook 45 on one of the free ends which can then be attached to the chassis in a manner known in the art.
FIG. 6 shows a simplified schematic of a hydraulic system used to operate one or more pulling [0024] assemblies 11 and to raise and lower the platform 3 with a lift assembly that includes a hydraulic cylinder 46. For simplification, the hydraulic circuit illustrates only one pulling assembly hydraulic cylinder 21, however, it is to be understood that any number of cylinders may be utilized in such a hydraulic circuit. Further, the platform 3 may also be elevated through the use of one or more hydraulic cylinders 46 and associated control valve 46V connected in flow communication with a hydraulic pump 47. Preferably, the cylinder 46 is a single acting cylinder since the platform weight can be used to effect retraction. The hydraulic pump 47 which is preferably of a single stage type is connected in flow communication with the cylinder 21. A line 48 connects the pump 47 in flow communication with the piston side of the cylinder 21. A line 49 connects the pump 47 with the rod side of the cylinder 21. Both lines 48 and 49 are connected to a suitable flow control valve 52 which is operable for allowing a worker to select whether the cylinder 21 can be extended or retracted under the influence of pressurized hydraulic fluid and also ports the fluid when in the center position to tank 54. The valve 52 can be a three way, four position, tandem, spring return solenoid valve. A pressure gauge 56 can be provided in an infeed line 57. An intake line 58 connects the pump 47 to the tank 54 and can include a screen 51 connected therein to filter incoming hydraulic fluid. The output pressure of the pump is less than a maximum of about 4000 psi. A line 50 connects the outlet tank port of the valve 52 to the tank 54.
In operation, an operator will select whether the [0025] cylinder 21 will extend or retract by use of the valve 52. A pressure regulating valve 60 can be provided to control the pressure of the hydraulic fluid supplied to the cylinder 21. As shown, the pressure regulating valve 60 is a pilot operated pressure relief valve. The pressure relief valve can be fixed or adjustable. Connected in flow communication between the lines 57 and 50 and will vent hydraulic fluid, when a pre-set pressure is reached, from the line 57 to the line 50 to tank 54. A pilot line 60P is connected to the line 57 to transmit the pressure therein and thereby effect opening and closing of the valve 60. It is preferred that the controller for valves 60 and 52 be mounted on the outside of guide 16. Preferably the controller for valves 60 and 52 are located at an elevation and location convenient for the operator, e.g., 30 to 40 inches above the floor. The hydraulic pressure in the hydraulic system will be indicated by the gauge 56 which can be calibrated with pressure indicia and/or force indicia 61 to indicate force applied by the cylinder on the extension stroke and/or the retraction stroke, see FIG. 7. Alternately, a gauge 56 could be provided in either or both of the lines 49 and 48 to indicate pressure and/or force on a respective end of the cylinder 21 and cylinder 46 instead of having only one gauge 56 in line 57 to indicate pressure on both ends of the cylinder 21, and the cylinder 46. In a force calibrated gauge, the force reading would only be valid for one end of the cylinder unless two force scales are provided, one for each end of the cylinder to compensate for the different surface areas due to the piston rod.
Pilot operated [0026] check valves 59A and 59B are connected in the lines 49 and 48 respectively. These check valves normally allow flow from the valve 52 to the manifold 61 which manifold facilitates connection of various cylinders to the hydraulic system. The valve 59A is piloted to the line 48 and the valve 59B is piloted to the line 49. Thus, when there is pressure in the line 49, the valve 59B will move to an open position to allow fluid to flow from the line 48 through port B to the port T and to the tank. This is with the valve 52 being shown with connections connecting the ports A to P and B to T, i.e., the left hand block shown in the valve 52 with the arrows in that block showing the direction of flow. When the line 48 is the pressure line, i.e., the port B connected to port P and port A connected to port T, pressure in the line 48 opens the valve 59A permitting flow of fluid from the line 49 back to the tank 54. With the ports B and T being connected and A and P being connected, the cylinders 21 and 46 may be extended thru operation of the valves 46V and 63 with valve 63 being connected in line 48. This will help prevent cavitation within the cylinder should an extension force be applied to the rod or the cylinder 21 which would reduce the pressure in the cylinder 21 on the piston side thereof. The cylinder 21 is preferably a single acting cylinder, but it can be a double action cylinder. Also, the cylinder is preferably a gravity return cylinder but if desired a spring return cylinder can be used. With valve 52 having the ports A and P connected and the ports B and T connected, the cylinder 21 may be retracted to apply a pulling force through a pulling assembly 11 or can be used simply to retract a cylinder 21. To accomplish retraction the valve 63 must be in an open position. To effect retraction of a cylinder 46 the valve 46V must be in an open position and valve 52 will have the ports B and T connected together and ports A and P being connected.
A controller may be provided to allow the activation of a single up or down switch for the [0027] cylinder 21 and an up and down switch for the cylinder 46 which control system would be connected to the various valves as would be apparent to one skilled in the art.
The [0028] bench 1 can be provided with a plurality of pulling assemblies 11 which are attached in a manner to not be movable relative to the platform 3 or pulling assemblies 11 can be mounted for movement relative to the platform 3, FIG. 1. FIG. 5 illustrates a pulling assembly that is substantially identical in construction to the pulling assembly shown in FIGS. 1-4 except that it can be pivotally mounted for selective pivoting movement on the platform as is known in the art. Such a pulling assembly has a different mounting frame 62 with a pivot mount 66. Locking mechanism (not shown) can be provided to secure a movable pulling assembly 11 in the desired position.
FIG. 4 illustrates a modified form of pulling [0029] assembly 11. A pulling attachment 70, such as a boom, is mounted on the guide 16 and during operation is substantially immovable relative to the head 17. The pulling attachment 70 includes a boom 72 having a guide member 74 mounted adjacent a free end 76 thereof and operable to guide and change the direction of pull of a flexible attachment member 35. The pivot end is pivotally mounted as at 77 to a collar 43 movably mounted or fixed to the guide 16 as described above. A bar 78 is pivotally connected to the boom 72 and a collar 43 as at 79 and 80, respectively. The bar 78 can be used to initially fix the angle of the boom 72 by having an adjustable length or by changing the distance between the upper and lower collars 43. Alternatively, a fluid cylinder, hydraulic cylinder, or other form of linear actuator could be used for the bar 78 and could be used to fix the angle of the boom 72 or to effect its lifting and lowering movement instead of or along with the cylinder 21, including a link chain 37 and a hook 45. The attachment member 35 is attachable to the head 17 and is supported by the guide 74, which during lifting is positioned above the head 17. When the head 17 retracts through retraction of the cylinder 21, the attachment member 35 is tensioned to apply a force to an object to effect movement, such as lifting, thereof. The use of such an attachment adds to the versatility of the bench 1. For the attachment member to lift during retraction of the head 17 as described, it is preferred that the free end 76 and guide member 74 be above the head 17 and catches 39 before lifting can commence. However, it can be above.
FIG. 8 illustrates an alternative form of pulling assembly operable to provide a lifting force similar to the embodiment shown in FIG. 4. As shown, a [0030] boom 81 has an end 82 pivotally mounted on the head 17 as at 83. The boom 81 also has a free end 84 and an attachment member 35 is connected to the boom 81 adjacent to free end 84 operable for being connected to an object to provide an upward lifting force such as a car engine (not shown). An adjustable length bar 86 is pivotally mounted on the boom 81 as at 87, for example, with the clevis and pin mount arrangement. The bar 86 is also pivotally secured as at 88 through a pin and clevis arrangement to a bracket 89 mounted on the column, preferably the guide 16. The bracket 89 may be permanently secured or removably mounted on the guide. In the illustrated embodiment a collar 43 is sized and shaped to be received over the exterior of the guide 16. Set screws, not shown, can be utilized to secure the collar 43 in place on the guide 16 in a removable manner. If the collar 43 or bracket 89 is permanently secured to the guide 16, the boom 81 and bar 86 may be easily removed from the point assembly 11 by a removal of the pins in the mounts at 83 and 88. In the form of boom attachment shown in FIG. 8, retraction of the cylinder 21 will cause the boom to pivot about the pivot point 87 raising the free end 84 to apply a lifting force via the attachment member 78. Extension of the cylinder 21 will lower the free end 84 and attachment member 35. The length of the bar 86 or the position of the collar 90 may be adjusted to determine the starting position and angle of the boom 81.
FIG. 9 shows a boom arrangement similar to that shown in FIG. 8 where like numbers designate like or similar parts. The difference in the structure is that the [0031] cylinder 21 does not need to be used to raise and lower the boom 81. In this embodiment, the bar 86 is replaced with a linear actuator such as a hydraulic cylinder 94 that is pivotally mounted to the boom 81 as at 87 and the guide 16 as at 88. With the collar 43 being fixed in position on the guide 16, extension of the cylinder 94 will effect lifting of the boom 81. To ensure that the head 17 does not move during extension of the cylinder 94, pressurized fluid can be maintained in the cylinder 21 to keep it in its retracted position or valves controlling the cylinder 21 may be kept closed to prevent fluid from flowing into and/or out of the cylinder 21.
It was described that the [0032] collar 43 can be secured in place on the column 16 for example by set screws to prevent it from moving longitudinally during operation of the boom 81. However, it is to be understood that by having the height H of the collar 43 less than a minimum value, the collar 43 will be self-locking in position on the guide 16 from application of force thereto via the bar 86 or cylinder 94. As shown, the bar 86 and cylinder 94 are connected to the respective boom 81 between the pivot 83 and free end 84.
An unexpected result achieved using a pulling assembly as described above was an increase in the efficiency of transmitting force from the hydraulic cylinder to the [0033] hook 45. The inventive pulling assembly achieved an increase in actually applied force of about 20 to 25% greater than a prior art pulling assembly wherein the hydraulic cylinder was positioned inside the guide tube resting on a floor thereof and pushing on the inside of the bottom of the holder 33. It is not clear why there was an improvement in the actually applied force.
In view of the above, it will be seen that several objects of the invention are achieved and other advantageous results attained. [0034]
The various changes can be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limited sense. [0035]

Claims

What is claimed is:

1. A pulling assembly adapted for coupling to a straightening bench, the pulling assembly including:

a frame mountable to a straightening bench;

a driver mounted on the frame, said driver including a guide, a double acting hydraulic cylinder positioned inside the guide, the driver further including a head moveably mounted on the guide and connected to the cylinder to effect longitudinal reciprocal movement of the head relative to the guide; and

an attachment member connected to the head for movement therewith, said attachment member adapted for connecting to a chassis to apply force thereto through movement of the head by the cylinder.

2. A pulling assembly as set forth in claim 1 wherein the cylinder is rigidly attached to the guide and to the head.

3. A pulling assembly as set forth in claim 2 wherein the cylinder includes a cylinder rod and a housing, a link connects one of the housing and the rod to the head and the other of the housing and the rod is connected to the guide.

4. A pulling assembly as set forth in claim 3 wherein the link is secured to the rod adjacent a free end of the rod.

5. A pulling assembly as set forth in claim 1 wherein the cylinder has a housing and a rod, the rod having a length outside of the cylinder when fully extended of less than about 5 times a diameter of the rod.

6. A pulling assembly as set forth in claim 1 wherein the cylinder includes a piston with a diameter of at least about 2½ inches and a rod having an exposed length when fully extended of less than about 5 times a diameter of the rod.

7. A pulling assembly as set forth in claim 1 including a pulling attachment associated with the guide and immovable relative to the head and a pulling member attachable to the head and associated with the pulling attachment such that retraction of the cylinder will effect tension in the pulling member and a lifting or pulling force to an object attached to the pulling member.

8. A pulling assembly as set forth in claim 7 wherein the pulling attachment includes a boom with a pulling member guide positioned above the head in both its extended and retracted positions of the head during lifting permitting the application of a lifting force by retraction of the cylinder.

9. A chassis straightening bench including:

a platform;

a support frame coupled to the platform;

a driver, said driver including an extendable and retractable column, said column including a guide and a head carried by the guide and movable relative thereto, the driver including a hydraulic cylinder connected to both the head and guide and operable to selectively effect relative movement of the guide and head and thereby extension and retraction of the column;

an attachment member connected to the head for movement of a portion thereby, said attachment member adapted for connecting to a chassis to apply a force thereto;

anchors associated with the platform for selectively retaining a chassis positioned on the platform against movement on the platform during application of force to the chassis by the attachment member; and

a source of pressurized hydraulic fluid with an output pressure limited to a maximum of about 4,000 psi, said cylinder is connected to the source to receive pressurized hydraulic fluid therefrom to effect at least one of the extension and retraction of the cylinder to apply a straightening force to a chassis on the platform.

10. A straightening bench as set forth in claim 9 wherein the cylinder has a piston with a diameter of at least about {fraction (2/12)} inches.

11. A straightening bench as set forth in claim 10 wherein the cylinder includes a rod with an extended exposed length of less than about 5 times a diameter of the rod.

12. A straightening bench as set forth in claim 9 wherein said guide is tubular and said head has a portion moveably mounted inside said guide, said cylinder is positioned inside said guide with one end attached to said guide and another end attached to said head.

13. A straightening bench as set forth in claim 12 including a link rigidly connecting a rod portion of the cylinder to the head.

14. A straightening bench as set forth in claim 13, including a support connected to the cylinder, said support, cylinder and link forming a substantially rigid structure.

15. A straightening bench as set forth in claim 9 wherein the cylinder is a double acting piston cylinder and is connected to the head and the guide to effect fluid powered extension and retraction of the column.

16. A pulling assembly adapted for coupling to a vehicle straightening bench, the pulling assembly including:

a frame adapted for mounting to a straightening bench; and

a driver mounted on the frame, said driver including a tubular guide, a hydraulic cylinder positioned inside the guide and extending longitudinally thereof, said cylinder having a housing with a movable rod extending therefrom, a head movably carried by the guide, said head including a sleeve section cooperating with the guide to guide movement of the head relative to the guide, said head also includes an attachment member holder, said cylinder and head being positioned such that the housing is outside of the sleeve throughout movement of the head, said housing being connected to the guide.

17. A pulling assembly adapted for coupling to a straightening bench and adapted to selectively apply either a straightening force to a chassis or a lifting force to lift an object, the pulling assembly including:

a frame adapted for mounting to a straightening bench;

a driver mounted on the frame, said driver including a telescoping column that includes a head movably mounted on a guide, a linear actuator operably associated with guide and the head to effect relative movement between the head and the guide to effect telescoping of the column; and

a boom mounted on the column and having an end movable between a lowered position and an elevated position and being operably connected to an actuator to effect movement between the lowered and elevated position

18. A pulling assembly as set forth in claim 17 wherein said boom is pivotally mounted on the head and is pivotally connected to the guide, and said actuator connected to the boom includes said linear actuator whereby contracting telescoping movement of the column effects pivoting of the boom and lifting of a free end of the boom.

19. A pulling assembly as set forth in claim 18 wherein the linear actuator is a double acting hydraulic cylinder.

20. A pulling assembly as set forth in claim 17 wherein said boom is pivotally mounted on the column and said actuator includes a hydraulic cylinder connected to the boom and column whereby extension and retraction of the hydraulic cylinder effects movement of the boom between lowered and elevated positions and movement to the elevated position can be used to lift an object.

21. A pulling assembly as set forth in claim 20 wherein the hydraulic cylinder is pivotally connected to the boom and the guide with the pivot connection to the boom being between the pivot connection of the boom to the column and a free end of the boom whereby extension of the hydraulic cylinder effects movement of the boom to an elevated position and retraction of the cylinder effects movement of the boom to a lowered position.

22. A chassis straightening bench for use in repair of a chassis, said bench including:

a lift including a work platform movable between raised and lowered positions, said lift including a loft mechanism associated with the platform to effect raising and lowering of the platform, said lift mechanism including at least one jack;

at least one pulling assembly associated with the lift and operable to apply a force to a chassis positioned on the platform, said pulling assembly including a driver including a guide, a hydraulic cylinder and a head moveably mounted on the guide and connected to the cylinder to effect longitudinal reciprocal movement of the head relative to the guide; and

an attachment member connected to the head for movement therewith, said attachment member adapted for connecting to a chassis on the platform to apply force thereto through movement of the head relative to the guide.

23. A chassis straightening bench as set forth in claim 22 wherein the cylinder includes a housing for its piston, the said head including a pulling arm receivable in and moveable within the guide, said housing being positioned in the guide such that the pulling arm does not travel along the housing during movement of the pulling arm.