Material or article handling – Traversing hoist type – Tow truck type
Reexamination Certificate
1997-08-08
2001-11-13
Werner, Frank E. (Department: 3652)
Material or article handling
Traversing hoist type
Tow truck type
C280S402000, C414S427000
Reexamination Certificate
active
06315515
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to tow trucks, for towing a disabled automobile, and more particularly to a tow assembly for tow trucks which engage and lift the two front wheels or the two rear wheels of an automobile.
Tow trucks, for towing disabled automobiles by lifting either the front or rear wheels off the ground, and towing the partially-lifted automobile on its remaining two wheels, have long been used. The more modern and readily used types of tow trucks are known as a “wheel-lift” tow trucks. A wheel lift tow truck engages and lifts the vehicle to be towed at either its front or rear wheels (tires).
Wheel-lift tow trucks generally employ a telescoping or folding main boom element attached to the rear of the truck and extending rearwardly from or out beyond the truck's rear deck (the space between the rear of the cab and the rear bumper). The boom or crane element represents the main lifting or leverage component for lifting one end of the vehicle to be towed. Such tow trucks also utilize a wheel engaging apparatus, hereinafter referred to as the wheel grid, for engaging and holding the front or rear wheels of a vehicle. The wheel grid typically consists of a cross arm or wheel boom pivotally attached to the end of the main boom, and wheel retainers or lifting arms for engaging the wheels of the vehicle to be towed. When positioning the system for towing, the wheel boom is maneuvered into a position against the tread of the tires and the lifting arms are then locked into a position securing the tires in place against the wheel boom.
Examples of such a wheel-lift tow truck include: Youngblood, U.S. Pat. Nos. 4,186,938 and 4,194,755; LoCodo, U.S. Pat. No. 4,264,262; Lind, U.S. Pat. No. 4,473,237; Brown, U.S. Pat. No. 4,473,334; Russ, U.S. Pat. No. 4,564,207; Capers et al., U.S. Pat. No. 4,678,392; Muller, U.S. Pat. No. 4,701,099; Carey, U.S. Pat. No. 4,741,661; Brown, U.S. Pat. No. 4,761,111; Shoup et al., U.S. Pat. No. 4,797,057; Nespor, U.S. Pat. No. 4,927,315; Schardt, U.S. Pat. No. 5,013,205; DeMichele et al., U.S. Pat. No. 5,013,209; Franken et al., U.S. Pat. No. 5,259,572; Elfstrom, U.S. Pat. No. 5,302,074; Russ, U.S. Pat. No. 5,326,216; Curten, U.S. Pat. No. 5,336,037, Weller, U.S. Pat. No. 5,350,271; Wern, Canadian Patent No. CA 2069809-A; and Jones, UK Pat. App. GB 2 238 290 A.
Wheel-lift tow trucks were introduced to minimize the potential for damage caused by crane and hook or sling type tow vehicles. These early model tow trucks became ineffective at safely and reliably towing newer model automobiles due to lower chassis heights, new bumper designs and air-dams. Various of the above mentioned prior art references, however, still exhibited limitations such as inability to utilize the truck's rear deck, potential damage to the automobile by engagement with the wheel grid and/or the main boom (this is more prevalent with vehicle designs exhibiting a substantial overhang of the body or chassis beyond the front and/or rear axle), lack of sufficient maneuverability of the main and wheel booms for tow positioning, and tipping of the tow truck due to the weight of the vehicle in tow. Shoup et al., U.S. Pat. No. 4,797,057, provides a wheel lift type tow truck, having an extensible main boom and a motor and linkage for raising and lowering the main boom, which fully addresses these limitations, and is incorporated by reference herein.
The prior art also lacks efficient safety or locking mechanisms for securing the towed vehicle within the wheel grid. With the hydraulic actuator configuration of Capers, supra, for example, a loss of hydraulic power would release the wheel supports (lift arms in the present invention) and enable the vehicle in tow to disengage from the lateral extension assembly (wheel grid in the present invention), and drop from the tow vehicle. The employment of a safety locking mechanism would be essential to guard against this dangerous potential.
Some references employ various types of locking mechanisms which, however, fail to achieve the advantages of the present invention. Carey, supra, discloses a manually operable latch means with a spring biased, slidable latch bolt which when in a locked position engages a notch in an adjacent pivot plate and thereby locks the wheel restraint assembly. Additionally, Nespor, supra, employs a pin lock which utilizes a pin inserted through a hole in a shoe at the end of the cross bar (wheel boom) which engages one of several notches in the tire retaining member (lift arm) and thereby locks the retaining member in place around the tire. Such locking mechanisms, however, unlike the present invention, require manual engagement, adding extra steps to the towing procedure and introducing additional human error into the safety of the towing process.
The present invention overcomes these limitations by providing an over-center locking mechanism which automatically secures the wheel engaging arms of the wheel grid in place without the assistance of the actuating mechanisms (hydraulic cylinders, screw drives, or the like). This over-center locking mechanism requires no manual engagement or extra steps beyond the normal procedure for engaging, lifting and towing the target automobile. Engagement of the lift arms and wheel boom with the wheels of the vehicle to be towed automatically sets the overcenter locking mechanism without the continued support of the linear actuators. The present invention further provides a reverse tilt lock or position lock which may serve as either a back-up or primary security system. The position lock, like the over-center lock, is automatic and requires no manual engagement.
The present invention further provides a wheel spacer which adapts the wheel boom for smaller sized wheels and flat tires. The wheel spacer adjusts the space between the parts of the wheel grid which engage the wheel of the vehicle to be towed. This wheel spacer engages wheels of varying sizes more efficiently than wheel grids disclosed in the prior art. The wheel spacer also positions the wheels of the vehicle in tow in a manner producing maximum ground clearance and maximum clearance between the underside of the vehicle in tow and the wheel grid itself. These increased clearances reduce the risk of damage to the vehicle during the towing process.
BRIEF SUMMARY OF THE INVENTION
The tow truck of the present invention includes a truck chassis with a bed frame made up of spaced frame members, and a deck assembly situated upon the bed frame. Attached to the end of a main boom is a wheel grid assembly for engaging either the front or rear wheels of the vehicle to be towed. The wheel grid assembly of the present invention includes a wheel boom pivotally connected to the outer end of the main boom, and inclined surfaces at each end of the wheel boom for engagement with an automobile wheel. A pair of lift arms extend rearwardly from the wheel boom, and generally perpendicular thereto. Each lift arm is comprised of an extension arm segment and an engaging arm segment which is pivotally connected to the end of the extension arm segment, remote from the wheel boom. The wheel boom and the extension arm segments are situated in a plane, and the engaging arm segments are positioned at upward angles with respect to that plane. The upward angles prevent the engaging arm segments from contacting the ground while pivoting from the open position to the closed or wheel engaging position during the loading of the vehicle to be towed.
Linear actuators, such as hydraulic cylinders, are provided for moving the engaging arm segments into a wheel engaging position for lifting an end of the vehicle to be towed. Each linear actuator connects to an over-center locking mechanism for locking the engaging arm segment in a wheel-engaging position, and thereby locking the engaging arm segment without aid of force from the linear actuator.
The over-center locking mechanism consists of a linkage apparatus whereby full extension of the linear actuator positions the linkage apparatus in a locking position, such that out
Watson Scott A.
Young Charles E.
Jerr-Dan Corporation
McDermott & Will & Emery
Werner Frank E.
LandOfFree
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