Cam-actuated lift assist for tow bar activated brake system
A lift assist system for lifting a tow bar and setting a tow bar-actuated brake system. The lift assist system includes a cam that may proportionally counter the moments imposed on the tow bar for a reduced and more uniform exertion force on the tow bar throughout the rotation of the tow bar. A brake actuation system can help provide retention of the tow bar in the upright configuration, eliminating the need for or providing redundancy to conventional latch and hook mechanisms.
1 . A lift assisted tow bar system, comprising:
a tow bar pivotally coupled to a towed vehicle to define a tow bar rotation axis, said tow bar being articulable about said tow bar rotation axis;
a cam coupled with one of said tow bar and said towed vehicle, said cam including a cam surface that at least partially surrounds said tow bar rotation axis; and
a cam follower assembly, including a cam follower contacting said cam surface and a plunger assembly configured to exert a cam force vector along an actuation axis that is imposed on said cam surface, wherein said plunger assembly includes a plunger rod coupled to an extension, said plunger rod extending through an aperture defined by a centering plate of a proximal end of a housing of the cam follower assembly, said extension extending through a centering sleeve disposed proximate a distal end of said housing, said cam follower being disposed at a distal end of said extension,
wherein said cam follower is configured to follow along said cam surface and exert said cam force vector on said cam for generation of a counter-moment that at least partially counters moments encountered about said tow bar rotation axis during operation of said tow bar.
2 . The lift assisted tow bar system of claim 1 , wherein said cam surface is configured to vary a counter-moment arm of said counter-moment about said tow bar rotation axis as said cam follower follows along said cam surface.
3 . The lift assisted tow bar system of claim 1 , wherein said cam surface defines an arcuate depression for registration of said cam follower when said tow bar is in a tow bar up configuration.
4 . The lift assisted tow bar system of claim 1 , wherein said cam surface defines stops at terminations of said cam surface.
5 . The lift assisted tow bar system of claim 1 , comprising a brake system coupled to said tow bar, said brake system being engaged when said tow bar is in a substantially vertical orientation, wherein said cam surface and a biasing element are configured to generate said counter-moment to substantially counter a brake system load moment about said tow bar rotation axis when said brake system is engaged.
6 . The lift assisted tow bar system of claim 1 , wherein said cam is in a fixed spatial relationship relative to said tow bar, wherein said cam follower assembly includes a follower arm pivotally rotatable about a follower arm pivot axis, said follower arm including a follower end portion that extends from said follower arm pivot axis, and wherein said follower arm includes a lever end portion that extends from said follower arm pivot axis, a biasing element being coupled to said lever end portion.
7 . The lift assisted tow bar system of claim 6 , wherein:
said follower end portion defines a follower arm length extending from said follower arm pivot axis to a central axis of said cam follower; and
said lever end portion defines a lever arm length extending from said follower arm pivot axis to an anchoring point of said biasing element on said follower arm;
wherein a ratio of said lever arm length to said follower arm length is in a range of 2:1 to 3:1 inclusive.
8 . The lift assisted tow bar system of claim 6 , wherein said follower arm is a bell crank.
9 . The lift assisted tow bar system of claim 8 , wherein said tow bar, said follower arm, and said plunger assembly are coupled to a steering assembly, said steering assembly being coupled to a running gear of said towed vehicle for steering of said towed vehicle.
10 . The lift assisted tow bar system of claim 1 , wherein said centering sleeve includes a grease fitting, and wherein said housing defines an access port adjacent said grease fitting.
11 . The lift assisted tow bar system of claim 1 , wherein said centering sleeve and said extension define a polygonal cross-section normal to said actuation axis.
12 . The lift assisted tow bar system of claim 1 , wherein said is plunger assembly comprises a compression spring that surrounds said plunger rod.
13 . The lift assisted tow bar system of claim 12 , wherein said compression spring includes a distal end and is captured at said distal end by a distal spring retainer.
14 . The lift assisted tow bar system of claim 1 , wherein said plunger rod defines a first lateral through hole that is proximate a distal end of said plunger rod, said plunger assembly including a catch pin disposed in said first lateral through hole.
15 . The lift assisted tow bar system of claim 14 , wherein said plunger rod defines a second lateral through hole that is distal to said first lateral through hole, said second lateral through hole being configured to receive a removable pin for seating against said housing.
16 . The lift assisted tow bar system of claim 15 , wherein said removable pin being selectively removable from said second lateral through hole to enable said second lateral through hole to pass into said housing.
17 . The lift assisted tow bar system of claim 1 , wherein a spacer shim disposed adjacent a proximal end of said extension, wherein said spacer shim is captured between said extension and a distal spring retainer, wherein said distal spring retainer is a collar, and wherein said spacer shim is dimensioned to pass into said centering sleeve.
18 . The lift assisted tow bar system of claim 1 , wherein a mounting flange is disposed at said distal end of a body of said housing, wherein said mounting flange defining an acute angle relative to said actuation axis, and wherein said acute angle is in a range of 60 degrees to 85 degrees inclusive.
19 . The lift assisted tow bar system of claim 1 , wherein said towed vehicle includes a chassis, said cam being coupled to and in a fixed spatial relationship relative to said chassis.
20 . The lift assisted tow bar system of claim 1 , wherein said towed vehicle includes a steering section and a chassis, said steering section being pivotally coupled to said chassis, said cam being coupled to and in a fixed spatial relationship with said steering section.