Kenneth
Washington, the state
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From the patent:
--quote--
Fishtail sway is caused by the large distance between the rear axle of the tow vehicle and the hitch assembly and is aggravated by lateral forces against the vehicle caused by winds or passing vehicles. Previous attempts to solve fishtail sway involve stiffening the connection between tow vehicle and trailer by using various methods of friction. While these methods help some, none completely correct the problem.
Fortunately, in U.S. Pat. No. 4,722,542, hereafter referred to as the "Hensley hitch", the sway problem is effectively corrected by forcing the hitch to turn through converging links that effectively move the pivot point between the tow vehicle and trailer to a point near the rear axle of the tow vehicle. Therefore, this design provides better steering and control of the trailer by eliminating trailer sway. While the converging links do this very well, the gross trailer weight is limited by the size and design of the converging links in '542 because so much of the tongue weight is supported by the converging links. As a result, increasingly heavier tongue weights require larger links, larger bearings, larger spindles, and larger related support systems. Increasing the size of these parts also increases both the hitch weight and the cost of manufacturing. In addition, the Hensley hitch needs workable brakes on the trailer controlled from the tow vehicle. Without trailer brakes or even with surge brakes the converging links tend to move to one side or the other due to the trailer pushing on the hitch assembly when the tow vehicle brakes are applied.
--end quote--
The original patent, #4,722,542
http://patft.uspto.gov/netacgi/nph-Parse........542.WKU.&OS=PN/4,722,542&RS=PN/4,722,542
The new hitch and its 2005 patent, #6,851,696
http://patft.uspto.gov/netacgi/nph-Parse........50&co1=AND&d=ptxt&s1='hensley+hitch'&OS=
I'm free of prostate cancer for 5 years now.
All men over age 50 should get an annual PSA blood test. Mine had a low reading, but the yearly jump was significant. The biopsy showed cancer just entering the aggressive stage. Dr. Hackenslash removed it.
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Kenneth
Washington, the state
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Hensley's new 2005 patent hitch drawings
The new Hensley hitch Patent #6,851,696
--quote--
Briefly stated, the invention is a hitch assembly comprising a hitch bar assembly coupled with a hitch receiver of a tow vehicle for transferring pulling and stopping forces to and from the tow vehicle. A hitch box assembly couples with the hitch bar assembly for transferring pulling and stopping forces to and from the hitch bar assembly, the hitch box assembly having a first pivot point. An overcenter latch assembly secures the hitch box assembly to the hitch bar assembly. A front support member pivotally connects to the hitch box assembly at the first pivot point for transferring pulling and stopping forces to and from the hitch box assembly and for pivoting during turns. A strut assembly pivotally connects to the front support member for transferring pulling and stopping forces to and from the front support member wherein the strut assembly can pivot vertically for accommodating uneven roads during driving. Also, the strut assembly includes a second pivot point. A ball mount assembly pivotally connects to the strut assembly at the second pivot point for transferring pulling and stopping forces to and from the strut assembly. The ball mount assembly laterally pivots about the second pivot point within the strut assembly during turns. The ball mount assembly includes a tail tube extending rearwardly. A ball plate assembly attaches to the ball mount assembly for transferring pulling and stopping forces to and from the ball mount assembly. The ball plate assembly includes a hitch ball for removable attachment of the trailer for transferring pulling and stopping forces to and from the trailer. A tail support assembly attaches to a trailer frame and couples with the tail tube whereby the tail support assembly restricts lateral movement of the tail tube and the ball mount assembly so the trailer remains relative to the ball mount assembly at all times. A slide assembly resides within the ball mount assembly such that forces inherent in towing the trailer are not transferred through the slide assembly. The slide assembly slides forwards and backwards to accommodate the change in radial movement of the converging links during turns. Converging links pivotally connect between the hitch box assembly at the first pivot point and the slide assembly whereby the angular position between the first pivot point and slide assembly can be varied. The converging links effectively move the pivot point between the tow vehicle and trailer forward of the hitch assembly. In addition, forces inherent in towing the trailer are not transferred through the converging links. A hanging support assembly attaches to the strut assembly including vertical links pivotally attached to the ball mount assembly for transferring tongue weight from the ball mount assembly through the strut assembly and front support member to the hitch box assembly and hitch bar assembly so tongue weight is not exerted on the converging links or the slide assembly. A jack assembly attaches between the trailer frame and the front support member for distributing tongue weight among tow vehicle wheels and trailer wheels.
--end quote--
The original hitch Patent #4,722,542
--quote--
Fishtail sway is caused by the large distance between the rear axle of the tow vehicle and the hitch assembly and is aggravated by lateral forces against the vehicle caused by winds or passing vehicles. Previous attempts to solve fishtail sway involve stiffening the connection between tow vehicle and trailer by using various methods of friction. While these methods help some, none completely correct the problem.
Fortunately, in U.S. Pat. No. 4,722,542, hereafter referred to as the "Hensley hitch", the sway problem is effectively corrected by forcing the hitch to turn through converging links that effectively move the pivot point between the tow vehicle and trailer to a point near the rear axle of the tow vehicle. Therefore, this design provides better steering and control of the trailer by eliminating trailer sway. While the converging links do this very well, the gross trailer weight is limited by the size and design of the converging links in '542 because so much of the tongue weight is supported by the converging links. As a result, increasingly heavier tongue weights require larger links, larger bearings, larger spindles, and larger related support systems. Increasing the size of these parts also increases both the hitch weight and the cost of manufacturing. In addition, the Hensley hitch needs workable brakes on the trailer controlled from the tow vehicle. Without trailer brakes or even with surge brakes the converging links tend to move to one side or the other due to the trailer pushing on the hitch assembly when the tow vehicle brakes are applied.
--end quote--
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tluxon
Kirkland, WA
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yepitsaCummins wrote:...Is it correct that two of the bars are effectively rigidly attached to the tow vehicle and the other to the trailer?
I don't have a Hensley, but I made the assumption that the centerline of the TT and the back bar form a fixed "T" as do the centerline of the TV and the front bar. Can anyone confirm this to be true?
Thanks for the links to Hensley's patents, Kenneth. Other than being designed to handle higher tongue weights, do you know of anything else that's different with the new Hensley?
Thanks,
Tim -
wife Beverly & 2 boys who love camping
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Claude B
Montreal, Canada
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Doe's this make sense ?
My humble theory
BTW, i'm sorry for all my english mistakes, i'm french canadian but i can tell you that i sure work hard ![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/smile.gif "smile")
Claude
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Ron Gratz
full time RVer
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Wow, this has turned into a great exchange of ideas and information!
Thanks to Will for getting it going, and thanks to Barney and Les for helping to keep the discussion on track.
My input is going to be somewhat limited (perhaps for the better) because Jean and I currently are in the process of disposing of 40 years of accumulated "stuff" with the goal of becoming fulltime Rvers on May 31st. Jean says I must keep off the internet during the daytime so people can respond to our ads. ![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/frown.gif "frown")
I do think we will find, as this topic continues, that there is only one "pivot point" of interest. I'm guessing it will be the "instantaneous center of rotation" which Tim referred to. And, it will make the analysis much simpler if we can show that the force vectors carried by the side links converge at this location making it a point at which only force and no moment is transferred to the TV.
Just some food for thought.
Back to the disposal process.
Ron
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Ron Gratz
full time RVer
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tluxon wrote:For the forces involved (as opposed to the Apparent Pivot Point), you actually have to start talking about something called the instantaneous center of rotation.
Tim et al.,
Here is a link to information about Instantaneous Centers of Rotation.
The right side of Figure 2.15 shows how the centers (pivot points) are defined.
Ron
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Ron Gratz
full time RVer
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Kenneth wrote:Depends on where you stand when you look at it. If you're standing behind the hitch looking forward, I guess one could say that the pivot was behind the hitch...actually meaning closer to the tow vehicle's front.
Ken
Ken,
I admire your ability to think outside the box. However, UniCacher's statement was, "The pivot point is actually BEHIND the ball, just forward of the trailer axles."
If UniCacher is following this thread, I would like to hear more about his model.
Ron
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Ron Gratz
full time RVer
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tluxon wrote:...Clearly, as the angle between the TV and the TT change, the point of intersection between their centerlines changes, and this way we have a name to reference that moving point.
Tim
Tim et al.,
I don't think there is any significance that can be attached to the point of intersection between the centerlines of the TT and the TV.
Please disregard the RED portion of the following paragraph. I now believe that it is incorrect. See my 5/13/05 4:59pm post for an explanation.
When towing, the usual condition is for the angle between the centerlines to be zero. In this limiting case, the "apparent" pivot point would be at infinity ahead of the TV. This means that, as the TT pivots through zero angle with a finite angular speed, all points on the TT would have to be moving at infinite tangential speed.
Ron
* This post was
edited 05/13/05 04:09pm by Ron Gratz *
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Ron Gratz
full time RVer
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willald wrote:Given the way the Hensely completely eliminates sway for us, I find it hard to believe that having the pivot point 20" behind the rear axle could do this. Always thought there was more to it than that, and perhaps there is.
Will
Will,
Now you've done it. You used the s... word.
I think it is quite possible that, by having the pivot point at 20" behind the TV's rear axle rather than at the approximately 70" for a conventional hitch, you have reduced the lever arm enough to eliminate any perception of s... for the conditions you have encountered.
Ron
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Kenneth
Washington, the state
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The HA looks something like this: (use your imagination...it looks fine on the compositon screen)
__|__
/_____\
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The tow vehicle is at top and the trailer is at bottom. All four corners pivot. The upper inverted T (in this diagram) and lower T are rigid. The upper T is solidly on the drawbar, and the lower T is on the ball for lateral and transverse tilting, but held in position by the struts.
(The pivots are tapered roller bearings much like wheel bearings. I had my '95 HA apart for new grease and new seals. The old grease was hard and dry, but no bearing damage.)
Ken
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