All Wheel Steer Mechanisms

[mloew]

I am currently looking for information on what mechanism are used to steer multiple axles in close proximity to another; specifically multi axle trucks. I am performing my due diligence by Googling and searching the USPTO site, but would like some specific input from the members of this forum to compliment my efforts. Any input would be appreciated. I will post my findings to this thread as well. Thanks in advance.


Best regards,

Matthew Ian Loew

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[GregLocock]

Deathly silence. There's a couple of British trucks may be worth looking at - details are very flaky.

The first is a six wheeler

http://www.stalwart.org/

primarily for the military, although I think BP may had some as well. The front two axles were steered, by recirculating ball. not much help if you are looking for a linkage type of setup.

Secondly there was a British lorry (hoho) called the Leyland Octopus that had four axles very close together. They weren't uncommon. 1960s or 1970s.

Some tanks could steer on the road without tracks, I don't know if they included a steering mechanism as such. Probably not.

LAV 25

Scammell rigid 8





Cheers

Greg Locock

 

[santorta]

Hi Mathew,
You could find some valuable information about All Wheel Steer or Quadrasteer or sometimes also called as E-Steer at Delphi Company website.
Many articles are available at SAE Transactions. goto

http://www.sae.org

and search for your topic and u will get the corresponding Transcation number and year, which can be reffered at library.
Now-a-days All wheel steer uses Electronics(ECU) to control the steering of rear wheel.The speed of the vehicle is sensed by the Wheel speed Sensor, and depending on the angle of the turn of the front wheel the rear servo motor actutator actuates the steering.Two conditions arise here,

1. At low speed, u need the shortest TCR (turning circle radius) and so the rear wheel has to turn the opposite direction to make shortest TCR.
2. At high speed, The rear wheel will turn in the same direction as that of the front wheel.

Hope this information is of some use to you,

Regards,

Santhosh Arasan.

 

[mloew]

Santhosh,

Thank you for your reply. I am quite familiar with 4ws systems for both passenger cars and light trucks. I have been researching the control systems for these applications. The mechanisms to steer the rear wheels are quite conventional. What I am looking for is some more information on the mechanisms for steering multiple axles.

Look at the following image (with thanks to Link Belt):

In a similar application (similar as in having three axles that all steer only, however), I would like to use a single actuator to steer the rear two axles. Reducing the system to a single actuator for the rear axles greatly simplifies the control system design. I should mention that this is an independent suspension application, thus both complicating some things and allowing for additional freedoms.

For contra steer (as shown in the image) the rear wheels do not have the same angle to produce a common turn center. I know the relationship between them through the geometric studies I have been conducting. If I implement a fixed relationship between the two rear axles in a turn, the in-phase steer (crab steer) would be compromised, as the angles would want to be equal. I am comfortable with this trade-off at this point.

Let me be clear, I know I can develop a mechanism to do this on my own, I am just looking for some additional input from those that are familiar with these type of systems. I have access to many technical papers and patents. Thanks again for any input.

BTW, Greg, ever heard of Multi-Drive (

http://www.multidrive.co.uk)?

Neat stuff there.


Best regards,

Matthew Ian Loew

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[BEATH]

Consider a conventional truck steering axle with a drag link from the steering box arm to the lever arm on the stub axle. For a twin steer system the drag arm from the steering box is connecting to an idler arm mounted on the chassis and swinging in the same plane as the arm on the steering box. Two drag links are connected to the end of this idler arm one to each stub axle arm. If the distance from the idler fulcrum to the connection with each drag link is in proportion to the wheelbase of the respective axle (measured from the rear axle)the axles should steer in correct proportion.

 

[evelrod]

Matthew, my input comes from operating the twin to your ~80T Link Belt. From what I remember, the rear steer was operated by a single hydraulic source via conventional linkage. A switch to the drivers right had left and right positions independant of front steer and a selection for all wheel steer including normal (as pictured) crab and, straight ahead (no rear steer). In my few days at the wheel I do recall that the center wheels turning geometry never quite suited the turn and some indication of side slip was always present. Perhaps I don't exactly understand what you are refering to by "single actuator". This was my only experience with rear steer as all the other cranes I was around with multiple steering were FWD type chassis with front only and using multiple rams. Just curious. I was rather surprised when the photo popped up.

Rod

 

[mloew]

Just to update everyone here, I had found some of the technical information I was looking for in the following technical papers from SAE International (

http://www.sae.org):

2000-01-3434: Synthesis of Multi-Axle Steering System of Heavy-Duty Vehicle Based on Probability of Steering Angle
1999-01-3781: Heavy- and Medium-Duty Vehicle Suspension-Related Performance Issues and Effective Analytical Models for System Design Guide
931919: Design and Analysis of Multi-Axle Steering System of Heavy- Duty Vehicle
933007: Effect of Rear-Axle Steering on Vehicle Controllability and Stability of a Medium-Duty Truck

I was also able to find this paper:
Design and Control of the 4WD System & 8WS System of Automobile for Transporting Bridge (

http://fluid.power.net/techbriefs/hanghzau/4_7.pdf)

I have been solving my problem through the use of Pro/ENGINEER's Behavioral Modeling and Mechanism Design functionality. I have also been exploring a mechanism synthesis package called SyMech (

http://www.symech.com)

and have been very impressed.



Best regards,

Matthew Ian Loew

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[Slowzuki]

Contrete trucks with twin steering front axles use a similar mechanism if this helps.
Ken

 

[mloew]

For those that are still interested, I recently found an alternative mechanism to the one I developed:

This and other images are available on DJH Engineering Center, Inc.'s website.

Best regards,

Matthew Ian Loew
"Luck is the residue of design."
Branch Rickey

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[GraviMan]

Interesting mech.

Must admit I'm starting to see the advantages of having a central pivot steering an ADT truck. Basically for one pivot you get all wheel steer, and a very small cornering profile. The clever bit is getting the mass distribution right and damping right, for high speed operation (laden and unladen).

The down side is that none of the tyres are really at the correct angle, so maybe a local trim steering isn't bad. Trim steering could also be designed in as part of a high roll centre system, by linking steering to dampers ror axle roll rate.

Making a 60 tonne truck handle like a Ferrarri is easy. Making a 60 tonne truck, that handles like a Ferrari, cost effective is difficult. ;-)

Mart