Design Possibility, can or CANT be doneà 2

[DDame]

I’m kicking around an idea and want to get some comments as to its possibilities and maybe even its practicality.

Ok, I spent the weekend watching rock climbers, no not people climbing mountains but modified trucks, Jeeps and moon buggies (Purpose built 4x4’s). I seen more broken parts (drive line of course) then I see in my 15 years of being a mechanic (12 years ago). The other observation was the current mechanical drive line creates more limitations then I could count. This includes traction, clearance, power and the list goes on and on. Ok, Ok… Here’s my question.

It seems like the power of fluid could solve so many of these problems I have to investigate. Is it possible with the current technologies in fluid power (Motors, Pumps, Valves and Controls) to build the ultimate 4x4 or even rock crawler using 100% fluid power? Now I said “Possible”, let’s assume for the monument that money is no object (wouldn’t that be nice). Could one take say a Ford truck and replace the axels with Hydraulic motors (all 4 wheels), replace the transmission with a pump and the steering wheel with say joy sticks. Now I KNOW it’s much more complicated than that but for the monument think simple, what do you experts think is this something that could be done?

I’m not looking for any designs or direction at this point, just your thoughts!!

 

[amorrison]

Hydraulic motors at the wheels on farm sprayers – no axels

http://www.servspray.com.br/indexing.htm

http://www.servspray.com.br/indexing.htm

Electric wheel drive here $$$$$$ ??

http://www.mining-technology.com/contractors/maintenance/cognis2/cognis21.html

 

[hydromech]

DDame...The simple answer to all of your questions is ABSOLUTELY YES.

Putting aside, for one moment, the inefficiency and the costs ETC...there is nothing that beats the power to weight ratio of hydraulics. It is possible to drive any piece of machinery with hydraulic actuators.

With the control technology available in modern valves it is possible to have infinite control, hydraulically or electronically.

This is a totally unbiased opinion of a Hydraulic Systems Engineer. Ask an Electrical Engineer and see if they agree.

Hydromech...

 

[kcj]

I agree. Totally possible, high mounted motors at each wheel, no differential pumpkin hanging down, etc.
using hydrsostaic drive, you would also have dynamic braking

controls are the difficulty. Simiply teeing all together would be like an open differential-one wheel unloaded, all the oil goes there and spins 4x normal speed. and no traction.

We are currently working on a 4 axle drive vehicle that is expected to unload one axle at a time as the axles cross bad joints. Similar to driving 4 separate wheels of your truck. Nothing secret about the drive, its copied from previous industry technology. We will use 4 pumps, 4 motors, (1 pump drives one motor drives one axle. All four are separate from each other.) This of course gives no load sharing at all, if one pump/motor/wheel is fractionally more or less efficient, that drive pressure goes to 5000 and the others go into dragging at 5000 psi. In this case, there will be F & R pressure transducers on each PM package, and speed sensors in each motor. Overall software and controls will provide displacement (speed) control, the next inner loop limits by pressure to provide load sharing between the four drives, and the final inner loop is wheelslip limiting, i.e. don't exceed a couple percent slip no matter how unbalanced the pressure is.

HST are typically very stiff drives: touch of displcement and pressure spikes up to maximum. Several companies have 'automotive controls' that approximate a torque convertor drive: slushy with light throttle theen gradually increasing power and response with pedal motion. This allows maximum control and is used for maneuvering applications. perfectly suited for fine traction control.

k

 

[jsummerfield]

Check out a company called Mammoet at

http://www.mammoet.com.

They provide self-propelled modular flat-bed transporters that can interconnect as required to provide about 25 rows of hydraulically controlled wheels. Each set of wheels turn and drive with a crane-type controller. These are not climbing trucks but transport trucks for moving 7500 ton offshore platform decks, etc.

John

 

[Nwaune]

I am biased towards the sprayers. I design high clearance row crop sprays with hydrostatic drives(

http://www.hagie.com).

We use two pumps with four motors(1 pump to 2 motors). Traction can be improved by linking the motors in a X design. For example, one pump drives the front left and rear right motors.

With the correct pump, motor and torque hub ratio, I'm sure you could climb over anything.

Nick

 

[cadstarsucks]

Another possability is traction motors:

http://www.e-traction.com/TheWheel.htm

I think there are a few other companies that make these sort of "wheel-motors" but i cant find them offhand

 

[danhelgerson]

There is a company called Ifield Motor out of England. They make an extremely efficient hydraulic motor. A system was developed with Ford Motor using those motors and accumulators to make a very efficient system for an SUV. The accelerator was actually controlling the computer which then directed the accumulator to supply fluid to the motor. It was very smooth and had excellent acceleration. The idea was put on the shelf and the engineer who helped develop the system went back to England, discouraged.

Dan Helgerson CFPS, AFPI, AJPP

http://www.cfpsos.com

 

[unclesyd]

Here is one of several news releases for wheel hub motors.

http://www.detnews.com/2003/autosinsider/0308/12/b02-242629.htm

 

[cadstarsucks]

Theres a surprize - they spent millions reinventing the wheel at probably 10x the price to keep from spending a nickel a unit on royalties

 

[danhelgerson]

Efficiency is another issue to consider. Many of the lower cost low speed, high torque motors are quite inefficient. Finding a motor that is efficient at the low end and still within an acceptable price range is challenging.

Dan Helgerson CFPS, AFPI, AJPP

http://www.cfpsos.com

 

[unclesyd]

I keep seeing hints of some very practical applications. The military is looking at this technology for the same reason as your requirements.

http://www.wavecrestlabs.com/index.html

 

[cadstarsucks]

True. The etraction system is on city busses and is doing quite well on the overall system.

Other info that i have been reading is saying that the gear trains and such max out at 50% eff. I think i was reading one of these as companies as saying that running one as a motor driving a second as a generator they were getting 80% system eff.

 

[95yukon]

I spent 7 years as a hydraulics/diesel tech working on oil exploration equipment around the world. We used specially made vehicles with hydrostatic drives in the Middle East to the Sahara to the Alaskan Arctic (on land and ice). In all applications the hydraulic drives were the only solution at the time.

I finished my BSME after the oil slump in the 80's and have been designing hydraulic systems since. Hydrostatic drive systems are gaining more popularity with off road equipment as well as in fan drive systems and high tech transmissions (hydrostatic and powershift combined). I think a hydrostatic transmission system installed on any off road vehicle has advantages over conventional systems.

The best system I ever used was a powershift transmission driven by a hydrostatic motor. I crawled over some of the steepest sand dunes and rock structures ever imaginable and was able to maintain good traction.

 

[zepp]

the kind of drive system you are asking about is already in use around the globe, used in open cast mines, here in Borneo for instance there are many trucks, and other ore handling vehicles, manufactured by Volvo/Michigan/Euclid (VME), Leibheirr, and Hitachi.
Your biggest problem is down to size, wheel motors like the Hagglunds Dennison viking range are quite huge, but then you could go onto the Vickers motors, or Staffa, or go as far as the german manufacturers, Brueninghaus, Rexroth, and Beauringers.
If you have any links with deep shaft mines, you could pick up some ideas from drawings supplied with Dosco machinery, or Mindev, BJD, Fletcher Sutcliffe and Wilde,
But basicaly speaking, the idea you had originaly, will work, can work and has already been proven to work, now, when it comes to areas like rock climbing or rough terain, then you have to think about putting your wheel motors on floating floating anchors, and these would have to be actuated by hydraulic cylinders that would be fed by a pressure sensitive control, thus allowing movement in both up and down to compensate the weight displacement of the vehicle, in short and elaborate shock absorber.
in truth, if you ever get a unit built, i would love t see it

 

[frans]

Just remember that if your vehicle is also going on the main roads at high speed you will want to minimize the sprung mass of the wheel assembly itself to ensure acceptable dynamics over uneven surfaces at speed. Hence a hydraulic wheel motor may not be suitable unless you use a CV joint type drive. Most wheel motor applications are low speed heavy vehicles.

 

[Jacc]

That kind of drive has a limited span of gear ratio. Optimize it for rock crawling and you will have about zero effiency at highway speed.

 

[tad1299]

I have the solution to which this is to be done. I have designed a buggy with hydraulics for its source of power. It runs on 49 inch tires, utilizes "Mud Hog" wheel motors, that are primarily used in rear wheel assist on combines in the ag industry. Utilizing pumps from Eaton/Vickers (the company which I work) If possible I will try to use aircraft pumps to keep the weight in the center of the vehicle down. I would eventually like to drive this with a turboshaft turbine engine, and utilize pressurized bladders for fuel and hydraulic storage, This will greatly reduce starvation and help with cavitation to the pumps when on steep inclines. I was planning on running three pumps, two for the drive wheels, going through flow splitters, and directional control after that via directional control valves. This would allow me to run either the front set of wheels or a side of wheels off one pump. Full hydraulic steering and suspension controlls. The steering would have enough degree of freedom to allow all four wheels to steer independantly, allowing both front and rear wheels to tow, and spin 360 deg without any forward travel. The suspension is a cantilever design with an adjustible upper shock/spring combination via hydraulic actuators. I have the planns, I just need to purchase the hydraulic equipment.
I design and test aircraft hydraulic systems for a living.
I would love to share these ideas with anyone.

 

[hydromech]

tad1299...

The only obvious issue I can see is using a flow divider to drive the wheels.

Going in a straight line...great, turning corners...that may be a problem.

When turning, the inside wheel will want to turn at a different speed to the outside one. Because its moving around a smaller arc it will want to go slower. The flow divider will keep both wheels turning at the same speed.

The handling of the buggy could be scary. But then again...that may be just what you are looking for???

Also, if the buggy has one drive wheel off the ground the flow divider will intensify the load in the motor that is still driving the buggy. That again may not be a problem for you, but it could potentially force the wheel of the buggy.

I wish I could tell you the best way to do it, but I have little experience with drive systems like this...sorry!

Best of Luck

Hydromech
Hydraulic Systems Engineer

 

[Deaks]

HST is absolutely the way to go, but flow dividers are useless in high steer angles and a high power drain to boot. Sauer-Danfoss have an electronic control and hydraulic flow control system (ASC - Anti spin control) that senses wheel speed and steer angle (2 or 4 wheel) and shuts down flow to a spinning wheel, whilst allowing for differential speeds due to steering.
Ian