Why no Hydraulic Drive Systems on roadcars??

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JaxsonIan
JaxsonIan
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Joined: Fri Aug 21, 2020 8:59 am

Why no Hydraulic Drive Systems on roadcars??

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I have spent several dozen hours trying to answer this single question, and have even looked for laws that ban its use, due to the fact that I cannot find the single point failure in the idea.

I appreciate any ideas, and I will try to cover any problems that I have already researched.

One would think that in this time of crisis, the 50hp motors that are required to drive a pump would be much more attractive than the 100hp engines that are the current trend.

Thanks in advance!

TimW
TimW
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Joined: Thu Aug 01, 2019 6:07 pm

Re: Why no Hydraulic Drive Systems on roadcars??

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Simply the higher losses compared to a geared system.

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Big Tea
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Joined: Sun Dec 24, 2017 7:57 pm

Re: Why no Hydraulic Drive Systems on roadcars??

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JaxsonIan wrote:
Sat Aug 22, 2020 10:59 am
I have spent several dozen hours trying to answer this single question, and have even looked for laws that ban its use, due to the fact that I cannot find the single point failure in the idea.

I appreciate any ideas, and I will try to cover any problems that I have already researched.

One would think that in this time of crisis, the 50hp motors that are required to drive a pump would be much more attractive than the 100hp engines that are the current trend.

Thanks in advance!

https://www.bonhams.com/auctions/21136/ ... egory=list


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Greg Locock
Greg Locock
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Joined: Fri Jun 29, 2012 11:48 pm

Re: Why no Hydraulic Drive Systems on roadcars??

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Weren't some Unimogs fully hydraulic, ie pump driven by the engine charges an accumulator and then oil is pumped to wheel motors? This means the wheels stick out below the chassis with no driveshafts, great for standing crops etc.

According to this pumps are 85-92% efficient (probably at their optimum ) https://www.machinerylubrication.com/Re ... drive%20it.

Pumps vary a lot, here's a Dowty one, which at its optimum is 94% but falls away to 70% worst case.

https://www.dowtyheritage.org.uk/conten ... lic-motors

So realistically you might average 92% for the pump, and run a big accumulator, and maybe 85% in the motors, to give an efficiency of 78%, less losses in the hoses and coolers and valve gear.

Your next job is to find out the efficiency of a conventional driveline. The diff is very important.

Brake Horse Power
Brake Horse Power
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Joined: Wed Oct 25, 2017 8:36 pm

Re: Why no Hydraulic Drive Systems on roadcars??

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The pumps and motors are even less efficient. Running idle or low loads ain't great. Also the valve block is extremely inefficient. Than indeed you have losses in pipes, hoses, filters.

The hydraulic losses in a modern excavator is 65%! So your engine size isn't reduced to 50hp, it actually needs to increase to 154hp.

You might increase efficiency by eliminating the valveblock and run closed loop systems for each pump and each motor. Next trouble you'll have is how to synchronize the speed of the motors etc.

Hydraulic is inherent to efficiency loss. Almost the only advantage is that you can have high lineair speed and force from an actuator which is quite compact (hydraulic cylinder).

Just_a_fan
Just_a_fan
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Joined: Sun Jan 31, 2010 7:37 pm

Re: Why no Hydraulic Drive Systems on roadcars??

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How good are hydraulic motors at giving walking pace up to motorway speeds? Do they need a gearbox to do that? Even if they can do it as direct drive, the efficiency is going to be rubbish at one end of the speed range.
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Zynerji
Zynerji
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Joined: Wed Jan 27, 2016 3:14 pm

Re: Why no Hydraulic Drive Systems on roadcars??

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https://radmaxtech.com/

I'd be interested to see these tried... One large one on the engine, and smaller ones in place of the wheel bearings.

It would even be able to use regenerative breaking with this setup.