Hydraulic power for a 1000 pound car for city driving

1. Aug 29, 2014

H012

I want to build a 1000 pound car for city driving with a 45 MPH limit. This totally something I want to do.just to say I can. But I'm a machinist with only basic engineering knowledge. My power plant will be a 16 HP OHV gas engine
driving a 1800 psi pump coupled to a Bi-directional hydraulic motor rated at 300 FtLbs.of torque at 400 RPM, This is of course a low RPM high torque motor. I will be running a rear wheel drive straight axle with a limited slip coupling No transmission. My question is what should my gearing be from the Hydraulic motor to my axle. If I left Anything out to help figure this I'm sorry.
Thanks'
Ray Mills

2. Aug 29, 2014

rcgldr

You need the effective radius of the tires (there's some deformation slightly reducing the effective radius from the actual radius). 45 mph = 66 ft / sec, and with a 1 foot effective radius, that's 6.283 ft / revolution which translates into about 630 rpm. You need a huge tire with a 1.576 foot radius to achieve 45 mph at 400 rpm. (assuming my math is correct here).

3. Aug 29, 2014

H012

Thanks for getting back. Maybe I didn't explain right. The hydraulic motor RPM is 400. My tire size would be a standard 14 inch tire
I thought I had included this My mistake. I would need to know what gear size for the hydraulic motor and the 2 inch axle. and 14 inch tire. Hope I said it correctly.

4. Aug 29, 2014

Baluncore

Hydraulics are inefficient in this application. Electricity is more efficient, easier to regenerate and to control.

With hydraulics there will be a loss of about 20% at each stage, you will need to factor that into the calculations. 80% pump * 80% motor = 64%. You will need a hydraulic fluid cooler to radiate the wasted 36%.

It would help to know your selected hydraulic pump and motor capacities in millilitre per revolution. That determines the effective hydraulic shaft ratio. You can eliminate all gearing by selecting the right capacity ratio.

If you were to use a combination such as a self regulating constant pressure pump and an adjustable capacity, (swash plate?), motor, you would not need any gas engine speed control.

5. Aug 29, 2014

jack action

This Gear Ratio Calculator will give you the pinion rpm.

6. Aug 29, 2014

jim hardy

Well,

a 185/60R14 tire has circumference of 71.44 inches. Call it six feet - so it'll go about six feet per revolution.
http://mcgrefer.com/sizeinfo/1856514 [Broken]
185/65 has circumference of 73.72 inches which would allow for the flattening at bottom as pointed out by rcgldr.
http://mcgrefer.com/sizeinfo/1856014 [Broken]

6feet/rev X 400rev/min = 2400 feet/minute = 27.27 miles per hour

to make 45 miles per hour you'd have to increase wheel RPM by factor 45/27.27 = 1.65 to 1.
That's the gear ratio you'd need, 1 turn of hydraulic motor gives 1.65 turns of wheel.

In the late 1970's a guy in Burnsville Minnesota built such a car as you describe.
He used a single rear wheel for simplicity. That also let owners in many states register it as a motor-driven cycle which was cheaper.
His drive train was a one cylinder aircooled Tecumseh engine with variable sheave pulleys for infinitely variable transmission. Nowadays there's a lot of those around surplus thanks to snowmobiles and ATV's. He offered a diesel but it wasn't cost effective given the gas version delivered 100mpg.

I saw one once in Miami - but down there with no airconditioning they didnt catch on.

courtesy http://automuseumonline.com/auto-freeway-cars-1981-hmv.html

sounds like fun.

old jim

Last edited by a moderator: May 6, 2017
7. Aug 31, 2014

H012

Thanks Jim I actually brought to life some old brain cells and found the formulas I needed. As my mentor quoted back years ago
when I was an apprentice machinist " You don't have to know everything just know where to find it". Anyway Your calulations
are the same as mine.I did some studying and a hydrostatic design is the most effiecent. Most designs I see incorporate accumalators. why? I contacted Eaton Corp. and they said there is no reason with proper design that a hydostatic design can"t be up to 88% efficent. I'm not going to use accumalators this is to bulky not to mention dangeous. As I have alot of planning to do the progress will be slow. As it doesn't appear the EPA green fund gives grants to one person for R&D. They cater to the big wheels. Again Thanks for your help and in time I will let the community know how I'm doing on this

8. Aug 31, 2014

jim hardy

I'll bet you have "Machinery Handbook".

If you ever get the chance , take in the "Florida Flywheelers" antique engine show in Zolfo Springs every February.
Scores of retired machinists from up North bring their projects to show.

http://www.floridaflywheelers.org/

9. Aug 31, 2014

H012

I have already taken a 550CC motor cycle engine and made a tractor it'a 12 ft. version of a real tractor. I did all the drive work myself
I actually had to engineer a drive system because the engine rotation is clockwise and the differential is counterclockwise..I'm born in Germany but moved to Tennessee when I was 6. My ancestors migrated in the 1700's to Arkansas then to Tennessee.

10. Dec 30, 2014

psycho rich

Tesla approached the navy with his turbine engine, as the story goes his design was overlooked. It may run a micro car very well.
I remember a quote From Lee Iacocca " the whole idea of driving a 4000 lb car across town to save 39 cents on a can of beans is ridiculous".
I wish you well on your quest for perfection.

11. Jan 2, 2015

H012

My thinking is more on the lines of decreasing the carbon footprint by making the power the engine produces more efficient to the wheels.. I don't see gasoline or diesel being replaced anytime soon. Not that it couldn't be done but that the Powers of governments are not going to allow it. Petro companies are too embedded in our political system. Profits always dominate. Enough about that! My idea of taking an existing car and converting it to hydraulics is achievable but my return on my time and investment to achieve this efficiency would not be seen for many years. The car would rust away first in the northeast US. So I have put my brainstorm at rest
and except that I am a " Small fish in a giant ocean " I just don't have the resources.

12. Jan 2, 2015

psycho rich

There is a french car that is similar it runs on compressed air . Porsche built turbine/hybrid , I haven't followed up on either of them.
An inventor once told me to sell your idea to industry, much easier trying to build it your self. Unless your Henry Kaiser.

13. Jan 2, 2015

Baluncore

It seems counter-intuitive at first but the rolling circumference of a tyre is not significantly changed by air pressure, tread wear or load.

The length of the fabric just below and against the tyre tread does not change. That fabric is locked to the bead of the wheel rim When the load increases the area of the tyre footprint increases and appears to flatten the tyre. The vehicle is slightly lower relative to the road surface, but the length of tread is like a track-layer's track plates, (bulldozer), and does not change. The deformations of the rubber generate heat in the sidewall of the tyre. Higher tyre pressures are needed when carrying greater loads and at higher speeds so as to reduce heating of the tyre sidewall.

14. Jan 2, 2015

Baluncore

Tesla's turbine is very inefficient and so is always avoided by engineers who are trying to improve fuel economy. You could not sell a vehicle fitted with a Tesla Turbine because it would cost 3 times as much to run as an electric car.

15. Jan 2, 2015

jack action

Not always true. Speed can have a notable effect on tire growth with some type of tires. The loaded radius of a top fuel dragster tire can grow up to 3.8" at 200 mph. The tire growth is so important that there is no need for a transmission to keep the engine in its rpm range:

16. Jan 2, 2015

rcgldr

I meant load and deformation in the direction of travel. Typically the tread compresses and slows down slightly in the direction of travel as it approaches the contact patch, then stretches and catches back up after it leaves the contact patch, so actual speed is slightlly less than unloaded radius of the driven tire. In the case of motorcycles, I seem to recall that it's 1% or so at high speed (higher load in the direction of travel). I don't know what the numbers are for other vehicle types.

17. Jan 2, 2015

Baluncore

We are discussing economic road legal vehicle tyres here. It is an uncommon practice to drive across town at 200mph and change the tyres every week.

18. Jan 5, 2015

H012

Thanks for getting back. The patent system as well as selling an idea has major flaw. In 1992 I invented and built a mechanical system in the textile industry.
Because there is nothing that keeps a design secret while a patent is pending all a company has do is make a small design change then it becomes their design.
It happened to me! Read up on it! Patent offices are corrupt and has been for many many years it's no secret. It's called Capitalization.

19. Jan 5, 2015

Baluncore

You should file a Provisional Patent to protect your intellectual property in a general way. That PP is used later to set the priority date on the Full Specification of your patent. A correctly written PP will not be invalidated by a small design change.

You also need an intellectual property agreement with the user of the invention. The user can then pay you to maintain your patents because they get an exclusive licence from you.

Patents can be very expensive. You must have a good relationship with the initial user of your invention and that user must benefit from the patent protection provided.

20. Jan 6, 2015

psycho rich

Good luck with your invention, we certainly need to move in the direction of 1000 lb. cars. I've been looking into hemp oil fueled cars, reduced weight / cleaner fuel / better tires, if you put all that together we could make substantial progress.