CVT on the cheap : Lawn tractor hydrostatic pump/motor unit

[smog]

I need your ideas and views on this :

older garden tractors used to have horizontal shaft engines driving hydrostatic transmisions with a simple v-belt.

You can remove the variable displacement pump/motor unit from the differential axle assembly.

we can easily fit a sprocket on the hydro motor output and belt drive the pump input.

...and yes, this unit can do reverse in case you need to back-up in your driveway....


the trottle cable could control the pump displacement to control final drive speed while you will need some kind of rabbit/turtle handle to control the engine rpm.


tell me what you think of this.


see this as a reference :

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0115818034
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0078688255

and this one similar to what I got in my own tractor

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0100659993

[Byrdman]

The biggest concern I see is engine shutdown or hydraulic failure. That woud stop the hydraulic flow instantly therfore locking the rear wheel up.

[smog]

The biggest concern I see is engine shutdown or hydraulic failure. That woud stop the hydraulic flow instantly therfore locking the rear wheel up.

yup that's real hydraulic brakes !!!!!

even shutting off the trottle handle (if linked to the displacement linkage on the hydro pump) can make the bike stop by locking it's rear wheel.

(as a chain or tranny failure will do)

but I understand your concern with the engine shutting off.

[Byrdman]

Maybe some sort of one-way slipper clutch could be the answer.

Let off the gas or have a hydraulic failure and she free-wheels?

[smog]

Maybe some sort of one-way slipper clutch could be the answer.

Let off the gas or have a hydraulic failure and she free-wheels?

or something to release pressure on the hydraulic motor (most pump/motor unit got that type of valve to allow the lawn tractor to be hand pushed with the engine shut down.

hydraulic failure will allow freewheel by design as the system will not be able to built pressure.

[smog]

Maybe some sort of one-way slipper clutch could be the answer.

Let off the gas or have a hydraulic failure and she free-wheels?

or something to release pressure on the hydraulic motor (most pump/motor unit got that type of valve to allow the lawn tractor to be hand pushed with the engine shut down.

hydraulic failure will allow freewheel by design as the system will not be able to built pressure.

or for the control freaks :


3 trottles :

1 for engine rpm
1 for the variable displacement hydraulic pump (like a manual CVT....)
1 for the hydraulic motor pressure (this one will allow freewheel when the trottle is released)

we could control speed by the pressure/flow at the hydraulic motor.

another handle elsewhere could control gear ratio (variable displacement lever) (can replace the shifter and be mounted at the handlebars)

[oilburner]

How much horsepower/torque can these CVTs handle?

Regarding controls and engine shutdown or hydraulic failure.

One solution that would also please control freaks would be to incorporate traditional throttle and clutch controls. The clutch lever would operate a bypass valve. When coming to a full stop with engine shutdown, pull the "clutch", move the pump displacement lever (which could be incorporated into a footshift lever with detents for go, go fast, neutral, etc.) to neutral and power off the engine.

Hmmm, I kinda like this already...

My $0.02

Avery

[smog]

How much horsepower/torque can these CVTs handle?

Regarding controls and engine shutdown or hydraulic failure.

One solution that would also please control freaks would be to incorporate traditional throttle and clutch controls. The clutch lever would operate a bypass valve. When coming to a full stop with engine shutdown, pull the "clutch", move the pump displacement lever (which could be incorporated into a footshift lever with detents for go, go fast, neutral, etc.) to neutral and power off the engine.

the hydraulic unit in my 1968 Massey-fergusson mf-7 is mated to a 12hp engine but was also OEM in a MF-14 with a 14hp. Some people swap honda v-twin with 24 hp without failure in those 35 to 40 years old garden tractors.

you can find John deere, Cub cadet, Bolens and other hydraulic units for cheap on ebay.

a real clutch lever would release pressure on the hydraulic motor line-in. so it would coast whatever happened to the engine or pump.

you could also infinitely "slip" the clutch for smooth start-up as there's no friction.

I would tie the pressure release valve and the engine trottle to the clutch lever. So pulling the clutch will let the hydraulic motor freewheel and take the engine to idle.

the trottle handle would only control the pump variable displacement lever (cvt effect)

this way the engine always run at peak efficiency/power but is still fuel efficient by allowed to idle while coasting to a stop and idling when fully stopped.

sure listening to a constant rpm engine when taking off from a stop doesn't sound sporty but at least you can tell YOU are doing thing the right way.

(Did you know that when Audi took his first CVT car to the dealers they received a lot of customers complains about the NON-SPORTY constant reving engine. The had to reprogram "shift points" to the transaxle software to please the drivers.... giving it up on peak efficiency for driving pleasure)

Here in Canada, CVT systems are easy to get ; every snowmobile from 1960 to now got them in... (from 10hp to 200hp)

but I still think the hydraulic system is better even if it's heavier than the traditional CVT strap/pulley. at least it's a lot more compact.

[oilburner]

I agree with your idea of using the throttle twist grip to control the displacement. Now all we need (Mk II version) is a hydraulic pressure sensor circuit that sends a signal to engine room when we call for more hydraulic gpm. Twist the throttle, the engine revs as necessary to supply the pressure/flow required for the displacement. When the throttle is rolled all the way shut, the pump goes into "neutral", i.e. no call for press/flow, and the sensor circuit tells the servo to move the throttle lever to idle position.

You're in Canada eh?

East or West? I'm near Cornwall ON.

Avery

[smog]

You're in Canada eh?

East or West? I'm near Cornwall ON.

Avery

2 hours east; I live close to St-Sauveur in Quebec.

I works on VW TDIs since 2000; selling high performance parts for them and importing some yanmar clones; also I may get a batch of Punsun aircooled vtwin for my various projects (reselling some engines to cover my own projects) !

[boneshaker]

Are you aware that there's a diesel bike that already uses this technology? I saw it at a bike show a couple years back. I believe on his, the throttle controlled the engine RPM, and the "shifter" controlled the hydrostatic drive. Could be mistaken. You can find more info at http://www.hydraulicinnovations.com/

[LocomotiveBreath]

Yes, the Hydrostatic Hog, a very dangerous machine. Hydraulic drives have there place, but a very expensive and inefficient drive system for our purposes. I think we went this route before.

I have extensive knowledge of these types of drives, good to talk about them, and learn something. But I personally wouldn’t give it a second thought. Simple is better.

Dave

[buickanddeere]

Another Canadian here. Ontario on the lake Huron shoreline.

[Diecycle]

Good day all, this is my second posting and first day on Dieselnet so please excuse the responding to old posts.

locomotive breath, I am very interested in what you have to say about hydrostaic drives, since you have worked with them. I have been into diesel bikes for some time now and think that Jeff's bike at hydraulic innovations is awesome. It appears that the hydrostatic drive is more efficient that chain/gear/belt alternatives.

Where do you see the problems?

Thank you

[sbrumby]

Anything hydraulic is expensive and very heavy and contrary to the last post not efficient, when cold will be working at its best, but as it warms up oil gets thinner and gets round the motor without doing any pushing. So to work at its best you need a radiator to cool the oil and a tank to hold it, all of which is heavy. Would probably be more use on a motorcycle and sidecar as weight is not so important & you can go instantly into reverse with just the pull of the four way valve.

[Diecycle]

Please Canadians do not spank me with your french. I know nothing but the popular bits.

However, to this post it seemed fitting.

The current hydraulic closed loop variable displacement pumps rate above 80% efficiency.
The power band of a diesel makes the petrol motorcycle geared transmissions not the best choice. The many gears and such in those transmissions also brings their power transfering ability below 80%.

CVT transmissions do provide good efficiency I believe better than 80% but they have many moving parts and need to spool up. (this was confirmed by that fellow a few years ago who built the cool green small diesel chopper sold on ebay)

The hydraulic pump/wheel motor transmission seems to provide greater efficiency with greater simplistiy.

The hydraulic system will increase the weight, but with the greater efficiency of small diesels over their petrol counterparts combined with the efficiency of a hydraulic transmission, good power/mpg figures have been reached (Hydraulic innovations bike can cruise all day at 80 mph and gets 65-70 mpg) I think with some slight modifications it should be possible to have an 80mph cruise getting 100+mpg.

But I am open to counterpoints, if for nothing else then for things to watch out for as I follow this route.

[reg hardlyrideables]

you need to see this bike
hydraulic does work and looks cool take a look at
http://www.hydraulicinnovations.com/index.htm

you can even order a how its made dvd you gotta see this

[balboa_71]

Probably should have said this before to the group: I work with several hydraulic chucking lathes. These are mostly W&S brand and are all inside our plant. We run AW68 or 30wt. ATF fluid in our equipment. All our equipment suffers from outside temp. changes which translate into inside shop temps going from 55 degs F. during winter to 110 degs. F. during summer. This fluid not only moves the chucking yokes, but lubricates the spindle bearings and gear boxes. We have a great deal of performance variation in the temp. range I mentioned, and I don't know if this translates to anything related to HYD. drive used in outside equipment. I will say this, I hate our W&S 1SC cause it blows hoses on a regular basis...... really sucks and would never buy another one again. Just my $.02 worth

Cris

[sideshow]

Maybe ask this guy for some advice!




Alex

[UAofE]

The biggest concern I see is engine shutdown or hydraulic failure. That woud stop the hydraulic flow instantly therfore locking the rear wheel up.

Use a snubber valve (basically, a check valve). It allows flow from the return side of the motor to recirculate to the inlet when there is negative pressure in the line.

It doesn't need to be complicated at all.
(Ignore the left side of the motor circuit, pretend the line goes directly from the valve to the motor)


The normal bike throttle controls engine speed and thus pump volume.
The clutch lever operates a spool valve to control pump pressure which will allow you to stop and accelerate smoothly and operate at less than 1:1 drive ratio.
The snubber (check) valve allows automatic overrun of the motor and instant return to work when pressure is reapplied. Opening the spool valve will also allow coasting with the engine at idle.

The simplest mode of operation would be the same as that of a mower; you set the engine at one RPM and use the spool valve (clutch lever) to control vehicle speed. The difference is the snubber will prevent any negative power from trying to drive the engine or lock the wheel.
The downsides are its very heavy, bulky and complex compared to the dead-simple CVT and you lose any possibility of engine braking.