[AT] OT: hydrostat mowers( Hydraulic drive)

[Steve W.]

Gene Dotson wrote:
>     Mowers do not use hydrostatic drive systems. They are hydraulic drives. 
> Big difference in their design. Hydraulic drives use a constant displacement 
> pump that always delivers the same volume of oil each revolution. The motor 
> is also constant displacement and requires a set amount of oil during each 
> revolution. Speed is controlled by the hydraulic drive system by controlling 
> the amount of oil bypassed. More oil bypassed, the slower the speed and more 
> heat from the bypassed oil, just like a stuck relief valve. in a hydraulic 
> system. You will get maximum torque with the high speed setting with no 
> bypassed oil.
> 
>     True hydrostatig like used in combines and large tractors use a variable 
> output  pump and a variable displacement motor. They have maximum torque at 
> the low speed setting as the pump output is reduced by shortening the stroke 
> and the pump displacement per revolution is increased by increasing the 
> length of piston stroke.
> 
>     There are certainly other systems that work on the same princilal.
> 
>     Link below may shed some light on the systems.
> 
> http://www.tpub.com/content/construction/14273/css/14273_221.htm
> 
>             Gene

Gene the Cub Cadets from the first hydro up to the current models are
true hydrostatic drive. They use a swash plate which not only controls
speed but direction by changing the pump displacement as the operator
moves the control lever. The motor is a unique unit that uses pistons
against a fixed swash plate to power the tractor.

The older Case garden tractors on the other hand do use hydraulic drive
with a bypass controlling the system.

-- 
Steve W.