Hydrostatic transmission and other types of lawn tractor transmission explained

Lawn tractor transmission

This is how Wikipedia describes what transmission is:

A transmission or gearbox provides speed and torque conversions from a rotating power source to another device using gear ratios … The most common use is in motor vehicles, where the transmission adapts the output of the internal combustion engine to the drive wheels. Such engines need to operate at a relatively high rotational speed, which is inappropriate for starting, stopping, and slower travel. The transmission reduces the higher engine speed to the slower wheel speed, increasing torque in the process.

A lawn tractor engine has to drive not only the wheels of the lawn tractor itself, but also the mower deck (and any other powered implements that may be attached to the tractor).

The mower deck has to run at a constant high speed in order to be able to cut grass efficiently. However, the lawn tractor itself has to be able to run at various speeds in order to be able to start, stop and manoeuver in the ordinary way. Therefore the transmission is one of the most important lawn tractor parts.

These different demands are accommodated by means of the Lawn tractor’s transmission. There are generally three types of transmission used on lawn tractors.

Hydrostatic Transmission

This type of transmission provides the best means of lawn tractor control and allows infinite speed adjustment in forward and reverse and easier manoeuvering.

Hydrostatic transmission operates by means of a hydraulic pump linked to a hydraulic motor which drives the lawn tractor wheels. It is operated by hand levers or foot pedals.

The downsides of hydrostatic transmission are that it is expensive – it increases the initial cost of the lawn tractor and leads to less fuel efficient operation – and it can be high maintenance, especially in keeping the system clean.

Gear Transmissions

A geared transmission on a lawn tractor is much like a manual transmission on a car. There may be a number of forward gears, together with a reverse gear.

The gears are operated by a lever and clutch mechanism – either a mechanical clutch or a belt system and are often combined with the axle into a ‘transaxle’.

Gear transmissions are usually reliable and efficient and are a relatively low cost option in terms of initial outlay and relevant replacement lawn tractor parts

Belt Transmission

This is the simplest and cheapest transmission system and is pretty effective on lower powered tractors.

Drive speed is controlled by a belt system between crankshaft and drive wheel mechanism. No separate clutch is needed.

The belts are adjusted by control levers operated by the driver so as to slow or increase the speed of the lawn tractor. Belt drives can be variable speed or fixed speed or associated with 2-5 gears.


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