How To Choose a Lawn/Garden Tractor - Power To Implements

Figure 1. Belt drive to mower deck.

Figure 2. Shaft drive to mower deck.

Figure 3. Mid-mount power-take-off (PTO).

A mower deck can’t cut grass unless it is connected to the tractor engine. This is usually done in one of two ways, with some possible permutations.

Belt drives are the simplest and cheapest drive systems (Figure 1). With a vertical-shaft engine, it is sometimes possible to drive the deck directly from the engine shaft with a belt. Older designs used a mechanical belt release to disengage the drive but usually added a brake that automatically engaged when the belt was disengaged. Most current tractors use an electrically operated clutch/brake. When a switch on the tractor is moved, the clutch is engaged and the brake disengaged; when the switch is moved the other way, the clutch is disengaged and the brake engaged. One advantage of belt drives is that the belt will slip if the mower blade hits an obstacle, thus protecting the rest of the drive train.

Shaft drives are used on the larger, more expensive machines (Figure 2). Shaft drives require one or even two right-angle gear boxes, as well as two universal joints. They are more expensive but will handle higher loads. This makes them well suited to larger mower decks. Although they cannot slip like a belt, protective slippage under overload is still available since most decks have a belt or belts running from the shaft-driven gear box to the blade spindles.

The larger tractors also provide means of transferring power to implements other than mower decks. This includes rear implements such as rotary tillers and front implements such as snow blowers.

PTO shafts are the connection points for transferring the power from larger tractors to implements. PTO (power take-off) shafts are splined shafts sticking out of the rear of the tractor (compact utility tractors), splined recesses in the rear of the tractor (garden tractors) or splined shafts protruding from some point underneath the tractor. There are industry standards for the speed of these shafts. The recessed PTO on garden tractors turns at 2,000 rpm. It uses the recessed design to prevent connecting an implement designed for the 540 rpm PTO used on compact utility tractors. Midmount PTO shafts (Figure 3) may be specific to a given mower deck, but they should normally have a speed of 540 or 1,000 rpm. Implements connect to the PTO shafts using a drive shaft with two or three universal joints to provide flexibility.

Hydraulic outlets are available on some of the larger garden and compact tractors. These tractors can provide pressurized oil to operate hydraulic cylinders or motors. Hydraulic motors can power rotary tillers, sweepers and other implements. Hydraulic cylinders are used on front-end loaders, backhoes and other implements needing linear action.

Electric linear actuators are used on some mid-sized tractors, typically lawn or lawn and garden tractors. These actuators consist of an electric motor that turns a screw to provide linear motion. Electric linear actuators can do much the same job as hydraulic cylinders, without the need for a hydraulic system. The most common use on a lawn tractor or lawn and garden tractor is providing a power lift for the mower deck.

12/1/2004 11:07:22 PM
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