Power take-off
A power take-off or power takeoff (PTO) is a term for methods of taking power from an operating power source, such as a running engine, which can be used to provide power to attachments or separate machines.
Most commonly, it is a splined driveshaft on a tractor or truck designed so that a PTO shaft, a kind of drive shaft, can be easily connected and disconnected. The power take-off allows implements to draw energy from the engine.
Semi-permanently mounted power take-offs can also be found on industrial and marine engines. These applications typically use a drive shaft and bolted joint to transmit power to a secondary implement or accessory. In the case of a marine application, such shafts may be used to power fire pumps.
In aircraft applications, such an accessory drive may be used in conjunction with a constant speed drive. Jet aircraft may have permanently installed PTO shafts which are used to power engine accessories. In some cases, aircraft power take-off systems also provide for putting power into the engine during engine start. [1]
History
Experimental power take-offs were tried as early as 1878, and various homemade versions arose over the subsequent decades, but International Harvester Company (IHC) was first to install a PTO on a production tractor, with its model 8-16, introduced in 1918.[2] Edward A. Johnston, an IHC engineer, had been impressed by a homemade PTO that he saw in France about a decade before, improvised by a French farmer and mechanic surnamed Gougis.[2] He and his IHC colleagues incorporated the idea into the 8-16, and designed a family of implements to take advantage of the feature. In 1920, IHC offered this option on their 15-30 tractor, and it was the first PTO-equipped tractor to be submitted for a Nebraska tractor test. The first PTO standard was adopted by ASAE (the American Society of Agricultural Engineers) in April 1927. The PTO rotational speed was specified as 536 ± 10 rpm; the direction was clockwise. The speed was later changed to 540 rpm.[3] The PTO was a competitive advantage for IHC in the 1920s, and other companies eventually caught up with PTO implementation.
In 1945, Cockshutt Farm Equipment Ltd of Brantford, Ontario, Canada, introduced the Cockshutt Model 30 tractor with live power take-off (LPTO). LPTO allows control of the PTO rotation independently of the tractor motion. This was an advantage when the load driven by the PTO required the tractor motion to slow or stop running to allow the PTO driven equipment to catch up. In modern tractors, LPTO is often controlled by push-button or selector switch. This increases safety of operators who need to get close to the PTO shaft.[4]
Safety
The PTO and its associated shafts and universal joints are a common cause of incidents and injury in farming and industry. According to the National Safety Council, 6 percent of tractor related fatalities in 1997 in the USA involved the PTO. When a piece of clothing, which can be as small as a single thread, touches a spinning part it can be pulled around the part. The clothing and the person wearing it are pulled into the shaft often resulting in loss of limb or death. On April 13, 2009 former Major League Baseball star Mark Fidrych died as a result of a PTO related accident; "He appeared to have been working on the truck when his clothes became tangled in the truck's power takeoff shaft", District Attorney Joseph Early Jr. said in a statement.
Some implements do use plastic guards to try to keep a person from becoming entangled in a PTO shaft, but even with guards people need to exercise caution around PTO shafts when they are plugged into a tractor or truck. In some countries it is illegal to operate a PTO without the shaft guard correctly fastened.[5][6] In the UK, Health and Safety Executive guidance is contained in a leaflet.[7]
Technical standardization
Agricultural PTOs are standardized in dimensions and speed. The ISO standard for PTOs is ISO 500, which as of the 2004 edition was split into three parts:
- ISO 500-1 General specifications, safety requirements, dimensions for master shield and clearance zone
- ISO 500-2 Narrow-track tractors, dimensions for master shield and clearance zone)
- ISO 500-3 Main PTO dimensions and spline dimensions, location of PTO.
The original type calls for operation at 540 revolutions per minute (RPM). A shaft that rotates at 540 rpm has 6 splines on it, and a diameter of 1⅜". Two newer types, supporting higher power applications, operate at 1000 RPM and differ in shaft size. The larger shaft has 20 splines (1¾" diameter), while the smaller has 21 (1⅜" diameter). All three types rotate counterclockwise when viewed from the tractor. A 10 spline type was used with some early equipment such as the 1948 Land Rover, a six spline adapter was usually supplied. It is customary for agricultural machines manufacturers to provide the nominal PTO power specification, an indication of the available instantaneous power at the shaft.
Commercial vehicle PTOs
Truck transmissions have one or more locations which allow for a PTO to be mounted. The PTO must be purchased separately and care is required to match the physical interface of the transmission with a compatible PTO. PTO suppliers will usually require details of the make, model and even serial number of the transmission. Care is also needed to ensure that the physical space around the transmission allows for installation of the PTO. The PTO is engaged/disengaged using the main transmission clutch and a remote control mechanism which operates on the PTO itself. Typically an air valve is used to engage the PTO, but a mechanical linkage, electric or hydraulic mechanism are also options.
Units will be rated according to the continuous and intermittent torque that can be applied through them and different models will offer different "PTO shaft rotation to engine RPM" ratios.
In the majority of cases, the PTO will connect directly to a hydraulic pump. This allows for transmission of mechanical force through the hydraulic fluid system to any location around the vehicle where a hydraulic motor will convert it back into rotary or linear mechanical force. Typical applications include:
- Running a water pump on a fire engine or water truck
- Powering a blower system used to move dry materials such as cement
- Raising and lowering a dump truck bed
- Operating the mechanical arm on a bucket truck used by electrical maintenance personnel or Cable TV maintenance crews
- Operating a winch on a tow truck
- Operating the compactor on a garbage truck
- Operating a Hiab/Grapple truck
It is also possible but less common to connect something other than a hydraulic pump directly to the PTO.[8]
See also
References
- ^ NASA Technical Memorandum 101731; Monitoring Techniques for "X-29A Aircraft's High Speed Rotating Power Takeoff Shaft"; David F Voracek, Ames Research Center, Dryden Flight Research Facility, Edwards, California, December 1990
- ^ a b Pripps & Morland 1993, pp. 37–39.
- ^ http://www.asabe.org/imis/StaticContent/4/October_2004/p_31_last_word.pdf
- ^ cockshutt.com
- ^
Power-Take-Off (PTO) Safety (PDF), National Safety Council, revised May 2009, retrieved 2009-12-14
{{citation}}: Check date values in:|date=(help) - ^ Privette, Charles (2002-03-01), Farm Safety & Health - PTO Safety, Department of Agricultural and Biological Engineering, Clemson University, archived from the original ([dead link]) on March 28, 2005, retrieved 2007-04-19
- ^ hse.gov.uk, AS24(rev1)
- ^ Power Take-Off (PTO), TractorData.com, retrieved 2007-04-19
Bibliography
- Pripps, Robert N.; Morland, Andrew (photographer) (1993), Farmall Tractors: History of International McCormick-Deering Farmall Tractors, Farm Tractor Color History Series, Osceola, WI, USA: MBI, ISBN 978-0-87938-763-1.
External links
