Trucks
First of Four Parts
Decide on the Right Power Take-Off
Selecting the right power take-off requires meeting the speed, torque and horsepower requirements of the application. There are a few pitfalls you should avoid in order to ensure you get the most out of your system.
Mikel Janitz
Selecting the right power take-off (PTO) is the first step in creating a robust application solution. A power take-off is a gearbox attached to the transmission, which transfers power from the engine to a hydraulic pump or auxiliary components. There are a few particular details one needs to know and apply to make the most of a PTO investment. First, what is the vehicle you are up-fitting? What kind of work will you need to perform and how often is the job done (duty cycle)? Will the PTO fit the vehicle without frame or exhaust system modifications? Finally, will the PTO interface electrically, hydraulically and/or pneumatically with the vehicle? Selecting the right power take-off requires meeting the speed, torque and horsepower requirements of the application. Given that, there are a few pitfalls you should avoid in order to ensure you get the most out of your PTO.
This article is the first in a four-part series designed to help end users, OEMs, installers and up-fitters pick, set up, troubleshoot and maintain vocational vehicles with mobile power units and auxiliary equipment. They will cover the important, and sometimes forgotten, topics needed to get the most out of their PTO.
Engine
A refuse vehicle is a large investment. You weighed many the factors in choosing it: gas vs. diesel, automatic vs. manual transmission and chassis make, etc. You need to select a PTO that works best for the vehicle. One basic consideration is: Is the refuse truck gas or diesel powered? This can be a big deal. Of high importance are the engine 鈥渟ignature鈥� and its affect on the PTO鈥檚 noise and torsional vibration. Gas engines typically run smoother and can provide for a quieter operation. Diesels usually provide more low speed torque capability. There are numerous locations to mount a PTO. For example, front engine mount, rear mount and side mount. For this, let鈥檚 assume side mount is the best choice. Determine the location of the transmission鈥檚 PTO aperture so that the PTO is oriented correctly. There are wiring considerations as well as exhaust routing to negotiate. Keep wires away from hot spots, like exhaust pipes, to reduce the likelihood of shorts.
Transmission
Whether you choose an automatic or manual, it is important in PTO selection to determine the transmission make and model number as well as which PTO aperture is used. Most often, manual transmission PTOs use a 鈥渄og clutch鈥� set up. This is where the drive gear freely rotates until a ring gear manually mates the transmission rotation to the PTO gear set. There is also an option to incorporate an electrically actuated version for manual transmissions. These 鈥渉ot shifts鈥�, as they have been called, allow for manual transmissions to be rotating then mesh gears with minimal noise and wear through the use of an electromechanical solenoid. Automatic transmissions typically incorporate clutch shift PTOs. These allow for PTO gear engagement while the transmission gear is rotating. This makes it possible to engage and disengage the PTO output shaft without bringing the vehicle to a complete stop, which is required with a manual transmission unless the electronic shift. Gears in clutch and electric shift PTOs typically show less wear over time as compared to other designs. That may affect maintenance cost in the long run.
Size and Weight
While the physical size of the PTO is not the primary concern, one does have to pay attention to size and weight. Mounting space is at a premium and it is important that the PTO and hydraulic pump (if so equipped) fit within the available envelope space. The final location of the auxiliary equipment can be a driving factor when selecting a PTO. Many refuse vehicles use extended shafts between PTOs and pumps. This configuration allows for larger pumps where they could not fit before.
Duty Cycle
Now that we have a solid understanding of the vehicle, we can now begin planning for the work it performs (duty cycle). Is it a single function or are there multiple tasks to consider? Knowing the type of work is important, as this defines the duty cycle. PTO duty cycles are classified as intermittent or continuous. Think of it this way: if the PTO is to run for more than five minutes out of a 15-minute period, it is continuous duty. Intermittent duty cycles are those, which last for less than five minutes at a time a few times a day. It is fair to say refuse vehicles are continuous duty applications. The PTO鈥檚 torque and horsepower ratings are reduced for continuous duty applications. If this is miscalculated, the life of the PTO will be much less than expected.
Selecting a PTO is all about finding a way to get the required work done. Work in this example is force times distance. Speed is rotations per minute (RPM) and power is the rate of doing work, horsepower (HP). When selecting a PTO for a particular task it is important to consider the application. What will the PTO drive? How fast will it need to rotate? What is the torque requirement? These questions are functions of speed, torque and power. A PTO鈥檚 speed is often stated in terms of a percentage of engine speed. A PTO鈥檚 horsepower is directly proportional to the output shaft RPM. This means that the faster it turns the more horsepower is produced. However, it is also important to realize that a PTO鈥檚 torque rating is constant no matter how fast it is turning. Torque is the limiting factor. If torque loads are too large for too long, the PTO can be damaged.
Rotation and Installation
The direction of rotation can also be an important consideration. PTOs rotate either the same as the engine crankshaft rotation (abbreviated as CRNK), or opposite the crankshaft rotation (abbreviated as OPP). Typically a good rule of thumb is that PTOs mounted on automatic transmissions provide a CRNK rotation and those on manuals provide an OPP rotation. If in doubt, use a manufacturer鈥檚 Web site to select the PTO. It is easy to navigate and investigate options.
Correctly installing the PTO on the refuse truck is key to durability and performance. When selecting a PTO, it is important to know the vehicle and chassis. It is not recommended to make modifications to vehicle components without first consulting the manufacturer. This could void warranties and create possible safety concerns. Speak to application engineers to resolve any questions and they will help you select the right PTO and accessories for the job.
Replacement
The last issue to think about is what not to do when you are selecting a PTO. If you are replacing an existing PTO, the simple method is to replace it with the exact model. However, be careful. There is a reason you are replacing it. Make sure you follow the earlier steps to ensure you are getting the best PTO for the job. Make sure pump size and flow rates have not increased over time. Make sure torques have not increased. A reputable manufacturer can help you walk through these steps. Don鈥檛 make a purchase based on price alone. There are non-standard parts and replacement units that look the same, but do not offer the performance and overall level of service of a leading manufactures. Time is money and getting the job completed is vital. Don鈥檛 buy a PTO on price alone or because a particular model is readily available. Don鈥檛 sacrifice reliability, durability and performance for convenience. Select the right PTO for your refuse vehicle even if it takes a little extra time. You will save money in the long run and have piece of mind knowing you made a right decision.
Selecting a PTO, or any other mobile power system component requires study, planning and some expertise. There are typically many good selections, a few really good choices, and then there is the optimum selection. Be sure to contact your local distributor or call the manufacturer directly to help you through the selection process. Incorporating the above concepts and thinking through the entire application can specify the best PTO for your refuse needs.
Part two of this series will discuss critical features to consider during the installation phase.
Mikel Janitz is the Manager of Engineering for Muncie Power Products (Muncie, IN), a global leader in power take-offs and a worldwide organization dedicated to solving the vocational industry鈥檚 mobile power issues. Mikel graduated from Oklahoma State University with a BS and MS in Engineering and Engineering Management. He can be reached at [email protected] or visit .