Power-take-off designs becoming more sophisticated

There are times when getting freight from point A to point B is not a truck's only, or maybe even its primary, purpose. Utility trucks, dumps, tow trucks, tankers, and refuse vehicles, for example, all have other work to do. And this work involves running accessories ranging from winches and cranes to pumps.

Here's where power take-off (PTO) units come into play. These devices, which can be considered a small collection of gears, play an integral role in providing the power necessary to run auxiliary equipment. Attached directly to the transmission, PTOs make it possible to transfer power from the vehicle's engine and transmission to an accessory.

According to the Chelsea Auxiliary Power Group of Dana Corp.'s Drivetrain Service Div., in addition to spec'ing a PTO that's right for the transmission, the requirement of the job must be taken into consideration.

For example, for low-speed, low-torque product pumps in applications such as fuel and propane hauling, Chelsea will add three internal gear ratios to its six-bolt 442 and eight-bolt 489 series in the near future. The A ratio will be an ultraslow speed; the C ratio, moderately slow; and the H ratio, a "middle of the road" speed.

Chelsea has developed a new thrust bearing that enables the A and C versions to better handle the high loads of low-speed PTOs. All three ratios will deliver 250 lb.-ft. of torque and about 48 hp. at 1,000 rpm on an intermittent service basis.

About half of all PTOs use air shift mechanisms, with lines that are relatively easy to install and troubleshoot. And in most cases, air supply isnot an issue.

But the primary downside of using this method to engage the PTO, says Chelsea, is that if an air line turns more than 90 deg., kinks are likely to form and block the line. Electronic shift mechanisms can help alleviate this problem, making it possible to snake wires "all over the place" to avoid crossmembers or frame rails without affecting performance. PTO makers expect use of this technology to become more common within the next five years.

Another challenge when installing PTOs is finding enough clearance under the truck to bolt them on. To address this issue, Chelsea recently developed a 24-position mounting flange that rotates 360 deg. With its two-piece construction, the flange can be spun without disturbing the PTO's output shaft seal, thus nearly eliminating the installation-related lip or gasket damage that could lead to oil leaks. The new flange is available as an option on Chelsea's 442, 447, and 489 series PTOs.

Muncie Power Products recently introduced a number of six-bolt PTOs that will work specifically with Allison Transmission's new 1000-2000 Series transmissions. The CS series has been modified to fit the new Allison transmissions, and will offer torque capacities to 300 lb.-ft. In addition, the GA series, which is based on the CS but in a more compact format, is available for situations where the PTO must be mounted in a particularly tight space. All PTO output speeds and shaft configurations will be available. TG series PTOs will also be offered for the Allison 1000-2000 transmissions.

Muncie points out that the PTO drive gears for these models are driven by a torque converter rather than an input shaft. The significance of the torque converter is that PTO speeds are dependent on the speed of the vehicle when in drive or reverse and operating at low vehicle speeds. In neutral and park, a torque converter lockup makes the PTO speed dependent on engine speed.

Muncie has also developed variations of its TG, CS and SH PTOs for Eaton Corp.'s Lightning Series transmissions. According to Muncie, these changes were necessary because the new transmissions are equipped with two six-bolt PTO provisions that have been rotated downward to avoid interference with suspension or exhaust components. They use an active transmission gear instead of a dedicated PTO drive gear, which requires a new helical PTO gear. Proper PTO gear alignment with the active transmission gear is achieved through dowel pin alignment on the PTO mounting flange.

The TG has wide range options for standard mechanical PTOs, with torque capacities up to 270 lb.-ft. The CS series, which has torque ratings up to 300 lb.-ft., offers clutch-shift capabilities that make engagement and use easier for remote-control applications such as liquid transport tankers. For very heavy-duty applications, SH PTOs provide maximum power output with torque capacities up to 400 lb.-ft.

Del Hydraulics makes a series of axial flow high-pressure piston pumps combined with universal fitting PTOs. The Del PTO/pumps fit on either the right, left, or bottom of various transmissions, including Allison, Clark, Eaton Fuller, Isuzu, Mack, Spicer, and ZF models.