Performance for all transit bus applications

Meritor has created what it says is the “next generation” single reduction drive axle, optimized for all length transit buses and all power trains

Meritor says its 79000 Series axle is the next-generation single reduction drive axle for transit bus vehicles. In an informative interview with BUSRide, John Wolf, senior sales manager – specialty products at Meritor, described this unique product’s inception and what it offers operators and agencies.

Please describe the 79000 Series rear-drive axle for transit buses.

The 79000 Series single reduction drive axle is Meritor’s latest in our line of industry leading axle products for transit buses.  It incorporates a patented and highly innovative gear design that significantly increases the life of the carrier when it is used in 35, 40, and especially 60-foot transit applications.   The robustness of the gearing and the carrier itself makes this product ideal for not just the drivetrains of today – diesel, CNG, and hybrid-electric, but the drivetrains of the future, as more emphasis is placed on all-electric vehicles.

How did this product come to be?

About 20 years ago, the transit bus industry started using hydraulic retarders built into automatic transmissions.  As a result, transit authorities were seeing maintenance benefits as the retarders extend the life of the buses’ brake pads and linings – thus reducing their maintenance cost.  As this benefit was recognized, transmission manufacturers, increased the retardation capabilities of their retarders to provide the end-users even longer brake life and reduced maintenance costs.

Unfortunately, when you use a hydraulic retarder, it puts the axle into a coast load situation.   Coast loads are very damaging to the carrier of the axle, as the gear teeth are not typically designed to handle the reversing loads that retarders generate.  So although operators were changing brake linings and pads less frequently; it was causing internal damage to the axle. This prompted upgrades to the axles a few times over the last 20 years.

While each upgrade added marginal improvement to axle carrier life, the retarders kept getting more powerful thereby generating higher coast condition torques into the axle, to a point that any improvements done to the axles were not sufficient to meet the life expectations of the transit industry. So Meritor did an exhaustive study spanning multiple years, several bus manufacturers and end users and several duty cycles to understand the effects of the entire power train system and their impact to the axle carrier life. This study bought into light the severe magnitude of negative impact the coast torque has on the axle carrier life, so Meritor developed a unique and comprehensive application approval process for transit bus applications that estimates the carrier life based on certain input parameters. While this approach was fairly successful in predicting the carrier life upfront and adding limitations on coast torque input to the axle, it was not meeting the transit industry expectation for carrier life or brake life.

So around 2011, Meritor started our ambitious journey to design, develop and launch our next generation single reduction drive axle for all transit bus applications (35 ft. to 60 ft. and combustion power trains to electric power trains).  Engineering parameters included:

1. Whatever was developed had to fit in the same packaging envelope of the current 71000 Series axle. Our current customers needed the ability to use this new axle without making other significant modifications to their vehicles.

2.The axle components had to meet APTA duty-cycle guidelines and life guidelines of five years or 300,000 miles before major repairs / replacement.

After about 6 years of persistent hard work and progressive thought process, we are now proud to launch the 79000 Series single reduction axle which meets or exceeds APTA duty-cycle guidelines. It can be used across the board from 35 ft. to 60 ft. transit buses and in combustion power trains to electric power trains.

What does it mean for end-users?

With the launch of 79000 series axle, the end users can now better harness the retardation / regeneration effects to increase brake pad life without having to replace carriers within APTA life guidelines, saving transit authorities significant amount of money / resources not just on the brake pad life but on reduced maintenance / down time.

And since we drove the design to fit in the same packaging space and the same suspension interfaces as the current 71000 Series axle, the new 79000 Series axle can easily be retrofitted into buses that have a 71000 Series axle already installed.   Another significant advantage for the end user is that the wheel-end equipment (brakes, hubs, rotors or drums, wheel bearings and seals) is all the same so the service parts / maintenance requirements for the axle are all the same as the current 71000 Series.

When can operators expect to see the 79000 Series Rear-Drive Axle by Meritor?

We intend to start converting current customers to the new axle in the first quarter of 2018. The transition will take some time as current customer contract requirements will drive the need to keep the 71000 Series axle in production for a limited time.  We will also need to support the 71000 Series product for another 12-plus years due to service life requirements of end-users.

Visit Booth #3413 at the American Public Transportation Association (APTA) EXPO to see the 79000 Series axle and discuss its benefits with a Meritor representative.