Hybrid Drive Systems

The essentials of their operation, care and safety

The Low Emission Electric Power (LEEP) from Azure Dynamics are compact hybrid systems that basically run off a vehicle's transmission's power takeoff to generate and capture clean electric power to supply a range of auxiliary systems and export power applications. The system requires little power, about the equivalent of running a cab air conditioner.

Kidron's Ultra Temp hybrid refrigeration solution for refrigerated distribution incorporates the LEEP system to deliver efficient power refrigeration while cutting fuel consumption and emissions by 90 percent, says Kidron.

The power generated is stored in the refrigeration system. When the vehicle engine is shut down, the stored energy of Ultra Temp maintains the cargo area temperature. Overnight, the Ultra Temp system can be plugged into either single or three-phase power sources, eliminating cost, fuel, noise and emissions from diesel engines and generators.

For the most part, hybrid vehicles operate just like any traditional vehicles, say Azure Dynamics and Eaton officials. However, the operator will have to get used to the quieter operation.


Eaton suggests service and maintenance professionals should be aware of a few distinct service procedures which, when adhered to, will go a long way to ensuring clean, reliable service. In conjunction with its OEM partners, Eaton outlines five keys to PM success for operations that have hybrid electric trucks.

• Check transmission lube - The transmission lube fill and drain plugs are located on the right side of the transmission main case. Eaton recommends checking the lube level at every vehicle PM interval.

The lube should be level with the bottom of the fill-plug hole. If it is not level, only approved CD-50 synthetic lubricant should be used to refill.

• Grease the clutch release shaft bushing - Also with every PM interval, Eaton advises that a couple of pumps of grease be applied to the zerks of the upper cross shaft bushing. These are located at the bottom of the clutch housing at the inspection cover. Early built units have the zerk fitting on the top of the housing.

• Change the PEC air filter - The air filter on the power electronics carrier (battery box) needs to be checked - and changed if needed - a minimum of every four months, says Eaton. The PEC is an air cooler unit that uses an electric fan to pull air through the filter, then over the batteries and electronic components inside the housing. Plugged air filters will reduce hybrid assist and reduce fuel economy.

• Check hybrid liquid cooling level - Eaton hybrid electric systems also have a cooling system that is separate from the diesel engine's cooling system. Yet, the coolant type and flush interval should be the same as the diesel engine's system.

Eaton advises that service professionals should also visually check the coolant level on a regular basis. The coolant should be between "½" and "¾" on the sight glass of the reservoir. If it is not, approved coolant needs to be added.

• Visual inspections - High-voltage wiring and connections also should be visually checked at every PM interval. Eaton says proper training and equipment is needed to repair high-voltage cables showing signs of damage or incorrect routing, and only a certified OEM dealer should be used to make the repairs.


Eaton and Azure Dynamics both say they place a very high priority on making hybrid systems as safe as possible. All of the components were selected and specified to provide safety for not only the driver, but also for any technician who might be working on the vehicle, and even for motorists and others who might be involved in an accident with a hybrid vehicle, Eaton points out.

With Eaton hybrid electric systems, all high-voltage components are totally isolated from the vehicle chassis, and high-voltage cables were purposely placed outside of the vehicle's cab and enclosed to safeguard the operator and passengers. High-voltage cables and connectors are bright orange - a color that signals caution to trained technicians, as well as emergency response professionals and others who may respond to an accident.

In addition, regenerative braking and anti-lock braking systems (ABS) are linked via the SAE J1939 datalink so that that the hybrid system does not have any negative impact on the vehicle during an ABS event.

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