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Belt Alternator Starter (BAS) Hybrid

Written by PFM Staff

Think of the gasoline engine in the Malibu Hybrid as a rope-pull engine. The belt around the alternator starter does the rope-pulling. On the BAS-hybrid, the alternator, usually driven by the engine’s serpentine belt, is replaced by an electric motor that serves as both a starting motor and an electricity generator. It is this motor that uses the serpentine belt to spin the engine to start it and to spin the engine during acceleration. This system does not use a flywheel-mounted starter.

The BAS-hybrid consists of five major components:
• An electric motor / generator. AC current from the motor / generator is converted to DC current to charge the batteries, and vice versa.
• A coolant-cooled power electronics that controls the motor / generator and provides 12 volts to the vehicle’s conventional battery.
• A nickel metal hydride battery pack capable of 10 kW of power.
• A separate engine-control module with Hybrid Supervisory Software to manage both the gas engine and hybrid system.
• A different engine accessory drive with a dual tensioner assembly and aramid cord belt. This belt transfers torque to the gas engine from the electric motor for starting and acceleration, and torque from the engine to the motor to generate electricity.

A major benefit of the BAS-hybrid powertrain is that it fits in the same space as a conventional gas engine. The belt-alternator starter is very easy to incorporate into a standard vehicle, unlike either a mild or full hybrid. The BAS-hybrid was introduced on the 2007 Saturn Vue Green Line. No chassis changes were required to accommodate the hybrid system. The battery pack is housed in the spare tire well. The BAS-hybrid Vue is produced on the same assembly line as the non-hybrid Vue.

The belt assist is designed to kick in and work in all of the gears and at all speeds, not just taking off in first gear. In other words, depending on the amount of throttle, the belt-assist can be activated both from a stop and during a downshift while driving. Under full throttle in either situation, the belt assist seems to help slightly at lower rpm and not much at all at higher rpm.

The dash on the Malibu Hybrid displays a green ECO light when you are exceeding the EPA fuel economy estimates, sort of a low-key, green light, atta-boy. The amount of ASSIST from the battery pack or the amount of CHARGE back into the battery pack is displayed in an instrument on the dash.

The Malibu Hybrid has TWO air-conditioner modes: A/C and A/C Hybrid. In A/C mode, the A/C compressor works all the time, thus, the engine never shuts off. In A/C Hybrid mode, the engine shuts off, the A/C compressor is not used, and the car recycles the air inside the passenger compartment. If the inside air temp rises beyond a preset limit, the engine automatically starts again to run the A/C compressor. We ran the entire 1,100 mile evaluation with the Malibu Hybrid in A/C Hybrid mode.

The BAS hybrid uses a conventional 4T45-E automatic transaxle, however, it has been modified with a lower, more fuel-efficient axle ratio and an electric power steering pump to provide fluid pressure when stopped.

This 4-speed trans is outdated, if not an obsolete relic. In fact, the 6-speed is not available with the non-hybrid I-4 until the higher trim levels. Don’t be surprised if a 2.4L I-4 with the 6-speed trans actually gets BETTER fuel mileage in real admin roles than a 2.4L I-4 hybrid teamed with the 4-speed trans.


Published in Police Fleet Manager, Jan/Feb 2009

Rating : 8.0


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