Although it wasn’t first to the market with a hybrid SUV, General Motors will be offering its Saturn VUE compact SUV in a trim level known as the “Green Line” later this year. What’s interesting about this approach is that compared with the hybrids available in other SUVs—the Ford Escape and the Toyota Highlander are two that are being targeted by the Saturn, particularly the former—is that it is far simpler. In fact, Larry Nitz, executive director, GM Global Hybrid Powertrain uses the words “simple hybrid” when talking about the electronically supplemented 2.4-liter four-cylinder Ecotec engine, modified 4T45E automatic transmission, and aero-improved body that are used by the Green Line VUE.
While there will be some people who debate whether or not what they’ve engineered is a “hybrid” in the sense of the competitive products, know that: 1. Compared with a base 2.2-liter VUE with a four-speed automatic, the Green Line VUE is not only more powerful (it is rated at 170 hp vs. 143 hp for the 2.2-liter engine), but provides a combined EPA city/highway of 29 miles per gallon, which is 20% better than the standard vehicle. 2. While pricing for the product has yet to be released, according to Lisa Hutchinson, director, Saturn Brand and Product Development, the price differential for the hybrid option will be on the order of $2,000 or less (for a total sticker on the order of $23,000).
Which is to say that if the purpose of a hybrid is to improve fuel efficiency, then this is doing what it is supposed to do. And at a price that might make consumers of competitive product somewhat green with envy.
The engine is fitted with a 5-kW electric motor/generator with three-phase cables where the alternator would be; it replaces both the starter and the alternator; it offers 115 lb-ft of torque. There is an engine accessory drive and a dual-tensioner assembly and Aramid-cord belt that allows the transfer of motoring or generator torque (“You don’t want to slip the belt under any conditions,” Nitz says, because the engine is being motored by the electric motor during the start of acceleration as well as at low speeds during deceleration). The engine control module is loaded with software that permits control of both the gasoline engine as well as the hybrid. There is a nickel-metal-hydride (NiMH) battery pack that can handle some 10-kW of peak power. The power electronics—including an inverter and a DC/DC converter—provides 12-v accessory power. The modified Hydra-Matic transmission adds an auxiliary oil pump and hybrid controls; the oil pump comes into play when the engine is shut off (say at a stop light) so there is oil in the forward clutch so the vehicle will start immediately when the accelerator is depressed. (There is also hill start assist: this is in the vehicle’s ABS system. Given that the engine can be shut off when at a stop on a hill, it would be possible for a vehicle to roll down, but the hill start assist keeps the vehicle in place until the engine starts.)
In addition to those modifications to the powertrain, the vehicle is lowered by 25 mm and the roof rails are removed. With these changes, there is an improvement in the coefficient of drag, to 0.36 from 0.38 for the standard model. Also, there is a modified HVAC system that permits operation even when the engine is shut off. There is an “Eco” light that illuminates in the gauge cluster when the vehicle is outperforming the EPA rating. The tachometer has a point labeled “Auto Stop”; when the needle is there it indicates that the vehicle is “on” even though the engine may be off. In addition, there is a hybrid charge dial that indicates the charging of the battery system. From outside or in, the Green Line package is discrete.
The ways that there are fuel savings for the VUE are:
- The engine is off when the vehicle is stopped
- There is early fuel cut-off during deceleration (there is torque smoothing so that it is transparent)
- There is regenerative braking
- There is electric power assist at start and decel
- Regenerative braking
- Charging of the hybrid battery at optimal times/conditions.
This leads to an EPA city rating of 27 mpg, EPA highway of 32 mpg. In other words, the system works.—GSV