It is pretty fair to say that the question "That thing gotta HEMI?" is one
that's not asked all that often today with the underlying air of envy.
But Chrysler engineers haven't sat on their hands when it comes to the powerful engine. They've made significant improvements in the 5.7-liter V8, particularly in anticipation of the forthcoming 2009 Dodge Ram 1500 pickup. Yet it isn't the Ram alone that the HEMI is used in. And while the importance of the Ram for the company cannot be underestimated, the use of the improved engine in the 2009 Chrysler Aspen HEMI Hybrid and the 2009 Dodge Durango HEMI Hybrid-yes, the engine's name is part of the products' names-is probably more clever by half.
The improved HEMI has variable valve timing (VVT). As it closes the air intake valve later, it reduces the engine's pumping work. Also, it increases the expansion of the combustion process so that rather than generating heat that goes out the exhaust port, more of the energy is used to do work, as in turning the crankshaft. What's more, the operating range of the company's cylinder-deactivation system-called "Multi-displacement System" (MDS)-has been increased, as well. Which means that the engine operates in four-cylinder mode rather than eight for a longer period of time. The higher compression ratio leads to an improve-ment in fuel economy on the order of 4%.
While many people nowadays, particularly those who might ask the aforementioned HEMI question with a tone of derision, have probably glommed on to the second word beginning with an "H" in the name of the two new vehicles, "Hybrid," the HEMI is potentially the proverbial competitive edge in the full-size SUV market.
Glenn Denomme is chief engineer, Hybrid Powertrain Programs for Chrysler. He doesn't work in Auburn Hills with numerous other Chrysler engineers. He works in Troy, Michigan. At the Hybrid Development Center. He points out, for example, that not too far away from his desk there is another engineer. No surprise there. Except for the fact that the other engineer's paycheck isn't from "Chrysler LLC," but "General Motors Corporation." That's because the Hybrid Development Center is the place where the two-mode hybrid system was developed. This is the hybrid system that is the result of efforts by Chrysler, GM, Mercedes, and BMW.
Essentially, the two-mode hybrid is to be contrasted with the widely available (think: Toyota) single-mode system. The big difference is that there is one mode that operates at low speed (this is the "input split mode"). Launching the vehicle, for example. When the vehicle is operating at a low speed, it can be run electrically, mechanically, or a mix of both. Then there is the compound split mode, which operates at higher speeds. These are not exactly binary (i.e., low/high), as the transmission is continuously variable, but instead of belts and pulleys, it uses the two electric motors that are attached to the transmission shaft. A controller determines which mode the transmission should be in. In order to achieve the necessary torque, there are gears within the assembly that multiply the torque delivered in the same way that a conventional step-gear (i.e., "automatic") operates.
The packaging of the two-mode is similar to that of a conventional automatic transmission. One interesting point that Denomme makes is that while the input side is specific to being attached to a HEMI and the output side is specific to attachment to the torque converter being used (the hybrid versions of the Aspen and the Durango are standard 4 x 4s), the part in the middle-that which contains the two electric motors, gears and other components-is precisely the same as that in the transmissions being used in the Chevy Tahoe and GMC Yukon*. All of these units, designated the "AHST," for "Advanced Hybrid System Truck," are built at the General Motors Baltimore Transmission Plant. According to Denomme, this is the case for a number of reasons, not the least of which is that given that these Chrysler and GM trucks are the first to be equipped with the two-mode system, so by combining the requirements, there is a boost in production versus having individual operations. After all, there needs to be a way to achieve some economies of scale for a technology that isn't exactly well-known by (or understood by) the buying public. (In the cases of Mercedes and BMW, which are going to be initially installing two-modes in cars rather than trucks (which leads to a slight modification of the architecture, as whereas the truck transmission is comparatively barrel-shaped, the car transmission is more conical), Mercedes will be running the transmission manufacturing for both companies.) And about the fuel efficiency: whereas, say, your typical 4 x 4 Aspen's numbers are 13/18 mpg, the estimated fuel economy for the hybrid is 19 city/20 highway.
What about scaling the two-mode system? Yes, it is scalable. Denomme laughs and says that they're certainly unlikely to scale it up (though he acknowledges that GM has two-modes for use in buses). But it could be reduced in size for car and crossover applications. Denomme points out, however, that there is the issue of cost. Whereas Chrysler, like all major vehicle manufacturers, has the capability to manufacture conventional transmissions, he notes, "It is hard to go out there"-to the market-"and buy some of the stuff that we're dealing with." Like high-current, high-power electronic devices. Or even the AC synchronous electric motors used in the two-mode system: "You have to set up a line with a supplier for that. And every time you have a different shape and size, you have to set up another line for the windings." In other words, the automotive supply base is currently not tooled up to produce hybrid powertrains. And the suppliers need to be convinced that if they do tool up, there will be sufficient volumes involved to provide them with a return on their not-insignificant investment.
Which brings us back to the 345-hp @ 5,300 rpm, 380 lb-ft of torque @ 4,200 rpm HEMI. Why did they use that engine rather than, say, the company's 4.7-liter V8 or even the 3.7-liter Magnum V6? Because, says Bob Feldmaier, chief engineer, Aspen/Durango/Dakota, "We didn't want to give anything up." Both vehicles have high trim levels standard. And the HEMI allows the vehicle to pass and even tow (up to 6,000 lb.). In other words, they wanted to produce a hybrid that is about efficiency, but not an amenity or operational deficiency.
One more thing. Remember the mention of the HEMI in the Ram? Well, the all-new 2009 Ram will be offered not only with the 5.7-liter HEMI, but also with the HEMI Hybrid.
*The GM Chevy Tahoe and GMC Yukon use the same-as in the exact same, right to the part numbers-two-mode transmission. The GM powertrain mates the transmission to the 6-liter Vortec V8 that produces 332 hp and 367 lb-ft of torque.