Global Hybrid Cooperation
[2]: 4 On September 30, 1993, the United States Department of Energy signed a contract with General Motors to develop and demonstrate hybrid electric powertrains for light duty vehicles.
[5] Negotiations had begun earlier in October, after engineering managers at both companies discovered they were independently working on similar dual-mode hybrid concepts while participating on the same conference panel.
[7] In 2006, an article published by Autoweek stated the three automakers planned to spend US$1 billion collectively to develop the front- and rear-wheel drive hybrid transmissions.
[8] The two-mode hybrid system was introduced to the light-duty vehicle market as a drivetrain option for the 2008 model year Chevrolet Tahoe and GMC Yukon,[9] with an observed improvement in fuel economy of 27–58% compared to a conventionally-powered equivalent.
[12] The dual-mode hybrid equipment added approximately 350 lb (160 kg), but this increase was offset completely by lighter seats, wheels, and 12-volt battery; aluminum engine and body components; and eliminating the starter motor.
[10] The GM products were followed by a hybrid Dodge Durango and related Chrysler Aspen for the 2009 model year in late 2008; the 5.7L HEMI V-8 engine on these was equipped with a stop-start system to improve fuel economy.
[17] Earlier, on March 1, 2007, BMW and DaimlerChrysler announced that they were entering a separate partnership to develop a mild hybrid module for rear wheel drive premium cars.
Daimler indicated that it wants to avoid investing in aftersales and service for a vehicle which will only be produced in small quantities, and will instead concentrate on modular hybrid building blocks with scalable lithium-ion batteries, based on the hybrid drive developed for the S-class and 7 Series sedans by the joint venture with BMW and auto supplier Continental AG.
[9] The dual-mode hybrid drive unit includes two AC motor-generators (MG-A and MG-B, each are three-phase permanent magnet machines with 82 kW (110 hp) peak output),[24] three interconnected planetary gear sets (P1, P2, and P3), four selectively engaging friction clutches (C1, C2, C3, and C4), and two oil pumps.
The lowest fixed gear ratio, which is in Mode I, synchronizes both motor-generators, allowing the vehicle to use these as motors to augment mechanical power for stronger acceleration, or as generators for regenerative braking.
[23]: col.11 ll.10–17 The second fixed gear ratio, also in Mode I, allows the motor-generators to freewheel which reduces losses at higher speeds and improves overall efficiency.
[23]: col.11 ll.45–49 Similarly, the third fixed gear ratio, which is in Mode II, synchronizes both motor-generators to allow electric motor boost or regenerative braking,[23]: col.12 ll.52–56 and the fourth fixed gear ratio, also in Mode II, allows both motor-generators to freewheel for improved efficiency, relying solely on mechanical power transmission to move the vehicle.
The two-mode hybrid drive system manufactured by Allison Transmission was first used in New Flyer transit buses which entered revenue service in 2004;[31] in testing at the National Renewable Energy Laboratory, measured fuel economy improved from 1.46–3.03 mpg‑US (161–78 l/100 km) for conventional diesel bus to 2.56–3.98 mpg‑US (91.9–59.1 l/100 km) with the hybrid drive unit in an equivalent bus over the same operating cycles, representing an improvement of 30.3 – 74.7%.
[33] Many transit operators since then have received buses with the Allison hybrid system, including: In 2020, Allison introduced its second generation two-mode hybrid drive units, branded eGen Flex, upgrading the existing H 40 EP and H 50 EP drive units with a disconnect clutch, allowing the engine to shut off completely, and adding a second line branded eGen Flex Max, which offers fully-electric propulsion with a lithium-titanate battery chemistry.
