Our Equinox, Joey:

Joey

The first year of Challenge X focused on research, modeling and simulation, and design of the teams' vehicle architectures, control systems, modes of operation, and vehicle technical specifications (VTS).  Akron's strength in controls and general background in automotive technology geared the team towards creating a power hybrid - with more emphasis on performance.

The team's competition Equinox, affectionately nicknamed Joey, has a Series-Parallel 2x2 hybrid drivetrain which uses B20 biodiesel and consists of the following major components:

• VW 1.9L TDI diesel engine
• DSG transmission (direct-shift gearbox)
• Ballard electric drive motor
• Johnson Controls battery pack & Maxwell ultracapacitors (the energy storage system, or ESS)
• Siemens generator

A particular feature of Joey's design lies with the control system which enables the vehicle to operate in 100% electric-only mode, 100% mechanical-only mode, or any percent combination of the two based upon vehicle speed, driver demand, and/or available electric power.

Modes of Operation

Electric-only Mode involves the rear wheels being driven by the Ballard electric drive motor which is powered through energy stored in the battery pack and the ultracapacitors.  The vehicle will operate in electric-only mode at initial start-up and at low speeds with low driver demand.  It is primarily used for in-city driving.

Series Mode will occur when there is not enough energy stored in the battery pack and ultracapacitors to power the Ballard drive motor or there is enough driver demand.  Energy will then be supplied by the engine through a generator.  The generator converts the mechanical energy created by the engine into electrical energy which can be used for the Ballard as well as the energy storage system.

Parallel and Split Mode involve the engine driving the front wheels and the drive motor driving the rear wheels working together to propel the vehicle.  The engine will operate based on not only the speed and driver demand but also on the available electric power.

Mechanical-only Mode will occur only when any part of the hybrid electric system fails.  This ensures that the vehicle will still operate, and Joey can make it home safely.

Vehicle Technical Specifications

Based on modeling and simulations performed by the team, the following Vehicle Technical Specifications (VTS) were established for Year 2 of the competition and are represented in the far right column, Akron YR2 VTS.  The Base Equinox values are the VTS for the stock 2005 Equinox, and the cX Target values were the VTS established by the Challenge X competition as targets for the teams.

Description	Base Equinox	cX Target	Akron YR2 VTS
IVM - 60 mph	8.9 s	≤9.0 s	≤7.5 s
50 - 70 mph	6.8 s	≤6.8 s	≤4.5 s
Vehicle Mass	3825 lb	≤4400 lb	≤4500 lb
MPG Combined EPA	23.3 mpgge	≥32.0 mpgge	≥35.6 mpgge
Highway Range	320 mi	≥200 mi	≥280 mi
Passenger Capacity	5	5	5
Emissions Cert. Level	Tier 2, Bin 5	Tier 2, Bin 5	Tier 2, Bin 5
Towing Capacity	3500 lb	2500 lb	2500 lb
Starting Time	2.0 s	<5.0 s	<5.0 s
Akron Specific VTS
Description	YR2
Noise Level	The vehicle noise level within the cabin will be lower than 85 dB
Battery Life	10,000 cycles/ 100,000 miles
Peak Power (Charge Depleting)	235 HP (175 kW) combined for 10 seconds

Joey's Architecture explained by team leader Nathan Picot:

Series-Parallel Hybrid Electric Architecture Overview 

            Before the series-parallel architecture can be described, it is necessary to look at series hybrids and parallel hybrids individually.  Both types of conventional hybrids have there advantages and disadvantages; the series-parallel hybrid takes the best of both and combines them.  The downside of the series-parallel hybrid is its increased complexity.

            In a parallel hybrid the engine size is decreased and then offset by one or more electric motors.  A conventional transmission is used, and for the most part the engine drives the wheels like in a conventional vehicle.  The engine is sized to meet worst case steady state situation, which is typically climbing a long hill when the vehicle is loaded to capacity.  The electrical system is then sized to meet the performance goals of the vehicle.  During heavy acceleration the motor assists the engine.  It is the combined power of the engine and motor that allow a small and efficient 4 cylinder to perform like a 6 cylinder engine.  The consumer could think of this as a sort of electrical supercharging where the motor provides “boost”.  Engine shut off, regenerative braking, and a good charging strategy all help fuel economy, but the smaller engine and lighter weight electronics make parallel hybrids the choice of most automobile manufacturers.

            In a series hybrid the transmission is completely electrical.  The engine is used to power a generator and motors are used to drive the wheels.  The motors will typically use a single gear ratio, so there is no conventional transmission.  Because the engine is not connected to the wheels mechanically, the engineer has complete control over the engine operating point.  This freedom gives a series architecture better fuel economy than a parallel architecture, as long as the weight is the same.  Weight is the problem with a series architecture.  The engine and battery can be sized in a similar fashion to a parallel hybrid, but there are now at least two electric machines.  The generator has to have the same power rating as the engine, and the motor that drives the wheels has to be large enough to accelerate the vehicle by itself.  In an automobile, the increased weight more than offsets the increases in efficiency, and fuel economy is generally worse than a parallel.  However, all diesel trains are series hybrids because the increase in weight is insignificant compared to the weight of the train.  Some heavy machinery are also series hybrids.

            The series-parallel architecture captures the best of both worlds.  The engine can send power through both a generator and a conventional transmission.  There is also a motor that can drive the wheels directly.  The transmission can be put into neutral to allow for series operation.  When not in neutral, the engine can be assisted in acceleration by both the “generator” and the “motor”.  An electric machine can be both a generator and a motor; the only limitation is the complexity of the controller.  The engine is again downsized compared to a conventional vehicle.  Like a parallel hybrid, the engine and the motors are sized together to maintain or improve performance.  Because the machines are sized to for a parallel hybrid, the performance when operating in series is severely limited.  However, the efficiency when in series mode is still higher than when in parallel mode without the added weight of a pure series system.  Series mode can be used for low power demands and is ideal for start and stop traffic and low-speed cruising.  Parallel mode can then be used for higher power demands like acceleration and highway cruising.

            The series-parallel architecture does have some downsides.  The mechanical transmission must be able to move in and out of gear smoothly when transitioning modes.  It also requires more processing power to handle the complex control strategy.  It also requires two motors, while a parallel hybrid can use just one motor.  Special care has to be taken when changing modes to ensure the transition is smooth.  A parallel hybrid drives like a conventional car and a series hybrid drives like an electric car; a series-parallel has to do both without the driver finding either mode objectionable.

            A series-parallel hybrid takes the offers the efficiency of a series hybrid and the performance of a parallel hybrid at the cost of engineering complexity.  As the engineering costs only occur during development, the series-parallel hybrid is a viable alternative to conventional hybrids.  With more consumers looking at hybrids and growing to accept them, innovative alternatives like the series-parallel hybrid could come to one day dominate the market.