Slipstream Drive

[dwightlooi]

Slipstream Drive

The Slipstream Drive is primary propulsion pack for the Chevrolet Slipstream diesel-electric hybrid. It combines the most efficient internal combustion engine with innovative energy recovery measures to achieve a 75 mpg fuel efficiency target without the inconvenience of a plug in. The power train is also designed from the outset to be roughly half the cost of the Voltec powertrain – through halving the number of electric motors and quartering the battery capacity.

The Slipstream drive is designed to be more refined than conventional diesel propulsion by eliminating idle operation of the diesel engine. The diesel engine is coupled directly to the 9-speed automatic transmission without a torque converter or clutch. It is technically in capable of idling in gear, initial acceleration from a standstill is always by pure electric power. The engine is always turning with the electric motor, just with or without its valves deactivated. At up to 50% throttle, the vehicle is operable in pure electric mode at up to 40 mph without activating the diesel engine.

The elements of the drive train is as follows:-

• 1.8L Inline-3 Naturally Aspirated Diesel engine (71 bhp)
• Exhaust Turbine Generator (13 kWe)
• Directly coupled 9-speed automatic Transverse FWD transmission
• 72 bhp (54 kWe) Synchronous Induction Motor
• No reliance on Rare Earth Metals
• No Plug-in Requirement / No exotic Fuels
• Lower cost / Lower Mass (vs Voltec)
• 75 mpg (city) / 70 mpg (Hwy)

Ecomax 1.8L Naturally Aspirated Diesel

The Ecomax Diesel engine shares the same bore, stroke & cylinder spacing dimensions with GM’s 2.5L 4-cylinder Gasoline Engines although the piston and block designs are completely different. This permits shared production lines and tooling. A 2-valve per cylinder SOHC head with roller cam followers is used to minimize valve train friction. Natural aspiration and the 3-cylinder configuration are selected to maximize compression ratio and cruise (low load) efficiency over a turbocharged diesel engine. The exhaust is routed through an exhaust gas turbine which – instead of driving a compressor to increase output of the engine – powers a small generator which recovers the otherwise wasted exhaust energy as electrical charge for the battery. This forms a second source of “free” energy recovery, enabling an increase in fuel efficiency over hybrids reliant purely on regenerative braking. The turbine uses a variable vane geometry housing to allow for efficient low load generation as well as unrestrictive high rpm gas flow.

• Layout: Inline-3 Cylinder with counter-rotating balance shaft
• Valvetrain: Chain Driven SOHC 6-valve w/ Cylinder Deactivation
• Aspiration: Naturally Aspirated w/ Exhaust Turbine Generator
• Construction: Aluminum Block & Heads
• Displacement: 1843 cc
• Bore x Stroke: 88 x 101 mm
• Compression Ratio: 23:1
• Fuel Supply: Direct Injected #2 Diesel Fuel
• Power Output: 71 bhp @ 4000 rpm
• Torque Output: 98 lb-ft @ 2000 rpm
• Generation Capacity: 13 kWe
• Maximum Engine Speed: 4200 rpm

Synchronous Induction Motor

The Slipstream Drive powertrain is equipped with a 54 kWe induction motor. An induction based design is selected over the more power dense and higher torque permanent magnet motor for three reasons. The first being its lower materials cost since it does not utilize expensive rare earth metals, and easier construction afforded by the elimination of magnetic forces during assembly. Secondly, because torque output – especially starting torque – is lower, it permits a transmission with lower torque capacity to be used for a given power output. Lastly, but perhaps most importantly, induction motors are more efficient at low output and loads because it is possible to vary core field strength.

• Type: 3-phase Induction Generator-Motor
• Generation Capacity: 54 kWe
• Nominal Efficiency: 92%
• Power Output: 72 bhp @ 4000 rpm
• Torque Output: 95 lb-ft @ 0~4000 rpm (Inverter Regulated)

Electramatic 9E40 9-speed Automatic Transmission

The 9E40 transmission shares the gear set and casing with the upcoming 9T40 9-speed automatic transmission. It is a transverse, FWD, design with axially located main shafts. Unlike a traditional automatic transmission, the Electramatic does not have a torque converter (or a clutch for that matter). The engine is coupled directly to the transmission input shaft and is incapable of idling. An electric motor is essential to the operation of the Electramatic transmission. At 400 rpm, cylinder deactivation is triggered to allow the engine to shutoff and freewheel without incurring pumping losses or compressional effort. Propulsion is purely electric from 0~500 rpm with the electric motor driving the vehicle and turning over the internal combustion engine. At input speeds above 500 rpm, the internal combustion engine may be started on demand by re-activating the cylinders and injecting fuel.

• Maximum Input Torque: 208 lb-ft
• Maximum Shift Speed: 4200 rpm
• Ratios: 9-forward, 1-reverse gears
• Ratio spread: 8.60:1

Battery

The Slipstream Drive powertrain uses a battery roughly ¼ the size and weight of the Volt’s battery pack but uses the same chemistry and cells. The battery is housed under the central tunnel between the seats. The same Lithium-Manganese chemistry as the Volt’s battery pack is used for its excellent thermal stability and low cost (from the absence of Cobalt), however the Slipstream battery is only 4.1 kWh in capacity instead of 16.5 kWh. This is roughly the same as the Prius Plug-in Hybrid (4.4 kWh) and roughly 3 times that of typical parallel hybrids. For longevity, only 80% the battery’s true capacity is normally accessed. Theoretically, the battery has sufficient capacity to power the Slipstream for up to 8~12 miles on pure electric power, although extended operation on pure electric power is rare.

• Chemistry: Lithium-Manganese Oxide
• True Capacity: 4.1 kWh
• Normally Utilized Capacity: 3.3 kWh
• Mass: 112lbs (51 kg)

Performance

The Slipstream Drive is able to provide lively, if not exhilarating performance from the relatively lightweight Chevrolet Slipstream. The 4-passenger vehicle, built on the Delta A platform shares much of the architecture with the Chevy Cruze and Volt, but utilizes an aluminum unibody and composite exterior panels to achieve a curb weight of 2,800 lbs. A covered rear wheel well, slightly narrower rear track, full underbody tray, low resistance tires and golf-ball like dimples on the exterior surface allow for a aerodynamic co-efficient of 0.22 – which is between the EV-1 and the 1^st Generation Honda Insight. Unlike most hybrids which have relatively small fuel tanks, the Slipstream has a relatively generous fuel capacity of 14.3 gallons – no less than most compact cars. The unrefueled range is a whopping 1000 miles; enough to drive from New York City to Jacksonville Florida on one tank of diesel fuel. This also means that a typical driver who drives 12,000 miles a year may see the gas station just once a month.

• Total Output: 143 bhp @ 4000 rpm
• Total Torque: 193 lb-ft @ 2000 rpm
• Electric Drive Output: 72 bhp @ 4000 rpm
• Electric Drive Torque: 95 lb-ft @ 0~4000 rpm
• 0-60 mph: 7.8 secs (2,800 lbs Chevrolet Slipstream)
• Unrefueled Range: 1000 miles (14.3 gallon diesel fuel tank)

Edited February 12, 2013 by dwightlooi