Chevrolet Silverado Hybrid
This vehicle employs a compact electric motor positioned between the engine and transmission. Similar in operation to a full hybrid, this motor acts as the ICE's starter and it offers regenerative braking to charge the batteries. Unlike a full hybrid, the motor does not assist the ICE during acceleration; hence, it's what is referred to as a mild hybrid.
Quite simply, when in two-wheel drive, the Silverado Hybrid's 5.3L V-8 engine powers the truck at all times except when the vehicle's speed drops below approximately 13 mph. Under this speed, the engine shuts off to conserve fuel. At a stoplight, the gasoline engine is off but the accessories continue to work on the batteries' stored electrical power. When the light turns green and the driver lifts his foot from the brake pedal, the ICE starts immediately. Fuel economy is also enhanced by quickly shutting off fuel any time the truck is coasting or braking. It's important to note that the engine-off feature of the Silverado Hybrid is canceled when in four-wheel drive.
Engineers were able to integrate the 14 kW electric induction motor in a patented, space-efficient manner between the engine and transmission. The electric motor and the transmission's torque converter are mounted in a concentric arrangement that doesn't require any additional powertrain length. In the 4L60-E four-speed automatic transmission, an auxiliary electric-transmission oil pump helps enable the automatic start feature by assuring sufficient line pressure to allow torque transfer immediately upon driver command, when the engine is started.
For those times when the engine is shut down, the truck uses a uniquely designed, engine-independent electro-hydraulic power steering (EHPS) system to provide variable-effort power steering. This system is powered by the truck's 42-volt battery pack and contains an electric motor, a hydraulic pump and an electronic control module. The EHPS also provides power assist for the brake system's HydroBoost hydraulic brake booster.
Another important piece of the system is the starter/generator control module (SGCM). This module controls the flow of torque/energy into and out of the starter generator. Overall, the SGCM controls the starter generator's engine cranking, torque control, speed control and torque smoothing/active damping functions. It also controls the accessory power module, which generates four types of power for the starter function.
Driving the Silverado isn't much different than driving a regular pickup. The only noticeable oddity is when the engine shuts off, an event which is punctuated by the tachometer and the oil-pressure gauge suddenly registering zero. The Silverado can also perform the duties of a generator, and it offers two bed-mounted 120-volt electrical outlets.
Who Gets the Best Mileage?
As a rule, you'll get the highest mpg when driving a hybrid in the city. The reason for this is that the stop-and-go traffic inherent to city driving allows the internal-combustion engine to shut down often, thus fuel is not being burnt and the electric motor(s) can aid in the repeated acceleration cycles that are part of that kind of driving. On the highway, the ICE must run constantly to provide propulsion. This is why mpg ratings for hybrids tend to be different from what we're used to, showing a higher number in the city and a lower number on the highway.
Super Batteries
Batteries are one of the key components in a hybrid vehicle. You'll probably recognize two of the major manufacturers of batteries for hybrids-Sanyo and Panasonic. In battery circles, engineers discuss things like overall power, energy density, electrode materials, cell-connection structure, internal resistance and cell-stack construction. One of the major battles related to batteries in vehicles is that they have a normal operating temperature, which is not often achieved without some sort of help. Thus, some hybrid cars feature heaters and cooling systems to keep the batteries in their comfort zones. Most batteries are found under the rear seats, as this drawing of the Lexus 400h shows. The bottom line is that the ongoing goal of battery manufacturers is to design batteries that are lightweight, powerful and small.
The End of Custom Rigs?
Can you slap some larger rubber on your hybrid? We asked General Motors tech gurus what would happen if we replaced the stock rubber on the Silverado Hybrid with a set of larger tires. After all, this is a very simple, common and effective upgrade for enhancing the Silverado's four-wheeling capabilities. Their response was that it's not recommended because there are so many parameters that this vehicle's computers are examining. All of which raises these important questions: Will hybrids be the death knell for vehicle mods, or will the aftermarket solve issues that confront those who wish to modify their hybrid rigs? Will the common person who has tools and knows how to use them embrace hybrids or exhibit signs of hybrid phobia?