4x4 Hybrid Vehicle Engines - Engines Au JuicePosted in How To: Engine on January 1, 2005
By now you've heard the term "hybrid" bandied about ad nauseum. Well, the fact is that you will probably hear it a lot more over the next few months and years, because hybrids are infiltrating the four-wheel-drive world faster than you can say, "high-power battery module." To fully understand what a hybrid-powered vehicle can or can't do for you, you must have a basic understanding of what makes 'em tick-or, more appropriately, what makes 'em hum.
First off, it's important to note that hybrid systems are extremely complex, often integrating multiple electronic control units. To further muddy the waters, each manufacturer has approached the design and operation of its specific hybrid system differently. To explain the detailed workings of each hybrid from each manufacturer would take far more pages than we have, so we'll highlight the basic technology of a few specific vehicles that are currently available.
First, the term hybrid is a catchall phrase. The reality is that there are two basic types of hybrids, and on the street they've come to be known as full and mild. A full hybrid is defined as a vehicle that sports a gasoline or a diesel internal combustion engine (ICE) and at least one electric drive motor. Full hybrids are capable of operating in gas or electric modes as well as in a mode that combines the power of the ICE and electric motor. Some full hybrids also include other electric motors that drive a second pair of wheels or serve a specific duty unrelated to direct propulsion. Further, these electric motors can vary in their activation time as well as in how much power they produce. Why would a vehicle need two sources of power? The answer is that most full-hybrid vehicles that are designed for fuel efficiency rely on small and fuel-efficient ICEs that lack performance. When the power of the ICE and electric motor are combined, performance is enhanced, delivering the best of both worlds. Full hybrids can produce almost double the fuel economy of a comparable gasoline-powered vehicle and they significantly reduce tailpipe emissions because many are low-emission ICEs and they're shut off often. Mild hybrids, on the other hand, don't utilize an electric motor to assist the ICE. Instead, they increase fuel mileage mainly by shutting down the ICE when the vehicle is stopped or decelerating. The rest of the time the engine runs normally. This design generally produces fuel economy increases of 10 to 15 percent.
Both types of hybrids forced engineers to think outside their usual cubicles during research and development. For instance, when an ICE shuts down, there is no power to spin pulleys and belts. Since hybrids shut down the engine often, engineers had to find a way to run items like the power-steering pump, air-conditioning compressor and the water pump. With the exception of the alternator, which is replaced by the electric motors integral to a hybrid, these problems were solved creatively. Take steering, for example. Many manufacturers utilized an electric pump to move the power-steering fluid. Transmissions were another sticking point. Some manufacturers began using a constantly variable transmission (CVT), while others merely added an electric pump to a standard automatic transmission. A by-product of eliminating these beltdriven items is that there are fewer items for the engine to power, thus improving fuel consumption.
So, is there a hybrid-powered 4x4 in your future? Will the hum of an electric motor soon replace the grumble of an internal-combustion engine as you creep along your favorite trail? Will you soon be shopping the aftermarket for upgraded battery systems? Will you be drooling over electric motor hop-up kits? It's likely, and it may happen sooner than you think. Read on.
It's not often you'll see a car on the pages of Four Wheeler, but this car is important to this story. After all, the Toyota Prius is arguably the hybrid that started it all. Sure, the Honda Insight was introduced in the United States a year before the Prius appeared, but to this day, the Prius remains the most popular of all hybrids. The Prius is a full hybrid that sports a 1.5L four-cylinder gasoline engine that produces 76 hp and 82 lb-ft of torque. The engine is mated to a permanent-magnet electric drive motor that produces 67 hp and 295 lb-ft of torque. Nickel-metal hydride batteries comprise the battery system. The Prius also features a continuously variable transmission.
Driving the Prius is a trip. First off, there's no reason to use the key to unlock and start the vehicle because the optional smart entry and start system senses a key fob you carry on your person, unlocks the doors when you tug on the handle and allows you to start the car using a PlayStation-like power button. If the ICE is cold it will start, but if it's warm, it may stay off. This is why the dash features a ready light that illuminates when the car is ready to drive. Gear selection is done via a small joystick mounted on the dash. It's an electronically controlled by-wire shift system, so it just takes a tap of the finger to shift. Acceleration is smooth and seamless via a by-wire throttle. As you drive, you can monitor electric-gas power distribution through the Hybrid Synergy Drive system on the standard 7-inch touch-panel display monitor.
The Prius usually runs on the ICE during highway driving. The electric motor propels the car at low speeds. Occasionally, both may team up to produce maximum power. We were amazed at how seamless the system is. Our testing returned a 41-mpg average in rural driving. We have a friend who drives a Prius in L.A. traffic regularly and reports a 51-mpg average.
We recently had the opportunity to drive the new Lexus RX 400h luxury hybrid throughout the Kohala Coast on the big island of Hawaii. This vehicle is based on the Lexus RX 330, but make no mistake, they're two very different animals. The all-wheel-drive 400h was designed to integrate luxury, performance, improved fuel efficiency and reduced emissions. It definitely highlights state-of-the-art hybrid technology.
Interestingly, the 400h is equipped with one ICE and three motor/generators. Its ICE propulsion system is a 3.3L V-6 engine that produces 208 hp and 212 lb-ft of torque. This engine is mated to a motor/generator (called MG2) that drives the front wheels and offers regenerative braking. It has a maximum output of 167 hp and 247 lb-ft of torque. Instead of a familiar rear axle and driveshaft, the 400h has a rear-mounted motor/generator (called MGR) that can create 68 hp and 96 lb-ft of torque, but drives the rear axle through a speed reducer that allows it to provide up to 650 lb-ft of axle torque. This motor/generator drives the rear wheels and offers regenerative braking. Additionally, a third electric motor/generator (called MG1) generates power, acts as a starter motor for the engine and controls the transmission ratio. Electrical current for the motors comes from a nickel-metal hydride battery pack that has a nominal voltage of 288 volts and a power output of 45 kW.
Driving the 400h is, on the one hand, surprisingly uneventful because of the seamless nature of the powertrain. The power just happens. On the other hand, it's an event unto itself, due to the vehicle's impressive horsepower and torque, finely tuned handling, luxurious appointments and impressive fuel economy. Lexus says the 400h can scoot from zero to 60 mph in about 7.3 seconds and accelerate from 30 to 50 mph in a respectable 3.4 seconds, all the while getting an EPA-estimated 30 mpg in the city. That's quite impressive for a 4,365-pound SUV. Since Lexus asked us to please refrain from deviating from the drive route to trail-test the 400h, we had to settle for some dirt parking lots to test the AWD system. Once again, seamless is the word, as the computer electronically varied the front and rear torque distribution to compensate for traction conditions. It was weird to think that a 90-pound electric motor was the sum total of the actual rear drive system and that it could produce so much torque.
Dodge is working on a diesel hybrid-a technology being pursued by DaimlerChrysler-that's based on the Ram Heavy Duty chassis. It will be equipped with the company's 325hp/600lb-ft Cummins diesel engine. Dodge says the truck will generate a real-world fuel economy improvement of approximately 15 percent over a comparable non-hybrid diesel-powered Ram Heavy Duty. Like the Silverado Hybrid, the Dodge Ram HEV will offer electric generator capabilities. It will provide enough 110/220-volt AC electricity to power four average U.S. households.
The hybrids of today are technological marvels, but the concept of hybrids began back in the late 1890s. The most important of them debuted at the Paris World's Fair in 1900, and was the Lohner-Porsche, built by Dr. Ferdinand Porsche and Jacob Lohner. It used an internal combustion engine to spin a generator that provided power to electric motors located in the wheel hubs. It's said that on battery power alone, the car could travel nearly 40 miles before needing a charge. About 800 of them were said to have been built.
In 1910 the Commercial Company built a hybrid truck, which used a four-cylinder gas engine to power a generator, eliminating the need for the transmission and battery pack. Completely electric cars were on a roll during this period because gasoline cars were noisy, smelly and, most importantly, difficult to start. However, electric and hybrid vehicle sales hit the skids in 1913 following invention by Clyde Coleman and Charles Kettering of the electric self-starter for internal-combustion engines. This was first installed on a Cadillac in 1911. Following that, sales of electric cars dwindled, but Ford Model T sales sharply increased thanks to the new invention.
It wasn't until 1997 that the first production hybrid was released by an automotive manufacturer. It was the Toyota Prius and it first went on sale in Japan. Three years later the Prius was introduced in the United States.
Unlike an internal-combustion engine, an electric motor has the ability to reverse. This reversibility allows the same motor that runs on electricity to reverse and use torque to generate electricity that can be used to charge the hybrid system's batteries. This would be like rolling your truck backwards and having the engine generate gasoline. Wouldn't that be cool? Exactly when regenerative braking occurs depends on the specific hybrid system, but the computer in most full hybrids tells the electric motor to switch to the electric generator when you lift your foot from the accelerator. As you decelerate, the wheels turn the electric generator (formerly the electric motor). This does cause drag in the driveline, which you can feel, but you still must use standard friction brakes to decelerate completely.
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.
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.
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.
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?