would like to know the benefit of a continuous variable valve timing in a four cylinder with a dual overhead camshaft. this is an automatic vehicle that I wish to purchase. A 2007 Dodge Caliber.
Answers from the Automotive Experts
Dear Tamara,
Continuous variable valve timing means that depending on the speed of the engine the valves act in different ways. An intake valve may stay open longer to allow more air, or an exhaust valve may stay open longer to allow the exhaust to escape. What this means for you? Better fuel efficiency. Four cylinder vehicles have their work cut out for them but are much more efficient and quicker with this type of valve system.
Lori
Here is a great article that details the advantage of this Chrysler technology improvement:
Dodge Caliber to be produced with new Continuously Variable Transmission
August
9, 2005 Chrysler has confirmed production of the Dodge Caliber, the
global concept car first shown at 75th Annual Geneva International
Motor Show in March, with a range of innovative engines and
transmissions designed to deliver world-class performance, fuel economy
and roadholding. The 2007 Dodge Caliber will be available in 2006 and
will be the first Chrysler Group vehicle to offer a continuously
variable transmission, the World Engine family of four-cylinder
gasoline engines, a new 2.0-liter diesel engine and all-wheel drive.
The all-new Dodge Caliber will use the newest generation of
continuously variable transmissions, CVT2, offering several advantages
compared with previous CVTs.
“Chrysler Group’s CVT2 has been calibrated to
delight customers with pleasing engine response, precise ratio control
and an AutoStick feature that allows for manual control and the
simulation of six stepped gears,” said Eric Ridenour, Executive Vice
President – Product Development, Chrysler Group. Through the use of
electronic controls, the Chrysler Group CVT2 provides a familiar feel
while delivering improved fuel economy. For example, drivers will
experience an appropriate rise in engine RPM during acceleration rather
than an instant rise to the maximum engine RPM. Chrysler Group’s CVT2
contributes a 6-8 percent improvement in fuel economy compared with a
traditional four-speed automatic transmission. Eliminating upshifts
allows the transmission to engage the torque converter clutch almost
immediately when accelerating and to keep it engaged throughout speed
changes. This eliminates torque converter slippage common in stepped
transmissions and results in more efficient operation, especially
during city driving. Customers will notice that CVT2 also improves
vehicle performance compared with a traditional automatic transmission.
Optimised gear ratios, especially in the 30-60 mph range, improve
passing manoeuvres and contribute to a responsive feel. Chrysler
Group’s CVT2 makes it possible to continuously vary the transmission
ratio, providing an infinite number of gear ratios. This allows the
engine to stay in its most efficient operating range. The transmission
uses two V pulleys and a steel push belt to vary the input speed to
output speed ratio instead of traditional discrete gear ratios
activated by clutches or bands. All-Wheel Drive
“In addition to being the first all-wheel-drive
C-segment vehicle from the Chrysler Group, Dodge Caliber will also use
the first electronically controlled all-wheel-drive system with
variable torque output ever offered on any Chrysler Group passenger
car,” said Ridenour. “An electronically controlled coupling manages
torque split from front to rear with no driver input needed for smooth
and automatic performance.” The system works on demand, driving only
the front wheels until power to the rear wheels is needed, which
optimizes fuel economy. All-wheel drive is also used between speeds of
25 and 65 mph to ensure precise handling during performance driving.
All-wheel drive will be available on vehicles sold in North America. World Engine
Fuel economy is a key factor in the
four-cylinder market. The Chrysler Group World Engine family is
targeted to improve fuel efficiency by five percent compared with the
engines they replace – rivalling the best four-cylinder engines in the
world. “The engines will be built through a joint venture and, simply
stated, the World Engine program allows us to build premium features
into our engines without a premium price,” said Ridenour. “We set and
met high standards in key customer attributes: fuel economy,
refinements, durability, quality and performance for our gasoline
engine offerings.” Chrysler Group brought its engineering expertise to
the World Engine program in the areas of cylinder port and intake
manifold design using advanced Computational Fluid Dynamics tools.
Chrysler Group engineers led the development work on dual Variable
Valve Timing (VVT), as well as an integrated 2:1 oil pump/balance shaft
assembly. Chrysler Group also refined the engines for exceptional
smoothness and sound quality, resulting in a pleasant engine feel and
sound for the customer. The 2007 Dodge Caliber will be available with
all three displacements in the World Engine family: 1.8-liter,
2.0-liter and 2.4-liter. Performance objectives are targeted to match
the best in the segment – 140, 150 and 170 hp, respectively. 2.0-liter Turbo Diesel
For Europe and other key diesel markets, the
all-new 2007 Dodge Caliber will also be available with an advanced
2.0-liter turbo diesel engine. “The advanced diesel engine is
technology readily available today that can dramatically reduce the
amount of crude oil consumed worldwide,” said Ridenour. “This is well
known in Europe where, in today’s competitive environment, customers
are looking for modern diesel engines with outstanding performance and
efficiency. Nearly 50 percent of all passenger vehicles sold in Europe
are powered by diesel engines. For the Chrysler Group, approximately 60
percent of vehicles sold in Europe are diesel powered.” The 2.0-liter
engine is a state-of-the-art, direct-injection turbo diesel with
high-pressure fuel injection, a variable geometry turbocharger and four
valves per cylinder. The injectors are electronically controlled,
allowing precise management of each combustion cycle with the optimum
quantity of fuel. This system can operate at pressures up to 2000 bar,
leading to finer atomization of fuel, high power and torque and optimal
fuel efficiency. The turbo diesel engine is expected to position the
Dodge Caliber sold in Europe among the best in its class for power,
torque and towing capacity. Maximum power is estimated at 134 hp DIN
(100 kW), and peak torque is estimated at 229 lb.-ft. (310 N•m).
http://www.gizmag.com/go/4394/