Brand: A primer on continuously variable transmissions

  • Article by: PAUL BRAND
  • Updated: November 4, 2013 - 1:26 PM

Q: I read your column with interest each Saturday in a local newspaper and was wondering if you would be willing to comment on the pros and cons of continuously variable transmissions (CVT) and multi-geared transmissions.

A: Absolutely! So that everyone is on the same page, let’s identify what a CVT transmission is. It’s important to recognize that the purpose of any automotive transmission is twofold — transmit engine power to the drive wheels and to optimize vehicle performance at any and all speeds by keeping the engine in its most efficient RPM range as much as possible.

Multi-gear transmissions have historically been the transmission of choice for this purpose. Either manually — the driver selects each gear with a lever — or automatically selecting individual gear ratios based on road speed and load, these transmissions do a reasonably efficient job of keeping the engine in its “power band” at varying road speeds.

But, of course, road speed is infinitely variable and these transmissions have only a fixed number of gear ratios. Remember the original GM Dynaflow and Powerglide transmissions? They had only two forward gears, coupled to a torque converter to multiply engine torque. Today’s electronically controlled automatic transmissions feature up to eight forward speeds to help optimize efficiency and performance.

CVTs feature a drive belt riding between variable pulleys. The pulleys change diameter in proportion to speed and load by varying the distance between the inner and outer tapered “sheaves.” When starting from a stop or under heavy load, the engine-driven pulley is smaller and the driveline pulley is proportionally larger so that engine RPM is higher, providing more torque to the drive pulley. As vehicle speed rises, the engine pulley gets larger in diameter while the driveline pulley gets proportionally smaller, meaning the engine is turning lower RPM as it drives the vehicle at a higher speed.

The fundamental advantage of CVTs is their ability to keep the engine in a very narrow, highly efficient RPM range to maximize performance, efficiency and fuel mileage.

Snowmobiles, ATVs and some motorcycles have had CVTs for decades and they have been used in cars since at least the early 1960s. In fact, the very first vehicle I ever drove — in 1960 at age 11 on a long, looping private driveway — was a very small Dutch-built DAF with a belt-driven, variable-ratio CVT.

While engineers and carmakers have known the advantages of CVTs for decades, it wasn’t until relatively recently that technology has provided a drive belt for them that could handle the much higher horsepower and torque of today’s engines. The belts are no longer fabric and rubber; they are steel and provide the strength and durability necessary for modern automobiles.

Driving a CVT-equipped vehicle is a somewhat peculiar experience. Under acceleration, engine speed rapidly climbs into its optimum RPM range, which tends to create a sense of slippage although none is occurring, and the vehicle speed “catches up” to engine speed. When slowing, engine speed falls until re-accelerating when RPM jumps back up and vehicle speed starts “catching up” again. The engine, under load, is always operating in its most efficient RPM range, maximizing performance and fuel economy.

  • get related content delivered to your inbox

  • manage my email subscriptions

ADVERTISEMENT

Toronto - D. Hutchison 12:05 PM
NY Yankees - M. Tanaka
Washington - S. Strasburg 12:10 PM
Miami - N. Eovaldi
NY Mets - J. deGrom 12:35 PM
Atlanta - E. Santana
Boston - J. Kelly 12:35 PM
Baltimore - M. Gonzalez
Milwaukee - W. Peralta 12:35 PM
Pittsburgh - V. Worley
Chicago WSox - J. Danks 12:40 PM
Tampa Bay - N. Karns
Cleveland - C. Kluber 1:10 PM
Minnesota - A. Swarzak
Detroit - R. Porcello 1:10 PM
Kansas City - J. Guthrie
Seattle - H. Iwakuma 1:10 PM
Houston - C. McHugh
Los Angeles - J. Wright 1:20 PM
Chicago Cubs - J. Turner
Texas - N. Tepesch 2:35 PM
LA Angels - C. Rasmus
Philadelphia - A. Burnett 3:05 PM
Oakland - S. Kazmir
San Francisco - R. Vogelsong 3:10 PM
San Diego - I. Kennedy
Arizona - W. Miley 3:10 PM
Colorado - C. Bergman
Cincinnati - A. Simon 7:05 PM
St. Louis - L. Lynn
San Diego 12:00 PM
Buffalo
Dallas 12:00 PM
St. Louis
Washington 12:00 PM
Philadelphia
Houston 12:00 PM
NY Giants
Minnesota 12:00 PM
New Orleans
Tennessee 12:00 PM
Cincinnati
Baltimore 12:00 PM
Cleveland
Green Bay 12:00 PM
Detroit
Indianapolis 12:00 PM
Jacksonville
Oakland 12:00 PM
New England
San Francisco 3:05 PM
Arizona
Denver 3:25 PM
Seattle
Kansas City 3:25 PM
Miami
Pittsburgh 7:30 PM
Carolina
Chicago 9/22/14 7:30 PM
NY Jets
NY Giants 9/25/14 7:25 PM
Washington
Columbus 12:30 PM
Carolina
Buffalo 4:00 PM
Washington
St. Louis 5:30 PM
Columbus
Calgary 7:00 PM
Edmonton
Edmonton 7:00 PM
Calgary
Connecticut 14 FINAL
So Florida 17
Old Dominion 45 FINAL
Rice 42
Troy 0 FINAL
(13) Georgia 66
Georgia Tech 27 FINAL
Virginia Tech 24
Eastern Mich 14 FINAL
(11) Michigan State 73
Iowa 24 FINAL
Pittsburgh 20
Bowling Green 17 FINAL
(19) Wisconsin 68
Maryland 34 FINAL
Syracuse 20
Tulane 13 FINAL
Duke 47
Hawaii 12 FINAL
Colorado 21
Marshall 48 FINAL
Akron 17
North Carolina 41 FINAL
East Carolina 70
Army 21 FINAL
Wake Forest 24
Virginia 33 FINAL
(21) BYU 41
(6) Texas A&M 58 FINAL
SMU 6
Rutgers 31 FINAL
Navy 24
Central Mich 10 FINAL
Kansas 24
Utah 26 FINAL
Michigan 10
Florida 21 FINAL
(3) Alabama 42
Louisville 34 FINAL
FIU 3
Fla Atlantic 19 FINAL
Wyoming 20
Indiana 31 FINAL
(18) Missouri 27
San Jose St 7 FINAL
Minnesota 24
Texas State 35 FINAL
Illinois 42
Massachusetts 7 FINAL
Penn State 48
Georgia State 14 FINAL
Washington 45
Appalachian St 20 FINAL
Southern Miss 21
Miss State 34 FINAL
(8) LSU 29
Northern Ill 14 FINAL
Arkansas 52
Middle Tennessee 17 FINAL
Memphis 36
Utah State 14 FINAL
Arkansas State 21
Miami-Ohio 24 FINAL
Cincinnati 31
Idaho 24 FINAL
Ohio U 36
Ball State 23 FINAL
Toledo 34
(14) So Carolina 48 FINAL
Vanderbilt 34
(4) Oklahoma 45 FINAL
West Virginia 33
Ga Southern 28 FINAL
South Alabama 6
UNLV 14 FINAL
Houston 47
Miami-Florida 31 FINAL
(24) Nebraska 41
New Mexico 38 FINAL
New Mexico St 35
(22) Clemson 17 FINAL
(1) Florida State 23
California 45 FINAL
Arizona 49
San Diego St 7 FINAL
Oregon State 28
(2) Oregon 38 FINAL
Washington St 31
Louisiana 9 FINAL
Boise State 34
Texas Tech 9/25/14 6:30 PM
(25) Oklahoma State
Appalachian St 9/25/14 6:30 PM
Ga Southern
(12) UCLA 9/25/14 9:00 PM
(15) Arizona State
Middle Tennessee 9/26/14 7:00 PM
Old Dominion
Fresno State 9/26/14 7:00 PM
New Mexico
(1) Florida State 9/27/14 2:00 AM
NC State
Duke 9/27/14 2:00 AM
Miami-Florida
North Carolina 9/27/14 2:00 AM
(22) Clemson
Texas-El Paso 9/27/14 11:00 AM
(20) Kansas State
Tennessee 9/27/14 11:00 AM
(13) Georgia
Vanderbilt 9/27/14 11:00 AM
Kentucky
Wyoming 9/27/14 11:00 AM
(11) Michigan State
Northwestern 9/27/14 11:00 AM
Penn State
TCU 9/27/14 11:00 AM
SMU
Iowa 9/27/14 11:00 AM
Purdue
Tulane 9/27/14 11:00 AM
Rutgers
So Florida 9/27/14 11:00 AM
(19) Wisconsin
Colorado State 9/27/14 11:30 AM
Boston College
Western Mich 9/27/14 11:30 AM
Virginia Tech
Maryland 9/27/14 12:30 PM
Indiana
Akron 9/27/14 12:30 PM
Pittsburgh
Bowling Green 9/27/14 2:00 PM
Massachusetts
Arkansas 9/27/14 2:30 PM
(6) Texas A&M
Kent State 9/27/14 2:30 PM
Virginia
Western Ky 9/27/14 2:30 PM
Navy
Minnesota 9/27/14 2:30 PM
Michigan
Wake Forest 9/27/14 2:30 PM
Louisville
FIU 9/27/14 2:30 PM
UAB
Miami-Ohio 9/27/14 2:30 PM
Buffalo
Colorado 9/27/14 3:00 PM
California
Louisiana Tech 9/27/14 3:00 PM
(5) Auburn
Texas 9/27/14 3:00 PM
Kansas
Temple 9/27/14 3:00 PM
Connecticut
(16) Stanford 9/27/14 3:15 PM
Washington
TX-San Antonio 9/27/14 4:00 PM
Fla Atlantic
South Alabama 9/27/14 4:00 PM
Idaho
Cincinnati 9/27/14 5:00 PM
(23) Ohio State
Rice 9/27/14 6:00 PM
Southern Miss
(18) Missouri 9/27/14 6:00 PM
(14) So Carolina
Boise State 9/27/14 6:00 PM
Air Force
Central Mich 9/27/14 6:00 PM
Toledo
Troy 9/27/14 6:00 PM
ULM
New Mexico St 9/27/14 6:30 PM
(8) LSU
Memphis 9/27/14 6:30 PM
(10) Ole Miss
Texas State 9/27/14 7:00 PM
Tulsa
Washington St 9/27/14 7:00 PM
Utah
(9) Notre Dame 9/27/14 7:00 PM
Syracuse
(7) Baylor 9/27/14 7:00 PM
Iowa State
UNLV 9/27/14 7:00 PM
San Diego St
Illinois 9/27/14 8:00 PM
(24) Nebraska
Oregon State 9/27/14 9:30 PM
(17) USC
Nevada 9/27/14 9:30 PM
San Jose St
Chivas USA 2:00 PM
Toronto FC
Toronto 40 FINAL
Brt Columbia 23
Edmonton 23 FINAL
Hamilton 25
Calgary 12:00 PM
Montreal
Ottawa 3:00 PM
Saskatchewan
Connect with twitterConnect with facebookConnect with Google+Connect with PinterestConnect with PinterestConnect with RssfeedConnect with email newsletters

ADVERTISEMENT

ADVERTISEMENT

ADVERTISEMENT

 
Close