Some detailed info on steering changes in 2008
06-11-2011, 10:10 AM
#1
Instructor
Thread Starter
Member Since: Apr 2010
Location: Louisville KY
Posts: 208
Likes: 0
Received 0 Likes
on
0 Posts
Some detailed info on steering changes in 2008
I beleive most of us already know efforts where made to increase the steering feel and tranmissions quickness in 2008...but did you know changes existed in 2009 as well...below are some technical details.
If Corvette chief engineer Tadge Juechter said “Corvette is the poster child for continuous improvement. Making our car look, feel and perform better is what we do every day.”
“Last year, we added a premium steering gear in response to owners who felt that Corvettes could benefit from improved on-center feel and precision,” adds Juechter.
For 2009, we found another means of making Corvette steering even better.
Quicker steering ratios make a car feel nimble and responsive. But if the ratio is too quick, the car is nervous at highway speeds. Juechter’s ‘even better’ development is a variable-ratio rack-and-pinion steering gear that provides the best of both worlds.
Terrel Johnson, a Corvette engineering team member for five years, is the lead steering design engineer.
Johnson explains:
“The new variable-ratio steering provides the same 17.1 to 1 on-center ratio that we’ve used successfully for years. But when the steering wheel angle exceeds 15 degrees of left or right turning, the ratio begins speeding up.
The change is so gradual that the driver notices nothing unusual, but after a little more than half a turn of the steering wheel, the ratio has changed to 14.6 to 1. This trims the number of turns lock-to-lock from 2.78 to only 2.54, a 9-percent improvement.
“With multiple ratios in one steering gear, we’re able to tune the on-center zone for excellent stability and reduced sensitivity at highway speeds without making Corvettes feel sluggish around town. The quicker off-center ratio helps the car feel more nimble and highly maneuverable while parking or negotiating a U-turn.”
Asked exactly how the variable-ratio gearing is achieved, Johnson answered with two words: helix angles. Some digging revealed what he was talking about.
Inside the rack-and-pinion steering system, the pinion gear teeth encircle their shaft in a spiral called a helix. This configuration increases the number of pinion teeth in contact with rack teeth.
The greater the gear-to-gear contact area (more teeth engaged), the less the likelihood of lash when the rack-and-pinion assembly is under load. Lash is steering precision’s bitter enemy.
Pinion gear teeth must be evenly spaced because each tooth contacts the rack at least twice during the two-plus turns lock-to-lock.
But, since each rack tooth is engaged only once throughout the rack’s full travel, how the rack teeth are configured can vary.
At the center of the steering rack, the teeth are cut at a 14-degree helix angle. This causes the rack teeth to engage the pinion teeth at their roots, yielding minimal rack motion for each increment of pinion rotation.
At the end of the rack, the teeth are cut at an 18-degree helix angle. Now the rack teeth engage the pinion gear teeth near their outmost tips. That larger-radius point of contact causes the rack to move substantially more for each increment of pinion rotation. Presto: a faster steering ratio.
Variable-ratio steering is another example of a seemingly miniscule change that yields a noticeable improvement in the Corvette’s daily-driving behavior.
From the engineer’s perspective, the Corvette is a Rubik’s cube of interlocking, interacting systems.
A small change here can inflict major consequences there. Corralling an additional 36 horses under the hood for 2008 sent transmission engineers scurrying to make sure their chunks of the cube could take the gaff.
Design release engineer Dave Howe, who’s responsible for the Corvette’s six-speed manual transaxle, explains, “Our objective was to provide the necessary torque capacity without major disturbances to the basic design. But while we were at it, we seized the opportunity to install improvements every customer will appreciate.”
Changes for 2008 included wider gears for increased torque capacity, higher-capacity synchronizers, finer splines and machined teeth for the dog clutches, and new single-piece (replacing two-piece) shift forks.
For increased stiffness at the front of the transmission, the oil-circulating pump has been moved inside the case and its flow rate has been increased by 15 percent.
Various ribs, reinforcements and flange thicknesses are increased, and the countershaft is a new, more robust single-piece (versus two-piece) design. Differential ring and pinion gears are now shot-peened twice for enhanced durability, and the span between their support bearings has been increased to the Z06 dimension.
When the chips settled, Howe and his platoon of colleagues had altered over 90 percent of the Corvette’s six-speed manual transmission’s components.
That prompted a new TR-6060 identification label to supersede the previous T-56 nameplate.
Validation testing proved that all the attention was warranted. The new gearbox is not only tough enough to stand up to the LS3 V8’s ferocity, it’s also slicker-shifting with a 10-percent reduction in motion and effort.
Across the hall at GM Powertrain, the engineers responsible for the Corvette’s six-speed automatic requested equal time to upgrade their game.
Control integration systems manager Jim Springer explains, “Corvette owners have urged us to tighten up the response between a command at the steering wheel paddle and an up- or downshift. That’s an area we’re always striving to improve, so we used the 2008 model year to implement strategies we’ve developed.”
During downshifts, a new “quick shift” technique automatically raises engine rpm in the brief interval between the release of one gear and the engagement of the next. It took an intense calibration effort and cooperation from Corvette engine experts to refine how it works, but the end result is a 40-percent quicker response.
“Thanks to the scope and sophistication of our electronic controls, this improvement was accomplished in software with no hardware changes necessary,” says Springer.
“To quicken upshifts, we implemented a strategy called torque management,” he says. A momentary reduction in the amount of engine output shortens the torque phase of each paddle-commanded upshift.
The net result is a 25-percent faster response. Since minimal torque management is used when the transmission handles upshifts automatically, the sport mode should still be used if the driver’s priority is flat-out acceleration
“Three years ago, when I joined the Corvette group, I saw a major opportunity,” recalls Jim Mero, the vehicle dynamics engineer responsible for ride and handling development.
“The sixth-generation was born with good but not great steering. Working on other programs at GM, I had witnessed what could be accomplished when a capable supplier teams with development engineers to create a world-class steering system.”
The engine may be the heart of a sports car, but the driver senses a car’s soul through its steering. Porsches, BMWs, Ferraris and other bluebloods earned their renown by providing impeccable steering sensitivity.
Now that Corvette plays in the world-class league, every aspect of its performance — including steering feel — is measured by a platinum yardstick.
Mero used a “build it and they will come” tactic to get the steering upgrades he sought approved. “Talk gets you nowhere. Until you install improvements in a car that anyone can drive and experience for themselves, there are no believers,” he explains.
Corvettes are equipped with Magnasteer variable-effort rack-and-pinion steering manufactured by Delphi Steering Systems. The ‘magna’ part of the name refers to one of the two channels by which power assistance is tuned to achieve the desired dynamic characteristics.
A magnetic field surrounding the pinion shaft is adjusted by an electronic controller to alter effort as desired. The second channel is hydraulic.
As effort rises, the control valve attached to the pinion shaft closes to deliver hydraulic pressure supplied by an engine-driven pump to an assist cylinder integral with the steering rack.
Magnasteer’s electronic controller monitors car speed and lateral acceleration via sensors. Corvette engineers program the controller to reduce the amount of steering assistance as speed and cornering g’s rise.
This allows the car to feel responsive to the driver’s inputs without sacrificing stability and predictability. Mero adds, “Generally speaking, lower steering friction yields a clearer communication between the tires and the driver. Steering effort must rise in a linear progression to send a clear message to the driver that the car is working harder in a corner.”
Mero sought improvements in linearity, sensitivity and precision beyond what could be achieved by routine external calibrations.
To achieve these gains, he challenged Joel Birsching, a product engineer at Delphi, to dig deep inside the Corvette’s steering gear.
To hit the ambitious performance metrics GM engineers established, Birsching’s team changed every major internal component.
Friction throughout the system was analyzed and materials and processes were altered as necessary to meet GM’s requirements. The gear set was redesigned with new geometry to improve how precisely and smoothly the teeth mesh together.
Operating clearances were tightened. A new algorithm was created for the Magnasteer controller to provide higher on-center stiffness. (Engineers define stiffness as the amount of motion at the steering wheel rim before the car responds with a change in direction. Less motion equals higher stiffness.)
A concerted effort paid handsome dividends. Steering feel is notably improved in the 2008 Corvette. Chalk up one more category where America’s favorite sports car meets or exceeds the blueblood standard.
If Corvette chief engineer Tadge Juechter said “Corvette is the poster child for continuous improvement. Making our car look, feel and perform better is what we do every day.”
“Last year, we added a premium steering gear in response to owners who felt that Corvettes could benefit from improved on-center feel and precision,” adds Juechter.
For 2009, we found another means of making Corvette steering even better.
Quicker steering ratios make a car feel nimble and responsive. But if the ratio is too quick, the car is nervous at highway speeds. Juechter’s ‘even better’ development is a variable-ratio rack-and-pinion steering gear that provides the best of both worlds.
Terrel Johnson, a Corvette engineering team member for five years, is the lead steering design engineer.
Johnson explains:
“The new variable-ratio steering provides the same 17.1 to 1 on-center ratio that we’ve used successfully for years. But when the steering wheel angle exceeds 15 degrees of left or right turning, the ratio begins speeding up.
The change is so gradual that the driver notices nothing unusual, but after a little more than half a turn of the steering wheel, the ratio has changed to 14.6 to 1. This trims the number of turns lock-to-lock from 2.78 to only 2.54, a 9-percent improvement.
“With multiple ratios in one steering gear, we’re able to tune the on-center zone for excellent stability and reduced sensitivity at highway speeds without making Corvettes feel sluggish around town. The quicker off-center ratio helps the car feel more nimble and highly maneuverable while parking or negotiating a U-turn.”
Asked exactly how the variable-ratio gearing is achieved, Johnson answered with two words: helix angles. Some digging revealed what he was talking about.
Inside the rack-and-pinion steering system, the pinion gear teeth encircle their shaft in a spiral called a helix. This configuration increases the number of pinion teeth in contact with rack teeth.
The greater the gear-to-gear contact area (more teeth engaged), the less the likelihood of lash when the rack-and-pinion assembly is under load. Lash is steering precision’s bitter enemy.
Pinion gear teeth must be evenly spaced because each tooth contacts the rack at least twice during the two-plus turns lock-to-lock.
But, since each rack tooth is engaged only once throughout the rack’s full travel, how the rack teeth are configured can vary.
At the center of the steering rack, the teeth are cut at a 14-degree helix angle. This causes the rack teeth to engage the pinion teeth at their roots, yielding minimal rack motion for each increment of pinion rotation.
At the end of the rack, the teeth are cut at an 18-degree helix angle. Now the rack teeth engage the pinion gear teeth near their outmost tips. That larger-radius point of contact causes the rack to move substantially more for each increment of pinion rotation. Presto: a faster steering ratio.
Variable-ratio steering is another example of a seemingly miniscule change that yields a noticeable improvement in the Corvette’s daily-driving behavior.
From the engineer’s perspective, the Corvette is a Rubik’s cube of interlocking, interacting systems.
A small change here can inflict major consequences there. Corralling an additional 36 horses under the hood for 2008 sent transmission engineers scurrying to make sure their chunks of the cube could take the gaff.
Design release engineer Dave Howe, who’s responsible for the Corvette’s six-speed manual transaxle, explains, “Our objective was to provide the necessary torque capacity without major disturbances to the basic design. But while we were at it, we seized the opportunity to install improvements every customer will appreciate.”
Changes for 2008 included wider gears for increased torque capacity, higher-capacity synchronizers, finer splines and machined teeth for the dog clutches, and new single-piece (replacing two-piece) shift forks.
For increased stiffness at the front of the transmission, the oil-circulating pump has been moved inside the case and its flow rate has been increased by 15 percent.
Various ribs, reinforcements and flange thicknesses are increased, and the countershaft is a new, more robust single-piece (versus two-piece) design. Differential ring and pinion gears are now shot-peened twice for enhanced durability, and the span between their support bearings has been increased to the Z06 dimension.
When the chips settled, Howe and his platoon of colleagues had altered over 90 percent of the Corvette’s six-speed manual transmission’s components.
That prompted a new TR-6060 identification label to supersede the previous T-56 nameplate.
Validation testing proved that all the attention was warranted. The new gearbox is not only tough enough to stand up to the LS3 V8’s ferocity, it’s also slicker-shifting with a 10-percent reduction in motion and effort.
Across the hall at GM Powertrain, the engineers responsible for the Corvette’s six-speed automatic requested equal time to upgrade their game.
Control integration systems manager Jim Springer explains, “Corvette owners have urged us to tighten up the response between a command at the steering wheel paddle and an up- or downshift. That’s an area we’re always striving to improve, so we used the 2008 model year to implement strategies we’ve developed.”
During downshifts, a new “quick shift” technique automatically raises engine rpm in the brief interval between the release of one gear and the engagement of the next. It took an intense calibration effort and cooperation from Corvette engine experts to refine how it works, but the end result is a 40-percent quicker response.
“Thanks to the scope and sophistication of our electronic controls, this improvement was accomplished in software with no hardware changes necessary,” says Springer.
“To quicken upshifts, we implemented a strategy called torque management,” he says. A momentary reduction in the amount of engine output shortens the torque phase of each paddle-commanded upshift.
The net result is a 25-percent faster response. Since minimal torque management is used when the transmission handles upshifts automatically, the sport mode should still be used if the driver’s priority is flat-out acceleration
“Three years ago, when I joined the Corvette group, I saw a major opportunity,” recalls Jim Mero, the vehicle dynamics engineer responsible for ride and handling development.
“The sixth-generation was born with good but not great steering. Working on other programs at GM, I had witnessed what could be accomplished when a capable supplier teams with development engineers to create a world-class steering system.”
The engine may be the heart of a sports car, but the driver senses a car’s soul through its steering. Porsches, BMWs, Ferraris and other bluebloods earned their renown by providing impeccable steering sensitivity.
Now that Corvette plays in the world-class league, every aspect of its performance — including steering feel — is measured by a platinum yardstick.
Mero used a “build it and they will come” tactic to get the steering upgrades he sought approved. “Talk gets you nowhere. Until you install improvements in a car that anyone can drive and experience for themselves, there are no believers,” he explains.
Corvettes are equipped with Magnasteer variable-effort rack-and-pinion steering manufactured by Delphi Steering Systems. The ‘magna’ part of the name refers to one of the two channels by which power assistance is tuned to achieve the desired dynamic characteristics.
A magnetic field surrounding the pinion shaft is adjusted by an electronic controller to alter effort as desired. The second channel is hydraulic.
As effort rises, the control valve attached to the pinion shaft closes to deliver hydraulic pressure supplied by an engine-driven pump to an assist cylinder integral with the steering rack.
Magnasteer’s electronic controller monitors car speed and lateral acceleration via sensors. Corvette engineers program the controller to reduce the amount of steering assistance as speed and cornering g’s rise.
This allows the car to feel responsive to the driver’s inputs without sacrificing stability and predictability. Mero adds, “Generally speaking, lower steering friction yields a clearer communication between the tires and the driver. Steering effort must rise in a linear progression to send a clear message to the driver that the car is working harder in a corner.”
Mero sought improvements in linearity, sensitivity and precision beyond what could be achieved by routine external calibrations.
To achieve these gains, he challenged Joel Birsching, a product engineer at Delphi, to dig deep inside the Corvette’s steering gear.
To hit the ambitious performance metrics GM engineers established, Birsching’s team changed every major internal component.
Friction throughout the system was analyzed and materials and processes were altered as necessary to meet GM’s requirements. The gear set was redesigned with new geometry to improve how precisely and smoothly the teeth mesh together.
Operating clearances were tightened. A new algorithm was created for the Magnasteer controller to provide higher on-center stiffness. (Engineers define stiffness as the amount of motion at the steering wheel rim before the car responds with a change in direction. Less motion equals higher stiffness.)
A concerted effort paid handsome dividends. Steering feel is notably improved in the 2008 Corvette. Chalk up one more category where America’s favorite sports car meets or exceeds the blueblood standard.
06-11-2011, 10:23 AM
#2
Team Owner
Member Since: Jun 2005
Location: Northern, VA
Posts: 46,104
Received 2,481 Likes
on
1,944 Posts
St. Jude Donor '15
"In honor of jpee"
v. interesting. 
06-11-2011, 02:18 PM
#3
Safety Car
Member Since: Jan 2009
Location: Mooresville (Race City USA) NC
Posts: 4,681
Likes: 0
Received 2 Likes
on
2 Posts
Of course variable ratio power steering is nothing new, GM just finally got around to incorporating it into the Corvette in 2009; many cars have had this dating back to the 1960s. But it was a welcome improvement along with bluetooth and chrome look surrounds on the crossed flags front and rear emblems intoduced in 2009.
And, I didn't need a MA/MS degree to understand it. 
06-11-2011, 03:36 PM
#7
Safety Car
Of course variable ratio power steering is nothing new, GM just finally got around to incorporating it into the Corvette in 2009; many cars have had this dating back to the 1960s. But it was a welcome improvement along with bluetooth and chrome look surrounds on the crossed flags front and rear emblems intoduced in 2009.
06-11-2011, 04:32 PM
#8
Safety Car
Member Since: Jan 2009
Location: Mooresville (Race City USA) NC
Posts: 4,681
Likes: 0
Received 2 Likes
on
2 Posts
What is your problem little man? I simply state facts. Some like you seem to get offended by facts. You seem to prefer living in a state of ignorance. Too bad!
06-11-2011, 06:29 PM
#9
Burning Brakes
06-11-2011, 07:40 PM
#10
Team Owner
Member Since: Jun 2005
Location: Northern, VA
Posts: 46,104
Received 2,481 Likes
on
1,944 Posts
St. Jude Donor '15
"In honor of jpee"
As to the inclusion of old ideas into the newer Corvettes, yes, variable ratio ps has been around quite some time. Seems to me that if there's good-tech sitting on the shelf from someone else, as long as it's not prohibitive to license or include it, why not do it? And sooner is always better than later. But later instead of never is good, too.
06-11-2011, 07:59 PM
#11
Team Owner
Member Since: Sep 2000
Location: Far NW 'burbs of Chicago
Posts: 23,938
Received 2,051 Likes
on
1,362 Posts
St. Jude Donor '13
Talon90 posted a few weeks ago about the 2008+ steering racks and why it would be prohibitively complicated/expensive to install them in previous years. Too bad.
