Ice Mode
11-06-2013, 10:34 PM
#1
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Ice Mode
Ran across this interesting explanation of ice mode on Sector 111's website:
The Lotus have suffered from a phenomena under braking that feels like you've lost your brakes - this is something we mentioned in our recent blog entry with our Switchblade. I found an explanation for this issue from a noted Lotus Engineer at the UK factory.
The symptoms being described are a result of the Electronic Brake Distribution (EBD) system operating. This system is also referred to as Dynamic Rear Proportioning (DRP) and is, as the name implies an electronic system which, through the ABS control valve block restricts the line pressure to the rear brakes automatically to a pre-programmed algorithm. You can consider it as an electronically controlled proportioning valve which measures parameters like the rate of deceleration and rate of pedal application and uses this data to anticipate a rear wheel lock-up and then reduces the braking effort at the rear wheels as necessary. If the ABS system is left to do this, it can only react to a wheel as it starts to lock and therefore the car can already start to spin before the ABS can start to work. In extreme circumstances, if the driver brakes very suddenly the EBD system can lock off the pressure to the rear wheels completely; what pressure was at the rear brakes as the EBD system engaged remains there and the rear brakes are still working as a result, but further increases in pedal effort will not increase the braking at the rear of the car because the pressure to the rear brakes cannot increase. When this happens the brake pedal goes hard, as it is now pushing against the front callipers and a closed valve only, instead of against the front and rear callipers. The rear callipers are single piston and therefore quite flexible, so they are a major factor in making the brake pedal feel 'soft'. When the valve closes, the brake pedal pressure no longer flexes the rear callipers, hence the increase in pedal hardness. The front brakes are still working just as well as before the valve closed and will give more braking if the pedal effort is increased, while with the rear brakes working as hard as they can the braking is NOT affected. The problem is the driver feels like braking is reduced (even though it is not) because of the change in pedal feel. If the driver continues to push hard on the pedal, the car will continue to slow as fast as it possibly can in the circumstances. If he increases the pedal effort the front braking effort will increase and the rear effort will remain where it was. If he was to back off the pedal for a fraction of a second, the valve will reopen and the rear brakes will operate as normal again, with the pedal feel going back to normal.
In the case of releasing and re-engaging the pedal the car should not be able to slow any faster than it was with the system engaged unless either 1: the driver triggered the system in the first place by stamping on the pedal too fast or 2: the system triggered because a rear wheel was unloaded when the brakes were applied and would have locked up but is now fully loaded once again and able to sustain a greater braking torque. If the rate of deceleration does improve when the pedal is reapplied then it is telling the driver that he is over braking either in terms of the ultimate ability of the brakes (cause 1 above) or the track condition (cause 2 above) and needs to adjust his driving style to suit. If the system were not fitted or disabled and he continued to drive that way he would be in danger of spinning when applying the brakes.
The suggestion that the system is running out of vacuum is just plain wrong. The system carries an internal reservoir of vacuum sufficient for three full brake applications. As with every servo system ever fitted to a car there is a one way valve which prevents the vacuum being lost when the car is on boost. The only way this reserve can be depleted is if the driver is maintaining boost while applying full brakes, i.e.: left foot braking very badly. In this instance I would argue that depleting the vacuum is probably a good thing as it should provide him with a warning that he is doing something awful to the car and it may reduce the speed of impact when he finally hits something as the brakes fade to nothing!! In normal use the throttle is closed when the brakes are applied, there is therefore no boost and the vacuum is automatically replenished as it is used."
So there it is, 'Ice Mode' is an inherent issue that can be addressed with some old school brake pedal pumping. I think the pedal feel, when it goes 'hard', tends to be the most disconcerting as it happens when you are approaching the corner at high speed. Many racers have disconnected the ABS system in an effort to reduce this issue and frankly it is a good solution for advanced drivers.
http://sector111.blogspot.com/2013/0...planation.html
The Lotus have suffered from a phenomena under braking that feels like you've lost your brakes - this is something we mentioned in our recent blog entry with our Switchblade. I found an explanation for this issue from a noted Lotus Engineer at the UK factory.
The symptoms being described are a result of the Electronic Brake Distribution (EBD) system operating. This system is also referred to as Dynamic Rear Proportioning (DRP) and is, as the name implies an electronic system which, through the ABS control valve block restricts the line pressure to the rear brakes automatically to a pre-programmed algorithm. You can consider it as an electronically controlled proportioning valve which measures parameters like the rate of deceleration and rate of pedal application and uses this data to anticipate a rear wheel lock-up and then reduces the braking effort at the rear wheels as necessary. If the ABS system is left to do this, it can only react to a wheel as it starts to lock and therefore the car can already start to spin before the ABS can start to work. In extreme circumstances, if the driver brakes very suddenly the EBD system can lock off the pressure to the rear wheels completely; what pressure was at the rear brakes as the EBD system engaged remains there and the rear brakes are still working as a result, but further increases in pedal effort will not increase the braking at the rear of the car because the pressure to the rear brakes cannot increase. When this happens the brake pedal goes hard, as it is now pushing against the front callipers and a closed valve only, instead of against the front and rear callipers. The rear callipers are single piston and therefore quite flexible, so they are a major factor in making the brake pedal feel 'soft'. When the valve closes, the brake pedal pressure no longer flexes the rear callipers, hence the increase in pedal hardness. The front brakes are still working just as well as before the valve closed and will give more braking if the pedal effort is increased, while with the rear brakes working as hard as they can the braking is NOT affected. The problem is the driver feels like braking is reduced (even though it is not) because of the change in pedal feel. If the driver continues to push hard on the pedal, the car will continue to slow as fast as it possibly can in the circumstances. If he increases the pedal effort the front braking effort will increase and the rear effort will remain where it was. If he was to back off the pedal for a fraction of a second, the valve will reopen and the rear brakes will operate as normal again, with the pedal feel going back to normal.
In the case of releasing and re-engaging the pedal the car should not be able to slow any faster than it was with the system engaged unless either 1: the driver triggered the system in the first place by stamping on the pedal too fast or 2: the system triggered because a rear wheel was unloaded when the brakes were applied and would have locked up but is now fully loaded once again and able to sustain a greater braking torque. If the rate of deceleration does improve when the pedal is reapplied then it is telling the driver that he is over braking either in terms of the ultimate ability of the brakes (cause 1 above) or the track condition (cause 2 above) and needs to adjust his driving style to suit. If the system were not fitted or disabled and he continued to drive that way he would be in danger of spinning when applying the brakes.
The suggestion that the system is running out of vacuum is just plain wrong. The system carries an internal reservoir of vacuum sufficient for three full brake applications. As with every servo system ever fitted to a car there is a one way valve which prevents the vacuum being lost when the car is on boost. The only way this reserve can be depleted is if the driver is maintaining boost while applying full brakes, i.e.: left foot braking very badly. In this instance I would argue that depleting the vacuum is probably a good thing as it should provide him with a warning that he is doing something awful to the car and it may reduce the speed of impact when he finally hits something as the brakes fade to nothing!! In normal use the throttle is closed when the brakes are applied, there is therefore no boost and the vacuum is automatically replenished as it is used."
So there it is, 'Ice Mode' is an inherent issue that can be addressed with some old school brake pedal pumping. I think the pedal feel, when it goes 'hard', tends to be the most disconcerting as it happens when you are approaching the corner at high speed. Many racers have disconnected the ABS system in an effort to reduce this issue and frankly it is a good solution for advanced drivers.
http://sector111.blogspot.com/2013/0...planation.html
11-06-2013, 11:01 PM
#2
Race Director
Thanks! Maybe a very fast pedal squeeze would work better than just a aggressive pedal stomp.
11-07-2013, 08:27 AM
#3
^^^ This, the stomp unsettles the car and can trigger the ABS and DPR. A squeeze (very quickly mind) is the way to go, it allows the CG to move forward and load the tyres plus its minimise slightly the temp spike of the brakes and temp differential across the disc that can cause excessive cracking
11-07-2013, 11:56 AM
#4
It is 100% the stomp - but it needs all the other things happening at the same time to create the dreaded high, hard, no stopping you're fvcked moment.
I wrote about this 3+ years ago - it is the rear valve closing that is the problem - I got this directly from my friend at GM who tracked down a Bosche contact for me and asked the question directly. In my opinion it is a faulty design as at this point the logic is flawed - I would rather have 100% braking ability and attempt to control a 'possible' spin (possible not probably) than 50% braking and now heading straight at something I am now guaranteed to hit - it makes no sense.
"In extreme circumstances, if the driver brakes very suddenly the EBD system can lock off the pressure to the rear wheels completely; what pressure was at the rear brakes as the EBD system engaged remains there and the rear brakes are still working as a result, but further increases in pedal effort will not increase the braking at the rear of the car because the pressure to the rear brakes cannot increase. When this happens the brake pedal goes hard, as it is now pushing against the front callipers and a closed valve only"
I wrote about this 3+ years ago - it is the rear valve closing that is the problem - I got this directly from my friend at GM who tracked down a Bosche contact for me and asked the question directly. In my opinion it is a faulty design as at this point the logic is flawed - I would rather have 100% braking ability and attempt to control a 'possible' spin (possible not probably) than 50% braking and now heading straight at something I am now guaranteed to hit - it makes no sense.
"In extreme circumstances, if the driver brakes very suddenly the EBD system can lock off the pressure to the rear wheels completely; what pressure was at the rear brakes as the EBD system engaged remains there and the rear brakes are still working as a result, but further increases in pedal effort will not increase the braking at the rear of the car because the pressure to the rear brakes cannot increase. When this happens the brake pedal goes hard, as it is now pushing against the front callipers and a closed valve only"
11-07-2013, 12:03 PM
#5
Rennlist Member
But the explanation seems to suit the Lotus more due to the single-piston / flexy rear caliper. (The article says that pedal goes hard because now you are pushing against the good calipers up front.. I am not sure if this would be the case for Porsches as all the GT3s have 4-pistons on the back.