Coming – Wedge Brakes

Hydraulic brakes were a huge improvement over the mechanical brakes originally used in motor cars.  Disk brakes replaced drum brakes and braking capacity was further improved.  ewb_0538_1_1315425.jpg

In the last thirty years ABS has gone from an option on exotic cars to a standard on most vehicles.  Each of these steps has resulted in shortened braking distances, enhanced control under braking, and proved to be more reliable.

Now comes a brake technology that might prove to be a quantum improvement over what is available today.  It is called Electronic Wedge Braking and the prototype has been developed by the Seimens Corporation of Germany.

This isn’t the first time that electronic braking has been explored.  The problem had been the limitations of the 12 volt systems being used in automobiles today being unable to drive a motor with enough power to stop your average car.  Siemens method uses the cars own energy to slow it down. 

As with most things in cars today, it relies on sophisticated sensor technology and micro processing to ensure that the brakes don’t just lock up.  Using the vehicle’s own kinetic energy, the new system claims to need only one tenth of the actuating energy used in today’s hydraulic systems.  The bottom line is that it should allow your car to stop in about half the distance you can today. 

This new electronic wedge braking system will integrate ABS and electronic stability programs with a reaction time 50 to 100 milliseconds faster than existing ABS systems.  Shorter braking distances will be combined with better vehicular control in adverse conditions.

This promises to save weight, eliminate the problems with hydraulic fluid, and provide you with a higher level of braking performance.  By 2009 you should start seeing them offered on cars and trucks.

Just make sure your battery stays in good working order and see that you have vehicle design protection from being rear ended.

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8 Responses to Coming – Wedge Brakes

  1. mark says:

    Jim,

    I’m intrigued, and a bit perplexed by how this will really reduce braking by 50% of the distance required? I would have thought, for most cars, that the stock tires would be more of the limitation in getting toward 1G in braking than the brake system. Obviously, you can put bigger rotors and bigger calipers with bigger pads, but at some point, you start to exceed the rubber’s grip. The anti lock, or any other technology will work to keep you just off that point. An engineer I worked for told me there was a formula that said maximum breaking occured as a % of the RPM of the wheel. We could argue that anti-lock doesn’t yet allow maximum force applied a high enough percentage of the time, so improving the “on” time via decreasing the pulse width could help. But again, I’m just back to bigger brakes and fatter tires with grippier compound. Some kind of a polar diagram showing the relation of these factors toward maximum theoretical braking would be cool to help understand this better. Any other resources you found to help visualize the interdependence?

  2. Noel says:

    This gets interesting. And raises a bunch of issues.

    I question that you could stop in half the distance required today. Would that mean a car with really good brakes, say, a Porsche Boxster that stops from 60 mph in about 120 feet, could stop in 60 feet? That seems unlikely. But getting more vehicles into the range of the Porsche would be a big advantage. Imagine stopping a big sedan, minivan or even an SUV in 120 feet from 60.

    However, there are other issues. I don’t know the formulas for the physics, but it seems that this is going to generate substantial g-forces on the passengers (so they had best be belted in) and those belts better have some kind of automatic tensioning systems beyond the current “pre-tensioners” that are often linked to airbag operation. There is definitely the potential to stop too fast or hard for some types of passengers–kids, older folks or people with some kinds of disabilities.

    Next, to generate sufficient braking force, it would seem that rotors and pads will have to substantially larger to provide larger swept areas. Again, I don’t know the physics, but a huge decrease in braking would require much greater swept areas. Suppose the diameter of a rotor had to be 1″ greater and needed the eqivalent of 4-pot calipers. This will demand larger wheels and tires which increases unsprung weight (not good) and cost over time (have you priced 17 or 18″ tires lately?). I suspect braking materials will also need upgrading to deal with the added heat and pressure. Ceramics, anyone?

    And speaking of tires, they are what really stops the car. Super-grippy brakes are going to require MUCH better tires to get the best results. And not all tires are created equal. High performance rubber is stickier, but wears faster than tires designed for high mileage. The balance of tire performance-braking-wear has to be evaluated.

    Finally there are electrical demands. We are already long past the stage where 12 volt systems are adequate. Automakers have been planning for 24 volt or (more likely) 48 volt systems for some time, but progress seems to have stalled. If these wedge brakes are to work the electrical systems will have to be upgraded first.

    Just curious, what to airplanes have for brakes? I know they are ABS discs, but are they hydraulic or electrical?

    And you raise the possibility of being rear-ended. This is likely to be a huge issue, especially with the tendency of so many people to tailgate. If a car with wedge brakes can stop in half the distance, it is decelerating at twice the rate of a car with conventional brakes. That means the car behind you needs at least twice the following distance as it does today. The rule of thumb for following distance is 2 seconds, preferably 3. But if a car has wedge brakes (which the person driving in another car will not know) the car behind them will need to be 4 to 6 seconds back. How do you get the yahoo in the car behind you to stay far enough back?

    Better brakes are great, but are not without issues. I know I’ve nearly been rear-ended on several occasions because my car stops harder than the guy behind me, and that’s with conventional brakes.

  3. Jim says:

    I agree with your thoughts and have the same questions. I believe tht the contention is that this design can be modulated or pulsed far more quickly and effectively than the current hydaulic brake systems that use ABS. That combines with the faster reaction time is what delivers the performance.

    Now here is a quote from an Internet article:

    “The electronic wedge brake works by a similar principle to that used in brakes for horse-drawn carriages, where a wedge was used to bring the wheel to a standstill. The EWB, however, relies on sophisticated sensor technology and electronics to prevent the brakes from locking and ensure highly efficient and controlled braking (see the following report). The wedge uses a vehicle’s kinetic energy, converting it into braking energy. By reinforcing itself this way, the EWB needs only one tenth of the actuating energy required by today’s hydraulic braking systems. Given this superior efficiency, the EWB will also have smaller dimensions, which will reduce total vehicle weight. What’s more, the EWB will dispense with the need for brake lines, a servo-unit and a brake fluid reservoir. This will free up a volume of about 22 liters in the engine compartment, giving vehicle designers additional scope.

    Likewise, the nearly ubiquitous antilock braking systems (ABS) and the less common electronic stability programs will be replaced by the software integrated into the EWB system. Plans call for a new algorithm to take on these functions, enabling the EWB to react faster than ABS systems. While a conventional ABS takes between 140 and 170 milliseconds to generate full braking power, the EWB needs only about 100 milliseconds and therefore shortens the braking distance because a car covers the distance of 1.40 meters in one second at a speed of 100 kilometers per hour. This also means the wedge brake will play an important role in making it possible for drivers to keep vehicles under control even in difficult situations.

    And the principle behind the electronic wedge brake isn’t only suitable for use in passenger cars: Trucks and trailers also could be equipped with the EWB. Today’s wedge technology can be used to brake virtually any spinning object. Possible applications include systems for elevators, high-speed trains, and for motors used in automation and conveyance technologies. ”

    Sounds like a Siemen’s press release.

    Good old Popular Science has their 25 words or less onthe subject as well…

    http://www.popsci.com/popsci/automotivetech/cd9a7178706d8010vgnvcm1000004eecbccdrcrd.html

  4. Noel says:

    Well maybe. Trains and elevators, though, don’t have some yahoo in a clapped out Kia, or some soccer mom in a minvan, jabbering on their cell phone while 20 feet of their rear bumper.

    And at 100 kph (62 mph) one is traveling about 27 meters per second, not 1.4 meters per second. So they must mean 1.4 meters in 70 milliseconds or something. Deceleration rate is then dependent on tires and brake size.

    Then of course this IS technology, and we all know that it can be a tad less than perfect. Imagine, if you will, a car that can stop even 30 % better than present vehicles, but one of the switches, solenoids, sensors, or other widgets goes south on the right front. So now this heavy duty braking is massively unbalanced, something you don’t want to find out when you stomp on the binders only to find the car pulling sharply left into oncoming traffic, with all that extra braking power pulling you right into a head on or setting you into a spin. You could mitigate this if the brake system can automatically balance itself but I can imagine lots of trouble.

    The better answer for implementation is to do it gradually and NOT providing ideal or ultimate braking levels–just a nice improvement. Otherwise the average nut holding the steering wheel is going to screw stuff up royaly.

    Still, I’d like to see more on this, maybe Siemens has a video or something.

  5. Mark says:

    Jim, Noel,

    Great points of discussion. Tracked vehicles that don’t have a nuetral in the control valve plumbing stop immediately when you stop going forward or back. My rubber tracked skid loader will do 8 mph wide open and if you don’t feather the controls toward slow before hitting nuetral it’s like running into a brick wall – the occupant goes flying. Noel is exactly right on considering the physics and the forces the seat belts will apply to occupants. How about cargo retention? I’ve already learned, and re-learned not to carry much more than paper in my Z06. Jim had cargo nets in his GSX and I always smiled when he’d carefully wrap up his purchases in them. Noel is also right that extreme performance introduced into a mixed traffic, especially high speed urban freeway setting will make for some catastrophic wrecks. On one hand, ABS and collision avoidance technologies are helping make up for cell phone abusers today who notice the impending disaster at the last possible second, but then it may make things worse for that Peterbilt hauling logs behind them. Maybe Wedgebrakes on Trucks, busses and trains first.

    On small planes, it’s unvented hydraulic disks. On large jets, I notice that they use thrust reversers and lots of hydraulically raised air dams on the wings to aid the brakes on the wheels.

  6. bolly says:

    With the ABS disconnected, I hit hit the cones sideways, and didn´t stop for about five meters after I hit them, and the car had turned 180 degrees. ABS connected, I hit the brakes, and nicely steered aside and came to a stop about five meters behind the cones. That showed us how useful ABS brakes can be. The tires had studs, but I tried another car that had summer tires, and at 50 km/h I didn´t stop until the 75-meter mark.

  7. CarKid says:

    Wow that is just simply amazing. Im in school for automotive technology, im acctually sitting in class right now and came upon this on accident. its amazing how much you can improve, and i doubt he have even come close to the potential we can actually achieve. it sounds crazy but the first land speed record was only about 36 mph. Now we go 0-60 in 4 sec or less with some vehicles. Being able to stop that fast is just a big perk that can also help inprove on the percentage of collisions. I am truely amazed. I cant wait to work on these new systems in the future.

  8. James says:

    1-Sorry, this claim of reduced distances is false. Todays stopping distances are always limited by the road/tire adhesion coef available. ABS typically cannot beat a professional driver’s ability to squeak in the best distances which are at best about sustained 1G. Race cars, with sticky rubber on an ideal surface can pull maybe 1.1Gs sustained. (Only .7 to .8Gs are needed to pass the FMVSS brake stop distances.)
    2-ABS’s main value is for the average driver. It gives near optimal braking for most drivers even under very tricky road conditions such as combined braking and turning or braking with your RH wheels on ice while the others are on pavement. Also, on hard snow or ice, it will let the average driver not loose his steering due to over braking.
    3-Cycle time of the electronics and control system will not improve the road friction which is what ultimately controls your stopping distance. The road/tire friction does not change fast enough to warrant more than a 20-50hz cycle rate on the ABS.
    4-ABS systems must anticipate the driver’s reaction also. Therefore they typically reserve some road friction for turning (unanticipated), while sacrificing stopping distance. For example , you are in a sudden impending head-on collison- some guy fell asllep at the wheel, crossed the median and is heading straight for you. You hammer the brake pedal and pull a 1.0G for 30 feet, but its now obvious he is still at full speed. You must make an emergency sudden left or right avoidance maneuver. If the tires were near impending slip for braking, you would have no traction left for the lateral tire force needed to steer out of trouble. That is why ABS systems don’t give 100% traction utilization. And this is why a professional test driver on a brake pad can typically beat a ABS system. (His foot modulates the pedal to full adhesion utilization- and he knows he will not be making a sudden turn!)
    Lucky for us, the ABS designers understood this!

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