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Brake-by-Wire, can this application be adopted for the Prius HSD brake
integration ? Found it in Yahoo-Prius Group.

IAA 2005: Brake it easy with brake-by-wire - Siemens VDO plans series production of the wedge brake this decade
Frankfurt, September 13, 2005


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At the 61st IAA Motor Show in Frankfurt Siemens VDO Automotive is exhibiting future braking technology with the electronic wedge brake, which will enable the launch of brake-by-wire series production for the 12-volt vehicle electrical system in this decade. The modern wedge brake offers considerable safety and comfort advantages over the hydraulic brake.

Future driver assistance systems will not only monitor the current traffic situation, but actively assist the driver in emergencies. Autonomous intervention in vehicle dynamics will increasingly help keep the vehicle under control, even in difficult operating situations. A rapid and intelligent braking system is one of the foundations for advancing the next generation of driver assistance systems. Siemens VDO sees its electronic wedge brake (EWB) brake-by-wire technology as the answer to future vehicle chassis safety, weight, reliability and space requirements.



Siemens VDO's EWB is based on innovative technology developed by eStop, a firm which was acquired by the company in early 2005, and its control-related foundations originate from German Aviation and Aerospace Center applications. During the braking operation a brake pad attached to a wedge is pressed between the brake caliper and the brake disk. As the wheel turns the wedge effect is automatically intensified. This allows any level of braking power with a minimum of intricacy.





Vehicles employing the electronic wedge brake solution will have an intelligent wheel-braking module fitted on each wheel. The module consists of the brake pad, the wedge attached to the wedge-bearing mechanism, the mechanical power transmission between the two electric motors and a sensor system for monitoring movement and force. The sensors measure current wheel speed approximately one hundred times per second and braking forces and wedge position to a high degree of accuracy and resolution. When the driver engages the brake pedal, the EWB system electronically transmits the activation signal to the interconnected brake modules. When the brake activation signal is received, electric motors actuate a wedge-bearing mechanism consisting of several rollers to move the wedge into the required position according to the sensor feedback values. This causes the brake pad to be pressed against the brake disk. Based on the principle of self-energization, the braking effect builds up very rapidly and the intelligent control prevents any danger of the wedge blocking. This principle of "unstable" control structures was taken from high safety-critical systems for aviation and aerospace applications and adapted for automotive purposes.





The EWB eliminates the need for components such as hydraulic pipes, brake cylinders, brake boosters or antilock braking control units. This lowers overall weight and makes for greater reliability for improved safety, with reduced servicing requirements. By doing away with the hydraulic braking system, it also helps to reduce the vehicle's environmental impact.





Finally, the EWB is not only for braking while the vehicle is moving, but also can be used as an automatic parking brake. This allows vehicle designers to do away with the traditional hand-pulled brake, while helping prevent the vehicle of the future against rolling away when parked. The mechanical decoupling of the brake pedal and the brake also can be used to reduce the often misunderstood pulsing of the brake pedal when ABS is in use, or to eliminate it altogether if desired. In the event of a collision, the mechanical decoupling of the brake pedal and the brake also makes for greater occupant protection in the foot area.





The use of the traditional 12-volt vehicle electrical system opens up new design potential for the automobile manufacturer, as the hydraulic-free wedge brake takes up less space both in the engine compartment and in the chassis. At the same time, it reduces assembly times on the production line and the number of components required for the brake. The electronic brake system also can be adapted more easily and faster to new types of vehicle helping to save time and development costs.





For Siemens VDO, the electronic wedge brake is another area of application in the development and production of x-by-wire technologies, which have been part of the company's day-to-day business for more than 20 years. The electronic accelerator pedal is now a standard feature on millions of vehicles. Today, any modern car with an electronically controlled fuel injection system already uses the mechanical pressure exerted by the driver on the accelerator pedal to electronically transmit the driver's input to the electronic engine control unit. In the future, electronics will replace other mechanical and hydraulic systems, thereby reducing costs, enabling new functions and increasing reliability.






About Siemens VDO


Siemens VDO Automotive is an internationally leading automotive supplier of electronics, electrical systems and mechatronics. As a developmental partner with the automobile industry, the company manufactures a comprehensive spectrum of products relating to the drivetrain, engine management electronics and fuel injection that simultaneously improve engine performance and reduce emissions. Driver comfort is enhanced and driving is made easier with information and car communication systems that include instrumentation, audio and navigation equipment, telematics and multimedia applications, up to entire cockpit designs. Safety is increased by Siemens VDO products for the chassis and body such as airbags, ABS or access control systems. An in-house sales department markets products for retrofitting passenger cars and trucks with a focus on fleet management and audio and navigation systems. In the 2004 business year (30.9.), Siemens VDO Automotive generated sales of EUR 9.0 billion.
 

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C.Rickey Hirose said:
Brake-by-Wire, can this application be adopted for the Prius HSD brake
integration ? . . .
Toyota could easily adopt it. The question is, would they. Depends on their engineers' analysis of cost and risk. Can they save money and/or make the car safer with it? There's really only two ways this gets adopted. Either someone convinces (bribes?) a government that this improves safety so much they should mandate it, or someone finds a way to convince many customers that this is a desirable feature (marketing).

It would be pretty hard to add as an after-market item without defeating the regenerative braking. Even if it's done, it's not at all clear that there's enough risk reduction (if any) to justify the cost. There's obviously no cost savings for an after-market item since you've already paid for the original braking system. There won't be enough weight savings to make most people care.
 

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But Mercedes-Benz already has Brake By-Wire on some of their high end models. It's dubbed SensoBrake (or sth along that line). Note for the new 2008 E-Class, they're dropping it in favour of conventional hydraulic braking.
 

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Tideland Prius said:
. . . Note for the new 2008 E-Class, they're dropping it in favour of conventional hydraulic braking.
So does that mean they failed at the marketing push? Or did they come across technical problems?
 

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That I'm not sure but I'm guessing the latter. They have been experience some problems, mostly to do with the jerk since it's supposed to help remove that spring rebound at the end of a stop but yeah, either people forget and lift off like they normally would near a end of a stop to reduce the front spring rebound motion and the sensobrake thing gets confused or the sensobrake's application isn't as linear as some would like it (I guess similar to our regenerative brake feel of the Classic Prius).
 

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EWB Brake by wire!

As nice as it may seem, I do not think it will happen!

One reason, if you lose 12 volt power you lose your brakeing system.

Now someone is going to say, "We will make it fail safe, if power goes out the brakes come on full force" Right if it happens on the freeway the person gets rear ended and lawsuit.

Same reason brake cables are still installed on most cars and trucks, a backup system.

I work for a airline fixing airplanes, they still use fluid brake systems at
3000 PSI. Aircraft started this whole fly by wire thing and how many years later I am still mounting 400 lb brake on an axle or 200 lb if its carbon fiber.

PS: The fly by wire on aircraft is just for control of the flight contol surfaces, it still fluid that moves them.
 

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Re: EWB Brake by wire!

Paul H said:
As nice as it may seem, I do not think it will happen!

One reason, if you lose 12 volt power you lose your brakeing system.

Now someone is going to say, "We will make it fail safe, if power goes out the brakes come on full force" Right if it happens on the freeway the person gets rear ended and lawsuit.

Same reason brake cables are still installed on most cars and trucks, a backup system.

I work for a airline fixing airplanes, they still use fluid brake systems at
3000 PSI. Aircraft started this whole fly by wire thing and how many years later I am still mounting 400 lb brake on an axle or 200 lb if its carbon fiber.

PS: The fly by wire on aircraft is just for control of the flight contol surfaces, it still fluid that moves them.
Prius uses a capacitor system as one of it's rundunancies for brake back-up. No reason something like that couldn't be integrated into a brake-by-wire system.
 

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Tideland Prius said:
But Mercedes-Benz already has Brake By-Wire on some of their high end models. It's dubbed SensoBrake (or sth along that line). Note for the new 2008 E-Class, they're dropping it in favour of conventional hydraulic braking.
Not quite(from Mercedes site):
Sensotronic brakes:
SBC™, the world´s first ever electro-hydraulic braking system, was conceived and developed by Mercedes-Benz. SBC™ (Sensotronic Brake Control) comes as standard on every E-Class. This revolutionary system has set new safety standards and improved stopping distances by monitoring and calculating the pressure necessary to stop each separate wheel. Electronic sensors ´feel´ your foot on the brakes and transmit the data to the braking system´s computer. SBC™ works in conjunction with the Electronic Stability Programme (ESP®) and Anti-lock Braking System.


This actually sounds a lot more like the Prius system, electically controlled/monitored hydrolic braking. There's still a hydrolic/mechanical brake just with advanced electonic control and monitoring.
 

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NEWSFLASH! The Prius brake system IS brake by wire, with hydraulic-mechanical backup.

Under normal conditions, the car senses the brake pedal position and speed of movement, and determines your intended brake needs. This is fed to the SKID ECU. Then, it asks the HV ECU for regenerative braking. The HV responds on how much braking it can actually deliver, and the SKID ECU applies the hydraulic brakes for the difference if needed. If it is detected that ABS control is needed, then regen is discontinued, and the SKID ECU applies the brakes hydraulically as appropriate.

Under the normal conditions, you do operate the master cylinder, but it is cut off from the rest of the hydraulic sustem. It is connected to a stroke simulator, to give you that hydraulic feel. In this state, you do not have any direct hydraulic connection from your foot to the wheels.

A pump provides hydraulic high pressure in an accumulator, and valves control how much pressure gets to the wheels, and another set of valves relieves the wheel cylinder pressures as appropriate.
Ever notice the hissing sound a few minutes after shutting of the car, followed by motorboat kind of noise? That's the brake system cycling by relieving brake pressure, then re-establishing the pressure. I guess that's how it attempts to bleed the brakes.

The car as 3 fail-safe backup systems. First, it has a capacitor power backup should there be a 12V supply failure.
2nd, if the automated hydraulic system or ECU should fail, valves would connect the master cylinder directly to the front wheel cylinders and cut off the stroke simulator. The hydraulics would be in this state in a power off state. I have a post somewhere on PriusOnline diagraming this mode.
Finally, you have the parking/emergency brake which has a cable linkage to the brake shoes in the rear, like all other cars have.
 

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Ah ha! Thanks doc!

But then this statement here: "Electronic sensors ´feel´ your foot on the brakes and transmit the data to the braking system´s computer"

That means it's brake by-wire right? I think when they mean electro-hydraulic they mean the whole system including the backup system (which is, of course, hydraulic).


So Dan, is that confirmed? Have we finally solved the mystery of whether our braking system is by-wire?
 

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I think the thing here is that the original system describes a pure (100%) 'by wire' system that employs a unique system for braking at the wheel itself.

The Mercedes system, if I read the paragraph correctly, uses electrical input from the pedal sensor to determine how best to activate the hydrolic brakes...but they're still hydrolic from the master cylinder to the brakes. I'm quite certain there is a mechanical back-up as well.

Prius is similar to the Mercedes in that it uses primarily 'by-wire' electrical control to determine whether to use regenerative braking, hydrolic braking or both under normal conditions. It uses the capacitor system as a back-up and then full hydrolic as a final fail-safe (better explained by Dan above).

But, ultimately, the actual control of brake pressure is by wire in Prius.
 

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so you're saying it's a quasi or partial by wire setup?

But I thought by wire is by using electronic chips e.g. drive-by-wire uses a sensor which is relayed to a receiver near the throttle body and tells it how much to open depending on pedal travel.
 
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