Newsweek Article on Drive by Wire.

Is it Prius is drive by wire correct?
So these "steer by wire has safety future?? Incase car computer has own its mind

 

yes the Prius does have steer by wire. that is one of the reasons why the steering is a bit sensitive.

whats even more impressive is some of the cars being tested in CA right now that has electronic lane sensing equipment that will sound a warning when you are about to travel outside your lane.

Infiniti will introduce a "lane departure" warning system that can "see" the road and warn the driver before he actually crosses the line.

other cars will have technology that will correct the steering if there is no response to the alarm.

 

bummer, i was under the impression that the whole car was drive by wire.

 

It's the Toyota hybrid prototype supercar that has drive-by-wire steering. I recall an article describing the ability to physically move the steering wheel to any one of 3 front seat positions. As for the pedals, I don't know if all 3 front seats are pre-equipped with break/gas pedals or not.

 

<div class='quotetop'>QUOTE(DaveinOlyWA\";p=\"46107)</div>

Please note that the brake is also not drive by wire.

Regards,
Ken@Japan

 

There are definitely mechanical brakes and they do need brake fluid However that does not NECESSARILY preclude brake by wire. "by wire" simply means there isn't a mechanical connection between the "user input" and the device being actuated. A computer reads the input and controls the device. You COULD have a nothing but a little joystick that you push, the computer could read the pressure and it could actuate the mechanical brakes. Serious safety issue though. If the computer crashed, so would you.

The Prius brakes are pressure sensitive, meaning push a little (above 8 MPH) and the braking is done by the electric motor, not the brake pads. No hydraulics involved. Stomp on them, and at 8 MPH or lower, the mechanical brakes WILL be used. So, there is AT LEAST a direct mechanical (brake fluid) connection between the brake pedal and the pads.

My conjecture - the amount of brake pedal pressure is read by the computer (direct at the pedal or in the master cylinder??) and before there is enough pressure to force the pads to the discs/drums, the electric motor slows the car.

 

wait a second....

i think we are being misguided by terminology.

if the brakes are "electric assist" that is drive by wire by any definition i know of.

yes the brakes are hydralic as all brakes are. but normal brakes when depressed has a mechanical arm that controls a lever that controls a hydraulic value that controls the brakes.

drive by wire is a brake pedal that controls an electronic actuator that feeds back to a computer that controls a valve that controls the hydaulic lever that controls the brakes.

in the Prius, you have a computer that decides what method will be used to stop the car and how much of that method will be employed and its controlled by how fast you are going and how fast and how hard you hit the pedal. no mechanical system can do that.

so its drive by wire in my book.

and another thing, when was Newsweek made the de facto standard for accurate reporting?? when is the last time you read an article concerning the Prius that was 100% accurate??

dont believe everything you read

 

You're all correct. With the exception of the steering which is mechanically linked, the car is throttle, shift, and brake by wire. Making it virtually a drive-by-wire vehicle. Toyota did their homework on this vehicle. The Doc is correct on his statement on the multiple back-up systems built into this vehicle. I'm sure that a vehicle with a single point of failure would never have made it past the Toyota legal department, let alone the engineers.

 

Breaking is usualy done by wire. The signal goes from the break pedal stroke system to the skid control ECU. This determines how much braking force the driver wants, and calculated a renegerative force value which is then transmitted to the HV ECU, which does the regenerative braking. The skid control ECU gets the acutal regenerative brake force value back from the HV ECU. Then it controls the solenoid vales to generate the hydraulic braking force value which is done by subtracting the generative brake force from the total brake force required by the driver.

Under certian circumstances, such as the break system stops or there is no accumlator pressure the skid control ECU opertaters is a fail-safe mode where the master cylinder solenoid valve in the brake actuator opens. This leads to a direct fluid passage between the master cylinder and the front wheel cylinders.

There is a power source backup unit incase the voltage of the car drops below 12V.

So the only things really directly connected is the stearing system and the parking brake.

One thing to think about drive by wire systems is what happens if your car malfunctions or shuts off while you are driving? You would have no control over where your car is going. This is the reason why even if they moved to drive by wire system, they would still need some sort of mechanical back up system.

 

Brakes are drive-by-wire. Brake pedal position is sensed electronically. ALSO, you are pushing on the master brake cylindar, but normally valves have it isolated from the rest of the brake system. However, not only is the brake pedal position sensed, but so is the hydralic pressure you apply to the master cylinder.

Steering- there is a direct connection between steering wheel and drive wheels. You can turn the wheels with the car off.
However, as demonstrated by the auto-park system in other markets, the steering can and is turned by an electric motor as well. How much torque the motor applies is proportional to the torque you apply to the steering wheel. Supposedly that ratio is adjusted by vehicle speed.
So steering is assist, since there is a direct couple, but could just as well be drive-by-wire, as proven by the auto-park.

 

<div class='quotetop'>QUOTE(DaveinOlyWA\";p=\"46142)</div>

Let's define what the "by wire" is.

Throttle by wire:
Prius has only a throttle position sensor, no mechanical connection between the throttle pedal and the engine throttle valve. So, it is by-wire.

Shift by wire:
Prius has just a joy stick shift lever, no mechanical connection between the stick and the trans-axle. So it is by-wire.

Brake by wire???
Prius ECU controls the regenerating and hydraulic brakes.
However, there is an oil flow between the master cylinder and the wheels for backup purpose. My definition is it is not by-wire.

Regards,
Ken@Japan

 

airplanes have been doing it for years havent they?? or am i way off base? sure you must have back up systems, that is becoming standard throughout the industry. the same concerns were raised over anti lock brakes and those concerns were basically unnecessary and i believe these are too.

what are air bags? they are just backup safety measures to prevent injuries. sideair bags, triple backups, and the list will continue until nearly all fatal accidents are eliminated.

when it comes to lives, 99% dont cut it, and responsible auto manufacturers will have fail safe systems.

the Prius maybe one of the safest vehicles you have ever driven. its performance in various crash tests has proven that its a very safe car to drive.

having dual methods of stopping (that is if you dont count B mode) forces failures in two different systems for a catastrophic event.

is it a perfect solution? no, of course it isnt. no such thing in this world. but its a d**n good one i think. sure its possible you could be barrelling down a mountain, air conditioning cranking, stereo blasting, and headlights on highbeam (in case your traction battery is fully charged) with overheating brakes, but i wouldnt lose sleep worrying over the possibility.

 

on the toyota prototype, the brakes and trottles are motorcycle style controls and travel with the steering wheel