HenrikM76 skrev:Lucidor skrev:Nicke Nyfiken skrev:bylund skrev:Steer by wire är väl fortfarande väldigt ovanligt? Mest koncept som jag känner till.
Det finns inga serietillverkade bilar med steer by wire. Finns bara på långsamtgående fordon typ traktor och liknande, som inte får gå fortare än 45 km/h.
Infiniti Q50 har haft steer by wire sedan 2013.
Nja, inte i den mening att ratten inte alls är länkad mekaniskt till styrningen. Det Nissan, (Infinity), kallar "steer by wire" har fortfarande en mekanisk styrstång, men i normalfall så går en hjälpmotor in och underlättar styrningen och du kan även ge den olika styrprogram hur responsiv du vill den ska vara i form av medhjälp, feedback m.m. Se nedan:
Nej, det stämmer inte. Bilen har visserligen en rattstång, men den är mekaniskt frikopplad från hjulen vid normal körning. Det är först vid fel på det elektroniska styrsystemet som den kopplingen greppar. Se beskrivningen nedan.
Steer-by-Wire - Infiniti Q50 Direct Adaptive Steering (2013)
You might not notice, most of the driver controls of modern cars have been replaced with electronic ones or so-called "by-wire" controls, such as electronic throttle, electronic gearshift and brake-by-wire. This allows computer to intervene the controls to improve safety and driving precision. Moreover, it paves the way for the future semi or full autonomous driving. The last control to accept by-wire conversion is steering. There are 2 major hurdles steer-by-wire has to overcome: 1. The system shall be fault-proof to avoid accidents. Many legislations require a mechanical backup system to function in case of electronic or software failures. 2. Since the physical connection between steering wheel and front wheels no longer exists, the steer-by-wire system should be able to generate artificial feedback to the driver, otherwise the driving experience would be as unreal as playing video games.
In 2013, Nissan's Infiniti Q50 became the first production car to employ steer-by-wire technology. Its DAS (Direct Adaptive Steering) system consists of the following parts:
How does it work?
1. The steering wheel sensor detects the steering angle and torque applied by the driver, then tells the ECU.
2. ECU takes also other parameters, such as speed and vehicle stability into account to determine the amount of steering needed.
3. Two assist motors at the steering rack actuate the steering according to the command of ECU.
4. ECU tells the steering wheel motor to generate resistance as a feedback to the driver.
How to avoid system failure?
1. The ECU actually consists of 3 individual ECUs doing the same computation in parallel. Their results will be compared before sending out commands. In case one of them fails, its result will be different from the other two, thus the system will adopt the result of the other two.
2. What if 2 of them or all of them fail? The system will activate the clutch and revert to mechanical steering connection. Since the clutch opens only when energized, in case of electronics failure or engine shutdown the clutch will close automatically.
What is the benefit of DAS?
Firstly, it allows the steering to be fully variable, no matter ratio or assistance, and the adjustment range could be widened as it is no longer limited by mechanical design. Secondly, the complete separation of steering rack from the steering wheel means the latter is no longer troubled by steering kickback or vibration, so the car can mount the steering rack rigidly to the chassis without using rubber bushings. This minimizes slack thus speeds up steering response and improves precision. Thirdly, steer-by-wire allows more parameters to be taken into consideration. For example, ECU can adjust the steering angle to offset the influence of bump steer, road camber or side wind. Lastly but not least, although this function is not yet available to Infiniti Q50, it is compatible with autonomous driving technology. The computer may simply use it to drive or park the car by itself without the intervention of human.
And the drawback?
Feel, or the lack of it. The DAS uses a simple motor to generate resistance back to the driver's hand. Judging from its actual performance on Q50, it is obviously not up to the job to mimic the feedback of conventional steering. Without a direct connection to the rack, in principle it is impossible to deliver the tactile feedback of a good steering, because the motor cannot generate kickback and small vibration which are also vital to know what's going on at the front wheels. Another drawback is the additional costs, especially the need for 3 powerful ECUs. That is probably why other manufacturers are reluctant to introduce steer-by-wire.