Recently, when I had dinner with friends, I talked about the runaway problem of some electric vehicles. Especially after Tesla's premiums doubled at the end of last year, this topic seems to have shown no signs of stopping the debate. In fact, what I want to say is that regarding the ins and outs of each accident, we will take the official investigation as the standard, and we will not speculate. But domestic car friends are very curious, why is there so many suspected out-of-control cases in Tesla?
Many people have thought of Tesla's proud "single-pedal" system. ----------------- Acceleration and deceleration are all done by the accelerator pedal (called the habit of being called this, which is easy for everyone to understand), and only when you need to brake sharply, you need to move your foot to the brake pedal. But if the owner of the car used to be a fuel car driver, will he encounter an unexpected situation and use the throttle as a brake when he is nervous?
Why don't Toyota, Honda, Volkswagen and the like like like the "single pedal"? Today I will explain Tesla's "single pedal" once and for all! First of all, whether it is a "single pedal" or not, the essence is "energy recovery". So how do electric vehicles do energy recovery, and why do they need energy recovery? Let's start with the most basics!
The essence of the "single pedal" is "energy recovery"
When the car is downhill for a long time, or when it is a long distance, we want the speed to become slower and slower, so we need to gently step on the brake pedal to control the speed. But if the vehicle has an "energy recovery" function, perhaps we don't need to slam on the brakes: when the accelerator pedal is released, the vehicle slowly slows down on its own.
Regarding the principle of "energy recovery", it is very clearly discussed in the undergraduate textbook "Electrical Engineering": it is nothing more than the "regenerative braking" working conditions in the "Motor 4 Quadrant", which is not complicated at all and not mysterious. In the most understandable words: "the motor becomes a generator". This creates resistance (with resistance, the speed is naturally controlled), and at the same time, it can generate electricity and charge the battery pack so that energy is not wasted.
RBS system: Parallel brake recovery system
Operating habits are similar to those of fuel vehicles
However, the efficiency of energy recovery is low
Therefore, serious electric vehicles have "energy recovery". At the beginning, the energy recovery system adopted by the majority of car companies was called the RBS system. We have said before, I don't know if the friends remember? It is "designing energy recovery on the brake pedal". After the driver releases the accelerator pedal, the vehicle is in a "neutral taxiing" state, and if the driver wants to control the speed or slow down, he will step on the brake pedal.
The brake pedal is equivalent to an "energy recovery switch", as long as the brake is stepped on, the energy recovery is activated (as for the strength of the recovery, it is not adjustable). Want to control the size of the brake deceleration force? It's simple: control the depth of the brake pedal! Because the more you pedal, the stronger the "mechanical brake" (like a conventional fuel vehicle).
The RBS system solves the "adaptation problem of fuel car drivers switching to trams", but the effect of power saving is much worse than that of "single pedal". One is that the intensity of energy recovery is not adjustable, and the other is that the efficiency of this energy recovery is low (if you want to be efficient, mechanical braking is best not to intervene, all rely on the motor to recover energy)
Therefore, from the perspective of energy consumption, although the RBS system can satisfy the drivers of traditional fuel vehicles, the energy saving effect is not ideal. So later ,TechNiksan had a sudden idea: Since the RBS system is "designed on the brake pedal", what will be the result if we "design the energy recovery on the accelerator pedal"?
"Single pedal" system: Throttle controls energy recovery
The recycling efficiency is extremely high
But the operating habits are diametrically opposed to those of fuel vehicles
Thus the famous "single pedal" system was introduced! In fact, the essential principle of "single pedal" is to "design energy recovery on the accelerator pedal". Whether energy recovery is required or not, how much energy is recovered, all depends on the depth of the throttle to decide!
When the vehicle needs to slow down (non-sharp braking), the driver only needs to release the accelerator pedal a little accordingly. Slightly loosen a little, the speed of the car drops slightly, and then stabilizes; completely released, the speed is significantly reduced (there is a significant slowdown feeling).
The "single pedal" system does not require the driver to step on the brakes, so when the energy is recovered, 100% of the motors are responsible for energy harvesting, so the efficiency is super high! In addition, compared to the right foot moving back and forth between pedals, the subtle control accuracy of the "single pedal" is much higher (reducing ineffective operation), so the energy consumption management and control effect of the "single pedal" vehicle is good.
However, the "single pedal" does not conform to the operating habits of traditional fuel vehicles after all, and we cannot deny that once an emergency is encountered, the driver may have a situation of "dead pedaling the brakes and not releasing". Unless the first car in life is a "single-pedal" electric car, there is really no guarantee that there will be no misoperation.
CRBS system: cooperative regenerative braking
High efficiency + good adaptability to operating habits
So the latest energy recovery system, the CRBS system, came into being! The full name of the CRBS system is "collaborative regenerative braking system", which we can basically understand as an "upgrade of the RBS system". It is no longer the recovery of motor energy, and the traditional mechanical brake "overlapped together", but can be intelligently distributed.
We know that the higher the speed, the more efficient the energy recovery, and vice versa. Therefore, when the speed is high, the motor energy recovery should be the main one, and the mechanical brake should be the main one at low speed. Only by cooperating and cooperating with each other can we achieve the most perfect brake match. ——When the speed of the car is fast, the brake is mainly based on motor energy recovery, supplemented by mechanical braking; when the speed is slow, the brake is mainly mechanical braking, and the motor energy recovery is supplemented.
Although the CRBS system is theoretically less efficient than that of the "single pedal", the actual gap is not large, and it perfectly solves the adaptation problem of the traditional owner, which is very easy to get started. So in theory, the most powerful and reasonable braking system for electric vehicles at present is the CRBS system, and it can even be said that all electric vehicles are equipped with CRBS systems as standard!
Tesla hardware has CRBS capability
But it looks like it should not be enabled
But as for why Tesla does not use CRBS, we do not know, many media say that Tesla is to save costs, but the truth is not so. Because Tesla is currently using the Bosch iBooster2 brake master pump, matching the latest Bosch ESP 9.3 system, from the hardware point of view, it already has CRBS function!
That is to say, as long as Tesla is willing, it can turn on the CRBS function at any time! Therefore, the reason why Tesla chose "single pedal" is even more strange, at least it is impossible to explain with the author's knowledge accumulation. Perhaps only tesla's calibration engineering team knows the real answer.