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"If you drive a single motor, you're embarrassed to say hello to people."
If the new version of "Big Shots" is remade in 2030, this line may be used. In the cognition of the fuel age, there has always been a deep-rooted after-driving cult. Even though the power of the car has improved over the years, the proportion of four-wheel drive under the high horsepower requirement has increased, but the status of the rear drive has not been shaken.
Four-wheel drive is more like another option than a rear-wheel drive. In terms of transmission efficiency, energy efficiency, fuel consumption, space weight, etc., the rear drive can still shout an advantage in me. At the top of the food chain, which has been light on performance, from the S600 to the Phantom to Mulsanne, it is all a back-end, and those top supercars that want both and want, the back-drive is always a little higher.
However, in the era of pure electricity, the situation may change, and the rear drive is becoming more and more like the label of the entry-level version of high-end models.
Weilai once said that it will never produce a single motor version, and the dual motor is the "bottom line" of high-end electric vehicles. Although the wording is somewhat fierce, it is not completely unreasonable: if the fuel vehicle rear drive and four-wheel drive have their own advantages and disadvantages, then the electric vehicle dual motor four-wheel drive has become a more ideal drive layout. The two used to occupy their respective positions, but now they are gradually rising and falling.
The motor is good, and the rear drive four-wheel drive knows
When people talk about the advantages of pure electricity, it is always indispensable to the liberation of the motor to the layout of the whole vehicle. The internal combustion engine is huge and bulky and carries a bunch of accessories, which need a whole cabin to accommodate and arrange; the mechanical transmission determines that if there is one more drive shaft, it must increase the weight and volume of the transmission shaft, the half shaft, etc., and more transmission loss.
The small size of the motor and the flexibility of the electric drive allow the electric vehicle to freely choose any drive layout, which is a solid good news for the rear drive and four wheel drive that need to invest more cost and sacrifice more practicality on the original fuel vehicle. In practice, you will also find that the threshold for choosing a rear-drive electric vehicle today is much lower overall than that of a rear-drive fuel vehicle (see ID.3).
But this is the reason alone, it can't explain why today's high-end electric vehicles have chosen dual-motor four-wheel drive - and there are few full-line rear-drive or high-power rear-axle single motors. For high-end electric vehicles, the rear-drive version is just to pull down the bar. The rear drive has become synonymous with low-quality, and the so-called "big super" of the fuel era is no longer popular.
Electric motors do bring flexible layout advantages, but four-wheel drive has become the mainstream of high-end pure electricity, not only because of the small size and flexibility of the motor.
The four-wheel drive temptation with big benefits and small costs
To achieve four-wheel drive in fuel vehicles, it is far from enough to "connect the wheels with a drive shaft". Because as long as the vehicle needs to be steered, the wheels must be able to rotate at different speeds, which requires the addition of a differential between the left and right wheels of the drive shaft. When both axles become drive shafts, the required differentials change from one to three (between the front axle wheels, between the rear axle wheels, between the front and rear axles).
This is only the first step. Ordinary open differential, when a wheel skidding will transfer most of the power to the sliding wheel, popularly speaking, it is "where it is easy to turn, go to where you go". It's even harder to accept for a four-wheel drive model, and you don't want one of the four wheels to get mud and slip wildly, and the other three wheels don't work.
What's more, the significance of the four wheel drive is not only "to make all four wheels 'can' have power", but also "when some of the four wheels slip, the remaining wheels can continue to work, and it is even best to help the top shift". To achieve this, differential devices with limited slip capacity, such as limited slip differentials and multi-plate clutches, are required. When a wheel loses grip, the power of the remaining wheels is effectively released, and even the power of the slippery wheel is magically transferred to the past.
Nissan GT-R, crazy front-engine rear-mounted transmission four-wheel drive, two drive shafts
Due to the difference in the type of differential between the center/front and rear axles, and because of the difference in the physical characteristics of each type of differential mechanism, the so-called full-time four-wheel drive and the timely four-wheel drive two major types have been formed. Instead of using a central differential and using a connectable, disconnectable transfer case, the so-called time-sharing four-wheel drive is formed, because it lacks the differential function between the front and rear axles, and they can only enter the four-wheel drive in the mud and snow without considering the difference problem.
If these do not understand in fact, it does not matter, here is just to say: mechanical transmission is a troublesome thing, fuel vehicles to do four-wheel drive is very troublesome, to get excellent four-wheel drive system is more troublesome.
Therefore, for electric vehicles, the front and rear axle motors form a four-wheel drive, eliminating not only a central drive shaft, but also the central differential, which is a core component that is crucial for mechanical four-wheel drive. The front and rear axle dynamics have been completely separated physically, and naturally there is no longer a need for any type of central differential mechanism, and there is no longer any need to consider what kind of differential device with limited slip capacity to use.
In the early years, overseas media compared the ability of the Model 3 and audi A5 Quattro to get out of the pulley group. Although it must be noted that the Quattro on the A5 is not a four-wheel drive system for getting out of trouble, the actual performance of the two proves the ability of the motor four-wheel drive. The front and rear axles are completely independent, without the need for any high-performance central differential, and it is easy to achieve similar or even better four-wheel drive sliding restriction effects. (Of course, take into account the advantages of the instantaneous high torque of the motor.) ）
If you ignore the difference in the output characteristics of the fuel engine and the motor, you may wish to think of the dual-motor four-wheel drive as a fuel vehicle with an internal combustion engine in front and behind it - naturally it is easy to achieve better four-wheel drive capabilities.
The electric vehicle's front and rear axle dual motors form a four-wheel drive, which not only replaces the mechanical four-wheel drive system of fuel vehicles, but also is almost equivalent to the "impossible layout" of an internal combustion engine in front and rear. The cost? Compared with fuel vehicles, the weight of an electric motor may not exceed a complete set of four-wheel drive weight gain; the demand for supply chains and production lines is far less than that of fuel vehicles to increase four-wheel drive models.
As for cost and battery life, don't forget that we are talking about the superstructure of the high-end market right now. The increased endurance due to reduced performance doesn't make much sense here, just as Rolls-Royce doesn't give the Phantom all-wheel drive system or considers weight savings and fuel savings.
Power Under Control
The era of fuel vehicles has come to this day, and four-wheel drive has a more mainstream trend, because the overall power level of the car is improving. With the blessing of turbo and hybrid, today's high-end fuel vehicles can easily have the powerful power that the original V8 and V12 engines can provide, and the rear drive has signs of "can't stand up".
Against this backdrop, high-performance first-class models are more widely used in all-wheel drive. While Rolls-Royce insisted that the Phantom remain rear-wheel drive, the smaller Gust was already four-wheel drive; the Mercedes-Benz S600 and S680 had always been pure rear-drive, while the S500 under it was equipped with a 4MATIC as standard. These "normal" luxury cars, which need to consider driving performance, have a hard time leaving the traction of all four tires.
This problem is exacerbated by pure electric drives, because the working principle is different, and in theory, the motor can get an instant maximum torque at any time, without waiting for the speed of the combustion engine to climb high to reach the peak. Such characteristics give more pressure to the traditional rear drive, when the vehicle needs a higher power level, the more part of the front axle, the front motor has become a general choice.
Current motors, on the other hand, are heavier and sometimes even require adjustments to the suspension structure.
Nio used the first five-link suspension for the first time on ET7, and the later ET5 continued to use it, indicating that this high probability will become the standard configuration of WEIlai in the future. Compared with the traditional double wishbone structure that ES8 and ES6 have been using, the main pin offset distance after changing to the front five-link structure is smaller, the inclination angle of the main pin is smaller, and the adaptability and control ability of high-power front axle power is stronger.
Note that the upper wishbone is split into two connecting rods, which is ET5
Behind the change is a change in the power system. ES6, ET7 and ET5 all use the power configuration of the front permanent magnet and the rear asynchronous motor, so the daily use of the front permanent magnet motor with better energy efficiency is used. But starting with ET7, the front motor power has been increased from 160kW to 180kW in the ES6, which is just near the "forbidden area" of traditional front-drive vehicles.
The experience of the fuel small steel gun era tells us that the current driving power reaches about 200kW, and it is easy to adapt to the high power of the front axle. Weilai changed the front suspension structure to a five-link structure, which should consider making the front motor power more fully meet the daily driving and reduce the need for rear motor intervention. From this action, it can be seen that its idea of rejecting a single motor rear drive is serious.
In order to protect the environment, add an extra motor
Another symbolic regret of rear-drive electric vehicles is kinetic energy recovery. Because the load shifts forward as the vehicle brakes, the braking pressure on the front wheels is greater (so the front discs tend to be larger than the rear discs). Therefore, when the motor is used to reverse the braking energy, the energy contained in the front wheel is significantly more than that of the rear wheel. For models with only a single motor on the rear axle, the maximum amount of energy recovered will be less than that of the front motor.
It is also for this reason that the Volkswagen MEB platform can change the rear brakes to drums, but never dare to make any changes to the front wheels. And in the new front-drive MEB configuration, although the pricing is more low-end and cheap, the front-drive MEB is replaced by a disc brake in the rear rotation, because the rear axle no longer has a motor to recover kinetic energy, and it can no longer help the mechanical brake to share the braking pressure.
Of course, the energy that electric vehicles can actually recycle is not a large part in itself, and the difference between the upper limit of the energy limit of the front and rear axles is even smaller. But not necessarily for the actual effect of the calculation, compared with the single motor rear drive, kinetic energy recovery in the front axle is ultimately able to make fuller use of energy, indicating that the dual motor with the front motor is a more comprehensive layout.
The root of the belief in the "rear drive first" in the era of fuel vehicles is that the rear drive has long been the most ideal driving form for fuel vehicles. Even if this status has gradually been gradually approached by four-wheel drive in recent years, the two have not reached the point of status exchange. However, for electric vehicles, with the flexible distribution of the power unit between the front and rear axles (motors), the rear drive no longer has a significant advantage other than cost over the dual motor four-wheel drive.
When the electric era in which the front and rear motors are the best layout for the four-wheel drive, the rear-drive electric vehicles will still occupy a piece of the market, but the pursuit of rear-wheel drive may be far away.