Climbing the wild hill is an SUV that I want to challenge.
But not all SUVs with four-wheel drive have a good ability to climb hills.
This is related to the four-wheel drive system of the model. How much does the four-wheel drive system do for hill climbing and vehicle handling?
The four-wheel drive system, as the name suggests, is to transmit the power of the engine to all four wheels, which sounds very simple, as long as the transmission system is added to the gear, add a point to the drive shaft can be done.
Just like the four-wheel drive car played as a child, a transfer device and a drive shaft can transmit power to the front wheel, the structure is very simple, of course, the earliest car with four-wheel drive system, but also a little more complicated.
Willis Jeep, who carried beautiful soldiers during World War II, was one of the originators of the four-wheel drive system, and unlike the four-wheel drive, a central differential was added between the two axles, and its power distribution ratio was fixed at 50:50 front and rear. This is the most primitive four-wheel drive system.
However, the four-wheel drive system is only used in off-road state or low grip state to get out of trouble and enhance traction. In ordinary road driving, maintaining the four-wheel drive state for a long time will reduce the driving efficiency and cause fuel consumption to rise. For example, The small body of Jimney with a 1.3L engine can also run out of 100 kilometers and 13L of fuel consumption.
Therefore, a variety of part-time four-wheel drive systems have gradually emerged with the development of technology.
Evolving from the full-time four-wheel drive, the driver can choose between two-wheel drive, low-speed four-wheel drive and high-speed four-wheel drive through the joystick of the transfer case (above) when parking. Because it is a pure mechanical meshing structure, its reliability is very high, and it is still the choice of mainstream hardcore off-road vehicle four-wheel drive systems such as Pajero and LC series.
In the four-wheel drive system that is not used for off-road, the structure is very diverse.
In the automatic transmission, the planetary gear structure has always been the most core structure, which can achieve the role of adjusting the front and rear power distribution by adjusting the speed of the three components. Based on this, the Towson differential was born.
Relying on axial force self-locking, Towson differentials achieve excellent responsiveness, autonomous power distribution and reliability. For decades after that, the purely mechanically constructed Towson differential remained the soul of Audi's quattro four-wheel drive system until the quattro ultra replaced the Towson differential with an electrically controlled multi-chip clutch and a dental clutch.
But when it comes to multi-piece clutches, this guy is a very important part of many of the current timely four-wheel drive structures. So at this point, some people will definitely ask: What is the difference between time-sharing four-wheel drive and time-time four-wheel drive? It is very simple: time-sharing four-wheel drive requires manual control, mechanical hard connection; timely four-wheel drive system automatic control, many times soft connection.
The role of the multi-plate clutch is to automatically distribute power according to the speed difference between the front and rear wheels. At this time, it needs another right-hand man - silicone oil.
Silicone oil has a great feature, that is, the faster it is stirred, the more viscous it is, which is suitable for transmitting power through viscous silicone oil in the case of a relatively large speed difference.
When the silicone oil is added to the multi-plate clutch, when the front and rear wheel speed difference is not large, the silicone oil will not be stirred in the multi-chip clutch, so there will be no power transmission. But when one side of the wheel is idling, the speed difference between the front and rear wheels will appear, at which point the silicone oil will be stirred, become viscous, and then deliver power to the wheel without idling.
Such a timely four-wheel drive system has a simple structure, but because it is a flexible transmission of power, and it requires a large speed difference to respond, its response speed is relatively slow. If the multi-chip clutch wants to respond quickly, it is either electrically controlled or not used in a ratchet structure like the Toyota RAV4 Rongfang.
A purely mechanical all-wheel drive system, the quattro with towson differential should be considered the pinnacle. But the advent of electrification is changing all that. Toyota was the first of them to eat crabs.
On the square box MPV Noah/Voxy they just released, Toyota installed a rear axle drive motor for it, which has a maximum power of only 30 kW and a maximum torque of 84 Nm. Among the E-Four SUV models sold domestically, the rear axle motor power increased to 40-50kW, but it was still a drop in the bucket.
The small power of the Toyota E-Four rear axle motor is determined by the structure and principle of THS. In the THS system, the power generation power of the No. 1 motor is small, and part of the power generated is also allocated to the No. 2 motor. So the power of the E-Four rear axle motor is even smaller.
So the responsibility of this small motor is obvious. On low-grip pavement, the small motor can adjust the output power in time according to the road surface conditions and control the vehicle's action when cornering. On high-grip roads, small motors can also output power in the low-speed range to give the vehicle a faster start, and the working principle is still very similar to the timely four-wheel drive system.
If you want more power output from the rear axle motor, the hybrid system will develop in the direction of high-power generators and high-power batteries. In this regard, BYD's DM-i AWD is one of the representatives.
Dm-i's generator power and battery power are much larger than Toyota THS's, which means that the rear axle motor is also allocated much more power when driven than the E-Four rear axle motor.
In addition to the engine being directly connected at high speed cruise, at other times the DM-i AWD can be seen as a four-wheel drive extended range hybrid with an engine driven by two motors. So I'm not surprised that the Song PLUS DM-i AWD can achieve a zero-hundred-plus acceleration of 5.9s at full power. In my opinion, dm-i AWD is one of the few hybrid systems that can combine high performance, smoothness, low fuel consumption and low cost.
The four-wheel drive system with the front and rear dual large motors is faster than the mechanical four-wheel drive in acceleration and corner control, while the power comes more directly and roughly, and the freedom of power distribution is also greater. Therefore, in theory, the performance of the four-wheel drive system of pure electric vehicles is better in all aspects.
But in pure electric four-wheel drive systems, there are also many different solutions.
The mainstream solution is front and rear dual motors + front and rear independent electronic control differentials. But for models that pursue performance, adding more motors will have a bigger leap forward.
The active abandonment of the mechanical quattro system that has been cultivated for many years has made everyone see Audi's determination to transform electrification, and the solution that Audi came up with is the e-tron S of the front single motor + the rear double motor.
Combined, three induction asynchronous motors give the e-tron S a maximum power of 370 kW and a maximum torque of 973 Nm. But the power output of the explosion is obviously not the essence of this three-motor four-wheel drive system, and the rapid response and precise control like the mechanical quattro are.
The rear axle dual motors can produce torque differences of up to 2000 Nm and can respond within 4 milliseconds, quickly allowing the body to produce a corresponding pendulum torque. Although the e-tron S weighs up to 2.7 tons with the blessing of multiple motors and large batteries, it does not have the taste of high weight at all.
Having said all this, do you want a four-wheel drive system when buying a car?
In a word: look at the use environment and requirements.
If you live in the northeast and often have to face low temperature and low grip environments such as ice and frost, the four-wheel drive system is still very necessary. Even if it's a passive multi-piece four-wheel drive when it's right, or a "pseudo-four-wheel drive" like the Toyota E-Four, the power assigned to the rear axle can still help you get out of trouble in a critical moment.
But if you run asphalt roads every day in the south, you will not go to the wild to run mountains and deserts, and the extra mechanical transmission system or motor will probably become an unnecessary burden.
Of course, if the four-wheel drive system can provide better control, I still recommend that you choose it.