Theory + practice, easy to understand the principle, simple to understand, reasonable.
This year's winter snow came early and fell heavily, and the usually unknown four-wheel drive vehicles immediately showed a chic posture.
Everyone knows the invincible existence of the Audi quattro four-wheel drive, so do you know what are the characteristics of the Mercedes-Benz 4matic and the BMW XDRIVE four-wheel drive in the German three masters?
Four-wheel drive not only has advantages in this kind of ice and snow road, but also has advantages in daily driving in medium and high-speed cornering, driving on slippery roads, and general escape scenarios.
In fact, Audi quattro, Mercedes-Benz 4matic, BMW xdrive, are all their own four-wheel drive, in the final analysis, are a combination of those methods. Moreover, there are several four-wheel drive structures under each brand, which are used in different car series.
To understand four-wheel drive, today I will teach you the easiest way to understand, which is to put the core of cognition on the differential, especially the ** differential, followed by the differential of the left and right wheels.
*The differential connects and balances the power of the front and rear axles, which needs to solve the wheel speed difference between the front and rear wheels, and at the same time can lock on the spot when one side slips. How to strike a balance between these two aspects represents its technical capabilities.
The front or rear axle differential balances the power of the left and right drive wheels.
AudiquattroThe originator of the most powerful mechanical four-wheel driveBut it is also changing to electronic control
When it comes to mechanical full-time four-wheel drive, the quattro is the undeserved originator. But now the quattro has ditched the Torsen mechanical differential in favor of an electrically controlled multi-plate clutch limited-slip differential.
The Audi quattro all-wheel drive system** differential, which was a mechanically self-locking Torsen differential in the early days, has a flexible torque distribution between the front and rear axles. The one-way power transmission of this structure makes the Torsen A-** differential have a self-locking function, normally distributing 50:50 power, and when the tires slip, the power is distributed to the wheels with better grip at that time to get out of trouble.
This purely mechanical Torsen differential has the following characteristics, the first is reliable, and the failure rate is extremely low. The second is extremely fast, as long as there is a slippage, it will have an immediate effect, the third is the torque that can be transmitted, and the fourth is extremely stable and reliable.
In 2006, the fifth-generation Quattro system with a next-generation Torsen** differential equipped with Type "C" was introduced. The Torsen C is not actually the early worm gear type that everyone talks about, but a planetary gear differential with friction discs that can mechanically lock itself. Torsen Type C is mainly used on the Q7 Q5.
In 2010, it was replaced with a crown gear ** differential, which is small in size and light in weight, and the power of the front wheels is automatically distributed between 15% and 70%, and the power of the rear wheels is automatically distributed between 30% and 85%, which is powerful, which is also a four-wheel drive system that focuses on road driving.
In 2016, Audi integrated Ultra technology into quattro technology to significantly improve fuel economy. The Quattro Ultra intelligent all-wheel drive system is better suited for the on-road performance needs of daily commuting. The biggest change is that the ** differential is already a crown gear differential with a multi-plate clutch, and this method is also used in the Mercedes-Benz 4matic, which is a bit able to adjust the front and rear power output ratio in a timely manner.
The average fuel consumption of the intelligent four-wheel drive system per 100 kilometers is 0 less than that of the conventional quattro system3L, the weight of the system is almost 4 kg less than that of the previous generation (8.).8 pounds). This also contributes to lower fuel consumption and improved handling.
In the event of an emergency, the Quattro Ultra intelligent all-wheel drive system can transfer up to 100% of the power to the front or rear axle, which has a stronger ability to get out of trouble.
It has been iterated, but when full-time drive is required, the capability is now stronger than that of the purely mechanical four-wheel drive quattro of the past.
Many riders think that the quattro without Thorsen has no soul, which is a matter of opinion.
Torsen differentials also have their own disadvantages, the power of the front and rear axles can only be controlled according to the mechanical passive program, but can not actively control the power distribution of the front and rear axles.
Mercedes4maticSmooth and efficientFuel efficient
Mercedes-Benz 4matic** differential is a set of combinations, and the planetary gear structure is used to solve the differential, which is smooth and reliable. However, this mechanical differential itself does not have a limited slip lock function, and if you want to lock it, you need to add a set of electronically controlled multi-plate clutches to complete it.
There are two types of differentials in the 4matic system**, the planetary differential is used on the C E S GLC class, the planetary carrier is the power input shaft, and the sun gear and ring gear correspond to the front and rear axle respectively.
By setting the diameter and number of teeth of the three, it is possible to distribute unequal torque and unequal power between the front and rear axles (the legendary torque of 45:55).
The second is the crown gear planetary differential on the GLE GLS (which is the kind of ordinary front and rear axle between wheels) that evenly distributes the power between the front and rear axles, which is characterized by the ability to adjust the front and rear power distribution at the right time.
Both kinds of mid-range can smoothly digest the speed difference between the front and rear axles, and there is no overheating, but they do not have a limited-slip function themselves, and they need to rely on a multi-plate clutch to lock the mid-difference.
4matic is lightweight, down to 66-70 kg;The second is good fuel economy, comfort and safety in the passive state.
BMWxdrive: Simple and efficient
The BMW xDrive is the only four-wheel drive among the three luxury brands that does not have a mechanical ** differential, and its ** differential uses an electronically controlled multi-plate clutch limited-slip differential from the beginning. That is, the kind of structure used in the timely four-wheel drive, but with stronger performance.
The xdrive's over-reliance on electronic systems and its poor tolerance to high-intensity and frequent rev differences have led to poor off-road durability for the BMW xdrive, and BMW's four-wheel drive system is also the most expensive to repair.
However, the xdrive has the advantages of simple structure, light weight and high efficiency, which makes it suitable for urban conditions.
The BMW XDRIVE four-wheel drive structure is closer to the timely four-wheel drive of urban SUVs, and the passability is not as good as that of Audi and Mercedes-Benz.
Left and right wheel differentialsDifferent
The core of the four-wheel drive is the ** differential, but the differential control of the left and right wheels of the drive shaft is also important for the four-wheel drive.
It's not just about getting out of trouble, it gives the outside wheels more drive force than the inside wheels when cornering at high speeds, which improves cornering precision and makes handling better.
The difference in the distribution of drive force between the inner and outer wheels when cornering improves handling.
On discontinuous surfaces (e.g. intermittent snow and ice roads), power loss from the skidded wheels can be limited instantly, and power can be given to the side with adhesion.
The power flow of a normal open differential is through the planets in turn to the two halves, and if it slips, it is wasted.
In the past, these brands have adopted the electronic brake slip method of the wheel. The principle is to use the automatic distribution of braking force of the ABS system. For example, if the ECU finds that one of your wheels is slipping, then the ECU will issue a command to start using ABS to brake the skidded wheels, and the open differential will naturally transmit power to the wheels that are not slipping.
This method is also the way that urban SUVs adopt in a timely four-wheel drive, and the characteristic is that there is no need to increase costs, and only software is required. However, it should be noted that in continuous cornering and discontinuous road surfaces, the frequent power consumption is not a problem at low speeds when the braking system is hot, but there will be energy loss at high speeds.
As a result, these major brands have adopted electronically controlled limited-slip differentials on high-end models, which control the pressure of the clutch friction plates through the motor drive oil pump, thereby controlling the flow direction of power.
Both electro-hydraulic differentials and BBAs are BorgWarner products.
Wrapping up
Going back to the beginning sentence, there are at least two or three four-wheel drive structures under the four-wheel drive name of each brand, which are used in different levels of models. For example, Mercedes-Benz A-Class, Audi A3, BMW Mini and other transverse engine models, the three solutions are similar to the four-wheel drive solution, all of which are set up next to the gearbox to set up a PTU (Power TransferUnit) to transmit half of the power to the rear axle through the transmission shaft, and put a multi-plate clutch limited-slip differential before the rear axle, and control whether the rear axle obtains power through an electronically controlled or hydraulic actuator. The vast majority of urban SUVs such as Tiguan and CR-V are also arranged in this way, which is simple, light, and low-cost.
What we are talking about today is mainly the four-wheel drive technology with high technical content that represents their own characteristics under each brand.
Pay attention to Huage and bring you the correct car knowledge in an easy-to-understand way.
By the way, don't believe the girl who graduated from the 985 automobile major said that the engine oil can be changed for tens of thousands of kilometers, the transmission oil can never be changed, and the spark plug can be changed for 100,000 kilometers. Because she has never been engaged in repairs, everyone forgive her.
Although I graduated from 211 automobile, our professional course textbooks are from the 985 college, and the most important thing is that I have opened a car 4S shop for more than ten years, and I have actual after-sales maintenance service experience.