In order to ensure the safety of driving on this bad road, it is necessary for the vehicle chassis to have good handling stability, and the most important thing is the tires. Whether the vehicle can run stably on the road depends on the grip of the tire, which plays an important role on the snowy and muddy road, which is why the vehicle should be equipped with snow tires or snow chains in the northern snow and ice season. The remaining performance depends on the chassis and body structure, as well as the chassis electronic control system.
Of course, it is obviously not enough to equip vehicles with four suitable tires in the northern winter. Now it is never the basic function configuration that determines the quality of a car, but the function that can help or even save our lives at critical times. Just like active safety systems such as AEB (active braking) or lane keeping, although we seldom use them, they can save our lives at critical moments. The ultimate goal of a good car in safety design is to minimize or even completely kill Murphy's law of road safety accidents. Therefore, if a car wants to have good driving performance and safety on icy and muddy roads, it needs not only suitable tires, but also other excellent chassis structures and electronic control systems to deal with more than 70% accidents, such as the four-wheel drive system of the chassis.
What more security can an excellent four-wheel drive system provide for us on the snowy road?
Compared with the two-wheel drive system, the four-wheel drive system has obvious advantages in some specific road conditions, such as potholes, roads with different four-wheel adhesion and ramps. And the passing capacity of four-wheel drive models will be stronger. On general roads, it also has advantages in extreme performance, acceleration ability and cornering stability. These advantages of four-wheel drive system are also applicable to ice and snow roads, which have more complicated four-wheel attachment under different working conditions.
At present, four-wheel drive systems are mainly divided into three categories: part-time four-wheel drive, full-time four-wheel drive and timely four-wheel drive. From the point of view of intelligence, convenience and fuel economy, timely four-wheel drive is undoubtedly the first choice for most high-end cars. Here we can take Buick Angkewei, an excellent timely four-wheel drive system, as some examples of driving on ice and snow roads.
In order to make it easier for everyone to understand, we can first illustrate the characteristics of Angkeqi's timely four-wheel drive through this simple four-wheel drive configuration diagram. A clutch will be arranged between the front and rear axles of the traditional timely four-wheel drive system (right). The chassis electronic control system realizes the switching between two-wheel drive and four-wheel drive by controlling the combination and separation of clutches, and the representative models include Volkswagen Tiguan L. The clutch is disengaged, and the backward transmission of power is interrupted (the four-wheel drive of Tiguan L is not completely separated, and there is still about 5% power), and the vehicle becomes a "two-wheel drive" mode; The clutch is combined, and the power is evenly transmitted to the left and right rear wheels. At the moment, it is a four-wheel drive mode. When one side of the rear wheel slips, the rear axle differential is locked to ensure that the other wheel can still get 50% driving force.
Angkewei (left)' s timely four-wheel drive system is different from the traditional timely four-wheel drive system. The front and rear axles are connected by PTU, which can realize combination and complete separation, thus realizing the switch between two-wheel drive and four-wheel drive. The advantage of this design is that it can save more fuel in the two-wheel drive mode, and the fuel economy in this mode is equivalent to that in the two-wheel drive mode.
In addition, the biggest difference between it and the traditional timely four-wheel drive is that the rear axle of Angkor Wat has a differential assembly, and the clutches are installed on the left and right half shafts respectively. The advantage of this design is that the power can be transmitted to the two rear wheels independently, and because the two clutches work independently, the power transmitted to the left and right wheels can be distributed freely, and the continuous distribution of 0- 100% can be realized. This means that 100% power distribution can be obtained even if one wheel completely loses grip and the other wheel has grip. In addition, Buick Angkewei's four-wheel drive system has been fully developed in terms of software and hardware, and the torque capacity of the rear axle has increased by 20% compared with the previous generation, reaching 3000N.m, which is helpful to improve the acceleration and disengagement ability. Therefore, compared with the traditional timely four-wheel drive system such as Tiguan L, Angkewei's timely four-wheel drive system has better ability to get rid of difficulties, such as when three wheels are stuck at the same time.
Improve the climbing and extricating ability of ice and snow pavement.
The winter in the north is longer, and snow or ice on the road becomes the norm. When a two-wheel drive vehicle runs on the ice and snow road, the total driving force is the product of the single axle weight and the friction coefficient of the ice and snow ground, while the front axle load of the front drive vehicle is only 50%~60% of the vehicle weight, and the front and rear axle loads of the rear drive vehicle are basically 50% evenly distributed, so the maximum driving force of the two-wheel drive vehicle on the ice and snow road is only 50%~60% of that of the four-wheel drive vehicle. Therefore, compared with four-wheel drive vehicles, the ability of two-wheel drive vehicles to get rid of difficulties on ice and snow roads is obviously weaker than that of four-wheel drive vehicles, and this gap can be infinitely enlarged when climbing in snow or driving on ice.
Improve the stability of curve control and the limit speed of curve crossing.
If you turn or change lanes quickly on the icy road surface, the front-driven vehicle is easy to understeer and the vehicle is easy to slide out of the lane, while the rear-driven vehicle is easy to oversteer and flick its tail because of the low adhesion coefficient of the road surface.
And if equipped with Angkor Wat timely four-wheel drive system, when the vehicle enters the corner, the system actively distributes more torque to the outer wheel, improving steering response and reducing understeer; When cornering, more torque is distributed to the outer rear wheel in combination with the state of the vehicle and the driver's intention, so as to achieve better yaw control, help the vehicle cornering and keep the driver's cornering expectation, and reduce the possibility of oversteering; When cornering, the torque is evenly distributed on the rear axle, and when accelerating, the maximum traction is given to the vehicle under the condition of road adhesion. During the whole curve process, the four-wheel drive system makes the vehicle have better curve stability. At the same time, through the management of the torque output of one-sided tire, the sliding friction is reduced, the anti-skid limit of tire is improved, and the vehicle has the limit ability of cornering faster.
Of course, the improvement of the handling limit is not only the four-wheel drive and electronic control system, but also depends on the mechanical structure of the chassis, such as the influence of the mechanical structure and support of the front and rear suspensions on the vehicle power drive. Angkewei's rear suspension adopts a five-bar structure which is rare in its class. From the point of view of handling stability, compared with four-bar linkage and torsion beam, five-bar linkage can better decompose the mechanical performance requirements of vehicle driving dynamics on the chassis, provide better support for the vehicle, make the wheels obtain more reliable driving trajectory, effectively improve the proper contact between the wheels on both sides and the road surface under different road conditions, and strengthen the handling stability of the vehicle.
Angkewei's entire rear suspension adopts a "soft" connection scheme with the body. The bushing of the connecting rod filters the vibration transmitted by the tire end, and the connection between the subframe and the car body also adopts the bushing, which further filters the transmission of vibration from the wheel end to the car, and the vibration of the ground is filtered twice, greatly improving the riding comfort.
Improve driving stability under extreme road conditions.
When driving on snowy roads in winter, the road conditions that most easily make vehicles out of control are not driving in snow or on ice, but driving on one side of the road with ice or snow, and the other side is a well-paved road. This situation is more common on the road after snow in the north.
When the vehicle runs on such a road surface, the adhesion of the left and right wheels is different. As long as the vehicle accelerates slightly or brakes suddenly, the wheels with poor adhesion will slip and the wheels will "float". At this time, if the driver corrects the direction in a hurry, the two-wheel drive vehicle will have a high probability of sideslip or tail flick, and when the driver does not have excellent rescue ability at this time, the vehicle is likely to get out of control and cause an accident.
If the vehicle is equipped with a real-time four-wheel drive system such as Angkor, through the perfect matching with ESC and TCS, when the vehicle brakes or accelerates, the electronic control system can adjust the torque output of the front and rear unilateral wheels in real time by monitoring the adhesion of the wheels, reducing sliding friction, improving the grip between the wheels and the road surface, making the vehicle trajectory quickly corrected, reducing the possibility of vehicle sideslip, ensuring the vehicle to run more smoothly and reducing accidents.
Of course, the driving conditions on ice and snow roads are far more than those I listed. Therefore, when calibrating and adjusting the four-wheel drive system, the main engine factory will pull the vehicle to the northernmost winter experimental field in China, such as Hailar and Heihe, to verify the durability of various extreme ice and snow road conditions and the chassis driving stability of the vehicle under various extremely cold road conditions.
To sum up, from the driver's point of view, standardizing driving and controlling the speed are the keys to driving on ice and snow roads. From the performance of the vehicle itself, choosing suitable tires or installing snow chains is a prerequisite for travel, but if the vehicle has such an excellent timely four-wheel drive system as Angkewei, the driving safety and passenger capacity of the vehicle can be improved.
In addition, the excellent performance of the timely four-wheel drive system is not only reflected in the ice and snow road, but also gives the vehicle better off-road and acceleration ability on other roads, so engineers will train some specific driving modes for the four-wheel drive system. For example, Buick engineers set cruise mode, sport mode, four-wheel drive mode and off-road mode for Angkor's four-wheel drive system, which made the vehicle more fun to drive.
This article comes from car home, the author of the car manufacturer, and does not represent car home's position.