【 Figure 】 Experience of power distribution between rear axle wheels ZF four-wheel drive technology
[Technology] The system can always ensure the most effective distribution of vehicle power to the front and rear axle wheels, but its biggest problem is that there is a certain degree of mechanical friction loss, which is not conducive to improving vehicle fuel economy. Faced with this problem, ZF has developed a set of ECOnnect system that takes into account both fuel economy and four-wheel drive demand.
● Composition and structure of ECOnnect
ZF’s ECOnnect system is developed for the horizontal platform, which greatly expands its application scope. The most important thing is that it can be used with ZF’s latest 9AT. This timely four-wheel drive system is only driven by the front wheel when the vehicle is driving normally. When the front wheel slips or the curve accelerates rapidly, the computer will make a judgment according to the needs of the vehicle’s grip and stability, and distribute part of the power to the rear axle.
-PTO components used to transmit power to the rear axle.
The ECOnnect system is mainly divided into two parts, one of which is called PTO, which is located at the transmission output end of the transverse powertrain, and its internal core is a fork mechanism, which cuts off and connects the power output to the rear axle through its movement. It should be noted that it has only two states, just like a switch, connected or disconnected.
These descriptions look similar to the traditional timely four-wheel drive system. Of course, its function is more than that. In fact, it can also distribute the power transmitted to the rear axle between the two rear wheels on this basis.
—— RDU that can realize power distribution between wheels.
To achieve this function, it is inseparable from another important component located at the rear axle-RDU, which is divided into two versions by ECOnnect: basic version and motion version. Among them, the function of the basic version is only to distribute the transmission from the front axle to the two wheels of the rear axle equally, and to adjust the required torque stepless through multiple pieces.
In the sports version, there are a set of multi-disc clutches on the left and right of the rear axle, and each clutch can independently control and distribute the torque required by the side wheel, which means that the power can be distributed between the left and right wheels in real time (omitting the traditional structure), so that more power can be distributed to the outer wheels as needed when accelerating in corners, which means that the yawing problem of the vehicle can be corrected by controlling the distribution of the driving force of the rear wheels, and in the most extreme case, the power transmitted to the rear axle can be completely distributed to the wheels on one side of the rear axle, thus improving the vehicle.
From the above description, we can find that PTO components are not available in the traditional four-wheel drive system, and its addition can make the power completely locked in the front axle in the two-wheel drive mode, saving unnecessary losses caused by idling of the transmission gear, which is also an important reason why the ECOnnect system is relatively more economical and energy-saving.
● control logic
The ECOnnect system is designed with full consideration of the actual needs of most driving conditions. For example, when driving in a straight line on a flat road, the four-wheel drive system will not bring additional advantages to the handling of the vehicle, but on rugged and slippery roads, the four-wheel drive system is very necessary. This four-wheel drive system needs PTO and RDU to work at the same time to be effective, and according to the requirements of the four-wheel drive system, the combination speed of ECOnnect is between 190-270ms (1s=1000ms), and the system will automatically judge when it should become a four-wheel drive mode and the power distribution ratio between the rear axle and the rear wheel.
● Driving experience
What we are experiencing is a diesel version equipped with the ECOnnect(RDU Sports Edition) system. In order to better reflect the difference between the ECOnnect system and the non-eConnect system, the staff installed a device in the car to manually switch the driving mode (the production version will not have this control device in the car), and at the same time, we can observe how the power is distributed in real time through the display screen in the car.
The whole experience process is carried out in a closed test field with good pavement. When the vehicle accelerates linearly, the rear wheel will not be distributed with power. If the front wheel is on a wet road, in theory, the system will transfer part of the power to the rear axle, but this time it failed to experience this situation.
When stepping on the accelerator lightly or accelerating sharply in a corner, you will see that part of the power is distributed to the rear axle, and at the same time, the power is redistributed through the RDU, and more power is transmitted to the outer wheels, thus ensuring the smooth and smooth cornering of the vehicle. The combination, separation and power distribution of the four-wheel drive system are completely intelligent, and there will be no notice in the car. Only through the display screen will we know that the four-wheel drive system is working silently.
Theoretically speaking, in extreme cases, this four-wheel drive system can distribute all the power to the wheel with grip on one side of the rear axle to help the vehicle get out of trouble, but it has not been experienced this time, so the four-wheel drive ability of this system needs further testing and experience in the future.
Summary:
Four-wheel drive system can improve the driving stability of the vehicle to the greatest extent and correct the yaw of the vehicle. Compared with the traditional full-time four-wheel system, ECOnnect can save up to 5% fuel consumption for the vehicle, and at the same time, this system can intelligently distribute the power according to the state of the vehicle, which reduces the difficulty of driving. Because of the small space occupied by the ECOnnect system, theoretically, this system can be installed on any vehicle with a front-drive horizontal platform in the future. (Text/car home Feng Jingyi)
Related links:
Stepping into a broader market ZF 9AT driving experience
http://www.autohome.com.cn/tech/201306/551899.html
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