Many car owners will encounter abnormal steering noise in winter, especially when they first drive and turn at low speeds and large angles. The squeaking sound sounds annoying, but after driving for a period of time, the abnormal noise will disappear. It will disappear automatically again. It feels very strange. Is there something wrong with our car? The answer is of course not. This is an inherent "flaw" of the steering mechanism. Let's talk about this topic in detail below.
The smooth turning of the car depends entirely on it: Ackerman mechanism
To answer why abnormal steering noise occurs, we must first introduce a more academic concept called Ackerman mechanism. Listen Isn’t it very grand to go up there? To use a more academic description, Ackermann steering geometry is a geometry that is used to solve the problem that the inner and outer steering wheel paths point to different center centers when the vehicle turns. You see, are you confused?
What it generally means is that when the vehicle turns, the two front wheels draw two arcs. Each of these two arcs must have a center of movement around it. In addition, the rear wheels do not rotate left or right. , so the two rear wheels are perpendicular to the wheel axis direction. The Ackerman mechanism is designed to make the front two wheels "draw an arc" around the same center of a circle, and this center of the circle must be on the extension line of the rear wheel axis. If you really can’t understand, just look at the picture below compared with the text.
Would it be impossible for an institution to pivot without Ackerman?
According to our existing ideas, the two front steering wheels should not be parallel whether driving straight or turning, right? If the front wheels are always parallel, then the rod responsible for steering must form a parallelogram (rectangle), because only the two opposite sides of a parallelogram will always be parallel no matter how it changes. In fact, you can turn this way, but the wheels will slip slightly, and the rods will have to bear greater force.
Because normal turning of a vehicle requires a centripetal force directed toward the inside of the curve. This centripetal force is provided by the friction between the four wheels and the road surface, and the direction of the friction is exactly the center of the circle pointed by the turning arc. direction, and the direction of the rear wheel axis extension line. The power of unity is great. Only when the axes of the four wheels point as much as possible towards the same center of the circle can a greater resultant force be generated, which is the centripetal force required for steering, and turning will be easier and smoother.
So how can we make the center of the circle pointed by the steering arc of the front steering wheel intersect at one point, and also intersect with the extension line of the rear axle (instantaneously, because the car is moving)? To achieve this, the wheel on the inside of the curve must have a steering angle approximately 2°-4° greater than the wheel on the outside. This was proposed by the clever German vehicle engineer "Lankensperger" in 1817, and later patented by his British agent Rudolph Ackermann in 1818, and finally it was called the Ackermann mechanism.
The connection shape of the steering rods (steering guide rod, steering horn, left and right wheel shaft connection lines) designed according to the Ackerman mechanism is roughly an isosceles trapezoid, so that when turning, the vehicle can be ensured to be in the right position. When turning, the steering angle of the wheel on the inside of the curve is slightly larger than the steering angle of the wheel on the outside. Of course, this is not just as simple as forming an isosceles trapezoid. The length and inclination angle of the steering rod must also be calculated, so the steering adjustment is very complicated.
Finally
Let’s go back to the original question of the article: abnormal noise in the steering mechanism of vehicles in winter. Because the temperature is low in winter, the steering rods are affected by thermal expansion and contraction, destroying the Ackerman mechanism from the beginning of the design. Therefore, when turning, especially when making large turns, friction and abnormal noise will occur between the connection points of the steering rods. If you still don’t understand it after reading the entire article, please save the article and read it carefully. Also, don't be afraid if the steering makes abnormal noise. It's not something wrong with your car. It will be fine after you drive for a while and the muscles and bones of each part can move.
This article is the original work of Auto Observer. Any plagiarism will be investigated according to law.
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This article comes from the author of Autohome Chejiahao and does not represent the views and positions of Autohome.