The two-point independent suspension structure of domestic vehicle has the most advantages compared with that of domestic vehicle; The first point is obviously that the manufacturing cost is very low. If you can reduce the material cost for car enterprises, you can reduce the vehicle guide price. Of course, the joint venture vehicle will not make concessions in terms of the guide price, that is, the use of torque beam, because it involves the ability of brand premium.

The second advantage is that the bearing capacity of torsion beam suspension is slightly stronger. Through a hard beam with certain torque capacity as the bearing, the bearing capacity and structural stability can be guaranteed under the dynamic state of vehicle driving; Therefore, some entry-level passenger and freight (passenger cars) will also use torsion beams, such as FF (front drive) vans and light passengers.

The advantages of torsion beam suspension have been explained. Let's take a look at the disadvantages.

The bearing capacity of torsion beam suspension is indeed stronger. Compared with the independent suspension fixed on the frame with loose knot "anchor", which can only rely on spiral spring or air bag spring, its torsion beam body has certain torsion resistance and bearing capacity. However, because the torsional limit of this steel beam is too low, only relying on the movable swing arm and spiral spring support will reduce the compression stroke; Some vernacular explanations are that after the coil spring is compressed to a certain extent and the torsion beam is twisted to a certain extent, it will reach the torsion limit of the beam. At this time, the torsion beam becomes a "lever". Please see the torsion state of the torsion beam below.

Hypothetical scenario: the vehicle is driving at a low speed on a rough road, and the road bulges up the right wheel; At this time, the swing arm and coil spring are propped up (compressed) and twist the torsion beam. What happens after the torsion beam reaches the torsion limit? The only way to deal with the car body is to prop up the right side, because the beam body and coil spring shock absorber have reached the limit, and the convex road surface is bound to lift the car body. In other words, the compression stroke limit of the coil spring of the torsion beam suspension is limited by the torsion beam, and the body roll is difficult to control; This structure can still be used for cars driving on urban roads, but it is a poor choice for SUVs driving on rough roads, because severe body roll will increase the probability of vehicle rollover.

The above is the first disadvantage of the torsion beam, and the second disadvantage is the influence of the "lever" state. Similarly, according to the hypothetical scenario, the torsion beam cannot be twisted again when the right wheel is lifted, and the beam body becomes a rigid lever; When the right side is lifted, the tire on the left side will be tilted, and the state of the tire is that the crown is in contact with the ground in a large area. After being tilted, the outer edge will mainly contact the ground, and the middle and inner parts will be tilted and separated from the ground by the torsion beam.

When driving forward in this state, the ground contact of the left tire will be too small, and the tire will be greatly compressed under the left heavy pressure after the center of gravity is offset; At this time, it is likely that the side wall of the wheel is squeezed and damaged, or the wheel hub directly hits the ground, resulting in damage. This is the reason why the rear wheel hub of many SUVs with front torque beam is easy to be bruised, or the side wall of the rear tire is aging faster.

Rear driving in the same state will cause more serious damage to the wheel hub tires and reduce the carrying capacity (skidding). The rear wheel of the front drive is the driven wheel, which is pulled by the front wheel and will not run at high speed, accelerate tire wear or wheel hub collision; However, the rear wheel of the rear drive is the power take-off wheel. At this time, if the contact surface with the ground is reduced, it will be easier to slip, and the damage will be accelerated during the high-speed operation of slip. Many vans or light passengers with rear drive integral axles are equipped with iron wheels, which are obviously parallel, which is caused by this reason.

Note: the structural characteristics of the integral bridge are similar to those of the torsion beam. The difference is that the torsion deformation is not allowed, but the wheels on both sides are fixed on the rigid hard bridge; Secondly, the rear drive will mainly choose the integral axle with integrated transmission tooth package, while the use of torque beam and rear wheel drive will have a more complex transmission structure and increase the failure rate of the rear axle. Fortunately, the driving behind the torsion beam has been stopped, such as the magical big 7 and the weird Vitra.

Knowledge point: there is a way to solve the above problems with torsion beam or integral axle suspension to a certain extent, that is to add watt connecting rod. The structure of the connecting rod is that a movable pin is added in the middle of the torsion beam, which is fixed to the wheels on both sides with two connecting rods respectively; When one wheel is lifted, it will pull the connecting rod to drive the movable pin in the middle to rotate. In the process of rotation, it will push the connecting rod on the opposite side to support the opposite wheel, which can increase the ground connection of the wheel. However, there are few options for mass production vehicles to use this structure, because the torsion beam is mainly to reduce the production cost, and the watt connecting rod will increase the cost; This structure is used by willang in cars and by road shakers in hardline SUVs.

Conclusion: torsion beam suspension is indeed an unsatisfactory structure, and the experience will be especially bad on rough roads; The use of torsion beam suspension on paved roads will also affect the handling limit of the vehicle, because the high-strength compression of the outer suspension will be caused when the vehicle turns at high speed. Once the compression limit is reached, the vehicle body will tilt at a greater angle; Tilting will cause the center of gravity of the body to deviate excessively, and the result must be that it is easier to lose control of side slip. Therefore, the choice is to use the vehicle equipped with torsion beam rear suspension, which should be used as a walking vehicle to drive steadily.