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What is the variable steering ratio?

1, a variable gear ratio

When the variable steering ratio i.e. the steering gear ratio is adjusted in accordance with the vehicle speed and the steering angle, when the car is parked starts, a lower vehicle speed or the steering angle is large , provides a small steering gear ratio; and when the car at high speed or steering angle is small, to provide a large steering gear ratio, thereby improving the steering stability.

2. Description

is called by different manufacturers of such systems are manifold, such as BMW called active steering system AFS (ActiveFrontSteering,), which Audi called dynamic steering system (AudiDynamicSteering), Lexus / Toyota used is variable gear ratio steering system VGRS (VariableGearRatioSteering), and the variable steering ratio Benz system uses a “direct steering system” name. Although similar functionality, but the technology they use is very different.

Variable Gear Ratio Steering system

is not a level at the technical level, there are mainly two ways to achieve this function, one way is to rely on a special rack, thus principle is simple, the cost is relatively low, not high technology content, while the other is more complex, it is achieved through the planetary gear mechanism and electronic systems.

Mechanical Variable steering

It is mainly an issue than the system on the “rack and pinion” and “rack”, by a special process from the gap teeth are not equal rack, so that when the steering wheel, and the gear pitch is not equal to the rack gear, will change the steering ratio, the left and right sides of the teeth from the intermediate position of dense, small rack displaced within this range, the steering small amplitude (e.g., minor adjustments during lane change, direction), the vehicle will become calm, while the distal end sides of the rack tooth pitch less dense, within this range, turning the steering wheel, the relative displacement of the rack becomes large, Therefore, when the steering substantial (e.g., parking, turn, etc.), the wheel willBecome more flexible. In addition to this technical process requirements more stringent rack, and not many “high tech” in which the gear ratio drawback is the limited range and can not be flexible and change, and the advantage is obvious – completely mechanical structure high reliability, durability, structure is very simple.

Electronic variable steering

higher than the system
technological content, compared to the variable steering ratio of the mechanical systems, electronic variable steering using a more complex structure than the mechanical system and the need to use in conjunction with an electronic system. Can better achieve “low-speed light sensitive, high-speed steady heavy” demand convenience and stability it brings the vehicle is traveling are ordinary variable power steering system and a simple “mechanical” Variable Gear Ratio steering can not match.

3, direct steering system

benz variable steering ratio is named “Direct steering system”, uses a mechanical variable ratio steering, when the steering angle is large, direct steering system uses a more direct steering ratio, such as when to stop or sharp turn, can improve the car’s agility and steering comfort. The key components of this system is a rack, the rack tooth pitch is varied, intermediate-pitch, two sparse. Therefore, when the steering angle is small, less direct, but after the steering angle becomes large, the steering becomes straightforward. Therefore, such a variable steering by simple purely mechanical manner ratio.

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4, advantages and disadvantages of direct steering system

direct addition to the steering system of rack processing requirements more stringent, and not many “high tech” in which the gear ratio disadvantage is the limited range and can not be flexibly changed, and the advantage is obvious – completely mechanical structure high reliability, durability, structure is also verysimple.
The active steering
The variable steering ratio BMW named “active steering”, uses an electronic variable ratio steering system, the core of which is integrated in the steering column of a planetary gearset. An electric motor assembly according to the current speed of the vehicle, according to the front wheel turning angle ratio adjustment.
At low speeds, for example in city traffic, the vehicle is parked or when traveling on winding mountain road, the steering angle is increased active steering system. For small steering wheel rotation, responds immediately to ensure that the driver can pass through tight spaces, without the need to repeatedly turn the steering wheel. Parking easier, flexibility has been strengthened.
at higher speeds, more gradual turn, requires less steering angle. Thus, the active steering system for reducing the steering angle of the steering wheel all the rotational amount of change. So the driver to obtain a more precise steering at high speed, and enjoy more stability and comfort.
If the vehicle is under threat of instability, or oversteer for example, when changing the brake surface, a DSC dynamic stability control system to identify the problem and to overcome the problem by the active steering system. For example, in order to reduce unsafe yaw, active steering angle of the steering wheel system can improve faster. Active steering system does not interfere with the direct connection between the steering wheel and the front wheel, so that even when the electronic system is a complete failure, the vehicle still remains fully controllable.

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