To ensure a comfortable ride, cars are equipped with a lot of additional options. The computer helps to eliminate the driver's flaws in all respects-automatic transmission, electronic throttle control, emergency braking help. The next step, AFS (Active Front Steering), is the active steering system. Appointment
Appointment
Now the driver can forget about the huge number of steering wheel turns in the parking lot. The innovation allows to accelerate the reaction of the car to the turn of the steering wheel. Thus, in order to turn the wheels from one extreme position to the opposite, it is enough to turn the steering wheel all by 360 degrees.
Background
Bosh and ZF were involved in the development of the system. Such a system is now a proprietary attribute of BMW cars.
AFS development took a lot of time and money. However, such a system would not have been possible without the use of hydraulic steering. You should thank the American, Francis Davies. In 1925, he patented a prototype hydraulic amplifier. The system was later refined using an electric motor to control the hydraulic pressure. It is this power steering system that implements the active steering system.
In addition to the hydro-amplifier, the exchange rate stability system or the ESP is important. This system records the data from the sensors and allows the car to maintain the specified trajectory in complex road situations. Applicable since 1995.
Having in the arsenal of the GRM and ESP, the Bavars were able to design a system of active steering, which is installed on BMW cars since 2003. There are similar systems in other cars, for example, Honda S2000.
Device and operating principle
AFS works on the basis of the classic steering system, which consists of the following parts and components:
-The rudder;
The steering wheel causes the beam to rotate, which in turn rotates the steering gear and turns the wheel. But the problem is that the difference in the ratio of steering wheel angle to wheels is too large. In order to turn the wheels from one extreme position to another, it is necessary to carry out about 3 full steering wheels. The ratio between the steering angle of the rudder and the wheels is referred to as the gear ratio. The smaller the number, the easier it is to manage the car.
The active steering system reduces the gear ratio, thereby reducing the number of revolutions of the rudder. A small turn to the right or left and the wheels shall take the given direction.
The structure of AFS is a complement to the classic steering system. The engineers cut the steering shaft and added a planetary gear (a mechanism that consists of gears closely coupled with each other). Gears come in motion with an electric motor. The gearbox drive can move the gears at a higher speed, thereby accelerating the wheel turns. This is the chain: the steering-response of the electric motor wheel-gear-the gears trigger rotation of the steering shaft-the wheels turn.
The system described above is running on a computer. Ease of rotation is provided by the electric hydro-amplifier. The gear ratio changes according to the situation. AFS retrieves data from sensors installed in the car:
-Steering wheel angle sensor;
-the sensor of the total steering angle;
-speedometer;
For greater accuracy, AFS uses data from the exchange rate stability sensors, which allows modification of the gear ratio in the event of a loss of wheel chaining.
The gear ratio is increasing at high speeds. The point is that, with quick rotation, the friction decreases and the wheels turn lighter. At a low speed, such as parking, the steering wheel is much more difficult because of the increased friction. The system analyts sensor data and selects the appropriate gear ratio for each situation. The change in the number directly depends on the speed of rotation of the gears, which is sufficient to regulate the power of the electric motor.
Operational issues
The mechanical component of the system is simple and usually does not fail. Complexity can only occur when you configure your system after the electronics are damaged. If AFS has ceased to signal LED activity on the dashboard, you should contact the service and run diagnostics. It is very difficult to independently restore the system, as it requires advanced knowledge of electronics and experience working with BMW cars.
