Kurt Andro – April 16th 2014
A somewhat unconventional idea that is particularly dear to my heart, as it has the potential to save lives and health. And it is likely to be technically and legally easier to implement than driver assistance systems in (semi-)autonomous vehicles, because the driver remains the actor and responsible for the steering wheel brake.
Brief description, objectives
New way of actuating the service brake for passenger cars, trucks, etc., which should lead to a shortening of the stopping distance during emergency braking in order to avoid collisions or, where a collision can no longer be avoided, to enable a lower collision speed. In other words, accidents should be avoided or the severity of accidents alleviated. Service braking is also possible.
In an emergency braking situation, moving the foot from the accelerator pedal to the brake pedal causes the loss of valuable time, which leads to an unnecessarily long stopping distance. There is also a risk that the driver will get stuck behind the brake pedal when changing foot in the rush of an emergency situation (shock) and that no braking will occur at all.
The steering wheel is given a new function: by applying force with one or both hands to the steering wheel rim, it can be braked at any time without delay, as at least one hand always grips the steering wheel rim. This function is an additional way to brake. This means that the brake pedal and everything else that goes with it stays as it is!
Mechanical, hydraulic or pneumatic methods are conceivable for the measurement of pressure forces on the steering wheel rim. The method described here envisages the use of piezoelectric foils, such as those already used in space travel (ESA) to measure the forces acting on the wings of the Hermes space shuttle or for crash tests (Volkswagen) to record the impact processes.
This method offers the most advantages because, as can be seen from the examples given, piezoelectric films are very resistant. In addition, they are very thin, flexible and also very resistant to temperature and ageing. Analogue to the mechanical pressure applied to them, they generate a small electrical voltage which can be amplified, processed and used to control actuators. Such actuators already exist. They are used in vehicles adapted for disabled people, which are equipped with electronic brake pedals and/or electronic brake rings (in front or behind the steering wheel). The company "Continental" also offers "Brake by Wire" systems.
Implementation and tests
To implement this new braking method and integrate it into an actual vehicle, here are a few detailed considerations that need to be questioned, supplemented and specified during the planning, calculation, implementation and test phases. The piezoelectric foils should be applied in the form of individual segments of the order of a few square centimeters around the steering wheel rim (underneath or inside the foam surround) in such a way that on the side facing the driver and on the rear side of the steering wheel rim separate and independently readable sensors are mounted.
The signal-processing control logic should only initiate braking if the threshold values of the front and rear sensors are exceeded at the same time. This is to ensure that leaning or pulling with one hand (or both hands), e.g. to change the sitting position, does not lead to unintentional braking. Only if pressure is applied to opposing sensors, i.e. if the steering wheel rim is squeezed, should the values measured by the sensors be used to calculate the desired braking force.
Furthermore, it should be determined whether individual thresholds (below which braking should not occur) are required for different drivers, or whether a general threshold can be specified for all drivers. The same applies to the maximum pressure value, which should then correspond to the maximum braking force. If necessary, a characteristics curve must be defined which specifies the resulting braking force in the event that the brake pedal is also pressed during braking via the steering wheel.
The throttle must be switched off when braking by the steering wheel, because the driver may leave his foot on the accelerator pedal (due to the shock situation). A renewed gas acceptance may only be possible again after the accelerator pedal has been reset.
The signal transmission from the steering wheel sensors to the control unit must be redundant, e.g. using two independent slip ring contact sets. Or a slip ring contact set plus an alternative transmission type. Both transmission paths must be permanently checked by the control unit for functionality and a failure must be indicated in an unacknowledgeable manner (in this case the system must be checked / repaired in a professional car workshop).