The present embodiments relate to a vehicle having a brake device for braking the vehicle and a method for braking the vehicle.
A vehicle may be a motor vehicle, a rail vehicle or an aircraft. An anti-lock brake system for at least one of the wheels of the vehicle is provided.
If a vehicle (e.g., a motor vehicle) rolls over a rolling surface of a carriageway, a force that acts parallel to the rolling surface may, over a wheel of the vehicle, be at maximum as large as the static friction acting between a tread of a tire of the wheel and the rolling surface of the roadway. This force that may be transmitted parallel to the rolling surface is divided into the driving force or braking force, and the lateral guiding force.
If the vehicle is braked strongly such that the maximum braking force that may be transmitted to the rolling surface is exceeded, the wheel locks and slides or skids over the rolling surface. In order to restore grip between the tread of the tire and the rolling surface of the roadway, the tread of the tire is to be accelerated again to such an extent that a relative speed with respect to the rolling surface is small enough to permit the grip again. For this purpose, in a vehicle with a hydraulic friction brake, the friction brake may be temporarily released by using an anti-lock brake system. The anti-lock brake system engages for this purpose in the hydraulic brake circuit via solenoid valves. In order to detect the need for intervention, the rotational speed of the wheel is measured. As soon as the rotational speed of the wheel drops too strongly compared to the velocity, the friction brake is released. As a result, the friction brake no longer applies any braking torque to the wheel. The wheel that slides over the rolling surface is subsequently made to roll again by the friction force acting between the wheel and the roadway and is accelerated. When the rotational speed of the wheel corresponds to the rotational speed of the other wheels again, a braking torque may be applied to the wheel again by the friction brake.
An anti-lock brake system (ABS) may not wait until a wheel locks to intervene. Instead, when a wheel is still rolling, the slip thereof with respect to the roadway is already controlled. This will be explained in more detail below with reference to FIG. 1. The braking force F that acts on a wheel of a vehicle that is rolling straight ahead firstly increases, starting from a free rolling wheel with a slip S=0% during the braking of the vehicle (and in a comparable way also during the acceleration thereof), with increasing slip S, up to a maximum value in order approximately to become lower again starting from a slip value of S=30%. In order to obtain the most favorable slip during the braking of the vehicle, the rotational speed of the wheel is alternately actively reduced using a braking intervention by the ABS and accelerated again passively over the roadway when the brake is released. As a result, the slip is controlled within a range of, for example, S=8% to S=35%. During the ABS control, the rotational speed of the wheel oscillates, for example, between corresponding rotational speed values.
DE 44 35 953 A1 discloses generating, for the purpose of braking a passenger car, a total braking torque that is composed of the braking torque of a hydraulic brake system and the braking torque of an electric motor operated in the regenerative region.