Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
  • B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
  • B60T8/17—Using electrical or electronic regulation means to control braking
  • B60T8/176—Brake regulation specially adapted to prevent excessive wheel slip during vehicle deceleration, e.g. ABS
  • B60T8/1764—Regulation during travel on surface with different coefficients of friction, e.g. between left and right sides, mu-split or between front and rear

Definitions

• the invention relates to a method for controlling the brake pressure in an anti-lock brake system of a vehicle having front and rear wheels, in which the rotational speeds of braked wheels are measured and given as a function of the ratio of the rotational speed and / or rotational acceleration of a braked wheel Threshold values of the brake pressure of the wheel are kept constant or lowered when there is a risk of locking.
• a large number of algorithms for controlling the brake pressure in an anti-lock vehicle brake system are known.
• the measuring devices, valves and control devices required to carry out an ABS brake control are also known in a variety of configurations.
• New methods for controlling the brake pressure in ABS systems are implemented using known measuring and control devices (speed sensors, valves, etc.) by appropriate programming of a processor.
• the lateral guidance of the rear wheels is particularly important for the good steerability of the vehicle. If the rear wheels slip too much when braking, the steerability of the vehicle is at risk due to a reduced cornering force. It is known that the ABS pressure can result in a so-called "overshoot" of the brake pressure, for example because the threshold values for the ABS control are set relatively insensitive for other reasons or because of the inertia of the system. Exceeding the brake pressure is particularly undesirable on the brakes of the rear wheels. If the rear wheels of a (two-axle, four-wheeled) vehicle slip too much, that is to say a so-called instability range, a highly undesirable torque occurs about the vertical axis of the vehicle, the so-called yaw moment.
• ABS control is particularly difficult when braking in curves and also in so-called split situations.
• split situation the wheels are found on one side of the vehicle a different braking force coefficient than the wheels on the other side of the vehicle. Such situations can occur, for example, when driving over partially icy surfaces.
• the aim of the invention is to provide a method for controlling the brake pressure in an anti-lock brake system which, even when braking in curves and when braking with different braking force coefficients on the individual wheels of the vehicle, enables the shortest possible braking distance with good maneuverability of the vehicle.
• the invention modifies a conventional ABS control method in which the rotational speeds of braked wheels are measured and, when the rotational speed and / or the rotational acceleration of a braked wheel exceed predetermined threshold values, that is to say a danger of locking If the brake pressure on the affected wheel is either kept constant or reduced, such that if there is still no risk of locking in the case of a rear wheel, but the brake pressure is kept constant in at least one front wheel, the brake pressure on the rear wheels also at least secondly is kept constant.
• the invention is therefore based on the knowledge that it is advantageous to avoid an overshoot of the brake pressure on the rear wheels and thus to achieve good stability (steerability) of the vehicle, if at the rear wheels still no ABS control takes place and also no front wheel experiences a pressure reduction as part of an ABS control, but the brake pressure on at least one front wheel is kept constant by actuating a corresponding holding valve will also keep the braking pressures on the rear wheels constant for at least a certain period of time. Under the conditions mentioned, the holding valve controls of the front wheels are copied onto the rear wheels.
• the pulsation or throttling of the pressure build-up on the rear wheels is interrupted according to a preferred embodiment of the invention when a predetermined number of control cycles has expired on both front wheels , for example three control cycles. Then the pressure builds up on the rear wheels unthrottled or non-pulsed, ie at a speed determined by the pressure in the master brake cylinder.
• the speed (rate) at which the pressure at the rear wheels increases depends on the conditions of the Front wheels set. If pressure is reduced in the course of an ABS control on a single front wheel (of two front wheels), then the brake pressure on the rear wheels (provided that these do not themselves show any risk of locking) is increased with a relatively flat gradient. With a pulsating pressure build-up, the pulse series thus has a relatively low pulse rate.
• the second front wheel also reaches an unstable area, pressure is reduced on this wheel, or if the brake pressures are reduced on both front wheels at the same time as part of an ABS control, the pressure build-up on the rear wheels takes place with a relatively steep gradient , ie with pulsating pressure build-up, the pulse row has a higher duty cycle in comparison with the case where only one front wheel is unstable.
• the individual duty cycles are experimentally optimized for a given braking system and vehicle.
• ABS control methods described above also ensure good lateral guidance on the rear wheels of the vehicle.
• the pressure-holding valve of the front wheel running at a low coefficient of adhesion is actuated when braking to different adhesion coefficients
• the pressure on the rear wheels is also kept constant according to the invention, so that the risk of the brake pressure overshooting the rear wheels is largely eliminated is.
• the front wheel, which has a low coefficient of adhesion becomes so unstable that the brake pressure in its brake is reduced, the pulsed pressure build-up that then begins on the rear wheels or the rear axle (which reduces the pressure build-up on the rear wheels or the rear axle compared to one) unthrottled pressure build-up means that an excess pressure in the brakes of the rear wheels is avoided.
• the wheel contact force of the front wheel on the inside of the curve is reduced and the front wheel on the outside of the curve is subjected to greater stress.
• the method according to the invention therefore yields corresponding advantages for the ABS control like braking on different coefficients of adhesion. If, however, pressure is reduced when braking on both front wheels in the course of an ABS control, the brake pressure is built up relatively quickly on the rear wheels (provided that the rear wheels themselves do not show a tendency to lock), so that the vehicle is not understeered .
• 1A and 1B a cornering of a braked vehicle
• Fig. 2 typical courses of the brake pressure on the two
• Front wheels and the rear wheels in an ABS control according to the invention are Front wheels and the rear wheels in an ABS control according to the invention.
• a vehicle wheel In the usual designation, a vehicle wheel is said to be “stable” if it runs in a region of the known coefficient of friction / slip curve that lies before a maximum of the coefficient of friction.
• a vehicle is considered stable and steerable when all wheels are stable.
• a vehicle When braking in a curve, a vehicle can enter a state in which it is stable but understeering if one or both front wheels are unstable. In this case, due to the large wheel slip, the front axle of the vehicle cannot provide as much lateral guidance as the still stable rear axle, so that the vehicle deviates from the ideal curve in the sense of so-called "understeering". This is in Fig. 1A shown. There the circle K is assumed as the ideal curve. However, the curve actually carried out by the vehicle does not follow the ideal curve K; instead, there is an understeer.
• the invention makes use of this knowledge for an ABS control.
• brake pressures P and P are plotted on the two front wheels and the brake pressure P on the rear axle above the time axis over a common time axis t.
• both front wheels become unstable (which is determined in a known manner by evaluating the signals from corresponding speed sensors).
• the brake pressure P " A is therefore built up with a further enlarged gradient. This corresponds to the curve section A ".
• the brake pressure on the wheels of the rear axle is built up in a pulsating manner with relatively short stopping phases, so that there is an increased gradient for the brake pressure P compared to the time t until t- . In this way, the vehicle comes into the "neutral" state described above, in which both the wheels of the front and rear axles are in brake slip and the vehicle as a whole can be regarded as stable.
• the brake pressure is built "9 at the wheels of the rear axle with rela ⁇ tively short holding phases pulsing to achieve on all wheels a desired brake slip and thus to improve the braking and steering behavior of the vehicle.
• the braking distance is also optimized.
• the ABS control algorithm can also provide that if the rear wheels are still stable and at least one front wheel is beginning to become unstable, the brake pressure on the wheels of the rear axle remains provisionally constant is held, i.e. is not increased further.
• the rear axle of the vehicle maintains sufficient lateral guidance. If pressure reduction is initiated on at least one front wheel, in this exemplary embodiment there is a flatter pressure build-up on the wheels of the rear axle. In this second stage of the ABS control cycle, at least one wheel on the front axle becomes unstable due to excessive brake slip. In order to prevent the vehicle path from deviating too much from the ideal curve K (FIG. 1), the brake pressure on the wheels of the rear axle is therefore increased slightly, that is, a brake slip is also generated, so that the so-called "neutral driving behavior" mentioned above is generated "occurs and the vehicle has improved steerability.

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• Engineering & Computer Science (AREA)
• Transportation (AREA)
• Mechanical Engineering (AREA)
• Regulating Braking Force (AREA)

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• 1989
  • 1989-10-13 DE DE19893934307 patent/DE3934307C3/de not_active Expired - Lifetime
• 1990
  • 1990-10-12 BR BR909007745A patent/BR9007745A/pt unknown
  • 1990-10-12 JP JP51390690A patent/JPH05501233A/ja active Pending
  • 1990-10-12 WO PCT/EP1990/001732 patent/WO1991005685A1/de not_active Application Discontinuation
  • 1990-10-12 EP EP19900915107 patent/EP0495838A1/de not_active Withdrawn

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