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
  • B60T8/1755—Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve
  • B60T8/17551—Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve determining control parameters related to vehicle stability used in the regulation, e.g. by calculations involving measured or detected parameters
• • 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
• • 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
  • B60T8/1755—Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
  • B60W10/00—Conjoint control of vehicle sub-units of different type or different function
  • B60W10/18—Conjoint control of vehicle sub-units of different type or different function including control of braking systems
  • B60W10/184—Conjoint control of vehicle sub-units of different type or different function including control of braking systems with wheel brakes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
  • B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units
  • B60W30/02—Control of vehicle driving stability
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
  • B60W40/00—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models
  • B60W40/02—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models related to ambient conditions
  • B60W40/06—Road conditions
  • B60W40/064—Degree of grip
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60G—VEHICLE SUSPENSION ARRANGEMENTS
  • B60G2400/00—Indexing codes relating to detected, measured or calculated conditions or factors
  • B60G2400/10—Acceleration; Deceleration
  • B60G2400/104—Acceleration; Deceleration lateral or transversal with regard to vehicle
  • B60G2400/1042—Acceleration; Deceleration lateral or transversal with regard to vehicle using at least two sensors
• • 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
  • B60T2210/00—Detection or estimation of road or environment conditions; Detection or estimation of road shapes
  • B60T2210/10—Detection or estimation of road conditions
  • B60T2210/12—Friction
• • 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
  • B60T2230/00—Monitoring, detecting special vehicle behaviour; Counteracting thereof
  • B60T2230/02—Side slip angle, attitude angle, floating angle, drift angle
• • 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
  • B60T2270/00—Further aspects of brake control systems not otherwise provided for
  • B60T2270/30—ESP control system
  • B60T2270/313—ESP control system with less than three sensors (yaw rate, steering angle, lateral acceleration)
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
  • B60W2422/00—Indexing codes relating to the special location or mounting of sensors
  • B60W2422/95—Measuring the same parameter at multiple locations of the vehicle
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
  • B60W2520/00—Input parameters relating to overall vehicle dynamics
  • B60W2520/12—Lateral speed
  • B60W2520/125—Lateral acceleration
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
  • B60W2520/00—Input parameters relating to overall vehicle dynamics
  • B60W2520/14—Yaw
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
  • B60W2520/00—Input parameters relating to overall vehicle dynamics
  • B60W2520/20—Sideslip angle
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
  • B60W2720/00—Output or target parameters relating to overall vehicle dynamics
  • B60W2720/14—Yaw
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
  • B60W2720/00—Output or target parameters relating to overall vehicle dynamics
  • B60W2720/30—Wheel torque

Definitions

• the invention relates to a brake system for motor vehicles with more than two wheels.
• the braking system contains several braking devices, with one brake device being assigned to each wheel.
• the braking devices are designed in such a way that they are able to exert moments on the respective wheel about the wheel axis of rotation which have the effect that the wheel rotation speed is reduced. These moments will be referred to as wheel braking torques in the following.
• the change in the rotational speed of the wheel has the result that forces which are referred to as braking forces are built up in the clearance surface from the roadway.
• the braking forces in turn produce a torque about the vertical axis (yaw moment) of the vehicle.
• the steering angle represents the curved path of the vehicle desired by the driver.
• the vehicle In the case of stable cornering, the vehicle should have an approximately constant float angle and remain the same the yaw angular velocity pass through the desired path. Deviations before or from this float angle
• the driver must compensate for yaw rate by countersteering. However, this is not always possible, especially not when the driver is driving through the target path at the cornering limit speed. In such situations, it is necessary to brake the vehicle in a targeted manner and at the same time apply additional yaw moments to the vehicle, which are intended to bring about an adjustment of the actual yaw rate.
• Today's vehicles are usually equipped with hydraulic brakes, which are designed either as disc brakes or drum brakes.
• the specific task is therefore to determine a braking pressure for the braking device of each wheel.
• the additional yaw moment to be realized should be achieved with the lowest possible pressures, ie with the lowest possible braking forces on the individual wheels in the individual braking devices.
• the invention proposes to determine a coefficient C xx for each wheel provided with a braking device and the wheel braking torques for the individual
• Each coefficient determines the relationship between the brake pressure in a braking device and the share of the braking forces on this wheel in the additional yaw moment.
• Parameters that change during the journey of a vehicle or from application to application of the vehicle are used as parameters when determining the individual coefficients. These are in particular - the steering angle,
• variables that are included in the calculation of the coefficients and that are vehicle-specific or brake-specific are, for example - the area of the brake piston - the number of pistons per brake device - the coefficient of friction between the disc and
• Brake pad (can change during braking, e.g. due to fading) -
• the proposed calculation method has the advantage that the corresponding brake pressures can be calculated very quickly from a predetermined additional yaw moment of the vehicle. If parameters change during the journey, this is done by changing the coefficients in the
• the term driving stability control combines four principles for influencing the driving behavior of a vehicle by means of presettable pressures in individual wheel brakes and by intervening in the engine management of the drive motor.
• This is brake slip control (ABS), which is intended to prevent individual wheels from locking during braking, traction control (ASR), which prevents the driven wheels from spinning, and electronic brake force distribution (EBV), which determines the ratio of the braking forces between Controls the front and rear axles of the vehicle, as well as a yaw moment control (GMR), which ensures stable driving conditions when cornering.
• ABS brake slip control
• ASR traction control
• EVS electronic brake force distribution
• GMR yaw moment control
• a vehicle is a motor vehicle with four wheels, which is equipped with a hydraulic brake system.
• the driver can build up brake pressure in the hydraulic brake system using a pedal-operated master cylinder.
• Each wheel has a brake, which is assigned an intake valve and an exhaust valve.
• the wheel brakes are connected to the master cylinder via the inlet valves, while the outlet valves lead to an unpressurized container or low-pressure accumulator.
• there is an auxiliary pressure source which is able to build up pressure in the wheel brakes regardless of the position of the brake pedal.
• the inlet and outlet valves can be actuated electromagnetically for pressure control in the wheel brakes.
• a yaw rate meter for the brake pressure generated by the brake pedal
• the pressure sensor can also be replaced by a pedal travel or pedal force meter if the auxiliary pressure source is arranged in such a way that a brake pressure built up by the driver cannot be distinguished from that of the auxiliary pressure source.
• a fall-back solution is advantageously implemented with such a large number of sensors. This means that if a part of the sensor system fails, only that part of the control system that is dependent on this part is switched off. If, for example, the yaw speedometer fails, yaw moment control cannot be carried out, but ABS, TCS and EBV are still functional. The driving stability control can therefore be limited to these three other functions.
• a critical situation is an unstable driving condition in which, in extreme cases, the vehicle does not follow the driver's instructions.
• the function of the driving stability control therefore consists in giving the vehicle the vehicle behavior desired by the driver within the physical limits in such situations.
• GMR yaw moment control
• Different vehicle reference models can be used for yaw moment control.
• the easiest way to calculate is using a single-track model, i.e. that front wheels and rear wheels in this model are combined in pairs to form a wheel which is located on the vehicle's longitudinal axis. Calculations become much more complex if a two-track model is used. However, since lateral displacements of the center of mass (roll movements) can also be taken into account in a two-track model, the results are more precise.
• the float angle ß and the yaw rate represent the state variables of the system.
• the input variable acting on the vehicle is the Steering angle ⁇ represents the vehicle's yaw rate received as an output variable.
• the model coefficients c ii are formed as follows:
• c h and c v stand for the resulting stiffness from tire, wheel suspension and steering elasticity on the rear and front axles.
• l h and l v represent the distances between the rear axle and the front axle from the center of gravity.
• ⁇ is the yaw moment of inertia of the vehicle, that is
• 1 is a block diagram of the overall structure of a system for driving stability control
• Fig. 2 is a block diagram of the structure of a
• Fig. 3 is a flow chart for determining a
• 7 is a block diagram for the direct determination of the slip angle speed from kinematic considerations as part of the combined method of FIG. 6,
• the slip angle difference of a vehicle can be taken from the float angle and the speed vector of the individual wheels.
• 12 to 15 is a block diagram of a control circuit for controlling the driving stability, in which the variables compared in the comparator represent derivatives of the yaw angular velocity,
• Fig. 18 block diagram for describing a
• Fig. 24 diagram for describing the side
• 26 shows a flow diagram with a decision logic within the distribution logic
• Fig. 29 basic block diagram for determining the wheel brake pressure. A general description of the process of a
• the vehicle forms the so-called controlled system:
• the vehicle 1 forms the so-called controlled system:
• the FSR system has four electronic controllers 7, 8, 9 and 10, each of which is the ABS anti-blocking system, the ASR traction control system
• Electronic brake force distribution EBV or the yaw moment control GMR are assigned.
• the electronic controllers for ABS 7, ASR 8 and EBV 9 can continue to correspond to the state of the art.
• the wheel speeds are fed to the controllers for the anti-lock braking system 7, the traction control system 8 and the electronic braking force distribution 9.
• the controller 8 of the traction control system additionally receives data about the prevailing engine torque, the actual engine torque
• M Motist M Motist .
• This information also goes to the controller 10 for yaw moment control GMR. He also receives the data about the lateral acceleration a transverse and the yaw rate from sensors of the vehicle. Since in the controller 7 of the ABS a vehicle reference speed v Ref is determined anyway via the individual wheel speeds of the vehicle wheels
• Reference speed is not calculated in the GMR controller 10, but is taken over by the ABS controller 7. Where the vehicle reference speed is calculated or whether a separate calculation is made for yaw moment control only makes a small difference for the course of the yaw moment control. The same applies, for example, to the longitudinal acceleration a long of the vehicle. Correspondingly, the value for this could also be determined in the ABS controller 7 and passed on to the GMR controller 10. This only applies to a limited extent for determining the road friction coefficient ⁇ , since a more precisely determined coefficient of friction is desirable for yaw moment control than is determined for the anti-lock system.
• the ASR controller 8 and the GMR controller 10 simultaneously calculate specifications M ASR and M StellM for the engine torque.
• the pressure specifications P GMR of the GMR controller 10 for the individual wheel brake pressures are determined as follows:
• the GMR controller 10 first calculates an additional yaw moment M G , which leads to the stabilization of the driving state within a curve when it is generated by appropriate brake actuation.
• This M G becomes one Distribution logic 2 supplied, which could also be represented as part of the GMR controller 10.
• the distribution logic 2 calculates yaw moment control brake pressures p GMR for the wheel brakes from the predetermined yaw moment MG and from the desired driver brake pressure, which can be very different individually for the individual wheels.
• Driver's desired wheel pressures p are intended for optimum driving stability. These setpoint pressures can either correspond to the pressure specifications of a single one of these four regulators or can represent an overlay.
• the engine torque is handled in a similar way to the wheel brake pressures. While ABS and EBV only act on the wheel brakes, GMR and ASR also intervene in the engine torque.
• the specifications M StellM and M ASR for the engine torque which are calculated separately in the GMR controller 10 and in the ASR controller 8, are again evaluated in a priority circuit 4 and superimposed on a setpoint torque.
• this target torque M target can just as well correspond to the calculated specification of one of the two controllers.
• the pressure controller 5 generates valve signals which are emitted to the control valves of the individual wheel brakes in the vehicle 1.
• the motor management 6 controls the drive motor of the motor according to M Soll
• Vehicle reference speed vRef passes through a filter 17, which sets a constant value above zero at low speeds, so that the denominator of a fraction does not become zero in further calculations.
• the unfiltered value of v Ref is only fed to an activation logic 11, which recognizes vehicle standstill.
• a vehicle reference model 12 is stored in the GMR controller, which model is based on the steering angle ⁇ , the filtered vehicle reference speed vRefFil and the measured
• Yaw rate a default for a change in yaw rate calculated.
• the road friction coefficient ⁇ is also required for these calculations, which is an estimated value in a friction coefficient and situation detection 13 is calculated. With sufficient accuracy of the coefficient of friction determined in the context of the anti-lock control, the latter can also be used. Or in ABS controller 7, the coefficient of friction calculated in GMR controller 10 is adopted.
• the friction value and situation detection 13 uses the filtered reference speed v RefFil , the measured vehicle lateral acceleration a transverse , the measured for their calculations
• the situation detection distinguishes different cases such as driving straight ahead, cornering, reversing and vehicle standstill.
• Vehicle standstill is assumed when the filtered vehicle reference speed v RefFil assumes its constant minimum value. Instead of the unfiltered vehicle reference speed, this information can also be supplied to the activation logic 11 for the detection of a vehicle standstill.
• the yaw rate is given at a given steering angle ⁇ oppositely oriented is like driving forwards. For this, the measured yaw rate with the target yaw rate specified by the vehicle reference model 12 compared. If the signs are always opposite and this also applies to the time derivatives of the two curves, then there is a backward drive always for
• the calculated value of the slip angle speed passes through a first-order low-pass filter 15, which gives an estimate of the slip angle speed
• Program 16 also uses the change specifications for the yaw rate, which is the difference from the measured yaw rate and based on the
• Vehicle reference model 12 calculated target yaw rate represents. This becomes the additional
• the activation logic 11 not only receives the value of the unfiltered vehicle reference speed v Ref and, as described, that of the slip angle speed , but also the amount of the deviation of the target yaw angle
• V RefFil takes its minimum value
• the measured lateral acceleration a transverse is above the threshold value a transverse , but in the next step it is recognized in diamond 55 that the amount of the steering angle ⁇ is smaller than a threshold value ⁇ min .
• the measured lateral acceleration a transverse is a measurement error that results from the fact that lateral accelerometers are usually permanently mounted in the vehicle's transverse axis and incline with the vehicle when the road is inclined to the side, so that a lateral acceleration is displayed that actually does not exist.
• the size of the longitudinal acceleration a long is considered in diamond 59. If the amount is smaller than a threshold value a longmin , constant straight-ahead travel is assumed.
• diamond 60 distinguishes between positive and negative longitudinal acceleration. If the value of a long above the threshold a long- min, then the vehicle is in an accelerated straight travel, so the situation ⁇ 2>. If the value of a long is below the threshold value a longmin , this means nothing else than that there is negative longitudinal acceleration, i.e. a delayed straight-ahead drive, the situation ⁇ 3>.
• diamond 56 queries whether the vehicle is now reversing.
• the detection of a reverse drive is only necessary at this point, since the yaw rate when driving straight ahead hardly differs from zero anyway and therefore no control intervention is carried out. Only when a cornering is detected, in which the yaw moment control itself becomes active, must a reverse travel be excluded with certainty. This is not possible solely on the basis of the signals from the wheel speed sensors, since such sensors only transmit the speed in terms of amount without allowing conclusions to be drawn about the direction of travel.
• the situation ⁇ 6> is, as already described, determined by the measured yaw rate is compared with the target yaw rate determined in the vehicle reference model 12.
• the threshold value a longmin is examined further in diamond 58, whether the longitudinal acceleration a long is positive or negative. With positive longitudinal acceleration a long , the vehicle is in an accelerated cornering, that is situation ⁇ 8>, while with negative longitudinal acceleration a long a decelerated cornering is recognized, corresponding to situation ⁇ 9>.
• the longitudinal acceleration a long can be different
• the situation detection according to FIG. 3 is continuously run through again, the last determined situation remaining stored and being available in diamond 53.
• a possible sequence for determining the coefficient of friction of the road is shown in FIGS. 4 and 5.
• the yaw moment control responds on the basis of an instantaneous driving situation, it can be assumed that the vehicle is at least in the vicinity of the limit range for unstable driving situations. It is thus possible to deduce the current road surface friction value by considering the current measured variables on the vehicle.
• Steps further updated. If the yaw moment control does not start within this update phase, the estimated coefficient of friction becomes reset to 1.
• the estimated coefficient of friction may not be adjusted or updated.
• Such situations are, for example, straight-ahead driving, reversing or vehicle standstill, i.e. situations ⁇ 0> to ⁇ 4>. These are situations in which yaw moment control is not carried out anyway, so that an estimation of the coefficient of friction is also unnecessary.
• An update of the coefficient of friction can be omitted if the time derivative of the coefficient of friction so is negative and the amount of the time derivative of the steering angle ⁇ , ie
• the coefficient of friction calculated in this way is that it is an average coefficient of friction for all four vehicle wheels. The coefficient of friction cannot be determined individually for each wheel in this way.
• the method of determining the coefficient of friction will now be explained with reference to FIG. 4.
• the prevailing road surface friction according to field 61 flows into the vehicle behavior.
• the measured transverse acceleration a is first transverse according to step
• Step 63 includes the situation detection according to FIG. 3.
• the detected driving situation is later important for the update phase in step 74.
• step 68 the reg old parameter for
• Step 65 set to 1.
• the counting parameter T ⁇ is set to 1 in accordance with the fact that the first coefficient of friction determination of the internal coefficient of friction has taken place.
• step 69 an estimated coefficient of friction is assigned to the calculated internal coefficient of friction , This is done on the assumption that the existing acceleration components are not yet on a full one
• the parameter determined in field 68 is not carried out because the update was made during a control.
• an estimated coefficient of friction ⁇ is assigned using a table, a non-linear relation or a constant factor. If it is determined in a run in diamond 64 that regulation is not required, diamond 71 continues to query whether the parameter reg old was last set to 0 or 1 for the regulation. If it was set to 1 in the last run, the number T ⁇ becomes the diamond 72
• T ⁇ 2 and so on. As long as the T ⁇ has not yet reached a specific T pEnd in step 72, it is increased by 1 in step 73 and a renewed update of the in step 74
• step 78 The criteria for an update of the internal coefficient of friction after step 74 are shown in FIG. 5. Based on the specification in field 77 that the internal coefficient of friction is to be updated, the time is in step 78
• Step 78 evaluated in step 80 A determination of the coefficient of friction is only carried out if - as already explained above - a decreasing coefficient of friction is not due to a steering maneuver. There is no update of the coefficient of friction if either the vehicle is traveling straight ahead - forwards or backwards - or when the vehicle is at a standstill, or if the estimated coefficient of friction drops is due to a steering maneuver.
• the kinematic -Determination 14 contains nothing other than that - detached from any vehicle models - the slip angle speed from measured or calculated values based on measured values, the following is determined using purely physical considerations: The acceleration a transverse to the vehicle's center of gravity
• the acceleration vector a is derived from time t as:
• the acceleration sensor measures the projection of the acceleration vector onto the transverse axis of the vehicle:
• the swimming angle speed can now be calculated according to the differential equation above. As parameter go next to the cross acceleration a trans the Gierwinkelgeschwindigkei , the scalar vehicle speed v and its time derivative on. To determine ß, that of the previous calculation can be numerically integrated, with the first -Determination Is accepted.
• Floating angle speed is derived directly from the sensor signals and can thus also be determined in the non-linear area of the transverse dynamics.
• the sensitivity of the method to measurement noise and the integration of measurement errors have a disadvantageous effect, as a result of which a determination of the swimming angle may become very imprecise.
• These disadvantages are avoided by the combination with a model-based method.
• a model-based method Like such a combination of kinematic determination of the angular velocity based on an observer model 6, which can be inserted instead of the block 18 shown in broken lines in FIG. 2.
• the steering angle ⁇ also flows as an input variable, as indicated by a dashed arrow.
• the observer vehicle model 84 uses the same input variable - likewise like the vehicle reference model 12 for determining the yaw rate - the steering angle ⁇ .
• the filtered vehicle reference speed v RefFil is used as a parameter.
• the measurable output variables lateral acceleration a transverse and yaw rate become kinematic Determination 83 is required, but not for the observer vehicle model 84, which in principle creates these variables itself.
• Another term Y which in the simplest case is identical to the additional yaw moment calculated by the GMR control law, represents the changes in vehicle behavior that are caused by a control intervention. Y thus serves to expose the observer's simulated vehicle to the same conditions as the real vehicle.
• Weighting factor k multiplied, while the size for the swimming angle speed originating from the observer vehicle model Y after addition with a correction factor from the measured yaw rate multiplied by a factor h determining the size of the correction - multiplied by a weighting factor (1-k).
• the value of k is always between 0 and 1. Without an observer vehicle model, k would be 1. After adding the two
• the sum of the slip angle velocities is integrated into an estimated slip angle , In addition to the kinematic slip angle speed, this is also the Scheme provided.
• the float angle becomes both kinematic - Determination 83 and passed on to the observer vehicle model 84.
• a similar correction quantity is the yaw angle acceleration calculated by the observer vehicle model 84.
• this is integrated into a yaw rate and flows back to the observer vehicle model 84 and is subtracted from the measured yaw rate. That difference
• Yaw rate therefore has the same dimension as the yaw acceleration , so that both quantities can be added together and, after further integration, form a returning correction quantity for the yaw rate.
• the term Y assumes values deviating from zero in accordance with the additional yaw moment M G applied.
• Y also contains the dimension of a yaw angle acceleration and is added to the sum of the yaw angle accelerations, so that the integrated correction variable also takes the control influences into account.
• the float angle determined in this way can also be passed on to the actual yaw moment controller 10.
• the filtered vehicle reference speed v RefFil is differentiated in field 93 from the vehicle reference acceleration , which is divided in field 94 by the filtered vehicle reference speed v RefFil , which leads to a factor f ⁇ after non-linear multiplication 95.
• This nonlinear multiplication 95 causes the factor f ⁇ to be set to zero for a small quotient and v RefFil
• the float angle ß becomes kinematic Provision taken into account.
• the used here is the combined as it is used both as a variable for the control and for the feedback according to FIG. 6. According to the calculation 91, the value determined for the slip angle speed passes through a low-pass filter 92 as already described above and results in the estimated slip angle speed.
• the filtered vehicle reference speed v RefFil is differentiated in field 93 to the vehicle reference acceleration , that in field 94 by the filtered vehicle reference
• the float angle ß becomes kinematic Determination taken into account.
• the used here is the combined as it is used both as a variable for the control and for the feedback according to FIG. 6. According to the calculation 91, the value determined for the low pass 92 passes through, as already described, and results in the estimated value
• FIG. 8 How the observer vehicle model 84 from FIG. 6 works is shown in FIG. 8. Here a matrix representation was chosen, with " ⁇ " representing scalar and " ⁇ " multidimensional structures.
• the matrix representation is based on equations F 1.1 to F 1.3.
• the state variables are ß and to a
• the input vector u (t) contains, as input variables, the steering angle ⁇ and the term Y, which represents the additional yaw moment generated by the yaw moment control.
• a weighting matrix K 1 and a are used for the weighted addition of the determined quantities
• Weighting vector k 2 used.
• the dynamics of the observer vehicle model is determined by a vector h, the first component h 1 of which is dimensionless and the second component h 2 of which has the dimension (1 / s):
• the system equations according to F 2.7 are formed in the adder 104.
• the system matrix A is multiplied by the state vector x and the input matrix d. multiplied by the input variables ⁇ and Y the input vector u.
• the only variable parameter that flows into both the system matrix A and the input matrix B is the current vehicle reference speed v RefFil .
• a direct angular velocity 103 becomes a float angle estimated.
• the filtered vehicle reference speed v RefFil and its time derivative, the measured cross, determined in the differentiator 102 (identical to 93 in FIG. 7)
• the scalar is multiplied by the weighting vector k 2 , so that the result is a vector whose first component has the dimension of an angular velocity and whose second component is zero. This vector is also fed to the adder 105.
• the time derivative ⁇ of the state vector x formed from the sum of the equation F 2.7 and that obtained from the multiplication by k 2
• Vector resulting vector is integrated in the integrator 106 to the state vector x.
• the integrator 106 By scalar multiplication with vectors c ⁇ and one of the components ß or from the state vector is hidden as a scalar and processed further. While the hidden on the one hand the GMR control law 16 and on the other hand the direct method 103, the calculated is used within the combined method only as a state variable within the observer and for estimation error determination. For this purpose, the difference between the yaw angular velocity determined from the observer vehicle model is formed in the adder 107 and the measured yaw rate. This difference is calculated using a vector h
• the vehicle reference model is explained below with reference to FIGS. 9 to 15.
• FIG. 9 shows the control circuit according to FIGS. 1 and 2 for controlling the driving stability of a vehicle again in a simplified manner.
• the controllers 7 to 9 in FIG. 1, the associated priority circuit 3 and the engine management 6 were omitted, and the distribution logic 2 was shown combined with the pressure controller 5.
• an additional yaw moment M G about the vertical axis of the vehicle is calculated and set so that the curved path desired by the driver is maintained.
• the additional yaw moment M G is generated by targeted braking processes on the individual wheels, the course of the braking processes and the selection of the wheels to be braked being determined by the distribution logic 2.
• the driver sets the desired direction of travel by means of a corresponding one Angular position of the steering wheel.
• the steering wheel is coupled to the steered wheels in a fixed transmission ratio (steering transmission ratio). In this way, a certain steering angle ⁇ of the wheels is set.
• the size of the change in the yaw angle per unit of time (yaw angular velocity) is calculated on the basis of the input data ) should be.
• the comparator 303 outputs an output quantity which is the difference between and
• the difference value determined in this way is fed to a control law 16 for controlling the yaw moment.
• the regulatory law is calculated on the basis of on
• the distribution logic 2 specifies output variables based on the additional yaw moment M G and possibly a driver request for pressure build-up in the brakes p driver .
• vehicle reference model 302 can be brake pressure values or valve switching times. Optimal operation of the vehicle reference model 302 is also important in the area of low speeds.
• the vehicle reference model 302 can also be provided with a stationary circular model 306 in addition to the linear dynamic single-track model 311 described above.
• the switchover between the computing models 306 and 311 is carried out automatically by a switch in the vehicle reference model 302, not shown in the drawing, as a function of the speed of the vehicle.
• a hysteresis of a few km / h is provided for switching from one model to another.
• the target yaw rate is below the switching threshold calculated according to the model of the stationary circular trip 306. If the speed comes from a low speed, it exceeds that in this direction
• the desired values calculated by the circular travel model such as and ⁇ , are used as start values for the single-track mode dell used. This avoids transients when switching.
• the further calculation is now carried out with the aid of the single-track model 311 until the speed threshold falls below the lower as the speed decreases.
• the correction factors and ß necessary for the circular model are correlated with those previously in the Einspurmo
• the correction values have the following size:
• a preferred model can be that of the stationary circular drive.
• the yaw rate can be calculated using the formula given above
• the target yaw rate is either calculated using a dynamic vehicle model (eg a single-track model) or using a static model (called a stationary circular value) and compared with the measured yaw rate. But with each of these approaches depends
• the specification (and therefore also the control intervention) directly depends on the quality of the vehicle model. Since these are linear replacement models, the model deviates significantly from the actual vehicle behavior in some cases.
• An important goal of the driving stability control is to coordinate the driving behavior in such a way that the reaction of the vehicle to steering, braking and accelerator pedal inputs by the driver is always predictable and easily controllable.
• under- and oversteering operating states of the vehicle must be recognized and corrected for neutral behavior by means of an appropriate brake or engine management intervention.
• the idea for a simplified control principle is to use a direct measure of under- / oversteering behavior as a control variable.
• the mean slip angles of the front and rear axles ( ⁇ v , ⁇ H ) are compared.
• the vehicle At larger slip angles at the front, the vehicle then has an understeering behavior, in the opposite case an oversteering behavior.
• neutral behavior is when the slip angles at the front and rear are the same.
• Understeer / oversteer can be used.
• a control is therefore possible which directly uses the calculated slip angle difference as the controlled variable.
• the requirement for this regulation is to keep the controlled variable small in order to achieve an approximately neutral behavior. It may make sense to set this tolerance threshold asymmetrically so that the tolerance can be selected to be less in the direction of overriding behavior.
• the target yaw rate can be determined based on these considerations calculate (F2.18). This target yaw rate is then compared with and according to FIG. 1 the Re
• a regulation of the driving behavior of the vehicle only makes sense as long as the adhesion of the vehicle wheels on the road allows the calculated additional torque to take effect on the vehicle.
• control system in any case forces the vehicle onto the curved path predetermined by the steering angle ⁇ if the steering wheel has been turned too hard or too quickly with regard to the existing vehicle speed.
• the maximum permissible lateral acceleration a qlim can essentially be determined as a function of the coefficient of friction of the speed v, the longitudinal acceleration a long and possibly other parameters.
• F 2.25 a ql im f (mu, v, a l ong , ... )
• the maximum yaw rate is calculated.
• One possibility for this can be, for example, that the activation logic 11 in FIG. 2 does not forward any current M G to the distribution logic 2 if an excessive float angle is determined,
• the program structure of the control law 16 of the yaw moment controller 10 is described below.
• the program uses four input variables to calculate the additional yaw moment M G around the vertical axis of the vehicle, which is necessary to maintain stable vehicle behavior, especially when cornering.
• the calculated yaw moment M G is the basis for the
• the input 503 is optional. It is available in particular when a so-called observer vehicle model 84 is provided in the overall calculation system.
• the value at input 500 is the difference between the measured yaw rate and the target yaw rate calculated using a vehicle reference model 12 ,
• the value at input 501 results either as a temporal change in the size at input 500 from calculation loop to calculation loop divided by the loop time T 0 , or as
• a calculation loop is understood to mean a calculation run through the FSR controller according to FIG. 1. Due to its structure, such a run takes up a certain real time, the loop time T 0 . For effective regulation, this must be kept sufficiently small.
• the values at inputs 500 and 501 namely and are first fed to a low-pass filter 510 and 511, respectively.
• the two low-pass filters are constructed identically and have a structure as shown in FIG.
• the input variable 520 of the low-pass filter according to FIG. 18 is denoted by u and the output variable 521 by y.
• the output variable 521 is fed to a register 522 and is available in the next calculation as the previous value y (k-1).
• the output value 521 for the calculation loop is then calculated using the following formula
• ⁇ can have values between 0 and 1
• ⁇ describes the value of the low-pass filter.
• k p is a linear weighting factor.
• the low-pass filtering just described takes place for the two input values 500 and 501 and leads to filtered values 515.516.
• the same low-pass filtering 512 takes place for the input variable 502, namely for ,
• the filtered value 517 is supplied to nonlinear filters.
• the purpose of these filters is for small ones initial values to set the output value to 0 and to forward an input value reduced by the limit value for input values that are above a certain limit value.
• the limitation takes place both in the negative and in the positive range.
• the limits and ß th can be variables that are permanently implemented in the program, but also variables that depend on further parameters, for example the coefficient of friction between the tires and the road surface. In this case, the limit values are calculated separately as a linear function of the coefficient of friction.
• All four sizes, namely 515, 516, 517 and 518 are weighted in a further step 530, 531, 532 and 533, each with a linear factor.
• the input variables are modified.
• the calculated yaw moment M G is a filtering
• the calculated target yaw rate can be corrected by additionally taking into account the values that a lateral acceleration sensor delivers.
• the evaluation can be done in different ways.
• a way is proposed in which the measured lateral acceleration is first converted into a slip angle speed. With this value a correction is made
• Threshold th may be after a low pass filtering with a first Threshold th compared (diamond 400). The significance of this comparison only arises after the target value for the yaw angular velocity has been corrected and is therefore explained in more detail below.
• Threshold th compared (diamond 401), wherein the second threshold is greater than the first threshold th 1 .
• an integration 402 of the slip angle speed over time takes place first.
• the slip angle speed is multiplied by the loop time T 0 and added to the previous integration result Intg il .
• the integration steps are counted with n, so that the number n is increased by 1 after the integration (step 403).
• the integration time is thus represented by the number n of integration steps that have taken place.
• the integration result Intg n is ver
• the threshold value size represents a maximum permissible deviation from a theoretically observed float angle.
• the threshold value ⁇ s is on the order of approximately 5 degrees.
• Target yaw rate reevaluated by an additive constant S (step 405), which is dependent on the current slip angle speed and the number n
• step 407 If intg n does not reach the threshold ß s , then not limited (step 407).
• a check is again carried out to determine whether the amount of the estimated slip angle velocity is less than the threshold th 1 . If this is the case, it is interpreted as meaning that the vehicle has stabilized again.
• the result of this is that n is reset to 0 in step 406 and that a target yaw angular velocity is used as the basis for the further calculation in step 407, which is not corrected, that is to say is identical to the value that is available as the result of the vehicle reference model.
• the start value Intg n-1 of the integration is set to zero.
• Another possibility is to manipulate the yaw moment M G , which is calculated by control law 16.
• the difference between the previous value M 1 (k-1) and the current value M 1 (k) is formed.
• the index 1 indicates that these values are the immediate results of the yaw moment controller and have not yet been calculated on the basis of the following correction.
• This difference is related to the loop time T 0 and results in ⁇ M 1 .
• a correction gradient is added to this gradient ⁇ M 1 , which is derived from mul multiplied by a correction factor.
• the gradient corrected in this way is multiplied by the loop time T 0 and added to the yaw moment M (k-1) of the previous calculation. This gives the current moment M G (k) that of the others
• Value M 1 is present, the value from the register 421 in the
• Register 422 shifted and the value in register 421 replaced by the new value.
• the values in the registers 421 and 422 are fed to a calculation logic 430 which calculates a ⁇ M according to the following formula:
• the calculation logic 430 also becomes kinematic -Determination of the estimated slip angle speed. Furthermore, is in a memory Value for a correction factor a with which the
• Floating angle speed is converted into a change in torque.
• the new moment M (k) is calculated using the following formula
• the current value of the corrected torque is stored in register 431, and the value from the previous calculation is stored in register 432.
• the value in register 431 is used as the basis for the further calculation.
• the steering angle represents the curved path of the vehicle desired by the driver.
• the vehicle In the case of a stable stationary cornering, the vehicle is to travel through the web with an approximately constant float angle and constant yaw rate. The driver must compensate for deviations from this float angle or from this yaw rate by counter-steering. However, this is not always possible, especially not when the driver is cornering at the cornering limit speed. In such situations, it is necessary to brake the vehicle in a targeted manner and to apply additional moments about the vertical axis to the vehicle which are to bring about an adaptation of the actual to the desired yaw rate. Control algorithms that describe these relationships have been described above and therefore do not need to be explained in more detail here.
• Each coefficient determines the relationship between the wheel brake pressure and the share of the individual wheel brake forces generated in this way in the yaw moment of the vehicle.
• Parameters that change while a vehicle is traveling are used as parameters when determining the individual coefficients. These are particular - The steering angle ⁇
• variables that are used in the calculation of the coefficients and that are vehicle-specific or brake-specific are surface area A of the brake pistons
• the proposed calculation method has the advantage that the corresponding brake pressures can be calculated very quickly from a predetermined additional yaw moment. If the above parameters change while driving, this is taken into account by changing the coefficients in the brake pressure calculation.
• FIG. 21 schematically shows a vehicle driving straight ahead with four wheels 601, 602, 603, 604.
• a wheel brake 605, 606, 607, 608 is assigned to each of the wheels. These can be controlled independently of one another, the braking forces exerted by the wheel brakes generating braking forces in the contact surfaces of the wheels on the road surface. For example, when the wheel brake 605 is activated on the wheel 601, a braking force F is generated which
• Such moments about the vertical axis of the vehicle can be used in a targeted manner in order to keep a vehicle stable on a track desired by the driver.
• Sensors are still present in the vehicle. These include wheel sensors that measure the angular velocity of the wheels
• the steering wheel angle is detected with a steering sensor 612.
• a sensor 613 is also provided for the yaw rate.
• control device 605, 606, 607, 608 controlled independently of one another, for which purpose a control device is provided which is part of a complex program for regulating driving stability.
• FIG. 22 The basic situation is shown in FIG. 22.
• 16 denotes a program module that calculates the yaw moment M G.
• FIG. 22 shows a control device that calculates pressures p xx that are in the individual wheel brakes 605,606,607,608 should be controlled.
• the determined pressure values 622, 623, 624, 625 can be evaluated further and can be converted into corresponding control signals for the wheel brakes
• 605,606,607,608 can be converted.
• the control device itself consists of two parts, namely a first part 630, in which coefficients c xx are calculated for the individual wheels.
• the coefficients c xx establish a linear relationship between the pressure in the wheel brake and the proportional yaw moment caused by the
• Braking force is caused on the corresponding wheel.
• the second part 631 are weighted by the individual
• the pressure values and the coefficients are designated with indices.
• x stands for either v / l or h / r
• the first calculation part 630 takes into account the steering angle, which is made available to the computing process via an evaluation 632 of the steering sensor 612. To calculate the coefficients, the coefficient of friction ⁇ is taken into account, which is derived from the wheel rotation behavior in an evaluation unit 633 (see also section 2.1). The wheel rotation behavior is in turn determined by a signal from the wheel sensors on the individual wheels. Furthermore, the vehicle mass flows as well Load distribution N z on , which are determined in an evaluation unit 634, in which the vehicle behavior is analyzed in different situations.
• the first program part 630 has access to a memory 635 which contains the above-mentioned vehicle-specific and wheel brake-specific values.
• a coefficient c xx is calculated for each wheel from the values mentioned, whereby the values 640,641,642,643 can be calculated in parallel or in succession.
• the calculation is based on a function that is implemented in the program.
• the known relationships between brake pressure and braking force are taken into account in this function. As a rule, the relationship is linear. Only the steering angle ⁇ has to be considered separately. How the steering angle can be taken into account in a suitable manner is described below.
• the individual coefficients are either produced in parallel or successively
• 640,641,642,643 determines the pressure values for the individual wheel brakes using the following formula:
• the calculation of the individual pressures according to this formula has the advantage that, in order to achieve the calculated braking torque, only relatively low pressures have to be applied to the wheel brakes.
• the brake pressure control can react very sensitively and quickly to changes, in particular the steering angle and the coefficients of friction.
• FIG. 23 shows a schematic illustration of a vehicle, the front wheels 601 and 602 being shown turned. S is the distance between the front wheels, l v is the distance of the
• the wheel planes 650, 651 include steering angles 652, 653 with the longitudinal axis of the vehicle. For the sake of simplicity, it is assumed that the steering angles ⁇ 652.653 are the same size.
• One method of applying unilateral braking forces is to control the wheel brakes in such a way that the wheels are braked to different degrees.
• One method of doing this has been described in the previous section.
• This method reaches a limit when driving stability control is to take place during pedal braking, ie when a certain brake pressure is already set in the wheel brakes due to the braking by the driver.
• the method described above can also be used for this case. Instead of absolute pressures, changes in the brake pressures already set are determined.
• braking force is no longer available.
• the limit of the braking force on one side of the vehicle, which should not be exceeded, can be compensated in the sense of a yaw moment control by reducing the braking force on the other side of the vehicle.
• the wheel brakes of at least one wheel are controlled in such a way that the longitudinal slip 2 of the wheel is set in such a way that it is greater than the longitudinal slip at which the maximum adhesion is achieved.
• This method takes advantage of the fact that the transmitted braking force, i.e. the longitudinal force on the tire, reaches its maximum value with a longitudinal slip of approx. 20% (0% - rolling wheel; 100% - blocked wheel) and with values over 20% the transferable braking force decreases only slightly, so that there is no significant loss in the deceleration of the vehicle with a wheel slip between 20% and 100%.
• the transmittable lateral force that is the force that acts perpendicular to the wheel plane
• it shows a strong dependence on the wheel slip, which manifests itself in the fact that the transmittable lateral force decreases sharply with increasing slip.
• the wheel behaves similarly to a blocked wheel. This means that hardly any lateral forces are applied.
• the selection of the wheel, which is driven at least briefly with increased longitudinal slip, is based on the following rules. To do this, consider a turn to the right that the driver wanted. Corresponding "mirrored" rules apply when cornering to the left. This can result in the vehicle not turning into the curve as much as expected. In other words, the vehicle is understeered. In this case, the rear wheel on the inside of the curve is operated with increased slip values. However, if the vehicle turns too strongly into the curve, this case is called oversteer, the front wheel on the outside of the curve is operated with high slip values.
• the pressure reduction on a front wheel can be prevented. This is done according to the following rules. In a driving situation in which the vehicle is understeering, the brake pressure reduction on the front wheel on the outside of the curve is prevented. In a situation in which the vehicle oversteers, the pressure reduction on the inside front wheel is prevented.
• the actual control of the brake pressure can be done as follows. As already explained above, the brake pressure in the individual wheel brakes is determined as a function of the yaw moment to be achieved and the weighted wheel coefficients.
• a factor dependent on the brake slip can be introduced, which is readjusted in such a way that the desired brake slip described above is achieved.
• the limitation of the pressure reduction on a wheel can be achieved by setting a lower threshold for the corresponding coefficient.
• the control program uses weighted coefficients to calculate the brake pressure that must be generated in each individual wheel brake. The calculation becomes more problematic when the vehicle is braked, in particular when it is decelerated using the adhesion limit between the tire and the road. In such cases, it is entirely possible that an anti-lock control is used first before a superimposed driving stability control becomes necessary.
• This diagram shows slip values ⁇ between 0 and 100% on the X axis, with 0% marking a free-rolling wheel and 100% marking a blocked wheel.
• the y-axis shows the friction and lateral force values ⁇ B and ⁇ s im
• the coefficient of friction decreases slightly towards 100%.
• the lateral force value for a slip angle of 10 °, the lateral force value for a slip value of 0% is 0.85 and for slip values it drops from almost 100% to 0.17.
• FIGS. 25 a, b show a vehicle in a schematic illustration in a right-hand curve. According to the radius of the curve and the speed of the vehicle, the vehicle must rotate about its vertical axis, that is to say there must be a certain yaw rate in the clockwise direction.
• the vehicle has a yaw angle sensor. Deviates the measured yaw rate of the to be achieved then an additional yaw angle sensor.
• the pressure in the right rear wheel brake is increased so that the wheel runs at slip values in the range between 40 and 80%.
• the wheel 604 is therefore marked with a " ⁇ ". As already explained, this has a significant reduction the side force. So there are only slight lateral forces on the right rear wheel, which has the consequence that the vehicle breaks out with the rear to the left, that is, begins a clockwise rotation. The minimization of the lateral force is maintained until the actual yaw rate of the target yaw rate
• FIG. 25b The situation of an oversteering vehicle is shown in FIG. 25b.
• the vehicle turns around the vertical axis faster than this corresponds to a calculated target yaw rate.
• it is proposed to lower the side force on the front left wheel 601. This is also done by setting slip values between 40 and 80% on this wheel.
• the wheel 601 is therefore marked with a " ⁇ " here.
• a subroutine can be stored in the control program, which brings about a further reduction in pressure on the outer front wheel 601 in the event of understeer (FIG. 25a) or on the inner wheel 602 in the event of oversteer (FIG. 25b). These wheels are each marked with “p min ". For cornering to the left, the corresponding controls are reversed.
• the pressure in the individual wheels can now be regulated in such a way that a coefficient is determined for each individual wheel which represents the relationship between the pressure change and the calculated additional yaw moment M G.
• These coefficients are a function of parameters that describe the vehicle or the wheel brakes, as well as variables that change during a journey. These are in particular the steering angle ⁇ and the coefficient of friction ⁇ of the pairing
• Changes in braking force or changes in braking pressure for the individual wheels are determined (program part 641).
• the determined brake pressures are compared with thresholds p th , which are determined, among other things, by the road / tire friction coefficient pairing (diamond 642).
• the thresholds p th determine whether there is another
• the pressures to be set in the wheel brakes are calculated from the additional yaw moment M G using a distribution logic (section 3).
• Control signals for intake and exhaust valves are calculated and output from these pressure values in a subordinate pressure control circuit.
• the actual wheel brake pressures are brought into line with the calculated ones in this subordinate pressure control circuit.
• control signals from other controllers (ABS7, ASR8, EBV9) are also to be included (Section 1.), it is necessary that their control signals are first converted into pressure values using a hydraulic model of the wheel brakes stored in the computer.
• the pressure requirements of the GMR controller 10 are then related to the pressure requirements of the ABS controller and other controllers. This takes place in a priority circuit, which decides which requirements are to be given preference or how far averaged pressures are output to the pressure controller 5 for the wheel brakes.
• the pressure controller 5 in turn converts the pressures into valve switching times.
• the priority circuit can also be supplied with set pressure changes instead of set pressures (see section 7).
• the priority circuit 3 carries out the output of the pressure changes ⁇ p at its output according to the rule that the demand for a pressure drop on one the wheels are preferably fulfilled and the requirement to maintain the pressure in a wheel brake has priority over the requirement to increase the pressure.
• the individual demands on the priority circuit are thus processed in accordance with the rule that if there is a demand for pressure reduction, demands for maintaining the pressure or for pressure buildup are ignored. In the same way, no pressure is built up when pressure maintenance is required.
• the distribution logic does not use the additional yaw moment M G to calculate pressures, but valve switching times directly, like the other controllers.
• the valve switching times of the GMR can thus be compared with the requested valve switching times, for example of the ABS.
• different pressure requirements are not assessed - as before - but different valve switching times.
• the distribution logic first calculates pressure changes to be set for each wheel brake.
• This non-linear control element can e.g. B. be a counter.
• This counter converts the specified pressure changes into cycle numbers.
• the loop time T 0 is divided into approximately 3 to 10 switching intervals (cycles).
• the maximum number of cycles per loop time is a fixed quantity, which is determined by the control quality to be achieved.
• the calculated number of cycles determines how long a valve should be activated within a loop time.
• clock numbers are fed to the priority circuit, which takes up the clock numbers of further controllers in further channels.
• the priority circuit decides which controller should be given priority, which cycle number is to be used for the actual valve control.
• the reaction of the vehicle to the braking forces generated by the actuation of the wheel brakes is a changed yaw rate. This is detected by the GMR controller 10, which in turn now determines a new additional yaw moment.
• Brake pressures are therefore not calculated or set at any point in the control loop.
• the control algorithms therefore do not require any information about the wheel brake, in particular no information about the relationship between the volume absorption of the wheel brakes and the brake pressures resulting therefrom.
• One possibility for calculating the cycle times is explained with reference to FIG. 27.
• the current value is written into the first register position 702.
• the previous value from the first register position 702 is recorded in the second register position 703, so that the print request from the previous calculation loop is written there. This value is referred to as p n *.
• a next step 705 the current print request p n is read from the first register position 702. If this value is 0 or less than a minimum value, the program branches into a loop 706, with which it is intended to ensure that so much pressure medium is removed from the wheel brake that the pressure which is set becomes zero. For this purpose, the inlet valve is closed and the outlet valve is opened for at least one loop time T 0 . If the currently requested pressure value is above this minimum value, the difference is formed from the two register values 702 and 703. This takes place in the difference generator 707.
• the calculated pressure change ⁇ p can either be greater or less than 0. If it is greater than 0, the pressure in the respective wheel brake must be increased. If it is less than 0, the pressure in the respective wheel brake must be reduced.
• the program passes through the right decision path 710. Taking into account the adjusted pressure difference and the pressure requirement or if appropriate signals are present, due to the actual pressure in the wheel brake, At is a calculated for the inlet valve an opening time.
• Exhaust valve is set to zero. Conversely (decision path 711), in the case of the requested the opening time t pressure-lowering one of the intake valve set to zero, whereas the opening time t out of the outlet valve from the requested pressure differential and the actual pressure in the wheel brake or the requested pressure, the is registered in the first register position 702.
• loop time T 0 the control signals for the valves of the wheel brakes being determined in the next loop as the result of a calculation.
• a loop time T 0 is approximately 3 ms.
• each loop time T 0 is divided into N time segments.
• n is set to the maximum value N (in the example shown to six).
• This calculation is carried out for each wheel brake, i.e. four times for a four-wheel vehicle.
• the calculations can be carried out in parallel or in succession.
• These values are fed to a modified priority circuit 720.
• the switching time requirement, also expressed in cycle times, of an ABS controller and further controllers flow into this priority circuit 720.
• This control is carried out so that there is a pressure change in the wheel brakes. This changes the braking forces and the moments exerted on the vehicle. This results in a change in the sizes that describe the driving dynamics of the vehicle. These are detected directly or indirectly by sensors and in turn fed to the calculation.
• Loop 706 branches off to calculate the switching times, which is intended to ensure that a pressure value of zero is actually set. This is done by setting the switching time ⁇ t off for the exhaust valve to at least the loop time T 0 .
• the FSR pressure regulator described up to section 4 provides brake pressure values for the wheel brakes. These values have to be realized.
• One method is to measure the pressures in the wheel brakes and with the values to compare.
• a pressure regulator which works according to the usual laws, regulates the wheel brake pressure to the specified setpoint. This method requires one pressure sensor per wheel brake, i.e. four pressure sensors for a four-wheel vehicle.
• each sensor represents another potential source of interference.
• the failure of a sensor can lead to the entire control system having to be switched off.
• the pressure in each wheel brake is regulated by two valves.
• the inlet valve controls the pressure medium supply, while the outlet valve controls the pressure medium discharge.
• the signals emitted by a pressure regulator are therefore control times that indicate how long a valve should be open or closed.
• a loop time is divided into a fixed number of time segments (cycles).
• the control times can then be represented as cycle clock, which indicates how many time periods a valve should be open or closed.
• the basic idea now is not only to send these control signals to the wheel brakes, but also as arithmetic variables to a vehicle model.
• the real vehicle reacts to the applied brake pressures, with a specific center of gravity v and wheel speeds ⁇ i of the individual wheels being set.
• the speed of the vehicle is not measured directly, but is also derived from the wheel speeds ⁇ i of the individual wheels in special calculation steps. It is therefore referred to as the reference speed v Ref .
• a correction variable for the pressure in the individual wheel brakes can be determined from a comparison of the actual values for ⁇ i , v Ref with the calculated or estimated values for ⁇ i and v Ref based on the vehicle model, with the aid of the correction variable using a hydraulic model calculated pressure can be modified so that a better estimate of the wheel brake pressures can be given.
• Designated at 800 is a pressure control which bears the number 5 in FIG. 1.
• the pressure controller calculates control times for the valves of the wheel brakes from a first value 801, which characterizes the pressure to be set, and from a second value 802, which marks an estimated or measured pressure present in the wheel brake.
• the control times are shown here as output variable 803.
• the vehicle is designated 810. This is to show that the vehicle reacts to the forces caused by the pressures set in the wheel brakes.
• the wheel speeds ⁇ i of the individual wheels also change.
• the vehicle 810 should also include wheel sensors which detect the wheel speeds of the wheels, so that the values ⁇ i are immediately available.
• the vehicle 810 also includes an evaluation unit for ⁇ i , which generally represents a sub-area of an ABS controller, which, under certain boundary conditions, calculates a so-called reference speed v ref from the wheel speeds ⁇ i of the individual wheels, which corresponds to the actual speed of the vehicle should.
• a slip ⁇ i can be calculated for each wheel from the individual wheel speeds and the vehicle reference speed.
• the values ⁇ i , v Ref are available as output values 811.
• the slip ⁇ i is available as a value 812.
• the calculation model used is designated 820 as a whole. It contains three sub-models, namely an 821 hydraulic model
• the hydraulic model 821 describes in two approximation formulas the relationship between brake pressure p and the volume V enclosed in the wheel brake as well as the change ⁇ V in the volume when the intake and exhaust valves are open for a certain time.
• Parameters a, b and c are variables that describe the braking system and are stored as values in the corresponding memory.
• p describes the current pressure in the wheel brake.
• V describes the current volume that is included in the wheel brake.
• ⁇ p is measured either via the inlet valve or via the outlet valve, the difference between a pressure source and p being detected when measuring via the inlet valve, while the difference between p and the pressure in a reservoir is determined when measuring via the outlet valve, the is generally 1 bar and can therefore be neglected.
• the change in volume and thus the pressure change in the individual wheel brakes can be tracked by tracking the valve opening times.
• the vehicle is generally described by a rigid body standing on one level at four contact points (wheel contact patches).
• the body can move parallel to the plane in the x and y direction and rotate around its center of gravity, the axis of rotation being perpendicular to the plane of movement.
• Forces that act on the body are the braking forces in the wheel contact patches as well as air resistance forces.
• the model essentially supplies the loads F x of the contact areas depending on the deceleration of the center of gravity.
• the wheel is viewed as a rotatable disc that has a certain moment of inertia.
• the deceleration moments that act on the wheel are determined linearly from the wheel brake pressure.
• the tire model assumes that the adhesion utilization f, namely the ratio of braking force to wheel load, changes linearly with the slip of the wheel.
• the accuracy of the estimate depends, of course, on the correction factor k, which may have to be determined beforehand by tests.
• This factor will vary from vehicle to vehicle and will also depend, among other things, on how well the vehicle model reflects the actual conditions.
• the additional volume can also contain a tolerance volume with which it should be taken into account that the volume throughput through the valves is not proportional to the switching times.
• the yaw rate is a particularly striking variable, since it serves as a control variable and its deviation should be minimized.
• the measured yaw rate in FIG. 12 is usually determined by means of a yaw rate sensor 321, which outputs the output signal g I.
• a yaw rate sensor 321 which outputs the output signal g I.
• Known yaw rate sensors of this type with direct delivery of the yaw rate are, however, of a complex design and are therefore very expensive. The same applies to the downstream comparator and the controller belonging to the control circuit. It is therefore sought to remedy this and to present a simpler sensor system and a more simply constructed controller.
• FIG. 13 shows a sketch of the mode of operation of a novel sensor 321, which has a first transverse accelerometer 322 and a second transverse accelerometer 323.
• the two accelerometers 322, 323 are each arranged on the vehicle longitudinal axis above the front and rear axles.
• the transverse accelerometers can be arranged at any point outside the center of gravity SP, with a corresponding conversion then taking place.
• the square outline 324 of a vehicle with its tires 325 and sensors is indicated. Based on these In the arrangement, the front lateral accelerometer 322 measures the lateral acceleration a qv at the front axle 326 and the rear lateral accelerometer 323 measures the lateral acceleration a qh at the rear axle 327.
• the two lateral accelerometers are able to indicate a variable depending on the yaw rate. From mathematical derivations it can be shown that the yaw angle acceleration and the lateral acceleration a across the center of gravity SP can be determined from the measurement results as follows:
• l v , l h are the distances of the lateral accelerometers 322, 323 from the center of gravity SP, while v is the speed of the vehicle and ß is the angle of attack. It can thus be determined from the lateral accelerations and the distances between the accelerometers 322.323 the yaw acceleration determine. It is therefore proposed to enter the yaw angle acceleration
• the yaw rate g and the float angle ⁇ can be determined from the yaw pressure and the
• Integration or a scaled low-pass filter of the first order can be calculated in order to obtain from the sensor 321 quantities which correspond in their dimensions to the output quantities of the vehicle reference model 302 (section 2.3.1).
• the float angle velocity is obtained after evaluating the relationship
• Transversal accelerometers can be replaced with a known yaw rate sensor. However, the measures just described must be taken to transform the yaw rate acceleration into the yaw rate. After formation of ⁇ g and the law 16 of FIG. 1 can follow unchanged. In Fig. 14, the torque M G thus calculated is additionally in the control law
• Result from the vehicle reference model 302 is fed to the comparator 303. Corresponding derivations must be formed within the vehicle reference model.
• the yaw moment regulation law 16 can additionally be supplied with the slip angle speed for more precise determination of the change in moment.
• the torque change ⁇ that is, the derivation of the additional yaw moment M G
• the pressure changes are distributed to the individual wheel brakes in such a way that the desired additional yaw moment M G results overall. Details of this are given below in connection with FIG. 16.
• two threshold switches S2, S3 are shown in the control law 16 according to FIG. 15, which are intended to improve the control behavior within the control law 16 and to optimally adapt the influence of the quantities introduced as a function of the speed to the ideal control behavior.
• the amplifiers k1 to k3 have a comparable task.
• the individual values are then added in an adder and output as the output signal of the GMR controller 10.
• General explanations of the regulatory law, which apply here accordingly, can be found in section 2.4.
• FIGS. 9, 14 shows the control circuit for regulating the driving stability of FIGS. 9, 14 again in a greatly simplified manner, the designations introduced there being retained.
• the GMR controller 10 according to FIG. 1 is modified here insofar as the change ⁇ of the additional yaw moment at the output
• the distribution logic 2 has a logic block 340 and a pressure gradient circuit 341.
• the essential task of logic block 340 is to ensure that, despite the intervention of the driving stability control, the vehicle as a whole is not braked more than the driver desires by specifying his pressure signal at the input of distribution logic 2. This is to prevent instabilities from being additionally caused by the driving stability control. If, due to the driver's braking request, braking pressure is provided on one wheel and, on the other hand, the FSR controller requires pressure build-up on one or two wheels and pressure reduction on the opposite wheels in order to achieve the additional yaw moment, then of the individual wheels there are contradicting requirements, namely pressure build-up with simultaneous pressure reduction.
• the pressure should be built up not only on the basis of the driver's braking request, but also on the basis of the stability control.
• the logic block now ensures that the brake pressure is first lowered in the corresponding wheels, while subsequently the brake pressure can be increased beyond the driver's request up to a certain limit value. This ensures that the average braking force seen across all wheels, taking into account the additional torque brought about by the FSR control, is not greater than that desired by the driver.
• a targeted increase in the longitudinal slip ⁇ on a wheel can be used to reduce the lateral forces while maintaining the braking force in the longitudinal direction. In this way, a yaw moment can be applied without the vehicle deceleration decreasing.
• the pressure gradient circuit 341 of the distribution logic 2 the pressure changes ⁇ P xx on the individual wheels xx due to predetermined constants d xx and the torque change
• the actual brake pressure p xxist is determined either by a
• Pressure gauge on the affected wheel removed or calculated using a brake model that follows the pressure changes prescribed on the wheel and is therefore an image of the pressure currently prevailing on the wheel (section 6).
• the calculated pressure requests are fed to a priority circuit 3 and evaluated there (see section 4 above).
• Kr xx is a gain factor that depends on the actual pressure of the individual wheels and when pressure builds up according to the following rule is calculated while for pressure reduction
• xx is again an index that identifies the position of the individual wheels.

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