US20040068358A1 - Anti-lock braking system controller for adjusting slip thresholds on inclines - Google Patents
Anti-lock braking system controller for adjusting slip thresholds on inclines Download PDFInfo
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- US20040068358A1 US20040068358A1 US10/264,685 US26468502A US2004068358A1 US 20040068358 A1 US20040068358 A1 US 20040068358A1 US 26468502 A US26468502 A US 26468502A US 2004068358 A1 US2004068358 A1 US 2004068358A1
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Classifications
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- 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
- B60T8/1761—Brake regulation specially adapted to prevent excessive wheel slip during vehicle deceleration, e.g. ABS responsive to wheel or brake dynamics, e.g. wheel slip, wheel acceleration or rate of change of brake fluid pressure
- B60T8/17616—Microprocessor-based systems
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L2220/00—Electrical machine types; Structures or applications thereof
- B60L2220/40—Electrical machine applications
- B60L2220/46—Wheel motors, i.e. motor connected to only one wheel
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- 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
- B60T2201/00—Particular use of vehicle brake systems; Special systems using also the brakes; Special software modules within the brake system controller
- B60T2201/04—Hill descent control
Definitions
- the present invention relates to braking systems for vehicles, and more particularly to antilock braking systems for vehicles.
- ABS Anti-lock braking systems
- ABS do not include costly brake pressure transducers, brake pedal force sensors, or attitude sensors.
- Conventional ABS include a “peak seeking” control method that slowly adjusts the wheel slip and wheel deceleration thresholds by applying rate controlled brake pressure increases. This peak seeking method may require several apply and release cycles to approach the correct slip and deceleration target thresholds. The adjustments made by these systems usually happen too slowly to adjust for inclines, turns, and/or vehicle loading.
- ABS do not compensate for changes in the distribution of vehicle weight when braking or turning a corner.
- Conventional ABS also do not compensate for changes in weight distribution and traction when additional items are added to vehicle storage compartments. For example, the driver may load a trunk of a vehicle or a bed of a pickup truck with heavy items such as luggage or loads such as gravel. Alternately, an interior compartment of the vehicle may be filled with passengers and/or other heavy items. The failure to adequately compensate for the additional vehicle weight may cause instability during braking.
- ABS when braking on a curve while traveling downhill, conventional ABS fail to optimize available traction to decelerate the vehicle as quickly as possible.
- Conventional ABS fail to account for changing steering angle and its impact on vehicle weight distribution and traction.
- a rear wheel located on an inner side of the downhill turn has dramatically reduced weight and traction.
- the front wheel on an outer side of the downhill turn has increased weight and traction.
- Vehicle control may be adversely impacted if too much brake torque is applied while engaging the brakes in a turn, particularly in a turn on a downgrade. Vehicle load is another factor that can dramatically impact ABS performance.
- a method and apparatus for operating a vehicle anti-lock braking system includes a brake pedal and a brake modulator.
- the anti-lock braking system reduces braking pressure by an initial pressure reduction after detecting insipient wheel lock.
- Vehicle deceleration is measured as a function of brake pedal position.
- a first table is updated with the vehicle deceleration and the brake pedal position.
- a coefficient of friction of a road surface is estimated based on the first table.
- a slip target for a wheel is generated based on an estimated maximum slip of the wheel before losing traction minus an estimated potential for vehicle rollover.
- a deceleration target for the wheel is generated based on an estimated maximum deceleration of the wheel before losing traction minus the estimated potential for vehicle rollover.
- rollover lateral acceleration is estimated.
- the estimated potential for vehicle rollover is based on the estimated rollover lateral acceleration.
- Grade is estimated based on rolling resistance, drag, engine braking, brake torque and acceleration. Vehicle weight, steering angle and steering rate are estimated.
- weight distribution for the wheel is estimated.
- the weight distribution is adjusted for roll, pitch, and lateral and longitudinal acceleration.
- Brake release and apply torque for each of the wheels is calculated based on the coefficient of friction, attitude, and weight distribution.
- FIG. 1 is a functional block diagram of an anti-lock braking system according to the present invention
- FIG. 2 is a graph showing deceleration as a function of brake pedal position
- FIG. 3 is a graph showing deceleration as a function of three brake pedal positions.
- FIGS. 4 A- 4 D are exemplary flowcharts illustrating steps performed by the anti-lock braking system controller to adjust slip thresholds according to the present invention.
- An ABS controller adjusts slip thresholds of wheels of the vehicle that are likely to cause instability on downhill turns.
- the slip thresholds are preferably set lower for the wheels that are likely to cause instability.
- the reduced slip thresholds and corresponding reduction in brake torque prevent vehicle spinout, rollover and/or other loss of control.
- the ABS controller may be used with vehicles with smart brakes (electro-hydraulic, dry interface, VSES, TCS, etc.). In these systems, the brake torque is adjusted at each wheel of the vehicle to provide improved vehicle stability and control on hills.
- the ABS controller according to the present invention may also be used with transmission controllers to prevent a transmission downshift that may make the vehicle unstable. This additional feature is particularly useful on vehicles with rear wheel drive.
- a coefficient of friction of the road surface can be calculated by establishing a relationship between pedal position and deceleration. For example, a table or formula may be trained during operation of the vehicle. Surface mu is also used to calculate brake heat, vehicle weight, and grade. A suitable method for calculating brake heat, vehicle weight and grade is disclosed in “Anti-Lock Brake Control Method Having Adaptive Initial Brake Pressure Reduction”, U.S. Ser. No. 09/882,795, filed Jun. 18, 2001, which is hereby incorporated by reference. Roll and Pitch may be calculated using attitude sensors, using fluid reservoirs with level sensors, or in any other suitable manner.
- a vehicle 12 includes hydraulically activated friction brakes 14 , 16 , 18 , and 20 at vehicle wheels 22 , 24 , 26 , and 28 , respectively.
- a driver-actuated brake pedal 30 is mechanically and/or electrically coupled to a master cylinder (MC) 32 for producing hydraulic pressure in proportion to the force that is applied to the brake pedal 30 .
- MC master cylinder
- the master cylinder 32 which may include a pneumatic booster (not shown), proportions the hydraulic pressure between front and rear brake supply lines 34 and 36 in a conventional manner.
- the front supply line 34 is coupled to the left front (LF) brake 14 by a LF anti-lock modulator (M) 38 and to the right front (RF) brake 16 by a RF anti-lock modulator (M) 40 .
- the rear supply line 36 is coupled to the left and right rear wheel brakes 18 and 20 by a rear anti-lock modulator (M) 42 .
- An ABS controller 50 receives various inputs, including wheel speed signals on lines 52 , 54 , 56 , and 58 from wheel speed sensors 60 , 62 , 64 , and 66 respectively.
- An attitude sensor 67 provides roll and pitch signals.
- the ABS controller 50 receives a brake pedal position signal on line 68 from pedal position sensor 70 .
- the ABS controller 50 outputs modulator control signals on lines 72 , 74 , and 76 during wheel lock-up conditions.
- the ABS controller 50 may also output diagnostic information signals for display on a driver information device (not shown) associated with an instrument panel.
- the ABS controller 50 preferably includes a processor, an input/output (I/O) interface, and memory such as read-only memory (ROM), random access memory (RAM), flash memory and/or other suitable electronic storage.
- the ABS controller 50 can also be implemented as an application specific integrated circuit (ASIC).
- ASIC application specific integrated circuit
- the ABS controller 50 monitors the measured wheel speeds to detect a condition of insipient wheel lock.
- the controller 50 adjusts modulators 38 , 40 , and 42 to modulate the respective hydraulic brake pressures to maximize the tractive force between the vehicle tires and the road surface.
- the modulators 38 , 40 , and 42 are activated to rapidly reduce the respective brake pressures to eliminate wheel slip.
- the amount of pressure reduction that is required to eliminate wheel slip varies with the coefficient of friction between the tires and the road surface.
- Conventional ABS controller 50 assume a low coefficient of friction such as glare ice since the actual coefficient of friction of the road surface is ordinarily unknown.
- the reduction in brake pressure provided by the ABS controller 50 allows the wheels 22 , 24 , 26 , and 28 to accelerate.
- the controller 50 measures the time that is required for the wheel acceleration to reach a reference acceleration value.
- Conventional ABS controllers estimate the coefficient of friction based on the measured time.
- the modulators 38 , 40 , and 42 are controlled to re-apply brake pressures based on the estimated coefficient(s) of friction.
- the ABS controller 50 estimates the coefficient of friction between the tires and the road surface prior to the initial pressure reduction. For example, if the coefficient of friction is relatively high, the initial pressure reduction can be relatively small and the performance of the ABS is improved. Brake pressure can be rapidly re-applied once the wheel acceleration reaches the reference acceleration value. As a result, shorter stopping distances are produced.
- the ABS controller 50 adaptively determines the coefficient of friction of the road surface.
- the ABS controller 50 determines the initial brake pressure reduction when insipient wheel lock occurs.
- the coefficient of friction is computed based on brake torque and vehicle weight.
- Brake torque and vehicle weight are adaptively determined based on a periodically updated table defining a relationship between brake pedal position and vehicle deceleration. The relationship is corrected for variations in brake heating.
- FIG. 2 graphically depicts a representative relationship between vehicle deceleration and brake pedal position for braking of the vehicle 12 .
- the relationship assumes that there is no lock-up condition and the modulators 38 , 40 , and 42 are inactive.
- a lower “knee” portion of the relationship varies considerably from stop to stop.
- the portion of the relationship above the knee portion tends to be linear and repeatable from stop to stop. For this reason, the lower knee portion of the relationship is preferably not used.
- the brake pedal position vs. vehicle deceleration relationship is preferably characterized for pedal positions and vehicle decelerations in the linear portion above the knee portion.
- Braking characterization data is collected by determining pedal positions that correspond to a plurality of different vehicle deceleration values.
- deceleration values Dl, D2 and D3 correspond to pedal position values P vsd (0), P vsd (1), and P vsd (2).
- the braking data is collected during braking operation when the pedal 30 is depressed at a “normal” rate or held in a static position for a predetermined period. Data is not collected while the brake pedal 30 is released or during panic braking. This eliminates the need to compensate for dynamic effects such as suspension, powertrain, tire and sensor dynamics. Additional details can be found in Walenty et al., U.S. Pat. No. 6,405,117, which is hereby incorporated by reference.
- Brake_Heat Brake_Heat - ( ( MPH + K coolspdmin ) 2 + K coolspd ) * ( Brake_Heat - ( Brake_Heat * K coolambient ) + ( Brake ⁇ ⁇ Torque * ( K heat * MPH ) ) * ( K maxtemp - Brake_Heat ) / K maxtemp ) ( 1 )
- Brake_Torque ( ( Pedal ⁇ ⁇ Position - ( P vsd ⁇ ( 0 ) ) * ( ( P vsd ⁇ ( 2 ) - P vsd ⁇ ( 0 ) / ( D3 - D1 ) ) * K brk_torque ) + ( ( Update_Brake ⁇ _heat - Brake_heat ) * K heat_crv ) (
- variables starting with a K are stored and/or calculated values.
- ABS Before ABS becomes active, the coefficient of friction, grade, vehicle weight, steering angle, steering rate, lateral and longitudinal accelerations are calculated and sent to the ABS controller. There are many ways of determining steering angle. For example,
- SteerAngle ( LF speed +LR speed ) ⁇ ( RF speed +RR speed )* K stang — spd . (6)
- K stang — spd is function that converts speed delta into steering angle.
- U.S. Pat. No. 5,465,210 which is hereby incorporated by reference, a steering wheel position sensor and a method for determining a vehicle steering wheel center position are disclosed.
- SteerAngle (Steer_wheel_center — pos ⁇ Steer_wheel_pos )* K stang — pos . (7)
- Steering wheel position is preferably an integer that ranges between 0 and 256. 0 corresponds to full left or right lock and 256 corresponds to full right or left lock. K stang — pos is a function that converts position into steering angle. Still other methods of sensing and/or calculating steering angle are contemplated.
- K slat converts angle and speed into lateral acceleration.
- K wt — trLF is preferably stored in a lookup table that provides the normal (calibratable) percentage of weight on the left front corner of the vehicle at various vehicle attitudes.
- K wt — trLF is modified by weight transference due to acceleration.
- K st — la is an anticipatory correction based on the steering rate to correct for tire scrub and actuator latency.
- the brake torque command is synonymous with a motor position of the brake actuator.
- the motor position vs. brake pedal position typically resides in a look-up table that is adjusted to optimize brake torque at each corner while on hills.
- ABS When ABS becomes active, an accurate amount of release pressure may be calculated based upon the surface mu, attitude, weight transference, and steering angle.
- K rel modifies the release target to slightly overshoot the release target on grades at which the tire(s) lose tractive cohesion with the road surface.
- Target brake torque for each corner is modified by surface mu and weight distribution as follows.
- K app modifies the apply target to slightly undershoot the real target on grades at which the tire(s) lose all tractive cohesion with the road surface.
- Vehicle stability enhancement (VSES) or Traction Control (TCS) slip thresholds are set lower on wheels that are likely to cause instability on downhill turns.
- the lower application of brake torque helps prevent spinout and rollover.
- Vehicles equipped with smart brakes electro-hydraulic, dry interface, VSES, TCS, etc. may use this invention to make brake torque adjustments at each corner to provide better vehicle stability control on hills.
- K roll — slip converts Roll_Lat_g's to wheel slip.
- LF Decel Target is the maximum deceleration that a tire may support before losing tractive cohesion with the road surface minus the potential for vehicle rollover.
- LF ⁇ ⁇ Decel ⁇ ⁇ Target ( ( Max ⁇ ⁇ LF ⁇ ⁇ Decel * 1 - surface ⁇ ⁇ mu ) * LFwt ) - Roll_Lat ⁇ _g ' ⁇ s . ( 18 )
- step 102 control begins.
- step 104 the ABS controller 50 reads brake pedal position, speeds, Form Slip, and Form Decel.
- the ABS controller 50 records a pedal position vs. deceleration table.
- the ABS controller 50 calculates brake heat, brake torque, vehicle weight, grade, and Surface Mu.
- the ABS controller 50 looks up the ABS_Table(decel,Slip) command.
- step 106 the ABS controller 50 determines whether ABS is equal to true. If true, the ABS controller 50 operates the ABS system as indicated at 108 . If step 106 is false, control continues with step 110 where the ABS controller 50 determines whether Veh accel >K accel . If false, control continues with step 114 where the ABS controller 50 determines whether Old pedpos>New pedpos. If false, control continues with step 118 where the ABS controller 50 determines whether (New pedpos ⁇ Old pedpos)>K brate . If false, control continues with step 122 where the ABS controller 50 determines whether (Veh accel ⁇ Onset accel ) ⁇ CalD1.
- step 122 determines whether ABS(SlipLF ⁇ oldslipLF)>K 5 %. If step 126 is false, control continues with step 130 where the ABS controller 50 determines whether Lataccel>K 0.15 g or if steerangle>K 5deg . If step 130 is false, control continues with step 132 . If any of the steps 110 - 130 are true, control ends at 133 .
- LFs Scal ( LF, 0)+ Scal ( LF, 1)+ Scal ( LF, 2)
- RFs Scal ( RF, 0)+ Scal ( RF, 1)+ Scal ( RF, 2)
- LFs Scal ( LR, 0)+ Scal ( LR, 1)+ Scal ( LR, 2)
- RRs Scal ( RR, 0)+ Scal ( RR, 1)+ Scal ( RR, 2)
- LF — bal — cal LFs/ ( LFs+RFs+LRs+RRs )
- RF — bal — cal RFs/ ( LFs+RFs+LRs+RRs )
- LR — bal — cal LRs/ ( LFs+RFs+LRs+RRs )
- RR — bal — cal RRs/ ( LFs+RFs+LRs+RRs )
- step 174 Control continues from step 170 to step 174 where the controller 50 performs the following:
- Brk — eff — nom (Pedal Position ⁇ ( P vsd — cal (0))* Brk — eff — cal
- Brk — eff _actual (Pedal Position ⁇ (P vsd — cal (0))*( P vsd (2) ⁇ P vsd (0))/( D 3 ⁇ D 1)
- LFs Svsd ( LF, 0)+ Scal ( LF, 1)+ Scal ( LF, 2)
- RFs Svsd ( RF, 0)+ Scal ( RF, 1)+ Scal ( RF, 2)
- RRs Svsd ( RR, 0)+ Scal ( RR, 1)+ Scal ( RR, 2)
- LF — bal — act LFs/ ( LFs+RFs+LRs+RRs )
- RF — bal — act RFs/ ( LFs+RFs+LRs+RRs )
- LR — bal — act LRs/ ( LFs+RFs+LRs+RRs )
- RR — bal — act RRs/ ( LFs+RFs+LRs+RRs )
- step 176 Control continues from step 174 to step 176 where the ABS controller 50 performs the following:
- Brake_Torque ((Pedal Position ⁇ ( P vsd (0))*(( P vsd (2) ⁇ P vsd (0))/( D 3 ⁇ D 1)))* K brk — torque )+((Update_Brake_heat ⁇ Brake_heat)* K heat — crv )
- Brake_Heat Brake_Heat ⁇ ((MPH+ K coolspdmin ) ⁇ circumflex over ( ) ⁇ 2* K coolspd )*(Brake_Heat ⁇ (Brake_Heat* K coolambient )+( Brake Torque *( K heat *MPH ))*( K maxtemp ⁇ Brake_Heat)/ K maxtemp )
- Vehicle_Weight LVW+ (((( P vsdold (2) ⁇ ( P vsdold (0)) ⁇ (( P vsd (2) ⁇ P vsd (0))/( D 3 ⁇ D 1)))*K veh — weight )+((Update_Brake_heat ⁇ Brake_heat)* K heat — crv )
- step 176 Control continues from step 176 to step 178 where the ABS controller 50 performs the following:
- Brk — eff — LF (( Brk — eff _ratio* K front — Brk eff )+(Brake_Heat* K front — fade — eff )+(Grade* K front — grade — wt — transfer )+(Vehicle_Weight* K front — wt — transfer ))* LF _bal_ratio
- Brk_eff ⁇ _RF ( ( Brk_eff ⁇ _ratio * K front_Brk ⁇ _eff ) + ( Brake_Heat * K front_fade ⁇ _eff ) + ( Grade * K front_grade ⁇ _wt ⁇ _transfer ) + ( Vehicle_Weight * K front_wt ⁇ _transfer ) ) * RF_bal ⁇ _ratio
- Brk — eff — LR (( Brk — eff _ratio* K rear — Brk eff )+(Brake_Heat* K rear — fade — eff )+(Grade* K rear — grade — wt — transfer )+(Vehicle_Weight* K rear — wt — transfer ))* LR _bal_ratio
- Brk — eff — LR (( Brk — eff _ratio* K rear — Brk eff )+(Brake_Heat* K rear — fade — eff )+(Grade* K rear — grade — wt — transfer )+(Vehicle_Weight* K rear — wt — transfer ))* RR _bal_ratio
- step 176 Control continues from step 176 to step 178 where the ABS controller 50 performs the following:
- Ramp_rate — LF K front — ramp — rate *( K front — eff — ramp — rate *Brk — eff — LF )
- ABS _Table LF ( i,j ) ( K slip — front(i,j) *Brk — eff — LF )+( K decel — front(i,j) *Brk — eff — LF )
- ABS _Table RF ( i,j ) ( K slip — front(i,j) *Brk — eff — RF )+( K decel — front(i,j) *Brk — eff — RF )
- ABS _Table LR ( i,j ) ( K slip — C(i,j) *Brk — eff — LR )+( K decel — Rear(i,j) *Brk — eff — LR )
- ABS _Table RR ( i,j ) ( K slip — C(i,j) *Brk — eff — RR )+( K decel — Rear(i,j) *Brk — eff — RR )
- the ABS controller may also be used in vehicles with electronic transmission control to prevent a transmission downshift to first or second gear that would make the vehicle unstable, which is useful in rear wheel drive vehicles.
- the ABS controller provides a more effective way of identifying the actual coefficient of friction for each corner when engaging the brakes while turning on steep hills, which allows the proper calculation of release and apply pressures and slip and decel targets.
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Abstract
Description
- The present invention relates to braking systems for vehicles, and more particularly to antilock braking systems for vehicles.
- Stopping a car quickly on a slippery road is challenging task for drivers. Anti-lock braking systems (ABS) have significantly improved stopping distances on both dry and slippery roads. On slippery roads, even professional drivers cannot stop a vehicle as quickly without ABS as an average driver can with ABS. ABS rely on the fact that a skidding wheel (where the tire contact patch is sliding relative to the road) of a vehicle has less traction than a non-skidding wheel. By preventing the wheels from skidding while the vehicle slows down, ABS operation stops the vehicle faster and allow the vehicle to be steered during a panic stop.
- Most ABS do not include costly brake pressure transducers, brake pedal force sensors, or attitude sensors. Conventional ABS include a “peak seeking” control method that slowly adjusts the wheel slip and wheel deceleration thresholds by applying rate controlled brake pressure increases. This peak seeking method may require several apply and release cycles to approach the correct slip and deceleration target thresholds. The adjustments made by these systems usually happen too slowly to adjust for inclines, turns, and/or vehicle loading.
- Normal front to rear weight distribution of a front wheel drive (FWD) vehicle at rest is 60% front and 40% rear (60/40). Left to right balance is typically 50/50. Weight transfer due to braking at 0.9 g on a level surface in a straight line creates a front to rear weight distribution of 84/16. Weight transference due to a right turn at 0.3 g on a level surface at a steady speed creates a left to right weight distribution of 65/35. Pitch and roll angles of the road surface further complicate these dynamics.
- Conventional ABS do not compensate for changes in the distribution of vehicle weight when braking or turning a corner. Conventional ABS also do not compensate for changes in weight distribution and traction when additional items are added to vehicle storage compartments. For example, the driver may load a trunk of a vehicle or a bed of a pickup truck with heavy items such as luggage or loads such as gravel. Alternately, an interior compartment of the vehicle may be filled with passengers and/or other heavy items. The failure to adequately compensate for the additional vehicle weight may cause instability during braking.
- For example, when braking on a curve while traveling downhill, conventional ABS fail to optimize available traction to decelerate the vehicle as quickly as possible. Conventional ABS fail to account for changing steering angle and its impact on vehicle weight distribution and traction. A rear wheel located on an inner side of the downhill turn has dramatically reduced weight and traction. The front wheel on an outer side of the downhill turn has increased weight and traction. Vehicle control may be adversely impacted if too much brake torque is applied while engaging the brakes in a turn, particularly in a turn on a downgrade. Vehicle load is another factor that can dramatically impact ABS performance.
- A method and apparatus according to the present invention for operating a vehicle anti-lock braking system includes a brake pedal and a brake modulator. The anti-lock braking system reduces braking pressure by an initial pressure reduction after detecting insipient wheel lock. Vehicle deceleration is measured as a function of brake pedal position. A first table is updated with the vehicle deceleration and the brake pedal position. A coefficient of friction of a road surface is estimated based on the first table. A slip target for a wheel is generated based on an estimated maximum slip of the wheel before losing traction minus an estimated potential for vehicle rollover.
- In other features of the invention, a deceleration target for the wheel is generated based on an estimated maximum deceleration of the wheel before losing traction minus the estimated potential for vehicle rollover.
- In still other features, rollover lateral acceleration is estimated. The estimated potential for vehicle rollover is based on the estimated rollover lateral acceleration. Grade is estimated based on rolling resistance, drag, engine braking, brake torque and acceleration. Vehicle weight, steering angle and steering rate are estimated.
- In other features, weight distribution for the wheel is estimated. The weight distribution is adjusted for roll, pitch, and lateral and longitudinal acceleration. Brake release and apply torque for each of the wheels is calculated based on the coefficient of friction, attitude, and weight distribution.
- Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
- The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
- FIG. 1 is a functional block diagram of an anti-lock braking system according to the present invention;
- FIG. 2 is a graph showing deceleration as a function of brake pedal position;
- FIG. 3 is a graph showing deceleration as a function of three brake pedal positions; and
- FIGS.4A-4D are exemplary flowcharts illustrating steps performed by the anti-lock braking system controller to adjust slip thresholds according to the present invention.
- The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
- An ABS controller according to the present invention adjusts slip thresholds of wheels of the vehicle that are likely to cause instability on downhill turns. In particular, the slip thresholds are preferably set lower for the wheels that are likely to cause instability. The reduced slip thresholds and corresponding reduction in brake torque prevent vehicle spinout, rollover and/or other loss of control.
- The ABS controller may be used with vehicles with smart brakes (electro-hydraulic, dry interface, VSES, TCS, etc.). In these systems, the brake torque is adjusted at each wheel of the vehicle to provide improved vehicle stability and control on hills. The ABS controller according to the present invention may also be used with transmission controllers to prevent a transmission downshift that may make the vehicle unstable. This additional feature is particularly useful on vehicles with rear wheel drive.
- A coefficient of friction of the road surface (surface mu) can be calculated by establishing a relationship between pedal position and deceleration. For example, a table or formula may be trained during operation of the vehicle. Surface mu is also used to calculate brake heat, vehicle weight, and grade. A suitable method for calculating brake heat, vehicle weight and grade is disclosed in “Anti-Lock Brake Control Method Having Adaptive Initial Brake Pressure Reduction”, U.S. Ser. No. 09/882,795, filed Jun. 18, 2001, which is hereby incorporated by reference. Roll and Pitch may be calculated using attitude sensors, using fluid reservoirs with level sensors, or in any other suitable manner.
- Referring to FIG. 1, an anti-lock braking system (ABS)10 is shown. A
vehicle 12 includes hydraulically activatedfriction brakes vehicle wheels brake pedal 30 is mechanically and/or electrically coupled to a master cylinder (MC) 32 for producing hydraulic pressure in proportion to the force that is applied to thebrake pedal 30. - The
master cylinder 32, which may include a pneumatic booster (not shown), proportions the hydraulic pressure between front and rearbrake supply lines front supply line 34 is coupled to the left front (LF)brake 14 by a LF anti-lock modulator (M) 38 and to the right front (RF)brake 16 by a RF anti-lock modulator (M) 40. Therear supply line 36 is coupled to the left and rightrear wheel brakes - An
ABS controller 50 receives various inputs, including wheel speed signals onlines wheel speed sensors attitude sensor 67 provides roll and pitch signals. TheABS controller 50 receives a brake pedal position signal online 68 frompedal position sensor 70. In response to the various inputs, theABS controller 50 outputs modulator control signals onlines ABS controller 50 may also output diagnostic information signals for display on a driver information device (not shown) associated with an instrument panel. - The
ABS controller 50 preferably includes a processor, an input/output (I/O) interface, and memory such as read-only memory (ROM), random access memory (RAM), flash memory and/or other suitable electronic storage. TheABS controller 50 can also be implemented as an application specific integrated circuit (ASIC). - In general, the
ABS controller 50 monitors the measured wheel speeds to detect a condition of insipient wheel lock. Thecontroller 50 adjustsmodulators modulators Conventional ABS controller 50 assume a low coefficient of friction such as glare ice since the actual coefficient of friction of the road surface is ordinarily unknown. - The reduction in brake pressure provided by the
ABS controller 50 allows thewheels controller 50 measures the time that is required for the wheel acceleration to reach a reference acceleration value. Conventional ABS controllers estimate the coefficient of friction based on the measured time. Themodulators - The
ABS controller 50 according to the present invention estimates the coefficient of friction between the tires and the road surface prior to the initial pressure reduction. For example, if the coefficient of friction is relatively high, the initial pressure reduction can be relatively small and the performance of the ABS is improved. Brake pressure can be rapidly re-applied once the wheel acceleration reaches the reference acceleration value. As a result, shorter stopping distances are produced. - The
ABS controller 50 adaptively determines the coefficient of friction of the road surface. TheABS controller 50 determines the initial brake pressure reduction when insipient wheel lock occurs. The coefficient of friction is computed based on brake torque and vehicle weight. Brake torque and vehicle weight are adaptively determined based on a periodically updated table defining a relationship between brake pedal position and vehicle deceleration. The relationship is corrected for variations in brake heating. - FIG. 2 graphically depicts a representative relationship between vehicle deceleration and brake pedal position for braking of the
vehicle 12. The relationship assumes that there is no lock-up condition and themodulators - Braking characterization data is collected by determining pedal positions that correspond to a plurality of different vehicle deceleration values. For example, in FIG. 3, deceleration values Dl, D2 and D3 correspond to pedal position values Pvsd(0), Pvsd(1), and Pvsd(2). The braking data is collected during braking operation when the
pedal 30 is depressed at a “normal” rate or held in a static position for a predetermined period. Data is not collected while thebrake pedal 30 is released or during panic braking. This eliminates the need to compensate for dynamic effects such as suspension, powertrain, tire and sensor dynamics. Additional details can be found in Walenty et al., U.S. Pat. No. 6,405,117, which is hereby incorporated by reference. -
- Surface— Mu=(Brake_Torque/Vehicle_Weight)*K mu
— Lambda (5) - where variables starting with a K are stored and/or calculated values.
- Before ABS becomes active, the coefficient of friction, grade, vehicle weight, steering angle, steering rate, lateral and longitudinal accelerations are calculated and sent to the ABS controller. There are many ways of determining steering angle. For example,
- SteerAngle=(LF speed +LR speed)−(RF speed +RR speed)*K stang
— spd. (6) - Kstang
— spd is function that converts speed delta into steering angle. In U.S. Pat. No. 5,465,210, which is hereby incorporated by reference, a steering wheel position sensor and a method for determining a vehicle steering wheel center position are disclosed. In U.S. Pat. No. 5,465,210: - SteerAngle=(Steer_wheel_center— pos−Steer_wheel_pos )*K stang
— pos. (7) - Steering wheel position is preferably an integer that ranges between 0 and 256. 0 corresponds to full left or right lock and 256 corresponds to full right or left lock. Kstang
— pos is a function that converts position into steering angle. Still other methods of sensing and/or calculating steering angle are contemplated. -
- where Kslat converts angle and speed into lateral acceleration.
-
- Roll, pitch, and lateral and longitudinal acceleration change weight distribution at each corner as follows:
- LFwt=LFwt+(K wt
— trLF (Roll, Pitch)+Lat — g+(1−Accel.)+(Steer Rate*K st— la)). (12) - Kwt
— trLF is preferably stored in a lookup table that provides the normal (calibratable) percentage of weight on the left front corner of the vehicle at various vehicle attitudes. Kwt— trLF is modified by weight transference due to acceleration. Kst— la is an anticipatory correction based on the steering rate to correct for tire scrub and actuator latency. - In one implementation of a smart brake system, the brake torque command is synonymous with a motor position of the brake actuator. The motor position vs. brake pedal position typically resides in a look-up table that is adjusted to optimize brake torque at each corner while on hills. Where:
- LF mpos =Lfi(bpos)*LFwt (13)
- When ABS becomes active, an accurate amount of release pressure may be calculated based upon the surface mu, attitude, weight transference, and steering angle. Where:
- LF_Release— tq=K rel*((Veh — wt*surface mu)*LFwt) (14)
- where Krel modifies the release target to slightly overshoot the release target on grades at which the tire(s) lose tractive cohesion with the road surface.
- Target brake torque for each corner is modified by surface mu and weight distribution as follows. Where:
- LF_Apply— tq=K app*((Veh — wt*surface— mu)*LFwt) (15)
- where Kapp modifies the apply target to slightly undershoot the real target on grades at which the tire(s) lose all tractive cohesion with the road surface.
- Vehicle stability enhancement (VSES) or Traction Control (TCS) slip thresholds are set lower on wheels that are likely to cause instability on downhill turns. The lower application of brake torque helps prevent spinout and rollover. Vehicles equipped with smart brakes (electro-hydraulic, dry interface, VSES, TCS, etc.) may use this invention to make brake torque adjustments at each corner to provide better vehicle stability control on hills.
-
-
-
- Referring to FIG. 4A, steps performed by the
ABS controller 50 are shown in further detail. Instep 102, control begins. Instep 104, theABS controller 50 reads brake pedal position, speeds, Form Slip, and Form Decel. TheABS controller 50 records a pedal position vs. deceleration table. TheABS controller 50 calculates brake heat, brake torque, vehicle weight, grade, and Surface Mu. TheABS controller 50 looks up the ABS_Table(decel,Slip) command. - Control continues from
step 104 to step 106 where theABS controller 50 determines whether ABS is equal to true. If true, theABS controller 50 operates the ABS system as indicated at 108. Ifstep 106 is false, control continues withstep 110 where theABS controller 50 determines whether Vehaccel>Kaccel. If false, control continues withstep 114 where theABS controller 50 determines whether Old pedpos>New pedpos. If false, control continues withstep 118 where theABS controller 50 determines whether (New pedpos−Old pedpos)>Kbrate. If false, control continues withstep 122 where theABS controller 50 determines whether (Vehaccel−Onsetaccel)<CalD1. - If
step 122 is false, control continues withstep 126 where theABS controller 50 determines whether ABS(SlipLF−oldslipLF)>K5%. Ifstep 126 is false, control continues withstep 130 where theABS controller 50 determines whether Lataccel>K0.15 g or if steerangle>K5deg. Ifstep 130 is false, control continues withstep 132. If any of the steps 110-130 are true, control ends at 133. - In
step 132, control determines whether F1 is true. (Flags F1, F2, and F3 are set False when the brake is not applied.) If true, control continues withstep 136 where theABS controller 50 determines whether F2 is true. Ifstep 136 is true, control determines whether F3 is true instep 138. Ifstep 138 is true, control ends instep 140. Ifstep 136 is false, control continues withstep 142 where theABS controller 50 determines whether (Vehaccel−Onsetaccel)>CalD2. If false, control ends instep 144. If true, control continues withstep 146 where theABS controller 50 sets p2=(p2+pedpos)/2, F2=true, and S2=S2+Slip(i)/2. Control continues fromstep 146 to step 144. - If
step 138 is false, control continues withstep 150 where theABS controller 50 determines whether (Vehaccel−Onsetaccel)>CalD3. If false, control ends instep 144. Ifstep 150 is true, control continues withstep 154 where theABS controller 50 performs the following calculations: p3=(p3+pedpos)/2, S3=S3+Slip(i)/2, Bc=Bc+1, F3=True, PS1=PS1+p1, PS2=PS2+p2, PS3=PS3+p3, S1=SS1+S1, SS2=SS2+S2, and SS3=SS3+S3. Control continues fromstep 154 to step 156 where theABS controller 50 determines whether Bc>=KBcc. If false, control ends instep 140. -
- Control continues from
step 160 to step 162 to where the ABS controller determines whether the ABS system is in Cal. is false, control continues withstep 164 and sets Bc=0. Ifstep 162 is true, control continues withstep 166 and determines whether Bc>=KBc. Is false, control ends instep 140. Ifstep 166 is true, control continues withstep 170 where theABS controller 50 performs the following: - Pvsdcal(0)=Pvsd(0), Pvsdcal(1)=Pvsd(1), Pvsdcal(2)=Pvsd(2)
- Scal(i,0)=Svsd(i,0), Scal(i,1)=Svsd(i,1) Scal(i,2)=Svsd(i,2)
- Cal=off, Bc=0,
- LFs=Scal(LF,0)+Scal(LF,1)+Scal(LF,2)
- RFs=Scal(RF,0)+Scal(RF,1)+Scal(RF,2)
- LFs=Scal(LR,0)+Scal(LR,1)+Scal(LR,2)
- RRs=Scal(RR,0)+Scal(RR,1)+Scal(RR,2)
- LF — bal — cal=LFs/(LFs+RFs+LRs+RRs)
- RF — bal — cal=RFs/(LFs+RFs+LRs+RRs)
- LR — bal — cal=LRs/(LFs+RFs+LRs+RRs)
- RR — bal — cal=RRs/(LFs+RFs+LRs+RRs)
- Control continues from
step 170 to step 174 where thecontroller 50 performs the following: - Brk — eff — cal=(P vsd
— cal(2)−P vsd— cal(0))/(D3−D1) - Brk — eff — nom=(Pedal Position−(P vsd
— cal(0))*Brk — eff — cal - Brk — eff_actual=(Pedal Position−(Pvsd
— cal(0))*(P vsd(2)−P vsd(0))/(D3−D1) - Brk_eff_ratio=Brk_eff_nom/Brk_eff_actual
- LFs=Svsd(LF,0)+Scal(LF,1)+Scal(LF,2)
- RFs=Svsd(RF,0)+Scal(RF,1)+Scal(RF,2)
- LFs=Svsd(LR,0)+Scal(LR,1)+Scal(LR,2)
- RRs=Svsd(RR,0)+Scal(RR,1)+Scal(RR,2)
- LF — bal — act=LFs/(LFs+RFs+LRs+RRs)
- RF — bal — act=RFs/(LFs+RFs+LRs+RRs)
- LR — bal — act=LRs/(LFs+RFs+LRs+RRs)
- RR — bal — act=RRs/(LFs+RFs+LRs+RRs)
- LF — bal_ratio=LF — bal — cal/LF — bal — act
- RF — bal_ratio=RF — bal — cal/RF — bal — act
- LR — bal_ratio=LR — bal — cal/LR — bal — act
- RR — bal_ratio=RR — bal — cal/RR — bal — act
- Control continues from
step 174 to step 176 where theABS controller 50 performs the following: - Update Inputs with Latest Table Data
- Brake_Torque=((Pedal Position−(P vsd(0))*((P vsd(2)−P vsd(0))/(D3−D1)))*K brk
— torque)+((Update_Brake_heat−Brake_heat)*K heat— crv)Brake_Heat=Brake_Heat−((MPH+K coolspdmin){circumflex over ( )}2*K coolspd)*(Brake_Heat−(Brake_Heat*K coolambient)+(Brake Torque*(K heat *MPH))*(K maxtemp−Brake_Heat)/K maxtemp) - Vehicle_Weight=LVW+((((P vsdold(2)−(P vsdold(0))−((P vsd(2)−P vsd(0))/(D3−D1)))*Kveh
— weight)+((Update_Brake_heat−Brake_heat)*K heat— crv) - Grade=Rolling Resistance+Aerodynamic Drag+Engine Braking+Brake Torque+Acceleration
- Control continues from
step 176 to step 178 where theABS controller 50 performs the following: - Brk — eff — LF=((Brk — eff_ratio*K front
— Brk eff)+(Brake_Heat*K front— fade— eff)+(Grade*K front— grade— wt— transfer)+(Vehicle_Weight*K front— wt— transfer))*LF_bal_ratio -
- Brk — eff — LR=((Brk — eff_ratio*K rear
— Brk eff)+(Brake_Heat*K rear— fade— eff)+(Grade*K rear— grade— wt— transfer)+(Vehicle_Weight*K rear— wt— transfer))*LR_bal_ratio - Brk — eff — LR=((Brk — eff_ratio*K rear
— Brk eff)+(Brake_Heat*K rear— fade— eff)+(Grade*K rear— grade— wt— transfer)+(Vehicle_Weight*K rear— wt— transfer))*RR_bal_ratio - Control continues from
step 176 to step 178 where theABS controller 50 performs the following: - Ramp_rate— LF=K front
— ramp— rate*(K front— eff— ramp— rate *Brk — eff — LF) - Ramp_rate— RF=K front
— ramp— rate*(K front— eff— ramp— rate *Brk — eff — RF) - Ramp_rate— LR=K rear
— ramp— rate*(K rear— eff— ramp— rate *Brk — eff — LR) - Ramp_rate— RR=K rear
— ramp— rate*(K rear— eff— ramp— rate *Brk — eff — RR) - ABS_TableLF(i,j)=(K slip
— front(i,j) *Brk — eff — LF)+(K decel— front(i,j) *Brk — eff — LF) - ABS_TableRF(i,j)=(K slip
— front(i,j) *Brk — eff — RF)+(K decel— front(i,j) *Brk — eff — RF) - ABS_TableLR(i,j)=(K slip
— C(i,j) *Brk — eff — LR)+(K decel— Rear(i,j) *Brk — eff — LR) - ABS_TableRR(i,j)=(K slip
— C(i,j) *Brk — eff — RR)+(K decel— Rear(i,j) *Brk — eff — RR) - The ABS controller may also be used in vehicles with electronic transmission control to prevent a transmission downshift to first or second gear that would make the vehicle unstable, which is useful in rear wheel drive vehicles. The ABS controller provides a more effective way of identifying the actual coefficient of friction for each corner when engaging the brakes while turning on steep hills, which allows the proper calculation of release and apply pressures and slip and decel targets.
- Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and the following claims.
Claims (20)
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
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US10/264,685 US6728621B1 (en) | 2002-10-04 | 2002-10-04 | Anti-lock braking system controller for adjusting slip thresholds on inclines |
DE10344911A DE10344911B4 (en) | 2002-10-04 | 2003-09-26 | Anti-lock braking system control for setting slip thresholds on slopes |
JP2003344241A JP2004123094A (en) | 2002-10-04 | 2003-10-02 | Anti-lock braking system controller for adjusting slip thresholds on inclines |
Applications Claiming Priority (1)
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US10/264,685 US6728621B1 (en) | 2002-10-04 | 2002-10-04 | Anti-lock braking system controller for adjusting slip thresholds on inclines |
Publications (2)
Publication Number | Publication Date |
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US20040068358A1 true US20040068358A1 (en) | 2004-04-08 |
US6728621B1 US6728621B1 (en) | 2004-04-27 |
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US10/264,685 Expired - Fee Related US6728621B1 (en) | 2002-10-04 | 2002-10-04 | Anti-lock braking system controller for adjusting slip thresholds on inclines |
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US (1) | US6728621B1 (en) |
JP (1) | JP2004123094A (en) |
DE (1) | DE10344911B4 (en) |
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WO2021257747A1 (en) * | 2020-06-19 | 2021-12-23 | Glydways, Inc. | Braking and signaling schemes for autonomous vehicle system |
CN113882290A (en) * | 2021-08-19 | 2022-01-04 | 宁波工程学院 | Novel domatic safe deceleration strip |
WO2024170919A1 (en) * | 2023-02-17 | 2024-08-22 | Panteris Ioannis | Anti-lock brake system with minimization of vehicle stopping distance |
Also Published As
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DE10344911B4 (en) | 2009-07-09 |
DE10344911A1 (en) | 2004-04-22 |
JP2004123094A (en) | 2004-04-22 |
US6728621B1 (en) | 2004-04-27 |
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