Vehicle braking system and methods for controlling it

Abstract

Vehicle braking system, including: a wheel speed detection unit (20) for detecting speeds of the respective wheels provided on the vehicle (FL, FR, RL, RR); and a control device (30) that calculates a vehicle speed based on the speeds of the respective wheels of the vehicle (302), calculates slip quantities of the respective wheels by comparing the vehicle speed and the speeds of the respective wheels (303), selects a slip quantity from the slip quantities of the respective wheels, compares the selected slip quantity with a reference slip quantity, determines a regenerative braking force according to an exceeding slip quantity if the selected slip quantity exceeds the reference slip quantity and The regenerative braking is controlled using the specific regenerative braking force. where the vehicle braking system the control device calculates rates of change of the slip quantities of the respective wheels (304), selects a slip rate of change from the slip rates of the respective wheels (305), compares the selected slip rate of change with a reference slip rate of change (306), gains a regenerative braking force corresponding to an exceeding slip rate of change if the selected slip rate of change exceeds the reference slip rate, and controls the regenerative braking using the gained regenerative braking force. and characterized by the fact that the control device compares the regenerative braking force according to the exceeding slip magnitude and the regenerative braking force according to the exceeding slip change rate when simultaneously the selected slip magnitude exceeds the reference slip magnitude and the selected slip change rate exceeds the reference slip change rate (307), and controls regenerative braking using the lower of the two regenerative braking forces (309).

Description

BACKGROUND 1. Area

[0001] Exemplary embodiments of the invention relate to a vehicle braking system and a method for controlling it, which ensures the braking stability of a vehicle. 2. Description of the state of the art

[0002] Recently, hybrid vehicles and electric vehicles have been equipped with an internal combustion engine and a motor powered by electrical energy from a high-voltage battery, thus becoming new generation of environmentally friendly vehicles powered by such a motor.

[0003] The high-voltage battery for supplying drive power to the motor is used in hybrid and electric vehicles. This high-voltage battery supplies electrical energy to the motor during operation and recharges electrical energy generated by the motor during regenerative braking or motor operation.

[0004] More precisely, the engine functions as an electric generator when a driver commands deceleration or braking, thus generating electrical energy. At this point, the battery is recharged. While the engine acts as a generator in this way, a braking torque is applied to the wheels; this braking torque is known as regenerative braking.

[0005] To ensure the braking force requested by a driver during braking, hybrid and electric vehicles use regenerative braking using the vehicle's motor and hydraulic braking using hydraulic brake pressure. The hydraulic braking force is a value obtained by subtracting the regenerative braking force generated by the motor from the requested braking force.

[0006] Furthermore, hybrid and electric vehicles stop regenerative braking and control a hydraulic braking force using hydraulic brake pressure when a safety function, such as ABS or ESC, is applied during regenerative braking, thus ensuring the vehicle's braking stability.

[0007] In this process, hybrid and electric vehicles go through a conversion phase between regenerative braking and hydraulic braking, and this can impair the vehicle's braking stability due to the maintenance or increase of drive wheel slip by remaining at regenerative braking force during the switching phase, in which regenerative braking is not stopped.

[0008] Furthermore, in hybrid and electric vehicles, a rapid change in hydraulic brake pressure due to the operation of a safety function, such as the ABS or ESC function, during the switching phase between regenerative braking and hydraulic braking, delivers undesirable fluctuations to the engine, which is not stopped according to the remaining level of regenerative braking force and can thus impair the braking stability of the vehicle.

[0009] Patent DE 10 2008 017 480 A1 relates to a method for operating a vehicle braking system and a corresponding vehicle braking system, in particular for motor vehicles. The vehicle wheels assigned to an axle of the motor vehicle are at least partially driven by an electric motor, which can be operated as a generator during the recuperation of braking energy and thereby exerts a braking recuperation torque on the respective axle. To prevent overbraking at the rear axle, it is proposed that the recuperation torque applied to the at least one rear axle (RA) be limited in such a way that the slip applied to at least one vehicle wheel of this rear axle (RA) does not exceed, or only insignificantly exceeds, a first slip threshold individually assigned to that vehicle wheel.

[0010] From the publication DE 10 2008 017480 A1, a method for operating a vehicle braking system and a corresponding vehicle braking system, in particular for motor vehicles, is known, in which the vehicle wheels of the motor vehicle assigned to an axle are at least partially driven by an electric motor (16) which can be operated as a generator during a recuperation of braking energy and thereby exerts a braking recuperation torque on the respective axle. SUMMARY

[0011] It is therefore an aspect of the present invention to provide a vehicle braking system and a control method that limit the regenerative braking force using at least one of several slip levels and slip change rates of respective wheels and then perform a safety function, such as the ABS or ESC function.

[0012] Another aspect of the present invention is to provide a vehicle braking system and a control method that minimizes a switching phase between regenerative braking and hydraulic braking by using at least one of several slip levels and slip change rates of the respective wheels in an operating range of a safety function, such as the ABS or ESC function.

[0013] Additional aspects of the invention are partly explained in the following description and partly are obvious from the description or can be learned by carrying out the invention.

[0014] According to one aspect of the invention, a vehicle braking system comprises a wheel speed detection unit that detects the speeds of the respective wheels provided on the vehicle, and a control device that calculates a vehicle speed based on the speeds of the respective wheels of the vehicle, calculates the slip magnitude of the respective wheels by comparing the vehicle speed and the speeds of the respective wheels, selects a slip magnitude from the slip magnitudes of the respective wheels, compares the selected slip magnitude with a reference slip magnitude, obtains a regenerative braking force corresponding to an exceedance of the slip magnitude if the selected slip magnitude exceeds the reference slip magnitude, and controls the regenerative braking based on the obtained regenerative braking force.

[0015] The control device calculates rates of change or change profiles of the slip parameters of the respective wheels. A slip change rate from a plurality of slip change rates is stored in advance in the control device.

[0016] The control device compares the regenerative braking force according to the exceeding slip magnitude and the regenerative braking force according to the exceeding slip change rate when the selected slip magnitude exceeds the reference slip magnitude and the selected slip change rate exceeds the reference slip change rate, simultaneously, and controls regenerative braking using the smaller regenerative braking force of the two regenerative braking forces.

[0017] The control device can stop regenerative braking and control hydraulic braking when a safety function is performed during regenerative braking control.

[0018] Regenerative braking forces corresponding to exceedance slip values ​​can be stored in advance in the control device.

[0019] In accordance with another aspect of the present invention, the method for controlling the braking of a vehicle comprises detecting speeds of respective wheels provided on the vehicle, calculating a vehicle speed based on the speeds of the respective wheels, calculating slip quantities of the respective wheels by comparing the vehicle speed and the speeds of the respective wheels, and calculating rates of change of the slip quantities of the respective wheels.

[0020] Furthermore, the method includes obtaining regenerative braking forces according to one of the slip magnitudes and slip change rates of the respective wheels and controlling the regenerative braking using the obtained regenerative braking force.Obtaining the regenerative braking force includes: selecting a slip parameter from the slip parameters of the respective wheels and comparing the selected slip parameter with a reference slip parameter; calculating rates of change of the slip parameters of the respective wheels; selecting a slip rate of change from the slip rates of change of the respective wheels and comparing the selected slip rate of change with a reference slip rate of change; obtaining a regenerative braking force corresponding to an exceeding slip parameter and a regenerative braking force corresponding to an exceeding slip rate of change if, at the same time, the selected slip parameter exceeds the reference slip parameter and the selected slip rate of change exceeds the reference slip rate; and obtaining a smaller regenerative braking force from the two regenerative braking forces by comparing the two obtained regenerative braking forces.

[0021] Maintaining regenerative braking force can also include maintaining a regenerative braking force corresponding to the exceeding slip magnitude when the selected slip magnitude exceeds the reference slip magnitude and the selected slip change rate is less than the reference slip change rate; maintaining a regenerative braking force corresponding to the exceeding slip change rate when the selected slip magnitude is less than the reference magnitude and the selected slip change rate exceeds the reference slip change rate; and maintaining a regenerative target braking force corresponding to a driver's braking request when, at the same time, the selected slip magnitude is less than the reference slip magnitude and the selected slip change rate is less than the reference slip change rate.

[0022] Selecting a slip size from the slip sizes of the respective wheels may include selecting the maximum slip size, and selecting a slip change rate from the slip change rates of the respective wheels may include selecting the maximum slip change rate.

[0023] Maintaining regenerative braking force can include storing regenerative braking forces in advance according to exceeding slip quantities and regenerative braking forces in accordance with exceeding slip change rates, maintaining regenerative braking forces in accordance with the exceeding slip quantity from the regenerative braking forces in accordance with the exceeding slip quantities, and maintaining regenerative braking forces in accordance with the exceeding slip change rate from the regenerative braking forces in accordance with the exceeding slip change rates. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] These and / or other aspects of the invention will become apparent and more easily recognizable from the following description of the exemplary embodiments, which are explained together with the accompanying drawings, in which: Fig. 1 a block diagram of a vehicle braking system in accordance with an embodiment of the present invention; Fig. 2 is a flowchart that represents a method for controlling the braking of a vehicle in accordance with an embodiment of the present invention; Fig. 3 is a flowchart that represents a method for controlling the braking of a vehicle in accordance with another embodiment of the present invention; and Fig. 4 is a flowchart that represents a method for controlling the braking of a vehicle in accordance with yet another embodiment of the present invention. DETAILED DESCRIPTION

[0025] Reference will now be made in detail to the embodiments of the present invention, examples of which are shown in the accompanying drawings, where the same reference numerals refer throughout to the same elements.

[0026] Fig. Figure 1 is a block diagram of a vehicle braking system in accordance with an exemplary embodiment. The vehicle braking system comprises a wheel speed detection unit 20, a pedal detection unit 10, a control device 30, a regenerative braking unit 40, a hydraulic brake unit 50, an ABS drive unit 60, an ESC drive unit 70, motors M and solenoid valves SV.

[0027] The wheel speed detection unit 20 comprises an FL wheel speed sensor installed on the front left wheel (Front Left FL) of a vehicle to detect the speed of the front left (FL) wheel, an FR wheel speed sensor installed on the front right (Front Right FR) of the vehicle to detect the speed of the front right (FR) wheel, an RL wheel speed sensor installed on the rear left (Rear Left RL) of the vehicle to detect the speed of the rear left (RL) wheel, and an RR wheel speed sensor installed on the rear right (Rear Right RR) of the vehicle to detect the speed of the rear right (RR) wheel. The respective wheel speed sensors of the wheel speed detection unit 20 transmit the detected wheel speeds to the control device 30.

[0028] The pedal detection unit 20 detects a pedal stroke of a brake pedal pressed by a driver during braking and transmits the pedal stroke to the control device 30.

[0029] The pedal detection unit 20 can use a position sensor that is installed on the brake pedal and estimates the driver's braking intention and the requested braking force.

[0030] The control device 30 evaluates the required braking force according to the driver's intention based on a detection signal transmitted by the pedal detection unit 20 and controls the regenerative brake unit 40 and the hydraulic brake unit 50 to generate a regenerative target braking force and a hydraulic braking force according to the required braking force.

[0031] The control device 30 calculates the regenerative target braking force generated by the motors M when performing regenerative braking during braking and determines the additional hydraulic braking force required to brake the vehicle's wheels by comparing the regenerative target braking force with the required braking force.

[0032] The control device 30 increases or decreases the pressure of the brake fluid by controlling the brake fluid supplied from a pre-tensioning cylinder to a master cylinder and by controlling the solenoid valves SV of the hydraulic brake unit 50, and then supplies the brake fluid to the respective wheel cylinders. Thus, the hydraulic braking force is communicated to the wheel cylinders of the respective wheels, causing the vehicle to brake.

[0033] The control device 30 calculates a vehicle speed by comparing the speeds of the front left and right wheels and compares the speeds of the rear left and right wheels based on the respective wheel speeds detected by the wheel speed detection unit 20, calculates the magnitudes or levels of the slip of the respective wheels by comparing the calculated vehicle speed with the respective wheel speeds, calculates the change profiles or rates of change of the slip magnitudes of the respective wheels, i.e., the slip change rates, and limits the regenerative braking force using the maximum slip magnitude of the slip magnitudes of the respective wheels and / or the maximum slip change rate of the slip change rates of the respective wheels.

[0034] The control device 30 determines whether the ABS drive unit 60 or the ESC drive unit 70 is driven during regenerative braking and stops the regenerative braking and controls the hydraulic braking when the ABS drive unit 60 or the ESC drive unit 70 is driven.

[0035] After calculating the yaw rates and yaw speeds of the front left and right wheels based on their speeds and a distance between them, and calculating the yaw rates of the rear left and right wheels based on their speeds and a distance between them, the vehicle speed can be estimated based on the yaw rates of the front left and right wheels and the yaw rates of the rear left and right wheels.

[0036] The vehicle braking system may also include a yaw rate detection unit (not shown) to detect the vehicle's turning circle when the front and rear parts of the vehicle yaw or rotate to the left and right, and may further include an acceleration detection unit (a G sensor; not shown) to detect the vehicle's acceleration and deceleration in the longitudinal direction.

[0037] The control device 30 can correct the vehicle speed based on a speed obtained by integrating the acceleration detected by the acceleration detection unit.

[0038] Furthermore, the control device 30 can calculate a speed correction value using the vehicle's turning circle or degree of rotation, detected by the yaw rate detection unit, and a predefined vehicle coefficient. It can correct the vehicle speed by subtracting the correction value from the speed when the vehicle is braking, and correct a reference speed by adding the correction value to the vehicle speed when the vehicle is accelerating. This allows for a more accurate estimation of the vehicle's speed.

[0039] If the control device 30 limits the regenerative braking force using one of the slip quantities of the respective wheels, i.e., the maximum slip quantity, the control device 30 compares the maximum slip quantity with a reference slip quantity, obtains a regenerative braking force corresponding to an exceeding slip quantity based on the regenerative braking forces corresponding to the exceeding slip quantities that were stored in advance, and limits the regenerative braking using the obtained regenerative braking force if the maximum slip quantity or slip level exceeds the reference slip quantity, and limits the regenerative braking using the regenerative target braking force if the maximum slip quantity is less than the reference slip quantity.

[0040] That is, the control device 30 stores regenerative braking forces in advance according to the exceeding slip values.

[0041] If the control device 30 limits the regenerative braking force using one of the slip change rates of the respective wheels, i.e., the maximum slip change rate, the control device 30 compares the maximum slip change rate with a reference slip change rate, obtains a regenerative braking force corresponding to an excess slip change rate based on regenerative braking forces corresponding to the excess slip change rates that were stored in advance, and limits the regenerative braking using the obtained regenerative braking force if the maximum slip change rate exceeds the reference slip change rate, and limits the regenerative braking using the regenerative target braking force if the maximum slip change rate is less than the reference slip change rate.

[0042] That is, the control device 30 stores regenerative braking forces in advance according to the exceeding slip change rates.

[0043] When the control device 30 limits a regenerative braking force using the maximum slip magnitude and the maximum slip change rate, the control device 30 compares the maximum slip magnitude with the reference slip magnitude and compares the maximum slip change rate with the reference slip change rate, obtains a regenerative braking force corresponding to an exceeding slip magnitude and obtains a regenerative braking force corresponding to an exceeding slip change rate, if simultaneously the maximum slip magnitude exceeds the reference magnitude and the maximum slip change rate exceeds the reference change rate, compares the regenerative braking force according to the slip magnitude and the regenerative braking force according to the slip change rate and limits the regenerative braking using the smaller regenerative braking force.

[0044] The control device 30 determines whether the ABS drive unit 60 or the ESC drive unit 70 is driven during regenerative braking and stops the regenerative braking and controls the hydraulic braking when the ABS drive unit 60 or the ESC drive unit 70 is driven.

[0045] As described above, by limiting the regenerative braking force using one of the slip parameters and the slip change rates of the respective wheels, a switching phase between regenerative braking and hydraulic braking can be minimized within the operating range of the ABS safety function or the ESC safety function, thus ensuring the braking stability of the vehicle.

[0046] The regenerative braking unit 40 causes the motors M, which are provided at the respective wheels, to rotate in forward / reverse directions to generate a driving force and a regenerative braking force of the vehicle, thereby performing the driving and regenerative braking of the vehicle.

[0047] The regenerative braking unit 40 comprises the motors M, which generate a counter-electromotive force (counter-EMF) according to the Fleming rule when the vehicle is driven and then braked according to a control signal from the control device 30, and batteries (not shown) which supply energy or current to the motors M according to a control signal from the control device 30.

[0048] This means that the regenerative braking unit 40 performs energy regeneration and simultaneously generates rolling resistance with a torque of the motors M according to the control signal from the control device 30, whereby regenerative braking is carried out.

[0049] Here, regenerative braking means braking the vehicle while the motors M absorb an inertial force of the vehicle, which tries to go straight ahead during braking, with the motors generating a counter-electromotive force and the generated energy being stored in the batteries.

[0050] The hydraulic brake unit 50 controls the solenoid valves SV, whereby a hydraulic pressure supplied from the master cylinder to the wheel cylinders of the respective wheels is set according to commands from the control device 30.

[0051] More precisely, the hydraulic brake unit 50 comprises the brake pedal, which is pressed or released by a driver and tells the vehicle to brake, whereby the booster increases the foot force on the brake pedal, the master cylinder generates the hydraulic pressure by increasing the foot force via the booster, a reservoir connects the master cylinder via hydraulic lines and stores brake fluid, the wheel cylinders installed at the respective wheels convert a hydraulic force supplied by the master cylinder via the hydraulic lines into mechanical force, a hydraulic pump pumps the brake fluid from the reservoir to supply the brake fluid to the respective wheel cylinders,A low-pressure accumulator temporarily stores the brake fluid pumped by the hydraulic pump, and the majority of solenoid valves supply the brake fluid delivered from the master cylinder to the wheel cylinders or return the brake fluid to the reservoir.

[0052] The solenoid valves include normally open (NO type) solenoid valves, which are located between the master cylinder and the wheel cylinders and are open in the normal operating state, or normally closed (NC type) solenoid valves, which communicate with the hydraulic lines of the wheels that connect the master cylinder and the NO type solenoid valves and are closed in the normal operating state.

[0053] The hydraulic brake unit 50 supplies the brake fluid from the low-pressure accumulator to the wheel cylinders via the NO type solenoid valves by opening the NO type solenoid valves and driving the hydraulic pump according to commands from the control device 30 when the hydraulic braking force of the wheel cylinders increases, thereby increasing the pressure of the wheel cylinders.

[0054] The hydraulic brake unit 50 returns the brake fluid from the wheel cylinders to the reservoir R via the NC type solenoid valves by stopping the hydraulic pump and opening the NC type solenoid valves according to commands from the control device 30 when the hydraulic braking force of the wheel cylinders drops, thereby reducing the pressure of the wheel cylinders.

[0055] The hydraulic brake unit 50 closes the NO type solenoid valves and the NC type solenoid valves depending on commands from the control device 30 when the correct pressure is applied to the wheel cylinders via the pressure drop and rise, thereby maintaining the pressure of the wheel cylinders.

[0056] The drive unit 60 of the anti-lock braking system (ABS) serves to prevent the brakes from locking due to slippage on a slippery road and allows the driver to steer the vehicle during braking and selectively increases or decreases the hydraulic brake pressures of the respective wheels Fr, FL, RR and RL depending on commands from the control device 30, so that the slip change rates of the wheels assume a predetermined slip change rate.

[0057] The drive unit 70 of the electronic stability control (ESC) selectively actuates the solenoid valves SV of the wheels requiring braking, the front and rear left and right wheels, depending on commands from the control device 30, when the vehicle slips during acceleration, braking, or cornering in an extremely unstable condition, thus changing the hydraulic assist force supplied to a steering gear proportionally to the vehicle speed, thereby achieving driving stability for the driver at high and low speeds, stabilizing the vehicle's attitude, and correcting driver error.

[0058] Fig. Figure 2 is a flowchart that illustrates a method for controlling the braking of a vehicle in accordance with an embodiment.

[0059] When a driver's intention to brake is detected by the driver pressing the brake pedal, the vehicle's braking system determines a braking force required according to the driver's intention to brake, based on a pedal stroke transmitted by the pedal detection unit 20.

[0060] The vehicle's braking system calculates a regenerative target braking force generated by the motors M during regenerative braking. This calculation is based on at least one of the following parameters: the rotational speeds of the motors M, the state of charge of the batteries (not shown), and the vehicle's operating condition.

[0061] Next, the vehicle's braking system calculates a hydraulic braking force that could correspond to the requested braking force, based on the calculated regenerative target braking force. That is, the vehicle's braking system calculates a hydraulic braking force necessary for braking the vehicle by comparing the requested braking force with the regenerative target braking force.

[0062] The vehicle braking system detects the respective wheel speeds via the wheel speed detection unit 20 (step 101).

[0063] Next, the vehicle braking system calculates a vehicle speed by comparing the speeds of the front left and right wheels and by comparing the speeds of the rear left and right wheels based on the speeds of the respective wheels (step 102).

[0064] Next, the vehicle braking system calculates the slip magnitude of each wheel by comparing the calculated vehicle speed and the speeds of the respective wheels (step 103) and selects the maximum slip magnitude from the slip magnitudes of the respective wheels.

[0065] Next, the vehicle's braking system compares the maximum slip magnitude with a reference slip magnitude (step 104), determines the regenerative braking force according to any exceedance of the slip magnitude, and limits regenerative braking using this determined regenerative braking force if the maximum slip magnitude exceeds the reference slip magnitude (step 105). The regenerative braking forces corresponding to the exceedances of the slip magnitudes were pre-stored.

[0066] On the other hand, the vehicle braking system limits regenerative braking using the regenerative target braking force when the maximum slip magnitude is less than the reference slip magnitude (step 106).

[0067] The vehicle braking system decides whether or not to drive the ABS drive unit 60 or the ESC drive unit 70, based on slip change rates of the respective wheels during regenerative braking, and stops the regenerative braking and controls the hydraulic brakes when it is determined that the ABS drive unit 60 or the ESC drive unit 70 is being driven.

[0068] Here, the vehicle's braking system increases or decreases the pressure of the brake fluid by controlling the brake fluid supplied from the pre-charge cylinder to the master cylinder and controlling the solenoid valves SV of the hydraulic brake unit 50, and then supplies the brake fluid to the respective wheel cylinders.

[0069] The vehicle's braking system applies the hydraulic braking force to the wheel cylinders of the respective wheels and brakes the vehicle, thereby executing the ABS or ESC function.

[0070] As described above, a switching phase between regenerative braking and hydraulic braking can be minimized within the safety function operating range of the ABS or ESC by limiting the regenerative braking force using the slip values ​​of the respective wheels, thus ensuring the braking stability of the vehicle.

[0071] Fig. Figure 3 is a flowchart illustrating a method for controlling the braking of a vehicle in accordance with another embodiment.

[0072] When a driver's intention to brake is detected by the driver pressing the brake pedal, the vehicle's braking system determines a braking force required according to the driver's intention to brake, based on a brake stroke transmitted by the pedal detection unit 20.

[0073] The vehicle's braking system calculates a regenerative target braking force generated by the motor M, with regenerative braking occurring during vehicle braking. This regenerative target braking force is calculated based on at least one of the following parameters: motor rotational speed, battery charge levels (not shown), and vehicle state.

[0074] Next, the vehicle's braking system calculates a hydraulic braking force that can match the required braking force, based on the calculated regenerative target braking force. That is, the vehicle's braking system calculates the hydraulic braking force necessary to brake the vehicle by comparing the required braking force with the regenerative target braking force.

[0075] The vehicle braking system detects the respective wheel speeds via the wheel speed detection unit 20 (step 201).

[0076] Next, the vehicle braking system calculates a vehicle speed by comparing the speeds of the front left and right wheels and by comparing the speeds of the rear left and right wheels based on the speeds of the respective wheels (step 202).

[0077] Next, the vehicle braking system calculates slip magnitudes of the respective wheels by comparing the calculated vehicle speed and the respective wheel speeds (step 203), calculates slip magnitude change rates (i.e., slip change rates) of the respective wheels as a function of the time change (step 204), and selects the maximum slip change rate from the slip change rates of the respective wheels.

[0078] Next, the vehicle's braking system compares the maximum slip change rate with a reference slip change rate (step 205), determines a regenerative braking force corresponding to any exceeding slip change rate, and limits regenerative braking using this determined regenerative braking force if the maximum slip change rate exceeds the reference slip change rate (step 206). Here, the regenerative braking forces were pre-programmed based on the exceeding slip change rates.

[0079] On the other hand, the vehicle braking system limits regenerative braking using regenerative braking force when the maximum slip change rate is less than the reference slip change rate (step 207).

[0080] The vehicle braking system determines whether the ABS drive unit 60 or the ESC drive unit 70 is driven, based on slip change rates of the respective wheels during regenerative braking, and stops the regenerative braking and controls the hydraulic braking after determining that the ABS drive unit 60 or the ESC drive unit 70 is driven.

[0081] Here, the vehicle's braking system increases or decreases the pressure of the brake fluid by controlling the brake fluid supplied from the pre-tensioning cylinder to the master cylinder and by controlling the solenoid valves SV of the hydraulic brake unit 50, and then supplies the brake fluid to the respective wheel cylinders.

[0082] In this process, the vehicle's braking system applies hydraulic braking force to the wheel cylinders of the respective wheels, thus braking the vehicle and activating the ABS or ESC.

[0083] As described above, a switching phase between regenerative braking and hydraulic braking can be minimized within the safety function operating range of the ABS and ESC by limiting the regenerative braking force using the slip change rate of the respective wheels, and consequently the braking stability of the vehicle can be ensured.

[0084] Fig.Figure 4 is a flowchart showing a method for controlling the braking of a vehicle in accordance with yet another embodiment.

[0085] When a driver's intention to brake is detected by the driver pressing the brake pedal, the vehicle braking system determines a braking force required according to the driver's intention to brake, based on a pedal stroke transmitted by the pedal detection unit 10.

[0086] The vehicle's braking system calculates a regenerative target braking force generated by the motors M, whereby regenerative braking is performed during vehicle braking. Here, the regenerative target braking force is calculated based on at least one of the following parameters: rotational speeds of the motors M, state of charge of the batteries (not shown), and a vehicle state.

[0087] Next, the vehicle's braking system calculates a hydraulic braking force that can match the required braking force, based on the calculated regenerative target braking force value. That is, the vehicle's braking system calculates the hydraulic braking force necessary for braking the vehicle by comparing the required braking force with the regenerative target braking force.

[0088] The vehicle braking system detects the respective wheel speeds via the wheel speed detection unit 20 (step 301).

[0089] Next, the vehicle braking system calculates a vehicle speed by comparing the speeds of the front left and right wheels and by comparing the speeds of the rear left and right wheels based on the speeds of the respective wheels (step 302).

[0090] The vehicle braking system then calculates slip magnitudes of the respective wheels by comparing the calculated vehicle speed and the respective wheel speeds (step 303) and calculates slip magnitude change rates (i.e., slip change rates) of the respective wheels depending on the time change (step 304).

[0091] The vehicle braking system then selects the maximum slip size from the slip sizes of the respective wheels and selects the maximum slip change rate from the slip change rates of the respective wheels (step 305).

[0092] Next, the vehicle's braking system compares the maximum slip magnitude with a reference slip magnitude and compares the maximum slip change rate with a reference slip change rate.

[0093] Then the vehicle braking system simultaneously determines whether the maximum slip magnitude exceeds the reference slip magnitude (A) or not and decides whether the maximum slip change rate exceeds the reference slip change rate (B) or not (step 306).

[0094] Next, the vehicle braking system decides whether the maximum slip magnitude exceeds the reference slip magnitude (A) or not, and simultaneously decides whether the maximum slip change rate exceeds the reference slip change rate (B) (step 307).

[0095] Here, the vehicle braking system provides a regenerative braking force corresponding to an exceeding slip quantity and provides a regenerative braking force corresponding to an exceeding slip change rate if, at the same time, the maximum slip quantity exceeds the reference slip quantity and the maximum slip change rate exceeds the reference slip change rate (step 308).

[0096] Here, the regenerative braking forces corresponding to the exceeding slip quantities and the regenerative braking forces corresponding to the exceeding slip change rates were stored in advance.

[0097] Next, the vehicle braking system compares the regenerative braking force according to the slip magnitude and the regenerative braking force according to the slip change rate and limits the regenerative braking using the smaller regenerative braking force from the two regenerative braking forces (step 309).

[0098] If only one of the maximum slip magnitude and the maximum slip change rate exceeds the corresponding reference value (the reference slip magnitude or the reference slip change rate), regenerative braking will be limited using the regenerative braking force according to the exceeding value.

[0099] More precisely, the vehicle's braking system determines whether the maximum wheel slip exceeds the reference slip (step 310). That is, if the maximum slip exceeds the reference slip and the maximum slip change rate is lower than the reference slip change rate, the vehicle's braking system limits regenerative braking using the regenerative braking force according to the maximum exceeding slip (step 311).

[0100] Next, the vehicle's braking system determines whether the maximum wheel slip change rate exceeds the reference slip change rate (step 312). That is, if the maximum slip magnitude is less than the reference slip magnitude and the maximum slip change rate exceeds the reference slip change rate, the vehicle's braking system limits regenerative braking using the regenerative braking force according to the maximum exceeding slip change rate (step 313).

[0101] If the maximum slip magnitude is less than the reference slip magnitude and the maximum slip change rate is less than the reference slip change rate, the vehicle braking system limits regenerative braking using the regenerative target braking force (step 314).

[0102] The vehicle braking system decides whether or not to engage the ABS drive unit 60 or the ESC drive unit 70, based on the slip change rates of the respective wheels during regenerative braking, and stops the regenerative braking and controls the hydraulic braking when it determines that the ABS drive unit 60 or the ESC drive unit 70 is being engaged.

[0103] The vehicle's braking system increases or decreases the brake fluid pressure by controlling the brake fluid supplied from the pre-charge cylinder to the master cylinder and by controlling the solenoid valves SV of the hydraulic brake unit 50, and then supplies the brake fluid to the respective wheel cylinders. In doing so, the vehicle's braking system applies a hydraulic braking force to the wheel cylinders of the respective wheels and brakes the vehicle, operating the ABS or ESC.

[0104] As described above, a switching phase between regenerative braking and hydraulic braking can be minimized within the safety function operating range of the ABS and ESC by limiting the regenerative braking force using the slip magnitudes and slip change rates of the respective wheels, thus ensuring the braking stability of the vehicle.

[0105] As is evident from the above description, a vehicle braking system and a control method in accordance with an embodiment limit the regenerative braking force using at least one of the slip variables and slip change rates of the respective wheels and then performs a safety function, such as the ABS or ESC function, thereby minimizing a switching phase between regenerative braking in an operating range of a safety function, such as the ABS or ESC, thus ensuring the braking stability of a vehicle.

Claims

[1] Vehicle braking system, comprising: a wheel speed detection unit (20) for detecting speeds of the respective wheels provided on the vehicle (FL, FR, RL, RR); and a control device (30) that calculates a vehicle speed based on the speeds of the respective wheels of the vehicle (302), calculates slip quantities of the respective wheels by comparing the vehicle speed and the speeds of the respective wheels (303), selects a slip quantity from the slip quantities of the respective wheels, compares the selected slip quantity with a reference slip quantity, determines a regenerative braking force according to an exceeding slip quantity if the selected slip quantity exceeds the reference slip quantity and The regenerative braking is controlled using the specific regenerative braking force. where the vehicle braking system the control device calculates rates of change of the slip quantities of the respective wheels (304), selects a slip rate of change from the slip rates of the respective wheels (305), compares the selected slip rate of change with a reference slip rate of change (306), gains a regenerative braking force corresponding to an exceeding slip rate of change if the selected slip rate of change exceeds the reference slip rate, and controls the regenerative braking using the gained regenerative braking force. and characterized by , that the control device compares the regenerative braking force according to the exceeding slip magnitude and the regenerative braking force according to the exceeding slip change rate when simultaneously the selected slip magnitude exceeds the reference slip magnitude and the selected slip change rate exceeds the reference slip change rate (307), and controls regenerative braking using the lower of the two regenerative braking forces (309). [2] Vehicle braking system according to claim 1, wherein the control device stops the regenerative braking and activates a hydraulic brake when a safety function is performed during the control of the regenerative braking. [3] Vehicle braking system according to claim 1, in which regenerative braking forces corresponding to exceeding slip quantities are stored in advance in the control device. [4] Vehicle braking system according to claim 1, in which regenerative braking forces corresponding to exceeding rates of change in slip are stored in advance in the control device. [5] Method for controlling the braking of a vehicle, comprising: Detecting (301) the speeds of the respective wheels provided on a vehicle (FL, FR, RL, RR); Calculating (302) a vehicle speed based on the speeds of the respective wheels; Calculating (303) slip quantities of the respective wheels by comparing the vehicle speed and the speeds of the respective wheels; Calculating (304) rates of change of the slip variables of the respective wheels; Gaining a regenerative braking force according to one of the slip quantities and slip change rates of the respective wheels and controlling a regenerative braking process using the gained regenerative braking force, wherein the gaining of the regenerative braking force includes: Selecting (305) a slip size from the slip sizes of the respective wheels and comparing (306) the selected slip size with a reference slip size; and Calculating the rates of change of the slip magnitude of the respective wheels, selecting a slip rate of change from the slip rates of the respective wheels, characterized by Comparing the selected slip rate with a reference slip rate; Gaining a regenerative braking force corresponding to an excess slip quantity and a regenerative braking force corresponding to an excess slip change rate when simultaneously the selected slip quantity exceeds the reference slip quantity and the selected slip change rate exceeds the reference slip change rate (307); and Gaining the lower regenerative braking force from the two regenerative braking forces by comparing the two gained regenerative braking forces. [6] Method for controlling the braking of a vehicle according to claim 5, wherein the recovery of regenerative braking force further comprises: Gaining regenerative braking force in proportion to the excess slip magnitude when the selected slip magnitude exceeds the reference slip magnitude and the selected slip change rate is lower than the reference slip change rate; Gaining regenerative braking force corresponding to the excess slip change rate when the selected slip size is less than the reference slip size and the selected slip change rate exceeds the reference slip change rate; and Gaining a regenerative target braking force corresponds to a braking request from a driver when, at the same time, the selected slip quantity is less than the reference slip quantity and the selected slip change rate is less than the reference slip change rate. [7] Method for controlling the braking of a vehicle according to claim 5, wherein: The selection of a slip size from the slip sizes of the respective wheels includes selecting the maximum slip size; and The selection of a slip change rate from the slip change rates of the respective wheels includes selecting the maximum slip change rate. [8] Method for controlling the braking of a vehicle according to claim 5, comprising the recovery of regenerative braking force: Storing regenerative braking forces in advance according to exceeding slip quantities and regenerative braking forces in advance according to exceeding slip change rates; Gaining a regenerative braking force corresponding to the excess slip from the regenerative braking forces corresponding to excess slip quantities; and Gaining regenerative braking force corresponding to the excess slip change rate from the regenerative braking forces corresponding to excess slip change rates.

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