Patent Publication Number: US-2023140481-A1

Title: Stably braking system and method using the same

Description:
This application claims priority of Application No. 110140146 filed in Taiwan on 28 Oct. 2021 under 35 U.S.C. § 119; the entire contents of all of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a braking technology, particularly to a stably braking system and a method using the same. 
     Description of the Related Art 
     Ground vehicles such as motorcycles or automobiles are widely used in daily life. However, the demand on braking stability is higher for ground vehicles at a high speed. Generally speaking, the higher the braking force is, the better the braking efficacy will be. However, if the braking force is higher than the grip of the tires, the braking force will cause the tire-locks, which causes the tire slip relative to the ground. The ground vehicle is thus possibly out of control. 
     For this reason, some companies have developed an anti-lock braking system (ABS). The ABS adjusts the brake pressure to make the brake pads inside the brake caliper quickly squeeze and release the brake disc (i.e., intermittent braking). Without ABS, the brake pads may act excessive positive clamping forces on the brake disc. Thus, ABS is necessarily equipped to prevent wheel lock-up when a ground vehicle brakes. ABS is helpful for all tires to rotate relative to the ground at a speed close to the actual moving speed of the vehicle. The applied tire forces will not exceed the boundary the road adhesion could provide. It further enables the vehicle to be controlled by the driver. Assume that a single axle of a ground vehicle is equipped with two wheels or that the ground vehicle may have multiple axles. 
     When a ground vehicle which is not equipped with ABS follows a straight line and then abruptly brakes the wheels, they tend to lock up as the static friction force to be used exceeds the limit value provided by the road surface. 
     When a ground vehicle equipped with an ABS brakes the wheels abruptly, the wheels will not be locked, but the ABS will not synchronously balance all the wheels on a single axle. Also, when it brakes inside a turn with high deceleration, the wheels on either axle may also be locked. The ground vehicle may easily deviate from the desired trajectory because the applicable tire forces no longer meet the demand for vehicle controls. 
     To solve the aforementioned problems and the prior art of ABS, the present invention provides a stably braking system and a method using the same. 
     SUMMARY OF THE INVENTION 
     The present invention provides a stably braking system and a method using the same, which improves the braking stability. 
     In an embodiment of the present invention, a stably braking system is arranged in a ground vehicle. The system includes a hydraulic braking system and an electronic control unit (ECU). The hydraulic braking system is arranged on wheels that are arranged on a single axle of the ground vehicle. The ECU is coupled to the hydraulic braking system and a dynamic sensing device. The dynamic sensing device is arranged on the ground vehicle. The ECU is configured to receive data sensed by the dynamic sensing device to calculate at least one of a wheel deceleration and an actual slip of each of the wheels. When the ECU receives a braking indication signal to perform a braking operation and detect that the wheel deceleration is higher than a first given value or that the actual slip is higher than a second given value, the ECU generates hydraulic control commands. The hydraulic control commands are configured to control the hydraulic braking system to decrease a wheel speed of each of the wheels and adjust the wheel speed of each of the wheels to be higher than 0 in a braking process. The hydraulic control commands include a pressure boosting command, a pressure holding command, or a pressure releasing command. A priority of the pressure releasing command is higher than that of the pressure holding command. A priority of the pressure holding command is higher than that of the pressure boosting command. When the ECU receives data sensed by the dynamic sensing device to detect that the ground vehicle drives in a straight line or turns with a first pose physical quantity greater than 0 and less than a third given value, the ECU replaces the hydraulic control command with a low priority by the hydraulic control command with a high priority and controls the hydraulic braking system to adjust the wheel speeds of the wheels based on the identical hydraulic control commands. 
     In an embodiment of the present invention, the ECU decreases a target slip of each of the wheels and controls the hydraulic braking system to adjust the actual slip of each of the wheels to follow the corresponding target slip based on the identical hydraulic control commands when the ECU receives data sensed by the dynamic sensing device to detect that the ground vehicle turns with the first pose physical quantity. 
     In an embodiment of the present invention, the wheels include a first wheel and a second wheel. When the ground vehicle drives in a lane and the ECU receives data sensed by the dynamic sensing device to detect that the ground vehicle turns to an inner side of the lane with a second pose physical quantity, the first wheel is close to an outer side of the lane, the second wheel is close to the inner side of the lane, and the ECU controls the hydraulic braking system to increase the wheel speed of the first wheel based on the pressure releasing command, increases a target slip of the second wheel, and controls the hydraulic braking system to adjust the actual slip of the second wheel to follow the target slip based on the pressure holding command or the pressure boosting command. Wherein, the second pose physical quantity is greater than or equal to the third given value, and the second pose physical quantity is less than a fourth given value. 
     In an embodiment of the present invention, the ECU replaces the hydraulic control command with a low priority by the hydraulic control command with a high priority and controls the hydraulic braking system to adjust the wheel speeds of the wheels based on the identical hydraulic control commands when the ECU receives data sensed by the dynamic sensing device to detect that the ground vehicle turns with a third pose physical quantity greater than or equal to the fourth given value. 
     In an embodiment of the present invention, the dynamic sensing device includes wheel speed sensors, a steering angle sensor, and a pose sensor. The wheel speed sensors are respectively arranged on the wheels and coupled to the ECU. The wheel speed sensors are configured to respectively sense the wheel speeds. The ECU is configured to receive the wheel speeds and estimate a vehicle speed of the ground vehicle according to the wheel speeds. The ECU is configured to calculate at least one of the wheel deceleration and the actual slip according to the vehicle speed and the wheel speeds. The steering angle sensor is arranged on a steering machine of the ground vehicle and coupled to the ECU. The steering angle sensor is configured to sense a steering angle of the steering machine. The pose sensor is coupled to the ECU and arranged on the ground vehicle. The pose sensor is configured to sense an actual pose physical quantity of the ground vehicle. The ECU is configured to receive the steering angle and the actual pose physical quantity, thereby detecting that the ground vehicle drives in a straight line or turns with the first pose physical quantity. 
     In an embodiment of the present invention, the pose sensor includes a gyroscope, an inertial measurement unit (IMU), a lean angle estimator, a lean angular velocity estimator, a yaw angle estimator, a yaw rate estimator, an accelerometer, or a combination of these. 
     In an embodiment of the present invention, the hydraulic braking system includes brake disks, brake calipers, and a hydraulic control unit (HCU). The brake disks are respectively arranged on the wheels and configured to respectively rotate with the wheels. The positions of the brake calipers respectively correspond to the positions of the brake disks. 
     The HCU is coupled to the ECU and connected to the brake calipers. When the ECU detects that the ground vehicle drives in a straight line or turns with the first pose physical quantity, the ECU controls the HCU to pressurize the brake calipers based on the identical hydraulic control commands, and the brake calipers respectively clamp the brake disks to adjust the wheel speeds. 
     In an embodiment of the present invention, the braking indication signal is a braking voltage value, and the ECU is coupled to a braking switch of the ground vehicle and configured to receive an actual voltage value through the braking switch. When the ground vehicle turns off the braking switch, the actual voltage value is unequal to the braking voltage value. When the ground vehicle turns on the braking switch, the actual voltage value is equal to the braking voltage value. 
     In an embodiment of the present invention, a stably braking method controls wheels on a single axle of a ground vehicle. The method includes: 
     calculating at least one of a wheel deceleration and an actual slip of each of wheels and generating hydraulic control commands when a braking operation is performed in response to a braking indication signal and it is detected that the wheel deceleration is higher than a first given value or that the actual slip is higher than a second given value, wherein the hydraulic control commands are configured to control a hydraulic braking system arranged on the wheels to decrease a wheel speed of each of the wheels and adjust the wheel speed of each of the wheels to be higher than  0  in a braking process, the hydraulic control commands include a pressure boosting command, a pressure holding command, or a pressure releasing command, a priority of the pressure releasing command is higher than that of the pressure holding command, and a priority of the pressure holding command is higher than that of the pressure boosting command; and when the ground vehicle drives in a straight line or turns with a first pose physical quantity greater than 0 and less than a third given value, replacing the hydraulic control command with a low priority by the hydraulic control command with a high priority and controlling the hydraulic braking system to adjust the wheel speeds of the wheels based on the identical hydraulic control commands. 
     In an embodiment of the present invention, a target slip of each of the wheels is decreased and the hydraulic braking system is controlled to adjust the actual slip of each of the wheels to follow the corresponding target slip based on the identical hydraulic control commands when the ground vehicle turns with the first pose physical quantity. 
     In an embodiment of the present invention, the wheels include a first wheel and a second wheel. When the ground vehicle drives in a lane and the ground vehicle turns to an inner side of the lane with a second pose physical quantity, the first wheel is close to an outer side of the lane, the second wheel is close to the inner side of the lane, the hydraulic braking system is controlled to increase the wheel speed of the first wheel based on the pressure releasing command, a target slip of the second wheel is increased, and the hydraulic braking system is controlled to adjust the actual slip of the second wheel to follow the target slip based on the pressure holding command or the pressure boosting command. Wherein, the second pose physical quantity is greater than or equal to the third given value, and the second pose physical quantity is less than a fourth given value. 
     In an embodiment of the present invention, the hydraulic control command with a low priority is replaced by the hydraulic control command with a high priority and the hydraulic braking system is controlled to adjust the wheel speeds of the wheels based on the identical hydraulic control commands when the ground vehicle turns with a third pose physical quantity greater than or equal to the fourth given value. 
     To summarize the contents above, the stably braking system and the method using the identical adjusts braking hydraulic pressures corresponding to all the wheels on a single axle to be equal, and therefore improves the braking stability when the ground vehicle brakes based on an anti-lock braking mechanism. In addition, the actual slip and the target slip of the wheel are controlled to improve the turning stability when the ground vehicle turns. 
     Below, the embodiments are described in detail in cooperation with the drawings to make easily understood the technical contents, characteristics and accomplishments of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram illustrating a stably braking system according to an embodiment of the present invention; 
         FIG.  2    is a schematic diagram illustrating two wheels on a single axle in a turning process according to an embodiment of the present invention; 
         FIG.  3    is a schematic diagram illustrating a HCU performing a pressure boosting command according to an embodiment of the present invention; 
         FIG.  4    is a schematic diagram illustrating a HCU performing a pressure holding command according to an embodiment of the present invention; 
         FIG.  5    is a schematic diagram illustrating a HCU performing a pressure releasing command according to an embodiment of the present invention; and 
         FIG.  6    is a flowchart of a stably braking method according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to embodiments illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. In the drawings, the shape and thickness may be exaggerated for clarity and convenience. This description will be directed in particular to elements forming part of, or cooperating more directly with, methods and apparatus in accordance with the present disclosure. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. Many alternatives and modifications will be apparent to those skilled in the art, once informed by the present disclosure. 
     The invention is particularly described with the following examples which are only for instance. Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the following disclosure should be construed as limited only by the metes and bounds of the appended claims. In the whole patent application and the claims, except for clearly described content, the meaning of the article “a” and “the” includes the meaning of “one or at least one” of the element or component. Moreover, in the whole patent application and the claims, except that the plurality can be excluded obviously according to the context, the singular articles also contain the description for the plurality of elements or components. In the entire specification and claims, unless the contents clearly specify the meaning of some terms, the meaning of the article “wherein” includes the meaning of the articles “wherein” and “whereon”. The meanings of every term used in the present claims and specification refer to a usual meaning known to one skilled in the art unless the meaning is additionally annotated. Some terms used to describe the invention will be discussed to guide practitioners about the invention. Every example in the present specification cannot limit the claimed scope of the invention. 
     Certain terms are used throughout the description and the claims to refer to particular components. One skilled in the art appreciates that a component may be referred to as different names. This disclosure does not intend to distinguish between components that differ in name but not in function. In the description and in the claims, the term “comprise” is used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to.” The phrases “be coupled to,” “couples to,” and “coupling to” are intended to compass any indirect or direct connection. Accordingly, if this disclosure mentioned that a first device is coupled with a second device, it means that the first device may be directly or indirectly connected to the second device through electrical connections, wireless communications, optical communications, or other signal connections with/without other intermediate devices or connection means. 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. 
     Unless otherwise specified, some conditional sentences or words, such as “can”, “could”, “might”, or “may”, usually attempt to express that the embodiment in the present invention has, but it can also be interpreted as a feature, element, or step that may not be needed. In other embodiments, these features, elements, or steps may not be required. 
     In the following description, a stably braking system and a method using the same will be provided. The system and the method adjust braking hydraulic pressures corresponding to all wheels on a single axle to improve the braking stability when a ground vehicle brakes based on an anti-lock braking mechanism. 
       FIG.  1    is a schematic diagram illustrating a stably braking system according to an embodiment of the present invention. Referring to  FIG.  1   , the stably braking system is arranged in a ground vehicle, such as an automobile or a motorcycle. The stably braking system includes a hydraulic braking system  1  and an electronic control unit (ECU)  2 . The hydraulic braking system  1  is arranged on wheels  4 _ 1  and  4 _ 2  that are arranged on a single axle  3  of the ground vehicle. The ECU  2  is coupled or connected to the hydraulic braking system  1  and a dynamic sensing device  5 . The dynamic sensing device  5  is arranged on the ground vehicle or the wheels  4 _ 1  and  4 _ 2 . For convenience and clarity, the number of the wheels  4 _ 1  and  4 _ 2  is two. The ECU  2  may be coupled or connected to a braking switch  6  of the ground vehicle. 
     The operation of the stably braking system is introduced as follows. Firstly, the ECU  2  receives data sensed by the dynamic sensing device  5  to calculate at least one of the wheel deceleration and the actual slip of each of the wheels  4 _ 1  and  4 _ 2 . When the ECU  2  receives a braking indication signal B to perform a braking operation and at least one of a first condition and a second condition is satisfied, the ECU  2  generates hydraulic control commands. The first condition defines that the wheel deceleration of each of the wheels  4 _ 1  and  4 _ 2  is higher than a first given value. The second condition defines that the actual slip D of each of the wheels  4 _ 1  and  4 _ 2  is higher than a second given value. The first given value and the second given value are set according to requirements. For example, the braking indication signal B is a braking voltage value. The ECU  2  receives an actual voltage value through the braking switch  6 . 
     When the ground vehicle turns off the braking switch  6 , the actual voltage value is unequal to the braking voltage value. When the ground vehicle turns on the braking switch  6 , the actual voltage value is equal to the braking voltage value. The present invention is not limited to the method of receiving the braking indication signal B. The hydraulic control commands are configured to control the hydraulic braking system  1  to decrease the wheel speed W of each of the wheels  4 _ 1  and  4 _ 2  and adjust the wheel speed W of each of the wheels  4 _ 1  and  4 _ 2  to be higher than 0 in a braking process, thereby avoiding locking the wheels  4 _ 1  and  4 _ 2 . The hydraulic control commands include a pressure boosting command, a pressure holding command, or a pressure releasing command. The actual slip D=(V−W)/V, wherein V represents the vehicle speed of the ground vehicle. In other words, the ECU  2  performs an anti-lock braking mechanism when at least one of the first condition and the second condition is satisfied. In order to further improve the braking stability, the ECU  2  sets the priority of the pressure releasing command to be higher than the priority of the pressure holding command, and sets the priority of the pressure holding command to be higher than the priority of the pressure boosting command. When the ECU  2  receives data sensed by the dynamic sensing device  5  to detect that the ground vehicle drives in a straight line or turns with a first pose physical quantity greater than 0 and less than a third given value, the ECU  2  replaces the hydraulic control command with a low priority by the hydraulic control command with a high priority and controls the hydraulic braking system  1  to adjust the wheel speeds W of the wheels  4 _ 1  and  4 _ 2  based on the identical hydraulic control commands, thereby providing the largest braking force for all the wheels  4 _ 1  and  4 _ 2 . When the ground vehicle is a motorcycle, the pose physical quantity is a lean angle or a lean angular velocity. The lean angle of the ground vehicle depends on the chassis of the body of the ground vehicle. When the normal vector of the chassis is vertical to the ground, the lean angle of the ground vehicle is set to 0 degree. When the lean angle keeps unchanged in unit time, the lean angular velocity is set to 0 degree/second. When the ground vehicle is an automobile, the pose physical quantity is a yaw angle or a yaw rate. The yaw angle of the ground vehicle depends on a plane parallel to the body of the ground vehicle and vertical to the ground. When the yaw angle is 0 degree, the traveling direction of the ground vehicle is vertical to the normal vector of the plane. When the yaw angle keeps unchanged in unit time, the yaw rate is set to 0 degree/second. For example, when the hydraulic control commands corresponding to the wheels  4 _ 1  and  4 _ 2  are respectively a pressure boosting command and a pressure holding command and the ground vehicle drives in a straight line or turns with the first pose physical quantity, the ECU  2  controls the hydraulic braking system  1  to adjust the wheel speeds W of the wheels  4 _ 1  and  4 _ 2  based on the pressure holding command. When the hydraulic control commands corresponding to the wheels  4 _ 1  and  4 _ 2  are respectively a pressure releasing command and a pressure holding command and the ground vehicle drives in a straight line or turns with the first pose physical quantity, the ECU  2  controls the hydraulic braking system  1  to adjust the wheel speeds W of the wheels  4 _ 1  and  4 _ 2  based on the pressure releasing command. When the hydraulic control commands corresponding to the wheels  4 _ 1  and  4 _ 2  are respectively a pressure releasing command and a pressure boosting command and the ground vehicle drives in a straight line or turns with the first pose physical quantity, the ECU  2  controls the hydraulic braking system  1  to adjust the wheel speeds W of the wheels  4 _ 1  and  4 _ 2  based on the pressure releasing command. 
     In order to increase the centripetal force during braking, the ECU  2  can reduce the longitudinal target slip when the ground vehicle turns. This is because each of wheels  4   1  and  4   2  has the maximum friction limit when the ground vehicle drives. The maximum friction has the longitudinal and lateral components of a vector. The maximum friction provides larger lateral friction to increase the lateral force and the centripetal force of the ground vehicle. When the ground vehicle stably turns, the ECU  2  decreases the longitudinal slip and maintains the larger lateral friction and the larger lateral force to increase the turning stability and the centripetal force. In some embodiments of the present invention, the ECU  2  decreases the target slip of each of the wheels  4 _ 1  and  4 _ 2  and controls the hydraulic braking system  1  to adjust the actual slip D of each of the wheels  4 _ 1  and  4 _ 2  to follow the corresponding target slip based on the identical hydraulic control commands when the ECU  2  receives data sensed by the dynamic sensing device  5  to detect that the ground vehicle turns with the first pose physical quantity. Preferably, the actual slip D may be less than or equal to the corresponding target slip. The actual slip D and the target slip are longitudinal slips. For example, when the original actual slip D and the original target slip of the wheel  4 _ 1  are respectively 10% and 11%, the ECU  2  decreases the target slip of the wheel  4 _ 1  to 7% such that the actual slip D of the wheel  4 _ 1  is adjusted to 6%. 
       FIG.  2    is a schematic diagram illustrating two wheels on a single axle in a turning process according to an embodiment of the present invention. Referring to  FIG.  1    and  FIG.  2   , the wheel  4 _ 1  is used as a first wheel and the wheel  4 _ 2  is used as a second wheel. In some embodiments of the present invention, when the ground vehicle drives in a lane and the ECU  2  receives data sensed by the dynamic sensing device  5  to detect that the ground vehicle turns to the inner side of the lane with a second pose physical quantity, the first wheel is close to the outer side of the lane, the second wheel is close to the inner side of the lane, and the ECU  2  controls the hydraulic braking system  1  to increase the wheel speed W of the first wheel based on the pressure releasing command, increases the target slip of the second wheel, and controls the hydraulic braking system  1  to adjust the actual slip D of the second wheel to follow the corresponding target slip based on the pressure holding command or the pressure boosting command. Wherein, the second pose physical quantity is greater than or equal to the third given value, and the second pose physical quantity is less than a fourth given value. Preferably, the actual slip D of the second wheel may be less than or equal to the corresponding target slip. The third given value and the fourth given value are set according to requirements. 
     The third given value and the fourth given value may be respectively  10  degrees and 50 degrees, but the present invention is not limited thereto. For example, when the original actual slip D and the original target slip of the wheel  4 _ 2  are respectively 10% and 11%, the ECU  2  increases the target slip of the wheel  4 _ 2  to 13%, such that the actual slip D of the wheel  4 _ 2  is adjusted to 12%. In other words, the wheel speed W of the second wheel is decreased. The difference between the wheel speeds W of the first wheel and the second wheel can help the ground vehicle turn to the inner side of the lane, lest the ground vehicle deviate from the desired driving trajectory. 
     The ECU  2  replaces the hydraulic control command with a low priority by the hydraulic control command with a high priority and controls the hydraulic braking system  1  to adjust the wheel speeds W of the wheels  4 _ 1  and  4 _ 2  based on the identical hydraulic control commands, thereby improving the braking stability when the ECU  2  receives data sensed by the dynamic sensing device  5  to detect that the ground vehicle turns with a third pose physical quantity greater than or equal to the fourth given value. 
     In some embodiments of the present invention, the dynamic sensing device  5  may include wheel speed sensors  52 , a steering angle sensor  53 , and a pose sensor  54 . The wheel speed sensors  52 , the steering angle sensor  53 , and the pose sensor  54  are coupled or connected to the ECU  2 . The pose sensor  54  may include a gyroscope, an inertial measurement unit (IMU), a lean angle estimator, a lean angular velocity estimator, a yaw angle estimator, a yaw rate estimator, an accelerometer, or a combination of these, but the present invention is not limited thereto. The wheel speed sensors  52  are respectively arranged on the wheels  4 _ 1  and  4 _ 2 . The steering angle sensor  53  is arranged on the steering machine of the ground vehicle. The wheel speed sensors  52  respectively sense the wheel speeds W of the wheels  4 _ 1  and  4 _ 2 , thereby estimating the vehicle speed of the ground vehicle. The ECU  2  receives the wheel speeds W of the wheels  4 _ 1  and  4 _ 2  and estimates the vehicle speed of the ground vehicle according to the wheel speeds W of the wheels  4 _ 1  and  4   2 . The ECU  2  calculates at least one of the wheel deceleration and the actual slip D according to the vehicle speed of the ground vehicle and the wheel speeds W of the wheels  4 _ 1  and  4 _ 2 . For example, the estimated vehicle speed may be a real-time average wheel speed of the wheels  4 _ 1  and  4 _ 2  or a reference vehicle speed. The reference vehicle speed is obtained according to a preset deceleration and the initial average wheel speed of the wheels  4 _ 1  and  4 _ 2 . The steering angle sensor  53  senses the steering angle U of the steering machine. The pose sensor  54  senses the actual pose physical quantity T of the ground vehicle and detects that the actual pose physical quantity T is the first pose physical quantity, the second pose physical quantity, or the third pose physical quantity. The ECU  2  receives the steering angle U and the actual pose physical quantity T, thereby detecting that the ground vehicle drive in a straight line or turns with the first pose physical quantity, the second pose physical quantity, or the third pose physical quantity. 
     In some embodiments of the present invention, the hydraulic braking system  1  may include brake disks  11 , brake calipers  12 , and a hydraulic control unit (HCU)  13 . The brake disks  11  are respectively arranged on the wheels  4 _ 1  and  4 _ 2 . The positions of the brake calipers  12  respectively correspond to the positions of the brake disks  11 . The HCU  13  is coupled or connected to the ECU  2  and connected to the brake calipers  12 . When the ECU  2  detects that the ground vehicle drives in a straight line or turns with the first pose physical quantity, the second pose physical quantity, or the third pose physical quantity, the ECU  2  controls the HCU  13  to pressurize the brake calipers  12  based on the identical or different hydraulic control commands. Then, the brake calipers  12  respectively clamp the brake disks  11  to adjust the wheel speeds W and the actual slips D of the wheels  4 _ 1  and  4 _ 2  and the vehicle speed. 
       FIG.  3    is a schematic diagram illustrating a HCU performing a pressure boosting command according to an embodiment of the present invention. Referring to  FIG.  3   , the HCU  13  may include a pressurizer  131 , a motor  132 , a first unidirectional valve  1331 , a second unidirectional valve  1332 , a third unidirectional valve  1333 , a fourth unidirectional valve  1334 , a fifth unidirectional valve  1335 , a sixth unidirectional valve  1336 , a seventh unidirectional valve  1337 , an eighth unidirectional valve  1338 , a first electromagnetic valve  134 , a second electromagnetic valve  135 , a third electromagnetic valve  136 , and a fourth electromagnetic valve  137 . The brake calipers  12 , the pressurizer  131 , the motor  132 , the first unidirectional valve  1331 , the second unidirectional valve  1332 , the third unidirectional valve  1333 , the fourth unidirectional valve  1334 , the fifth unidirectional valve  1335 , the sixth unidirectional valve  1336 , the seventh unidirectional valve  1337 , the eighth unidirectional valve  1338 , the first electromagnetic valve  134 , the second electromagnetic valve  135 , the third electromagnetic valve  136 , and the fourth electromagnetic valve  137  connected to each other through oil pipes. The pressurizer  131  has an oil room that stores braking oil  138 . A solid line represents an oil path where the braking oil  138  passes. A dashed line represents an oil path where the braking oil  138  does not pass. The pressurizer  131  is connected to the third unidirectional valve  1333 , the fourth unidirectional valve  1334 , the seventh unidirectional valve  1337 , the eighth unidirectional valve  1338 , the second electromagnetic valve  135 , and the third electromagnetic valve  136 . The first unidirectional valve  1331  is connected to the second unidirectional valve  1332 , the motor  132 , and the first electromagnetic valve  134 . The second unidirectional valve  1332  is connected to the motor  132  and the third unidirectional valve  1333 . The third unidirectional valve  1333  is connected to the fourth unidirectional valve  1334 , the seventh unidirectional valve  1337 , the eighth unidirectional valve  1338 , the second electromagnetic valve  135 , and the third electromagnetic valve  136 . The fourth unidirectional valve  1334  is connected to the fifth unidirectional valve  1335 , the seventh unidirectional valve  1337 , the eighth unidirectional valve  1338 , the second electromagnetic valve  135 , and the third electromagnetic valve  136 . The fifth unidirectional valve  1335  is connected to the motor  132  and the sixth unidirectional valve  1336 . The sixth unidirectional valve  1336  is connected to the motor  132  and the fourth electromagnetic valve  137 . The fourth electromagnetic valve  137  is connected to the brake caliper  12 , the eighth unidirectional valve  1338 , the third electromagnetic valve  136 , and the sixth unidirectional valve  1336 . The eighth unidirectional valve  1338  is connected to the seventh unidirectional valve  1337 , the second electromagnetic valve  135 , and the third electromagnetic valve  136 . The seventh unidirectional valve  1337  is connected to the second electromagnetic valve  135 , the third electromagnetic valve  136 , the brake caliper  12 , and the first electromagnetic valve  134 . The ECU  2  is coupled or connected to the motor  132 , the first electromagnetic valve  134 , the second electromagnetic valve  135 , the third electromagnetic valve  136 , and the fourth electromagnetic valve  137 . 
     When the HCU  13  performs the pressure boosting command, the ECU  2  uses the second electromagnetic valve  135  and the third electromagnetic valve  136  to open the corresponding oil path, turns off the motor  132 , and uses the first electromagnetic valve  134  and the fourth electromagnetic valve  137  to close the corresponding oil path. The pressurizer  131  pressurizes the braking oil  138 , such that the braking oil  138  passes through the second electromagnetic valve  135  and the third electromagnetic valve  136  and increases pressures for pressurizing all the brake calipers  12 . Thus, the brake calipers  12  respectively clamp the brake disks  11  to decrease the wheel speeds and the vehicle speed of all the wheels  4 _ 1  and  4 _ 2 . 
       FIG.  4    is a schematic diagram illustrating a HCU performing a pressure holding command according to an embodiment of the present invention. Referring to  FIG.  4   , the ECU  2  turns off the motor  132  and uses the second electromagnetic valve  135 , the third electromagnetic valve  136 , the first electromagnetic valve  134 , and the fourth electromagnetic valve  137  to close the corresponding oil path when the HCU  13  performs the pressure holding command. Because the braking oil  138  is confined between the first electromagnetic valve  134  and the second electromagnetic valve  135  and confined between the third electromagnetic valve  136  and the fourth electromagnetic valve  137 , the braking oil  138  can maintain the pressures for pressing all the brake calipers  12 . Thus, the brake calipers  12  respectively rub against the brake disks  11  to maintain the braking pressures and change the wheel speeds of the wheels  4 _ 1  and  4 _ 2  and the vehicle speed in response to the braking pressures. 
       FIG.  5    is a schematic diagram illustrating a HCU performing a pressure releasing command according to an embodiment of the present invention. Referring to  FIG.  5   , the ECU  2  turns on the motor  132 , uses the first electromagnetic valve  134  and the fourth electromagnetic valve  137  to open the corresponding oil path, and uses the second electromagnetic valve  135  and the third electromagnetic valve  136  to close the corresponding oil path. The motor  132  can draw the braking oil  138  from the oil pipe to the oil room of the pressurizer  131 , thereby releasing the pressurizer  131 . Thus, the braking oil  138  can decrease the pressures for pressurizing all the brake calipers  12 , such that all the brake calipers  12  respectively clamp all the brake disks  11  to decrease the braking pressure and increase the wheel accelerations of all the wheels  4   1  and  4   2 . As a result, the braking oil  138  can pass through the first electromagnetic valve  134 , the fourth electromagnetic valve  137 , the first unidirectional valve  1331 , the second unidirectional valve  1332 , the third unidirectional valve  1333 , the fourth unidirectional valve  1334 , the fifth unidirectional valve  1335 , the sixth unidirectional valve  1336 , the seventh unidirectional valve  1337 , and the eighth unidirectional valve  1338 . 
     The ECU  2  can generate the different hydraulic control commands to change the wheel speeds W of the wheels  4 _ 1  and  4 _ 2 . When the wheel speed W of the wheel  4 _ 1  changes in response to the pressure boosting command, the ECU  2  uses the third electromagnetic valve  136  to open the corresponding oil path, turns off the motor  132 , and uses the fourth electromagnetic valve  137  to close the corresponding oil path. When the wheel speed W of the wheel  4 _ 1  changes in response to the pressure holding command, the ECU  2  turns off the motor  132  and uses the third electromagnetic valve  136  and the fourth electromagnetic valve  137  to close the corresponding oil path. When the wheel speed W of the wheel  4   1  changes in response to the pressure releasing command, the ECU  2  turns on the motor  132 , uses the fourth electromagnetic valve  137  to open the corresponding oil path, and uses the third electromagnetic valve  136  to close the corresponding oil path. When the wheel speed W of the wheel  4 _ 2  changes in response to the pressure boosting command, the ECU  2  turns on the second electromagnetic valve  135  and turns off the motor  132  and the first electromagnetic valve  134 . When the wheel speed W of the wheel  4 _ 2  changes in response to the pressure holding command, the ECU  2  turns off the motor  132  and uses the second electromagnetic valve  135  and the first electromagnetic valve  134  to close the corresponding oil path. When the wheel speed W of the wheel  4 _ 2  changes in response to the pressure releasing command, the ECU  2  turns on the motor  132 , uses the first electromagnetic valve  134  to open the corresponding oil path, and uses the second electromagnetic valve  135  to close the corresponding oil path. 
       FIG.  6    is a flowchart of a stably braking method according to an embodiment of the present invention. Referring to  FIG.  1    and  FIG.  6   , the stably braking method of the present invention is introduced as follows. 
     Firstly, in Step S 10 , the ECU  2  receives data sensed by the dynamic sensing device  5  to obtain the wheel speed W of each of the wheels  4 _ 1  and  4 _ 2 . Then, in Step S 11 , the ECU  2  calculates at least one of the actual slip D and the wheel deceleration of each of the wheels  4 _ 1  and  4 _ 2 . In Step S 12 , the ECU  2  determines whether the ECU  2  receives the braking indication signal B. If the result is yes, the procedure proceeds to Step 
     S 14 . If the result is no, the procedure proceeds to Step S 16 . In Step S 16 , the whole procedure is ended. In Step S 14 , the ECU  2  controls the dynamic sensing device  5  to estimate the vehicle speed. After Step S 14 , Step S 18  is performed. In Step S 18 , the ECU  2  determines whether the vehicle speed is larger than a preset speed, such as  10  km/hr. If the result is no, the procedure proceeds to Step S 20 . If the result is yes, the procedure proceeds to Step S 24 . In Step S 20 , a braking operation is performed without performing an anti-lock mechanism. In Step S 24 , the ECU  2  determines whether the anti-lock mechanism has been already performed. If the result is no, the procedure proceeds to Step S 20 . If the result is yes, the procedure proceeds to Step S 26 . For example, when the wheel deceleration of each of the wheels  4 _ 1  and  4 _ 2  is higher than the first given value or the actual slip D of each of the wheels  4 _ 1  and  4 _ 2  is higher than the second given value, the ECU  2  determines that the anti-lock mechanism has been already performed. When the wheel deceleration of each of the wheels  4 _ 1  and  4 _ 2  is not higher than the first given value or the actual slip D of each of the wheels  4 _ 1  and  4 _ 2  is not higher than the second given value, the ECU  2  detects that the anti-lock mechanism is not performed. In Step S 26 , the ECU  2  receives data sensed by the dynamic sensing device  5  to obtain the actual pose physical quantity T of the ground vehicle and the steering angle U of the steering machine. Finally, in Step S 28 , the ECU  2  detects that the ground vehicle drives in a straight line or turns with the first pose physical quantity, the second pose physical quantity, or the third pose physical quantity according to the actual pose physical quantity T of the ground vehicle and the steering angle U of the steering machine. Besides, the ECU  2  modifies the hydraulic control commands according to the traveling state of the ground vehicle and controls the hydraulic braking system  1  to adjust the wheel speed W of each of the wheels  4 _ 1  and  4 _ 2  based on the modified hydraulic control commands. According to the embodiments provided above, the stably braking system and the method using the same adjust braking hydraulic pressures corresponding to all wheels on a single axle to be equal, thereby improving the braking stability when the ground vehicle brakes based on an anti-lock braking mechanism. In addition, the actual slip and the target slip of the wheel are controlled to improve the turning stability when the ground vehicle turns. 
     The embodiments described above are only to exemplify the present invention but not to limit the scope of the present invention. Therefore, any equivalent modification or variation according to the shapes, structures, features, or spirit disclosed by the present invention is to be also included within the scope of the present invention.