Hybrid brake-by-wire system using a motor-magnetostrictive actuator combination

The present invention discloses a motor-magnetostrictive actuator hybrid brake-by-wire system. The system includes a motor, a transmission mechanism, a magnetostrictive-driving piston mechanism and a floating-caliper disc mechanism. The transmission mechanism includes a planetary gear set and a screw set, and is driven by the motor. The linear motion of the sleeve is achieved by the planetary gear set and screw set. The sleeve pushes forward the piston head of the magnetostrictive-driving piston mechanism and the piston head pushes forward the brake pad back plate of the floating-caliper disc mechanism to clamp the brake disc, which accomplishes braking. The present invention uses the motor and the magnetostrictive-driving piston mechanism as a combined BBW system, which will simultaneously solve the problems of slow response, low precision and motor stalling effect of the only motor-driving braking systems and, also avoid the drawback of insufficient mechanical capabilities of the only magnetostrictive actuator-driving braking systems.

TECHNICAL FIELD

The present invention relates to a disc brake, and more particularly to a hybrid brake-by-wire system using a motor-magnetostrictive actuator combination.

BACKGROUND OF THE INVENTION

Automobiles, as one of the most important means of transportation vehicles, have developed, updated and innovated with dramatically fast development of science and technology. No matter how the automotive technology develops, vehicle's safety and energy saving have been always the core topics in the automotive industry and also the most concerned points of the customers. As one of the major automotive systems, the braking system plays a vital role in driving safety. At present, brake-by-wire system is rapidly developing as a new type of automobile braking system besides the traditional hydraulic, pneumatic and electromagnetic braking system. The new brake-by-wire system try to avoid the congenital defects of the traditional hydraulic, pneumatic and electromagnetic braking system such as the complexity of the system, high energy consumption and relatively low response speed (which means longer braking distance), but the brake-by-wire system itself is still in pre-researching and explore stage.

At present, specifically, a vast majority of automobiles are currently using conventional hydraulic disc brakes. Structurally, the hydraulic disc braking system comprises a brake pedal, a master cylinder, brake pipelines, wheel cylinders, a brake disc and brake pads. When driver send out the braking signal, braking pressure generated by the master cylinder is delivered by brake pipelines to generate corresponding pressure in each wheel cylinder to push the piston as well as the brake pads and clamp the brake disc to generate friction to achieve braking. Functionally, further, the auxiliary functions of anti-lock braking system (ABS), acceleration slip regulation (ASR) and electronic brake force distribution (EBD) can be realized by matching appropriate electronic control systems. However, there are inherent drawbacks of the conventional braking systems as follows:(a) The long and sophisticated pipelines/valves of hydraulic and/or pneumatic braking systems lead to slow braking pressure transfer and then braking delay, which results in the increase of brake distance and unguaranteed vehicle braking safety.(b) The complex pipelines and valves greatly increase complexity of the system and control, reduce reliability thereof, and thus the cost of braking system remains high.(c) The pipelines, valves or electromagnetic actuators greatly increase the weight of the systems. Undoubtedly, the conventional hydraulic, pneumatic and electromagnetic braking systems are unbeneficial to achieve energy saving and emission reduction. (Data shows that the fuel consumption increases by 6%-8% while the mass of an automobile increases by 10%.)(d) The hydraulic oil fulfilled in the hydraulic braking systems is flammable and may leak, which would possibly cause environment pollution and even threatens crash safety of automobiles.

The newly-proposed concept of BBW systems has potentially brought essential changes to the braking systems and the automotive industry. The new types of BBW systems are expected to solve the problems that the conventional brakes cannot avoid. However, it is presently at very start phase of investigation and industrial applications, and there are still some fatal problems of the existing BBW systems:(a) Majority of the existing BBW systems are using motors as the only actuator. When braking, the motor and the related braking mechanism (often the ball-screw mechanism) are required to provide enough braking torque. However, the driving power of the motor is limited because of quite limited installation space. Then, a speed reduction mechanism, which is used to increase the driving force by decreasing speed, must be matched for the needed braking torque. But the excessive speed reduction ratio may equal to long response time of driving mechanism based on the motor and ball-screw set. Because the braking torque is generated by the output torque from the motor, and also the gap between the brake pads and the brake disc is clamped through pushing the piston.(b) When the ABS works, the processes of reducing the torque (the counterpart of the “torque” herein in the BBW systems is the “pressure” in the conventional hydraulic braking systems), holding the torque and increasing the torque are completed in quite short time. The action from the motor to the piston is realized through the mechanical transmission mechanism. Thus, the accuracy of the states of reducing the torque, holding the torque and increasing the torque of ABS cannot be guaranteed. The braking distance increases and braking safety is threatened in turn.(c) What is more important, for the BBW systems using motors as the only actuator, the motor may be stalling during long-time braking and could lead to motor burnout, which would directly lead to the failure of braking systems.

SUMMARY

The present invention is to solve the existing technical problems, providing a hybrid brake-by-wire system using a motor-magnetostrictive actuator combination to simplify the braking system and greatly reduce the system quality, and finally improve the system performances, especially the braking safety.

The present invention discloses a hybrid brake-by-wire system using a motor-magnetostrictive actuator combination. The system includes a motor, a transmission mechanism, a magnetostrictive-driving piston mechanism and a floating-caliper disc mechanism, wherein the transmission mechanism including a planetary gear set and a screw set is driven by the motor. The linear motion of the sleeve is achieved by the planetary gear set and screw set. The piston head of the magnetostrictive-driving piston mechanism pushed forward by both the sleeve and the magnetostrictive rod drives the brake pad back plate to clamp the brake disc through the right and left brake pads of the floating-caliper disc mechanism, which accomplishes braking.

The motor includes a stator and a rotor. The ring gear of the planetary gear set fixedly connected with the rotor is driven by the motor, and the screw of the screw set is coaxially assembled with the carrier and the sun gear of the planetary gear set. The screw and the carrier are connected via a connecting key. The nut and the screw are connected via threads, and the sleeve is which cases the nut fixedly connected with the nut at the rear end through bolts is driven to move linearly.

A pushrod is screwed into the piston head of the magnetostrictive-driving piston mechanism, and a gland is connected with the front end of the piston body by threads. The pushrod is installed onto the front end of a magnetostrictive rod by a bias spring, the piston body connected with the front end of the sleeve is driven to move linearly. The coil winding is wound on the bobbin installed outside of the magnetostrictive rod, which realizes controllable axial extension under the controlled electromagnetic field generated by the coil winding with applied current.

The left brake pad is fixed to the inner side of the left caliper arm of a caliper body, and the right brake pad is fixed to the left side of the brake pad back plate. The brake disc is sandwiched between the left brake pad and the right brake pad. The right side of the brake pad back plate is connected to the front end of the piston head in a “T” shape, and the brake pad back plate driven by the piston head pushes the right brake pad to squeeze the brake disc, forcing the caliper body to push the left brake pad towards the right to squeeze the brake disc, which realizes braking.

Further, a guide rail is penetrating the brake pad back plate in the caliper body from which the brake pad back plate (118) gets guided.

A prestress bolt is installed onto the rear end of the magnetostrictive rod for adjusting the initial position/stress of the magnetostrictive rod.

The braking control process are set as follows: when braking, the motor and the magnetostrictive-driving piston mechanism work coordinately to push the right and left brake pads to overcome the brake clearance and the corresponding resistance, and the brake disc is clamped by the right and left brake pads. When the braking torque reaches a preset value, the applied current to the motor is cut off and the screw set enters a self-locking state. No initial current is applied to the coil winding of the magnetostrictive-driving piston mechanism. At this point, if the wheel braking torque is insufficient, the coil winding is applied with an appropriate high-level current, ABS enters the stage of increasing the torque. If the wheel is in the optimal braking state, ABS enters the stage of holding the torque. If the wheel approaches to the locking state, the coil winding is applied with an appropriate low-level current, then ABS enters the stage of reducing the torque. At the end of braking, an appropriate reverse current is applied to the motor, simultaneously the applied current to the coil winding of the magnetostrictive-driving piston mechanism is cut off, and the magnetostrictive-driving piston mechanism resets.

A wedge-shaped caliper disc mechanism is used to replace the structure of the floating-caliper disc mechanism, and the wedge is connected with the front end of the magnetostrictive-driving piston mechanism. A roller is installed between the bevel of the floating wedge-shaped caliper disc mechanism and the bevel of the wedge.

A ball-screw set is used to replace the screw set, and a check structure consisting of a ratchet and a pawl is assembled on the ball-screw set.

A ball-screw set is used to replace the screw set, and a clutch is assembled between the ball-screw set and the planet carrier.

During the initialization of the braking process and/or the long-time braking process of ABS, if the magnetostrictive-driving piston/wedge mechanism fails to work, the main control system starts the backup controller. If fails again, the main control system cuts off the control signal to the magnetostrictive-driving module, meanwhile, starts the only motor-driving module, and simultaneously sends the warning signal to driver. The magnetostrictive-driving module for braking with ABS performance, motor-driving module for braking with ABS performance, and motor-driving regular braking with no ABS performance will be potentially functioning with descending priority with consideration of the fail-safe behavior.

Compared with the prior art:

1. Advantageously, the present invention can solve the safety problems caused by slow response of the conventional hydraulic or pneumatic braking systems, the drawbacks of relatively high power consumption caused by the increased vehicle mass due to the complex pipelines/valves and the potential safety issues caused by hydraulic oil leakage in the hydraulic braking systems. Moreover, the present invention also can avoid the defects of the insufficient braking torque of the electromagnetic braking systems and overweight mass, and greatly simplifies the braking systems and enhances braking safety.

2. Advantageously, the present invention uses the motor and the magnetostrictive-driving piston mechanism cascaded in series as a combined driving assembly for the new BBW system, which can simultaneously solve problems of slow response (i.e., poor braking system performance) of only motor-driving braking systems and the issues of limited strokes of the only magnetostrictive actuator-driving braking systems. At the same time, both the advantages of the motor-driving braking systems, including long stroke and large driving torque (force), and very fast response of the magnetostrictive actuator-driving braking systems, are kept for the present invention.

3. Advantageously, the present invention uses the motor and the magnetostrictive-driving piston mechanism cascaded in series as a combined driving assembly for the new BBW system, which can enhance the fail-safe performance of the magnetostrictive actuator-driving braking systems. The motor-driving mechanism will provide emergency braking capability when the magnetostrictive-driving piston mechanism fails. Braking safety can be guaranteed.

4. Advantageously, the present invention can effectively reduce the power of the motor using the self-reinforcing effect of wedge mechanism and in turn solve the issue of insufficient braking torque of only motor-driving braking system. The braking efficiency is improved.

5. Advantageously, the present invention uses a mechanical motion converter of screw set with self-locking property between the motor and the magnetostrictive-driving piston mechanism. For the motor-magnetostrictive actuator combination, when braking torque reaches the preset value, applied current of the motor could be cut off and the braking system is driven only by the magnetostrictive-driving piston mechanism, which can effectively eliminate motor stalling effect with no influences on ABS and other auxiliary functions of the braking system.

Notation: the sequential numbers and the corresponding parts in the FIGs are listed:

DETAILED DESCRIPTION OF EMBODIMENTS

FIGS. 1 and 2show a hybrid brake-by-wire system using a motor-magnetostrictive actuator combination, which in detail consists of a motor101, transmission mechanism104, magnetostrictive-driving piston mechanism114and floating-caliper disc mechanism115in the present embodiment.

FIG. 1is a view showing that the motor101includes a stator102and a rotor103, and the transmission mechanism104includes a planetary gear set105and a screw set110. The planetary gear set105includes a ring gear106, planet gears107, a sun gear108and a carrier109. The ring gear106is fixedly connected with the rotor103and driven by the motor101, and the carrier109is coaxially assembled with the sun gear108and the screw111. The screw111is assembled on the carrier109via a connecting key. The nut112and screw111are connected via threads. The rear end of the sleeve113is fixedly connected to the nut112through bolts and driven by the motor101. The linear motion of the sleeve113is achieved by the transmission of the planetary gear set105and the screw set110.

As shown inFIGS. 1 and 2, the piston head10of the magnetostrictive-driving piston mechanism114is connected to the output end of the pushrod18via threads. The gland11is screwed to the front end of the piston assembly12, and the pushrod18is compressed onto the front end of the magnetostrictive rod17by a bias spring19. For adjusting the initial position of the magnetostrictive rod17, a prestress bolt16is attached to the rear end of the magnetostrictive rod17. The rear end of the piston body12is connected to the front end of the sleeve113, and the outlet hole15is provided for the coil lead. The linear motion of the piston assembly12is driven by the sleeve113. The coil winding13is wound on the bobbin14installed outside of the magnetostrictive rod17, which realizes controllable axial extension under the controlled electromagnetic field generated by the coil winding13with applied current.

Referring now toFIG. 1, the floating-caliper disc mechanism includes a left brake pad121fixed to the left caliper arm of the caliper body116, a right brake pad119fixed to the brake pad back plate118, using left brake pad121and right brake pad119to provide squeeze force on brake disk120. The right side of the brake back plate118is connected to the front end of the piston head10in a “T” shape, and the brake pad back plate118driven by the piston head10pushes the right brake pad119to squeeze the brake disc120, forcing the caliper body116to push the left brake pad121towards the right to squeeze the brake disc120, which generates braking torque. In the caliper body116, a guide rail117is penetrating the brake back plate118which could be guided through guide rail117.

In the embodiment, the coarse adjustment of the braking process is realized by the control of the motor101, meanwhile the fine adjustment of the braking process is realized by the control of magnetostrictive rod17through applied current regulation in the coil winding13.

The motor101turns the screw111through the planetary gear set105, pushing the sleeve113through the nut112to the left. When the braking torque reaches the preset value and the sleeve113in an expected position, the reverse locking function of the screw set110prevents the sleeve113from pushing the screw111reverse rotation. This reverse locking function can also be achieved by a check structure302. The magnetostrictive-driving piston mechanism114is connected with the output end of the motor101through a transmission mechanism104, pushing the brake pads against the brake disc120to achieve the purpose of deceleration.

The brake control modes are set that: when braking, the motor101and the magnetostrictive-driving piston mechanism114work coordinately, the motor101pushes the right and left brake pads119,121to overcome the brake clearance and the corresponding resistance, and then the brake disc120is compressed by the right119and left121brake pads. When the braking torque reaches the preset value, the applied current of the motor101is cut off, and the screw set110enters self-locking state. No initial current is applied to the coil winding13of the magnetostrictive-driving piston mechanism114. At this point, if the braking torque is insufficient, the coil winding13is applied with an appropriate high-level current, and ABS enters the stage of increasing the torque. If the wheel is in the optimal braking state, ABS enters the stage of holding the torque. If the wheel approaches to the locking state, the coil winding13is applied with an appropriate low-level current, then ABS enters the stage of reducing the torque. At the end of braking, reverse current is applied to the motor101, simultaneously the applied current to the coil winding13of the magnetostrictive-driving piston mechanism114is cut off, and the magnetostrictive-driving piston mechanism114resets.

Referring now toFIG. 3, another embodiment of the present invention is shown. A wedge-shaped caliper mechanism202is used to replace the structure of the floating-caliper disc mechanism115as shown inFIG. 1. The wedge205is installed onto the front end of the magnetostrictive-driving piston mechanism114. The self-reinforcing effect in braking process is realized through the interaction between two bevels of the wedge205and the wedge-shaped caliper mechanism202. The required power of the motor for braking is much lower than the system with no wedge accordingly. When braking, the motor101and the wedge-shaped caliper disc mechanism202work coordinately. The motor101pushes the right and left brake pad119,121to overcome the brake clearance and the corresponding resistance, then the brake disc120is compressed by the right119and left brake pad121. When the braking torque reaches the preset value, the applied current to the motor101is cut off and the screw set110enters self-locking state. No initial current is applied to the coil winding13of the magnetostrictive-driving wedge mechanism201. At this point, if the wheel brake torque is insufficient, the coil winding13is applied with an appropriate high-level current, and ABS enters the stage of increasing the torque. If the wheel is in the optimal braking state, ABS enters the stage of holding the torque. If the wheel approaches to the locking state, the coil winding13is applied with an appropriate low-level current, then ABS enters the stage of reducing the torque. At the end of braking, reverse current is applied to the motor101, simultaneously the applied current to the coil winding13in the magnetostrictive-driving wedge mechanism201is cut off, and the magnetostrictive-driving wedge mechanism201resets.

Referring now toFIG. 4, yet another embodiment of the present invention is shown. The ball-screw set305is used to replace the screw set110in the structure shown inFIG. 1. A check structure302composed of a ratchet wheel304and a pawl303is installed on the ball-screw305. The ball-screw set has a higher transmission efficiency but doesn't has a self-locking function, so a locking device is further needed for the system. When braking, the motor101pushes the right and left brake pads119,121to overcome the brake clearance and the corresponding resistance, then the brake disc120is clamped by the right119and left121brake pads. When the braking torque reaches the preset value, the applied current to the motor101is cut off, and the ratchet wheel304and the pawl303prevent the sleeve113to push the screw306reverse rotation under the retroaction of the braking torque. No initial current is applied to the coil winding13of the magnetostrictive-driving piston mechanism114. At the mean time the system will estimate the wheel braking condition. If the wheel brake torque is insufficient, the coil winding13is applied with an appropriate high-level current, and ABS enters the stage of increasing the torque. If the wheel is in the optimal braking state, ABS enters the stage of holding the torque. If the wheel approaches to the locking state, the coil winding13is applied with an appropriate low-level current, then ABS enters the stage of reducing the torque. At the end of braking, releasing the pawl303firstly, then reverse current is applied to the motor101, simultaneously the applied current to the coil winding13of the magnetostrictive-driving piston mechanism114is cut off, and the magnetostrictive-driving piston mechanism114resets.

Referring now toFIG. 5, the check structure302composed of a ratchet wheel304and a pawl305as shown inFIG. 4has another potential substitute of the clutch402. In the case of piston holding motionless in long-time/distance braking, the motor will not stall due to the use of the clutch402. When braking, the motor101pushes the right and left brake pads119,121to overcome the brake clearance and the corresponding resistance, then the brake disc120is clamped by the right and left brake pads119,121. When the braking torque reaches the limit of the force that the clutch can deliver, the motor101remains rotating and the magnetostrictive-driving piston mechanism114plays the ABS role at this point. No initial current is applied to the coil winding13of the magnetostrictive-driving piston mechanism114. At the mean time the system will estimate the wheel braking condition. If the wheel brake force is insufficient, the coil winding13is applied with an appropriate high-level current, and ABS enters the stage of increasing the torque. If the wheel is in the optimal braking state, ABS enters the stage of holding the torque. If the wheel approaches to the locking state, the coil winding13is applied with an appropriate low-level current, then ABS coming into the stage of reducing the torque. At the end of braking, the reverse current is applied to the motor101, meanwhile the applied current to the coil winding13of the magnetostrictive-driving piston mechanism114is cut off, and the magnetostrictive-driving piston mechanism114resets.

Referring now toFIG. 6, the diagram of this invention being applied to an automotive ABS is shown. The whole system includes an ABS electronic control unit (ECU), wheel speed sensors20, by-wire brakes21, electronic brake pedal22and an angle sensor23. The ECU receives the signal of angle of the electronic brake pedal22transmitted by the angle sensor23and the signal of the wheel speed from the wheel speed sensor20, then evaluates the vehicle braking state and appropriately controls the by-wire brakes21. There are an ABS indicator24, a parking brake indicator25, an ignition switch26and a battery27inFIG. 6. The core of this brake-by-wire system is the signal reception and processing of the ECU and the braking execution of the commands issued by the ECU. The entire system removes braking master cylinder and wheel cylinder in the conventional hydraulic braking systems, sophisticated pipelines and a variety of valve components required by ABS, resulting in a greatly simplified system.

Referring now toFIG. 7, diagram of the circuit inFIG. 6is shown. The entire circuit system is mainly composed of a master central processing unit (CPU), an auxiliary CPU, a regulator module circuit, a motor-driving module circuit, a magnetostrictive-driving module circuit, a drive module and signal processing module circuit components of check device and a safety protection circuit. If the transmission mechanism is using a screw set, the check device drive module is not needed. If the transmission mechanism is using clutch, the check device drive module needs to be replaced by the clutch control module. The two CPUs of ABS and ECU receive the same input signal of vehicle states, then the results of the processing of the two microprocessors are compared by communication. If the results of the two microprocessors are not consistent, the microprocessor immediately issues a control command to make ABS quit work to prevent system logic errors. The auxiliary CPU receives the signal and processes the signal. The master CPU receives the signal processed by the auxiliary CPU and issues a corresponding instruction to the corresponding drive module circuit. The main function of the drive circuit is to power the output digital signal of CPU amplification and drive the executing components (the motor and magnetostrictive rod in the invention), to achieve the vehicle braking and the adjustment function of “reducing”, “holding” or “increasing” the torques.

Referring now toFIG. 8, simulation block diagram of fuzzy control system used in ABS in automotive braking system is shown. The fuzzy control system is a dual-input single-output module based on the slip ratio, so using the slip ratio error e and rate of change de/dt as the inputs. The fuzzy output u is used as the current adjustment value of the magnetostrictive rod coil in the brake, controlling the slip ratio S of the vehicle to approach the optimal slip ratio. Where the slip ratio error e is the difference between the expected slip ratio S0and the measured slip ratio S, and the rate of change de/dt is the derivative of e.

Referring now toFIG. 9, the control flow chart of the logic threshold method of ABS used in the automotive braking system is shown. When braking, the motor101and the magnetostrictive-driving piston mechanism114work coordinately. The motor101pushes the right and left brake pads119,121to overcome the brake clearance and the corresponding resistance as soon as possible. When the braking torque reaches the preset value, the applied current to the motor101is cut off, and the magnetostrictive-driving piston mechanism114is controlled to realize the ABS function by adjusting the applied current in the coil winding13. No initial current is applied to the coil winding13of the magnetostrictive-driving piston mechanism114. As shown inFIG. 9, at the start stage of ABS braking, the applied current in the coil winding13increases, resulting in increasing braking torque. At the end of the stage {circle around (1)}, the wheel acceleration reaches the preset threshold −a, the applied current remains unchanged so that the wheels are fully braked. When control process enters the stage {circle around (2)}, there is no need to reduce the applied current at this time until the slip ratio is greater than the reference slip ratio threshold S0. Reducing the applied current, the control process enters the stage {circle around (3)}. Since the applied current reduces, the braking torque reduces and the wheel is accelerated by the inertia. The wheel deceleration starts to rise, and when the wheel acceleration is higher than the threshold value −a, the applied current remains unchanged and the control process enters the stage {circle around (4)}. During this, the applied remains unchanged and the wheel continues to accelerate due to the inertia until the acceleration exceeds the threshold a. At the end of stage {circle around (4)}, if the wheel acceleration exceeds the preset upper bound acceleration threshold A (A>a), the applied current increases until the acceleration is below the threshold A and then the applied current remains unchanged. If the wheel acceleration is below the threshold a, it indicates that the wheel is in the stable zone of the adhesion coefficient slip ratio curve at the end of stage {circle around (4)}. Thus, in the stage {circle around (5)}, the applied is continuously switched by increasing or holding until the wheel acceleration is again lower than the threshold value −a. All above is for a complete cycle of ABS when using the BBW in present invention, then it is time for entering the next cycle of ABS.

Referring now toFIG. 10, the control flow chart of braking function of ABS (and/or long-time braking) of the braking system and the system failure in the present invention applied to the automotive braking system is shown. Taking the control failure of the system as an example as shown inFIG. 10. The magnetostrictive-driving module for braking with ABS performance, motor-driving module for braking with ABS performance and motor-driving regular braking with no ABS performance will be potentially functioning with descending priority with consideration of the fail-safe behavior. If the magnetostrictive-driving piston/wedge mechanism fails to work (i.e., If the brake system demands to start ABS, the system starts the initial inspection and the ABS control process. If the failure of the ABS control system is detected), the main control system starts the backup controller to continue commanding ABS. If fails again, the main control system cuts off the magnetostrictive-driving module and its control signal, meanwhile, starts the only motor-driving module, and simultaneously sends the warning signal to the driver. The main system attempts to realize the ABS function using the motor-driving module. If fails, the driver is forced to park for repairing.