Segmentation of tracks and market applications

BBW: How it works

If the brake pedal is only connected to a brake pedal position sensor, and there is no rigid or hydraulic connection between the pedal and the braking system, it can be regarded as a brake-by-wire system.

Brake-by-wire separates the power transfer between the brake pedal and the brake and replaces it with a wire connection; The original brake pedal is replaced by an analog generator, the brake intention of the driver is monitored by the brake pedal position sensor, the brake signal is generated, the brake pedal mechanical signal is converted into an electronic control signal, and the signal is transmitted to the control system and the actuator, the braking force is realized by the electronic control module, and the pedaling feeling is simulated and fed back to the driver according to a certain algorithm; The wire transmits energy, and the data wire transmits the signal, so this kind of braking is called brake-by-wire.

BBW: Faster, lighter, safer

The brake-by-wire system has the advantages of stronger safety, more efficient energy recovery, and indirectly improved fuel/electric energy economy, and has gradually become the standard configuration in the context of vehicle electrification and intelligence.

1) Electronic: The response speed of the brake-by-wire system is much faster than that of traditional hydraulic braking, and the expected pressure build-up time of active braking can be shortened from 400-600ms for conventional braking to less than 200ms (Brembo can do 90ms), and provides ≥0.9g of automatic emergency braking force, reducing the braking distance and significantly improving safety.

2) Integration and lightweight: Through the integration of control, drive, and power assist modules, the brake-by-wire system greatly simplifies the actuator structure (including the hydraulic system), and the iBooster 2.0 version launched by Bosch further reduces the weight by about 10% compared with the 1.0 version, which will further improve the fuel/power economy of the vehicle.

3) Efficient energy recovery: The brake-by-wire system solves the problem of lack of vacuum power source for new energy vehicles, and at the same time decouples the pedal force and braking force, gives priority to the motor feedback braking, and intervenes in friction braking when the braking force is insufficient, which can achieve coordinated recovery, improve energy recovery efficiency, and then improve mileage.

BBW: EHB is the current mainstream, and EMB needs to be verified

According to the different implementation forms of passenger car brake-by-wire, brake-by-wire can be divided into electro-hydraulic braking (EHB) system and electromechanical braking (EMB) system. At present, the mainstream technical solution of brake-by-wire system is EHB, which replaces the function of some mechanical components with electronic components, but still retains brake fluid as the power transmission medium, and has a hydraulic backup braking system.

The mechanical brake-by-wire system (EMB) is closer to a true full drive-by-wire, generating the required braking force through four wheel end motors, and controlling the motor to achieve stability functions such as ABS, but the reliability of mass production needs to be verified.

Due to the need to consider safety redundancy issues in the brake-by-wire system, the current application scheme presents Two Box decoupling solution, One Box + electronic redundancy scheme and EMB + multi-redundancy scheme coexist.

At present, the mainstream technical scheme of brake-by-wire is still EHB, of which Two The box solution has a high degree of technical maturity, One With the cost advantage, the assembly rate of the BOX solution is gradually increasing. The EMB solution is completely controlled-by-wire and is currently the best product for brake-by-wire. However, at this stage, there are still problems such as safety redundancy and cost in EMB technology, and it is predicted that mass production is expected to be achieved in the industry in 2026~2027.

Brake-by-wire: Gaining the approval of OEMs and building an independent and controllable supply chain are the core challenges

1) Algorithm barriers: BBW involves complex algorithms for braking, body stability and other functions, and the product must be iterated step by step. The technical difficulties of the ESC system include the accumulation of complex algorithms to realize the functions of anti-lock braking system (ABS), electronic brake-force distribution (EBD), traction control system (TCS), vehicle dynamic control system (VDC) and the performance and stability of MEMS sensor elements. Taking the TCS function as an example, when the slip rate is controlled within a certain range, it is necessary to ensure that the wheels have good longitudinal and lateral adhesion coefficients to the road surface, so as to provide the best driving force for the vehicle. From ESC to One-box, a large number of software algorithms need to be upgraded.

2) Engineering barriers: EHB requires precise hydraulic braking force control. The quality of the pressure control effect directly affects the final control quality of the system, which needs to rely on advanced algorithms. At the same time, when determining the key influencing parameters according to the hardware characteristics of the product, a large amount of calibration engineering needs to be completed.

3) Safety barriers: For example, redundant design, especially in order to meet the needs of high-level autonomous driving, requires that the braking system must form a multi-level safety redundancy system with a main line control system, backup system, EPB and other drive-by-wire systems, with a deceleration of > 0.25g.

Steer-by-wire: the core component of high-end intelligent driving

Steer-by-wire is a key technology for high-level autonomous driving. The steering system of automobiles has gone through several stages of development, from the most primitive purely mechanical transmission steering, to the first hydraulic power steering of General Motors, the electro-hydraulic power steering and electric power steering (EPS) launched by Toyota, and then gradually developed to the current steer-by-wire system (SBW).

Among them, the EPS takes the angle applied by the driver as the input signal, which is recorded by the torque sensor and transmitted to the electronic control unit, and then calculates the required steering power to control the servo motor to work, and its turn signal is still essentially derived from the driver. The steer-by-wire system gets rid of the structural limitations of the traditional steering mechanism, and its angle transmission characteristics and force transmission characteristics are realized through the electric energy of the fly-by-wire mechanism, and the intelligent vehicle steering is realized through the control algorithm.

The electronic power steering (EPS) system has a high degree of technical maturity and is the standard configuration of most passenger cars at present, which can meet the intelligent driving functions below L3 level. The steer-by-wire (SBW) system eliminates the steering column gimbal and realizes the pure drive-by-wire of the system. It has significant advantages in response speed and accuracy, and is the core component for high-level intelligent driving at L3 level and above.

Steer-by-wire: more integrated, more efficient and safer

The advantages of steer-by-wire systems stem from the complete physical decoupling of the steering wheel and steering machine:

1) Space-saving and lightweight: The elimination of the steering column can reduce the weight of the system, and at the same time provide more design space for OEMs, which is convenient for the deployment of other subsystems of autonomous driving, including perception system, power system, etc.

2) Optimized driving experience: After the restriction of mechanical connection is removed, the steering wheel layout control and vehicle steering command design are more flexible, and the steering ratio changes with speed, which can achieve a stable steering experience at high speed and light steering at low speed. At the same time, the road surface information will be fully realized through software simulation, and the driver can independently choose the road sense feedback level to achieve a personalized road sense experience.

3) Improve safety: steer-by-wire actually decouples the driver's operation from the vehicle's driving, which can improve the correctness of the steering operation in an emergency, and the cancellation of the steering axle completely avoids the possible injury to the driver during the collision; 4) Strengthen system integration: The motor control is used to directly drive the vehicle to steer, which can facilitate its communication and integrated control with other active safety control subsystems of the vehicle, and provides a good hardware foundation for the autonomous steering of autonomous vehicles.

Steer-by-wire: There has been a breakthrough in research and development, but mass production will take time

Electronic Power Steering (EPS): The adoption rate of passenger cars has exceeded 98%, and remains at a high level.

Steer-by-wire (SBW): It is currently only available on a few production models, such as the Infiniti Q50L/QX50/Q60, Tesla Cybertruck (which is scheduled to be used in the new Model S/X model in 2024Q2), the NIO ET9, and the Lexus RZ.

With the further improvement of steer-by-wire technology, the assembly rate of steer-by-wire in smart cars will undoubtedly increase rapidly, on the one hand, based on the advantages of steer-by-wire technology itself in terms of safety and driving experience, and on the other hand, it is based on consumers' more differentiated needs for autonomous driving functions and configurations of new car companies.

Intelligent suspension: improve ride comfort and operating stability

The controllable suspension system is the most easily perceivable actuator in the intelligent chassis system, which can give users a better driving experience in different road conditions and driving situations:

1) When the vehicle is driving on a flat road, the dynamic stroke of the controllable suspension is small, and the stiffness generated by the instantaneous pressure of the elastic medium is also small, which strengthens the driving stability.

2) When the vehicle is driving on undulating roads, the elastic force of the controllable suspension shows a nonlinear change and the amplitude increases, absorbing more impact energy, effectively playing a buffering role, avoiding the direct transmission of energy to the body, and improving the vehicle's mobility and riding comfort.

3) When using air springs, air is used as the medium, and the internal friction is small, which gives the suspension low noise performance.

4) Lateral support is provided in the corner, which significantly reduces the roll angle.

Intelligent suspension: comparison of three suspension features

The suspension system can be divided into passive suspension and active suspension system according to its stiffness and adjustability of damping, and the industry is currently in the stage of transformation from passive suspension to active suspension. Depending on whether or not it relies on an external power source, the active suspension is further subdivided into semi-active suspension and fully active suspension.

Intelligent suspension: At present, semi-active suspension is the mainstay, and active air suspension is an important direction

At present, most of the new energy models are mainly equipped with "semi-active suspension system", and the most common is the electronic control suspension system. The price of domestic assembled models is between 20-450,000 yuan, which basically covers the relatively mainstream price band, especially has basically become a common configuration of 20-300,000 yuan independent new energy models.

The active air suspension system will be an important direction for the intelligent upgrading of the automobile chassis in the future. The air suspension system is based on the electronically controlled shock absorber, and further uses air pumps and air springs to replace the traditional coil springs. At present, most of the models equipped with active air suspension systems are high-end models with more than 400,000 yuan.

Chassis domain control: The centralized electronic and electrical architecture drives the demand for domain controllers

In the context of the gradual development of vehicle intelligent driving functions as the industry standard, the centralized electronic and electrical architecture continues to develop, evolve and gradually become the mainstream, and the domain controller that bears the heavy responsibility of software and hardware decoupling has also come into being, becoming a bridge from distributed architecture to integrated automotive electronic and electrical architecture.

Chassis domain control: shorter cycle, lower cost, better effect

In addition to supporting high-level autonomous driving functions and strengthening system safety, as the "brain" of the architecture, the domain controller can also bring many advantages such as reducing vehicle manufacturing costs and shortening the development cycle.

1. Reduce manufacturing costs: The domain controller reduces the number of ECUs under the original distributed architecture of the car to several DCUs in the centralized architecture, which is more conducive to reducing the cost of car manufacturers. If chassis components including steering and braking, power and body parts control are integrated into the same domain controller, the number of microprocessor chips, power chips, and memory chips will be reduced from multiple to one, and the number of communication chips will also be reduced by half. As a result, the cost can be reduced by nearly 30% when the security performance, control accuracy, sampling accuracy and response level of the controller hardware are improved.

2. Shorten the development cycle: In the past, chassis control related technologies have been owned by international manufacturers, and all ECUs related to chassis-related shock absorbers, air suspensions, EPBs and other parts need to be customized and tuned from the corresponding partners, and it generally takes 8 months to meet the rapid FOTA needs. With the use of domain controllers, the time for FOTA can be significantly shortened to 1.5 months, and the algorithm development cycle for chassis functions can also be shortened by about 50% because of the reduced communication required for coordination between various parts.

Chassis domain control: cross-domain integration is the direction of development

The cross-domain integration of the intelligent chassis is currently in the 2.0 stage, and the integration of the chassis domain and the intelligent driving domain provides support for the implementation of the intelligent driving function at the L3 level and above. Under the premise of the evolution of automotive EE architecture from distributed to centralized, with the maturity of technology and further breakthroughs in chip computing power, the progress of cross-domain integration between the chassis domain and the cockpit domain will be accelerated, and the integration of five domains will be realized.

At present, some OEMs, such as Wei Xiaoli and GAC Aion, have made rapid progress in central computing, adopting the architecture of "central computing + regional control", integrating functions such as intelligent driving and intelligent cabin. However, due to the strict requirements for functional safety of chassis domain control, it is more difficult than "cabin-driver integration", and it still takes time to realize the central computing architecture of five-domain integration.