1.1 Summary

Thispaper is dedicated to the design of an actuator for an electromechanical brake(EMB) system for electric vehicles.

1.2 Research significance

In 2018,global electric vehicle sales exceeded 2 million mark, reaching 2.018 millionunits, while the electric vehicle sales in China accounted for more than halfof global sales. On October 18, 2018, the "World Intelligent NetworkingAuto Conference" was held in Beijing, and automotive intelligenttechnology is gradually being widely used. Intelligent technology makes the careasier to operate and safer to drive. The hottest future application ofintelligent technology is driverless technology. For driverless technology,driving safety has always been the focus of attention.

Atpresent, modern vehicles mainly adopt hydraulic brake systems, which are mainlycomposed of pedals, hydraulic lines, disc or drum brakes, brake mastercylinders, vacuum boosters, brake wheel cylinders and so on. When the vehicleneeds to brake, the driver presses the brake pedal, with the help of the vacuumbooster, through a series of mechanical transmissions, the oil in the brakemaster cylinder flows into the wheel cylinder through the brake pipe, andfinally drives the disc or drum brakes to achieve braking. Nowadays, thehydraulic brake of the car has developed into a very mature and reliabletechnology. Modern vehicles basically use hydraulic brake systems. However,there are some problems that are difficult to solve in the hydraulic brakesystem: there are many mechanical parts and hydraulic lines; the vacuum boosteris bulky; especially after integrating the electronic control functions such asABS, TCS, ESP, etc. the whole brake system is more bulky and complex; brakehydraulic oil needs to be replaced regularly; for electric vehicles that lack abooster vacuum device and have a brake energy recovery system, the hydraulicbrake system is difficult to match and its use is limited.

Comparedto conventional hydraulic brake systems, EMB removes hydraulic lines, brakecylinders, vacuum boosters, hydraulic pumps and other parts. Easy to integratewith active safety control functions such as ABS, TCS, EBD and ESP withoutadding additional components. Coordination with other wire control systems canalso be achieved via the in-vehicle communication network, facilitating chassisintegration control and intelligent driving assistance functions. It is thedevelopment direction of automobile modularization, integration andmechatronics. At present, there is no relatively complete, reliable, andmass-produced EMB, so it is significant to conduct research on EMB.

1.3 Status of foreign research

Since the late 1990s, the world's leading manufacturers ofautomotive electronic components, such as Continental.Teves, Bosch, Siemens.VDO; American TRW, Delphi, Australia's PBR, Sweden's SKF, Haldex, and Mando(South Korea), have researched EMB and developed their own EMB actuators. Thedesign schemes of the above EMB actuators of the company include the two partsof the deceleration and torque-increasing mechanism and the motion conversiondevice. The difference is mainly the specific structural scheme and functionrealization principle of the two parts.

Some automakershave also begun to study the EMB system. Since the EMB system eliminated themechanical and hydraulic connection between the brake pedal and the brakes.That did not meet the requirements of the existing legal regulations. So, therelated technology was applied to the concept cars. The Novanta concept carjointly developed by SKF and the famous Italian car design company Bertone,GM's world's first driving line fuel cell vehicle Hy-wire, Nissan developedbased on the first generation Murano sports and leisure wagon EA2 concept car,the concept car FILO exhibited by Bertone in Italy at the 71st GenevaInternational Automobile Exhibition, the BMW Z22 concept car exhibited by BMWat the 2000 Paris Motor Show, the Hy-light concept car launched by Michelin in2007, Nissan The concept cars "Pivo" and "Pivo2" exhibitedat the 39th/40th Tokyo Motor Show and the "C5" prototypes released bythe French Citroen 2008 have all applied EMB technology.

The EMBsystem has also attracted the attention of government departments. 13 unitsincluding DaimlerChrysler AG, Continental AG, and Budapest University, with thesupport of the European Union, set up a PEIT project team to study theapplication of EMB technology in heavy-duty vehicles and trailers, and carriedout bench tests and actual vehicle tests. In addition, major projects with EMBas research objects include the SPARC (Secure Propulsion with AdvancedRedundant Control) project and the "X-BY-WIRE" project. SPARC membersinclude 18 units such as DaimlerChrysler AG, e-Stop, and Siemens-VDO; membersof the “X-BY-WIRE” include 9 units including BOSCH, University of Chalmers,Volvo, Fiat, and Ford.