雖然在汽車工程師眼中，電動(dòng)車輪制動(dòng)系統(tǒng)(electric wheel-braking system)擁有巨大的潛力，但目前尚無任何量產(chǎn)車型搭配了此類系統(tǒng)。雖然該系統(tǒng)本身就可以提高制動(dòng)的精確度，但更重要的是,線傳操控制動(dòng)(brake-by-wire)系統(tǒng)不但有助于應(yīng)對政府日趨嚴(yán)苛的強(qiáng)制性節(jié)能減排規(guī)定，而且還能更加輕松地整合到半自動(dòng)和自動(dòng)駕駛汽車之中。
頂級意大利制動(dòng)系統(tǒng)供應(yīng)商布雷博(Brembo)在北美國際車展（簡稱NAIAS展）就發(fā)布了這樣一款已經(jīng)與眾多汽車生產(chǎn)商見過面的線傳操控制動(dòng)系統(tǒng)。布雷博對電動(dòng)基礎(chǔ)制動(dòng)的研究已經(jīng)進(jìn)行了大約15年，而且正如公司首席技術(shù)官Georgio Ascanelli告訴《汽車工程雜志》(Automotive Engineering)的那樣，這項(xiàng)技術(shù)未來仍擁有相當(dāng)大的進(jìn)步空間。
Ascanelli指出，到目前為止，其他現(xiàn)有的電動(dòng)制動(dòng)系統(tǒng)都存在一定程度的不耐用或不可靠問題。為了應(yīng)對這一問題，布雷博的設(shè)計(jì)采用了一個(gè)中央電子控制單元（簡稱ECU），及四個(gè)分布在角落的獨(dú)立制動(dòng)單元。
“我們的系統(tǒng)可以在另外四個(gè)獨(dú)立單元中任何一個(gè)出現(xiàn)故障時(shí)繼續(xù)工作。”他表示，這個(gè)系統(tǒng)甚至可以在多個(gè)部件同時(shí)出現(xiàn)故障的情況下正常工作。公司還將為電動(dòng)制動(dòng)系統(tǒng)配備了獨(dú)立的供電系統(tǒng)。只要系統(tǒng)的所有故障模態(tài)分析結(jié)果對安全相關(guān)系統(tǒng)而言均屬正常，電動(dòng)制動(dòng)系統(tǒng)甚至可以提供自動(dòng)駕駛級別的置信水平。
Ascanelli表示，布雷博在一輛跑車上安裝了自己的線傳操控系統(tǒng)，并對其進(jìn)行測試，目前已經(jīng)累計(jì)了超過50萬公里的安全行駛里程。公司還在打造一款展示車，從而提供更多可以說服廠商的證據(jù)。他表示，從技術(shù)層面而言，這種系統(tǒng)可在2020年前做好量產(chǎn)準(zhǔn)備，但的確仍有部分廠商認(rèn)為此類創(chuàng)新具有很高的風(fēng)險(xiǎn)。
傳感器剎車踏板
系統(tǒng)的“剎車踏板”為一款彈簧加載機(jī)電傳感器（未來有再設(shè)計(jì)或精簡的潛力），可向ECU單元發(fā)送成比例的信號。該模塊可以確認(rèn)電池系統(tǒng)的電荷狀態(tài)，并操作電機(jī)/泵向6活塞前制動(dòng)卡鉗輸送液壓信號。這不就是一個(gè)電動(dòng)液壓系統(tǒng)嗎？對于較大車型來說，的確是這樣。采用這種設(shè)計(jì)，是因?yàn)楝F(xiàn)有的分火頭和卡鉗無法提供純電動(dòng)系統(tǒng)所需的輪間空間。
Ascanelli解釋說，布雷博的全電動(dòng)系統(tǒng)采用了基本架構(gòu)，適用于雷諾(Renault)的Twingo等小型車。未來隨著產(chǎn)品的設(shè)計(jì)發(fā)展和持續(xù)優(yōu)化，全電動(dòng)制動(dòng)系統(tǒng)也有望現(xiàn)身于一些較大車型。
目前，布雷博線傳操控制動(dòng)系統(tǒng)的響應(yīng)時(shí)間僅為90ms，而搭配助力器和防死鎖促動(dòng)器的傳統(tǒng)液壓制動(dòng)系統(tǒng)則需300ms。他指出，該制動(dòng)系統(tǒng)的響應(yīng)速度更快，可以為基本的碰撞減緩系統(tǒng)(collision-mitigation system)和更高要求的自動(dòng)駕駛系統(tǒng)(autonomous driving system)提供更加優(yōu)化的自動(dòng)制動(dòng)支持。
車輛的后方制動(dòng)系統(tǒng)采用了一臺電機(jī)和一臺變速箱，屬于純機(jī)電系統(tǒng)，本身也可以發(fā)揮停車制動(dòng)的功能。
可伸縮活塞
雖然系統(tǒng)的前方制動(dòng)系統(tǒng)的確采用了液壓設(shè)計(jì)，但由于其電路完全受到電機(jī)和ECU單元的控制，系統(tǒng)的純電氣操作保證了前后活塞可以進(jìn)行快速自由伸縮。Ascanelli表示，活塞進(jìn)行伸縮的最小間隙為0.2毫米，完全可以消除分火頭摩擦面上的阻力，在城市工況下可將汽油發(fā)動(dòng)機(jī)的燃油經(jīng)濟(jì)性提高10%。
此外，電動(dòng)制動(dòng)系統(tǒng)的精準(zhǔn)控制還允許電動(dòng)車或混動(dòng)車進(jìn)行精確校準(zhǔn)，提高制動(dòng)動(dòng)能的回收效率，從而提升車輛燃油經(jīng)濟(jì)性。他補(bǔ)充說，減少阻力和優(yōu)化制動(dòng)動(dòng)能回收都能降低二氧化碳的排放。
電動(dòng)制動(dòng)系統(tǒng)雖然增加了一些零部件，卻省去了傳統(tǒng)制動(dòng)系統(tǒng)中必不可少的制動(dòng)助力器和防死鎖促動(dòng)器。Ascanelli表示，因此，相信電動(dòng)制動(dòng)系統(tǒng)的總重量將低于傳統(tǒng)制動(dòng)系統(tǒng)。他承認(rèn)，在最初階段，電動(dòng)制動(dòng)系統(tǒng)必須與傳統(tǒng)制動(dòng)系統(tǒng)打價(jià)格戰(zhàn)，即使這種系統(tǒng)本身的成本更高。
不過，他認(rèn)為供應(yīng)商可以通過提高產(chǎn)量，并積極利用市場反饋修正新設(shè)計(jì)（特別是與安全有關(guān)的新設(shè)計(jì)）中經(jīng)常出現(xiàn)的過度設(shè)計(jì)問題，最終“取得一個(gè)市場可接受的價(jià)格”。
作者：Paul Weissler
來源：SAE 《汽車工程雜志》
翻譯：SAE 上海辦公室
Brembo brake-by-wire will be production-ready before 2020
The potential market for an electric wheel-braking system is apparent to automotive engineers, but none is now in vehicle production. Such a system adds a level of precision to braking itself, but even more important, brake-by-wire fits into the engineering picture to meet the low-emissions/higher fuel economy mandates in government regulation. And it could be easier to integrate into semi-autonomous and autonomous operation.
Premium braking system supplier Brembo, in a display at NAIAS, featured a system it already has shown to many car makers. Electric foundation braking has been in development at Brembo for some 15 years, and as Chief Technical Officer Georgio Ascanelli told Automotive Engineering, it has potential for considerable further development.
Other electric braking systems developed to date have posed durability/reliability questions, Ascanelli noted. For contrast, he pointed to the Brembo design's use of one central ECU and four corner modules.
"It could operate with a failure of the other four," he said, so there is coverage for even simultaneous multiple failures. Some separation of the battery supply system also would be needed to fit into this picture. With all the failure mode analysis normal for safety-related systems, there should be an overall confidence level even for autonomous driving.
The Brembo test system has accumulated over 500,000 km (300,000 mi) of safe operation on a sports car, Ascanelli said, and the company is completing a demonstrator to provide further evidence to vehicle OEMs. Technically, he expects the system to be ready for use well before 2020, while admitting that some OEMs consider such innovations to be risky.
Brake pedal just a sensor
The system begins at the "brake pedal," in this case a spring-loaded electro-mechanical sensor (with potential for redesign/downsizing) that produces a proportional signal to the ECU. This module both confirms battery system state of charge and operates a pump/motor assembly to produce a hydraulic output to the front caliper, a six-piston unit. Doesn't this make it an electro-hydraulic system? For larger cars, yes, because the design of the present rotor and caliper do not provide the wheel space needed for a purely electrical system.
Using the basic architecture, an all-electric system could be produced for small cars, such as the Renault Twingo, Ascanelli explained. And with product redesign and continuous improvement, the potential of all-electric foundation brakes for larger models can be anticipated.
At its present state, the system response time is just 90 ms, vs. 300 ms on a conventional all-hydraulic braking system with booster and anti-lock braking actuator. The fast response time means the system can provide auto-braking improvements for both basic collision-mitigation systems and the more demanding requirements of autonomous driving, he noted.
Because the rear system is "dry" (i.e., fully electro-mechanical), using a motor and gearbox, it lends itself also to serving as the parking brake.
Pistons positively retracted
Although the system does use hydraulics for the front brakes, the overall electrical operation permits quickly and positively retracting pistons front and rear because the circuits are being controlled with motors and an ECU. The retracted piston clearance, 0.2 mm (.001-in) or more totally eliminates piston drag on the rotor friction surfaces, Ascanelli said, which he claims accounts for about 10% of fuel consumption in city operation with a gasoline engine.
The precise control of an electric braking system also permits calibration to improve the efficiency of regenerative braking on electric vehicles and hybrids, so it boosts fuel economy for these cars. Those two factors—no drag and improved regen braking—therefore lower carbon dioxide emissions, he added.
An electric braking system does add components, but in addition to a simpler parking brake it eliminates the brake booster and anti-lock brake actuator. So Ascanelli said he believes the overall system can be lighter than a conventional one. The initial selling price to OEMs would have to be competitive with the conventional systems in use, he admitted, even if it costs suppliers more.
However, he believes suppliers can "get to a comparable price" by increasing volume and using feedback from the market to correct the natural over-engineering that is typical of a new design, particularly one so safety-related.
Author: Paul Weissler
Source: SAE Automotive Engineering Magazine
布雷博的線傳操控制動(dòng)系統(tǒng)包括機(jī)電踏板傳感器（中上）和內(nèi)置電機(jī)/泵送系統(tǒng)的ECU單元（中下），其中電機(jī)/泵總成也會(huì)向6活塞前制動(dòng)卡鉗輸送液壓信號。
踏板傳感器可以將司機(jī)腳下的制動(dòng)信號傳送給ECU單元。
ECU總成可以與壓力傳感器協(xié)同工作，確認(rèn)電池系統(tǒng)的電荷狀態(tài)，并操作電機(jī)和泵送系統(tǒng)，向6活塞前制動(dòng)卡鉗輸送液壓信號。
布雷博的后方制動(dòng)系統(tǒng)為純電動(dòng)設(shè)計(jì)，其電機(jī)可通過變速箱促動(dòng)浮動(dòng)制動(dòng)卡鉗。該制動(dòng)系統(tǒng)也能作為停車制動(dòng)設(shè)備使用。 
系統(tǒng)的前制動(dòng)卡鉗擁有6個(gè)活塞，可為大型車輛提供充足的制動(dòng)力。此外，系統(tǒng)的制動(dòng)襯面還配備有磨損傳感器。