電動扭力梁（eTB）－緊湊型電驅動解決方案

Christoph Elbers博士 Shinya Kamo 朱治國

1 簡介

在該項目中，小型乘用車被挑選作為研究對象。由于在該車型區(qū)間中，前麥弗遜后扭力梁結構形式占據了最大市場份額（＞80%），它們?yōu)榧呻婒屜到y(tǒng)提供了最好的應用環(huán)境，并且無需對車輛結構作過多改動。

對于麥弗遜懸架的安裝空間（考慮車輪行程和轉向角度），若要集成一套電驅系統(tǒng)，會遇到較大問題，這些問題只能通過重新布置運動學硬點（如橡膠襯套和球鉸鏈）來解決。除了在底盤設計方面需要做出的妥協外，作用在車輪上的驅動力矩對轉向性能的影響（“扭力轉向作用”）也是一個限制因素?；谶@些主要考慮，我們開發(fā)出了“電動扭力梁”（eTB）車橋（圖1）。

1）采埃孚，德國Dielingen

2）采埃孚，日本

3）采埃孚（中國）投資有限公司，上海

2 技術方案描述

該系統(tǒng)展示了如何在傳統(tǒng)車橋的安裝空間內，在靠近扭力梁兩側車輪的位置集成兩個電驅單元（圖2）。兩個驅動單元的總峰值功率為80kW，連續(xù)狀態(tài)輸出功率為35kW，能夠提供總共為1440 Nm的驅動扭矩。

圖1 電動扭力梁（eTB）Fig.1 Electric Twist Beam （eTB）

1 Introduction

In this project，small passenger cars were chosen as the target vehicle segment.Since strut front axles and twistbeam rear axles have the largest market share in this vehicle segment（＞80%），they provide the best conditions to integrate an electric drive with a limited number of required modifications regarding the vehicle architectures.

With a view to the installation space of a strut axle （considering wheel travel and steering angles），the integration of an electric drive poses significant problems that can only be avoided by relo－

圖2 電動扭力梁安裝空間Fig.2 Installation space of the Electric Twist Beam

每個驅動單元包含一個驅動電機和一套變速傳動系統(tǒng)，它們被完全集成在扭力梁的縱向擺臂中。這樣一來，這些底盤零部件和驅動單元殼體可以集成為一個單獨完整的零件。通過這樣的功能集成，驅動單元零部件將不再與車身直接相連。而且，這種設計可以省去其它零部件如兩根傳動半軸和副車架。所有上面提到的設計特征，與車橋系統(tǒng)加驅動單元（與車身連接）的傳統(tǒng)設計方案相比，極大的減小了整個系統(tǒng)重量（圖3）。

由于非簧載質量對底盤集成式驅動方案性能有較大影響，因此，通過選擇大一些的傳動比，以保證盡可能小的電機重量（稱為“高速方案”）。由此帶來的另一個好處是：由于電機尺寸減小，可以較容易的實現驅動單元與車橋的集成。

圖3 系統(tǒng)重量（相比于與車身連接的驅動系統(tǒng)）Fig.3 System weight compared to a body mounted drive

車橋系統(tǒng)與車身通過兩個橡膠襯套連接，并且作為車輪上跳和下行運動的旋轉中心。為了進一步減小對非簧載質量的影響，驅動電機被布置在車輪中心和橡膠襯套連接點中間－通過傳動電機軸和變速傳動裝置輸出軸的偏移來實現（圖4）。通過將驅動電機布置的更靠近旋轉中心點，可以減少其在車輪上跳和下行時的運動，從而實現較小的非簧載質量（與布置于車輪中心的驅動電機相比）。cation of kinematics points（represented by rubber bushings and ball joints）.In addition to this compromise in chassis design，the impact of wheel－individual drive torques on the steering behavior （socalled“”torque steer effect”）is a further restriction.Based on these findings and fundamental considerations，the Electric Twist Beam has been developed（Fig.1）.

1）ZF Friedrichshafen AG，Dielingen，Germany

2）ZF Japan Co.，Ltd.

3）ZF（China）Investment Co.，Ltd.，Shanghai，China

2 Description of Concept

This system demonstrates how to integrate two electric drive units adjacent to the wheels of a twistbeam axle without leaving the installation space of a conventional axle （Fig.2）.The total power of both drive units is 80kW in peak conditions and 35kW in continuous conditions.In total，the two units provide a wheel－related drive torque of 1440Nm.

圖4 通過布置電機的位置以減小非簧載質量Fig.4 Reduction of unsprung mass by positioning of the motor

Each drive unit consists of an electric motor and a transmission whereas the drives are fully integrated into the trailing arms of the twistbeam.In such a way，these chassis components and the drive housings are merged to one integral part.Resulting from this functional integration，there are no body mounted drive components.Further，other components like both half－shafts and a subframe can be omitted.All of these aforementioned design features lead to a significant lower system weight compared to a system，in which a body－mounted drive is combined with a conventional axle system （Fig.3）.

Because the unsprung mass represents an important aspect of chassis integrated drives，the gear ratio was intentionally chosen high to keep the mass of the motor as low as possible （so－called “highspeed concept”）.Another advantage is given by the fact that the motor size decreases，which simplifies the integration into the axle.

Two rubber bushings establish the kinematic coupling of the axle to the vehicle body and are the pivot points of the wheel’s motion during jounce and rebound.To further reduce the influence on the unsprung mass，the motors were installed between the wheel center and these rubber bushingsachieved by an axial offset between motor shaft and gearbox output shaft（Fig.4）.A relocation of the motors closer to these points results in a reduction of the motor motion during jounce and rebound，which，in turn，leads to a smaller unsprung mass（compared to a motor placed in the wheel center）.

As mentioned before，central components of the system are the two trailing arms.Here，powertrain and chassis merge，as these arms are suspension part and drive housing at the same time.Although this leads to a reduced number of parts，it increases the requirements on these components due to higher complexity.For example，the trailing arms transmit forces between wheel and car body.These forces may lead to deformation of the housing，which could，in turn，result in tilting of the gears to each other.Therefore，specific stiffness requirements for all relevant regions of the housing must be fulfilled in order to guarantee an unaffected performance of the gearbox with respect to e.g.acoustics or durability.

如前所述，該系統(tǒng)的主要部件是兩根縱向擺臂。通過對傳動系統(tǒng)和底盤部件的整合，兩根擺臂既作為懸架零部件，同時又作為驅動單元的殼體。雖然這樣做可以減少零部件的數量，但同時由于復雜性增加，對相應零件的要求也有所提高。例如，縱向擺臂傳遞車輪和車身之間的力，這些力可能會引起殼體的變形，從而使齒輪之間相互產生傾斜。因此，必須使殼體的所有相關區(qū)域滿足特定的剛度要求，以保證傳動系統(tǒng)的性能不會受到影響，如聲學性能或耐久性能。

對于安裝空間，一個主要的目標是使系統(tǒng)能夠與目標車型區(qū)間的典型車身設計實現較為簡便的集成（圖2）。例如，我們所展示的概念方案允許該系統(tǒng)在較為典型的位置（針對傳統(tǒng)的扭力梁車橋）與車身實現連接（通過彈簧，減震器，橡膠襯套）。而且，也充分考慮了驅動電機與車身周邊部件之間所需的間隙，以滿足足夠的車輪行程要求。

由于驅動單元也可以產生制動扭矩，所以，從技術角度出發(fā)，是否需要一套額外的機械制動系統(tǒng)主要取決于電機可以提供的功率。此外，能否省去摩擦式制動系統(tǒng)還取決于法規(guī)限制。在這點上，特定的使用環(huán)境將起到最終的決定作用。因此，從提高系統(tǒng)模塊化考慮出發(fā)，傳統(tǒng)的鼓式制動器（仍然是目標車型區(qū)間所使用的技術）進入我們的選擇范圍－正如我們在電動扭力梁（eTB）樣件上所展示的。

與制動系統(tǒng)相似，輪輞也是一種常規(guī)零件。因此，更換車輪（比如當車輪受損，更換冬季輪胎，或車輛改裝等）將和傳統(tǒng)車輛一樣方便 －與大多數車輪集成電機式電驅車概念相比，這具有明顯優(yōu)勢。而且，電動扭力梁（eTB）車橋可以使用小到14″的輪輞，對于減小非簧載質量，這也是一個優(yōu)勢。

3 結論

我們開發(fā)并測試了一種適用于小型乘用車的底盤集成式驅動系統(tǒng)－電動扭力梁（eTB）。在開發(fā)過程中，至關重要的一點是需要同時考慮驅動系統(tǒng)和底盤性能要求，以找到一種可以滿足所有必要功能的設計概念。該設計的主要優(yōu)點可以歸納如下：

重量輕：通過功能集成和高速驅動概念，極大的減小了系統(tǒng)總重量。

所需安裝空間?。河捎谡麄€驅動單元完全集成于底盤，車身部分可以得到較充裕的空間，在設計車輛結構時所受的限制也較小。

非簧載質量小：與車輪集成式驅動電機概念相比，通過重新布置電機的位置和使用高速驅動概念，非簧載質量得到極大的減小。

With a view to the installation space，a major objective was to allow easy system integration in typical body designs of the target vehicle segment（Fig.2）.For example，the presented concept permits body－mounting points of the system （spring，damper，rubber bearings）at typical locations（as known from conventional twistbeam axles）.Moreover，it has been considered，that the clearance between the motors and the side members of the body allows sufficient wheel travel.

Since the drive units can generate braking torques as well，the technical necessity for an additional mechanical brake system essentially depends on the provided motor power.In addition，legal constraints are another challenge to be overcome in order to omit the friction brake.Finally，the specific circumstances are deciding at this point.Hence，for the benefit of an increased modularity of the system，the integration of a conventional drum brake（still state of the art in the target vehicle segment）was taken into account－just as shown in the prototypes of the Electric Twist Beam.

As the brakes，the rims are conventional parts as well.Hence，wheel change （e.g.in case of damage，need of winter tires or because of aesthetic reasons）is still as simple as known from conventional vehicles－an essential advantage compared to most in－wheel motor concepts.Further，rims with a size starting at 14”can be used，which is another advantage with respect to the unsprung mass.

3 Conclusions

With the Electric Twist Beam，a chassis integrated drive system for small vehicles has been developed and tested.During this development，it was essential to consider both aspects regarding driveline and chassis，to find a concept which fulfills all necessary functions.The fundamental advantages of the resulting system can be summarized by the following points：

相互獨立的車輪驅動扭矩：由于對每個車輪的驅動扭矩可以單獨控制（稱為“矢量扭矩”），車輛的靈敏性和駕駛安全性得到明顯提高。此外，相比較于摩擦式制動器，電機具有更加快速的響應，以及更高的穩(wěn)態(tài)控制精度，這些都對車輪滑移控制提供了提升空間。

車輛集成簡便：由于在開發(fā)過程中已經充分考慮到了傳統(tǒng)車身的設計，并且與車身的安裝點也保持在比較典型的位置，所以電動扭力梁（eTB）車橋可以方便的與目標車型區(qū)間的傳統(tǒng)車輛實現集成。

Low system weight：Achieved by functional integration and the high－speed drive concept，the system weight can be significant reduced.

Reduced installation space：Because the drive units are fully integrated in the chassis，additional space at the body－side is available and the vehicle architecture can be designed with fewer restraints.

Low unsprung mass：Compared to known inwheel motor concepts，the unsprung mass is signif－icantly reduced by the advantageous positioning of the motor and the high－speed drive concept.

Wheel－individual drive torques：Because drive torques of each traction wheel can be controlled individually （so－called “torque vectoring”），agility and driving safety are clearly improved.In addition，electric motors provide a faster response characteristic and a better steady－state control accuracy compared to friction brakes，which gives potential to improve wheel slip control.

Simple vehicle integration：As conventional body designs were considered during the development and body－mounting points were kept at typical positions，the Electric Twist Beam can easily be integrated into conventional vehicles of the target segment.