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資 料 及 譯 文
譯文題目： A magnetorheological clutch for efficient
automotive auxiliary device actuation
磁流變離合器的高效汽車輔助設(shè)備驅(qū)動(dòng)
學(xué)生姓名： 學(xué) 號(hào)：
專 業(yè)：
所在學(xué)院：
指導(dǎo)教師：
職 稱：
20xx年 02 月 25 日
英語(yǔ)原文
A magnetorheological clutch for efficient automotive auxiliary device actuation
ABSTRACT .
In this paper the results of a project funded by Regione Toscana aimed at reducing the power absorption of auxiliary devices in vehicles are presented. In particular the design, testing and application of a magnetorheological clutch (MR) is proposed, aimed at disengaging the vacuum pump, which draws in air from the power-brake booster chamber, in order to reduce the device power absorption.
Several clutch preliminary studies done to choose the clutch geometry and the magnetic field supply are illustrated. The final choice consisted in an MR clutch with permanent magnet, which satisfied size, torque and fail-safe specifications. The clutch characteristics, in terms of torque versus slip, were obtained experimentally for three different clutch prototypes on an ad-hoc developed test bench.
As result of a preliminary simulation, a comparison between the power absorption of a current production vacuum pump, an innovative vacuum pump and both vacuum pumps coupled with the MR clutch is presented. The New European Driving Cycle is considered for simulating the vacuum pump operation both in urban and highway driving. Results show that the use of the innovative vacuum pump reduces the device consumption of about 35%, whereas the use of MR clutch coupled with the innovative vacuum pump reduces it up to about 44% in urban driving and 50% in highway driving.
KEYWORDS. Magnetorheological fluid; Magnetorheological clutch; Permanent magnet; Test bench, Experimental testing; Automotive; NEDC.
INTRODUCTION
Nowadays, the reduction of consumption and emissions represents, together with safety and comfort issues, some of the leading trends for vehicle development. Fuel saving is promoted by the increasing attention devoted to environment protection and, at the same time, it is enforced by the pressing regulations on emissions (e.g. current EURO 5 and future EURO 6 emission standards).
The reduction of consumption and emissions is pursued by different strategies, which involve several research fields. The most radical approach deals with the design and implementation of innovative drive-train technologies, such as hybrid applications for the short to medium term period, or the use of different fuels (e.g. hydrogen, ammonia, bio-fuels etc.) or different energy supply-chain (pure electric vehicles) for the long term period. However, these solutions often present a long time-to-market and, in some cases, collide with energy processing and storage .
Another research field deals with the enhancement of transportation efficiency; current trends aim at reducing the consumptions and emissions by enforcing public transportation or encouraging private vehicles sharing.
At the same time the main OEMs component suppliers and research institutes have been studying several particular solutions aimed at reducing the incidence of auxiliary device absorption (e.g. oil, water and vacuum pumps, air conditioning system etc.), improving the component efficiency (e.g. bearing resistance, seal friction etc.) and reducing the component mass. In particular, the reduction in consumptions is actually analysed with reference to the NEDC driving cycle, which takes into account several driving cycles including engine warm-up.
The reduction of oil pump absorptions has been recently studied in by controlling the oil pressure as a function of the engine speed and engine temperature. Other studies focus on the control of variable displacement pumps on the basis of the engine oil request. In a switchable water pump was designed in order to disconnect the auxiliary device from the engine when the engine temperature results lower than a threshold value.
Multiphysics research also led to the use of smart materials in vehicle performance optimization. In [9] and [10] the engine cooling fan is driven by a controllable magnetorheological clutch. The use of smart materials permits the regulation of speed and, consequently, of power absorbed by the cooling fan optimizing its operation on the basis of temperature control (e.g. the cooling fan could be disengaged during engine warm-up). The use of smart materials in the automotive industry has been pursued since many years, especially in suspension design , in order to improve the driver’s comfort and the vehicle dynamic performance by changing the apparent viscosity of the MR fluid filling the dampers.
In this paper a multiphysics research aimed at reducing the absorption of vacuum pumps in Diesel engines is presented. The activity was carried out in co-operation between Pierburg Pump Technology (Livorno, Italy) and the University of Pisa, the University of Bologna and the Politecnico of Torino (Italy). Aim of the research, which was funded by Regione Toscana in the framework of the “Bando Unico 2008”, was the design of a new vacuum pump, actuated by a magnetorheological clutch.
In particular, this paper describes the development of a fail -safe magnetorheological clutch [14] which was designed for disengaging the vacuum pump from the cam-shaft when its operation is not strictly necessary. The mechanical and magnetic design of the clutch, respectively conceived and developed by the Department of Civil and Industrial Engineering and the Department of Energy, Systems, Territory and Constructions of the University of Pisa, have been proposed and discussed in. In this paper, the experimental characteristics of the clutch in the different operating conditions, which were measured on an purposely designed test bench , are discussed in comparison with the absorption data of a vacuum pump currently on the market, in order to evaluate the feasibility of a new integrated MR clutch-vacuum pump system.
POWER-BRAKE AND VACUUM PUMP OPERATION
I n conventional cars, the braking maneuver is imposed by the driver’s pressure on the brake pedal, but the resultant force on the braking master cylinder is amplified exploiting the difference of pressure between two chambers, one connected with ambient air and one (the booster chamber) with the intake manifold, for a throttled gasoline engine,or to the vacuum pump driven by the cam-shaft in Diesel engines [18] .
In case of Diesel engines, starting from atmospheric pressure, the vacuum pump draws in air from the booster chamber till the pressure reaches the steady value pm , as shown in Fig. 1. The emptying time, which is the time taken to reach the pressure steady value pm , results a function of the cam-shaft speed (it is half the engine speed in 4-stroke engines). In Fig.1 the emptying trends are shown with reference to a current production vacuum pump (C.P.) and an innovative one (New), which was designed in the framework of the funded project. The engine speed was set at 4000rpm, which corresponds to 2000rpm at the cam-shaft.
If the emptying characteristic is similar for both solutions, significantly different profiles can be found for the absorbed torques, as shown in Fig. 2. The torque profiles were experimentally measured on a vacuum pump test rig. During tests, the oil temperature was imposed at 120°C and the torque was measured at several steady speed values for both the current production and innovative vacuum pump, and the data were interpolated by a piecewise function. During operation, once the saturation pressure pm is reached in the chamber, the vacuum pump goes on rotating even if its operation is no longer necessary. The power loss could be avoided by disengaging the vacuum pump. The dissipated power can be easily estimated on the basis of the plots of Fig.2, which give the absorbed torque as a function of the cam-shaft speed.
Figure 1: Power-brake booster chamber pressure profile.
Figure 2: Vacuum pump torque absorption.
VACUUM PUMP DISENGAGING CLUTCH
In order to carry out the disengagement of the vacuum pump, a clutch could be interposed between the can shaft and the vacuum pump with strict packaging requirements. Due to the pressing safety requests of the braking system, the clutch has to be fail-safe. In addition, no axial load must be exerted on the cam-shaft, so a traditional friction clutch could not be used. The design choice fell on the use of a magnetorheological (MR) fluid clutch, thanks to the peculiar properties of MR fluids listed in the next section.
Magnetorheological fluids
Magnetorheological fluids are suspensions of micro -sized ferrous particles in a carrier fluid [19]. Their main characteristic consists in changing their rheological properties if subjected to a magnetic field. In particular, when not subjected to a magnetic field they behave as Newtonian fluids (N. M.), whereas under the effect of a magnetic field they exhibit a viscoplastic behavior, which can be modeled in first approximation by the Bingham-plastic model . According to this model, the stress versus shear-rate characteristic can be considered as the superposition of a rigid perfectly-plastic Behavior (characterized by a yield stress value τy , which is a function of the magnetic field H ) and a linear viscous contribution as shown in Fig. 3.
Figure 3: Newton and Bingham models
As regards the vacuum pump disengagement, the following favorable properties of MR fluids have to be considered (numerical values are referred to Lord Corporation MRF140CG fluid):
- low power loss with disengaged clutch due to low viscosity for the unmagnetized fluid (~0.28 Pas);
- high engaged clutch transmissible torque due to high yield stress for the magnetized fluid (~ 55 kPa at 200 kA/m);
- no axial load needed to generate shear stress;
- fast switching time (~10ms) from unmagnetized to magnetized fluid.
Clutch design
On the basis of the design specification listed in Tab. 1, several preliminary design concepts (Fig. 4) were considered in order to define a suitable configuration. The comparative analysis of the possible solutions included several FE magnetic simulations which were carried out by the research team of the Department of Energy, Systems, Territory and Constructions of the University of Pisa.
External Diameter
< 70 mm
Overall length
< 50 mm
Engaged torque
> 2.5 Nm
Disengaged torque
< 0.5Nm
Maximum speed
3000rpm
Table 1: Design specifications.
The external diameter and the overall length were limited by the available volume in the proximity of the vacuum pump. The engaged clutch had to assure the torque transmission necessary for the vacuum pump operation, whereas the disengaged clutch torque had to be lower than the torque absorbed by the vacuum pump at steady pressure pm (Fig. 1).
The maximum speed is equal to the maximum envisaged speed of the cam-shaft.
The four basic design given in Fig.4 were taken into consideration. In all solutions with the exception of the first one, the magnetic field is provided by permanent magnets (PM), which assure a fail-safe actuation against possible battery faults. The analysis of the different geometries allowed to confirm, with the support of quantitative numerical values, that, in order to have a high torque it is necessary to put the MR gap at the larger diameter and, at the same time, to achieve a high magnetic field in the MR gap. Those issues make the solution shown in Fig. 4d, which has a relatively large permanent magnet and an outer MR gap, advantageous with respect to the others; such a solution resulted also conveniently simpler than the multi-disc or multi-cylinder configurations.
A more detailed discussion of the examined geometries can be found in [15].
In addition, in order to compare the capability of the developed prototypes two performance indexes were also proposed in [22]: an exploitation index which is a measure of the magnetic design effectiveness and an efficiency index which is a measure of the overall spurious torque, other than the pure viscous one.
The former is the ratio between the actual (experimentally measured) magnetorheological torque and the maximum ideal magnetorheological torque, which would be available if the entire MR gap was subjected to a uniform magnetic field (the one which takes the MR fluid to saturation).
The latter is the ratio between the ideal spurious torque given by the viscous action of the unmagnetized MR fluid and the actual (experimentally measured) spurious torque, which also includes friction in bearings and seals and any possible unwanted magnetization of the fluid for ineffective shielding of the MR gap.
The above indexes are bound in the (0-1) range and can be used to analyze any MR device. In particular, the efficiency index results important in the context of the present research, with respect to the minimization of losses, when the clutch is in the disengaged configuration.
Clutch prototypes
Three prototypes were manufactured on the basis of the layout shown in Fig. 4(d). Each prototype (Fig. 5) consists of an input and an output coaxially shafts. The gap between the two groups is filled the MR fluid, which can be magnetized by a rare earth NeFeB PM. The PM can slide in a cylindrical room. When the magnet is positioned close to the fluid it assures fluid magnetization and the engaged clutch condition, whereas when it is placed away from the fluid its magnetic field is shielded by a ferromagnetic ring fixed to the input shaft and the clutch results disengaged.
中文翻譯
磁流變離合器的高效汽車輔助設(shè)備驅(qū)動(dòng)
摘 要
本文由托斯卡納區(qū)政府資助項(xiàng)目的結(jié)果，旨在減少在車輛輔助設(shè)備的功率吸收。特別是提出設(shè)計(jì)、測(cè)試和磁流變離合器（MR）中的應(yīng)用，旨在脫離真空泵，它將空氣吸入功率制動(dòng)助力器的增壓室，以減少設(shè)備的功率吸收。
幾個(gè)離合器做選擇，說明離合器幾何及磁場(chǎng)供應(yīng)的初步研究。最后的選擇包括磁離合器與永久磁鐵，滿足大小、扭矩和故障安全規(guī)格。離合器的特性，在轉(zhuǎn)矩與滑移方面，實(shí)驗(yàn)臺(tái)上的三個(gè)不同離合器原型在一個(gè)特設(shè)的開發(fā)測(cè)試平臺(tái)上實(shí)驗(yàn)獲得。
由于一個(gè)初步的模擬，提出了當(dāng)前生產(chǎn)真空泵、一種創(chuàng)新的真空泵和加磁離合器兩真空泵功率吸收的比較。新的歐洲行駛工況考慮模擬真空泵運(yùn)行這兩個(gè)在城市和公路駕駛。結(jié)果表明，使用創(chuàng)新的真空泵降低設(shè)備消耗的約35%，而加上創(chuàng)新的真空泵的磁離合器的使用降低了它在市區(qū)開車約占44%和50%在高速公路上行駛。
關(guān)鍵字 磁流變液；磁流變離合器；永久磁鐵；試驗(yàn)臺(tái)；實(shí)驗(yàn)測(cè)試；汽車；NEDC。
概況
如今，減少消耗和排放量表示的內(nèi)容以及安全和舒適的問題，是一些車輛發(fā)展的主導(dǎo)趨勢(shì)。燃料節(jié)約是促進(jìn)越來越多的關(guān)注，致力于環(huán)境保護(hù)，并在同一時(shí)間，它是強(qiáng)制性的排放法規(guī)（如目前歐元 5 和未來 6 歐元排放標(biāo)準(zhǔn)）。
消費(fèi)和排放量的減少是由不同的策略，涉及多個(gè)研究領(lǐng)域的追求。最激進(jìn)的方法涉及創(chuàng)新的驅(qū)動(dòng)列車技術(shù)，如混合應(yīng)用的短期至中期階段，或使用不同的燃料（如氫，氨，生物燃料等）或不同的能源供應(yīng)鏈（純電動(dòng)汽車）長(zhǎng)期周期的設(shè)計(jì)和實(shí)施。然而，這些解決方案往往存在很長(zhǎng)一段時(shí)間的市場(chǎng)，在某些情況下，碰撞的能量處理和存儲(chǔ)。
另一個(gè)研究領(lǐng)域涉及提高運(yùn)輸效率，目前的趨勢(shì)旨在減少消耗和排放量可實(shí)行公共交通或鼓勵(lì)私家車共享。
同時(shí)主要的OEM零部件供應(yīng)商和研究機(jī)構(gòu)一直在研究幾種特定的解決方案，旨在減少輔助裝置吸收率（如油、水和真空水泵、空調(diào)系統(tǒng)等），提高組件效率（例如軸承阻力，密封摩擦等）和減少組件質(zhì)量。尤其是，在消費(fèi)減少的實(shí)際上是參照了NEDC循環(huán)分析，它考慮到包括發(fā)動(dòng)機(jī)預(yù)熱的不同駕駛循環(huán)工況。
最近關(guān)于石油泵吸收減少的研究，通過控制油壓力隨發(fā)動(dòng)機(jī)轉(zhuǎn)速和發(fā)動(dòng)機(jī)的溫度。其他的研究專注于可變排量泵的基礎(chǔ)上，發(fā)動(dòng)機(jī)機(jī)油的控制要求。其中可切換的水泵被為從發(fā)動(dòng)機(jī)斷開輔助設(shè)備，當(dāng)發(fā)動(dòng)機(jī)溫度結(jié)果低于一個(gè)閥值。
多場(chǎng)物理研究也導(dǎo)致在車輛性能優(yōu)化的智能材料的使用。由可控磁流變離合器驅(qū)動(dòng)發(fā)動(dòng)機(jī)冷卻風(fēng)扇。智能材料的使用允許轉(zhuǎn)速調(diào)節(jié)，因此，電力由冷卻風(fēng)扇溫度控制的基礎(chǔ)上優(yōu)化其運(yùn)行吸收(例如冷卻風(fēng)扇能脫離發(fā)動(dòng)機(jī)預(yù)熱期間)。很多年以來智能材料一直在汽車工業(yè)中使用，特別是在懸架設(shè)計(jì)，提高駕駛員的舒適和整車動(dòng)態(tài)性能，通過改變磁流變液填充阻尼器的表觀粘度。
本文提出了多場(chǎng)物理的研究旨在減少柴油發(fā)動(dòng)機(jī)真空泵的吸收。是皮爾博格泵技術(shù)(利沃諾，意大利)、比薩大學(xué)、博洛尼亞大學(xué)和都靈理工大學(xué)(意大利)之間的合作開展的活動(dòng)。本研究，是由托斯卡納區(qū)政府資助的“Bando Unico2008年”的框架，目的是通過驅(qū)動(dòng)磁流變離合器，設(shè)計(jì)一個(gè)新的真空泵。
特別是，本文介紹了的故障的旨在切斷真空泵從凸輪軸時(shí)其操作不是嚴(yán)格必要的安全磁流變離合器。分別對(duì)比薩大學(xué)土木與工業(yè)工程系、能源、系統(tǒng)、國(guó)土、建筑等部門的機(jī)械和磁力設(shè)計(jì)進(jìn)行了構(gòu)想和探討。在本文中，在不同的工況下，在一個(gè)故意設(shè)計(jì)的試驗(yàn)臺(tái)上進(jìn)行了測(cè)量，再比較真空泵，目前在市場(chǎng)上的吸附數(shù)據(jù)，以評(píng)估一個(gè)新的集成磁離合器真空泵系統(tǒng)的可行性。
動(dòng)力制動(dòng)和真空泵操作
傳統(tǒng)的汽車，制動(dòng)動(dòng)作是踩剎車踏板，由此產(chǎn)生的驅(qū)動(dòng)壓力，制動(dòng)主缸上的力被放大，利用兩個(gè)腔，一個(gè)環(huán)境空氣(增壓室)與進(jìn)氣歧管，節(jié)流的汽油發(fā)動(dòng)機(jī)，與空氣之間的壓差或到真空泵驅(qū)動(dòng)凸輪軸柴油機(jī)。
在柴油發(fā)動(dòng)機(jī)的情況下，從大氣壓開始，真空泵吸進(jìn)空氣從增壓室直到壓力達(dá)到穩(wěn)定值pm，如圖1所示。排空的時(shí)間，是達(dá)到壓力穩(wěn)定值pm所需的時(shí)間，結(jié)果是一個(gè)凸輪軸速度的函數(shù)(它是在四沖程發(fā)動(dòng)機(jī)的一半發(fā)動(dòng)機(jī)轉(zhuǎn)速)。圖1示參照當(dāng)前生產(chǎn)真空泵排空趨勢(shì)（C.P.）和創(chuàng)新（新的），這是在資助項(xiàng)目的框架設(shè)計(jì)。發(fā)動(dòng)機(jī)轉(zhuǎn)速在4000rpm，對(duì)應(yīng)于2000rpm在凸輪軸成立。
如果排空的特點(diǎn)是相似的兩種解決方案，明顯不同的配置文件可以找到相應(yīng)的吸收扭矩，如圖2所示。在真空泵試驗(yàn)臺(tái)上實(shí)驗(yàn)測(cè)量扭矩的分布。在測(cè)試中，油的溫度被穩(wěn)定在120℃和扭矩測(cè)量了幾個(gè)穩(wěn)速值的當(dāng)前生產(chǎn)和創(chuàng)新的真空泵，和數(shù)據(jù)點(diǎn)進(jìn)行插值的分段函數(shù)。在操作過程中，一旦在腔室中達(dá)到飽和壓力，真空泵進(jìn)行旋轉(zhuǎn)，即使它的操作不再需要。功率損耗可以避免由脫離真空泵。耗散功率可以在圖2中的圖的基礎(chǔ)上很容易估計(jì)，這是吸收扭矩相對(duì)于凸輪軸的速度函數(shù)。
圖1：動(dòng)力制動(dòng)增壓室壓力曲線。
圖2: 真空泵轉(zhuǎn)矩吸附
真空泵分離式離合器
為了實(shí)現(xiàn)真空泵脫開，離合器可以插入軸和包裝有嚴(yán)格要求的真空泵之間。由于制動(dòng)系統(tǒng)的安全要求，離合器必須要萬無一失。此外，在凸輪軸上不必施加軸向載荷，所以不能使用傳統(tǒng)的摩擦離合器由于在下一節(jié)中列出的磁流變液特有的屬性，設(shè)計(jì)選擇使用了磁流變(MR)液離合器。
磁流變液體
磁流變液體是一種在載液中的微大小的亞鐵粒子懸浮液。它們的主要特點(diǎn)在于如果磁場(chǎng)作用下可改變其流變性能。尤其是，不受磁場(chǎng)時(shí)他們表現(xiàn)為牛頓流體(N.M.)，而在磁場(chǎng)的作用下，他們表現(xiàn)出一粘塑性行為，可以由賓漢塑性模型近似模擬。根據(jù)這一模型，剪切速率特性曲線應(yīng)力可以視為理想剛塑性的疊加行為(屈服應(yīng)力值的特點(diǎn)y，這是磁場(chǎng)H函數(shù))，如圖3所示的線性粘性模型。
圖3: Newton 和 Bingham 模型
至于真空泵脫離接觸，磁流變液的下列有利屬性必須加以考慮(數(shù)值指主公司MRF140CG流體):
——低功率損耗與離合器由于低粘度為非磁化液(~0.28Pas)；
——高結(jié)合的離合器傳遞扭矩為高屈服應(yīng)力磁流體(~55kpa在200mkA)；
——沒有軸向載荷需要生成剪切應(yīng)力；
——快速切換時(shí)間(~10ms)從非磁化的磁流液。
離合器的設(shè)計(jì)
根據(jù)表1中列出的設(shè)計(jì)指標(biāo)，幾個(gè)設(shè)計(jì)的初步概念(圖4)被認(rèn)為是為了定義一個(gè)合適的配置[15-16]?？赡艿慕鉀Q方法的對(duì)比分析，包括幾個(gè)鐵磁模擬由能源部、系統(tǒng)、領(lǐng)土和建筑比薩大學(xué)研究小組進(jìn)行了研究。
External Diameter
< 70 mm
Overall length
< 50 mm
Engaged torque
> 2.5 Nm
Disengaged torque
< 0.5Nm
Maximum speed
3000rpm
表1.設(shè)計(jì)規(guī)范
外部直徑和整體長(zhǎng)度是有限的可用體積接近的真空泵。接合的離合器必須保證真空泵運(yùn)行所需的扭矩傳輸而離合器轉(zhuǎn)矩必須低于吸收由真空泵在穩(wěn)態(tài)壓力p的扭矩m最大速度等于凸輪軸設(shè)想的最大速度。
在所有解決方案中，除了第一個(gè)，磁場(chǎng)都是由永久磁鐵(PM)組成，這保證了故障安全致動(dòng)對(duì)應(yīng)的可能的電池故障。根據(jù)分析的不同的幾何形狀確認(rèn)，以及定量數(shù)值的支持，即為了有一個(gè)高的轉(zhuǎn)矩，它是必要的，以使原先的直徑有較大的差距，并在同一時(shí)間，以實(shí)現(xiàn)高磁場(chǎng)的磁隙。這些問題使示圖4d所表示的解決方案里，其中有一個(gè)具有較大的永久磁鐵和一個(gè)原先間隙是有利方案；這樣的解決方案也可以方便簡(jiǎn)單的實(shí)現(xiàn)多盤或多缸配置。
此外，為了能力的比較，開發(fā)原型的性能指標(biāo)，還提出了開發(fā)指數(shù)，這是一個(gè)衡量磁設(shè)計(jì)的有效性和效率的指數(shù)，這也是一個(gè)衡量整體的轉(zhuǎn)矩和粘性的一個(gè)參數(shù)。
前者是實(shí)際(實(shí)驗(yàn)測(cè)量)的磁流變轉(zhuǎn)矩和最大理想磁流變轉(zhuǎn)矩之間的比率，如果整個(gè)磁隙受到一個(gè)均勻磁場(chǎng)（需要磁流體飽和的一個(gè)）的作用，則可獲得最大理想磁流變轉(zhuǎn)矩。
后者是理想轉(zhuǎn)矩給出的磁化磁流變液的粘滯作用和實(shí)際（實(shí)測(cè)）轉(zhuǎn)矩之間的比率，其中還包括摩擦軸承和密封件以及任何可能有害的磁化流體無效屏蔽MR的差距。
上述指標(biāo)所顯示的約束范圍，可以用來分析任何MR設(shè)備。
在三個(gè)原型的基礎(chǔ)上，生成了圖4（2）顯示的布局制造。每個(gè)原型由一個(gè)輸入軸和輸出軸同軸。兩組之間的間隙填充MR流體，可以由稀土釹鐵硼永磁磁化。流體可以在一個(gè)圓筒狀的空間里滑動(dòng)。此時(shí)磁鐵定位接近的流體可以保證流體磁化和離合器的接合狀態(tài)，而當(dāng)它是位于遠(yuǎn)離流體的磁場(chǎng)屏蔽的位置時(shí)，磁環(huán)固定在輸入軸和離合器脫離的位置。