輕型商用車(chē)混合動(dòng)力傳動(dòng)系統(tǒng)

1 動(dòng)因

雖然近期由于經(jīng)濟(jì)危機(jī)的影響,燃油價(jià)格有所下降,但從長(zhǎng)遠(yuǎn)來(lái)看,石油儲(chǔ)量的減少會(huì)導(dǎo)致燃油價(jià)格的上漲。而且嚴(yán)格的二氧化碳排放法規(guī),尤其針對(duì)城市交通的規(guī)定逐漸完善。筆者認(rèn)為,未來(lái)對(duì)油電混合動(dòng)力車(chē)的需求會(huì)不斷上升。

2 傳動(dòng)系統(tǒng)概念

本章將提出LCV混合動(dòng)力傳動(dòng)系統(tǒng)的幾個(gè)概念。之后將介紹關(guān)鍵的評(píng)價(jià)標(biāo)準(zhǔn)?；旌蟿?dòng)力傳動(dòng)系統(tǒng)應(yīng)當(dāng)是為用于城市運(yùn)輸?shù)腖CV設(shè)計(jì)的。這些運(yùn)輸任務(wù)通常由車(chē)隊(duì)完成。對(duì)于車(chē)隊(duì)擁有者來(lái)說(shuō),單位里程成本是決定所用車(chē)型的最重要因素。公共法規(guī)和環(huán)保形象也是考慮因素之一。額外費(fèi)用和混合動(dòng)力車(chē)節(jié)省的燃油是單位里程成本的重要部分。額外費(fèi)用主要由混合動(dòng)力車(chē)中必須安裝的附加零部件和研發(fā)代價(jià)決定。兩者都是LCV混合動(dòng)力概念的重要評(píng)價(jià)標(biāo)準(zhǔn)。節(jié)省的燃油等同于二氧化碳排放的降低。短時(shí)電驅(qū)行駛也是評(píng)價(jià)標(biāo)準(zhǔn)之一,某些LCV生產(chǎn)商注重此項(xiàng)特性。HEV駕駛舒適度是一項(xiàng)限制,不應(yīng)劣于普通車(chē)輛。

1 Motivation

In the long term reducing oil stocks will increase the fuel price,although at present the fuel price drops due to the w orldwide economical crisis.Furthermore rigorous CO2emission regulations especially for urban traffic are expected.Therefore the author expects an increasing demand for hybrid electric vehicles(HEV)for the future.

2 Powertrain Concept

A hybrid powertrain concept for LCV will be proposed in this chapter.Several concepts are discussed.In the following the deciding criteria are introduced.

The hybrid transmission system should be designed for LCV,which are used in urban delivery missions.These missions are mainly carried out by fleets.For the owners of these fleets the cost per mileage is most important for the decision,which kind of vehicle they use.Public regulations as well as a green image have also an impact on the product decision.

總結(jié)起來(lái),評(píng)價(jià)標(biāo)準(zhǔn)有如下幾項(xiàng)：

●燃油節(jié)省量/二氧化碳排放減少量;

●零部件成本;

●研發(fā)代價(jià);

●電驅(qū)行駛(短時(shí));

由于燃油節(jié)省/二氧化碳排放降低的重要性越來(lái)越高,此項(xiàng)標(biāo)準(zhǔn)的權(quán)重應(yīng)大于零部件成本;由于體積的限制,零部件成本標(biāo)準(zhǔn)的權(quán)重又大于研發(fā)成本。電驅(qū)行駛的潛力重要程度與研發(fā)成本相似,因?yàn)榇斯δ懿挥绊憜挝焕锍坛杀?。為了?jiǎn)化決策矩陣,以“3”代表燃油節(jié)省/二氧化碳排放降低的權(quán)重,“2”代表零部件成本的權(quán)重,“1”代表研發(fā)代價(jià)和電驅(qū)行駛能力。

同時(shí),與下列混合動(dòng)力系統(tǒng)概念進(jìn)行比較：

●輕度混合動(dòng)力;

●單離合器混合動(dòng)力;

●雙離合器混合動(dòng)力;

●串聯(lián)混合動(dòng)力;

輕度混合動(dòng)力系統(tǒng)的動(dòng)力結(jié)構(gòu)如表1所示,電機(jī)功率約20千瓦。在單離合器和雙離合器混合動(dòng)力系統(tǒng)中,電機(jī)功率應(yīng)達(dá)40千瓦,以優(yōu)化節(jié)油率及系統(tǒng)成本,見(jiàn)(3)。串聯(lián)混合動(dòng)力系統(tǒng)所需的電機(jī)功率與內(nèi)燃機(jī)相近。在(1)中討論了這一情況。

從節(jié)油率方面看,輕度混合動(dòng)力系統(tǒng)劣于其他設(shè)計(jì),因?yàn)榇祟愊到y(tǒng)不具備電驅(qū)行駛和電驅(qū)起動(dòng)能力,回饋制動(dòng)的能力也很有限。其他混合動(dòng)力系統(tǒng)能以全混合狀態(tài)運(yùn)行,見(jiàn)第4節(jié)。

從零部件成本看,輕度混合動(dòng)力系統(tǒng)優(yōu)于單離合器和雙離合器系統(tǒng),因?yàn)镠EV不需要電動(dòng)轉(zhuǎn)向和制動(dòng)。單離合器系統(tǒng)的成本小于雙離合器系統(tǒng)。由于有兩套電機(jī)驅(qū)動(dòng)器,串聯(lián)混合動(dòng)力系統(tǒng)成本較高。

一項(xiàng)對(duì)研發(fā)代價(jià)的估計(jì)顯示,雙離合器混合動(dòng)力系統(tǒng)與單離合器混合動(dòng)力系統(tǒng)類似。輕度混合動(dòng)力系統(tǒng)的研發(fā)代價(jià)最低。串聯(lián)混合動(dòng)力系統(tǒng)的研發(fā)代價(jià)最高,因?yàn)槠渥兯倨髟O(shè)計(jì)不能仿照常規(guī)的動(dòng)力系統(tǒng)。

表1中的決策矩陣總結(jié)了上述各條。系統(tǒng)以“-”“0”“+”和“++”來(lái)計(jì)分?；谏鲜鲈u(píng)價(jià)標(biāo)準(zhǔn)和權(quán)重而分析,單離合器混合動(dòng)力系統(tǒng)最適用于LCV,其次是輕度混合動(dòng)力系統(tǒng)。

表1 LCV混合動(dòng)力傳動(dòng)系統(tǒng)的決策矩陣Table 1 decision matrix hybrid transmission system for LCV

The extra charge and the fuel savings of the hybrid vehicle play a decisive role for the cost per mileage.The extra charge is essentially affected by the cost of the additional components,which have to be installed in the hybrid vehicle,and the R&D effort.Both have to be considered as deciding criteria for the hybrid concept for LCV.The fuel savings are equivalent with CO2emission reduction.

Furthermore the possibility of short-time electric driving is introduced as deciding criteria,because this feature is requested by some LCV manufacturer.

The driving comfort of the HEV is recognized as a constraint.It should not be worse than the basic vehicle.In summary the following criteria are taken into account：

fuel savings/CO2emissions,

component cost,

R&D effort

electric driving(short-time).

Because of the increasing importance of fuel savings/CO2emissions this criteria is weighted higher than component cost and this criteria is weighted higher than R&D effort due to the expected volume.The potential to drive electrically is weighted in the same manner as R&D effort,because this feature does not improve the cost per mileage.In order to keep the resulting decision matrix simple‘3'is chosen as the weight for fuel savings/CO2emissions,‘2'for component cost,and‘1'for R&D effort and electric driving.

3 系統(tǒng)設(shè)計(jì)

下面闡述單離合器混合動(dòng)力系統(tǒng)的實(shí)現(xiàn)。系統(tǒng)的設(shè)計(jì)目標(biāo)如下：

●單離合器混合動(dòng)力傳動(dòng)系統(tǒng)

●降低系統(tǒng)成本

●降低研發(fā)代價(jià)

混合動(dòng)力傳動(dòng)系統(tǒng)由下列部分組成：

●自動(dòng)變速器

●電機(jī)

●逆變器

這里討論的系統(tǒng)不包括高壓(HV)電池及轉(zhuǎn)向、制動(dòng)等部分。這些部分由LCV制造商提供。六速自動(dòng)變速器由手動(dòng)變速器改造,加裝了機(jī)電執(zhí)行器和控制單元。為了降低系統(tǒng)成本,同步環(huán)被取消,換擋時(shí)的同步由電機(jī)完成。實(shí)車(chē)測(cè)試表明,電機(jī)同步完成的時(shí)間與同步器相當(dāng)或更快?？紤]加工成本,變速器殼體不作改變。雖然可以縮短長(zhǎng)度,但這在實(shí)際汽車(chē)的制造中并不必要。

電機(jī)與逆變器已經(jīng)量產(chǎn),經(jīng)少量改動(dòng)即可使用。電機(jī)選用永磁磁阻電機(jī),是永磁同步電機(jī)與磁阻電機(jī)的組合。由于此種電機(jī)質(zhì)量較大,考慮典型的功率消耗,不需要水冷系統(tǒng)。電機(jī)的定子和轉(zhuǎn)子安裝在獨(dú)立的殼體中,置于內(nèi)燃機(jī)和自動(dòng)變速器之間。殼體中還包含離合器分離系統(tǒng)和電機(jī)的高功率接觸件。電機(jī)由水冷逆變器控制,不使用轉(zhuǎn)子位置傳感器?；旌蟿?dòng)力控制功能塊應(yīng)集成在變速器控制單元內(nèi),應(yīng)同時(shí)適應(yīng)這兩個(gè)任務(wù)的需要。圖1所示為混合動(dòng)力變速器。

圖1 混合動(dòng)力變速器Fig.1 Hybrid transmission

4 系統(tǒng)功能

系統(tǒng)功能的目標(biāo)是優(yōu)化燃油消耗和二氧化碳排放。下列功能由混合動(dòng)力系統(tǒng)實(shí)現(xiàn)：

●電驅(qū)行駛和啟動(dòng)

The following hybrid concepts are compared：

●Mild hybrid,

●Single clutch hybrid,

●Two clutch hybrid,

●Serial hybrid.

The mild hybrid is here defined as a hybrid system with the powertrain structure as show n in table 1 and an electric motor with a power of approximately 20 kW.For the single and the two clutch hybrid the power of the electricmotor should be approximately 40 kW in order to optimize fuel savings and system cost as examined in(3).The serial hybrid needs an electric power comparable to the combustion engine.This concept is also discussed in(1).

Regarding fuel savings the mild hybrid is inferior to all other concepts,because this hybrid system does not have the possibility of electric driving and setting-off and only a very limited potential for regenerative braking.All other hybrid systems can be used as a full hybrid with functionality as characterized in chapter 4.

Regarding component cost the mild hybrid is superior to single and two clutch hybrid,because the HEV does not need electric steering and braking.The single clutch hybrid generates lower component cost than the two clutch hybrid,because it needs only one clutch system.The serial hybrid is expensive due to the two electric drives.

An estimation of the R&D effort shows,that the tw o clutch hybrid is comparable to the single clutch hybrid.The lowest R&D effort can be expected with the mild hybrid.The serial hybrid demands the highest R&D effort,because the transmission cannot be carried-over from a conventional powertrain.

The decision matrix in table 1 summarizes the discussion above.All systems are evaluated with‘-',‘0',‘+',and‘++'.An overall analysis based on the chosen criteria and weights leads to the result,that the single clutch hybrid is the best choice for LCV followed by the mild hybrid.

●工作區(qū)間切換

●回饋制動(dòng)

●怠速停機(jī)

系統(tǒng)具備電驅(qū)行駛能力。然而整個(gè)系統(tǒng)并非是為長(zhǎng)時(shí)間電驅(qū)行駛而設(shè)計(jì)。低速時(shí),電機(jī)的扭矩與內(nèi)燃機(jī)的扭矩相當(dāng)。在上坡條件下可以用電機(jī)啟動(dòng)。在電驅(qū)模式下,換擋操作無(wú)需離合器作用。

工作區(qū)間切換,指的是通過(guò)智能分配內(nèi)燃機(jī)和電機(jī)的扭矩來(lái)優(yōu)化整個(gè)混合動(dòng)力傳統(tǒng)系統(tǒng)的效率。如果駕駛者需要極低的扭矩,若完全由內(nèi)燃機(jī)提供扭矩,其效率很差。如果使內(nèi)燃機(jī)工作在效率較高的區(qū)域,而由電機(jī)提供一個(gè)反向的扭矩,整體效率將得到優(yōu)化。發(fā)電產(chǎn)生的電流給高壓電池充電,以用于電驅(qū)行駛。此功能靠電機(jī)在混合動(dòng)力模式下產(chǎn)生的恒值反向扭矩實(shí)現(xiàn)。(參見(jiàn)圖2)

回饋制動(dòng),指利用電機(jī)的發(fā)電機(jī)模式來(lái)降低車(chē)速。這個(gè)功能僅當(dāng)剎車(chē)踏板的釋放方式與“A級(jí)”制動(dòng)系統(tǒng)的ECE R13H一致時(shí)才觸發(fā)。雖然應(yīng)當(dāng)有一種智能的制動(dòng)系統(tǒng),在需要回饋時(shí)關(guān)閉傳動(dòng)制動(dòng)方式,但這種系統(tǒng)對(duì)于LCV來(lái)說(shuō)過(guò)于昂貴。在回饋制動(dòng)時(shí),換擋操作應(yīng)被禁止,因?yàn)橹苿?dòng)力的損失會(huì)使駕駛者感到不適。仿真研究還表明,換擋時(shí)回饋制動(dòng)能量的損失會(huì)影響混合動(dòng)力系統(tǒng)的節(jié)油效果。

怠速停機(jī)功能指車(chē)輛停駛時(shí)關(guān)閉內(nèi)燃機(jī),當(dāng)駕駛者需要再次行駛時(shí)自動(dòng)啟動(dòng)。

4.1 電池充電模式下的啟動(dòng)

與雙離合器混合動(dòng)力系統(tǒng)相比,單離合器系統(tǒng)在下面的行駛狀況下表現(xiàn)不佳：如果高壓電池的荷電量(SOC)下降到某個(gè)閾值以下,需要充電。此時(shí)電機(jī)由內(nèi)燃機(jī)驅(qū)動(dòng),以發(fā)電機(jī)模式運(yùn)行。此時(shí)如果車(chē)輛靜止,變速器必須置于空擋,離合器接合。即使駕駛者并不期望空擋,這些動(dòng)作也是必須自動(dòng)完成的。當(dāng)駕駛者踩下加速踏板時(shí),單離合器混合動(dòng)力系統(tǒng)要帶動(dòng)車(chē)輛行駛。因此,離合器必須分離,電機(jī)要與變速器同步,接合齒輪,車(chē)輛然后才開(kāi)始啟動(dòng)。與雙離合器系統(tǒng)相比,單離合器系統(tǒng)不可避免地會(huì)有約500毫秒的延時(shí)。通過(guò)聲光信息提示駕駛者此種情況,可改進(jìn)這一缺陷。

5 節(jié)油效果

混合動(dòng)力傳動(dòng)系統(tǒng)的目標(biāo)是在某種城市運(yùn)輸循環(huán)下節(jié)油30%,尤其是日本10模式和新歐洲行駛循環(huán)(NEDC)的城市部分。過(guò)去曾對(duì)日本和歐洲生產(chǎn)的一種典型LCV做過(guò)仿真,也進(jìn)行過(guò)實(shí)車(chē)測(cè)試。該車(chē)凈重4.5頓,由3.0 L四缸柴油引擎驅(qū)動(dòng),最大扭矩375 Nm。帶自動(dòng)變速器的常規(guī)車(chē)輛油耗與單離合器混合動(dòng)力系統(tǒng)車(chē)輛的油耗比較。

3 System Design

Below the implementation of the single clutch hybrid is explained.The targets of the system design are：

●single clutch hybrid transmission system,

●reduce system cost,

●reduce R&D effort,

The hybrid transmission system consists of the following components：

●automated transmission,

●electric motor,

●inverter.

The considered system does not include the high voltage(HV)battery and any steering and braking components.These components should be supplied by the LCV manufacturer.

The 6-speed automated transmission is based on a manual one,which is automated by electromechanical add-on actuators and a control unit.

In order to reduce the system cost,the synchronizer rings are left out.Transmission synchronization during shiftings is carried out by the electric motor.Vehicle tests show,that the synchronization time with an electric motor is faster or equal to the time,which is achievable with synchronizers.

The transmission housing remains unchanged due to tooling cost,although the system could be shortened,because the actual vehicle packaging studies does not show the need for this.

Electric motor and inverter are already in volume production and can be carried over with minimal modifications.The electric motor is a permanent magnet reluctance motor,which is a composition of a permanent magnet synchronous motor and a reluctance motor.Because of the high mass of this motor and the typical electrical power consumption,there is no need for w ater cooling of the electric motor.

在仿真中考慮了混合動(dòng)力部件的附加重量。附屬系統(tǒng),如電制動(dòng),轉(zhuǎn)向模塊或電池冷確系統(tǒng)的損失也計(jì)算在內(nèi)。高壓系統(tǒng)用鎳鐵混合電池的模型來(lái)仿真。鋰離子電池效率更高,重量更輕,會(huì)提高仿真結(jié)果。在電驅(qū)模式中使用實(shí)測(cè)的效率特性。在日本10模式的仿真中,節(jié)油達(dá)27%,NEDC的城市部分仿真中節(jié)油28%。在日本10模式的滾動(dòng)測(cè)功機(jī)試驗(yàn)中,測(cè)得節(jié)油量為29.1%。文獻(xiàn)[2]中提到了另一種類似系統(tǒng)的節(jié)油效果。圖2展示了日本10模式的一次實(shí)車(chē)測(cè)試。

圖2 日本10模式下的實(shí)車(chē)測(cè)試Fig.2 Vehicle measurements Japan 10 mode

6 展望

在日本10模式以外的行駛循環(huán)中,要用此種混合動(dòng)力系統(tǒng)節(jié)省30%或更多的燃油較為困難。為此,必須在混合動(dòng)力變速器之前的汽車(chē)部件上采取措施。比如,本文中的小型化指在混合動(dòng)力車(chē)中使用較小的內(nèi)燃機(jī)。如果需要達(dá)到最大扭矩,內(nèi)燃機(jī)需要電機(jī)的支持。一個(gè)明顯的不足是,混合動(dòng)力車(chē)不能長(zhǎng)時(shí)間維持常規(guī)汽車(chē)的最高車(chē)速。對(duì)于用于城市運(yùn)輸?shù)纳逃密?chē),這個(gè)缺點(diǎn)也許是可以忍受的。進(jìn)一步提高節(jié)油性能則需要智能制動(dòng)系統(tǒng)或低阻輪胎。全混合動(dòng)力系統(tǒng)的高研發(fā)代價(jià)至今仍阻礙了此系統(tǒng)的應(yīng)用。為對(duì)應(yīng)未來(lái)上漲的油價(jià)和嚴(yán)格的排放法規(guī),針對(duì)排放的車(chē)輛稅會(huì)有助于這種混合動(dòng)力系統(tǒng)的推廣。

The stator and rotor of the electric motor are installed in a separate housing,w hich is arranged between combustion engine and automated transmission.This housing contains also the clutch release system and the high power contacts of the electric motor.

The electric motor is controlled by a watercooled inverter without the use of a rotor position sensor.

The hybrid control functionality should be integrated into the transmission control unit,which performance must be suitable for both tasks.Figure 1 shows the hybrid transmission：

4 System Functionality

The target of the system functionality is to optimize fuel savings and by this CO2emissions.

The following functions are realized by the hybrid transmission system：

●electrical driving and setting-off,

●transition of operation range,

●regenerative braking,

●idle stop.

The system is able to drive electrically.However the overall system is not designed for long term electricdriving.The torque of the electricmotor is comparable to the torque of the combustion engine at low speed.It allow s electrical setting-off even in uphill condition.In electric driving mode the shiftings are carried out without clutch operation.

Transition of operation range means to optimize the overall hybrid powertrain efficiency by intelligent torque distribution between combustion engine and electric motor.If e.g.the driver is requesting a very low torque,the combustion engine would be operated at a very bad efficiency,if it supplies the torque exclusively.The overall efficiency can be improved,if the combustion engines torque is increased to an optimal operation range and if the surplus of torque is balanced by a negative electric motor torque.The generated electric current can be used to store energy in the HV battery,which is available for electric driving later.This function is realized by a constant negative torque of the electric motor in hybrid driving mode as a first step(refer to figure 2).

Regenerative braking means to use the electric motor in generator mode to reduce the vehicle speed.This functionality should be activated by releasing the accelerator pedal only in compliance with ECE R13 H for“class A” braking systems.An intelligent braking system,which disables the conventional braking system during regenerative braking,is desirable,but usually such systems are judged as too expensive for LCV applications.During regenerative braking shiftings should be inhibited,because the loss of braking force is an uncomfortable feeling for the driver and simulation studies show,that the loss of energy regeneration during shiftings reduces the fuel savings of the hybrid system.

The idle stop functionality means to stop the combustion engine in vehicle standstill condition and to restarts it automatically,if the driver wants to continue his mission.

4.1 Setting-Off in battery charge mode

In comparison with the tw o clutch hybrid the single clutch hybrid is sometimes criticized because of the following driving situation：

If the state of charge(SOC)of the HV battery falls below a certain threshold,it is necessary to charge it.This can be done by the electric motor in generator mode,driven by the combustion engine.To do this in standstill condition the transmission has to be in N and the clutch has to be closed.This condition has to be adopted automatically even if the driver does not request N.If the driver presses the accelerator pedal in this situation,the single clutch hybrid system has set-off the vehicle.For this,the clutch has to open,the electric motor has to synchronize the transmission,the gear has to be engaged and after this the setting-off maneuver starts.

An inevitable delay of approximately 500 ms happens,if the single clutch hybrid is compared to the conventional vehicle or the two clutch hybrid system.

This disadvantage could be reduced by display indications or acoustical indications,which makes the situation aware for the driver.

5 Fuel Saving Results

The target of the hybrid transmission system is to save up to 30%fuel in certain urban delivery cycles.Especially the Japan 10 mode and the city share of the New European Driving Cycle(NEDC)are considered.

Vehicle simulations for a typical LCV produced in Japan and Europe were done in the past.Actually also vehicle measurements are available.

The gross vehicle weight is 4.5 t.It is driven by a 3.0l diesel engine with four cylinders and a maximal torque of 375 Nm.

The fuel consumption of the conventional vehicle with an automated transmission is compared to the fuel consumption of the vehicle fitted with the single clutch hybrid transmission system.

During the simulations the additional weight of the hybrid components is considered.The losses of auxiliaries like electric braking and steering units or battery cooling systems are taken into account.For the HV battery a simulation model of a nickel metal hybrid battery is used.A lithium ion battery with a higher efficiency and less weight would improve the simulation results.For the electric drive measured efficiency characteristics are used.

Fuel savings of 27%are simulated for the Japan 10 mode and 28%for the city share of the NEDC.On a roller dynamometer 29.1%fuel savings were measured for the Japan 10 mode.

The correspondence between simulation and measurements seems to be very good.

Fuel saving results with a similar system are also published in[2].Figure 2 show s an example of a vehicle measurement of the Japan 10 mode.

6 Outlook

Fuel savings of 30%or more are difficult to reach with the proposed hybrid system in other driving cycles than the Japan 10 mode.For this purpose measures on vehicle side beyond the hybrid transmission system are necessary to perform.

E.g.downsizing means in this context to use a smaller combustion engine for the hybrid vehicle as for the conventional vehicle.The combustion engine has always to be supported by the electrical motor,if the maximum torque is requested.The inevitable disadvantage is that the maximum speed of the conventional vehicle cannot be hold for a longer time with the hybrid vehicle.For a commercial vehicle,used in urban delivery missions,this disadvantage might be acceptable.

Further potential to improve fuel savings are e.g.intelligent braking systems or?-low tires.

High R&D effort and the component cost of a full hybrid system are slowing till now a comprehensive application of this powertrain concept.For the future an increasing fuel price,rigorous emission regulations,and a more emission oriented vehicle taxation will support such hybrid systems.

[1]Vahlensieck,B,Speck,F.-D.,and Kubalzyck,R：Economic Concepts and Solutions for Hybrid Drivelines.Technical Congress of JSAE,Yokohama,May 2008.

[2]Griesmeier,U.,Blattner,S.,Mittelberger,C.：Parallel-hybrid mit automatisiertem Schalt-getriebe in einer Trans-porteranwendung,Technical Congress of VDI,Dresden,November 2008.

[3]Lamke,M.,Speck,F.-D.,H?gele,J.：Modulare Nkw-Getriebefamilie von Handschalt- zu Hybridausführung.Technical Congress of VDI,2008.