工程机械用混合型动力传动系统

1 前言

对于工程机械而言,不断增加的燃油价格和环保要求使得降低油耗日趋重要。此外,排放法规Tier 4的引入将导致车辆做出重大改进,因为需进行废气后处理。车辆的变动在部分程度上会对油耗起负面影响。目前正在开发的变速器和驱动桥将是今后机动车传动系统的重要基础。这些系统通过不断提高效率和优化与内燃机、变速器和液压系统的协同工作可明显地降低油耗。在提高性能的同时进一步降低油耗和排放,则必须采用其他途径。这就可以看出电力驱动和混合动力在机动车方面应用的巨大潜力。但是,从这些技术的应用经济性考虑,必须抓住在机动车各个分支方面的应用可能性,例如商用车辆。

2 ZF的混合动力系统

在ZF公司,各种形式的商用车辆混合动力系统正处于产品开发阶段。它们包括适用于城市公交的EcoLife-Hybrid和适用于货车的Hy-Tronic。上述两系统使用的电动机为120和60 kW,并具有强混合动力系统的功能。

1 Introduction

Increasing fuel prices and increased environmental requirements lead,for construction machinery,to an increased importance of measures to reduce fuel consumption.Also,the introduction of the exhaust regulation Tier 4 leads,for meeting the regulation,to drastic changes on the vehicle because of the required exhaust gas after-treatment.These changes on the vehicle partly affect the fuel consumption in a negative w ay.An important basis for future drivetrains of mobile machinery is provided by the currently developed transmissions and axle systems.These systems lead,through their continuous optimisation with regards to efficiency and an optimalcooperation ofcombustion engine,transmission and hydraulics,to clear fuel savings.To further reduce fuel consumption and exhaust emissions,whilst increasing the performance,additional degrees of freedom have to be created.This is where an electrification and hybridisation can show a great potential for application to mobile machinery.However,for an economic application of these technologies,despite the relatively low production volumes,one has to seize all possible synergies with other vehicle branches,e.g.commercial vehicles.

ZF所提供的产品除了变速器集成和电动马达之外,还包括锂离子蓄电池、动力逆变器和混合动力控制单元等必要的混合动力组件。系统还能配备用于随车供能DC/DC转换器以取代交流发电机。由ZF提供的混合动力控制软件具有部件控制、混合动力功能运转和车辆功能策略等功能。

图1是为轿车和商用车辆开发的ZF模块化软件系统中关于混合动力主要功能的一览表。它包括典型的混合动力功能例如发动机起停系统、制动能量回馈、发动机工作点的换档、电力驱动以及在内燃机和电动汽车之间动力管理的混合动力策略。

这些模块化的硬件和软件系统作为机动车混合动力系统的基础。附加功能例如改善排放的换档工作点、发动机稳定性和辅助动力需求等主要集中在工程机械和农业机械方面。

ZF-部件

ZF公司在开发电力驱动方面已有超过15年的经验。在2008年5月ZF向奔驰公司S级轿车提供混合动力模块的批量化产品。该混合动力系统的电动马达是带单个线圈的永磁同步电机。其优点的无需水冷、耐用、高转矩和功率密度和高效率。

用于工程机械和农业机械的Hy-tronic的电机功率提高到85 kW,此外EColife的电机功率为120 kW;而且采用了较小的法兰直径(SAE2/3).持续功率依据电机尺寸不同在50 kW到70 kW之间。

2 Hybrid Systems at ZF

At ZF,various hybrid systems for commercial vehicles are in production development.These include amongst others,the EcoLife-Hybrid for city buses and the Hy-Tronic for trucks.The electric machines,used on these tw o systems have a power of 120 and 60 kW respectively and offer the functionalities of a full-hybrid system[1].

The scope of supply of ZF includes not only the,in the transmission integrated,electric machine,but also all other necessary hybrid components ranging from the Li-Ion battery over to the power inverter and a hybrid control unit.The system can be furthermore equipped with a dc/dc con verter for onboard power supply to replace the alternator.The software on the hybrid control unit provided by ZF can include functions for component control,operative hybrid functions and strategic vehicle functions.

图1 各种用途的混合动力系统功能Fig.1 Functions of hybrid systems for different applications

产生旋转磁场和控制电机工作的功率逆变器采用弹簧接触型IGBT(绝缘栅场效应晶体管)和二极管以获得所需的耐用性和和高功率密度。经优化的动力电子设备用来控制电机工作和提供高效率。这是ZF公司专门为商用车辆开发的,并且结构坚固、使用寿命长。

混合动力蓄电池与大陆公司联合开发,特别针对商用车辆的高耐久性要求,该电池是水冷锂电池,带电池集成管理系统。电池设计模块化,因而能够组成两个不同能量的电池尺寸。

图2所示的部件构成了一个并联式混合动力系统的基础,也适用于各种机动车。特别是那需要工作在高车速和高牵引力(例如商用车辆或装载机、物料输送机)的混合型动力传动系统,该系统的布局优点明显。同时,这些部件还能应用于一系列的混合动力系统,例如回转驱动式挖掘机或小型叉车等。

图2 ZF开发的并联式混合动力产品Fig.2 ZF-Components in parallel hybrid architecture

ZF-系统功能

图3是未来机动车动力传动系统概念中最重要的需求。电力混合动力能够满足每项需求。

特殊需求的辅助设备,例如发动机停机时的空调压缩机,对机动车而言是非常重要的。采用电力混合动力后发动机的启动可很方便地通过电机实现。

图4显示了当辅助动力为5 kW电动机、车辆处于静止状态时内燃机的间隙工作状况。这里,辅助动力由蓄电池供电,一旦SOC(储电量状态)过低则继续充电。随后,内燃机必须工作一小段时间用于向蓄电池充电。在短时充电期间如果伴随高负载,内燃机将在燃油消耗率较低的点上工作。这样可平均节省22%的油耗。静止状态时性能规格越低,节能潜力越高。由于储存在蓄电池中的能量可在较长的时间内向辅助动力供能,因此内燃机的起动频率降低。根据文献[2],在一辆轮式装载机的负载周期内,怠速工况可达14%。

Figure 1 shows an overview over theimportant hybrid functions out of the ZF modular software system for different production projects for passenger cars and commercial vehicles.This includes typical hybrid functions like stop/start of the engine,recovery of brake energy,shift of engine operating point,electric driving and a hybrid strategy for a power management between combustion engine and electric machine.

This modular system of hardware-and software components serves as a basis for the hybrid system for mobile machinery.Additional functions like shift of operation point for improved exhaust emissions,stabilization of the engine and power on demand operation of vehicle auxiliaries are developed focussing on the requirements of construction and agricultural machinery.

ZF-Components

ZF has experience with the development of electric drives for over 15 years.In May 2008 the ZF production facility for hybrid modules for supply of the Mercedes S-class hybrid was opened.The electricmachines used in the hybrid systems are of permanent magnet synchronous type with single coils.These excel through their no-wear behaviour,robustness,high torque and powerdensity and through their high efficiencies.

The power of the electric machine from the Hy-tronic was increased to 85 kW for use in construction and agricultural machinery,thus represents,besides the bigger electric machine from the EColife with 120 kW,a powerful variant for smaller flange diameters(SAE2/3).The permanent power depends on the size of the electric machine and amounts to either 50 kW or 70 kW.

The power inverter employed to produce the rotating magnetic field and to control the electric machine is build up with spring contacted IGBT's(insulated gate bipolar transistor)and diodes in order to achieve the required durability and has a high power density.The power electronics are optimised for the control of the electricmachine and offer a high efficiency.It was developed by ZF specifically for the mechanical and electric requirements of commercial vehicles and thus features a rugged construction and high durability.

图3 需求和功能Fig.3 Requirements and functions

图4 带起停系统和不带起停系统的对比Fig.4 Comparison of a system with and without stop/start

The hybrid battery was developed together with Continental specifically for the high durability demands of commercial vehicles and is of water cooled Li-Ion type with integrated battery management system.The design of the battery is modular and can hence be built up in tw o different sizes with different energy contents.

The components depicted in Figure 2 form the basis for a parallel hybrid architecture,which is also favoured for most applications for mobile machinery.Specifically,for the hybridisation of the drivetrain,which requires operation at relatively high vehicle speeds and tractive efforts(e.g.commercial vehicles or wheel loader,material handling machinery,etc.),this system layout provides clear advantages.However,the available components can also beemployed for a serial hybrid system,for application in,e.g.an excavator swing drive or for small fork lifts.

在工程机械和农业机械在道路上行驶时,也就是在运输作业或进行稳定的重复工作循环并使用制动工况时,对制动能量的回收有兴趣。这些被回收的能量能够储存在蓄电池中用来驱动辅助动力装置或通过电动机辅助内燃机驱动车辆。这附加的动力能够提升总工作性能。而且总工作性能的提升还可通过电气化辅助装置的能量管理来实现。电气化辅助装置响应迅速,因而优于液压或机械辅助装置。当动力传动系统和液压工作系统需要的动力多于内燃机能够提供给辅助装置时,通过短时间关闭辅助装置,可使被动推进变成可能。

起停系统和内燃机稳定工作可使发动机怠速和瞬变工作状态时的排放降低。在图中,颗粒物的增加是由于转矩的突然增加所致。通过平稳增加内燃机转矩(稳定性)避免转矩突然增加,可消除颗粒物的峰值。混合型动力传动系统能够在动转矩阶段补偿发动机动态性能的降低和维持车辆动力特性。

除了有益于发动机稳定工作之外,内燃机工作点的切换也成为可能,因而影响颗粒物过滤器的再生性能(主动和被动)和利用所需的自由燃烧功率使颗粒物过滤器以一种积极的方式再生。

另一种降低油耗和减少排放的途径是通过缩小发动机尺寸以降低发动机功率。较小的内燃机所减少的功率由电动机补偿,推动功率来源于存储在蓄电池中的能量。这仅适用于那些短时全功率或经常处于低功率的场合。较小内燃机减少的成本可部分补偿混合系统所带来的较高成本。由于减少了排放废气后处理系统变得简单,这将有益于降低总成本。另外这些简化有益于整个废气后处理系统。

粗看的话,电力驱动对于工程机械兴趣不大。但是零排放在某些场合(货物搬运)尤为重要,特别是那些对排放严格限制或零排放的场所(港口、机场等)。部分电力驱动也可用于短距离机动、辅助驱动、回转(场地尽头)、建筑物内的短时工作等。

液力与电力混合驱动的对比

液力混合驱动能够覆盖高功率并且在加大推力时能够快速驱动传动系统。但是电力混合驱动的优势在于效率、总存储能量、能量存储长时间稳定性和系统动力性和可控性等。因此,发动机工作点的切换、发动机稳定工作和能量回收等能够被理想地利用。图6给出了20km/h车速时液力和电力系统能量回收和助力的差异。在制动能量回收的仿真中,液力混合驱动的效率为59%而电力混合驱动为73%。因此电力系统具有更高的助力特性。即便加上可忽略不计的牵引损失,电力混合系统由于能量回收和助力性能优越因而效率更高、燃油经济性更好。

ZF-System Functions

Figure 3 shows the most important requirements for future powertrain concepts for mobile machinery.Every one of these requirements can be covered by a function of an electric hybrid.

Specifically the supply of auxiliaries,like e.g.the climate(a/c-)compressor,during engine stop,has a high importance for mobile machinery.With electric hybrids a fast cranking of the engine can be carried out comfortably through the electric machine.

Figure 4 shows the intermittent operation of the internal combustion engine when the auxiliaries must be supplied with 5 kW electrical power during standstill.Here,the auxiliaries are fed from the battery until the lower SOC(state-of-charge)-is reached.Subsequently,the internal combustion engine must be operated again for a short period of time in order to charge the battery.During this short recharge period with high load,the operating point of the combustion engine can be raised to a point with lower specific fuel consumption.Doing this,an advantage of 22%can result in fuel consumption reduction.The lower the performance requirement is during standstill,the higher the reduction potential will be.The frequency of combustion engine starts decreases,because the energy stored in the battery can supply the auxiliaries for a longer time period.According to[2],the timeshare in idling lies at 14%for the load cycle of a wheel loader.

图5 转矩突变时颗粒物排放峰值(左图)和发动机稳定工作的颗粒物排放(右图)Fig.5 Particulate matter emission peak during sudden torque step(left)and principle of engine stabilization(right)

In roading conditions of construction and agricultural applications,i.e.during transport w ork or steadily recurring work cycles with braking opera-tions,the recovery of brake energy is interesting.Such recovered energy can be stored in the battery in order to operate the electrical auxiliaries or to support the combustion engine(boost)with the electric machine.An increase of overall performance can be achieved by this additional active boost.Furthermore,the overall performance can be increased by smart power management of the electrified auxiliaries.Electrified auxiliaries have an advantage over hydraulically or mechanically fixed ones in the ability to be operated on-demand.By switching the auxiliaries off for a short period of time,a so-called passive boost becomes possible,when drivetrain and working hydraulics need more power than the combustion engine could supply in auxiliary loaded condition.

图6 液力和电力系统效率对比Fig.6 Comparison of Efficiencies of the hydraulic and electric system

同样,电气化辅助装置额外的潜能也是液力混合系统所不具备的。理论上,起停功能也能在液力系统中实现。但是,当发动机停机时需要辅助装置(例如空调压缩机)工作时,液力系统很难以最优的方式实现,因为液力传动损失和液压蓄能器较低的长期储存性。而且在使用高动力性功能时(例如发动机稳定),不管最大功率是否较小,电力混合系统在转矩突然变化时在动力性和可控性方面具有优势。基于能够大幅度降低油耗和明显增强功能,ZF公司首先开展了电力曲轴起动机系统的研发。在建筑机械和农业机械领域,ZF公司预见到电力混合系统在中长期应用方面的明显优点。

混合系统在工程机械上的应用

电力混合系统在工程机械方面的应用见图7。请注意应用于动力传动系统的混合系统,ZF关注的是并联结构,这里电动机安装在发动机和变速器之间,向发动机提供附加动力(并联)或单独驱动。系统以两种方式构成。

1、作为完整系统的一部分,电动机被集成在变速器的壳体上(见图8)。

With the stop-start function and by stabilizing the combustion engine,exhaust emissions can be reduced during engine idle and transient operating conditions.In Figure 5,the increase of raw emissions of particulate matter can be seen,as caused by a sudden torque rise.Avoiding sudden torque steps by slowly guiding the combustion engine torque(stabilization),eliminates emission peaks of particulate matter.The hybrid drivetrain compensates for the reduced engine dynamics and keeps the overall vehicle dynamics unaffected during dynamic torque steps.

图7 工程机械用并联式混合系统Fig.7 Parallel hybrid system for construction machinery

图8 ZF ERGOPOWER混合动力系统Fig.8 ZF ERGOPOWER Hybrid

Besides the advantages of engine stabilization,a shift of the operating point of the combustion engine is also possible,thus influencing the regeneration behaviour(active and passive)of the particle filter and the required free-burning power to regenerate the particle filter in a positive way.

An additional approach to reduce fuel consumption and exhaust emissions is to reduce combustion engine power by downsizing the engine.The power reduction of such a smaller combustion engine will be compensated by the electric machine and boost pow er from stored energy in the battery.This is a specifically viable option in applications that need full engine power for only short periods of time or be operated in low load conditions frequently.The usage of smaller combustion engines reduces cost and partially compensates for the higher cost of a hybrid system.Due to reduction of emissions,exhaust gas after-treatment can be simplified,w hich will in turn again positively affect overall cost.Additionally these simplifications can lead to advantages in the packaging of complex exhaust gas after-treatment systems.

Electric driving appears to be less interesting for mobile construction machinery at first glance.

2、作为一个模块,电动机安装在自带的壳体上,与内燃机或变速器联接。

电动机(85或120 kW)通过功率逆变器和650V直流连接器与锂电池相连接。ZF公司的混合系统不仅包括硬件,也包括用于控制混合系统组件(起停系统、能量回收等重要功能)的软件和混合驱动策略软件(动力管理)。并联式混合系统具有多种应用场合,例如轮式装载机、集装箱起重机、伸缩臂叉车、升降式叉车、自卸货车和拖拉机等。

图8是一套混合系统,包括Ergopower变速器以及集成在混合驱动模块壳体上的电动机、分离轴承和位于液力变矩器(包括锁止离合器)前方的扭转减振器。这样布置非常紧凑。在可以利用变速器润滑油回路时,行星齿轮从电动机处获得更大动力或通过离合器切断内燃机是可行的。混合驱动模块也能和ZF公司的其它变速器相连接,例如最新开发的液力机械动力换档无级变速器cPOWER。

图9 开凿机混合驱动系统Fig.9 Hybrid system for excavators

图9是开凿机混合系统的设计图。系统由动力传动系统和工作液压系统组成的并联式混合驱动,为回转驱动提供连续的混合驱动。在这里,相同的混合驱动模块可被应用于上述提及的并联式混合系统,例如轮式装载机等。将混合驱动模块安装在内燃机和液压马达之间,并联式混合驱动的典型功能(例如起停、助力)可由液力马达和动力传动系统实现。安装在混合驱动模块中的电动机和逆变器也能用于回转作业。与锂电池相联后,回转运动的能量能够被回收和再次用于助力。图9是开凿机的混合驱动系统,可安装在轨道和轮式开凿机上。

However,the possibility of zero-emission operation can be of particular importance for some applications(material handling),particularly on sites with highly restricted emission limits or even zero-emission requirements(ports,airports or similar).Partial electric driving could also be useful e.g.over short distances,launch assist drive,turning around(field end),short-term operation in buildings,etc.

Comparison of hydraulic and electric hybrid

Hydraulic hybrids are able to recover high power and quickly supply it back into the drivetrain when boosting.However,electric hybrids have advantages over the hydraulic hybrids,such as efficiency,amount of storable energy,suitability for long-term storage as well as system dynamics and controllability.Therefore,functions like shift of engine operation point,stabilization and energy recovery can be utilized ideally.Figure 6 shows the recovery of energy and boosting from 20 km/h and the difference in efficiency between the hydraulic and electric system.In the simulation of this recovery of braking energy the hydraulic hybrid showed an efficiency of only 59%,whereas theelectric system showed an efficiency of 73%.Therefore more boosting energy is available in the electric system.This efficiency advantage of the electric hybrid system,together with the negligible drag losses of the electric hybrid,leads to significantly higher fuel consumption advantages for functions like energy recovery and boosting.

Also,the additional potentials through an electrification of auxiliaries and implements cannot be obtained with a hydraulic hybrid system.Theoretically,a stop-start function can be realized with a hybrid system as well.However,when the supply of auxiliaries(like an air conditioning compressor)is required during engine standstill,this can not be achieved in an optimal way with a hydraulic system,because of losses in the drives and the low-er long-term storability of a hydraulic accumulator.Furthermore,when using highly dynamic functions(e.g.stabilization)the electric hybrid system has advantages regarding dynamics and controllability during sudden torque step demands,despite the lower max.power capability.Based on the significant higher reduction of fuel consumption and because of significantly increased functional possibilities,ZF pursues simple electric crankshaft-starter systems with and without additional battery already in the first step.In all construction and agricultural applications ZF sees significant advantages for the electric hybrid system on a mid-and long-term basis.

Hybrid System for Construction Machinery

The layout of an electric hybrid system for construction machinery is show n in Figure 7.Looking at hybrid systems for the drivetrain,ZF focuses on the parallel architecture,in which the electric machine sits betw een combustion engine and transmission,supplying the power additional(parallel)to the combustion engine or alone by itself.This system can be implemented in two ways：

1. As an integrated layout,which means that the electric machine is integrated in the transmission housing(see Figure 8)

2. As a modular layout,which means that the electric machine is located in its own housing,being mounted either on the combustion engine or the transmission?

The electric machine(85 or 120 kW)is connected to the Li-Ion battery through a power inverter and a 650 V DC linkage.TheZF hybrid system comprises not only the hardware,but also the software for the control of the hybrid components(operative functions like stop-start,energy recovery,etc.)and the hybrid strategy software(power management).

This parallel hybrid system can be utilized in multiple applications,such as wheel loaders,reachstacker,tele-handler,forklift trucks,dump trucks and tractors.

Figure 8 show s the hybrid system with the Ergopower transmission in an integrated setup with a hybrid module housing the electric machine,individual rotor bearings and torsional vibration damper being situated in front of the hydraulic torque converter(including lock-up clutch).This layout is very compact.By possible usage of the transmission oil circuit,a simple enhancement with a planetary gearset to gain higher power from the electric machine or with a clutch to disconnect the combustion engine is feasible.The hybrid module can indeed also be w ell combined with different ZF transmission systems,like the newly developed hydrostatic mechanicalpowersplitCVT transmission cPOWER.

Figure 9 show s the layout of a hybrid system for excavators.The depicted system combines a parallel hybrid for the drivetrain and w orking hydraulics with a serial hybrid for the swing drive.In this layout the same hybrid module can be utilized like in the above mentioned parallel hybrid for e.g.wheel loaders.With the hybrid module being situated between combustion engine and pump drive,also typical functions of a parallel hybrid(i.e.stop-start,boost)can be realized for pump drive and drivetrain.The electric machines and inverters,which are installed in the hybrid module,can also be utilized for the electrified swing drive.Combined e.g.with the Li-Ion battery,the energy of the swing movement can be recovered and can be boosted back into the system.Figure 9 show s the excavator hybrid system,which can be installed in tracked and w heeled excavators.

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