重型汽车冷却系统设计中的协同仿真应用0.doc

Heavy Duty Truck Cooling System Design Using Co-Simulation重型汽车冷却系统设计中的协同仿真应用ABSTRACT摘要In order to meet the legislated emissions levels, future diesel engines will likely utilize cooled exhaust gas re-circulation (EGR) to reduce emissions. The addition of the EGR cooler to the conventional vehicle coolant system creates several challenges. Firstly, the engine cooling system flow and heat rejection requirements both increase as it is likely that some EGR will be required at the rated power condition. This adversely affects packaging and fuel economy. The system design is further complicated by the fact that the peak duty of the EGR cooler occurs at part load, low speed conditions, whereas the cooling system is traditionally designed to handle maximum heat duties at the rated power condition of the engine. To address the system design challenges, Ricardo have undertaken an analytical study to evaluate the performance of different cooling system strategies which incorporate EGR coolers. This was achieved by performing a co-simulation using commercially available 1-dimensional codes.为了符合法规的排放水平，未来的柴油发动机将有可能采用冷却时废气再循环(EGR)技术，以减少温室气体排放。增加的废气再循环(EGR)冷却器给常规汽车冷却系统也带来一定挑战。首先，由于增加的废气再循环(EGR)可能会导致发动机冷却系统的流量和散热的额定功率增大。这对发动机的包装和燃油经济性有非常不利的影响。由于废气再循环(EGR)冷却器的增加导致该系统设计更加复杂是个现实问题，特别是在部分负载和低转速条件下，而冷却系统通常被设计处理的是在额定功率情况下的最大热负荷时的发动机工况。为了解决系统设计的挑战，里卡多进行了大量的分析研究，以评估不同性能的冷却系统的策略，其中包括EGR冷却器。这是通过使用市面上一维协同仿真代码。INTRODUCTION引言The coolant system of current vehicles is already limited on performance due to package and styling constraints. Thus, any future incremental demands on the coolant system will need to be managed effectively so as to remain within these constraints. Further, the drive to increase fuel economy, particularly in the Class 7 & 8 trucks, requires reduced drag coefficients and frontal area. Since the cooling pack in the vehicle has a major influence on frontal area, it is important that the thermal management of the cooling requirements be given a high priority.由于包装和造型的限制，当前车辆冷却系统的性能已经非常有限。因此，未来在冷却液系统上的任何增量式改进都需要被有效地管理，以便满足这些限制和约束。此外，推动提高燃油经济性，特别是7和8类卡车，需要降低风阻系数和迎风面积。由于车辆中的冷却组件对迎风面积有重大影响，所以给与对散热管理高度重视是很有必要的。It is also anticipated that future diesel engines will make use of cooled EGR in order to meet the performance and emissions levels required. This places further demands on the cooling system that need to be managed appropriately. Traditionally, the heat rejected to cooling systems by the engine peak around the rated power condition of the engine, as illustrated in Figure 1. This plot also illustrates that the heat rejected by the engine at low speeds and loads is relatively small compared to the peak level. In fact, in most applications the cooling capacity on the coolant side is more than enough to cope with the demand.我们预计，未来柴油发动机使用EGR冷却，以满足性能的需要和排放水平的需求。这个冷却系统的进一步改进需要进行适当的管理。传统上，在发动机额定功率工况附近的发动机峰值时拒绝热冷却系统，如图1所示。这一点也体现了热拒绝了发动机在低速和负荷相对比较小时的峰值水平。事实上，在大多数应用中的冷却能力冷却一侧不仅仅是足以应付需要。Figure 1. Typical Truck Engine Heat Rejection To Coolant图1.典型的汽车发动散热冷却Figure 2. Example Of Truck Engine EGR Strategy (EGR Rate) Needed To Meet US Fed Transient Test图2.满足美国联邦瞬态试验需求的汽车发动机废气再循环策略(EGR)的范例A typical strategy for EGR for truck diesel engines, over the operating range of the engine, is shown in Figure 2.在发动机额定工作范围内的一个典型的卡车柴油发动机的废气再循环策略，如图2所示。From this it can be seen that the high levels of EGR occur at the part load and part speed conditions. Taking into account the total mass flow rate of exhaust gas and the exhaust gas temperature, the required heat rejection from the EGR can be calculated. Figure 3 shows a plot of EGR heat rejection for a truck engine.从这可以看出，在部分负荷和部分速度条件下产生高水平的废气再循环。考虑到排气气体的总质量流速和排气温度，所需的热量抑制从废气再循环可以计算出来。图3所示的是卡车发动机的废气再循环散热曲线。Figure 3. Typical Truck Engine EGR Heat Rejection.图3.典型的卡车发动机废气再循环散热曲线As a result of the difference in cooling requirements between the engine and the EGR cooler, it is important that the coolant system is designed such that both needs are meet whilst maintaining a minimum fuel consumption. Hence the water pump will now need to deliver coolant at a correct temperature and flow rate to the EGR cooler at low engine speed, without producing excess coolant flow rates and pressure rises at rated engine speed and to avoid boiling in the EGR cooler. Also, engine and passenger compartment warm up time is a concern for emissions and passenger comfort needs. Thus, the incorporation of the EGR cooler needs to minimize any penalty in cooling system.由于在发动机和EGR冷却器之间的不同冷却需求的缘故，同时以满足这两个需求的冷却系统的设计是非常重要的，同时还必须保证最小的燃油消耗。因此，在发动机低速时水泵需要提供恰当温度和流速的冷却水到EGR冷却器，在发动机额定转速情况下没有产生过大的冷却水流量和压力上升，避免在废气EGR冷却器里沸腾。此外，发动机和乘客舱预热时间是一个关系到发动机排放和乘客舒适度的需求。因此，把EGR冷却器对冷却系统的反馈尽量减少。Obviously, more complex controlled coolant systems can be designed to cope with these demands relatively easily. However, to derive a design that best meets the needs for fuel economy, emissions, passenger comfort and, also importantly, cost, a more detailed analysis of all the options available is necessary.很显然，用更复杂的冷却系统控制设计来应付这些需求相对比较容易。然而，为了获得最好的设计，为了获得最恰当的燃油经济性、排放、乘员的舒适性、以及更详细地成本，这都是最有必要的。Traditionally, these systems have, somewhat, been designed in isolation. That is, the coolant system designer has little understanding of the impact of the coolant system on engine performance and vice versa. Also, the controls engineer will implement strategies based on discussion with the systems engineers but will have little direct experience on how his function influences the overall systems performance. Thus, there is a need to look at all the implications on the coolant system design of a large truck engine due to the incorporation of cooled EGR.传统上，这些系统有时被孤立地设计。那是因为，冷却系统的工程师很少了解冷却系统对发动机性能的影响，反之亦然。此外，控制工程师在实施控制策略时是基于系统工程师的讨论结果的，但是很少有直接的经验了解该系统是如何影响整体系统性能的。因此，有必要仔细研究当一个大卡车发动机由于增加了冷却的废气再循环系统对汽车冷却系统的影响。In order to do this Ricardo have developed detailed models that could simulate the dynamic system interaction between engine, EGR and cooling system. This was achieved by performing a co-simulation using commercially available 1-dimensional codes for engine and EGR system (WAVE), thermal-fluid analysis (FLOWMASTER) and control system analysis (MATLAB Simulink). The intention of this analysis tool is to aid in the design of the coolant system as well as to help calibrate the vehicle controller.为了做到这一点，里卡多已经制作出详细的模型，可以模拟发动机，废气再循环及冷却系统的动态系统之间的相互作用。这是通过执行一个使用可用一维代码的发动机和废气再循环系统(WAVE)联合仿真，以及(FLOWMASTER)热流体分析和(MATLAB SIMULINK)控制系统分析。本文所说的分析工具可以帮助设计冷却系统，以及帮助校准车辆控制器。This paper details the development of the vehicle model co-simulation, its use to evaluate different cooling system options, and some observations on potential fuel economy savings. The work includes an investigation of active components including solenoid coolant valves and an electric water pump.本文详细介绍了汽车联合仿真模型的发展，评估其使用不同的冷却系统的效果，以及潜在的节省了燃油经济性上的一些建议。这项工作包括研究主动组件，并包括电磁冷却阀和电动水泵。CO-SIMULATION BACKGROUND仿真背景The term co-simulation is often used to describe various types of analysis and thus it is worth providing some discussion as to how it is used here. The simplest method of analysis is to derive a model in a single code that simulates a system or multiple systems. This has limitations due to the level of complexity needed and the fact that there are dedicated codes designed to model specific systems that are more effective. Very often the next step is to build more complex models in individual codes. The data transfer between these codes is conducted off-line (i.e. the output data from the first simulation is manually input into another simulation to run). This is useful since each model runs separately and thus quickly and a reasonable level of complexity can be simulated. However, to gain true transient capability and to increase the level of interaction between systems it is necessary to link these models dynamically. Co-simulation has been investigated for other applications and the benefits of it discussed in other publications 1.协同仿真这个术语是经常被用来描述不同类型的分析，因此把它用在这里需要值得讨论。最简单的方法是分析得出一个模拟了一个系统或多个系统的一个单一代码的模型。这有它的局限性，由于其复杂性的需要，事实上具体系统的专有代码设计模型会更有效果。通常下一步是建立更复杂的个别代码模型。这两者之间的代码数据传输采用离线方式(即从第一模拟的输出数据是手动输入到另一个模拟运行)。这是非常有用的，因为每个模型是分开运行，所以可以快速模拟出恰当的复杂程度。然而，为获得真正的瞬态性能和提高系统之间相互作用的水平，将这些模型的动态链接是非常有必要的。仿真研究了其他应用程序和讨论过的其他出版物的好处。True co-simulation, as conducted in this study, involves writing code to link the various sub-models, in different software codes, such that the sub-models solve together in parallel and communicate with each other at the required time-steps. In this study, three commercially available 1-dimensional codes are linked in this manner in order to create a complete model of engine performance (including gas dynamics), coolant system and control system.为进行这样研究，真正的联合仿真是在不同的软件代码间编写代码来连接各子模型，并在规定的时间步长内将子模型并联在一起，并相互沟通。在这个研究中，三个商用的一维代码以这种方式相互联系，以建立一个完整的发动机性能模型(包括气体动力学)，冷却系统和控制系统。Firstly, MATLAB Simulink is used to model the control of the coolant system. It is also used as the code that produces the links to the other software codes, manages the information flow between the sub-models, and controls the time-step of the simulation. The engine performance model, which includes the effects of gas dynamics in the engine and EGR system, is modeled using Ricardos commercially available software WAVE. In fact a link between MATLAB Simulink and WAVE has existed for some time, as it is often used to control the engine and run multiple WAVE simulations, and is included in the WAVE package as supplied. Finally, the coolant system is modeled using FLOWMASTER.首先，MATLAB Simulink是用于模拟冷却系统的控制。作为产生链接到其他软件代码的代码，它也可以用来管理子模型之间的信息流，并控制仿真的时间步长。发动机的性能模型是仿照里卡多的市售软件WAVE，其中包括了在发动机和废气再循环(EGR)系统的气体动力学影响。事实上，MATLAB Simulink和WAVE之间的联系已经存在一段时间了，因为它往往是用来控制发动机和运行多个WAVE仿真，并包含它所提供的WAVE组件。最后，冷却系统的建模使用FLOWMASTER。Figure 4. Co-Simulation Architecture & Information Flow图4.协同仿真体系架构和信息流Figure 4. illustrates the co-simulation architecture and flow of information within the models. Currently,FLOWMASTER provides a link to MATLAB Simulink but this is only done by using FLOWMASTER as the information and link manager. Thus, in order for this study to proceed a link in the opposite direction was desired.图4说明了协同仿真体系架构和信息流的模型。目前，FLOWMASTER提供了一个链接到MATLAB Simulink，但是这仅仅是通过FLOWMASTER的信息和链接管理器。因此，继续向上链接的研究是有所必要的。MATLAB TO FLOWMASTER LINK - In conjunction with FLOWMASTER, Ricardo have developed a script in MATLAB Simulink that will initiate the FLOWMASTER solver module and provide communication to and from it. The co-simulation developed here uses DCOM software technology to communicate between the software platforms of MATLAB Simulink and FLOWMASTER. The co-simulation is controlled from Simulink, through an M-file S-function.MATLAB到FLOWMASTER的链接：结合FLOWMASTER，里卡多已经在MATLAB Simulink中开发以了一个脚本，这将启动FLOWMASTER求解器模块和提供与它的通信。这里开发的协同仿真软件使用的是MATLAB Simulink 和FLOWMASTER之间进行通信的软件平台DCOM软件技术。Simulink协同仿真控制是通过一个M文件的S函数实现的。Traditionally, an S-Function is used to describe some sort of dynamic system, i.e. a system that has inputs, outputs, and states. It may contain integrators, derivatives and other equations that are used to compute the states and outputs of the system. Therefore Simulink treats the S-Function as a transfer function, such that it gives the transfer function an input, and follows the required directions (denoted by the script in the S-Function) to receive an output. The rest of the simulation subsequently acts on this output. In the case of this co-simulation, the S-function structure is actually used to handle the exchange of information with a client program (here FLOWMASTER). The client program handles the integration and other computations required to advance its simulation. The S-Function therefore still uses inputs, outputs and states, although Simulink only monitors the states, which represent a small subset of possible model states that FLOWMASTER utilizes.传统上，S函数是用来描述某种动态系统，即系统的输入、输出和状态。它可能包含了被用来计算该系统的状态和输出的其他方程和其导数的集合。因此，Simulink把S函数当作传递函数，这样，它给出传递函数的输入，并如所要求的方向(以S函数的脚本表示)接收输出。其余部分的仿真随后在此处输出。在协同仿真的情况下，S函数的的结构实际上是用于处理与客户端程序(此处FLOWMASTER)的信息交流。客户端程序处理的一体化和其他计算所需的先进仿真。S函数仍然使用Simulink的输入、输出和状态，虽然Simulink只是监测状态，其中一小部分的模型仍然采用FLOWMASTER。SAMPLE TIMES - The co-simulation operates by synchronizing the two simulations, and for proper synchronization needs to have FLOWMASTER running at a faster (or equal) rate that is an integer multiple of the rate of the S-Function execution. For example, if FLOWMASTER executes at 0.2 sec, the S-Function needs to execute at 0.4 sec, 0.6 sec, 1.0 sec, etc.采样时间：协同仿真通过同步的两个模拟操作，为了能正确的同步，需要由FLOWMASTER以更快的(或等于)一个整数倍速率运行S函数。例如，如果FLOWMASTER的执行时间在0.2秒，S函数需要执行在0.4秒，0.6秒，1.0秒等等。For this reason, sample times of all blocks in the Simulink system should be an integer multiple of the system sample time specified in the Simulation/Parameter dialog box. The current configuration of the co-simulation S-Function inherits the fastest sample time of the entire Simulink system. Thus, if all blocks have integer sample times, then the co-simulation should inherit the fastest time from the dialog box.由于这个原因，在Simulink系统中所有模拟/参数模块的采样时间是对话框中指定的系统采样时间的整数倍。协同仿真S函数的当前配制继承了Simulink整个系统的最快采样时间。因此，如果所有的模块采用整数倍的采样时间，然后协同仿真应该从对话框中继承最快的时间。For the co-simulation and control system development, FLOWMASTER was set to run at 0.1 sec and Simulink at 1.0 sec (inherited from Simulation Parameters). This gives reasonable results for the long (1000 seconds) test files.对于协同仿真和控制系统开发，FLOWMASTER设置为在0.1秒内运行，Simulink设置在1.0秒(从模拟参数继承)内运行。对于长期(1000秒)的测试文件，这是合理的结果。CO-SIMULATION MODEL仿真模型SIMULATION CONTROL & COMMUNICATION As discussed earlier, the control of the simulation and communication between the system models is conducted by blocks within Simulink. The primary function of these blocks is to transport data from one system model, whether in Simulink or the other codes, to another. This data falls into two distinct types, control data and physical data. The flow of information communicated can be seen in Figure 4.模拟控制和通信：正如前面所讨论的，仿真的控制和系统模型之间的通信全部在Simulink模块中进行。这些模块的主要功能是从一个系统模型传输数据到另外一个，无论是在Simulink或其他代码。此数据分为两个不同的类型，分别是控制数据和物理数据。从图4可以看出信息流的传递过程。Control data is that used by the control system whether in actuation or feedback from a sensor. This data will be transmitted to the electronic control module in the real-world application. The flow of this type of data is only to and from the control system and only one of the other models, the engine or coolant system, has knowledge of this data.控制数据是由控制系统使用，无论来自于传感器的动作或反馈。在实际应用中，这些数据将被发送到电子控制模块。这种类型的数据流只是来自于控制系统，或只有一个发动机或冷却系统数据积累的其他车型。The physical data is purely required for the modeling purposes. This data describes the interaction between the engine and coolant system. This data is primarily related to the heat rejection to coolant within the engine and the EGR cooler. Strictly speaking the pump speed in the mechanical pump circuits is also physical data but as the control system looks after the pump speed in the other two circuits it was decided to do so in all instances. In Figure 4 this data is represented as passing through the dotted Simulink interface.获取物理数据是建模目的的最直接的需求。此数据描述了发动机和冷却剂系统之间的相互作用。此数据主要涉及在发动机内冷却液的热抑制和EGR冷却器。严格的来说，在机械泵电路中的泵的速度也是物理数据，但作为控制系统来看在其他两个电路后泵的转速，在所有情况下都会这样决定。Figure 5. Engine Model Layout图5.发动机模型布局ENGINE MODEL - The model of the engine includes definition of the intake and exhaust manifolds, including the EGR system, and allows for control of various engine parameters such as EGR rate, engine speed, fueling etc.发动机型号-发动机模型包括定义的进气和排气歧管，包括废气再循环系统，并允许控制各种发动机参数，如废气再循环率，发动机转速，燃油等。发动机型号：发动机型号包括进排气歧管的定义，包括废气再循环(EGR)系统，并允许用于控制发动机的各种参数，如EGR效率、发动机转速、燃料体积等。A representation of the engine layout is included in Figure 5. The engine performance model is executed on a crank angle basis and results are output as cycle averaged values after each completed cycle. This level of fidelity is required for accurate performance analysis. Obviously, to run the rest of the model at this time-step would mean that a high level of processing power is needed. For this reason, data is passed to MATLAB Simulink intermittently on a much more realistic time-step.图5所示是其中一种发动机布局型式。发动机的性能模型是在曲轴转角的基础上运行的，输出的结果是每完成一个周期后的周期平均值。这个水平的精确度需要精确的性能分析。很显然，在这个时间步长内运行其余的模型，这将意味着需要更高的处理能力水平。处于这个原因，数据在一个更为实际的时间步长内间隙性地传递到MATLAB Simulink。COOLANT SYSTEM MODEL This study will investigate four possible concepts for the design of a coolant system, as illustrated in Figurse 6a to 6d. They illustrate a progression from a simple mechanical system which is cheap, tried and tested, up to a more complex electrically controlled system. Obviously, the choice of system is best considered on a case by case basis.冷却液系统模型：本研究将探讨冷却系统的四个可能的设计概念，如图6a至图6d所示。它们展示了从一个最廉价最简单的机械系统，经过尝试和测试以后，最后形成一个复杂的电控系统的发展历程。显然，系统的选择最好是考虑在某个案例的基础上进行。Figure 6a. Simple Coolant Circuit图6a.简单的冷却液回路In the simple coolant circuit, Figure 6a, the EGR cooler is connected in parallel to the engine. The outlet from the pump is split into two, analogous with an outlet from the cylinder block adjacent to the pump or directly from the pump scroll casing. The coolant that passes through the EGR cooler is fed back to the engine just before the mechanical thermostat. This ensures that the maximum pressure drop across the cooler can be achieved.如图6a所示，在简单的冷却液回路中，EGR冷却器是被关联链接到发动机上。从泵的出口被分为两个，类似与从汽缸体相邻的泵，或直接从滚动泵壳体的出口。通过EGR冷却器的冷却剂被反馈到发动机的机械式自动调温器。这将确保通过冷却器的最大压力的压降可以得到实现。Figure 6b. Single Control Valve Coolant Circuit图6单一控制阀冷剂回路The coolant flow rate through the EGR cooler is governed by the total flow rate and the respective flow resistances in the engine and cooler circuit.通过EGR冷却器中的冷却液的流速是由总流速和在发动机及冷却器回路中的各自的流动阻力确定的。In the second coolant circuit a solenoid activated control valve (EV) is fitted to the cooler circuit, while the rest of the circuit remains the same. The addition of the control valve allows for some variation in the restriction through the cooler leg of the system and thus will help regulate flow through it.在