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1、Drive force control of a parallel-series hybrid systemAbstractSince each component of a hybrid system has its own limit of performance, the vehicle power depends on the weakest component. So it is necessary to design the balance of the components. The vehicle must be controlled to operate within the
2、 performance range of all the components. We designed the specifications of each component backward from the required drive force. In this paper we describe a control method for the motor torque to avoid damage to the battery, when the battery is at a low state of charge. Society of Automotive Engin
3、eers of Japan, Inc. and Elsevier Science B.V. All rights reserved.1. IntroductionIn recent years, vehicles with internal combustion engines have increasingly played an important role as a means of transportation, and are contributing much to the development of society. However, vehicle emissions con
4、tribute to air pollution and possibly even global warming, which require effective countermeasures. Various developments are being made to reduce these emissions, but no further large improvements can be expected from merely improving the current engines and transmissions. Thus, great expectations a
5、re being placed on the development of electric, hybrid and natural gas-driven vehicles. Judging from currently applicable technologies, and the currently installed infrastructure of gasoline stations, inspection and service facilities, the hybrid vehicle, driven by the combination of gasoline engine
6、 and electric motor, is considered to be one of the most realistic solutions. Generally speaking, hybrid systems are classified as series or parallel systems. At Toyota, we have developed the Toyota Hybrid System (hereinafter referred to as the THS) by combining the advantages of both systems. In th
7、is sense the THS could be classified as a parallel-series type of system. Since the THS constantly optimizes engine operation, emissions are cleaner and better fuel economy can be achieved. During braking, Kinetic energy is recovered by the motor, thereby reducing fuel consumption and subsequent CO2
8、 emissions. Emissions and fuel economy are greatly improved by using the THS for the power train system. However, the THS incorporates engine, motor, battery and other components, each of which has its own particular capability. In other words, the driving force must be generated within the limits o
9、f each respective component. In particular, since the battery output varies greatly depending on its level of charge, the driving force has to be controlled with this in mind.This report clarifies the performance required of the respective THS components based on the driving force necessary for a ve
10、hicle. The method of controlling the driving force, both when the battery has high and low charge, is also described.2. Toyota hybrid system (THS) 1,2As Fig. 1 shows, the THS is made up of a hybrid transmission, engine and battery.2.1. Hybrid transmissionThe transmission consists of motor, generator
11、, power split device and reduction gear. The power split device is a planetary gear. Sun gear, ring gear and planetary carrier are directly connected to generator, motor and engine, respectively. The ring gear is also connected to the reduction gear. Thus, engine power is split into the generator an
12、d the driving wheels. With this type of mechanism, the revolutions of each of the respective axes are related as follows. Here, the gear ratio between the sun gear and theFig. 1. Schematic of Toyota hybrid system (THS).ring gear is :where Ne is the engine speed, Ng the generator speed and Nm the mot
13、or speed. Torque transferred to the motor and the generator axes from the engine is obtained as follows: where Te is the engine torque.The drive shaft is connected to the ring gear via a reduction gear. Consequently, motor speed and vehicle speed are proportional. If the reduction gear ratio is, the
14、 axle torque is obtained as follows: where Tm is the motor torque.As shown above, the axle torque is proportional to the total torque of the engine and the motor on the motor axis. Accordingly, we will refer to motor axis torque instead of axle torque.2.2. EngineA gasoline engine having a displaceme
15、nt of 1.5 l specially designed for the THS is adopted 3. This engine has high expansion ratio cycle, variable valve timing system and other mechanisms in order to improve engine efficiency and realize cleaner emissions. In particular, a large reduction in friction is achieved by setting the maximum
16、speed at 4000 rpm (=Ne max).2.3. BatteryAs sealed nickel metal hydride battery is adopted. The advantages of this type of battery are high power density and long life. this battery achieves more than three times the power density of those developed for conventional electric vehicles 4.3. Required dr
17、iving force and performanceThe THS offers excellent fuel economy and emissions reduction. But it must have the ability to output enough driving force for a vehicle. This section discusses the running performance required of the vehicle and the essential items required of the respective components. R
18、oad conditions such as slopes, speed limits and the required speed to pass other vehicles determine the power performance required by the vehicle. Table 1 indicates the power performance needed in Japan.3.1. Planetary gear ratioThe planetary gear ratio () has almost no effect on fuel economy and/or
19、emissions. This is because the required engine power (i.e. engine condition) depends on vehicle speed, driving force and battery condition, and not on the planetary gear ratio. Conversely, it is largely limited by the degree of installability in the vehicle and manufacturing aspects, leaving little
20、room for design. In the currently developed THS, =0.385. 3.2. Maximum engine powerSince the battery cannot be used for cruising due to its limited power storage capacity, most driving is reliant on engine power only. Fig. 2 shows the power required by a vehicle equipped with the THS, based on its dr
21、iving resistance. Accordingly, the power that is required for cruising on a level road at 140 km/h or climbing a 5% slope at 105 km/h will be 32 kW. If the transmission loss is taken into account, the engine requires 40 kW (=Pe max) of power. The THS uses an engine with maximum power of 43 kW in ord
22、er to get good vehicle performance while maintaining good fuel economy.3.3. Maximum generator torqueAs described in Section 2, the maximum engine speed is 4000 rpm (=Ne max). To attain maximum torque at this speed, maximum engine torque is obtained as follows:From Eq. (3), the maximum torque on the
23、generator axis will be as follows:This is the torque at which the generator can operate without being driven to over speed. Actually, higher torque is required because of acceleration/deceleration of generator speed and dispersion of engine and/or generator torque. By adding 40% torque margin to the
24、 generator, the necessary torque is calculated as follows:3.4. Maximum motor torqueFrom Fig. 3, it can be seen that the motor axis needs to have a torque of 304 Nm to acquire the 30% slope climbing performance. This torque merely balances the vehicle on the slope. To obtain enough starting and accel
25、erating performance, it is necessary to have additional torque of about 70 Nm, or about 370 Nm in total.From Eq. (2), the transmitted torque from the engine is obtained as follows:Consequently, a motor torque of 300 Nm (=Tm max) is necessary.3.5. Maximum battery powerAs Fig. 2 shows, driving power o
26、f 49 kW is needed for climbing on a 5%slope at 130 km/h. Thus, the necessary battery power is obtained by subtracting the engine-generated power from this. As already discussed, if an engine having the minimum required power is installed, it can only provide 32 kW of power, so the required battery p
27、ower will be 17 kW. If the possible loss that occurs when the battery supplies power to the motor is taken into account, battery power of 20 kW will be needed. Thus, it is necessary to determine the battery capacity by targeting this output on an actual slope. Table 2 lists the required battery spec
28、ifications.Table 3 summarizes the specifications actually adopted by the THS and the requirements determined by the above discussion. The required items represent an example when minimum engine power is selected. In other words, if the engine is changed, each of the items have to be changed accordin
29、gly.4. Driving force controlThe THS requires controls not necessary for conventional or electric vehicles in order to control the engine, motor and generator cooperatively. Fig. 4 outlines the control system.Fig. 4. Control diagram of the THS.Inputs of control system are accelerator position, vehicl
30、e speed (motor speed), generator speed and available battery power. Outputs are the engine-required power, generator torque and motor torque.First, drive torque demanded by the driver (converted to the motor axis) is calculated from the accelerator position and the vehicle speed. The necessary drive
31、 power is calculated from this torque and the motor speed. Required power for the system is the total of the required drive power, the required power to charge the battery and the power loss in the system. If this total required power exceeds the prescribed value, it becomes required engine power. I
32、f it is below the prescribed value, the vehicle runs on the battery without using the engine power. Next, the most efficient engine speed for generating engine power is calculated; this is the engine target speed. The target speed for the generator is calculated using Eq. (1) with engine target spee
33、d and motor speed. The generator torque is determined by PID control. Engine torque can be calculated in reverse by using Eq. (3) and the torque transferred from the engine to the motor axis can be calculated from (2). The motor torque is obtained by subtracting this torque from the initially calcul
34、ated drive torque. Since it is not possible to produce a torque whereby the motor consumption power exceeds the total of the generator-generated power and the power supplied by the battery, it is necessary to control the motor power (torque) within this total power. Fig. 5 shows the control method.
35、The sum of the power form the generator and the available battery power become the power that can be used by the motor. The available motor torque can be obtained by dividing this combined power by the motor speed. When the motor speed is low, if the calculated motor torque exceeds the motor specifi
36、cation of torque the motor torque is determined by the specification. By controlling the motor torque requirement with this limited torque, the motor consumption power can be controlled to within the available power. If the available battery power is large enough, the available motor torque hardly l
37、imits the motor torque. Conversely, when the charge is low, the motor torque is frequently limited.Fig. 6 shows the respective maximum drive torque of the battery, the engine, and the engine plus the battery while running based on the controls above, when the THS has the components as specified in S
38、ection 3. 5. ConclusionsThis paper discussed the control of drive power in the Toyota Hybrid System. The following conclusions were obtained:l The performance required for each component can be determined by reversely calculating power performance required for a vehicle.l The available battery power
39、 varies according to its state of charge. However, by limiting the motor torque, the battery power can be controlled to within the batterys available power.混合动力系统驱动力的串并联控制摘要由于混合动力系统的每个部分都有自己的极限性能，所以汽车动力取决于最脆弱的哪一个组成部分。因此，有必要对各个部件进行平衡设计。因为车辆必须在所有部件的控制范围内从事经营活动，所以我们根据所要求的驱动力反过来进行各部件的设计。在本文中，我们描述一种扭矩控制方
40、法，以避免在低电量时损坏电池。日本B.V.科技公司的汽车工程协会保留所有版权。1. 简介近年来，内燃机车辆作为一种交通工具发挥了越来越重要的作用，为社会的发展做出了很多贡献。然而，车辆排放的废气使空气遭到污染，甚至使全球气候变暖，这就需要有效地对策去解决。在减少废气的排放方面正在取得各种各样的进展，但是，仅仅从提高引擎和传动装置已不再有很大希望得到改善。因此，发展电力、混合动力和天然气驱动的车辆是目前的最大期望。从当前使用的技术和汽油站检测服务设施，结合当前已安装的基础设施，以汽油发动机和电动机驱动的混合动力汽车是最现实的解决方案之一。总的来说，混合动力系统分为串联和并联系统。在丰田，我们通过
41、将这两个系统的优点结合起来，开发了丰田混合动力系统（以下简称THS）。在某种意义上THS可以称作串并联控制系统。由于丰田混合动力系统对发动机操作和排放的不断优化，因此可以取得更好的燃油经济性。在制动的过程中，动能被电动机重新回收，从而减少燃油消耗和随后的CO2排放量。通过使用丰田混合动力系统作为动力驱动系统，废弃的排放量和燃油经济性得到大大提高。然而，丰田混合动力系统采用了发动机、电动机、电池和其他组件，每个组件都有自己的特殊能力。换句话说，每个组件必须在自己的能力限制范围内生成驱动力。特别是由于电池的输出很大水平上取决于其充电量，因此要时刻铭记驱动力必须被限制。这份报告澄清了基于车辆必须的驱
42、动力对与丰田混合动力系统各组件的性能要求。驱动力在电池高低压时的控制方法也作了先关描述。2. 丰田混合动力系统如图.1所示，丰田混合动力系统由混合动力传动装置、发动机和电池组成。 2.1. 混合动力传动系统混合动力传动系统由发动机、发电机、动力分配装置和减速器组成。动力分配装置是一个行星齿轮机构。太阳轮、齿圈和行星架分别直接连接到发电机、电动机和发动机，齿圈也直接连接到减速器。因此，发动机的动力被分配到发电机和驱动轮。使用这种机械装置，各轴的转速有以下关系。在这里，太阳轮和齿圈之间的传动比是：这里，Ne是发动机的转速，Ng是发电机的转速，Nm是电动机的转速。Fig. 1. Schematic
43、of Toyota hybrid system (THS).传递到电动机的转矩和发电机从发动机获得的转矩如下：这里，Te是发动机的输出转矩。驱动轴通过减速器连接到齿圈，因此，车连行驶速度与电机转速成正比。如果减速器的减速比为，则驱动轴获得的扭矩如下式：这里Tm为电动机速出扭矩。如上式所示，驱动轴获得的扭矩与发动机和电动机轴上输出的总扭矩成正比。因此，我们会参考电动机轴输出扭矩而不是驱动轴上获得的扭矩。2.2. 发动机丰田混合动力系统采用专门设计的排量为1.5L的汽油发动机。为了提高发动机的效率、实现情节的排放，这台发动机采用了高膨胀率循环、可变相位配气系统以及其他机构。特别是实现了转速为400
44、0r/min（最高转速）时最大限度的减少了摩擦力。2.3电池电池是采用了密封镍金氢化物电池。这种电池的优点是功率密度高、寿命长。这种电池的功率密度可以达到3倍以上常规电动车开发的电池。3. 驱动力和性能要求丰田混合动力系统提供了有意的燃油经济性和废气排放，但是它必须还要具备足够的车辆动力输出要求。本节讨论车辆运动性能要求以及各组件的基本要求。汽车的动力性能由通过的道路条件（如斜坡）、车速限制、所需超车速度等来确定。表.1所示为在日本汽车行驶的动力性能要求。3.1. 行星排特性参数行星排特性参数对车辆燃油经济性或排量几乎没有影响。这是因为，车辆的行驶速度、驱动力和电池条件取决于所需发动机功率（即
45、发动机状态），而不是行星排特性参数。相反，他很大程度上受限制于车辆的总体布置预留的设计空间。目前在先进的丰田混合动力系统=0.385。3.2. 最大发动机功率由于电池存储容量的限制，其使用范围不能超出其限制范围。大部分驱动力是仅仅依靠发动机提供的能量。图.2所示基于本田混合动力系统的车辆行驶阻力对车辆动力的规格要求。相应地，车辆以140km/h的速度行驶在平整的公路上或以105km/h的速度在坡度为5%坡道上行驶所需要的功率为32kw。如果考虑传动系的损失在内，就需要发动机提供40kw的功率。为了在保持良好的燃油经济性的同时得到良好的车辆动力性能，丰田混合动力系统采用最大功率为43kw的发动机
46、。3.3. 发电机最大扭矩如第二节所述，发动机最高转速为4000r/min，要达到这一转速是的最大扭矩从发动机获得的最大扭矩如下：根据式（3），作用在发电机上的最大扭矩如下：这是在不超速行驶的情况下驱动发电机运转的扭矩。实际上需要跟大的扭矩，因为发电机的加速或加速以及发电机扭矩的分散。因此要增加40%的扭矩作用在发电机上，所需扭矩计算如下：3.4. 电动机输出最大扭矩从图.3中可以看出，为了获得30%的爬坡性能，电动机需要提供304Nm的扭矩。这个扭矩仅仅是为了平衡车辆的坡道阻力，要获得足够的启动和加速性能，需要额外提供70Nm的扭矩或提供总扭矩为370Nm。根据式（2），从发动机传输传输的扭
47、矩可以通过下面计算获得：因此，电动机必须能够提供300Nm的最大扭矩。3.5. 电池的最大功率如图.2所示，当车辆以130km/h的速度爬上坡度为5%的斜坡时需要提供49kw的功率。因此减去发动机提供的功率剩下的就是电池所要提供的功率。正如前面所述，如果安装了小功率的发动机，它仅能提供32kw的功率，剩下所需的17kw的功率需要由电池来供应。如果将可能发生的损失考虑在内的话，电池需要提供20kw的功率。因此，有必要针对实际的坡道通过能力来确定电池的供电能力要求。表.2列出了所需要的电池规格。表.3概括了在上述讨论的情况下实际采用的电池规格要求。所需的项目为实例时选择了最小的发动机功率，换句话说
48、，如果发动机做了更改则每个项目都要进行相应的更改。4. 驱动力控制为了控制发动机、电动机以及发电机之间的合作，丰田混合动力系统采用了常规汽车或电动汽车所不必拥有的控制系统。图.4列出了控制系统图。Fig. 4. Control diagram of the THS.加速踏板位置、车辆行驶速度（电动机转速）、发电机转速以及电池可用电量的相关参数均作为变量输入到控制系统。输出参数有所需发动机功率、发电机输入扭矩、电动机输出扭矩。首先，驱动力矩由驱动程序依据加速踏板位置和车辆行驶速度计算确定。所需要的驱动功率是通过当时的扭矩和电动机转速计算获得。系统系统所需的动力是所需驱动力、电池充电所需动力以及系统动力损失动力的和。如果所需的总功率超过预定值，它将成为所需的发动力功率。如果低于预定值，车辆依靠电池功能而无需使用发动机。其次，发动机最高性能转速下产生的能量是由计算得到，这时发动机的目标转速。目标速度是利用发动机的目标转速和电动机转速利用式（1）计算得到。发电机输入转矩由PID控制确定。发动机输出扭矩可由式（3）计算得到。电动机输出扭矩由最初计算的驱动力矩减去发动机输出扭矩得到。因为电动机产生扭矩所消耗的能量不可能超过依靠发电机和电池同时供应的能量，所
