启停系统在欧洲已非常成功，但着重于美国市场的研发团队仍致力于达到最佳燃油效率和舒适性。在消费者满意度评级方面，顺畅的再启动和对调频广播音量的影响也位列最大挑战之中。

启停系统在欧洲和日本的应用已十分普遍，但北美市场的接受度仍然有限。由于油价较低，4-10%的燃油节约量并非很有吸引力，并且启停系统的噪声较大，重启时有抖动现象，也影响了其推广。但随着法规的落实，以及系统越来越精密，这些情况可能会有所改变。

“系统使用率比2007-08年的预测值低很多，但随着燃油使用效率标准（CAFE）的制定，使用率应该会快速提升，”IHS汽车动力系统预测总监Devin Lindsay表示。“系统已经降低发动机运行的噪声和抖动感了，今后很多系统会设计一个按钮，驾驶员可以选择关闭这个功能。”

美国的汽车制造商正在努力为消费者提供更多选择。启停系统将成为通用汽车多款2016凯迪拉克车型的标配。客户知识普及和技术进步将成为影响启停系统发展的两个非常重要的因素。

“启停技术发展的最大难题就是进行客户知识普及，我们需要让客户了解系统的工作方式，这样他们才会更认可这种技术，”通用汽车启停系统全球工程主管Kathi Walker表示。“从设计的角度来说，保持整个汽车平台的快速、无缝的自动启动是非常有挑战性的。”

通用汽车使用了大陆公司（Continental Automotive Systems）的电压稳定系统，该系统配置了麦克斯威科技公司（Maxwell Technologies）的超级电容器，有助于稳定电流，并在启动器开始发动时保证广播和空调正常运行。此外，超级电容器也可以减轻发动机的振动，使重启更加顺畅，并且可以降低影响电池寿命的重复循环次数。

超级电容器也有助于通用汽车达到一系列低温环境的技术要求。相关部件配有等效串联电阻（ESR），因此车辆的冬季操作性能得以优化。

“在低温环境中，电池的ESR有所增高，因此启动器所需的启动功率低于正常重启操作的要求，” Maxwell高级产品营销经理Jens Keiser表示。“超级电容器的ESR在-40摄氏度以上的环境中都很稳定。”

不论在何种温度环境中，发动机启动时，电压通常会下降到4-6 V左右。一些对电压、电流有较高要求的系统会受此影响，比如娱乐信息节目系统，与其他数字装置不同，该系统的很多部件不能在3.3 V或1.8 V的低压环境中运行。

 “比较棘手的领域之一是音频系统，”意法半导体公司（STMicroelectronics）市场研发部的首席工程师Bill Cleaver表示。“音频系统的很多敏感模拟部件需要在5V的电压环境中操作，比如AM/FM调谐器和功率放大器，这些部件有固定阻坑，需要用高电压维持声级。如果音乐太响，音量会下降，除非功率系统中有增压支持装置。”

为了解决这些问题，通用公司将超级电容器装配到凯迪拉克系统中，有助于减小电池尺寸，并降低重量。

“车辆启动时，能量需求是很低的，但功率需求却非常高，所以必须增加电池尺寸，以便满足这些高功率要求，” Keiser表示。“通过添加超级电容器满足高功率要求，可以减小电池尺寸，并着重满足能量需求。超级电容器的功率密度约为常规铅酸蓄电池的六到十倍。”

最大的挑战来自主流的美国市场，也就是自动档的内燃机车型。我们需要确保在这种车型上系统可以顺畅地顺畅，并且要保证合理的成本。

“所有混合动力车都有控制元件，所以很容易实现系统顺畅运行，” 意法半导体公司汽车产品部（APG）MCU营销高级总监Roger Forchhammer表示。“但如果不是混合动力车，成本会剧增。”

许多电池制造商正在竭力实现稳健增长。在城市，车辆在行驶中重启发动机的情况，要求电池寿命更长，充电速度更快。据预计，在配有启停系统的车辆中，吸附式玻璃纤维隔板电池（AGM）和增强型富液式电池（EFB）技术的应用将稳健增长。

 “我们预计，到2020年，启停系统将覆盖40%的新车，江森自控（Johnson Controls Power Solutions）的高级市场技术策略师Craig Rigby表示。“主流汽车制造商纷纷表示要大力发展启停系统，并将其作为新的动力传动基本策略。我们已经开始努力扩大AGM和EFB电池的容量，以便满足日益增长的需求。”

作者：Terry Costlow

来源：SAE《汽车工程杂志》

翻译：SAE上海办公室

Can turning off the engine turn customers on?

Stop-start systems have seen success in Europe, but development teams focused on the U.S. market are still working to get the right combination of fuel efficiency and comfort. Smooth restarts and radio volume are among for biggest challenges for garnering desired customer satisfaction ratings.

Stop-start is common in Europe and Japan, but acceptance in North America has been limited. The 4-10% fuel savings hasn’t been a big lure given fairly low fuel prices and noticeable noise and shuddering during restarts. That may change as regulations take hold and systems become more sophisticated.

“Adoption has been much slower than people anticipated back in 2007-08, but it should go forward quicker because of the CAFE credits available,” said Devin Lindsay, Powertrain Forecasting Director at IHS Automotive. “Systems have reduced the feeling when the engine engages, and many will have a button that lets the driver turn the function off.”

U.S. carmakers are increasing their offerings. General Motors is making stop-start a standard feature on many 2016 Cadillac models. Customer education and technology are both critical factors in the future of the technology.

“The most challenging part of the stop-start technology is educating the customers so they understand how the system works and they become more accepting/comfortable with the technology,” said Kathi Walker, GM Global Engineering Lead for Stop/Start Systems. “From a design perspective, repeatability of quick and seamless auto starts across vehicle platforms is very challenging.”

GM uses Continental Automotive Systems’ voltage stabilization system, which employs Maxwell Technologies’ ultracapacitors. The ultracapacitor helps maintain current to keep radios and air conditioners running when the starter is cranking. It also lessens engine vibration to smooth out restarts while reducing repeated cycling that can shorten battery life.

The ultracapacitor also helps GM meet requirements in cold environments. These components have equivalent series resistance (ESR) capabilities that give them better winter performance.

“In cold temperatures, the battery ESR is increasing and therefore, cranking power for the starter is below what is required for a reliable restart,” said Jens Keiser, Senior Product Marketing Manager at Maxwell. “The ESR of ultracapacitors is stable until -40 degrees Celsius.”

Regardless of the temperature, voltage levels often fall to around 4-6 V when the engine is started. That can impact systems that have higher voltage and current requirements such as infotainment, where some components don’t have the low 3.3 or 1.8 V levels of many digital devices.

“One of the trickiest areas is the audio system,” said Bill Cleaver, Principal Engineer, Market Development at STMicroelectronics. “A lot of sensitive analog parts in the audio systems operate at 5V—things like the AM-FM tuner and power amps, which have a fixed impedance so they need higher voltages to maintain sound levels. If music is loud, volume will be reduced unless you have boost support built into the power system.”

Concerns like these prompted GM to include ultracapacitors in the Cadillac system. That helps reduce battery size and weight.

“The energy demand of a cranking event is very low, but the power demand is very high, therefore the battery has to be oversized to meet these high power requirements,” Keiser said. “By adding an ultracapacitor to address the high power requirements, the battery can be downsized and focus on the energy demands. Ultracapacitors have approximately six to 10 times the power density of the typical lead-acid battery.”

The challenges are greatest in the mainstream of the U.S. market: internal combustion engines with automatic transmissions. The systems needed to ensure that restarts occur smoothly are a fair cost-adder.

“Any hybrid vehicle has the controls, so it’s easy to keep everything running,” said Roger Forchhammer, Senior Manager, Automotive Product Group (APG) MCU Marketing at STMicroelectronics. “If it’s not a hybrid, there’s a significant cost bump.”

Some battery makers are ramping up for solid growth. Restarting engines during city driving will require longer lifetimes and quicker recharging. Absorbent glass mat and enhanced flooded battery technologies are expected to see solid growth in vehicles with stop-start.

We expect it to reach 40% of new vehicle production by 2020,” said Craig Rigby, Advanced Market & Technology Strategist at Johnson Controls Power Solutions. “All the major automakers have indicated the move to start-stop as the new baseline powertrain strategy. We have already committed to expanding the capacity for AGM and EFB batteries to meet the increasing demand.”

Author: Terry Costlow

Source: SAE Automotive Engineering Magazine