软件更新如何解决柴油排放问题?

软件更新如何解决柴油排放问题?

3年后“Dieselgate”的后遗症还在隆隆作响,最近逮捕了施泰德的首席执行官奥迪和德国当局迫使戴姆勒召回成千上万的汽车软件更新,我想我们还没有看到或听到Dieselgate最后的麻烦。奥迪的rupert stadler但是,一个简单的软件更新是如何解决这些问题的呢?如果真的那么简单,为什么制造商一开始要作弊呢?要理解这一点,我们必须看看柴油发动机的性能和排放。柴油发动机的工作原理是压缩点火燃料,不像传统的汽油发动机使用火花塞点燃空气-燃料混合物。在现代柴油发动机中,当发动机对进气进行加压和加热时,柴油在非常高的压力下以超精密的方式注入燃烧室。燃料在气缸中点燃,由于燃烧时的高压和高温,它燃烧得非常有效,发动机可以捕获更多产生的能量。这种高温高压燃烧使柴油发动机具有很高的热效率,这反过来意味着每加仑(l/100公里)燃油消耗更好,二氧化碳含量更低2排放。使燃料完全燃烧。典型柴油机燃油系统示意图到目前为止,情况还不错,但正是这种高温高压燃烧导致了NOx和细颗粒物在发动机尾气中形成。所以柴油的优势从效率的角度来看也是它的弱点从污染的角度来看,通过共轨高压柴油喷射系统和高压涡轮增压,我们在创造非常高效的高温高压燃烧方面做得越来越好,这导致了氮氧化物和颗粒物的生产问题。(注意:这也是高效汽油直接点火发动机GDI, HCCI系统的问题)为了控制有害氮氧化物和PM的形成,采用了各种技术。降低燃烧温度和压力的技术可以控制发动机内部的产量,但会降低基本燃烧性能,从而降低柴油发动机的效率。这包括使用废气再循环,EGR和改变燃油喷射到发动机相对于压缩的时间。EGR的工作原理是将废气从排气流中抽出,冷却后再将其放回发动机的进气口。这实际上是在减少发动机进气中的氧气含量降低燃烧温度。这有助于减少氮氧化物,但对燃料消耗有负面影响。所以EGR的使用需要仔细管理,以达到发动机良好的燃油效率。 The amount of EGR is controlled by a valve that is operated by the engine management system and controlled by the management software depending on the operating conditions of the engine. Adjusting the timing of the fuel injection into the engine can also reduce NOx and PM formation but again this has a negative impact on fuel consumption so there is a balance to try and maintain the best fuel efficiency but minimise the formation of PM and NOx. The injection system is operated by the engine management system controlling the point and duration of the fuel injected into the engine under all different engine operating conditions. Finally, there is after treatment for the diesel exhaust. After treatment systems for diesel engines take the exhaust gas and treat it to remove harmful NOx and PM. A typical exhaust after-treatment system will consist of a particulate filter to remove most of the particulates and then either a Selective Catalytic Reactor (SCR) or a Lean NOx trap (LNT) to remove NOx. Selective Catalytic Reaction or SCR involves spraying a fine mist of ammonia solution (marketed as AdBlue) into the exhaust system. The ammonia reacts with the exhaust gas to reduce the NOx content in the exhaust. SCR can be very effective but requires the right conditions to work, principally the exhaust gas needs to be hot enough for the reaction to take place. NOx traps (LNT) were favoured by some vehicle manufacturers over SCR because the SCR systems were relatively more expensive and require an additional fluid (AdBlue) to be stored on the vehicle and consumed in use. In an LNT the NOx is stored in what is basically a chemical filter in the exhaust system and then reduced during a regeneration cycle where the NOx is converted to less harmful compounds. Once the LNT is “full” it stops absorbing NOx so it must then be regenerated. This regeneration process uses fuel and has a negative impact on fuel efficiency. It was this LNT regeneration that has been the main cause of trouble in the industry. OEM’s were allowing the LNT to remain full and therefore inoperative in order to minimise fuel consumption. So many of the software updates done are to simply increase the frequency of the LNT regeneration, and also increase the use of EGR and injection timing controls to ensure NOx stays within limits. This has the impact of increasing fuel consumption and also reducing the performance of the vehicle.氮氧化物的陷阱当发动机达到其工作温度并且排气温度在右侧范围内,SCR系统具有高转换效率非常有效。当发动机不在正确的SCR工作的正常工作温度范围内时,发动机管理系统将利用EGR和喷射时间来减少燃烧中的NOx生产。但这具有降低燃料效率的负面影响。在某些情况下,即使在带有SCR制造商的车辆上也被发现减少了EGR和注射定时控制的功能,当车辆不在排放测试时,这意味着当发动机冷却时,排放会增加排放量。Because of the cost of the SCR systems themselves and also the operating cost from the use of AdBlue, OEM’s have been incentivised to minimise the size of the SCR systems and their use to the emissions testing driving cycles which are very lightly loaded when compared to real-world driving, this has resulted in SCR systems that are undersized and result in a test pass but are significantly undersized to deliver real-world results. The old testing regimes for passenger vehicles were also conducted against a very controlled driving cycle (NEDC etc.), basically, no one actually drives like this cycle in real life, someone once commented to me that you would probably fail your driving test for driving so gently on the road! Unlike heavy-duty engines where a wide range of operating points including very heavily loaded portions of the engines operating cycle were covered in the emissions testing cycles. Using these lightly loaded driving cycles it was possible to highly optimise the performance of the vehicle in this very narrow operating band meaning that whilst the vehicle passed the tests it never came close to achieving the standards under real-world driving, note that whilst this is clearly not in the spirit of the emissions legislation this is considered to not be illegal and vehicles with such highly optimised emissions and wide variance between as tested and real world are not subject to the various recalls. The term “Defeat device” is being used to describe software control that reduces LNT regeneration frequency and reduces EGR and injection timing intervention when the vehicle is not specifically on the emissions test cycle there is no physical piece of hardware in the system. The “Defeat device” software in the engine control unit recognised when the vehicle was following the emissions driving cycle test pattern and allowed higher LNT regeneration, EGR operation and injection timing controls ensuring the emissions test was passed but then reverting back to a lower level of performance when the vehicle was in normal use. All diesel cars currently on the market do not achieve Euro 6 RDE and there are significant challenges to make this happen whilst still maintaining acceptable fuel consumption and CO2排放。这导致了许多技术的部署,包括:
  • 使用更大的可控硅系统,更宽的温度操作范围
  • EGR系统的再开发/部署,一些制造商删除了这些系统,只依赖后处理系统。
  • 更先进的发动机热管理策略的实施,以减少发动机预热和保持更一致的工作温度,如
    • 拆分缸体/缸盖冷却循环,允许单独控制冷却液在发动机缸体和缸盖的流动
    • 电子驱动和控制的恒温阀
    • 电动变速发动机冷却泵
  • 使用轻度和全混合动力系统可以减少发动机负载,并在发动机运行区域提供扭矩填充,还可以改善驾驶性能,以抵消各种排放控制策略的使用。
总之,各制造商正在进行软件更新,以移除“失败装置”,以增加LNT再生,更好地利用EGR和喷射定时控制来控制排放。这对使车辆符合排放法规有积极的影响,这意味着测试性能在没有专门运行排放测试时保持。但是,这将对车辆在正常运行时的燃油效率和性能产生负面影响。此外,这仍然是在排放测试制度的极轻负载条件下进行的,这意味着仍有可能有很大一部分发动机操作窗口明显超过排放限制。在旧的轻负荷测试和新的实际世界驾驶中,实现排放性能有很大的差距,这导致了一系列技术的部署,包括在汽车驱动系统和混合动力系统中使用更多的电气化组件。了解更多有关AVID如何帮助您开发电动动力系统和零部件滚球体育app最新版供应的信息今天联系我们滚球体育app最新版AVID Learning Electric Vehicle Technology播客封面艺术

额外的信息

想要了解更多电动汽车技术,请下载并收听流行的“AVID Learning: EV technology”播客。滚球体育app最新版iTunes 钉箱机 Spotify Youtube参考资料及进一步阅读:https://onlinelibrary.wiley.com/doi/pdf/10.1111/misp.12060 https://www.dieselnet.com/tech/cat_nox-trap.php https://www.theicct.org/sites/default/files/publications/ICCT_Euro6-VI_briefing_jun2016.pdf

关于作者

瑞安·莫恩

瑞安·莫恩

AVID Technology Group Ltd.董事总滚球体育app最新版经理。滚球体育app最新版AVID总部位于英格兰东北部,是重型高性能汽车电气化动力系统设计和制造的领导者。