一般来说，排量区区1.0L的3缸汽油发动机可能并不是气缸钝化技术“大展拳脚”的最佳舞台，但福特（Ford）却有意打破常规，计划在2018年推出一款应用气缸钝化技术的EcoBoost 3缸发动机。简单来说，气缸钝化技术可以让这款3缸发动机在特定负载条件下转为一款670cc的双缸发动机，预计该技术可将车辆的燃料经济性提升6%，并取得一定程度的减排效果。
福特表示，这款EcoBoost将成为世界首款采用气缸钝化技术的3缸发动机。与一些怀疑论者的看法不同，福特坚信气缸钝化技术完全可以满足3缸发动机的改进与NVH要求。
在气缸钝化技术的协助下，EcoBoost发动机可以在巡航或轻负载条件下进入双缸模式，从而优化车辆能效。福特声称，当环境发生变化时，EcoBoost可在14毫秒内重回3缸模式，具体时长则取决于节流阀的具体位置。
福特全球动力系统工程副总裁Bob Fascetti表示，气缸钝化版EcoBoost展示了汽油发动机技术的持续研发潜力。
之前，福特还曾与舍弗勒集团（Schaeffler Group）共同合作研发了一款可变排量系统。该系统经过专门设计，可利用油压激活一款特殊的气门摇臂，断开曲柄与一个气缸间的连接，最高转速可达4500转。福特的工程师透露，与EcoBlue柴油发动机采用的曲柄很类似，这款一件式曲柄模块也可以在气缸头位置腾出更多空间，用于新油路和阀门转换组件的设计安装。
此外，这款常规发动机还采用了新型双质量飞轮和减振离合盘，从而解决双气缸模式下的发动机振动问题。这种设计必不可少，否则发动机的振动将比较明显，特别是在低转速的情况下。福特的工程师表示，系统活动时的进气阀和排气阀均处于关闭状态，这可以将气体封在气缸内部，产生“弹簧效应”，从而协助保持气缸的受力平衡和内部温度，随时为重新激活做好准备。
除此之外，该系统还采用了新的发动机支架、传动轴、悬挂衬套、凸轮轴链，以及金属注塑成型工艺的气门摇臂。
2015年，福特在欧洲市场的新车销售中，有20%的车辆（具体来说，共有11款车型）采用了这款1.0L的3缸发动机。
目前，福特并未透露气缸钝化技术会给发动机增加多少成本，也未表明增加的成本是否会反映到最终用户的购车价格中。
A 1.0-L three-cylinder gasoline engine may not seem a likely candidate for cylinder deactivation, but Ford is doing just that with diminutive EcoBoost triple. Production is slated to begin by early 2018 with the technology—which turns the engine into a 670-cc twin under certain load conditions—expected to deliver up to a 6% fuel saving with associated CO2 emissions reduction.
Claimed as a “world first” for a triple, Ford believes its deactivation technology will meet refinement requirements and confound skeptics that such a system applied to a 3-cylinder engine would be unacceptable in NVH terms.
The EcoBoost effectively enters twin-cylinder operation in some cruise and light engine load conditions. Depending on throttle position it reverts to 3-cylinder operation when conditions change—in a claimed 14 ms.
According to Bob Fascetti, Vice President Global Powertrain Engineering, the development demonstrates the continuing potential of gasoline engine technology.
Ford worked with Schaeffler Group on the variable displacement system, which will operate up to 4500 rpm, using oil pressure to activate a special valve rocker to interrupt the connection between the camshaft and one cylinder. Ford engineers reveal that a single-piece camshaft module similar to that used for its EcoBlue diesel provides added space in the cylinder head for new oil channels and the valve switching components.
Further changes to the regular engine include the use of a new dual-mass flywheel and a vibration damping clutch disc to help counter engine oscillations set up in twin-cylinder mode that would otherwise manifest vibration, particularly at low revs. Intake and exhaust valves are closed when the system is active, trapping gases to provide a “spring effect” to help balance forces across all cylinders and to retain temperatures inside the cylinder to ensure fuel efficiency when reactivated, engineers report.
Also included in the system are new engine mounts, drive shafts and suspension bushes, a new camshaft chain and metal-injection-molded valve rockers.
About 20% of all Ford models sold in Europe during 2015 used the 1.0-L triple, which can be specified for 11 models sold there.
Ford gave no indication as to what the cylinder deactivation system will add to unit cost, nor how much, if any, of that would be passed to the end-user.
Author: Stuart Birch
Source: SAE Automotive Engineering Magazine
