作为记者，每当有机会率先试驾一款仍在研发之中，可能世上绝无仅有的技术演示车时，我总是精神高度集中，而如果这一切又发生在英国北部海岸泥泞的乡村道路上，则又会给我的经历平添了更多风味。

正是在这样的环境之下，Torotrak公司向《汽车工程》杂志展示了公司旗下新款V-Charge增压器的无穷潜力。具体来说，V-Charge是一款由传统皮带轮驱动的CVT控制机械传动可变压强增压器，其压缩器转速不受发动机转速的限制。此外，这款增压器还经过专门设计，可提供低端扭矩并解决小型汽油发动机存在的涡轮滞后问题。

Torotrak公司选择采用一款1.0L福特福克斯（Ford Focus）作为技术演示平台（Torotrak正在与福特合作开展该项目），展示V-Charge增压器的非凡潜力。据了解，目前这款技术演示车正在欧洲各地进行路演。

Torotrak集团业务开发经理RichardDunne表示，为了满足欧VII排放标准的要求，多家公司均将目光转向了米勒循环发动机，V-Charge也顺应趋势采用了小型化设计。目前，英国巴斯大学正在进行相关独立测试。

Dunne解释说，要“无中生有”一直都是工程师面临的挑战之一。V-Charge增压器并不能减少常规1.0L发动机的燃耗，这并不是我们的首选计划。但相比同样常规的1.5L福特西格玛（Sigma）系统，V-Charge预计最高可节省12%的燃料消耗，并同时降低相当比例的CO2排放。

V-Charge增压器并不需要求助于48V轻混合动力技术，而是采用了一款现成的标准压缩器。Dunne表示，与e-boost系统不同，V-Charge系统可以实现持续增压。他说，“这并不复杂；这款可变压缩比牵引驱动器就是一款微缩版的CVT变速器，而我们CVT技术已经得到了大家的认可。”据了解，V-Charge系统的重量约为6公斤（13.2磅）。

试驾

在本次试驾中，这款手动福克斯演示车由本文作者驾驶控制，而Dunne则使用笔记本控制开关，从而直观地对比发动机在是否使用V-Charge系统时的性能差异。据了解，这款福克斯采用的涡轮增压器比标准EcoBoost单元略大，可提供110kW（147hp）的输出，比后者高18kW（24hp）。

经过试驾，V-Charge的性能在以下情况下体现最为明显：首个陡坡、十字路口的起步、三档下发动机转速降至1000转时的90°转弯等。发动机的低转速和高扭矩（相对）配合非常默契，一般不需要换到较低档位。

对于一款输出在92kW（123hp）的常规福特3缸发动机，其在1000转时的基线额定扭矩为100Nm（74 lb·ft），1400转时的基线额定扭矩为170Nm（125 lb·ft）。在使用V-Charge之后，以上两个数据可分别提升至145 N·m (106 lb·ft)和240 N·m (177 lb·ft)，输出水平与1.5L的4缸发动机相仿。这种增压器最合适重量在1289kg（2841lb）左右的C级或小型车。

Dunne解释道，由于V-Charge的变速比为10，因此可将转速在1100转的发动机提升至10,000转到100,000转之间。该系统经过专门设计，可在发动机的较大转速范围（怠速到2500转）内保持最高效率，具体可采用逐渐降低的方式避免过度增压。据了解，V-Charge系统可在400ms内完成增压。

此外，这款增压器的工作过程非常安静。Dunne表示，V-Charge的工作噪音比与同级别的罗茨式增压器小97%，因此可以轻松安装在发动机后方，无需专门采取降噪措施。

V-Charge增压器通过一款电动促动器调整增压比，而非液压控制，因此可以在最大程度上减少寄生损失。CVT系统选用了性能有保证的牵引液，不存在金属部件直接接触的情况。V-Charge的增压比范围为0.28至2.82:1。当没有增压需求时，车辆可将V-Charge的增压比可降至最低水平，并不需要断开离合器。

这款V-Charge采用了一款非标准涡轮，以提升发动机的最大功率输出，但Dunne并未透露涡轮供应商的名称。通过试驾我们可以感受到，如果不使用V-Charge，福克斯演示车在较高档位，发动机转速较低时明显动力较弱。

V-Charge增压器经过专门设计，可提供高达17kW（23hp）的持续功率容量。

据称，由于系统本身会增加发动机的负载（约100W），因此当采用V-Charge系统时，1.0L发动机的燃耗和排放均比采用V-Charge之前高2-5%，但1.5L发动机的燃耗和排放数据均降低12%左右。

成本与VGT可变截面涡轮增压器相仿

由于Torotrak公司本身并不是制造商，因此可能会将V-Charge技术出售或许可给一级供应商使用。公司首席技术官Doug Cross表示，V-Charge的成本与VGT相仿。

“在确定成本效益比时，我们必须把所有成本都考虑在内。”Cross告诉《汽车工程》，“当你把一项技术卖给厂商时，消费者最终需要买单的价格很可能比你当初的技术转让价格高一倍。”但由于V-Charge可以提高发动机性能，因此一些厂商可以选择用成本更低的3缸发动机替代4缸发动机，从而在不牺牲性能的情况下节约一些成本。

Cross认为，考虑到这些因素，事实上应用V-Charge增压器可能仅会少量增加成本，甚至还有可能为厂商节约成本。

Cross曾效力于雷诺和丰田的F1车队担任发动机设计经理，也是KERS开发供应专家公司Flybrid（目前为Torotrak的一部分）的联合创始人。

最近，福特宣布，公司计划在2018年为旗下1.0L 3缸发动机配备气缸钝化功能。Cross认为，V-Charge可为气缸钝化技术提供有力补充。

可兼容米勒循环发动机

过去，只要提到CVT技术，人们总是会担心系统中的牵引液在极端低温下的表现。Cross解释说，“我们已经通过大量研发工作，成功开发出了一种在零下30ºC时仍能保证泵送性能的牵引液产品。”

Cross表示，考虑到很多开发商都在进行米勒循环发动机（或类似产品）的研发，因此V-Charge一定要能够与这种技术兼容。

虽然过去V-Charge的“用武之地”主要是汽油发动机，但事实上这种增压器也同样适用于涡轮增压的柴油发动机，可在油门踩到底时克服瞬时载荷步带来的负面影响。

为了满足驾驶员的需求，厂商一般会减少对EGR（尾气循环系统）的使用，从而导致车辆的NOx排放激增，或者通过额外给油推动涡轮的旋转，从而造成燃料燃烧不充分而带来的尾气排放。

“因此，这就是在颗粒物和氮氧化物的排放之间进行权衡，”Cross表示，“对于柴油发动机来说，车辆大约40%的NOx排放均源自瞬间给油活动。但如果采用持续运行的V-Charge增压器，系统可通过调整增压比，轻松提供额外的增压。这并不会影响对EGR系统的应用，而且无需增加燃料用量。”

截至目前，Torotrak尚未完成V-Charge系统在柴油发动机中的测试。但Cross相信，V-Charge一定可以有效解决柴油发动机的NOx排放激增问题。

Being the first journalist to test drive the only example of a new piece of technology still in development always concentrates the mind. Doing so in wet and windy weather battering rural roads close to England’s North Sea coast, brings an added dimension to the experience.

But that was how Torotrak demonstrated to Automotive Engineering the potential of its new, CVT-controlled V-Charge pressure charger—a mechanical, gearless, fully variable pressure charger driven by a conventional pulley. It allows compressor speed to vary independent of engine speed. It's designed to provide low-end torque and tackle the effects of turbo-lag on downsized gasoline engines.

Fitted to a 1.0-L Ford Focus as a technology demonstrator (Torotrak is partnering with Ford on this project), it is currently being shown to industry engineers and senior executives across Europe.

As well as general downsizing V-Charge is proving of particular interest to those companies working on Miller-cycle engine applications to meet Euro 7 emissions legislation, says Richard Dunne, Torotrak’s Group Business Development Manager. Independent testing has been conducted by the U.K.’s University of Bath.

Getting something for nothing has always been a problem for engineers. So V-Charge does not reduce fuel consumption of the regular 1.0-L; that is not Plan A, Dunne explained. But compared to the equally regular Ford Sigma 1.5-L it is claimed to lower consumption by up to 12%, with a comparable cut of CO₂emissions.

It does this without recourse to 48-volt mild hybrid technology and uses a standard off-the-shelf (OTS) compressor. Unlike an e-boost system, this provides continuous boosting, asserted Dunne: “It is not complex; the variable ratio traction drive is a scaled down version of our established and proven toroidal CVT technology,.” he noted. System weight is 6 kg (13.2 lb).

The test drive

With the author behind the wheel of the manual-gearbox Focus demonstrator, Dunne used laptop control to switch the system in or out to give direct engine behavior comparisons. The development car uses a turbocharger slightly larger than that of the standard Ecoboost unit to give 110 kW (147 hp), an 18-kW/24-hp) increase.

The efficacy of the V-Charge was apparent on the first steep hill encountered; the initial step-off from an intersection; and a 90° bend tackled with engine speed dropping towards 1000 rpm in 3rd gear. Low engine speed and (relatively) high torque were smooth partners typically without the need for downshifting.

Baseline rated torque for a regular Ford 92-kW (123-hp) triple is 100 Nm (74 lb·ft) from 1000 rpm and 170 N·m (125 lb·ft) from 1400 rpm. With V-Charge the figures rise to 145 N·m (106 lb·ft) and 240 N·m (177 lb·ft) respectively, very similar to those for the 1.5-L 4-cylinder. It is perfectly amenable for C-segment or smaller cars with a curb weight of 1289 kg (2841 lb).

With a CVT ratio spread of 10, an 1100-rpm engine speed can be converted to anywhere between 10,000 and 100,000 rpm at the impeller without any traditional gearing, explained Dunne. The system is designed to provide greatest efficiency from idle to 2500 rpm, tapering off to avoid over-boosting. It provides a ratio change in a maximum 400 ms.

All this happens very quietly; Dunne said the system is 97% quieter than a comparable Roots-type supercharger. It is easily packaged at the rear of the engine. No noise attenuation is required, he claims.

An electric actuator is used to change ratios (there are no control hydraulics), so parasitic losses are minimized. There is no metal-to-metal contact in the CVT which uses traction fluid of proven performance. The ratio spread provides 0.28 to 2.82:1 gearing. When the charger is not needed, the ratio moves to its minimum and there is no need for a disconnect clutch.

Bearing in mind that a non-standard turbo—Dunne would not name the supplier—was fitted to increase maximum engine power, without the V-Charge the test Focus was distinctly lethargic at low revs in higher gears on the test drive.

The system is designed to provide a power capacity of up to 17 kW (23 hp) and can run at that level continuously.

Claimed fuel consumption and emissions for the 1.0-L with V-Charge are 2 - 5% higher than the standard engine due to the added load (about 100 W) caused by the system. However, the figures are estimated to be 12% lower than the 1.5-L's for similar or improved performance.

Cost similar to a VGT

Torotrak is not a manufacturer; it would sell or license V-Charge technology to a Tier 1 supplier. Doug Cross, Torotrak’s Chief Technical Officer, says the V-Charge would represent cost comparable to a variable geometry turbocharger.

“The complete on-cost needs to be considered to determine a cost:-benefit ratio," Cross told AE. "When you sell technology to an OEM, your transfer price is effectively doubled by the time it reaches the customer.” But offsets include cost saved by using a triple instead of a 4-cylinder engine without loss of performance.

It is possible, therefore, that by adding V-Charge only a modest cost penalty might be involved — and even a cost saving, Cross believes.

A former engine design manager for the Renault F1 team and before that with Toyota F1, Cross was co-founder of Flybrid, (now part of Torotrak), which became a specialist KERS (Kinetic Energy Recovery System) developer and supplier.

Ford recently announced that it plans to add cylinder de-activation capability to its 1.0-L triple for MY2018. Cross believes V-Charge could be used to complement that technology.

Miller-cycle compatible

One concern regarding use of any CVT was once the behavior of its traction fluid in extremely low temperatures, explains Cross: “We have done a huge amount of development and we now have a traction fluid that is liquid pumpable down to -30º C.”

With many OEMs involved in Miller-cycle engine development (or variations of it), Cross is confident that V-Charge would be compatible with the technology.

Although Torotrak has concentrated on gasoline engine applications for V-Charge, it would also be applicable to turbodiesels, overcoming the negative aspects of transient load steps when the accelerator is floored.

To meet the driver’s demand, either the amount of EGR is reduced, which can bring a NOx spike, or the injection of extra fuel is used to help spin up the turbo which results in unburned fuel in the exhaust.

“So it’s a trade-off between particulates and NOx,” said Cross. “These transient tip-in events are responsible for about 40% of the NOx emissions from a diesel engine. But a V-Charge, running constantly, just changes its ratio to provide added boost. The EGR is unchanged and no fuel is added.”

So far this has not been tested by Torotrak on a diesel engine. But Cross is confident that it would provide an effective solution to the problem of NOx spikes.

Author: Stuart Birch
Source: SAE Automotive Engineering Magazine