If the words “Ford Mondeo powered by 1.0-L 3-cylinder EcoBoost engine” sound a bit incongruent, now consider that the company is researching cylinder deactivation for its little triple.
Ford, working with European partners, has examined both single and “rolling” deactivation strategies for its smallest spark-ignited passenger car engine. After proving itself in the B- and C-segment Fiesta and Focus models, the 92-kW (69-hp), 1.0-L—smaller than many motorcycle engines—is now also available in the D-segment Mondeo in Europe.
How does this diminutive engine perform in the roomy sedan when all three cylinders are on the job? A test drive in the U.K. by this Automotive Engineering editor of the production version of the Mondeo triple largely dispelled doubts of its general suitability to propel a 1455 kg (3207 lb) curb weight car. Acceleration from zero to 100 km/h takes 12 s and claimed top speed is 200 km/h (124 mph). Official economy figures for the 1.0-L Mondeo include a combined figure of 5.1 L/100 km (about 46 mpg) with CO2 emissions of 119 g/km.
My test drive was particularly impressive regarding NVH levels both generally and in the cruise. And it is in the cruise that two-cylinder operation for the Mondeo could be viable, just as it may be for the smaller Fiesta and Focus.
Two deactivation strategies
Research into the feasibility of cylinder deactivation for a production triple has been carried out by a high-level Ford team led by Dr. Andreas Schamel, Director, Global Powertrain, Research and Advanced Engineering. He said that when installed in a Focus and dependent on various factors, a fuel consumption reduction of between 4% and 6% is achievable when operating in 666-cm3 twin-cylinder mode.
The general deactivation system would be complemented by further technology that Ford has now researched, including a specifically developed pendulum absorber. Integrated into the driveline, the absorber enables a broader operating range during cylinder deactivation at lower engine speed, explained Schamel in a technical paper he presented during the 2015 Vienna Motor Symposium.
The paper notes Ford's collaboration with Schaeffler Group (Dr. M. Scheidt), including Schaeffler's LuK division (Dr. H. Faust). Dipl-Ing C. Weber of Ford Cologne is also a key member of the research team.
As well as incorporating the pendulum absorber, a cylinder deactivation Focus prototype was also fitted with a Schaeffler dual-mass flywheel (DMF) and a tuned clutch disc, to achieve vibration isolation between transmission and engine.
Mandatory development targets were met and results noted no NVH deterioration compared to the standard production 1.0-L EcoBoost.
Two different cylinder deactivation strategies were examined: deactivation of a single cylinder, and what is termed a “rolling cylinder” deactivation, which would effectively run the EcoBoost triple in a “half-engine” mode, with freedom to vary the number and sequence of deactivated cylinders.
Schamel explained that on a 3-cylinder engine, different strategies for cylinder deactivation are applicable. One "is to apply an appropriate valve deactivation mechanism to one cylinder," effectively creating a 666-cc twin but with the disadvantage of an uneven firing sequence. However, Ford has investigated other technologies which provide the freedom to vary the number and the sequence of deactivated cylinders.
Such a set-up offers the opportunity for a rolling cylinder deactivation and could be used to run the engine in half-engine mode, corresponding to a 500-cm3 active displacement but now with the advantage of an even firing order, he noted in the paper.
The research teams found that the half-engine mode offered a greater potential of avoiding throttle losses at very low loads, but at an overall lower load limit compared to the two-thirds mode. Schamel added: “In the operating area in which the two deactivation strategies overlap, the rolling cylinder deactivation shows a bigger fuel saving potential related to the full engine operation compared to fixed cylinder activation.”
The fuel economy for the 1.0-L engine during rolling cylinder deactivation would be better than that for the fixed cylinder deactivation in low load drive cycles, but the magnitude of the additional benefit would depend on vehicle application and cycle. A small car at light load would get the biggest potential benefit, with smallest achieved by a large car during mid to high load cycle. So a Fiesta with a 1.0-L engine would be able to gain another 1.2% fuel efficiency benefit in NEDC compared to the improvement already achieved with fixed cylinder deactivation. But for a Mondeo using the engine the gain would be negligible in the WLTP (Worldwide Harmonized Light Vehicles Test Procedure) cycle, considered to be more representative of real-world driving.
While fuel consumption reduction is the salient plus factor regarding the general application of cylinder deactivation, the downside can be negative NVH effect.
Schamel explained “On the one hand, NVH requirements constrain the maximum torque at lower engine speeds and on the other, the human perception of low frequencies does not allow the operation at very low engine speeds. The NVH objective is the minimization of low engine order excitations caused by cylinder deactivation.
"The NVH limits can be moved to higher torque levels and lower engine speeds by optimization of the powertrain and introduction of new technologies,” he noted.
The use of the dual-mass flywheel with tuned clutch disc counteracts the 0.5th or 0.75th engine-order excitation and the pendulum damper reduces the 1.5th engine order by more than 90%, according to Ford testing.
The baseline production DMF flywheel and clutch facilitates comfortable cruising from 1500 rpm upwards on 2nd gear and above 2000 rpm in 6th. The absorbing system allows the lower speed limit to be “significantly” reduced in all gears and maximum acceptable torque to be increased close to the mechanical design limit of the DMF, bringing a 1% NEDC fuel economy benefit. The rolling mode deactivation would see an extra 0.5% achieved.
Summing up the pros and cons of single or rolling cylinder deactivation, Schamel and his colleagues reported, “The fulfillment of the mandatory development target, no NVH deterioration, is achievable for all cylinder deactivation strategies. Without a significant compromise regarding fuel economy, the single cylinder deactivation strategy is preferred regarding complexity, controls efforts, and cost effectiveness."
Ford calculations show the ratio of total functional benefit and cost to be "advantageous" for the single cylinder deactivation strategy versus the rolling approach. A high level contemplation shows a 90% fuel economy benefit for 40% of the cost—good "bang for the buck." The research team concluded that "even highly downsized engines can benefit from a cylinder deactivation strategy, with fuel consumption reduction gained in various global drive cycles – and under real conditions.”