Refinement, Efficiency Hallmarks Of Mahindra’s 4D15 Marazzo Engine

Technology February 2019 Refinement Efficiency Hallmarks Mahindra 4D15 Marazzo Diesel Engine

SUVs are known to offer a more practical answer to mobility across tough conditions, while vehicles in the MPV segment are essentially large people-carriers offering comfort and convenience. This required Mahindra & Mahindra Ltd (M&M) to develop a vehicle much different from its usual offerings, for which the Mahindra Research Valley (MRV), along with the Mahindra Automotive North America (MANA), Detroit, and Pininfarina carried out collaborative engineering. The Marazzo was thus born as the company’s first multi-purpose vehicle (MPV) in September 2018.

The Mahindra Marazzo is an MPV that offers a host of first-in-segment engineering and technology features in the Indian automotive space. These features range from patented ‘Body-on-Frame-Front-Wheel-Drive’ architecture, electric power steering and all-wheel disc brakes, to the quietest cabin and Surround Cool Technology with fully-automatic temperature control. However, this article focusses on the powertrain of the new Marazzo, which in itself features a range of technologies that are aimed at making the engine and transmission combination as refined as possible.

Velusamy R, Senior Vice President, Product Development – Automotive Division, M&M, who works out of the MRV in Chennai, took us through a detailed journey of the development of the Marazzo’s powertrain. Velusamy focussed on the technologies utilised to achieve the three main goals of the new engine – increased fuel efficiency, high levels of refinement and weight reduction. He also brought out the work that the company has carried out with regards to the transmission, which also leads to improved vehicle efficiency and reduced noise vibration and harshness (NVH) levels.

The Marazzo is the first attempt from M&M in placing a product in the MPV segment, for which it has researched, analysed and developed suitable technologies to address the demands of refinement that are expected out of this segment

MAIN REQUISITES

Following the success that M&M has seen with its 2.2 l, mHawk diesel engine that is featured in multiple models of the brand, the company has been toying with the idea of making a refined engine, noted Velusamy. The MPV segment is a comfort segment, where overall refinement is a key criterion. This required the company to make fundamental, architectural changes that would lead to increased levels of refinement, but without raising costs, he added.

In addition, this segment also has a requirement to offer more space as compared to the SUV segment, along with lower NVH levels. This necessitated the need for a better design to package the powertrain as compactly as possible, for the sake of freeing up more space for occupants. The ratio of the size of the powertrain, when compared to that of the occupants, needs to be as low as possible, in order to offer comfort in the form of expanded cabin space, noted Velusamy. This compact packaging of the powertrain is possible only in monocoque architectures, which on the downside have refinement issues in form of tyre noise, for example, he said.

From a powertrain perspective, Velusamy said there were four main challenges while developing M&M’s first MPV. This was in developing a body-on-frame-based vehicle with low powertrain space occupancy, with improved refinement levels, along with overall weight reduction, and improved engine performance, he observed. These four criteria were equally important while developing the powertrain for the Marazzo, he noted. In addition, all these need to be achieved with the lowest cost increment. While the three areas of space, weight and performance were believed to be present with M&M, the refinement area was where significant work needed to be carried out, Velusamy opined.

The east-west placement of the engine, combined with the transaxle to form the front-wheel drive setup in the Marazzo ensures maximum space inside the cabin for occupants

POWERTRAIN TECHNOLOGIES

The Mahindra Marazzo is powered by the company’s 4D15 engine, which is a 1,497 cc, four-cylinder diesel unit that develops 121 hp of power at 3,500 rpm and 300 Nm of torque in the range of 1,750-2,500 rpm. The engine is mated to a six-speed manual transmission, which features a dual-mass flywheel – a first in the segment. Velusamy said the transmission has been developed to ensure low friction and high efficiency, featuring micro-geometry of the tooth surfaces that are optimised for NVH. It also features a compact design that complements the engine packaging and further optimises cabin space.

Space:

To address the challenge of space offered, M&M resorted to east-west direction placement of the engine, when compared to the north-south direction that is typically of ladder chasses architectures. The engine and transmission power the front wheels through the transaxles, which negates the need for additional components such as propeller shaft, axles and differential in the case of typical rear-wheel powered ladder chassis architecture vehicles. This powertrain architecture in itself is unique for frame-based vehicles, claimed Velusamy, also adding that this design choice results in shaving-off over 80 kg due to the reduced number of components.

The non-existence of rear-wheel drive components liberated space of the wheelbase, which would otherwise be taken up by the transmission tunnel, noted Velusamy. He said it also enabled the Marazzo to be offered with lowered seat height for more comfort and overall lower centre of gravity. This packaging of the powertrain has enabled the vehicle to offer best-in-class occupant space.

Refinement:

The peak firing pressure of the Marazzo’s engine has been set at 180 bar in order to deliver 120 hp power and 300 Nm torque from its 1.5 l capacity. This leads to a high amount of cyclical torsional vibrations, noted Velusamy, for which new technologies in the driveline were needed. The Marazzo has been equipped with a wide-angle dual-mass flywheel, which splits the mass of the flywheel into two using springs that helps in reducing the amount of noise arising from the gears in the crank. It offers the highest spring travel among any benchmarks as well as the highest filtration efficiency of torsional vibrations, besides resulting in no transmission rattle and body boom issues, offering a more refined and quite cabin, explained Velusamy.

The dual camshafts in the engine have gears to drive them, and the oscillations from the crank will reach these gears as well. The helical gears of the camshafts have been fitted with scissor gears, which help eliminate the noise coming from the gears. This scissor gear technology has been developed for the first time by M&M, for the Marazzo and has been patented for its application, Velusamy said. This technology is found on premium vehicles, and has been brought to a lower segment for the first time in India cost-effectively.

Acoustic covers for the engine top as well as flip and the damper ensure improved NVH levels of the powertrain. The wrap shields of the catalytic converter of the exhaust system as well as the oil sump design are also claimed to improve refinement levels, in terms of acoustics for the Marazzo’s powertrain.

Weight Reduction:

The company carried out numerous steps to reduce the overall engine weight. The front-wheel drive design architecture by itself helped reduce weight due to the lower number of components present. In addition to this, ‘plastification’ of components, or substituting metal parts with plastics has helped reduce the weight of the Marazzo’s powertrain by up to 8 kg as compared to competitors that were benchmarked, noted Velusamy.

Additionally, the module concepts with integration of components lead to compactness in the dimensions of a number of parts, which addressed the needs of weight reduction as well as released additional space for occupants. The modular concepts and use of plastics have also eased the manufacturing technology, Velusamy observed. The steps taken by M&M in reducing the weight of the powertrain to about 141 kg has also translated into better fuel efficiency, which is claimed to be at 17.3 km/l.

Improving Efficiency:

The main methodology adopted to improve fuel efficiency in a vehicle is to reduce the level of friction in the engine, explained Velusamy. Crank offset is a major contributor to the reduction of friction within the engine, thereby directly leading to improved fuel economy. The crank offset of 8 mm in Marazzo’s engine reduces piston side forces by 38 %, hence cutting down on the overall engine friction as well as noise. The effect of friction from the piston rings is also a major contributor to the efficiency of the engine. And to address this, M&M introduced torque plate honing technologies in the block that ensures lower pressure being exerted by the rings, while the pistons expand inside the engine.

Furthermore, M&M has introduced a new concept in the lubrication system, which has reduced the size of the oil pump, and thereby cuts down on related friction. However, Velusamy chose to maintain confidentiality over the concept. He also noted that the thermal management, which consists of cross-flow cooling water jacket for improved engine cooling, and inlet-controlled thermostat for faster engine warm up addressed the improved efficiency.

The second main step needed to improve engine efficiency is by engaging turbo machinery, Velusamy said. The aim is to reduce the engine speed at which the maximum amount of torque can be extracted, which then enables the reduction of gearing in the transmission. The combination of these two actions helps in bringing down the engine speed for a given vehicle speed, which directly translates into reduced friction and improved efficiency.

The turbocharger for the Marazzo has been sourced from, and developed together with Turbo Energy Ltd. The set-up consists of a Gen6 Evo turbo, and Variable-geometry turbocharger (VGT) cartridge and vane. Earlier, the regulated two-stage turbocharger (R2S) was usually required to get high low-end torque as well as high-end power. However, the single-stage VGT (Gen 6 EVO +) turbocharger used in the Marazzo leads to the ability to achieve both low-end torque and high-end power of R2S in the single stage itself, Velusamy explained. He noted that the turbocharger also features a pre-guide blade ring (PGBR) that provides impressive turbine efficiency at low end.

Other notable features of the turbocharger include an optimised compressor wheel for best low-end torque as well as optimised turbine wheel for improved efficiency. Additionally, the air intake system for the turbocharger has been optimised with an innovative ported design, which was developed by using computational fluid dynamics (CFD) simulation. This intake design has won a joint patent for M&M and Turbo Energy Ltd.

The driver information system placed inside the instrument cluster offers a range of data in a clear interface that eases driving duties of the MPV

CONCLUSION

Velusamy said that in order to enable optimum R&D, a procedure consisting of four main actions is required. It involves observing and collecting data, followed by gaining insights about the collected data, then setting down rules and framework, and finally providing solutions based on the framework. He noted that the following procedures in the development of products will lead to a final product that is well-rounded, with the ability to be tweaked and modified according to required alterations.

Around 80 engineers of the company worked on the development of the Marazzo MPV over a period of about three and half years. The main focus has been on creating an MPV, but also one that offers a number of best-in-class features. The amount of technologies adopted and localised by the company to develop various components and systems to enable a potent offering in the MPV segment in India is in a class of its own. M&M’s development of the Marazzo’s powertrain makes it look like it has been placed as an offering that not only beats vehicles in its class, but also in certain segments above as well.

TEXT: Naveen Arul

PHOTO: Mahindra & Mahindra Ltd