How do Davinci dampers in Mahindra XUV 7XO work?

One of the big updates on Mahindra XUV 7XO is the new DaVinci dampers for the suspension. This has replaced the older FDD dampers, with the Davinci dampers claiming to have major improvements to ride quality, while improving NVH in the cabin and also delivering best-in-class driving dynamics to the 7XO.

We weren’t expecting to see them so soon though. If you remember, the DaVinci damper was announced last year and was to be seen on the Mahindra NU IQ platform, with the production versions of concepts like the Vision S, Vision X and Vision T. However, the development timelines allowed them to squeeze it in to the Mahindra XUV 7XO. We spent some time with R Velusamy, president of Mahindra’s automotive business and their suspension partner Tenneco to understand how the system works.

DaVinci Dampers claim to be have major improvements over the older FDD ones

Damping explained

To understand the DaVinci damper, you need to first understand how a conventional damper works. A conventional damper is a fairly simple, but critical component of a suspension system — its main role is to absorb tyre shocks, isolate the car body from road imperfections and keep the tyres in contact with the road for comfort, stability and control.

Fundamentally, the spring lets the wheel move over bumps, but if you only had springs the car would bounce like a pogo stick. The damper resists this motion. The faster the suspension tries to move, the more resistance the damper generates. That resistance comes from forcing oil through small valves inside the damper body which in turn generates heat. That’s why you hear of dampers going “soft” which is when the oil overheats and loses its viscosity.

For the sake of simplicity, I’m not going to get into every component within a damper. What we will focus on are the valves and shims. The valve is the key component within the damper, regulating the flow of oil and providing damping force. A key component within the valve unit is the shim stack: thin metal discs stacked one on top of the other that act as flexible valves, bending according the pressure that the oil applies on them and thus changing the rate of flow of oil.

Many conventional dampers behave closer to linear over part of their operating range. Simply, in a “linear” damper, the basic idea is that damping force rises in direct proportion to how fast the piston is moving through the oil. Double the speed (of the piston, not the car), roughly double the force, at least over a certain range of speeds. This forces a compromise between ride comfort and body control, as they can’t be tuned separately.

Which is where the DaVinci damper comes in.

The DaVinci damper

The DaVinci’s basic construction is similar to a double tube damper, but the real magic is happening inside the valve, and more specifically, the shim stack. Tenneco, who are the supplier of this damper, say the difference is in the shim shape and arrangement. These plates allow for different rate of flow through the valve at different points in the damper’s travel and it changes with the nature of the forces applied to them. These plates allow for decoupling of the primary ride and secondary ride control, and allow for a wider breadth of ability.

This damper doesn’t have a linear velocity-force curve. Mahindra says it’s tuned to be rather soft at very low shaft speeds and then quickly dials it up, past this threshold and then levels off flat. Compared to a conventional damper, it is more compliant for low piston velocities, and mid-range piston velocities offer strong balance between body control and comfort, while at really high piston velocities (like a sharp bump) the damping is less than on a conventional damper and allows those hits to feel less jarring.

How does this work practically? At very low damper shaft speeds it’s softer, then it ramps up quickly once inputs get larger or faster. This allows it to filter out a lot of the smaller ripples and smaller bumps and imperfections in the road, without transferring it to the body. However, once past this lower threshold, the damper firms up significantly — for example, if you hit the lip of a massive pothole at speed, the dampers will be firmer and ensures the wheel is not moving uncontrollably on impact. But that said, at extreme forces that stretch the dampers to its limit, it remains more compliant than a conventional damper.

The cost advantage of DaVinci

These DaVinci dampers are completely passive units. A lot of dampers allow for this sort of a non-linear damping force to be applied but these are usually active or semi-active systems. In the case of the Davinci damper, the whole thing is a mechanical unit with the valves controlling the damping forces independently — there’s no sensors and controllers managing the suspension. This is critical for it to be cost effective. It costs 25-30 per cent of the semi-active units on the Mahindra BEVs. With none of the electronics and wiring involved, the cost of manufacturing (therefore also servicing or replacing) will be much more affordable.

This system is also modular. While it has debuted on the 7XO, you can expect a whole range of Mahindra vehicles to feature them in the future. As Mahindra announced earlier, these dampers will make their way to Mahindra’s next generation of compact and mid-size SUVs. I suspect, they will be a real game changer in that space.

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Advanced Hydraulic Rebound Stopper (AHRS) explained

Another innovation on the 7XO’s dampers is the AHRS. Advanced Hydraulic Rebound Stopper or the hydraulic top-out stops. In certain scenarios, the suspension can extend very fast and hit its extension limit (“top out”), which creates noise and a kick. A hydraulic rebound stop adds an extra, progressively increasing hydraulic resistance right near full extension so the last part of extension is cushioned instead of ending with a hard mechanical stop. It reduces both the NVH and the forces felt in the process. It does away with a traditional bush in the top stop, and relies entirely on a hydraulic unit that reduces weight and is also highly tuneable.

Where do you see this in action? Imagine driving down the highway and seeing an unmarked speed breaker at the last second — an all-too common phenomenon in India. You slam the brakes and the nose dives down as you approach the bump. You’ve not slowed down enough and slam into the speed breaker. The speed breaker forces your suspension to compress. As you roll off the speed breaker, the compressed spring is storing incredible amounts of energy and pushes the wheel away from the body with massive force. If the force is enough, it would cause the damper to reach the end of its travel at full extension. This is called topping out. At this point, with a conventional rebound stop, the suspension would be unable to extend any more and you can hear and feel a clunk, while the rear can unload too fast and rear passengers feel like they’re being tossed upwards.

It is at this point that a hydraulic rebound stop is useful. It adds an additional layer of cushioning. Once the main piston damper is out of travel, forces are transferred into this hydraulic stop. Just like in the main damper, a hydraulic system is used to cushion the blow further and round off the harshness that you would usually feel. In this case, when the suspension extends, it wouldn’t slam into the rebound stops but instead eases into them. You feel less or a hit in the cabin, and the damper hitting the rebound stop makes less noise as well, giving you a sense that the suspension is far more robust.

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Engineering this into the 7XO

Mind you, this was not as simple a job of swapping out the older damper for the new unit. The whole system needed a rework. The new dampers mean the springs had to be changed. Bushings were changed as well, while the anti-roll bar was tweaked. The suspension system needs to work in unison to provide the right balance — changing one component means every other component that it interacts with also needs to be updated and fine-tuned to work in the right window.

A lot of the questions on social media were about whether this damper would be compliant with the current 700. Technically yes, it is possible. However, changing out the damper would mean changing out every other component that was updated to make this damper work — the springs, bushings, anti-roll bar. Not a practical thing to do. The costs would be rather high — both in terms of parts and labour for a job like this and may not be worth the gains.

What does all this do for ride quality?

It works wonders. The first thing you feel is how it irons out the smaller imperfections in the road. What would normally be a constant pitter patter in the cabin quietens down significantly and becomes smoother. Of course, it’s no magic carpet — you’re still aware you’re going over uneven surfaces but the sensations in the cabin are more muted. I’m actually glad that it’s not ironed out completely as that would have made the SUV too disconnected. That isn’t the case here. You’re comfortable while being well aware of what is going on underneath.

High speed ride over smooth tarmac is imperious. You’d think a set up that has so much comport baked into it would be too bouncy on the highway. Not the case. Over Rajasthan’s constantly undulating roads, there’s a sense of steadiness and confident body control that is hard to find in cars made in the eastern hemisphere. Vertical movement is very well contained and even when you find yourself hitting long-wave crests and dips at triple-digit speeds, the suspension’s composure is very impressive. No launching you into the sky, no slamming down into its lower bump stops. Just great body control. I was pleasantly surprised by this — the XEV 9S doesn’t do this very well and is far too softly sprung. It doesn’t settle down as quickly as you would want. I was worried the XUV might inherit some of those traits, but that is not the case. Despite the 9S having the more sophisticated semi-active damper, the 7XO does ride quality far better.

Over a bumpy trail, the 7XO does a competent job of cushioning you. You’re aware the suspension is working hard as the dips and bumps in the surface come at you at speed, but most of it is filtered out before it reaches you. You do feel some degree of pitching here as all four corners work their best to maintain traction, but never does it feel uncomfortable. You also get a sense of robustness from the suspension. It feels like it can take a beating, and that honestly urges you to push harder.

I did try to hit a breaker at speed as well to see how it reacts, and I was deeply impressed. Those short, sharp yellow and black rumbler strips that are generously used around toll booths all over the country didn’t faze the 7XO. I didn’t lift as I hit them, and while you do feel it a bit in the cabin, the car didn’t unsettle nor did it make too much noise as it hammered over them.

A larger tarmac speed breaker was next. I hit this a little slower, but with the intention to bottom out the suspension travel to see how the AHRS behaves. The car hit the breaker reasonably hard, but again, remained unperturbed. The suspension system rounded off the worst of the hit, making the breaker feel much smaller than it really was. Again, the body remained very settled, not pitching too much as front and rear axle went through the bump. It was here that I was convinced that one of the biggest drawbacks of the older suspension has been fixed — the 700’s ride was good, but it felt a little fragile over really harsh bumps. That is not the case here. Again, it felt very robust and very strong. Just as you would want your SUV to feel.

You really don’t need to be hitting bumps at speed to feel the advantages of the new suspension system either. Something as simple as the nose-dive when you hit the brakes has reduced with the new system. This makes for a much calmer drive all around, with the car reacting the changes in speed without getting too unsettled.

Handling has also been impacted. For the better. There is some roll, particularly at the moment you initiate a turn — a combination of the height of the car and its high centre of gravity and the design of the Davinci damper. The initial part of the travel in the damper is quite soft, but once you’re through that, it firms up nicely and gives you the ability to carve up corners with confidence. The XUV 700 was always a pleasure to drive, and I’m glad that hasn’t been messed with in the 7XO. Combined with its enthusiastic engines, the 7XO remains a benchmark for driver thrills and engagement in the segment.

Davinci dampers: real gains or marketing gimmick?

The improvements in ride quality to the 7XO are not hard to see. Or rather, feel. A few metres in to driving over our broken roads and you’re convinced of the advantages that this new system brings. It has a wide breadth of operation and compromises, if any, were hard to ascertain during this short first drive experience. I’m keen to spend more time with the car, and seeing how it performs in real world conditions over time — particularly on roads I am more familiar with. On social media many queries were raised on the reliability of a new system, and whether it has gone through enough testing and validation for Indian conditions but nothing I saw or heard at the first drive gave me any indication that shortcuts have been taken. So no, this is not a marketing gimmick. And yes, Mahindra have certainly moved the game forward on the chassis front, with this new damping system.