[amalji]

I recently changed the Rubber engine mounts on my Etios with a hydraulic engine mount ( the same one used on Etios 2013 facelift ).

The very evident differences that I could feel are

• better vibration control during cranking up/switching off the engine. Feels very subtle now.
• Once the engine warms up, even the sound seems to have come down.

I would like to start a discussion on the positives/negatives of a hydraulic engine mount and the technical reasons why it is so.

One negative, I've heard about the hydraulic mount is that there is more torque loss ( on the wheels ) compared to the rubber mount.
Another one is its durability.

Hoping for an interesting discussion on the same.

Reference posts regarding my personal experience with the replacements -

http://www.team-bhp.com/forum/long-t...ml#post3106682

[SPIKE ARRESTOR]

Originally Posted by amalji

One negative, I've heard about the hydraulic mount is that there is more torque loss ( on the wheels ) compared to the rubber mount.

Could not understand the part in bold above, could you explain what you are implying by torque loss on the wheels?

Spike

[amalji]

Originally Posted by SPIKE ARRESTOR

Could not understand the part in bold above, could you explain what you are implying by torque loss on the wheels?

Spike

I'm also not 100% sure about it. I saw a reference about it on http://www.bobistheoilguy.com/forums...Number=2941903

I guess, it's comparable to rear suspensions on a cycle which is thought to waste some of the energy from the person who is cycling making it harder to cycle.

[SPIKE ARRESTOR]

The difference between the two is in the storage and loss stiffness behavior. The theory behind it is a big complicated, I will post a short note sometime later.

Spike

[tbppjpr]

Originally Posted by amalji

One negative, I've heard about the hydraulic mount is that there is more torque loss ( on the wheels ) compared to the rubber mount.
Another one is its durability.

Logically I don't agree with both the above points. Hydraulic mount should be more durable compared to rubber mount since the rubber tends to wear up faster whereas hydraulic mount doesn't have any such rubber cushioning.

And why the torque will be reduced at wheels? The engine keeps vibrating at same rate, its just that the hydraulic mount absorbs more vibration compared to the rubber mount so that the engine vibration doesn't transfer inside the cabin at the same rate which is produced in case of rubber mount.

The main reason behind choosing rubber mount in place of hydraulic is the cost. Rubber mount costs low compared to hydraulic mount, hence manufacturers fit the rubber mounts in some of the cars where they want to keep the cost and price low.

(The above reply is based on my personal understating about the mounts, please feel free to correct me if I am wrong)

[amalji]

Originally Posted by tbppjpr

Logically I don't agree with both the above points. Hydraulic mount should be more durable compared to rubber mount since the rubber tends to wear up faster whereas hydraulic mount doesn't have any such rubber cushioning.

There's an alternate view that fluid filled mounts tend to leak and lose its effectiveness faster compared to rubber mounts which last the life time of the vehicle.

Originally Posted by tbppjpr

And why the torque will be reduced at wheels? The engine keeps vibrating at same rate, its just that the hydraulic mount absorbs more vibration compared to the rubber mount so that the engine vibration doesn't transfer inside the cabin at the same rate which is produced in case of rubber mount.

As I mentioned in my 2nd post, I too am not sure about it. I've given the reference link from where I took that info, and it's open for debate.

Originally Posted by tbppjpr

The main reason behind choosing rubber mount in place of hydraulic is the cost. Rubber mount costs low compared to hydraulic mount, hence manufacturers fit the rubber mounts in some of the cars where they want to keep the cost and price low.

Ofcourse the price being low is the main reason why manufacturers chose rubber over hydraulic. But, that doesn't mean rubber will not have any advantages. I'm just trying to find out as much technical difference as possible.

[Sankar]

Pl upload the pics of the Etios engine mount, hope you have taken some.

Originally Posted by amalji

One negative, I've heard about the hydraulic mount is that there is more torque loss ( on the wheels ) compared to the rubber mount.

The torque loss at the wheels is due to the engine+drive train movement. When a typical transverse engine FWD lays down the power the engine+gb tries to twist in the opposite direction (some torque is wasted here), this affects the torque that's being put down on the road by the wheels. Stiffer engine mounts arrest the engine+gb twisting helping to better put the power on the road, a hydraulic engine mount being less stiffer will not be able to prevent this twisting as good as a solid rubber mount. On a road car this isn't an issue and lower NVH offered by hydraulic mounts is desirable.

[amalji]

Originally Posted by Sankar

Pl upload the pics of the Etios engine mount, hope you have taken some.

Done. I have uploaded it in my ownership thread

Originally Posted by amalji

I couldn't get the photos of the hydraulic mounts before we fitted it. Service advisor was a bit cautious about giving access. I didn't push as well.

So, I took the photos of both the mounts when fitted and also the rubber mounts after removing them.

The rubber mounts before we replaced it
Attachment 1083272

The new hydraulic mounts fitted
Attachment 1083273

Pictures of hydraulic mount after removing.
Attachment 1083274
Attachment 1083275

Originally Posted by Sankar

The torque loss at the wheels is due to the engine+drive train movement. When a typical transverse engine FWD lays down the power the engine+gb tries to twist in the opposite direction (some torque is wasted here), this affects the torque that's being put down on the road by the wheels. Stiffer engine mounts arrest the engine+gb twisting helping to better put the power on the road, a hydraulic engine mount being less stiffer will not be able to prevent this twisting as good as a solid rubber mount. On a road car this isn't an issue and lower NVH offered by hydraulic mounts is desirable.

Ahh, the similar phenomenon for cycles with suspension. This is the same reason why sports cycles don't prefer to have suspensions. Even if they have one, it has the option to lock/unlock the suspension.

Also, I read a good article about the effect of engine mounts specifically on 'noise damping' ( not vibrations ).

Pasting the relevant parts of the article regarding its effect on noise inside the cabin.

The primary contributors were airborne noise and noise transferred through the engine mounts. A new bracket was developed to reduce the engine mount contribution

The FAST TPA results showed that the airborne contribution was the largest at 49%, engine mounts contributed 40%, and the suspension accounted for the remaining 11%. The fast analysis technique also determined that the airborne contribution was higher on the customer vehicle because of a high airborne noise source as well as a high acoustic transfer from the engine compartment to the vehicle cavity. This method, which was developed by LMS Engineering Services, relies on an advanced indirect source identification method in which each noise contribution is considered to be the product of an equivalent source strength and an equivalent transfer path. It does not provide details, such as which engine mounts are the primary contributors.

The two vehicles were compared in terms of construction choices, such as engine mounting layout and trim materials, in order to gain an understanding of the differences. The detailed TPA determined that the right engine mount was the source of most of the noise.

A running mode analysis was performed to identify the root cause of the right engine mount contribution. The results highlighted the large impact of structural modes on the part, indicating the need for stiffening.

The next step was making simple modifications to determine how they affected critical transfer mechanisms before investing the time and money needed to make realistic changes. Structural modifications were performed to try and change the acceleration levels of the panels in order to change the resonant behavior and radiation to the microphones. Acoustical modifications were also done to try to insulate the cabin by adding a mass-spring system on the vibrating panels. For example, engineers weakened engine mounts by drilling holes in them, added dampening treatments on interior trim panels, added a combination of foam and insulating fabric on the firewall to isolate the airborne noise from the engine, stiffened an engine bracket by welding a beam to it, etc.

[sgiitk]

The hydraulic will always transmit less NVH than its rubber cousin. This is why the Amaze Diesel has Hydraulic or Oil filled mounts, while the Petrol borrows the rubber ones from the Brio.

[amalji]

Originally Posted by sgiitk

The hydraulic will always transmit less NVH than its rubber cousin. This is why the Amaze Diesel has Hydraulic or Oil filled mounts, while the Petrol borrows the rubber ones from the Brio.

Even though it's effect on vibration and harshness are very obvious, I was not too sure about how it's going to affect noise. It seems it blocks the noise which transmits through the frame.

[Skyline GT-R]

I had similar thought while my 2011 Figo was new (wanted to replace the engine mounts with Fiesta hydraulic mounts) but dealer told engine warranty may be void. Now the Fiesta Classic also comes with rubber mounts i believe. My 60K service is due in 2-3 weeks will try to fix hydraulic mounts this time & update the feedback if successful.

[FlatOut]

If the fluid-filled mounts are soaking up energy, then this energy must be turned to heat.

[gd1418]

Are these hydraulic mounts available only for sedans, hatchbacks or small cars or are available for big diesels? If yes, what brand and are they OEM or aftermarket?

[apachelongbow]

Regarding engine mounts, I have a quick question. In the RE bullets the engines are bolted on to the chassis, acting like a stressed frame member. If I remember correctly its bolted on to the chassis using common bolts, that is, there is no rubber or hydraulic mountings. When the engine vibrates, it transmits all the vibration to the motorcycle itself,leading to vibes.
Is it possible to rubber mount the bullet engine? Will it be possible? Will it alter the bike's character and will it get expensive to do so?

[CHINMAYAN]

Originally Posted by tbppjpr

Logically I don't agree with both the above points.
=========
(The above reply is based on my personal understating about the mounts, please feel free to correct me if I am wrong)

It is a false concept that hydraulic mounts doesn't have rubber parts. Actually they are having two rubber mounts separated by a diaphragm just upon which there is a hydraulic chamber and a valve..... actually the main problem in using the hydraulic mounts are their initial cost and in some cases (mainly if you regularly change your part supplier due to cost constraints), reliability issues. If a leakage occurs then the vibrations will be higher....please see the attached figure.....figure courtesy AGCO automotive repair services