Freelander - Engine Mounts
Engine Mounts
At the same time as the suspension was being refined, engineers worked on improving the design of the engine mounts. Engine vibration, induced both by movements of the vehicle and the engine, is one of the major obstacles to achieving good secondary ride qualities.
To control the low frequencies of engine movement or 'engine shake', induced by a reaction to drive torque and road bumps, the mounts need to be stiff. However, these tend to feed unwanted engine noise into the passenger cabin
To prevent the higher frequency vibrations of engine noise from disturbing the tranquillity of the passenger compartment, the mounts need to be soft. However, these are less well able to cope with low frequencies, and can compromise secondary ride comfort.
Normally, there is a trade-off between these two conflicting requirements.
Land Rover engineers reconciled the conflict with a unique hydraulic engine mount strategy, which has now been applied to the Freelander.
Hydra mounts; spring and damper
The hydraulic engine mount operates like a combined spring and damper unit, using the rubber element as the spring, and the fluid pumped back and forth through a hole as a vibration absorber.
This is used on the Freelander petrol models in the form of the 'hydra' mount; giving maximum stiffness at engine shake frequencies, and reduced stiffness at engine noise frequencies - resulting in substantial improvements in secondary ride quality.
In addition, a twin tie bar system has been introduced. Together with the 'hydra' mount, this enables each powertrain to be tuned to the Freelander's body.
Freelander Td4 diesels: de-coupler
The very high torque output of the Td4 Freelander models required further development of this strategy. Here, Land Rover's innovation was to include a 'de-coupling' diaphragm within the hydraulic mount, which lowers the stiffness much further at higher frequencies.
Both petrol and diesel Freelander drivers therefore get the best of both worlds - control of the engine vibration for good secondary ride, and isolation of engine noise for refinement.
Torque axis engine mounting system
Freelander's 'Torque Axis' engine mounting system means that the mounts which carry the weight of the engine are positioned each side of it on the torque axis.
This is the axis of minimum rotary inertia for the complete engine/transmission unit. This design provides minimum deflection of the mounts in reaction to engine and driveline movements, and hence minimum transfer of noise and vibration.
It also provides the largest scope of movement for the mountings to control engine shake, and it locates the mountings in inherently rigid parts of the bodyshell, again to inhibit the transfer of noise and vibration.
The Benefits
- Controls of full range of engine frequencies; ride comfort and refinement
