Wednesday, 02 May 2007 13:56

Technology changes result in more requirements for engine mount performance

Written by I-CAR Advantage Online
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    Automotive engine mounts are designed to support the engine and reduce vibrations and force, transmitted from the engine to the vehicle structure, and from road surface irregularities. Providing adequate engine support requires a firm engine mount, while controlling vibration and force requires a flexible mount.

    With changes in vehicle technology, there are more requirements being placed on engine mount performance. Standard hard rubber, passive mounts provide firm support for the engine. However, the use of hard rubber allows engine vibrations to be easily transmitted to the chassis.

    Active engine mount systems overcome these conflicting requirements by combining an engine mount that provides good support properties with an actuator to control engine vibrations, and vibrations from road surface irregularities.
Active systems
    Vehicles that may be equipped with an active engine mount system include, but are not limited to, the 2006 Jaguar XJ, 2007 Hyundai Veracruz, 2007 Lexus RX350, and 2007 Toyota Camry.
    The 2006 Jaguar XJ equipped with a 2.7 twin-turbo diesel features electronically controlled active engine mounts, designed to cancel most of the engine vibration at idle. Because diesel engines generate higher levels of vibration than gasoline engines, electronically controlled active engine mounts are used on all 2006 XJ diesels.
    The 2007 Hyundai Veracruz has electronically controlled engine mounts on both diesel and gasoline engine models (see Figure 1). The Hyundai engine mount system consists of three passive mounts integrated with active controls, to offset vibrations.
    Some Lexus and Toyota models also use an active engine mount system. The engine mount system used on the 2007 Lexus RX350 and Toyota Camry is called the Active Control Engine Mount (ACM) system. On this system, the rear of the engine is attached to the chassis by a fluid-filled mount to control vibration and noise. The front of the engine is attached to the chassis by an electronically controlled active mount that continuously adapts to the driving conditions.
    The ACM system decreases engine vibration at idling using a vacuum-switching valve (VSV). The VSV is controlled by a pulse signal, which is transmitted to the VSV from the electronic control module. The frequency of this pulse signal is matched to the engine speed to decrease engine vibration.
Hydraulic systems
    Some vehicle models, such as the 2006 Ford Fusion, Lincoln Zephyr, and Mercury Milan are equipped with passive hydraulic engine mounts (see Figure 2). A hydraulic engine mount is commonly called a hydromount. These mounts have two chambers filled with a fluid, typically a glycol mixture. A large orifice valve and a small orifice valve connect the chambers. A hydromount produces variable damping as a result of the transfer of liquid from one chamber to another. {mospagebreak}
Magneto-rheological system
    One equipment maker is developing yet another type of mount, a magneto-rheological (MR) fluid powertrain mount. Damping properties of the mount are controlled instantly during a variety of road surface conditions by adjusting the state of the fluid. The MR powertrain mount also helps control engine vibrations.
    The MR powertrain mount system works with both front- and rear-wheel-drive engine mounting configurations. An MR powertrain mount system includes the appropriate MR mount(s), sensor(s), an electronic control unit, and the associated wiring.
Damage analysis
    When analyzing damage on an active engine mount system check for visible damage. Inspect hydraulic or electronic engine mounts for fluid leaks, damaged or pinched vacuum hoses, improper connections, or damaged electrical parts.
    When analyzing damage on an engine mount assembly on a 2007 Lexus RX350, apply a vacuum to the engine mount and verify that there is no change in the needle movement of the vacuum pump gauge. If vacuum pressure remains steady, the engine mount assembly is good. If the vacuum pressure drops or no vacuum pressure exists, the engine mount assembly needs to be replaced.
Replacing an engine mount
    Replacing an engine mount can be a challenge. It will typically require working from both above and below the vehicle. Replacing an active engine mount requires additional attention to electrical and vacuum actuators and connections.
    Replacing an engine mount may require raising and supporting the engine. Raising and supporting the engine requires using the proper equipment and following appropriate procedures. Always check for clearance before attempting to raise the engine to avoid damage to adjacent parts that could get pinched or crushed.
    Always use safe working practices when inspecting or replacing engine mounts. Use the appropriate tools and follow vehicle maker recommendations.
    Changes in vehicle technology are making the use of standard engine mounts inefficient. Active engine mount systems can provide the engine support properties required in newer vehicles along with improved engine idle and road surface vibration control.
    Vehicles equipped with an active engine mount system can make analyzing damage and collision repair more challenging. As more vehicle makers use active engine mount systems in vehicle construction, technicians and estimators will need to keep current on engine mount technology.

This article first appeared in the I-CAR Advantage Online, which is published and distributed free of charge. I-CAR, the Inter-Industry Conference on Auto Collision Repair, is a not-for-profit international training organization that researches and develops quality technical education programs related to collision repair.

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