
           !" #  $ !%Active Engine Mount& '()*+, -./01 0
2 3456 789:;<6;988 =<>?@ ABCDEFB56GDH8I6BJKDL89;M N@ OPOQN A9<<6@ =6B<9GR
STUVWSXVYZ[\][^_Z[`a bZ[cdef^_Z[ `[g h]_ij^ k]gdb^_Z[ e]`cdk]c `_e]g `^ `[ Zf^_e_l`^_Z[ Zm eZg]k[ ][i_[]cdcf][c_Z[ cnc^]eco dcd`aan a]`g ^Z `[ _[bk]`c] _[ \_pk`^_Z[c `b^_[i Z[ ^j] fZh]k^k`_[ cdcf][c_Z[ eZd[^cq rn`ffa_b`^_Z[ Zm `b^_\] ][i_[] eZd[^co ^j]c] \_pk`^_Z[co hj_bj `k] a_e_^]g ^Z cf]b_`a ][i_[] Zkg]kco `k]g]bZdfa]g mkZe ^j] cdpmk`e]q sj] g]c_i[ `[g Zf]k`^_[i fk_[b_fa] Zm ^j] `b^_\] ][i_[] eZd[^ `k] ]tfa`_[]gqu`k^_bda`k mZbdc _c Z[ ^j] c]a]b^_Z[ bk_^]k_` mZk ^j] `b^d`^Zk `c h]aa `c ^j] _[^]k`b^_Z[ `[g bZZkg_[`^_Z[ h_^j^j] bj`k`b^]k_c^_b eZd[^ f`k`e]^]kcq v[Z^j]k mZb`a fZ_[^ Zm ^j_c k]fk]c][^`^_Z[ _c ^j] g]cbk_f^_Z[ Zm ^j] bZ[^kZacnc^]e _[badg_[i ^j] []b]cc`kn pZd[g`kn bZ[g_^_Z[cq sj] Zf]k`^_[i fk_[b_fa] `[g ]mm]b^ Zm `b^_\] ][i_[]eZd[^c _[ ^j] bZefa]^] cnc^]e _c g]eZ[c^k`^]g pn ^`w_[i k]cda^c Zp^`_[]g mkZe e]`cdk]e][^c _[ ^j] \]j_ba]_[^Z `bbZd[^qUxyySWz{]aa|w[Zh[ e]`cdk]c ^Z Zf^_e_l] md]a bZ[cdef^_Z[ `[g k]gdb] h]_ij^ _[ eZg]k[ fZh]k^k`_[ cdcf][c_Z[ci][]k`aan a]`g ^Z j_ij]k \_pk`^_Z[c _[ ^j] fZh]k^k`_[ cdcf][c_Z[ eZd[^cq {_^j ^j] `_g Zm `b^_\] ][i_[] eZd[^co^j]c] g_c^dkp_[i \_pk`^_Z[co hj_bj `k] a_e_^]g ^Z cf]b_`a ][i_[] Zkg]kco `k] _cZa`^]g mkZe ^j] cdpmk`e]q sj]
c^kdb^dk] `[g ]mm]b^ Zm `[ `b^_\] ][i_[] eZd[^ `k] ]tfa`_[]gq }f]b_`a bZ[c_g]k`^_Z[ _c i_\][ ^Z ^j] bk_^]k_` mZkc]a]b^_[i ^j] `b^d`^Zk `c h]aa `c ^j] _[^]k`b^_Z[ `[g bZZkg_[`^_Z[ h_^j ^j] bj`k`b^]k_c^_b eZd[^ f`k`e]^]kcq v
mdk^j]k mZbdc Zm ^j_c `k^_ba] _c ^j] g]cbk_f^_Z[ Zm ^j] `g`f^_\] bZ[^kZa h_^j ^j] []b]cc`kn pZd[g`kn bZ[g_^_Z[cqsj] ]mm]b^ Zm `b^_\] ][i_[] eZd[^c _[ ^j] Z\]k`aa cnc^]e _c cjZh[ pn e]`[c Zm e]`cdk]e][^c _[ ^j] \]j_ba]q~]nhZkgc }Zd[go [cda`^_Z[o sk`[ce_cc_Z[
1. INTRODUCTIONsj] `d^ZeZ^_\] _[gdc^kn _c e`w_[i e`[n ]mmZk^c ^Z k]gdb] md]a bZ[cdef^_Z[ `[g ^jdc ^j] Y]e_cc_Z[c Zm _^c ma]]^q _mm]k][^ `ffkZ`bj]c `k] p]_[i fdkcd]gq [] fZcc_p_a_^n _c ^Z k]gdb] ^j] eZ\_[ie`cc]c pn k]gdb_[i ^j] [dep]k Zm bna_[g]kcq _ij]k bZefk]cc_Z[ _[ ^j] bZepdc^_Z[ bj`ep]kc `[g ^j]dc] Zm ^dkpZbj`ki]kc bZd[^]k`b^ ` k]gdb^_Z[ _[ f]kmZke`[b]q v[Z^j]k fZcc_p_a_^n _c ^Z g_cf][c] h_^j^j] p`a`[b_[i cj`m^o hj]k] ^j] e_cc_[i eZe][^ Zm _[]k^_` `acZ a]`gc ^Z ` k]gdb^_Z[ _[ bZ[cdef^_Z[q v[_[^]k]c^_[i `a^]k[`^_\] _c p`c]g Z[ ^j] fZcc_p_a_^n Zm `d^Ze`^_b`aan ch_^bj_[i Zmm bna_[g]kc _[ ^j] aZh]kf]kmZke`[b] k`[i]q ]k]o jZh]\]ko _^ _c [Z^ ^j] k]gdb^_Z[ Zm ^j] eZe][^ Zm _[]k^_` ^j`^ _c _[ ^j]mZk]ikZd[go pd^ k`^j]k ^j] cj_m^_[i Zm ^j] Zf]k`^_[i fZ_[^ h_^j ` aZh|bZ[cdef^_Z[ cf]]g k`[i]qva^jZdij `aa ^j]c] e]`cdk]c `k] md]a|]mm_b_][^o ^j]n a]`g ^Z ` g]^]k_Zk`^_Z[ _[ gk_\_[i bZemZk^o `cg_c^dkp_[i \_pk`^_Z[c `k] ^k`[ce_^^]g \_` ^j] ][i_[] eZd[^c `[g ^j] cdpmk`e] ^Z ^j] f`cc][i]kbZef`k^e][^q u`cc_\] eZd[^c `k] Zm^][ d[`pa] ^Z k]cZa\] ^j] bZ[ma_b^ p]^h]][ ^Zk d] cdffZk^ `[g k_g]bZemZk^q sj_c _c hjn ch_^bj`pa] eZd[^c `k] `ak]`gn p]_[i dc]g _[ e`[n \]j_ba]c ^Zg`nq sj] g`ef_[i`[g ^jdc ^j] gn[`e_b j`kg][_[i Zm ^j] eZd[^c b`[ p] aZh]k]g ]a]b^kZ[_b`aan Zk f[]de`^_b`aan _[ Zkg]k^Z id`k`[^]] ` k]gdb^_Z[ _[ c^_mm[]cco ]cf]b_`aan hj][ _ga_[i q Zk ^j] bZ[c_c^][^ _efa]e][^`^_Z[ Zm` gZh[c_l_[i bZ[b]f^o eZd[^c edc^ Zmm]k ^j] ]tf]b^]g bZemZk^ ]\][ d[g]k aZ`gq sj_c _co jZh]\]kohj]k] ch_^bj`pa] eZd[^c k]`bj ^j]_k a_e_^cqsj] dc] Zm `b^_\] ][i_[] eZd[^c _c ^j]k]mZk] _[bk]`c_[ian p]_[i ^]c^]gq sj] p`c_b _g]` _c ^Z k]gdb]^j] eZd[^ c^_mm[]cc mZk ^jZc] \_pk`^_Z[c h_^j hj_bj ^j] ][i_[] ]tb_^]c ^j] eZd[^ gd] ^Z d[p`a`[b]g][i_[] ^Zk d]cq sj_c k]gdb^_Z[ _[ c^_mm[]cc ^jdc a]`gc ^Z ` k]gdb^_Z[ _[ \_pk`^_Z[c ^k`[ce_^^]g ^Z ^j]cdpmk`e]q3257

2. BASICS
Active engine mounts are based on the well-known hydraulically damping engine mounts andperform their basic function. These consist of an elastomer main spring component to absorb the static
preload and to support the elastic mounting of the engine (see Figure 1, left). The engine is usuallyconnected to the inner part via an engine support. On the outside, the main spring component is fixed
to the subframe by means of a housing. For hydraulic damping, a working chamber filled with ahydraulic fluid is located below the main spring component, which is closed at the bottom by a channel
plate. As a rule, the fluid used is a glycol mixture. The channel in the channel plate now connects theworking chamber with a second, so-called compensating chamber, which is usually located below thechannel plate and which is closed off by a bottom compliance of high resilience. This compensating
chamber serves to accommodate the hydraulic fluid flowing through the channel and, due to its highflexibility, balances the static pressure in the mount. A decoupling membrane is located in the centerof the channel plate to adapt the high-frequency stiffness of the mount.

Figure 1 – Sectional view of a conventional hydraulic engine mount: - LH: Design with main spring
component (a), inner part (b), channel plate with lower compliance (c), channel plate (d), bottom
compliance (e), housing including screwing (f) – RH: Switchable version with membrane and air
chamber (g), tractive electromagnet (h) and lock with seal (i).
The deflection of the main spring component reduces the volume V of the working chamber. A
characteristic measure for the displacement potential of the main spring component is the so-called
effective area A = dV / dz, where z is the deflection of the mount. With harmonic excitation at low
frequency, hydraulic fluid is pumped through the channel between the working chamber and thecompensating chamber. Due to the viscosity η of the fluid, hydraulic damping occurs in the channel
due to the internal friction according to Hagen and Poiseuille [1]. A measure for the hydraulic damping
is the phase shift occurring between displacement excitation z and reaction force F, which is also
referred to as the loss angle. With increasing frequency, an oscillating system becomes more important,which consists of the elastic deformation of the main spring component and the mass of the liquid in
the channel. When the mount is excited in the resonance range, the amplitude of the liquid movementin the channel increases significantly, and with it the damping. The elastic properties of the mountalso change considerably here. The resonance system can be adjusted by channel length and diameterand adapted to the axle natural frequency as well as to the resonance of the engine mass with themount stiffness.
For frequencies above the resonant frequency, the inertia of the amount of liquid in the channel

3258

prevents a liquid exchange between the chambers. When the main spring component deflects, thepressure in the working chamber changes because the volume changes have to be absorbed by theinternal deformation of the main spring component and the decoupling membrane. A measure of thevolume absorption dV of the main spring component without its own deflection when the pressurechanges dp is the volumetric flexibility = dV / dp = A dz / dp. This pressure fluctuation at deflection
z finally causes an additional stiffness over the effective area, which is referred to as buckling strengthor dynamic hardening.
In the case of a switchable mount for idle decoupling, there is an additional membrane with an air
chamber on the side of the working chamber instead of the decoupling membrane in the channel plate(see Figure 1 right). With the volume of the air chamber, an additional flexibility is created in theworking chamber and thus dynamic hardening according to customer requirements is provided. This
air chamber is now connected to the environment via an opening, which is closed by a tractive
electromagnet. In this condition, the mount shows hydraulic damping and thus dynamic hardening.
The open air chamber, on the other hand, takes over the fluid displaced by the deflection of the main
spring component without changing the pressure in the working chamber. Without pressure changes,
however, no liquid is pumped through the channel. As a result, the hydraulic damping and the dynamic
hardening are missing. This decoupling in particular has a positive effect on smooth running at idling
speed and increases comfort.

3. ACTIVE ENGINE MOUNTThis chapter describes the specific features of the active engine mount. In addition to the overalltuning of the mount, the selection and design of the actuator is of central importance and will besummarized below. The description of the overall system includes the mount and the control unit withthe algorithm to map an adaptive control system. The chapter concludes with a consideration of theeffect in the vehicle.

3.1 Design
With active engine mounts, the variation of the pressure in the working chamber is modified in asimilar way to switchable mounts. In contrast to the switchable mounts, where stiffness and damping
characteristics can be changed in two states, here the influence on stiffness is frequency-selective.
Instead of the membrane with the air chamber, there is an elastically suspended actuator plate in thechannel plate, which is moved by the armature of an actuator. Figure 2 shows a sectional view of anactive engine mount. The stator of the actuator, like the outside of the main spring component and thechannel plate, is connected to the housing shell and thus firmly to the subframe. The frequency range
in which the active engine mounts operate is above the hydraulic resonance. We, therefore, consider
the case that no fluid is exchanged by the channel.
The following consideration is decisive for understanding the mode of action of an active engine
mount: The stiffness of a rubber mount, more precisely the transfer stiffness, causes a force fluctuationon the output side due to a deflection on the input side. Engine mounts support with their main spring
component on the subframe side when the main spring component is excited on the engine side. In
addition, the buckle strength becomes effective due to the pressure fluctuation. Active mounts are now
able to considerably reduce the force fluctuations on the subframe side for certain adjustablefrequencies. This practically means a frequency-selective reduction of the mount stiffness. The
frequency in question is derived from the unbalanced engine torques to the instantaneous engine speed.
This is known from the evaluation of the crankshaft sensor, but changes permanently during operation.

3259

Figure 2 – Schematic representation of an active engine mount : Inner part for travel excitation (a), main
spring component with effective area AT and volume compliance κT (b), channel plate with channel (c),decoupling membrane (d), actuator disk with cross section area AA (e), actuator membrane withcompliance κA (f), armature of actuator with mass mA (g), stator of actuator (h), set of springs withstiffness cA for elastic connection of armature (i).
An active engine mount is not only capable of compensating for the increase in pressure when theengine, but also of generating a negative pressure which compensates for the force effect of the main
spring component via the effective surface. This is done by moving the actuator plate, which is
attached to the actuator and elastically suspended in the channel plate, downwards. This enlarges theworking chamber so that instead of an overpressure as with conventional mounts, a negative pressureis created. If, on the other hand, the engine pulls on the mount, the actuator disc is moved upwards sothat not only the negative pressure is compensated but also an overpressure in the working chambercompensates the tensile forces exerted by the main spring component. If the actuator is excited in thecorrect phase, force fluctuations on the output side can be eliminated despite excitation on the engine
side. This eliminates the stiffness of the mount for this frequency. The mount therefore does notcounteract the deflection but avoids the movement. This is one of the most important findings anddecisive for understanding.
The fact that a reduction in stiffness leads to a reduction in the force acting on the subframe is dueto the type of excitation. Due to the high moments of inertia of the unbalanced engine orders, theengine generates an excitation by a displacement at the mounts. In the case of force excitations, which
predominantly occur in the chassis area, a reduction in stiffness would only lead to an increase in the
excitation amplitude. Therefore, the concept of active engine mounts cannot easily be transferred tomounting points in the chassis.
3.2 Actuator selection
The requirements analysis as a starting point for actuator selection and subsequent optimization of
the actuator parameters is of decisive importance. Customer requirements are taken into account andown objectives need to be formulated. These include an upper limit for the total weight of the actuator
as well as the frequency range in which the mount control is to operate. The maximum power
consumption and the associated coil design are also of decisive importance for the design.
Beyond the total weight, the frequency range and the power limit, there are parameters, which can
only be evaluated together with the installation situation in the mount. The force of the actuator and3260

the linear stroke are such parameters, whose limit values can be determined by the ratio of the effective
areas of the main spring component and actuator as well as by the volume compliance of the working
chamber. Two values have to be distinguished, especially for the movement of the actuator: on the
one hand, the stroke of the armature caused by the force effect, which determines the compensating
capacity via the flexibility of the working chamber, and on the other hand the linear free travel of thearmature. It must be taken into account that the forced movements may be superimposed by further
movements due to pressure fluctuations in the working chamber which lead to displacements of theworking point. Outside the linear clearance, the armature is slowed down elastically by end stops.
Finally, customer-specific overall optimizations are carried out with the help of the coil design.
After defining the yoke geometry of the actuator and the winding window, the force spectrum, i.e. theforce effect as a function of the frequency, can be adapted by varying the wire cross-section and thenumber of turns. However, it must be taken into account that the electrical cutoff frequency, which isdetermined by the inductance of the coils in the magnetic circuit, is well below the working range ofthe control system. The thermal properties can also be modified here.

Figure 3 – Two actuators with different operating principles for power generation: Shown are stator (a),armature (b) , solenoid coil (c) and permanent magnet (d) – LH: Lorentz force with electro-dynamic modeof operation – RH: Reluctance drive with electro-magnetic mode of operation
In order to implement a linear drive with the boundary conditions described above, there arebasically two principles of action that need to be narrowed down. The first is the electrodynamic drive,
whose operating principle goes back to Hendrik Antoon Lorentz [1]. A possible implementation isshown in Figure 3 on the left. A coil dips into an annular gap containing a magnetic field. This is
generated by a permanent magnet and guided through an iron yoke. This plunger coil is drawn into
the iron annular gap by current (Lorentz force). The current/force characteristic curve is very linear,since saturation effects in the iron do not occur here when current is applied. If the plunger coil islonger than the height of the radial magnetic field, the force/displacement characteristic curve is alsolinear. A technological challenge that can be overcome is the contacting of the moving coil. On theother hand, the power yield, which is not achieved under the described general conditions, isproblematic.
An alternative is the reluctance drive (see Figure 3 on the right). Here, too, two magnetic fields
interact, one generated by a permanent magnet and one by a coil. Preferably, the permanent magnet is
located as a ring on the inner armature and the coil in the outer stator. Variants of this are also known
[4].

3261

Figure 4 – Results of a simulation using Finite Element Analysis for optimization of the drive – LH: Field
distribution when the solenoids are energized. The structural interference at the lower end and thedestructive interference at the upper end can be identified. The action of force on the armature is here
towards the top – RH: Force mapping after optimization. The force is applied as a function of the stroke
and the coil current.
The force effect results from the only partial overlapping of the front surfaces of the yokes of statorand armature on the upper and lower side of the actuator. Without current, the fields generated by thepermanent magnet in the annular gap between the yoke ends and thus the forces on both sides are thesame. A second magnetic field is generated around the coil by current supply, which is superimposedconstructively at one end with the magnetic field of the permanent magnet and destructively at theother end. On the side of the constructive superposition, the force increases which wants to reduce theresistance of the magnetic circuit by the yokes overlapping each other more strongly. On thedestructive superposition side, the counterforce decreases. An example of a field distribution is shownin Figure 4 on the left. As a result, Figure 4 on the right shows the force field, i.e. the force as afunction of the stroke and the coil current.
The superposition processes generally do not lead to linear characteristic curves. However, since two
sub-processes compete in the reluctance drive shown here, linear characteristics can be set in a
restricted stroke range. It is important that linearity and force can be adapted to the application. Thismeans that the requirements agreed above can be implemented.
3.3 Control unit
In order to design an active mount from a hydraulically damping mount, the implementation of an
actuator is not sufficient. In addition, a control unit is required which calculates a control signal on
the basis of the acceleration signal together with other input variables and uses this to control theactuator via power electronics. The architecture of this ECU (electronic control unit) is shown
schematically in Figure 5. The target frequencies for which the active mount is to isolate are first
calculated from the signal from the crankshaft sensor. The signal supplied by the acceleration signal
is filtered for harmonic components with these target frequencies. An algorithm then calculates theamplitude and phase of the current required to isolate the contributions at the target frequency anduses this signal to control the power electronics (H-bridge), which then supply the actuator withcurrent. The force effect of the actuator influences the signal at the acceleration sensor, which provides

3262

its signal again for adaptation. In addition, the ECU performs diagnostic jobs and monitors the CAN(Controller Area Network) for communication with the vehicle ECU.

Figure 5 – System architecture of the active engine mount
3.4 Effect in the vehicle
To assess the functionality of the overall system, the mode of action in the vehicle is described
below. In the following application, the active engine mounts carry an in-line four-cylinder engine.
With this engine, the second engine order is the first order not balanced due to the ignition processes.
Another unbalanced engine order is the fourth. The aim now is to eliminate the force fluctuations withthe frequencies belonging to these orders on the mount housing despite the harmonious engine-side
excitation. A measure for these force fluctuations is the signal transmitted by the acceleration sensor.
Figure 7 on the left shows the signal from the accelerometer mounted on the housing as a function of
the engine orders and the engine speed in the form of a Campbell diagram. The high acceleration
values of the second and fourth engine orders can be seen. This diagram was created with the engine
mounts deactivated. In contrast, Figure 7 on the right shows the same diagram with active engine
mounts, where the system eliminates both orders. A reduction of the second and fourth engine orders
to noise level can be seen.

Figure 7– Acceleration as a function of revolutions per minute (speed), applied via the engine order of afour-cylinder engine. The color shows the acceleration according to the scaling RH. – LH: Recording withdeactivated engine mounts – RH: Recording with activated engine mounts.

3263

For the quantitative evaluation, the temporal course of the switch-on and switch-off of the mounts
is to be considered. Figure 8 on the left shows the acceleration as a function of the engine orders at a
speed of 2000 rpm during the switching operations of the second order. Here, too, the signal is reduced
to the level of the noise.

Figure 8– Acceleration as a function of speed, plotted over the engine order of a four-cylinder engine. The color shows the acceleration value according to the scaling on theright. - Left: Right: image with activated engine mounts.
Figure 9– Development over time of acceleration at a fixed speed of 2000 rpm during

activating and deactivating of active engine mounts, applied via the engine order of afour-cylinder engine. – LH: The color shows the acceleration figure according to thescaling RH. – RH: The development of the second engine order is shown.
Finally, Figure 8 on the right shows the time course of the acceleration at a speed of 2000 rpm
during the switching operations. A reduction of 20 dB within 300 ms and a total reduction of up to 30
dB can be seen.

4. Conclusions
Only by application of active engine mounts it is possible to eliminate the conflict of objectives
between firm powertrain suspension systems on the one hand and isolation of disturbing vibration andnoise on the other hand. Thus, the range of possible measures to reduce consumption in engine
suspension systems increases significantly. A precondition is, however, a design that is tailored to thespecific needs of the individual application case. This representation describes the structure and modeof operation of active engine mounts. In this respect, special aspects such as the selection of theappropriate operating principle for the actuator play a key role and are the precondition for the
manufacture of tailor-made systems. Thus, active engine mounts enable the consistent implementationof the consumption reduction measures.

REFERENCES
1. Gerthsen, Vogel: „Physik“, 17. Auflage, Springer-Verlag, 1993
2. Heißing, Ersoy: „Fahrwerkhandbuch“ 2. Auflage, Vieweg+Teubner, 2008, S. 475ff
3. Patentanmeldung 10 2011 088 924.8: Steifigkeitsanpassung bei Motorlagern
4. Patentschrift: DE 198 39 464 C 2
5. P. Lueg, „Verfahren zur Dämpfung von Schallschwingungen“, Deutsches Reichspatent r. 655508, 19333264