In this paper, a novel structure of a controlled
multi-channel semi-active magnetorheological (MR) fluid mount is proposed,
including four controlled channels and one rate-dip channel. Firstly, the
magnetic circuit analysis, rate-dip channel optimization design, and MR
fluid mount damping analysis are given. Secondly, the mathematical model of the controlled
multi-channel semi-active MR fluid mount is constructed. We analyze the effect
of controlled multi-channel closing on the dynamic characteristics of
the mounts and the effect of the presence or absence of the rate-dip channel on
the low-frequency isolation of the mount. Finally, the controlled
multi-channel semi-active MR fluid mount was applied to the
Numerical simulation shows the following points. (1) The controllable multi-channel semi-active
MR fluid mount can achieve adjustable dynamic stiffness and damping with
applied 2
The engine rotational unbalanced reciprocating inertial force and uneven road surface excitation are the main excitation sources of vehicle vibration (Lee et al., 1994). As a vibration isolation element, the mounts connect the power train to the vehicle frame. The main role of the mounts is to support the engine static load-bearing capacity, isolate the transmission of engine vibration to the vehicle frame, reduce the impact of road impact on the engine, and limit the engine movement space (Li et al., 2019). Ideal engine mounts should exhibit large stiffness and large damping at low frequency and low stiffness and low damping at high frequency to achieve the vibration isolation requirements for different vehicle operating conditions (Christopherson et al., 2012; Yu et al., 2001a). At present, mounts used for engine vibration isolation can be divided into rubber mounts, hydraulic mounts, semi-active mounts, and active mounts. Compared to rubber mounts, hydraulic mounts (Fan, 2006) improve noise, vibration, and harshness (NVH) performance at low frequency, but the greater dynamic stiffness at high frequency due to hardening is not conducive to noise reduction. Active mounts can achieve better NVH performance in a wider band under automotive driving conditions, but their complex structure and high cost are only used in a few luxury vehicles (Hausberg et al., 2015; Römling et al., 2003; Fan et al., 2020). Semi-active mounts require less energy and can achieve vibration isolation over a wide frequency range. Therefore, semi-active mounts have a higher prospect of utilization compared to other mounts. The semi-active mount is mainly characterized through controllable structural parameters or controllable fluid parameters (Fan et al., 2020). Controllable parameters include controllable inertia channel cross-sectional area, inertia channel length, the flexibility of the upper chamber. Controllable fluid parameters include smart materials such as MR fluid and electrorheological fluid (ER). Wang et al. (2014) used an electric motor to simultaneously adjust the length and cross-sectional area of the hydraulic mount inertia channel to achieve wide-frequency vibration isolation. Tikani et al. (2010) and Truong and Ahn (2010) used a mechanically controllable inertial channel cross-sectional area to achieve engine vibration isolation (Tikani et al., 2010; Truong and Ahn, 2010). Mansour added an MR fluid chamber to the upper chamber of the hydraulic mount in order to solve the vibration caused by the VDE engine, and they changed the flexibility of the upper chamber through a magnetic field to achieve adjustable dynamic stiffness of the mount (Mansour et al., 2011). MR fluid has a fast response, low energy consumption, and favorable controllability (Shah and Choi, 2015; Zhu et al., 2012). Although ER fluid has a fast response, it requires high voltage and has some drawbacks in automotive applications. The operating modes of MR fluid mounts can be classified as flow mode, squeeze mode, shear mode, and pinch mode (Imaduddin et al., 2013). Chen et al. (2016) proposed a squeeze model of semi-active MR fluid mount for passenger vehicle vibration isolation. Nguyen et al. (2013) proposed a flow working mode MR fluid mount in which the flow channel structure uses a combination of annular and radial channels to improve the damping force of the mount. John and Kumar (2016) proposed a shear working mode of MR fluid mount. In summary, the existing semi-active mount study has the following problems. (1) Although the semi-active mount with controllable structural parameters can meet the vibration isolation in a certain frequency range, the structure and control are complicated. (2) Controllable fluid parameters of the semi-active mount can only be continuously adjustable for a specific frequency damping and cannot achieve engine wide-frequency isolation.
In order to solve the conflicting design requirements of engine mounts for
stiffness and damping characteristics under different frequency operating
conditions, a controllable multi-channel semi-active MR fluid mount with
adjustable stiffness and damping is proposed. The structure of the
semi-active mount consists of four controllable channels and one rate-dip
channel. Applying current to the four controllable channels to achieve
controllable channel closing indirectly changes the cross-sectional
area of the total channels of the semi-active mount and finally achieves
adjustable dynamic stiffness and damping of the mount. Analysis of the
effect of controlled channel closing on the dynamic characteristics of
the mount was performed. We analyzed the effect of the presence or absence of the rate-dip channels on
the low-frequency vibration isolation performance of the mount. Finally, a
Schematic configuration of controllable multi-channel semi-active MR fluid mount.
Controlled channel and coil arrangement
Characteristic of MR fluid
There are two conditions. (1) The engine reciprocating inertial force requires the mount to provide small stiffness and small damping, and (2) the road excitation requires the mount to provide large stiffness and damping (Yu et al., 2001b). To satisfy conditions (1) and (2), a controlled multi-channel semi-active MR fluid mount is designed to change the yield stress of the MR fluid in the damping gap by applying a current. This allows channel closing for the semi-active MR fluid mount with adjustable stiffness and damping.
The controllable multi-channel semi-active MR fluid mount is shown in Fig. 1, with its main components labeled. Figure 1 shows that the MR fluid mount consists of mainspring rubber, flexible rubber diaphragm, rate-dip channel, inertia channel, and magnetic circuit assembly. Among them, the magnetic circuit assembly consists of a coil, iron core, and spacer, as shown in Fig. 2a.
The MR fluid chamber is divided into upper and lower chambers by channels, and each chamber is filled with MR fluid. The semi-active MR fluid mount consists of four controllable channels and one rate-dip channel. In Fig. 2a the coil (in red) applied current to change the yield stress of the MR fluid in the middle part of the channel to achieve switching of the channel. The MR fluid selected was supplied by Lord (type 126CD). In Fig. 2, the copper coil is shown in red, the high-permeability material (generally pure iron for electricians) is shown in gray, and the controllable channel is shown in green. The semi-active MR fluid mount at higher current to achieve channel closing is shown in Fig. 2b in the green area of the Z-shaped channel diagram. The advantage of this design is that three different operating states can be achieved as follows. (1) When a higher current is applied to the middle part of the controllable channel, the MR fluid instantly gathers in the direction of the generated magnetic field. This increases the yield stress of the MR fluid, which prevents the flow of the fluid and indirectly controls the total cross-sectional area of the MR fluid mount controllable channel. (2) When a lower current is applied, the mount returns to the conventional inertial channel flow mode of operation, in which the mount achieves continuously adjustable damping without the channel being closed. (3) When no current is applied, the mount returns to a multi-channel passive hydraulic mount.
MR fluid type 126CD with a viscosity of
The fitted polynomials are as follows:
The shear yield stresses fitting polynomial is given by
Structure and structural parameters of the magnetic core assembly. 1 is coil, 2 is core, 3 is magnetic spacer, 4 is magnetic flux line, and 5 is the controllable channel.
Design of magnetic circuit size.
Single controlled channel magnetic circuit characteristics:
In order to easily calculate the MR fluid mount magnetic circuit, Fig. 2
is simplified to Fig. 4. If we assume that the flux in the magnetic circuit is
uniformly distributed and that there is no magnetic leakage, then according to the law
of conservation of magnetic flux, the flux density in the closed magnetic
circuit is determined by the following equation.
The magnetic circuit is analyzed using the magnetic Kirchhoff's law as
follows:
According to the MR fluid controllable channel shown in Figs. 2 and 4, the effective length of the
Combining Figs. 2 and 4, the equivalent cross-sectional area of each
part can be calculated based on the structural dimensional parameters as
follows:
According to Hu et al. (2017), Eq. (8) can be obtained:
From Eqs. (5)–(9),
the magnetic flux intensity in the
controllable channel region is further deduced as
To ensure that the controlled channel MR fluid channel is the primary
saturation state, the magnetic flux intensity of
Rate-dip channels with different structures.
Equivalent hydraulic mount when all controllable channels are
closed:
Relative displacement transmissibility of the three structures.
Relative displacement transmissibility of the three optimized structures and the conventional channel structure.
To avoid applying large currents to the four controllable channels, all four controllable channels are blocked leading to oscillatory states in the dynamic stiffness and damping of the semi-active MR fluid mount at low frequency. Adding a rate-dip channel to the controllable multi-channel semi-active MR fluid mount avoids oscillatory states of dynamic stiffness and damping. Three different rate-dip channel structures were chosen, as shown in Fig. 6. Structure 1 is a circular pipe with the same inlet and outlet, whereas structure 2 is an abruptly enlarged pipe, and structure 3 is an abruptly reduced pipe.
When all four controllable channels are closed, Fig. 1 can be simplified
to the hydraulic mount shown in Fig. 7. Figure 7a shows the structure
and Fig. 7b shows the lumped parameter model. In Fig. 7b,
In order to address the large value of engine vibration due to road
excitation, all four controllable channels are closed, and the design
criteria for the mount, in this case, are based on the displacement transfer
rate
if we assume that the hydraulic mount is excited by
In order to achieve the minimum relative displacement transmissibility of
the mount, three different rate-dip channels are used as the study objects.
The design objective function is the minimum of the maximum value of the
relative displacement transfer rate
Multi-channel magnetorheological fluid mount of the lumped parameter model.
Controlled multi-channel magnetorheological fluid mount flow,
damping force, upper chamber pressure,
Controllable multi-channel semi-active MR fluid mount dynamic
characteristics
According to the lumped parameter model of controlled multi-fluid
semi-active MR fluid mount in Fig. 10 and combined with Nguyen et al. (2013), the following equation can be found for the pressure
difference between the upper and lower chambers of the mount.
The pressure drop of the
So, the damping force of the
We performed numerical simulation of the MR fluid mount subjected to an external excitation
frequency of 12.5
Effect of the presence or absence of the rate-dip channel on the dynamic
characteristics of MR fluid mount
Transmissibility of MR fluid semi-active mount switching for different controllable channels.
Effect of different excitation sources on the mount:
For the frequency domain analysis, the parameters for evaluating the dynamic
characteristics of the MR fluid mount are dynamic stiffness and loss angle.
Dynamic stiffness is the ratio of vibration response force amplitude to
vibration displacement amplitude at the external excitation frequency. The
loss angle responds to the angle at which the displacement lags behind the
force and characterizes the magnitude of the vibration isolator damping
force. The complex stiffness
According to Figs. 1 and 10, the mathematical equations of the
controllable multi-channel semi-active MR fluid mount
single-degree-of-freedom system can be derived as
According to the above equations, the dynamic stiffness and loss angle of the controllable multi-channel semi-active MR fluid mount can be obtained as shown in Fig. 12.
In Fig. 12, the solid black line represents the four controllable channels where a 2
Based on the optimal rate-dip channel structure proposed in Sect. 2.2, the effect of the presence and absence of rate-dip channels on the dynamic characteristics of the MR fluid mount is simulated numerically. The chaotic state of dynamic stiffness and loss angle of the mount without rate-dip channel is compared to with rate-dip channel in the structure of controlled multi-fluid semi-active MR fluid mount (black oval region in the Fig. 13). In Fig. 13b there is even a negative loss angle. Therefore, the designed controllable multi-channel semi-active MR fluid mount needs to consider the effect of the rate dip on its dynamic characteristic.
Numerical simulation of the variation of displacement transmissibility for
different channels with 2
According to Fig. 14, the graphs and controllable areas of different
frequency bands with different displacement transmissibility are divided.
Between
The controllable multi-channel semi-active MR fluid mount is considered to
be subjected to a road excitation with a frequency of 20
Effect of mount isolation of the
Automotive designers can better predict the mount vibration isolation
performance by analyzing the
The
When the system is subjected to a large-amplitude excitation of the road
surface with a frequency of 0–30
So, in practical use, once the type of vehicle is selected, the excitation
frequency range of the engine is known. When the vehicle is driven on rough
roads, a 2
Semi-active MR fluid mount with four controllable channels and one rate-dip
channel, characterized by applying a current to the four controllable channels,
making the controllable channel switching. Controlled channel switch
close makes the total cross-sectional area of the MR fluid mount channel
change, thus realizing adjustable mount dynamic stiffness and damping.
rate-dip channels are unaffected by magnetic fields and are always flowing.
As a result, the following conclusions can be drawn. (1) The designed
magnetic circuit structure can meet the channel switching requirements, different
channel applied currents, and can realize the design of controllable
multi-channel MR fluid mount to achieve wide-frequency vibration isolation.
(2) The rate-dip channel improves semi-active mount low-frequency isolation
performance when all four controllable channels are closed. Simultaneously,
currents are applied to different controllable channels to derive the
optimal range of vibration isolation frequencies. (3) For the
Controlled multi-channel semi-active magnetorheological fluid mount parameters.
All data included in this study are available upon request from the corresponding author.
ZL is responsible for the methodology proposal and the writing of the draft paper. MW contributed to the grammar check.
The authors declare that they have no conflict of interest.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
This research has been supported by the Quanzhou City Science&Technology Program of China (grant no. 2018Z016).
This paper was edited by Zi Bin and reviewed by three anonymous referees.