The aim of this project is building a magneto-rheological device to demonstrate how changing the electricity current affects the damping force. Manufacturing an MR valve and use it as a controllable component is necessary to achieve this goal.
MR Fluid is a fluid with high density of magnetic particles, which are typically micrometer scale and suspended within the carrier oil. The particles are distributed randomly and in suspension under normal circumstances. Following figure illustrate MR fluid.
When a magnetic field is applied, the microscopic particles align themselves along the lines of magnetic flux. The fluid greatly increases its shear stress, to the point of becoming a viscoelastic solid. The yield stress of the fluid can be controlled very accurately by varying the magnetic field intensity.
MRF-132DG from LORD Company has been used in this project. In the following curve fluid's yield stress versus magnetic field strength has been shown.
A magnetorheological valve is a valve filled with magnetorheological fluid, which is controlled by a magnetic field, usually using an electromagnet. This allows the damping characteristics of the system to be continuously controlled by varying the power of the electromagnet. This type of shock absorber has several applications, most notably in semi-active vehicle suspensions which may adapt to road conditions, as they are monitored through sensors in the vehicles.
parameters such as core and body material and shape, number of coil turns has effect only on hydraulic properties or magnetic properties of the valve, but gap size is a parameter with positive effect on MR pressure drop and negative effect on hydraulic pressure drop. So, the challenge is designing a valve with minimum hydraulic pressure drop and maximum magnetic pressure drop in the same time. Tighter gap provides more magnetic pressure loss at system's on state. On the other hand, tight gap cause more hydraulic pressure loss which is not desirable. In the other word, an ideal MR Valve is a valve with zero hydraulic pressure loss and infinite magnetic pressure loss. Such a valve is 100 percents controllable regarding applied current.
Designed MR Valve CAD model and manufactured parts have been presented in following figures.
- Orange part: It has two functionalities. The first is magnetic coil's core and the second is acting as the inner part of the channel to make narrow gaps.
- Yellow part: By winding the winding wires around it coil will be made.
- Gray Part: It has been used as mounting parts to keep the core in the proper place.
- Red Part: It is the valve shield that keep the whole parts in their place and prevent fluid leaking. In addition hydraulic pipes will be connected to its inlet and outlet.
Manufactured parts have been shown in following figures. 3 O-rings have been used to prevent fluid leakage. outer bolts prepare comparison force to squeeze them.
Magnetic field FEM analysis result shows that magnetic flux is significant at fluid gaps. So, this is an acceptable design which is worth to be manufactured.
DOUBLE ACTING HYDRAULIC CYLINDER
In the double acting cylinders, the pressure from the fluid is applied in both the directions.
HYDRAULIC LINE AND FITTINGS
Conventional hydraulic steel pipe with brass compression fittings has been used to make the hydraulic line and connect the components. Compression x NPTF Male has been used to connect the pipe sides to the components.
Lever mechanism with long handle has been used to move the hydraulic cylinder with less force and more moving range. In addition this mechanism is so compatible with hydraulic cylinders and solves the cylinder mounting problems. This mechanism has been shown in the following image.
ADJUSTABLE POWER SUPPLY
Magnet wire is a copper or aluminum wire coated with a very thin layer of insulation. It is used in the construction of transformers, inductors, motors, speakers, hard disk head actuators, potentiometers, electromagnets, and other applications which require tight coils of wire.
Used to connect power supply to coil's winding wires.
Components and budget
|MR Fluid||Free - Esa Kostamo|
|Winding Wire||Free - Esa Kostamo|
|Steel Bar||Free - Esa Kostamo|
|Aluminum Bar||Free - Esa Kostamo|
|Sealant||Free - Hydraulic Lab|
|Hydraulic Line and Fittings||Free - Hydraulic Lab|
|Hydraulic Cylinder||Free - Hydraulic Lab|
|Lever Mechanism||Free - Hydraulic Lab|
|Power Supply||Free - Mechatronics Lab|
|Cables||Free - Mechatronics Lab|
A power supply with adjustable current and voltage is necessary to run the system. 0 to 5 voltage and 0 to 5 current is the suitable range of voltage and current.
- Switch the power supply on and turn the voltage knob to 5 V and current knob to 0 A.
- Connect the valve's wires to the power supply (no polarity).
- Move the handle to see hydraulic pressure drop and frictions effect.
- Move the handle slowly and in the same time increase the current amount to the maximum (5 A). It is obvious how increasing the voltage increases the damping force.
- As the experimental result of the manufactured valve 3 Amp current is applicable for an unlimited time. So applying up to 5 Amp for some minutes should not cause overheating the valve. Exceeding current more than 5 Amp is not recommended.
- Do not forget to switch the system off when it is not in use, long time current flow may cause overheating the coil and damaging the winding wires.
Conclusions and suggestions
The effect of magnetic field was obvious on lever moving force which represents damping force in a vibrational system. But I am pretty sure by optimizing the affecting parameters damping force can increase dramatically. Some suggestion for future work has been presented below.
- Drawing damping force versus current curve, since it provides a clear overview of the system in vibrational aspect.
- Studying gap size effect on damping force and hydraulic pressure drop at magnet off state by using different cores with different outer dimensions.
- Studying coil turns effect on the valve damping force.
- going through an iterative procedure to optimize the valve performance by finding the best amounts of gap size, material and coil turns.
Part CAD drawing files: