INTRODUCTION TO MAGNETIC
SHOCK ABSORBERS
The idea for a magnetic shock absorber (for
automobiles and two-wheelers), makes use of the magnetic repulsion between
dipoles (two poles) to achieve shock absorption
It observed that the like poles of two magnets
of the same properties and strength repulse each other and they keep a constant
distance between each other because of their magnetic fields.
The unit comprises of two circular magnets and
a rod (straight cylindrical rod which can be used as axle). One magnet is
attached at the bottom of the rod and is the base magnet. The other magnet is
free, with a float and has the similar pole placed towards the base magnet. The
similarity of poles creates repulsion and a certain distance is maintained. As
per load condition, the floating magnet moves and closes the gap until the
magnetic repulsion is strong enough to create the damping action. In this
manner a shock absorber without springs working on the basic law of magnets
-opposite poles attract and similar poles repel- is prepared.
SHOCK ABSORBERS
A shock absorber in common
parlance (or damper in technical use) is a mechanical device designed to smooth
out or damp sudden shock impulse and dissipate kinetic energy. It is analogous
to a resistor in an electrical circuit.
Shock absorbers must absorb or dissipate
energy. One design consideration, when designing or choosing a shock absorber
is where that energy will go. In most dashpots, energy is converted to heat
inside the viscous fluid. In hydraulic cylinders, the hydraulic fluid will heat
up. In air cylinders, the hot air is usually exhausted to the atmosphere. In
other types of dashpots, such as electromagnetic ones, the dissipated energy
can be stored and used later.
Shock absorbers or damper types for shock absorbers, linear dampers and dashpots can be hydraulic, air, gas spring, or elastomeric. The absorption or damping action can be compression or extension. Important parameters to consider when searching for shock absorbers, linear dampers and dashpots include absorber stroke, compressed length, extended length, maximum force (p1), and maximum cycles per minute. Absorber or spring stroke is difference between fully extended and fully compressed position. Compressed length is the minimum length of shock (compressed position). Extended length is the maximum length of shock (extended position). The maximum rated force for shock absorber or damper, referred to as the p1 force. The maximum cycles per minute are the rated frequency of compression/extension cycles.
Important physical specifications to consider when searching shock absorbers, linear dampers and dashpots include the cylinder diameter or maximum width, the rod diameter, mounting, and body material. The cylinder diameter or maximum width refers to the desired diameter of housing cylinder. The rod diameter refers to the desired diameter of extending rod. Mounting choices include ball and socket, rod end, clevis, eyelet, tapered end, threaded, and bumper or rod end unattached. Choices for body materials include aluminum, steel, stainless steel, and thermoplastic. Common features for shock absorbers, linear dampers and dashpots include adjustable configuration, reducible, locking, and valve. An adjustable configuration allows the user to fine tune desired damping, either continuously or at discrete settings. A reducible shock absorber, linear damper or dashpot has an adjustment style for gas shocks in which gas is let out to permanently reduce force capacity. In a locking configuration, the position can be locked at ends or in the middle of stroke. Valves can be included for fluid absorbers, a valve or port, which can be used to increase or decrease fluid volume or pressure.
USES OF SHOCK ABSORBERS
VEHICLES
SUSPENSION
In a vehicle, it reduces the effect of
traveling over rough ground, leading to improved ride quality. Without shock
absorbers, the vehicle would have a bouncing ride, as energy is stored in the
spring and then released to the vehicle, possibly exceeding the allowed range
of suspension movement. Control of excessive suspension movement without shock
absorption requires stiffer (higher rate) springs, which would in turn give a
harsh ride. Shock absorbers allow the use of soft (lower rate) springs while
controlling the rate of suspension movement in response to bumps. They also,
along with hysteresis in the tire itself, damp the motion of the unsprung
weight up and down on the springiness of the tire. Since the tire is not as
soft as the springs, effective wheel bounce damping may require stiffer shocks
than would be ideal for the vehicle motion alone.
Spring-based shock absorbers commonly use coil
springs or leaf springs, though torsion bars can be used in torsional shocks as
well. Ideal springs alone, however, are not shock absorbers as springs only
store and do not dissipate or absorb energy. Vehicles typically employ both
springs or torsion bars as well as hydraulic shock absorbers. In this
combination, "shock absorber" is reserved specifically for the
hydraulic piston that absorbs and dissipates vibration.
STRUCTURES
Applied to a structure such, as a building may
be part of a seismic retrofit or as part of new earthquake resistant
construction. In this application, it allows yet restrains motion and absorbs
resonant energy, which can cause excessive motion and eventual structural
failure.
DIFFERENT SHOCK ABSORBERS IN USE
There are several commonly-used approaches to
shock absorption:
- Hysteresis
of structural material, for example the compression of rubber disks,
stretching of rubber bands and cords, bending of steel springs, or
twisting of torsion bars. Hysteresis is the tendency for otherwise elastic
materials to rebound with less force than was required to deform them.
Simple vehicles with no separate shock absorbers are damped, to some
extent, by the hysteresis of their springs and frames.
- Dry friction
as used in wheel brakes, by using disks (classically made of leather) at
the pivot of a lever, with friction forced by springs. Used in early
automobiles. Although now considered obsolete, an advantage of this system
is its mechanical simplicity; the degree of damping can be easily adjusted
by tightening or loosening the screw clamping the disks, and it can be
easily rebuilt with simple hand tools. A disadvantage is that the damping
force tends not to increase with the speed of the vertical motion.
- Solid state,
tapered chain shock absorbers, using one or more tapered, axial
alignment(s) of granular spheres, typically made of metals such as nitinol,
in a casing.
- Fluid
friction, for example the flow of fluid through a narrow orifice
(hydraulics), constitute the vast majority of automotive shock absorbers.
An advantage of this type is that using special internal valving the
absorber may be made relatively soft to compression (allowing a soft
response to a bump) and relatively stiff to extension, controlling “jounce”,
which is the vehicle response to energy stored in the springs; similarly,
a series of valves controlled by springs can change the degree of
stiffness according to the velocity of the impact or rebound. Some shock
absorbers allow tuning of the ride via control of the valve by a manual
adjustment provided at the shock absorber. In more expensive vehicles the
valves may be remotely adjustable, offering the driver control of the ride
at will while the vehicle is operated. The ultimate control is provided by
dynamic valve control via computer in response to sensors, giving both a
smooth ride and a firm suspension when needed. Many shock absorbers
contain compressed nitrogen, to reduce the tendency for the oil to foam
under heavy use. Foaming temporarily reduces the damping ability of the
unit. Another variation is the magneto rheological damper which changes
its fluid characteristics through an electromagnet.
- Compression
of a gas, for example pneumatic shock absorbers, which can act like
springs as the air pressure is building to resist the force on it. Once
the air pressure reaches the necessary maximum, air dashpots will act like
hydraulic dashpots. In aircraft landing gear air dashpots may be combined
with hydraulic damping to reduce bounce. Such struts are called oleo
struts(combining oil and air).
- Magnetic
effects. Eddy current dampers are dashpots that are constructed out of a
large magnet inside of a non-magnetic, electrically conductive tube.
- Inertial
resistance to acceleration, for example prior to 1966 the citroen 2cv had
shock absorbers that damp wheel bounce with no external moving parts.
These consisted of a spring-mounted 3.5 kg (7.75 lb) iron weight inside a
vertical cylinder and are similar to, yet much smaller than versions of
the tuned mass dampers used on tall buildings
- Composite
hydropneumatic devices which combine in a single device spring action,
shock absorption, and often also ride-height control, as in some models of
the citroen automobile.
- Conventional
shock absorbers combined with composite pneumatic springs with which allow
ride height adjustment or even ride height control, seen in some large
trucks and luxury sedans such as certain lincoln and most land rover
automobiles. Ride height control is especially desirable in highway
vehicles intended for occasional rough road use, as a means of improving
handling and reducing aerodynamic drag by lowering the vehicle when
operating on improved high speed roads.
- The effect
of a shock absorber at high (sound) frequencies is usually limited by
using a compressible gas as the working fluid and/or mounting it with
rubber bushings.
WHAT SHOCKS DO?
Let us start our discussion of shock absorbers
with one of very important point: despite what many people think, conventional
shock absorbers do not support vehicle weight. Instead, the primary purpose of
the shock absorber is to control spring and suspension movement. This is
accomplished by turning the kinetic energy of suspension movement into thermal
energy, or heat energy, to be dissipated through the hydraulic fluid.
Hydraulic fluid in the pressure tube. As the
suspension travels up and down, the hydraulic fluid is forced through tiny
holes, called orifices, inside the piston. However, these orifices let only a
small amount of fluid through the piston. This slows down the piston, which in
turn slows down spring and suspension movement.
The amount of resistance a shock absorber develops depends on the speed of the suspension and the number and size of the orifices in the piston. All modern shock absorbers are velocity sensitive hydraulic damping devices – meaning the faster the suspension moves, the more resistance the shock absorber provides. Because of this feature, shock absorbers adjust to road conditions. As a result, shock absorbers reduce the rate of:
The amount of resistance a shock absorber develops depends on the speed of the suspension and the number and size of the orifices in the piston. All modern shock absorbers are velocity sensitive hydraulic damping devices – meaning the faster the suspension moves, the more resistance the shock absorber provides. Because of this feature, shock absorbers adjust to road conditions. As a result, shock absorbers reduce the rate of:
- Bounce
- Roll or sway
- Brake dive
and acceleration squat
Shock absorbers work on the principle of fluid
displacement on both the compression and extension cycle. A typical car or
light truck will have more resistance during its extension cycle then its
compression cycle. The compression cycle controls the motion of a vehicle’s
unsprung weight, while extension controls the heavier sprung weight.
WORKING OF SHOCK ABSORBERS
Shock absorbers work in two cycles -- the compression
cycle and the extension cycle. The compression cycle
occurs as the piston moves downward, compressing the hydraulic fluid in the
chamber below the piston. The extension cycle occurs as the piston moves toward
the top of the pressure tube, compressing the fluid in the chamber above the
piston. A typical car or light truck will have more resistance during its
extension cycle than its compression cycle. With that in mind, the compression
cycle controls the motion of the vehicle's unsprung weight, while extension
controls the heavier, sprung weight.
COMPRESSION CYCLE
During the compression stroke or downward
movement, some fluid flows through the piston from chamber b to chamber and
some through the compression valve into the reserve tube. To control the flow,
there are three valving stages each in the piston and in the compression valve. At
the piston, oil flows through the oil ports, and at slow piston speeds, the
first stage bleeds come into play and restrict the amount of oil flow. This
allows a controlled flow of fluid from chamber b to chamber a.
At faster piston speeds, the increase in fluid pressure below the piston in chamber b causes the discs to open up away from the valve seat.
At faster piston speeds, the increase in fluid pressure below the piston in chamber b causes the discs to open up away from the valve seat.
At high speeds, the limit of the second stage discs phases into the third stage orifice restrictions. Compression control, then, is the force that results from a higher pressure present in chamber b, which acts on the bottom of the piston and the piston rod area.
EXTENSION CYCLE
As the piston and rod move upward toward the
top of the pressure tube, the volume of chamber a is reduced and thus is at a
higher pressure than chamber b. Because of this higher pressure, fluid flows
down through the piston’s 3-stage extension valve into chamber b.
However, the piston rod volume has been withdrawn from chamber b greatly increasing its volume. Thus the volume of fluid from chamber a is insufficient to fill chamber b. The pressure in the reserve tube is now greater than that in chamber b, forcing the compression intake valve to unseat. Fluid then flows from the reserve tube into chamber b, keeping the pressure tube full.
Extension control is a force present as a result of the higher pressure in chamber a, acting on the topside of the piston area.
DIFFERENT SHOCK
ABSORBER DESIGN
There are several shock absorber designs in
use today:
- Twin tube
designs
- Gas charged
- ASD
- PSD
- Mono tube
design
BASIC TWIN TUBE
DESIGN
The twin tube design has an inner tube known
as the working or pressure tube and an outer tube known
as the reserve tube. The outer tube is used to store excess
hydraulic fluid.
There are many types of shock absorber mounts used today. Most of these use rubber bushings between the shock absorber and the frame or suspension to reduce transmitted road noise and suspension vibration. The rubber bushings are flexible to allow movement during suspension travel. The upper mount of the shock absorber connects to the vehicle frame.
Bore size is the
diameter of the piston and the inside of the pressure tube. Generally, the
larger the unit, the higher the potential control levels because of the larger
piston displacement and pressure areas. The larger the piston area, the lower
the internal operating pressure and temperatures. This provides higher damping
capabilities.
Ride engineers select valving values
for a particular vehicle to achieve optimal ride characteristics of balance and
stability under a wide variety of driving conditions. Their selection of valve
springs and orifices control fluid flow within the unit, which determines the
feel and handling of the vehicle.
TWIN TUBE – GAS
CHARGED DESIGN
The development of gas charged shock absorbers
was a major advance in ride control technology. This advance solved many ride
control problems which occurred due to an increasing number of vehicles using
uni-body construction, shorter wheelbases and increased use of higher tire
pressures.
The design of twin tube gas charged shock
absorbers solves many of today’s ride control problems by adding a low pressure
charge of nitrogen gas in the reserve tube. The pressure of the nitrogen in the
reserve tube varies from 100 to 150 psi, depending on the amount of fluid in
the reserve tube. The gas serves several important functions to improve the
ride control characteristics of a shock.
The prime function of gas charging is to
minimize aeration of the hydraulic fluid. The pressure of the nitrogen gas
compresses air bubbles in the hydraulic fluid. This prevents the oil and air
from mixing and creating foam. Foam affects performance because it can be
compressed – fluid cannot. With aeration reduced, the shock is able to react
faster and more predictably, allowing for quicker response time and helping
keep the tire firmly planted on the road surface.
An additional benefit of gas charging is that
it creates a mild boost in spring rate to the vehicle. This does not mean
that a gas charged shock would raise the vehicle up to correct ride height if
the springs were sagging. It does help reduce body roll, sway, brake dive, and
acceleration squat.
This mild boost in spring rate is also caused
by the difference in the surface area above and below the piston. With greater
surface area below the piston than above, more pressurized fluid is in contact
with this surface. This is why a gas charged shock absorber would extend on its
own. The final important function of the gas charge is to allow engineers
greater flexibility in valving design. In the past, such factors as damping and
aeration forced compromises in design.
ADVANTAGES:
Improves handling by reducing roll, sway and dive.
Reduces aeration offering a greater range of
control over a wider variety of road conditions as compared to non-gas units.
Reduced fade – shocks can lose damping
capability as they heat up during use. Gas charged shocks could cut this loss
of performance, called fade.
DISADVANTAGES:
·
Can only be mounted in one direction.
Current uses:
·
Original equipment on many domestic passenger
car, SUV and light truck applications.
TWIN TUBE – PSD DESIGN
In our earlier discussion of hydraulic shock absorbers,
we discussed that in the past, ride engineers had to compromise between soft
valving and firm valving. With soft valving, the fluid flows more easily. The result
is a smoother ride, but with poor handling and a lot of roll/sway. When valving
is firm, fluid flows less easily. Handling is improved, but the ride can become
harsh.
With the advent of gas charging, ride
engineers were able to open up the orifice controls of these valves and improve
the balance between comfort and control capabilities available in traditional
velocity sensitive dampers.
A leap beyond fluid velocity control is an
advanced technology that takes into account the position of the valve within
the pressure tube. This is called position sensitive damping (PSD).
The key to this innovation is precision
tapered grooves in the pressure tube. Every application is individually tuned,
tailoring the length, depth, and taper of these grooves to ensure optimal ride
comfort and added control. This in essence creates two zones within the
pressure tube.
The first zone, the comfort zone,
is where normal driving takes place. In this zone, the piston travel remains
within the limits of the pressure tube’s mid-range. The tapered grooves allow
hydraulic fluid to pass freely around and through the piston during its
midrange travel. This action reduces resistance on the piston, assuring a
smooth, comfortable ride.
The second zone, the control zone,
is utilized during demanding driving situations. In this zone, the piston
travels out of the mid-range area of the pressure tube and beyond the grooves.
The entire fluid flow is directed through the piston valving for more control
of the vehicle’s suspension. The result is improved vehicle handling and better
control without sacrificing ride comfort.
ADVANTAGES:
- Allows ride
engineers to move beyond simple velocity sensitive valving and use the
position of the piston to fine tune the ride characteristic.
- Adjusts more
rapidly to changing road and weight conditions than standard shock
absorbers
- Two shocks
into one – comfort and control
DISADVANTAGES:
·
If vehicle ride height is not within
manufacturer’s specified range, piston travel may be limited to the control
zone.
CURRENT USES:
·
Primarily aftermarket under the sensa-trac
brand name.
TWIN TUBE – ASD DESIGN
We have discussed the compromises made by ride
engineers to bring comfort and control together into one shock absorber. This
compromise has been significantly reduced by the advent of gas charging and
position sensitive damping technology.
A new twist on the comfort/ control compromise
is an innovative technology which provides greater control for handling while
improving ride comfort called acceleration sensitive damping (ASD).
This technology moves beyond traditional velocity sensitive damping to focus and address impact. This focus on impact is achieved by utilizing a new compression valve design. This compression valve is a mechanical closed loop system, which opens a bypass to fluid flow around the compression valve.
This technology moves beyond traditional velocity sensitive damping to focus and address impact. This focus on impact is achieved by utilizing a new compression valve design. This compression valve is a mechanical closed loop system, which opens a bypass to fluid flow around the compression valve.
This new application specific design allows
minute changes inside the pressure tube based on inputs received from the road.
The compression valve will sense a bump in the road and automatically adjust
the shock to absorb the impact, leaving the shock with greater control when it
is needed.
ADVANTAGES:
·
Control is enhanced without sacrificing driver
comfort.
·
Valve automatically adjusts to changes in the
road condition.
·
Reduces ride harshness.
DISADVANTAGES:
·
Limited availability
CURRENT USES:
·
Primarily aftermarket applications under the
reflex brand name.
MONO-TUBE DESIGN
These are high-pressure gas shocks with only
one tube, the pressure tube. Inside the pressure tube there
are two pistons: a dividing piston and a working
piston. The working piston and rod are very similar to the twin tube
shock design. The difference in actual application is that a mono-tube shock
absorber can be mounted upside down or right side up and will work either way.
In addition to its mounting flexibility, mono-tube shocks are a significant
component, along with the spring, in supporting vehicle weight. Another
difference you may notice is that the mono-tube shock absorber does not have a
base valve. Instead, all of the control during compression and extension takes
place at the piston. The pressure tube of the mono-tube design is larger than a
twin tube design to accommodate for dead length. This however makes it
difficult to apply this design to passenger cars designed with a twin tube
design. A free-floating dividing piston travels in the lower end of the
pressure tube, separating the gas charge and the oil.
The area below the dividing piston is
pressurized to about 360 psi with nitrogen gas. This high gas pressure helps
support some of the vehicle’s weight. The oil is located in the area above the
dividing piston.
During operation, the dividing piston moves up
and down as the piston rod moves in and out of the shock absorber, keeping the
pressure tube full all times.
ADVANTAGES:
- Can be
mounted upside down, reducing the unsprung weight
- May run
cooler since the working tube is exposed to the air
DISADVANTAGES:
- Difficult to
apply to passenger cars designed oe with twin tube designs.
- A dent in
the pressure tube will destroy the unit
CURRENT USES:
- Original
equipment many import and performance domestic passenger cars, suv and
light truck applications
- Available
for many aftermarket applications
THE MAGNETIC SHOCK ABSORBER
Shock absorbers are a key component of all
automobiles. They control the vehicle’s suspension movement to provide a
stable, comfortable ride. Since they were installed on the first automobiles,
the principle of shock absorber operation has remained essentially the same.
Now a new type of shock absorber is entering the market, and it may change the way
suspensions are controlled. They are called the magnetic shock absorbers or the
new MagneRide shock system.
Magnetic shock absorber is a continuously
variable shock absorber that uses simple magnetic principles but very high
technology to control suspensions. Conventional shock absorbers (or struts on
many cars) use oil passing through orifices to dampen suspension movement. When
a tire hits a bump, the suspension moves up, moving the body of the shock
absorber up too. A rod connected to the top of the shock and mounted to the
body or frame, passes through a seal in the top of the shock and has a piston
mounted on the bottom end. This piston has small ports in it that allow oil
contained in the shock body to flow from one side of the piston to the other. Different
size ports allow different flow rates, so larger ports allow the suspension to
move easier and smaller ports slow the movement.
Conventional shock absorbers use check valves
on the ports so that fluid can pass easier one way than the other can. Typically,
the wheel is allowed to move up quickly, but let back down slower. This
prevents the suspension from bouncing; the effect you get when the shocks are
badly worn.
Gas-filled shocks use pressure inside the
shock to reduce oil foaming as it passes through the ports. Suspension control
becomes very erratic with foamy oil inside the shock. Vehicles with selectable
shock dampening vary the size of ports by turning a shaft inside the piston rod
that changes port size to change vehicle handling. Magnetic shock absorber
makes mechanically varied systems obsolete.
The heart of a magnetic shock absorber or MagneRide
is the magneto-rheological (MR) fluid. It is a suspension of magnetically soft
particles such as iron microspheres in a synthetic hydrocarbon base fluid. Place
a magnet near the fluid and the particles form a fibrous structure, increasing
its shear factor. In simple terms, the fluid gets thicker so it does not flow
through the shock’s piston ports as easy.
By using a magnet placed in the shock piston,
the MR fluid only changes viscosity where it passes through the ports. Wires
run down the hollow piston rod so a computer module can vary the strength of
the magnet and the dampening of the shock continuously. The system is five
times faster than mechanical ride control systems.
THE NEW WAVE IN
SHOCK ABSORBERS
Over the past two model years, general motors
(gm) has introduced one of the most interesting and potentially far-reaching
new technologies ever developed for automobiles.
A hydraulic shock absorber dampens suspension
movement by forcing a piston to move through oil. Spring-loaded valves cover
holes in the piston. These valves slow the flow of oil through the holes to
control damping rate: the smaller the valve opening, the slower the oil flow
and the greater the damping. Adjustable shock absorbers vary the shock’s
damping rate by varying the size of the valve opening, either by adjusting the
spring preload or by selecting a different size oil flow orifice. By using a
small motor or a solenoid to operate the valve, damping rate can be adjusted “on-the-fly”
by the driver and/or by the computer.
Exactly the same results can be achieved by
varying the viscosity of the oil instead of the size of the valve opening. The
technology that allows changing oil viscosity on the fly presents some exciting
possibilities that go far beyond adjustable shock absorbers.
MAGNETO-RHEOLOGICAL
FLUID
Rheology is a science that studies the
deformation and flow of materials. Rheological fluids have flow characteristics
that can be changed in a controllable way using electrical current or a
magnetic field. Depending on the base fluid and the strength of the electrical
current or magnet, the fluid’s viscosity can be varied from thinner-than-water
to almost-solid and any stage in between. The fluid’s response is
instantaneous, completely reversible and extremely controllable, but there are
some limits.
Electro-rheological (er) fluid changes
viscosity when an electric current is applied directly to the fluid itself. Er
fluid was first invented and patented in the 1940s, and to varying degrees,
development has continued ever since. It has been tested in a wide range of
applications, from torque converters, clutches and dampers to synthetic muscles
and dampers in powered prosthetic arms and legs. It works, but its shear
strength – that is, its resistance to shearing movement – is limited. Despite
huge investments in research and development, er fluid is still far from ready
for any practical applications.
Magneto-rheological (MR) fluid has a shear
strength about 10 times stronger than er fluid. Invented at the same time as er
fluid, the two have many similarities. Both can use oil, silicone, water or
glycol as the base fluid, and both contain polarizable particles suspended in
the fluid. Polarizable means the particles can be forced to align in a specific
way. These suspended polarizable particles are the basic difference between er
and MR fluids. Er fluid uses particles that polarize when directly exposed to
an electric current. MR fluid uses somewhat larger particles of iron that
polarize when surrounded by a magnetic field.
The typical MR fluid particles are soft iron
spheres measuring 3 to 5 microns (3 to 5 thousandths of a millimeter) in
diameter. Depending on the application, the fluid will be 20 to 40 percent
saturated with the iron particles, and other additives will be used to control
particle settling and mixing, fluid friction and fluid viscosity. Specific
gravity is generally between 3 and 4; for reference, water’s specific gravity
is 1. Thus, a 55-gallon drum of MR fluid can weigh almost a full ton. MR fluids
are developed specifically for the application. For instance, in addition to
automotive uses, MR fluids have been developed for use in dampers that protect
buildings and other structures from earthquake damage. These dampers sit still
for long periods, so different additives are needed to keep the particles in
suspension.
SHOCK ABSORBER
VALVES
It was not hard to develop a synthetic oil-MR
fluid with viscosity and lubrication qualities similar to normal hydraulic
shock absorber oil. The challenge was to develop seals, O-rings and other
components that can withstand the fluid’s “particle contamination,” which is part
of the reason it’s taken so long for MR fluid to escape the laboratory. He said
they were first used on open-wheeled racecars, where cost and durability are
not quite as critical as in production cars. Working with lord corp., which
manufactures the MR fluid, Delphi has finally developed MR shock absorbers that
are suitable for real-world applications.
The ‘valve’ in the center of the tube is a block
with oil passages surrounded by an electromagnet coil. The magnetic particles
in the fluid align with the magnetic field when the magnet is turned on. The
fluid resists flow perpendicular to the field lines just as if an orifice plug
were suddenly inserted into the passage.
With the fluid and other materials properly
matched, developing the valve itself was the simplest part of the system. There
are no moving parts, just passages in the piston that the fluid moves through.
The oil passages are surrounded by an electro-magnet; it is a solenoid coil
without the valve core that generates a magnetic field when current is passed
through it. When the magnet is turned on, the iron particles in the oil
passages align to form fibers in the oil, making the fluid thicker and,
therefore, resistant to flow. The thickness or viscosity of the fluid can be
infinitely adjusted from that of the base oil to almost plastic in less than
two milliseconds simply by adjusting current flow through the coil. When the current
is turned off, the fluid reverts to its base viscosity just as quickly. Only
the fluid in the oil passage is involved, so the magnet’s coil can be small
enough to ride on the piston itself. The wires from the coil are routed through
the piston rod to a connector on the end of the shock housing. This basic
design is currently being used in long-haul truck seats, shocks, struts and
air-inflated load-leveling shocks.
CONTROL SYSTEM
Because adjustable damping has been around for
a while, all of the other bits and pieces needed for the MagneRide system are
already in place. The control module uses suspension height data supplied by
position sensors at each corner. With throttle position sensor (TPS),
transmission and wheel speed data supplied by the powertrain control module
(PCM), the suspension controller can predict lift and dive at each end of the
car and operate the shocks’ “valves” to counteract it. With data from a
steering wheel position sensor, a two-plane acceleration sensor and a yaw rate
sensor, the shocks can be operated as needed to control body roll during any
maneuver. The system also checks body movement during antilock brake system
(abs) operation using vehicle speed, wheel speed and other data supplied by the
abs control unit.
The MagneRide controller itself is a
stand-alone unit equipped with two parallel processors: one for input signals
and one for output. It operates the shocks on 5 volts dc that is pulse-width
modulated to adjust current to the magnets. Current draw can spike shortly at
about 5 amps per shock, but normal current draw is about half that much, and
there is always some current flowing whenever the key is on.
Like earlier versions, this is a semi-active
suspension system. In addition to its main function of keeping the wheels in
contact with the road, it can check body motions and, within certain limits,
adjust weight bias at each corner by preventing suspension compression. However,
it is a reactive system, not proactive, and it cannot extend the suspension to
make the car lean into a turn. Still, it provides a significant amount of
increased control with base settings that are tuned for a more comfortable
ride.
A PERMANENT MAGNET SYSTEM SHOCK
ABSORBER
A permanent magnetic suspension apparatus for
maintaining a spaced relationship between a first movable member and a second
fixed member, wherein the motion of the movable member requires dampening,
cushioning, stabilizing, harmonic balancing, and/ or reflexive re-centering.
The suspension apparatus includes a plurality
of sets of permanent magnets located within a case, which is coupled to one of
the members. The sets of permanent magnets are coupled to an elongated support
member, which is couple to the second member. The support member extends within
the case, with the support member and the case being adapted for relative axial
movement.
The sets of permanent magnets are arranged in
bidirectional repulsion configuration with additional magnet fixed within the
case. The sets of permanent magnets are being moved relative to the fixed permanent
magnets, such that the magnetic forces of repulsion produced by the permanent
magnets are increased in response to relative movement between the support
member and the case, creating dampening, cushioning, stabilizing, harmonic
balancing, and/or re-centering forces.
In one embodiment, the control mechanism is coupled between the frame of a vehicle and a wheel support assembly. The permanent magnetic suspension apparatus, however, is for use with any type of equipment or machinery having a movable and non-movable, or fixed, member. This includes, but is not limited to, cars, trucks, motorcycles, scooters, all terrain vehicles, semi-tractors, semi-trailers, and the like, as well as, but not limited to, industrial equipment and machinery, hospital and office machinery and equipment, such as being coupled between the frame of an office chair and the chair seat.
In one embodiment, the control mechanism is coupled between the frame of a vehicle and a wheel support assembly. The permanent magnetic suspension apparatus, however, is for use with any type of equipment or machinery having a movable and non-movable, or fixed, member. This includes, but is not limited to, cars, trucks, motorcycles, scooters, all terrain vehicles, semi-tractors, semi-trailers, and the like, as well as, but not limited to, industrial equipment and machinery, hospital and office machinery and equipment, such as being coupled between the frame of an office chair and the chair seat.
REGENERATIVE ELECTROMAGNETIC
SHOCK ABSORBER
A regenerative electromagnetic shock absorber
comprising: a linear electromagnetic generator comprised of a central magnet
array assembly comprising a central magnet array comprised of a plurality of
axially-aligned, stacked cylindrical magnets having like magnetic poles facing
one another, a plurality of high magnetic permeability, high saturation
magnetization, centrai cylindrical spacers positioned at each end of said
stacked central magnet array and between adjacent stacked central magnets, and
a magnet array support for mounting said magnets and said spacers; an inner
coil array comprising a plurality of concentric cylindrical coil windings
positioned adjacent to said central spacers and said magnetic poles of said
central magnets, said inner coil windings surrounding an outside perimeter of
said central spacers, said inner coil array mounted on a movable coil support,
said movable coil support providing for reciprocating linear motion of said
coil array relative to said magnet array; and an outer magnet array assembly
comprising an outer magnet array comprised of a plurality of axially-aligned,
stacked concentric toroidal magnets having like magnetic poles facing each
other, said outer magnet array surrounding said inner coil array, said stacked
outer concentric magnets being aligned and positioned essentially coplanar with
said stacked central cylindrical magnets with the magnetic poles of said outer
magnets aligned with and facing opposing magnetic poles of said central
cylindrical magnets, and a plurality of high permeability, high saturation
magnetization, outer concentric toroidal spacers positioned at each end of said
stacked outer magnet array and between adjacent stacked outer magnets, said
outer magnet array assembly attached to said magnet array support; wherein a
predetermined location, configuration and orientation of said central magnet
magnetic poles, said central spacers, said inner coil windings, said outer
magnet magnetic poles and said outer spacers provide for superposition of a
radial component of a magnetic flux density from a plurality of central and
outer magnets to produce a maximum average radial magnetic flux density in the
inner coil windings; and a voltage conditioning circuit electrically connected
to said coil windings, said voltage conditioning circuit providing an output
voltage and output current to an electrical load.
An electromagnetic linear generator and
regenerative electromagnetic shock absorber is disclosed which converts
variable frequency, repetitive intermittent linear displacement motion to
useful electrical power. The innovative device provides for superposition of radial
components of the magnetic flux density from a plurality of adjacent magnets to
produce a maximum average radial magnetic flux density within a coil winding
array. Due to the vector superposition of the magnetic fields and magnetic flux
from a plurality of magnets, a nearly four-fold increase in magnetic flux
density is achieved over conventional electromagnetic generator designs with a
potential sixteen-fold increase in power generating capacity. As a regenerative
shock absorber, the disclosed device is capable of converting parasitic
displacement motion and vibrations encountered under normal urban driving
conditions to a useful electrical energy for powering vehicles and accessories
or charging batteries in electric and fossil fuel powered vehicles. The
disclosed device is capable of high power generation capacity and energy
conversion efficiency with minimal weight penalty for improved fuel efficiency.
HOW
IT WORKS
A conventional automotive shock absorber
dampens suspension movement to produce a controlled action that keeps the tire
firmly on the road. This is done by converting the kinetic energy into heat
energy, which is then absorbed by the shock’s oil.
MANUFACTURING
CONSIDERATIONS
Manufacture of the power-generating shock
absorber will require a machined main shaft with embedded permanent magnet
stack, a strong air-gap cylinder housing, high quality stator windings, and
robust slide bearings. Other systems, such as microprocessor-controlled
voltage, current, and dampening regulation, external casing, protective
bellows, etc. Will also need to be designed and tested.
References
·
www.howstuffworks.com
·
www.mrfluids.com
·
www.popularmechanics.com
·
en.wikipedia.org
·
www.researchandmarkets.com/reports
·
www.shockabsorber.co.uk
·
www.mindbranch.com
·
www.automotive-online.com/suspension-steering/shock-absorbers.htm
·
www.car-stuff.com/monroeshocks.htm
I enjoy reading a lot and your stories are worth reading, nice blog, keep it up.
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A CHAIN OF MORE THAN TWO MAGNETS CAN BE USED TO TOLERATE THE SHOCKS OR WEIGHT AND MAKE THE VEHICLE MORE COMFORTABLE.
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ReplyDeletei like the absorption system
ReplyDeleteWhy use magnetic fluid at all? Why not just calibrate two opposing magnets that create sufficient repell under any force? Would the ride be too stiff when not under duress? This would eliminate the need for electronics, fluid, computers, lending a simple implementation to physical mechanical. Why not? Cost? Not sure what the fluid is providing beyond variable tensile strength.
ReplyDeletei agree...but i feel for a luxury car or a sports car it would make sense to have a computer to calculate the compression and react according to the situation...but why fluid???? btw what fluid?? ferro-fluid?? anyway for a normal car it doen't make sense to have a fluid or computers to do the calculations....
ReplyDeleteP.S.--this thing is very intriguing....I'll take it up as a project this year in college.
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You broke my heart. I was shopping for some magnets and the idea of using magnets as shocks and wrapping them with a coil so that the up and down everyday motion of a shock would generate electricity to power or at least help to power your vehicle. I thought i had finally had an original idea. :-(
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