Tuesday, March 27, 2012

California Freeway Legacy

Monday, December 30, 1940 California’s first modern freeway, the "Arroyo Seco," was born. The event initiated the population’s full embrace of limited access freeways and expressways in a building boom. A year after the passage of Eisenhower’s 1956 Interstate Highway and Defense Act, the California Division of Highways proposed construction of a vast system; 12,250 miles of controlled access highways would serve every city with a population greater than 5,000. In the next decade the dream was made possible by a large infusion of Federal cash (in California, the federal burden clocked in at 91% percent of the costs for designated Interstate Highway mileage), top down planning and few environmental controls. Infrastructure investment throughout the fifties was an extension of post-depression economic development intended to stave off recession, as well as providing one face of the coin for access to the Modern Suburban American Dream.

 Sixty years later, cruising around the State, we alternatively take this infrastructure for granted while also being astounded at the scale of change accomplished in such a short time. Here in Oakland, at the landing of the Bay Bridge’s eastern shore, four highways converge in one of the Nation’s largest distribution systems, completed in the late 1950s. Arguably the zenith of California highway building, it is known locally as "The Maze.”


 
Of course, while they offered new mobility, freeways came at the expense of the health and aesthetic form of a neighborhood. Urban communities were routinely demolished, and concrete barriers entrenched dividing lines that still affect both today’s crime rates and real estate price points.  In West Oakland alone there are 54 Acres of empty space under its freeways; some used for parking, but most is overgrown or used for illegal dumping. Looking back one can almost see the large flows of our Nation’s capital dollars flowing out of the urbanized and industrial urban centers (where labor was strong) and redistributed into greenfield, suburban landscapes where districts could define their own terms with their surroundings.

 The freeway system, followed quickly by BART, shuttled people past the rooftops of minority neighborhoods and into new areas that could afford to ignore perceived “urban problems.” In Alameda, multifamily housing was outlawed in the City’s 1973 charter.
 
Fast forward to today. The last freeway was built in 1991; very few are now proposed. California’s suburban expansion is, arguably, complete. We are now saddled with a strongly anti-tax population that has scaled back its ability to invest in infrastructure, while simultaneously, the cost of infrastructure construction has risen.

 High Speed Rail (HSR) is emblematic of this new reality. Despite its real value as a visionary solution to congestion on the 1-5 corridor, it again is representative of a broad  re-distribution of wealth-- both federal and state capital back once again into our urban centers. HSR has been using rational planning arguments to battle against what is mostly emotional and fear based, and an entrenched anti-urban position. For many, it is the recognition that those “urban problems” must be shared more broadly. The project is in stalemate, trapped by both the courts and the environmental processes, and may yet be either litigated or legislated out of existence, or return in some scaled-down form.

 The result for the near future is arguably a focus on smaller scale, urban and multi-modal corridor development. These are a broad range of interventions that are less threatening and can have immediate benefit on surrounding populace in safety health and aesthetics. I’ve seen many of these homegrown, community-led conversations throughout northern California, and increasingly in Los Angeles County with a focus on urban-scaled mobility and affordable interventions. While they lack the monumental appeal of a highway program or HSR, the conversations here in the East Bay focus on bridging gaps, rebuilding, and even reintroducing portions of the older systems, such as the East Bay Key system.

 
This year, the City of Oakland is initiating a study (for yes, the third time) to look into the feasibility and potential economic development opportunities that would result from a streetcar line connecting Jack London Square with Oakland's Uptown and MacArthur BART. A $300,000 grant from CalTrans will pay for an updated study. Similarly, AC Transit is on route to construct the Bay Area’s first real BRT along Telegraph Avenue (another of the Key System routes).

 Many around our region are in agreement that dollars should be spent where they will benefit the greatest number of people, such as improving those areas that are already fully serviced by good transportation infrastructure and/or mass transit.  However, consensus building takes time, and it has become an increasingly desperate reflection of our times. It's not a comfortable outcome for everyone, including both those who will see their share of investments shrink, and those who are fighting for a bigger share.

Driving the future of transmission control

 As the leading international supplier of automatic transmission system control units, we provide our customers with solutions for all types of transmissions. Today‘s transmission electronics optimize driving comfort, reduce fuel consumption and emissions from vehicles of all classes, which is why our product portfolio ranges from high-end systems to cost optimized solutions for the growing markets.

Depending on the vehicle and transmission concept, we offer a wide range of control unit solutions, from external control units mounted separately from the transmission to fully integrated applications including electronics, sensors, actuator, wiring and electric set within the transmission.


Packaging and functional benefits

We actively drive forward the integration of control units inside the transmission. On top of saving installation space and weight while reducing the complexity of logistics, integrated applications can be installed as a fully tested sub-system. Moreover, from a logistical point of view, integrated solutions facilitate handling for the vehicle or transmission manufacturer.
Since the control unit is immersed in transmission fluid, this system profits considerably from our extensive expertise in electronics design and manufacturing, ranging from printed circuit boards (PCBs) to extremely shock- and temperature resistant ceramic substrate technology, e.g. Low Temperature Co-fired Ceramics (LTCCs) or Thickfilm Ceramics.


Control unit for double clutch transmission

This innovative transmission technology has been in series production since 2003;
with its smooth gearshifts and no shuddering or traction torque interruption, the DCT combines the ease of an automatic transmission with the dynamism of a manual gearshift, saving fuel and reducing emissions. The heart of the DCT is Continental‘s control unit – one of our development highlights, of which we are proud of and which proofs our expertise and innovative strength.


Electro-hydraulic transmission control module

Another recent example of our expertise is the new transmission electro-hydraulic control module (TEHCM) that integrates the control module, hydraulic pressure switches, solenoids and filter plate in one single unit.  
The first production application is a transversely-mounted six speed automatic transmission which requires sophisticated control functions and precise timing control in particular. To facilitate the highly compact gearbox design, all gear shifts except the first-to-second upshift are done via a clutch-to-clutch concept instead of a freewheeling mechanism. Our high-performance TEHCM contributes to the compact construction of this transmission as well as the freewheeling level of  perfect timing between shifts.


Thursday, March 15, 2012

Magnetism

Certain metals and metallic oxides have the ability to attract other metals. This property is called magnetism, and the materials which have this property are called magnets. Some magnets are found naturally while others must be manufactured.

Magnetism is a result of electrons spinning on their own axis around the nucleus (Figure 1).


Figure 1 Electron Spinning Around Nucleus Produces Magnetic Field

In magnetic materials, the atoms have certain areas called domains. These domains are aligned such that their electrons tend to spin in the same direction (Figure 2).


 
Figure 2 Magnetic Domains
The alignment of these domains results in the formation of magnetic poles at each end of the magnet. These poles are called the north pole and the south pole. The law of magnetism states that like magnetic poles repel and unlike magnetic poles attract one another (Figure 3).



 Figure 3 The Law of Magnetic Attraction and Repulsion

Magnetic Flux

The group of magnetic field lines emitted outward from the north pole of a magnet is called magnetic flux. The symbol for magnetic flux is (phi). The SI unit of magnetic flux is the weber (Wb). One weber is equal to 1 x 108 magnetic field lines.

Example: If a magnetic flux (phi) has 5,000 lines, find the number of webers.

Phi = (5000 lines)/(1 x 108 lines/Wb) = (5 x 10^3)/10^8 = 50 x 10^-6 Wb = 50 µWb

Magnetic Flux Density

Magnetic flux density is the amount of magnetic flux per unit area of a section, perpendicular to the direction of flux. Equation (1) is the mathematical representation of magnetic flux density.

B = phi/A……..(1)

where
B = magnetic flux density in teslas (T)
phi= magnetic flux in webers (Wb)
A = area in square meters (m^2)

The result is that the SI unit for flux density is webers per square meter (Wb/m^2). One weber per square meter equals one tesla.

Example: Find the flux density in teslas, when the flux is 800 µWb and the area is 0.004 m^2
Given: phi = 800 µWb = 8 x 10^-4Wb
A = 0.0004 m^2 = 4 x 10^-4m^2
B = phi / A = 8 x 10^-4 Wb/4 x 10^-4m^2 = 2 Wb/m^2

Magnetic Materials

Magnetic materials are those materials that can be either attracted or repelled by a magnet and can be magnetized themselves. The most commonly used magnetic materials are iron and steel. A permanent magnet is made of a very hard magnetic material, such as cobalt steel, that retains its magnetism for long periods of time when the magnetizing field is removed. A temporary magnet is a material that will not retain its magnetism when the field is removed.

Permeability (µ) refers to the ability of a material to concentrate magnetic lines of flux. Those materials that can be easily magnetized are considered to have a high permeability. Relative permeability is the ratio of the permeability of a material to the permeability of a vacuum (µo).
The symbol for relative permeability is µR (mu).

µR = µo/ µo , where µo = 4 x 3.14 x 10^-7H/m …….(2)

Magnetic materials are classified as either magnetic or nonmagnetic based on the highly magnetic properties of iron. Because even weak magnetic materials may serve a useful purpose in some applications, classification includes the three groups described below.

Ferromagnetic Materials: Some of the ferromagnetic materials used are iron, steel, nickel, cobalt, and the commercial alloys, alnico and peralloy. Ferrites are nonmagnetic, but have the ferromagnetic properties of iron. Ferrites are made of ceramic material and have relative permeabilities that range from 50 to 200. They are commonly used in the coils for RF (radio frequency) transformers.

Paramagnetic Materials: These are materials such as aluminum, platinum, manganese, and chromium. These materials have a relative permeability of slightly more than one.
Diamagnetic Materials: These are materials such as bismuth, antimony, copper, zinc, mercury, gold, and silver. These materials have a relative permeability of less than one.

Diamagnetic Materials: These are materials such as bismuth, antimony, copper, zinc, mercury, gold, and silver. These materials have a relative permeability of less than one.

Electromagnetism

The relationship between magnetism and electrical current was discovered by a Danish scientist named Oersted in 1819. He found that if an electric current was caused to flow through a conductor, the conductor produced a magnetic field around that conductor (Figure 4).



Figure 4 The Magnetic Field Produced by Current in a Conductor

Polarity of a Single Conductor

A convenient way to determine the relationship between the current flow through a conductor and the direction of the magnetic lines of force around the conductor is the left-hand rule for current carrying conductors, as illustrated in Figure 5. The student should verify that the lefthand rule holds true for the examples shown in Figure 4.



Figure 5 Left-hand Rule for Current Carrying Conductors

Magnetic Field and Polarity of a Coil

Bending a straight conductor into a loop has two results: (1) magnetic field lines become more dense inside the loop, and (2) all lines inside the loop are aiding in the same direction. When a conductor is shaped into several loops, it is considered to be a coil. To determine the polarity of a coil, use the left-hand rule for coils (Figure 6).

Adding an iron core inside of a coil will increase the flux density. The polarity of the iron core will be the same as that of the coil. Current flow is from the negative side of the voltage source, through the coil, and back to the positive side of the source (Figure 7).
 


Figure 6 Left-hand Rule to Find North Pole of an Electromagnet

Magnetomotive Force

Magnetomotive force (mmf) is the strength of a magnetic field in a coil of wire. This is dependent on how much current flows in the turns of coil: the more current, the stronger the magnetic field; the more turns of wire, the more concentrated the lines of force. The current times the number of turns of the coil is expressed in units called "ampere-turns" (At), also known as mmf. Equation (3) is the mathematical representation for ampere-turns (At).
Fm = ampere-turns = NI………(3)

where
Fm = magnetomotive force (mmf)
N = number of turns
I = current


Example: Calculate the ampere-turns for a coil with 1000 turns and a 5 mA current.
N = 1000 turns and I = 5 mA
substitute
N = 1000 turns and I = 5 x 10^-3
NI = 1000 (5 x 10^-3) = 5 At

Field Intensity

When a coil with a certain number of ampere-turns is stretched to twice its length, the magnetic field intensity, or the concentration of its magnetic lines of force, will be half as great. Therefore, field intensity depends on the length of the coil. Equation (1-14) is the mathematical representation for field intensity, which is related to magnetomotive force as shown.

H = FM / L = NI / L………………..(4)
where
H = field intensity, At/m
NI = ampere-turns (At)
L = length between poles of coil (m)
FM = Magnetomotive force (mmf)

Example 1: Find field intensity of an 80 turn, 20 cm coil, with 6A of current.
Solution:
N = 80, I = 6A, and NI = 480 At
H = 480 At / 0.2 m = 2400 At/m

Example 2: If the same coil in Example 1 were to be stretched to 40 cm with wire length and current remaining the same, find the new value of field intensity.
Solution:
N = 80, I = 6A, and NI = 480 At
H = 480 At / 0.4 m = 1200 At/m
Example 3: The 20 cm coil used in Example 1 with the same current is now wound around an iron core 40 cm in length. Find the field intensity.
Solution:
N = 80, I = 6A, and NI = 480 At
H = 480 At / 0.4 m = 1200 At/m

*) Note that field intensity for Examples 2 and 3 is the same.




Figure 7 Different Physical Forms of Electromagnets

Reluctance

Opposition to the production of flux in a material is called reluctance, which corresponds to resistance. The symbol for reluctance is R, and it has the units of ampere-turns per weber (At/wb).
Reluctance is related to magnetomotive force, mmf, and flux, phi, by the relationship shown in equation (5).

R = mmf / phi ........(5)

Reluctance is inversely proportional to permeability (µ). Iron cores have high permeability and, therefore, low reluctance. Air has a low permeability and, therefore, a high reluctance. Generally, different types of materials have different values of reluctance (Figure 25). Air gap is the air space between two poles of a magnet. Since air has a very high reluctance, the size of the air gap affects the value of reluctance: the shorter the air gap, the stronger the field in the gap. Air is nonmagnetic and will not concentrate magnetic lines. The larger air gap only provides space for the magnetic lines to spread out.

Summary

The important information contained in this chapter is summarized below.
• Magnetic flux - group of magnetic field lines that are emitted outward from the north pole of a magnet
• Magnetic flux density - amount of magnetic flux per unit area of a section, perpendicular to the direction of the flux
• Weber - measure of magnetic flux
• Permeability - ability of a material to concentrate magnetic lines of flux
• Ferromagnetic materials - iron, steel, nickel, cobalt, and commercial alloys with relative permeability ranging from  50-200
• Paramagnetic materials - aluminum, platinum, manganese, and chromium with relative permeability of slightly more than one
• Diamagnetic materials - bismuth, antimony, copper, zinc, mercury, gold, and silver with relative permeability of less than one
• Magnetomotive force (mmf) - strength of a magnetic field in a coil of wire dependent on current flowing through coil
• Ampere turns - current flowing through a coil times the number of turns in the coil
• Field intensity - identifies the magnetic flux density per unit length of a coil
• Reluctance - opposition to the production of flux in a material

Saturday, March 10, 2012

Methods Of Producing Voltage (Electricity)

This article provides information on the following methods of producing electricity:
• Electrochemistry
• Static (friction)
• Induction (magnetism)
• Piezoelectric (pressure)
• Thermal (heat)
• Light
• Thermionic emission

Electrochemistry
Chemicals can be combined with certain metals to cause a chemical reaction that will transfer electrons to produce electrical energy. This process works on the electrochemistry principle. One example of this principle is the voltaic chemical cell, shown in Figure 1. A chemical reaction produces and maintains opposite charges on two dissimilar metals that serve as the positive and negative terminals. The metals are in contact with an electrolyte solution. Connecting together more than one of these cells will produce a battery.



Figure 1 Voltaic Chemical Cell
Example: A battery can maintain a potential difference between its positive and negative terminals by chemical action. Various types of cells and batteries will be studied in more detail in Module Batteries.

Static Electricity
Atoms with the proper number of electrons in orbit around them are in a neutral state, or have a "zero charge." A body of matter consisting of these atoms will neither attract nor repel other matter that is in its vicinity. If electrons are removed from the atoms in this body of matter, as happens due to friction when one rubs a glass rod with a silk cloth, it will become electrically positive as shown in Figure 2. If this body of matter (e.g., glass rod) comes near, but not in contact with, another body having a normal charge, an electric force is exerted between them because of their unequal charges. The existence of this force is referred to as static electricity or electrostatic force.



Figure 2 Static Electricity
Example: Have you ever walked across a carpet and received a shock when you touched a metal door knob? Your shoe soles built up a charge by rubbing on the carpet, and this charge was transferred to your body. Your body became positively charged and, when you touched the zero-charged door knob, electrons were transferred to your body until both you and the door knob had equal charges.

Magnetic Induction
A generator is a machine that converts mechanical energy into electrical energy by using the principle of magnetic induction. Magnetic induction is used to produce a voltage by rotating coils of wire through a stationary magnetic field, as shown in Figure 3, or by rotating a magnetic field through stationary coils of wire. This is one of the most useful and widelyemployed applications of producing vast quantities of electric power.

Figure 3 Generator – Electromagnetics Induction
Magnetic induction will be studied in more detail in the next two chapters "Magnetism," and "Magnetic Circuits."

Piezoelectric Effect
By applying pressure to certain crystals (such as quartz or Rochelle salts) or certain ceramics (like barium titanate), electrons can be driven out of orbit in the direction of the force. Electrons leave one side of the material and accumulate on the other side, building up positive and negative charges on opposite sides, as shown in Figure 4. When the pressure is released, the electrons return to their orbits. Some materials will react to bending pressure, while others will respond to twisting pressure. This generation of voltage is known as the piezoelectric effect. If external wires are connected while pressure and voltage are present, electrons will flow and current will be produced. If the pressure is held constant, the current will flow until the potential difference is equalized.

When the force is removed, the material is decompressed and immediately causes an electric force in the opposite direction. The power capacity of these materials is extremely small. However, these materials are very useful because of their extreme sensitivity to changes of mechanical force.

Figure 4 Pressure Applied to Certain Crystals Produces an Electric Charge
Example: One example is the crystal phonograph cartridge that contains a Rochelle salt crystal. A phonograph needle is attached to the crystal. As the needle moves in the grooves of a record, it swings from side to side, applying compression and decompression to the crystal. This mechanical motion applied to the crystal generates a voltage signal that is used to reproduce sound.
Thermoelectricity

Some materials readily give up their electrons and others readily accept electrons. For example, when two dissimilar metals like copper and zinc are joined together, a transfer of electrons can take place. Electrons will leave the copper atoms and enter the zinc atoms. The zinc gets a surplus of electrons and becomes negatively charged. The copper loses electrons and takes on a positive charge. This creates a voltage potential across the junction of the two metals. The heat energy of normal room temperature is enough to make them release and gain electrons, causing a measurable voltage potential. As more heat energy is applied to the junction, more electrons are released, and the voltage potential becomes greater, as shown in Figure 5. When heat is removed and the junction cools, the charges will dissipate and the voltage potential will decrease. This process is called thermoelectricity. A device like this is generally referred to as a "thermocouple."


Figure 5 Heat Energy Causes Copper to Give up Electrons to Zinc
The thermoelectric voltage in a thermocouple is dependent upon the heat energy applied to the junction of the two dissimilar metals. Thermocouples are widely used to measure temperature and as heat-sensing devices in automatic temperature controlled equipment.
Thermocouple power capacities are very small compared to some other sources, but are
somewhat greater than those of crystals. Generally speaking, a thermocouple can be subjected to higher temperatures than ordinary mercury or alcohol thermometers.

Photoelectric Effect
Light is a form of energy and is considered by many scientists to consist of small particles of energy called photons. When the photons in a light beam strike the surface of a material, they release their energy and transfer it to the atomic electrons of the material. This energy transfer may dislodge electrons from their orbits around the surface of the substance. Upon losing electrons, the photosensitive (light sensitive) material becomes positively charged and an electric force is created, as shown in Figure 6.



Figure 6 Producing Electricity from Light Using a Photovoltaic Cell
This phenomenon is called the photoelectric effect and has wide applications in electronics, such as photoelectric cells, photovoltaic cells, optical couplers, and television camera tubes. Three uses of the photoelectric effect are described below. Photovoltaic: The light energy in one of two plates that are joined together causes one plate to release electrons to the other. The plates build up opposite charges, like a battery (Figure 6). Photoemission: The photon energy from a beam of light could cause a surface to release electrons in a vacuum tube. A plate would then collect the electrons. Photoconduction: The light energy applied to some materials that are normally poor conductors causes free electrons to be produced in the materials so that they become better conductors.

Thermionic Emission
A thermionic energy converter is a device consisting of two electrodes placed near one another in a vacuum. One electrode is normally called the cathode, or emitter, and the other is called the anode, or plate. Ordinarily, electrons in the cathode are prevented from escaping from the surface by a potential-energy barrier. When an electron starts to move away from the surface, it induces a corresponding positive charge in the material, which tends to pull it back into the surface. To escape, the electron must somehow acquire enough energy to overcome this energy barrier. At ordinary temperatures, almost none of the electrons can acquire enough energy to escape. However, when the cathode is very hot, the electron energies are greatly increased by thermal motion. At sufficiently high temperatures, a considerable number of electrons are able to escape. The liberation of electrons from a hot surface is called thermionic emission.

The electrons that have escaped from the hot cathode form a cloud of negative charges near it called a space charge. If the plate is maintained positive with respect to the cathode by a battery, the electrons in the cloud are attracted to it. As long as the potential difference between the electrodes is maintained, there will be a steady current flow from the cathode to the plate. The simplest example of a thermionic device is a vacuum tube diode in which the only electrodes are the cathode and plate, or anode, as shown in Figure 7. The diode can be used to convert alternating current (AC) flow to a pulsating direct current (DC) flow.


Figure 7 Vacuum Tube Diode
Summary
The important information contained in this article is summarized below.
• Electrochemistry - Combining chemicals with certain metals causes a chemical reaction that transfers electrons.
• Static electricity - When an object with a normally neutral charge loses electrons, due to friction, and comes in contact with another object having a normal charge, an electric charge is exerted between the two objects.
• Magnetic induction - Rotating coils of wire through a stationary magnetic field or by rotating a magnetic field through a stationary coil of wire produces a potential.
• Piezoelectric effect - Bending or twisting certain materials will cause electrons to drive out of orbit in the direction of the force. When the force is released, the electrons return to their original orbit.
• Thermoelectricity - Heating two joined dissimilar materials will cause a transfer of electrons between the materials setting up a current flow.
• Photoelectric effect - Dislodging of electrons from their orbits by light beams creates positively-charged objects.
• Thermionic emission - Freeing electrons from a hot surface causes electrons to escape.

Thursday, March 8, 2012

AC Motor Construction

Three-phaseAC induction motors are commonly used in industrial applications. This type ofmotor has three main parts, rotor, stator, and enclosure. The stator and rotordo the work, and the enclosure protects the stator and rotor.


StatorCore
Thestator is the stationary part of the motor’s electromagnetic circuit. Thestator core is made up of many thin metal sheets, called laminations.Laminations are used to reduce energy loses that would result if a solid corewere used.


StatorWindings Stator laminations are stacked together forming a hollow cylinder.Coils of insulated wire are inserted into slots of the stator core.

Whenthe assembled motor is in operation, the stator windings are connected directlyto the power source. Each grouping of coils, together with the steel core itsurrounds, becomes an electromagnet when current is applied. Electromagnetismis the basic principle behind motor operation.

RotorConstruction
Therotor is the rotating part of the motor’s electromagnetic circuit. The mostcommon type of rotor used in a three-phase induction motor is a squirrel cagerotor. Other types of rotor construction is discussed later in the course. Thesquirrel cage rotor is so called because its construction is reminiscent of therotating exercise wheels found in some pet cages.

Asquirrel cage rotor core is made by stacking thin steel laminations to form acylinder.
 Ratherthan using coils of wire as conductors, conductor bars are die cast into theslots evenly spaced around the cylinder. Most squirrel cage rotors are made bydie casting aluminum to form the conductor bars. Siemens also makes motors withdie cast copper rotor conductors. These motor exceed NEMA Premium efficiencystandards.

Afterdie casting, rotor conductor bars are mechanically and electrically connectedwith end rings. The rotor is then pressed onto a steel shaft to form a rotorassembly.

 
Enclosure
Theenclosure consists of a frame (or yoke) and two end brackets (or bearinghousings). The stator is mounted inside the frame. The rotor fits inside thestator with a slight air gap separating it from the stator. There is no directphysical connection between the rotor and the stator.


Theenclosure protects the internal parts of the motor from water and otherenvironmental elements. The degree of protection depends upon the type ofenclosure. Enclosure types are discussed later in this course.
 
Bearings,mounted on the shaft, support the rotor and allow it to turn. Some motors, likethe one shown in the following illustration, use a fan, also mounted on therotor shaft, to cool the motor when the shaft is rotating.