Monday, December 31, 2007
Friday, April 15, 2005
15.April.Friday
p. 56, Engines Text
Vibration Damper – Viscous (fluid-filled) finds the off-center position of the crankshaft to dampen vibration. This is the most sensitive type: the end result of minor damage to a viscous vibration damper will be a broken crankshaft.
Establish the timing marks before disassembly – check the relationship of gears prior to disassembly because determining any problems which may have resulted from incorrect timing must first be indicated and noticed by incorrect relationships between the engine’s timing gears.
Valve Overlap / Valve Rock –
Figure, 4-27, p. 66
Portion of the cycle, and what the piston is doing mechanically
Valve overlap occurs 10-16 degrees before TDC and ATDC on 4-cycle engines.
Find the valve overlap position for the #1 cylinder before our engines come apart.
Vibration Damper – Viscous (fluid-filled) finds the off-center position of the crankshaft to dampen vibration. This is the most sensitive type: the end result of minor damage to a viscous vibration damper will be a broken crankshaft.
Establish the timing marks before disassembly – check the relationship of gears prior to disassembly because determining any problems which may have resulted from incorrect timing must first be indicated and noticed by incorrect relationships between the engine’s timing gears.
Valve Overlap / Valve Rock –
Figure, 4-27, p. 66
Portion of the cycle, and what the piston is doing mechanically
Valve overlap occurs 10-16 degrees before TDC and ATDC on 4-cycle engines.
Find the valve overlap position for the #1 cylinder before our engines come apart.
Monday, April 11, 2005
11.April.Monday
11.April.Monday
p. 128, in Textbook
Cam-Ground Pistons (fig. 7-6, p. 128) – Shape of the cam-ground piston is elliptical, although its shape appears round to us. Pistons are cam-ground because of the coefficient of linear expansion: every object will change its shape/size as we add or take away heat energy. Objects get longer, fatter, thicker, when we add heat energy to them because their molecules can travel farther in shorter amount of time than those same molecules with a lower level of heat energy. I.e. thermometers are speedometers for molecule energy: molecules whose temperature is being measured impact with the molecules of the thermometer: the more heat energy they give up to the molecules of the thermometer, the higher the temperature the thermometer will register.
The piston has more mass at the pin bore – more mass at the pin boss – than the area of the piston skirt w/o the pin bosses. The area with more mass will expand more rapidly than the area with less mass, therefore because the manufacturer intends for the piston to be round when the piston is loaded, pistons are cam-ground in order to be elliptical when cold and to become round at the engine comes up to operating temperature. The opposite expansion of the piston will occur with overheating: pistons are intended to operate within engineered specifications, somewhere b/w 165 and 230 degrees Fahrenheit.
Wear often occurs because of dynamic size changes directly related to the coefficient of linear expansion – through a kind of relative motion between components which we would not normally expect. Relative motion is one of the three manners in which components wear, the other two being load and contact (if we can identify what the load is, where is the contact, and where is the relative motion, we can always identify why and how wear has occurred). Relative motion b/c of the coefficient linear expansion can even account for the inner chafed surfaces of hoses which are clamped onto steel or aluminum necks. Another example is the wear on cylinder head gaskets which also occurs because of the coefficient of linear expansion.
Because clearances b/w pistons and cylinder walls vary b/w .020” to .025”, nicks in piston skirts are very damaging.
p. 128, in Textbook
Cam-Ground Pistons (fig. 7-6, p. 128) – Shape of the cam-ground piston is elliptical, although its shape appears round to us. Pistons are cam-ground because of the coefficient of linear expansion: every object will change its shape/size as we add or take away heat energy. Objects get longer, fatter, thicker, when we add heat energy to them because their molecules can travel farther in shorter amount of time than those same molecules with a lower level of heat energy. I.e. thermometers are speedometers for molecule energy: molecules whose temperature is being measured impact with the molecules of the thermometer: the more heat energy they give up to the molecules of the thermometer, the higher the temperature the thermometer will register.
The piston has more mass at the pin bore – more mass at the pin boss – than the area of the piston skirt w/o the pin bosses. The area with more mass will expand more rapidly than the area with less mass, therefore because the manufacturer intends for the piston to be round when the piston is loaded, pistons are cam-ground in order to be elliptical when cold and to become round at the engine comes up to operating temperature. The opposite expansion of the piston will occur with overheating: pistons are intended to operate within engineered specifications, somewhere b/w 165 and 230 degrees Fahrenheit.
Wear often occurs because of dynamic size changes directly related to the coefficient of linear expansion – through a kind of relative motion between components which we would not normally expect. Relative motion is one of the three manners in which components wear, the other two being load and contact (if we can identify what the load is, where is the contact, and where is the relative motion, we can always identify why and how wear has occurred). Relative motion b/c of the coefficient linear expansion can even account for the inner chafed surfaces of hoses which are clamped onto steel or aluminum necks. Another example is the wear on cylinder head gaskets which also occurs because of the coefficient of linear expansion.
Because clearances b/w pistons and cylinder walls vary b/w .020” to .025”, nicks in piston skirts are very damaging.
Thursday, April 07, 2005
7.April.Thursday
Purpose of the Crankshaft – The crankshaft converts reciprocating, linear motion to radial or turning motion: torque.
Crankshafts are precision-manufactured, and are one, if not the, most expensive components which make up a diesel engine. The care and responsibility levels for their maintenance and installation – including maintaining clean environments in which they operate - is rigorous, as is the level of maintaining crankshaft bearing health. Critical portions of the crankshaft – the main and connecting rod journal areas – are selectively hardened to extend the life of these areas, which themselves are what allow reciprocating engines to perform useful work. This hardening process, known as nitriding, is itself very expensive and labor intensive, adding to the cost of crankshafts considerably. These facts about crankshaft manufacture should indicate that, for all their considerable strength – e.g. being subjected to forces in the range of ten of thousands of pounds many times per second – crankshafts nonetheless require deliberate, careful attention to proper procedures in order to maintain their value and their safe and reliable operation.
The nitriding process for crankshafts generally only extends .030” from the surface of the journals into the shaft. Hardening at this seemingly shallow depth gives the critical journal surfaces great longevity, while permitting the great mass of the shaft itself retain a kind of flexibility necessary to sustain the great forces applied to it: a through-hardened shaft would soon fracture under the stain of operating conditions, even light ones. The depth of the journal hardening process means that even seemingly innocuous scratches or nicks can and will permanently damage the journals. The repair of scratches or nicks on crankshaft journals, which on other surfaces would not concern us, is both extremely expensive and reduces the useful life of the crank. One scratch which is .005” deep will effectively damage the crankshaft to a depth of .010” because the repair involves an annular grinding of the surface. In other words, to remove a nick of .005”, double that thickness must be removed because the journal is a circular surface. The removal of ten-thousandths of an inch of hardened journal material is the equivalent of the total of the entire first re-grind procedure of a crankshaft. First re-grind of the crank generally occurs at an engine’s first overhaul. Failure to care for a crank responsibly through attention paid to cleanliness and appropriate storage procedures can therefore add a prohibitive expense to vehicle maintenance, an expensive that could even cause a loss of jobs if not an isolated occurrence.
Crankshafts, when ground upon repair, are then referred to as “undersized.” Consequently, a bearing to fit an undersized crankshaft main or rod journal is thicker, or oversized. A bearing marked .010” is therefore intended to be installed on a crankshaft that is .010” undersized.
Order of Sizes for repairs to Crankshaft Main Journals, Connecting Rod Journals, and Thrust Faces (to commit to memory):
1) First size always refers to the Main Journal(s) –
2) Second size always refers to the Connecting Rod Journals
3) Third size always refers to the thrust faces. The terminology for thrust faces includes both flanged bearings which act as thrust faces and separate thrust washers themselves.
“STD” is the reference if the size of the component in question – whether journal or thrust face - is original, i.e. not previously ground.
Examples:
STD STD STD
STD .010 STD
STD STD .020
STD .020 .010
Assignment
Quantity: 2 Crankshafts
We will be looking for taper, hour-glass, or barrel-shaping of journal down to .0001”.
Tapers will cause thrust forces to be produced at the rod journals (thrust forces of a different nature will also be produced at tapered main journals). Hourglass shapes will make the dispersement of oil under the bearing uneven. Barrel shaped journals will also disturb the even dispersement of oil.
We will be also be checking for perpendicularity of the flywheel to the crankshaft. If we don’t have the flywheel on the crankshaft, we will dial indicate the face of the crankshaft.
These assignments will require a spreadsheet for the report. We have to measure every journal in four places, two at each axially-opposed position on each journal. We will also take an unrecorded fifth measurement in the middle of the journal to see if there is a barrel-shape to the journal. If so, this unmeasured fifth measurement must be on the report.
We also must include a three-dimensional drawing of the journals we measured and the manner in which we measured them. For example,
[top row] A-B C-D
[top column] # 1 Measurement.
Crankshafts are precision-manufactured, and are one, if not the, most expensive components which make up a diesel engine. The care and responsibility levels for their maintenance and installation – including maintaining clean environments in which they operate - is rigorous, as is the level of maintaining crankshaft bearing health. Critical portions of the crankshaft – the main and connecting rod journal areas – are selectively hardened to extend the life of these areas, which themselves are what allow reciprocating engines to perform useful work. This hardening process, known as nitriding, is itself very expensive and labor intensive, adding to the cost of crankshafts considerably. These facts about crankshaft manufacture should indicate that, for all their considerable strength – e.g. being subjected to forces in the range of ten of thousands of pounds many times per second – crankshafts nonetheless require deliberate, careful attention to proper procedures in order to maintain their value and their safe and reliable operation.
The nitriding process for crankshafts generally only extends .030” from the surface of the journals into the shaft. Hardening at this seemingly shallow depth gives the critical journal surfaces great longevity, while permitting the great mass of the shaft itself retain a kind of flexibility necessary to sustain the great forces applied to it: a through-hardened shaft would soon fracture under the stain of operating conditions, even light ones. The depth of the journal hardening process means that even seemingly innocuous scratches or nicks can and will permanently damage the journals. The repair of scratches or nicks on crankshaft journals, which on other surfaces would not concern us, is both extremely expensive and reduces the useful life of the crank. One scratch which is .005” deep will effectively damage the crankshaft to a depth of .010” because the repair involves an annular grinding of the surface. In other words, to remove a nick of .005”, double that thickness must be removed because the journal is a circular surface. The removal of ten-thousandths of an inch of hardened journal material is the equivalent of the total of the entire first re-grind procedure of a crankshaft. First re-grind of the crank generally occurs at an engine’s first overhaul. Failure to care for a crank responsibly through attention paid to cleanliness and appropriate storage procedures can therefore add a prohibitive expense to vehicle maintenance, an expensive that could even cause a loss of jobs if not an isolated occurrence.
Crankshafts, when ground upon repair, are then referred to as “undersized.” Consequently, a bearing to fit an undersized crankshaft main or rod journal is thicker, or oversized. A bearing marked .010” is therefore intended to be installed on a crankshaft that is .010” undersized.
Order of Sizes for repairs to Crankshaft Main Journals, Connecting Rod Journals, and Thrust Faces (to commit to memory):
1) First size always refers to the Main Journal(s) –
2) Second size always refers to the Connecting Rod Journals
3) Third size always refers to the thrust faces. The terminology for thrust faces includes both flanged bearings which act as thrust faces and separate thrust washers themselves.
“STD” is the reference if the size of the component in question – whether journal or thrust face - is original, i.e. not previously ground.
Examples:
STD STD STD
STD .010 STD
STD STD .020
STD .020 .010
Assignment
Quantity: 2 Crankshafts
We will be looking for taper, hour-glass, or barrel-shaping of journal down to .0001”.
Tapers will cause thrust forces to be produced at the rod journals (thrust forces of a different nature will also be produced at tapered main journals). Hourglass shapes will make the dispersement of oil under the bearing uneven. Barrel shaped journals will also disturb the even dispersement of oil.
We will be also be checking for perpendicularity of the flywheel to the crankshaft. If we don’t have the flywheel on the crankshaft, we will dial indicate the face of the crankshaft.
These assignments will require a spreadsheet for the report. We have to measure every journal in four places, two at each axially-opposed position on each journal. We will also take an unrecorded fifth measurement in the middle of the journal to see if there is a barrel-shape to the journal. If so, this unmeasured fifth measurement must be on the report.
We also must include a three-dimensional drawing of the journals we measured and the manner in which we measured them. For example,
[top row] A-B C-D
[top column] # 1 Measurement.
Wednesday, April 06, 2005
6.April.Wednesday
6.April.Wednesday
Cycle – set of actions that start in once place and then end when that place is reached again, such as one complete AC phase cycle, i.e. when all the functions of a cycle have been performed.
Assignment for tomorrow –
Describe a cycle of some kind that is not related to diesel engines: where it starts, the phases it goes through, and where it ends.
Two-stroke cycle / Four-stroke cycle - STROKE is the operative term
Four-stroke Cycle
1) The first stroke is always the intake stroke. This is so because the engine requires air to operate – without it there is no combustion to operate the engine.
2) The second stroke is the compression stroke. This is so because heat energy is required to ignite the fuel charge of a diesel engine.
3) The third stoke is the power stroke.
a. Power = Work / Time
4) The fourth stroke is the exhaust stroke.
a. Temperature, particulates, other (Nitric oxides, etc.)
Two-stoke Cycle
The two strokes in this type of engine refer to the physical movement of the piston, and from the region of Top Dead Center to Bottom Dead Center
When the piston moves down is the cylinder’s first stroke, and creates an increasing space. This is not an intake stroke, but a power stroke. The first stroke of a two-stroke engine is always the power stroke.
The upward stroke, the second stroke, is always compression. The only two strokes of a two-stroke cycle are power and compression.
Like a four-stroke cycle, we need the other two events to occur: intake and exhaust. Both occur at Bottom Dead Center. There is no stroke of the piston that is responsible for intake and exhaust – a separate component, a blower, is required to perform this functions. Without the blower, the engine will not run – it may idle, badly, but there is no way for a two-stroke engine to inhale and exhale properly without the blower.
In a four-stroke cycle engine, atmospheric air pressure (14.7 psi, at sea level on Earth) is responsible for intake and exhaust. When the piston moves down, assuming that it started at TDC, it creates a space. What was in that space was the material of the piston – when we move the piston, there is nothing in that space – a void exists. To fill this void, what is best is 100% volumetric efficiency.
When we crank an engine over at 300 RPM (1/2 of idle speed), there is plenty of time for atmospheric air pressure to fill the void. But at 5000 RPM, the time factor is much less for atmospheric pressure to fill this void. When the peak RPM is reached, valves float and the piston is going so fast the void cannot be filled by atmospheric pressure – you have to slow down to properly fill the cylinder void. Volumetric efficiency decreases with increases in engine speed.
Peak Horsepower is always at a very high RPM. Peak Torque falls off at a much lower specific RPM. Peak Torque occurs at peak volumetric efficiency – when we can get the most air into the cylinder and combust the fuel in the most efficient manner. Volumetric efficiency also, consequently, decrease with impeded air flow. Performance issues will always occur when volumetric efficiency is deprecated by any number of factors. Volumetric efficiency and its parameters must be applied to engine diagnosis, instead of waiting for “experience” to fill the in the troubleshooting voids we will encounter.
There is a difference between HP and Torque because of TIME: as long as the theoretical work and time increase, the horsepower will increase. Torque is key, however, to what we need to know about volumetric efficiency. Generated Torque – not theoretical horsepower – is what we’re after.
The piston moving down on the intake stroke generates a space where atmospheric pressure at 14.7 psi can completely fill the cylinder on a naturally-aspirated engine. Turbochargers help atmospheric efficiency to fill the cylinders.
If an engine cannot breathe out – back pressure, at whatever level, for whatever reason – will prevent the engine from taking in a fresh air charge.
100% volumetric efficiency (100% full of air because of atmospheric pressure) means that all of the oxygen in the air (~28%) is usable for combustion.
Compression
A 10 to 1 compression ratio means that the pressure in the cylinder would be 10 times the original atmospheric pressure of 14.7 psi, or 147 psi, in a naturally aspirated engine. Pressure increases when we add heat energy – i.e. checking compression with a quick increase in pressure will not let the heat dissipate from the pressurized air, increasing the pressure. Generally, a 14:1 compression ratio is the lowest, and 22:1 is the highest compression ratio. The shape of the turbulence chamber, the shape of the top of the piston, what the fuel looks like when it hits the piston (i.e. level of atomization), whether the engine is naturally-aspirated - all make major differences in compression ratios required for service. Pre-compressed air in the intake manifold (i.e. turbo-charged air) will allow a drop in the compression ratio an engine is engineered to have in order to operate efficiently.
Proper compression is achieved with, and must include, 5 factors:
1) We need 100% volumetric efficiency.
2) We need the heat of compression to ratio the compression ratio
3) We need to retain that heat – to keep it from moving into the water jacket
4) We need our rings to seal well enough to keep that air in the cylinder
5) We need the valves to close tightly enough to prevent the air from escaping
6) We need the engine to turn over fast enough to generate the heat energy of friction
Lacking any of these will lower compression, therefore lower performance and heighten emissions, because all of these directly effect volumetric efficiency!
BTU Values, General information
145,000 BTUs per Gallon (No. 2D, Cetane value of 46.7-49)
125,000 BTUs per gallon of Gasoline
95,000 BTUs per (quantity?) of Propane
Meaning of the terms BTU & Calorie:
1 BTU is the amount of energy required to raise the temperature of 1 lb. of water 1 Fahrenheit degree - 1 BTU per pound, per Fahrenheit degree.
The SI equivalent of the BTU, the Calorie, is the amount of energy required to raise the temperature of one gram of water 1 Celcuis degree - 1 Calorie per gram, per Celcius degree.
____________________
Assignment for tomorrow, 7.April.Thursday – Read Chapter 6, and complete and turn in the review questions for Chapter 6. Plan to usethis reading to get to both the entire Chapter 6 workbook set of questions, as well as the ASE-type questions for Chapter 6.
Cycle – set of actions that start in once place and then end when that place is reached again, such as one complete AC phase cycle, i.e. when all the functions of a cycle have been performed.
Assignment for tomorrow –
Describe a cycle of some kind that is not related to diesel engines: where it starts, the phases it goes through, and where it ends.
Two-stroke cycle / Four-stroke cycle - STROKE is the operative term
Four-stroke Cycle
1) The first stroke is always the intake stroke. This is so because the engine requires air to operate – without it there is no combustion to operate the engine.
2) The second stroke is the compression stroke. This is so because heat energy is required to ignite the fuel charge of a diesel engine.
3) The third stoke is the power stroke.
a. Power = Work / Time
4) The fourth stroke is the exhaust stroke.
a. Temperature, particulates, other (Nitric oxides, etc.)
Two-stoke Cycle
The two strokes in this type of engine refer to the physical movement of the piston, and from the region of Top Dead Center to Bottom Dead Center
When the piston moves down is the cylinder’s first stroke, and creates an increasing space. This is not an intake stroke, but a power stroke. The first stroke of a two-stroke engine is always the power stroke.
The upward stroke, the second stroke, is always compression. The only two strokes of a two-stroke cycle are power and compression.
Like a four-stroke cycle, we need the other two events to occur: intake and exhaust. Both occur at Bottom Dead Center. There is no stroke of the piston that is responsible for intake and exhaust – a separate component, a blower, is required to perform this functions. Without the blower, the engine will not run – it may idle, badly, but there is no way for a two-stroke engine to inhale and exhale properly without the blower.
In a four-stroke cycle engine, atmospheric air pressure (14.7 psi, at sea level on Earth) is responsible for intake and exhaust. When the piston moves down, assuming that it started at TDC, it creates a space. What was in that space was the material of the piston – when we move the piston, there is nothing in that space – a void exists. To fill this void, what is best is 100% volumetric efficiency.
When we crank an engine over at 300 RPM (1/2 of idle speed), there is plenty of time for atmospheric air pressure to fill the void. But at 5000 RPM, the time factor is much less for atmospheric pressure to fill this void. When the peak RPM is reached, valves float and the piston is going so fast the void cannot be filled by atmospheric pressure – you have to slow down to properly fill the cylinder void. Volumetric efficiency decreases with increases in engine speed.
Peak Horsepower is always at a very high RPM. Peak Torque falls off at a much lower specific RPM. Peak Torque occurs at peak volumetric efficiency – when we can get the most air into the cylinder and combust the fuel in the most efficient manner. Volumetric efficiency also, consequently, decrease with impeded air flow. Performance issues will always occur when volumetric efficiency is deprecated by any number of factors. Volumetric efficiency and its parameters must be applied to engine diagnosis, instead of waiting for “experience” to fill the in the troubleshooting voids we will encounter.
There is a difference between HP and Torque because of TIME: as long as the theoretical work and time increase, the horsepower will increase. Torque is key, however, to what we need to know about volumetric efficiency. Generated Torque – not theoretical horsepower – is what we’re after.
The piston moving down on the intake stroke generates a space where atmospheric pressure at 14.7 psi can completely fill the cylinder on a naturally-aspirated engine. Turbochargers help atmospheric efficiency to fill the cylinders.
If an engine cannot breathe out – back pressure, at whatever level, for whatever reason – will prevent the engine from taking in a fresh air charge.
100% volumetric efficiency (100% full of air because of atmospheric pressure) means that all of the oxygen in the air (~28%) is usable for combustion.
Compression
A 10 to 1 compression ratio means that the pressure in the cylinder would be 10 times the original atmospheric pressure of 14.7 psi, or 147 psi, in a naturally aspirated engine. Pressure increases when we add heat energy – i.e. checking compression with a quick increase in pressure will not let the heat dissipate from the pressurized air, increasing the pressure. Generally, a 14:1 compression ratio is the lowest, and 22:1 is the highest compression ratio. The shape of the turbulence chamber, the shape of the top of the piston, what the fuel looks like when it hits the piston (i.e. level of atomization), whether the engine is naturally-aspirated - all make major differences in compression ratios required for service. Pre-compressed air in the intake manifold (i.e. turbo-charged air) will allow a drop in the compression ratio an engine is engineered to have in order to operate efficiently.
Proper compression is achieved with, and must include, 5 factors:
1) We need 100% volumetric efficiency.
2) We need the heat of compression to ratio the compression ratio
3) We need to retain that heat – to keep it from moving into the water jacket
4) We need our rings to seal well enough to keep that air in the cylinder
5) We need the valves to close tightly enough to prevent the air from escaping
6) We need the engine to turn over fast enough to generate the heat energy of friction
Lacking any of these will lower compression, therefore lower performance and heighten emissions, because all of these directly effect volumetric efficiency!
BTU Values, General information
145,000 BTUs per Gallon (No. 2D, Cetane value of 46.7-49)
125,000 BTUs per gallon of Gasoline
95,000 BTUs per (quantity?) of Propane
Meaning of the terms BTU & Calorie:
1 BTU is the amount of energy required to raise the temperature of 1 lb. of water 1 Fahrenheit degree - 1 BTU per pound, per Fahrenheit degree.
The SI equivalent of the BTU, the Calorie, is the amount of energy required to raise the temperature of one gram of water 1 Celcuis degree - 1 Calorie per gram, per Celcius degree.
____________________
Assignment for tomorrow, 7.April.Thursday – Read Chapter 6, and complete and turn in the review questions for Chapter 6. Plan to usethis reading to get to both the entire Chapter 6 workbook set of questions, as well as the ASE-type questions for Chapter 6.
Monday, February 28, 2005
24.February.Thursday
Reference Section 7-1 (Deere FOS) - Starting Circuits
The process of starter motor disassembly and repair in the shop is simply too expensive at this point in time. We can, however, effectively troubleshoot starter motor and starting circuitry malfunctions with multimeters, but only insofar as we understand the functions – and the reasons for these functions – of starter motors and the circuitry in which they are engineered.
A motor, as opposed to an engine, takes electrical energy and converts it to one of the three cardinal uses of electricity: producing a magnetic field, and then using that magnetic field to do useful work. Although motors produce some heat (another of the three uses of electricity, the last being the production of light), that is not the design objective – motors are intended to do work by converting the "push and pull" of the magnetic fields created inside them to mechanical energy in the form of torque.
The armature is the component that rotates within a starter motor, and is attached to the pinion gear which engages the engine’s flywheel. The purpose of the armature turning is to turn the pinion gear. If the armature cannot turn, the pinion gear will not turn, and the engine simply will not start.
Something has to push and pull the armature in order for it to produce a torque at the pinion gear. In isolation, one magnetic field pulls on one copper band inserted into the laminations of the armature, and, as soon as that reaches the “center” or “apogee” of that force, that “pull” will become a “push.” At the same time, another magnetic field will grab that same copper band in the armature and propel the mass of the band, over and over again.
__________________
When we perform a starter load test, either free spin or on vehicle, we typically have a high initial current reading, then a current reading that is lower than the initial reading as the speed of the motor increases. This means that when an engine is started from a dead stop, the highest torque on the part of the starter motor– and the highest current to produce it – is required. At cranking speed, however, less torque from the starter motor is required to maintain starter motor/engine speeds, therefore less current is required to maintain cranking speed. Cranking speed is generally half of idle RPM.
Overspeeding a starter motor – i.e. if the pinion gear does not disengage from the flywheel after the engine is operating under its own power, for whatever reason - will begin the process of deterioration of the armature, i.e. the components which comprise the armature will begin to separate. The copper bands embedded in the laminated iron core will begin to be loosened from their positions in the core because of inertial forces exceeding the engineered limitations of the starter motor during overspeeding.
A physical connection from the battery passes electricity through the motor terminal lug on the starter housing, which passes to the motor’s brushes. The motor’s brushes make contact with the commutator (similar to the slip ring in AC generators). Each section of the commutator is attached to a section of the motor’s field winding.
Surrounding the armature, attached to the frame of the starter motor, are pole pieces and field windings. The pole pieces sit in a field coil/winding, so-called because the wires are wound in such a way that a cavity for the pole piece is formed. The pole piece – an iron core – intensifies the magnetic field produced by the field coil. The iron core has a higher magnetic permeability than air – i.e. air has a far higher magnetic reluctance than iron.
The magnetic fields of the armature and the field coils attract and repel each other in turn, producing torque.
There are deliberately engineered differences between the internal connectivity in starter motors intended for different applications. Starter motors are wound in series internally, parallel internally, or series-parallel internally. These differences in connectivity are designed to produce torque values specific to various applications with specific current requirements.
Current will always increase as a starter motor wears because resistance in the motor itself will increase with wear. With increased resistance within the motor, increased current is required to overcome this additional resistance.
When an engine will not start, either the starter motor’s armature won’t turn because it is dragging, or high internal engine resistance will not permit the engine to start. High internal engine resistance could be the result of a cylinder full of liquid, a frozen fuel pump, the engine is in gear, etc. In this case, we must attempt to physically turn the engine with a wrench. If we find high internal engine resistance, this resistance itself must be considered in part or in whole as the factor preventing starting. This means that the starter motor must not initially be suspected - and should not be replaced – until any internal engine resistance which precludes starting is addressed and corrected, and further attempts are made to start the engine.
A starter motor is somewhat like a throw-out bearing, in that it is loaded seldomly – unlike wheel bearings which are constantly loaded. Starter motors are designed to be placed in dramatically over-loaded conditions for temporary use.
The process of starter motor disassembly and repair in the shop is simply too expensive at this point in time. We can, however, effectively troubleshoot starter motor and starting circuitry malfunctions with multimeters, but only insofar as we understand the functions – and the reasons for these functions – of starter motors and the circuitry in which they are engineered.
A motor, as opposed to an engine, takes electrical energy and converts it to one of the three cardinal uses of electricity: producing a magnetic field, and then using that magnetic field to do useful work. Although motors produce some heat (another of the three uses of electricity, the last being the production of light), that is not the design objective – motors are intended to do work by converting the "push and pull" of the magnetic fields created inside them to mechanical energy in the form of torque.
The armature is the component that rotates within a starter motor, and is attached to the pinion gear which engages the engine’s flywheel. The purpose of the armature turning is to turn the pinion gear. If the armature cannot turn, the pinion gear will not turn, and the engine simply will not start.
Something has to push and pull the armature in order for it to produce a torque at the pinion gear. In isolation, one magnetic field pulls on one copper band inserted into the laminations of the armature, and, as soon as that reaches the “center” or “apogee” of that force, that “pull” will become a “push.” At the same time, another magnetic field will grab that same copper band in the armature and propel the mass of the band, over and over again.
__________________
When we perform a starter load test, either free spin or on vehicle, we typically have a high initial current reading, then a current reading that is lower than the initial reading as the speed of the motor increases. This means that when an engine is started from a dead stop, the highest torque on the part of the starter motor– and the highest current to produce it – is required. At cranking speed, however, less torque from the starter motor is required to maintain starter motor/engine speeds, therefore less current is required to maintain cranking speed. Cranking speed is generally half of idle RPM.
Overspeeding a starter motor – i.e. if the pinion gear does not disengage from the flywheel after the engine is operating under its own power, for whatever reason - will begin the process of deterioration of the armature, i.e. the components which comprise the armature will begin to separate. The copper bands embedded in the laminated iron core will begin to be loosened from their positions in the core because of inertial forces exceeding the engineered limitations of the starter motor during overspeeding.
A physical connection from the battery passes electricity through the motor terminal lug on the starter housing, which passes to the motor’s brushes. The motor’s brushes make contact with the commutator (similar to the slip ring in AC generators). Each section of the commutator is attached to a section of the motor’s field winding.
Surrounding the armature, attached to the frame of the starter motor, are pole pieces and field windings. The pole pieces sit in a field coil/winding, so-called because the wires are wound in such a way that a cavity for the pole piece is formed. The pole piece – an iron core – intensifies the magnetic field produced by the field coil. The iron core has a higher magnetic permeability than air – i.e. air has a far higher magnetic reluctance than iron.
The magnetic fields of the armature and the field coils attract and repel each other in turn, producing torque.
There are deliberately engineered differences between the internal connectivity in starter motors intended for different applications. Starter motors are wound in series internally, parallel internally, or series-parallel internally. These differences in connectivity are designed to produce torque values specific to various applications with specific current requirements.
Current will always increase as a starter motor wears because resistance in the motor itself will increase with wear. With increased resistance within the motor, increased current is required to overcome this additional resistance.
When an engine will not start, either the starter motor’s armature won’t turn because it is dragging, or high internal engine resistance will not permit the engine to start. High internal engine resistance could be the result of a cylinder full of liquid, a frozen fuel pump, the engine is in gear, etc. In this case, we must attempt to physically turn the engine with a wrench. If we find high internal engine resistance, this resistance itself must be considered in part or in whole as the factor preventing starting. This means that the starter motor must not initially be suspected - and should not be replaced – until any internal engine resistance which precludes starting is addressed and corrected, and further attempts are made to start the engine.
A starter motor is somewhat like a throw-out bearing, in that it is loaded seldomly – unlike wheel bearings which are constantly loaded. Starter motors are designed to be placed in dramatically over-loaded conditions for temporary use.
Monday, February 14, 2005
14.February.Monday
Rules for Testing & Charging Batteries-
pp. 110 & ff., Shop Manual
“We’ll know 24 hours from now after we trickle-charge the battery.” This is a typical repair facility response to customer battery complaints. Fast-charging is NEVER effective as a repair. It takes times to internally repair a battery. Battery repair – if a battery is reparable at all – is only possible through the passing of low current through the battery’s plates for long periods of times.
24 hours is a logical time period for a battery charging procedure. A slow charge of this duration enables any sulfate crystals (lead sulfate) which have formed throughout the plates (and which preclude the reversed polarity of charging current to flow through a battery) to be converted to lead peroxide. Lead peroxide is the chemical compound intended to comprise the plates to produce the electrochemical reaction required to make a battery function.
In contrast, fast charging only converts the lead sulfate back to lead peroxide on the surface of the plates. If the lead sulfate is not converted throughout a battery’s plates – which is what takes place during a fast-charge - in all likelihood this would cause such a battery to fail a CCA test.
In addition to sulfation of a battery’s plates, general battery problems include internally open or shorted circuits. When a battery has an internal open or short, there is no possibility of repairing the battery, outside of procedures conducted by battery manufacturers themselves.
Internal shorts and opens are not the most common problems, however. Sulfation is one of the most common problems. The material on the plates undergoes intentionally engineered changes when we’re using the battery to either chemically produce electricity (such as to operate the starter motor to start a vehicle), or when the charging system is recharging the battery. In other words, a battery’s plates are intended to be used, and although the changes that lead to sulfation occur and are reversed during normal operation, batteries which sit unused develop “hard” sulfate crystals on the surface on the plates, which only have the possibility of being removed – and thereby restoring the battery to a condition of reliability – through a low-current, trickle charge.
Fast-charging, on the other hand, brings a battery to a state of charge that may allow a vehicle to be started in the short term. Such a procedure is intended to permit the operator to either be able to complete an assignment, for example, or to permit the vehicle to be driven to a repair facility. Another reason for a fast-charge is the hope that the charging system will eventually remove sulfation and bring the battery up to a full charge during operation. However, during a fast-charge the lead sulfate on the outside of the plates gets converted back to lead peroxide. Fast-charges must NEVER be performed for more than 2 hours, and must not exceed 30 amps. In addition, do not allow the voltage of a 12V battery to exceed 15.5V, nor allow the temperature of the battery’s electrolyte to rise above 125 degrees F.
____________________________________________
When a vehicle won’t start, it takes a clear, calm head to determine how to start the vehicle. Some basic figures will help us approach such a problem logically and effectively.
1. CCA (Cold Cranking Amps) –
The ability of the battery to deliver a specific amount of current flow for a specific amount of time. When we test a battery to determine whether it can really deliver its CCA, we’re really field-testing the battery. We do this to make a determination about a so-called “now” problem/complaint: the customer wants to know “Is the battery good, or bad?” (The other test for a “now” complaint would be a hydrometer test; however, the hydrometer test is non-dynamic.). The CCA test is a dynamic stress-test to see how well the battery holds up under a specific load. The results from this test can be used to verify a complaint.
Other reasons to test batteries include essential, periodic maintenance
Opens, shorts and sulfation will cause failures of CCA tests.
CCA tests must be conducted in the same environment as the operating conditions of the vehicle.
We disconnect the negative terminal of the battery. Next, we hook up the battery load tester to the battery, and determine the battery’s CCA. If we can’t find the CCA rating, we must take the measurements of the battery and find the BCI Group Number to get a standard CCA rating for that group.
Once the CCA rating is determined, we divide this number by 2, and load the battery at this current for 15 seconds. If there’s an open, it will open; if there’s a short, it will short; and if there’s a sulfation problem, the surface charge will quickly dissipate, indicating that the plates will not take a full charge.
After this, we will test the electrolyte with a hydrometer. If all cells are within 50 gravity points of one another, a trickle charge is indicated to relieve any level of sulfation problem. However, fast-charging a sulfated battery can dislodge sulfate crystals to such a degree that the plates that a short across the sediment tray as a result.
_________________
Minimum voltage for the CCA field test is 9V. ECMs have minimum voltage requirements - varying by OEM, but which must be met for the ECM to boot in order to permit a the vehicle to start. The coils of gasoline engines require 9V, absolute minimum, to bridge spark plug gaps. Most specifications indicate minimum voltages while loading a battery at ½ its CCA at between 9-9.6V. It is worth noting, however, that if a vehicle will not start when the battery is producing ½ the CCA for 15 seconds at between 9V-9.6V, the battery is NOT the problem. Other impediments to starting must be investigated – internal starter motor drag, for example.
2. Reserve Capacity (RC) –
The number of minutes a battery can deliver 25A at a voltage of 10.lV or higher. Deep cycle batteries have very high RCs - or depths of charge - and the ability to deliver a low amount of current for a long period of time.
The majority of the applications in the Heavy Duty Industry are concerned with CCA, not with RC, however.
Specific Gravity of Electrolyte related to State of Charge -
1. Specific gravity of water is 1 g/cubic cm [cc, or ml]
pp. 110 & ff., Shop Manual
“We’ll know 24 hours from now after we trickle-charge the battery.” This is a typical repair facility response to customer battery complaints. Fast-charging is NEVER effective as a repair. It takes times to internally repair a battery. Battery repair – if a battery is reparable at all – is only possible through the passing of low current through the battery’s plates for long periods of times.
24 hours is a logical time period for a battery charging procedure. A slow charge of this duration enables any sulfate crystals (lead sulfate) which have formed throughout the plates (and which preclude the reversed polarity of charging current to flow through a battery) to be converted to lead peroxide. Lead peroxide is the chemical compound intended to comprise the plates to produce the electrochemical reaction required to make a battery function.
In contrast, fast charging only converts the lead sulfate back to lead peroxide on the surface of the plates. If the lead sulfate is not converted throughout a battery’s plates – which is what takes place during a fast-charge - in all likelihood this would cause such a battery to fail a CCA test.
In addition to sulfation of a battery’s plates, general battery problems include internally open or shorted circuits. When a battery has an internal open or short, there is no possibility of repairing the battery, outside of procedures conducted by battery manufacturers themselves.
Internal shorts and opens are not the most common problems, however. Sulfation is one of the most common problems. The material on the plates undergoes intentionally engineered changes when we’re using the battery to either chemically produce electricity (such as to operate the starter motor to start a vehicle), or when the charging system is recharging the battery. In other words, a battery’s plates are intended to be used, and although the changes that lead to sulfation occur and are reversed during normal operation, batteries which sit unused develop “hard” sulfate crystals on the surface on the plates, which only have the possibility of being removed – and thereby restoring the battery to a condition of reliability – through a low-current, trickle charge.
Fast-charging, on the other hand, brings a battery to a state of charge that may allow a vehicle to be started in the short term. Such a procedure is intended to permit the operator to either be able to complete an assignment, for example, or to permit the vehicle to be driven to a repair facility. Another reason for a fast-charge is the hope that the charging system will eventually remove sulfation and bring the battery up to a full charge during operation. However, during a fast-charge the lead sulfate on the outside of the plates gets converted back to lead peroxide. Fast-charges must NEVER be performed for more than 2 hours, and must not exceed 30 amps. In addition, do not allow the voltage of a 12V battery to exceed 15.5V, nor allow the temperature of the battery’s electrolyte to rise above 125 degrees F.
____________________________________________
When a vehicle won’t start, it takes a clear, calm head to determine how to start the vehicle. Some basic figures will help us approach such a problem logically and effectively.
1. CCA (Cold Cranking Amps) –
The ability of the battery to deliver a specific amount of current flow for a specific amount of time. When we test a battery to determine whether it can really deliver its CCA, we’re really field-testing the battery. We do this to make a determination about a so-called “now” problem/complaint: the customer wants to know “Is the battery good, or bad?” (The other test for a “now” complaint would be a hydrometer test; however, the hydrometer test is non-dynamic.). The CCA test is a dynamic stress-test to see how well the battery holds up under a specific load. The results from this test can be used to verify a complaint.
Other reasons to test batteries include essential, periodic maintenance
Opens, shorts and sulfation will cause failures of CCA tests.
CCA tests must be conducted in the same environment as the operating conditions of the vehicle.
We disconnect the negative terminal of the battery. Next, we hook up the battery load tester to the battery, and determine the battery’s CCA. If we can’t find the CCA rating, we must take the measurements of the battery and find the BCI Group Number to get a standard CCA rating for that group.
Once the CCA rating is determined, we divide this number by 2, and load the battery at this current for 15 seconds. If there’s an open, it will open; if there’s a short, it will short; and if there’s a sulfation problem, the surface charge will quickly dissipate, indicating that the plates will not take a full charge.
After this, we will test the electrolyte with a hydrometer. If all cells are within 50 gravity points of one another, a trickle charge is indicated to relieve any level of sulfation problem. However, fast-charging a sulfated battery can dislodge sulfate crystals to such a degree that the plates that a short across the sediment tray as a result.
_________________
Minimum voltage for the CCA field test is 9V. ECMs have minimum voltage requirements - varying by OEM, but which must be met for the ECM to boot in order to permit a the vehicle to start. The coils of gasoline engines require 9V, absolute minimum, to bridge spark plug gaps. Most specifications indicate minimum voltages while loading a battery at ½ its CCA at between 9-9.6V. It is worth noting, however, that if a vehicle will not start when the battery is producing ½ the CCA for 15 seconds at between 9V-9.6V, the battery is NOT the problem. Other impediments to starting must be investigated – internal starter motor drag, for example.
2. Reserve Capacity (RC) –
The number of minutes a battery can deliver 25A at a voltage of 10.lV or higher. Deep cycle batteries have very high RCs - or depths of charge - and the ability to deliver a low amount of current for a long period of time.
The majority of the applications in the Heavy Duty Industry are concerned with CCA, not with RC, however.
Specific Gravity of Electrolyte related to State of Charge -
1. Specific gravity of water is 1 g/cubic cm [cc, or ml]
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