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Directional Brake Pads – Apec Technical Bulletin

With the constant demand for improvement in all aspects of performance, vehicle manufacturers have designed brake pads for numerous applications that must be mounted directionally. Apec follow suit and offer pads that match the OE, in line with specification and performance. The main reason for directional brake pads is to eliminate noise.
NB: Failure to fit the pads correctly could result in noise and poor performance.
If there is an arrow present on the back of the pad, then it should always face in the direction of disc rotation. If no arrow is present, then please observe the following scenarios.

Chamfer: 

If one chamfer is present, it should oppose disc rotation. If two

chamfers are present, then the large chamfer should oppose disc rotation.

crescent-or-half-moon

Crescent or Half-moon:

The crescent or half-moon should oppose disc rotation.

chamfer

For more information on Directional Pads, please refer to the full article on Apec’s Website.Apec Large Logo Further

information on this or any other issue can be obtained from the Apec Trade Helpline 01454 285054

 

Apec’s EPB Service Tool – Everything you need to know

The new NT415 Electronic Park Brake Service Tool is specially designed to allow the service and maintenance of brake systems on multiple brands of vehicles where electronic brake systems are fitted. This powerful tool is invaluable for every workshop.

EPBtool

Features and Benefits
• Coverage includes 13 manufacturers
• Compatible with global OBDII/EOBD vehicles
• Deactivates and re-activates brake control system
• Retracts calipers for brake pad replacement
• Advances calipers after servicing to the original position
without affecting the current calibration
• Reads and clears trouble codes
• Turns off brake warning light
• Initializes the wear indicator if new pads installed
• Diagnoses EPB/SBC caliper functionality
• Resets the brake pad thickness after AUDI A8 service
• Performs ECU controlled brake fluid change
• Shows ECU information
• Supports all 10 OBDII test modes, including reading/
clearing codes, live data and so much more
• Provides live data graphing
• Merges graphs for easy and intuitive diagnosis
• As easy as 1-2-3 with large TFT colour screen and menu
driven operations
• Multilingual menu options and code definitions
• TF memory card for data backup and software update
• Ergonomic and robust housing

Technical Specifications
DISPLAY Backlit, 240 x 320 TFT colour display
WORKING TEMPERATURE 0 to 60˚C (32 to 140˚F)
STORAGE TEMPERATURE -20 to 70˚C (-4 to 158˚F)
EXTERNAL POWER 8-18 Volts powered by vehicle battery
DIMENSIONS 200 x 100 x 38mm (LxWxH)

Applications
ASIA Honda, Toyota
EUROPE Audi, BMW, Citroen, Jaguar, Land Rover,
Mercedes Benz, Opel, Peugeot, Renault,
Volkswagen, Volvo

Apec_EPB-tool Flyer

Ceramic diesel glow plugs – their function and how to install

Glow plug technology can be divided into two major categories – metal sheathed types and  ceramic types. Ceramic glow plugs utilise a heating element which is encased in a special type of ceramic – Silicon Nitride. Ceramic glow plugs have the ability to heat up more quickly than metal types and in addition can gain higher operating temperatures for an extended period of time. They are also more compact making these features especially advantageous in modern engines.

THE MAKE-UP OF A CERAMIC GLOW PLUG

Insulator – The insulator separates the electrically positive (Connection terminal) from the electrically negative part (Metal shell) of the glow plug.

Thread – The thread of a high-quality glow plug is always rolled and never cut. By this production method fast, accurate threads are formed, eliminating the possibility of damage to the glow plug bore in the cylinder head.

Centre electrode – The supply voltage is applied to the coils via the solid centre electrode.

Heating coil – Contrary to a metal glow plug, a ceramic glow plug uses a ceramic heating element.

Ceramic casing – The heating coil or heating element of a ceramic glow plug is encased in a high performance ceramic material: silicon nitride. It protects the coil from the high temperatures and vibrations created by the combustion process. It is also an excellent heat conductor, allowing the heat energy of the coil to be rapidly released into the combustion chamber.

Connection terminal – The supply voltage is applied at the connection terminal. This may be a threaded post to suit a connector which is secured by a nut or an unthreaded post to suit a push-on connector.

Metal shell – The metal shell of a glow plug usually provides the electrically negative pole (ground connection).

Taper seat – The taper seat provides simple but effective gas-tight sealing of the combustion chamber without the need for sealing gaskets, etc. Its compact form also allows bore sizes to be kept to a minimum. The taper faces also provide an excellent electrical ground (earth).

Contacting ring – The contacting ring provides the electrical connection at the junction of the centre electrode and the heating element.

INSTALLATION ADVICE

Particular care must be exercised when installing ceramic glow plugs. When fitted, the ceramic is designed to withstand the arduous events that occur within in the combustion chamber, however they are more susceptible than metal types to damage caused by unsupported side loads or impact. Improper installation can make it unusable or even lead to damage to the engine.

1. Where possible the removal of a glow plug should take place with the engine at operating temperature to assist in releasing the plug.
2. Carefully loosen the glow plug.
3. Remove any loose debris around the glow plug with compressed air.
4. Unscrew the old glow plug.
5. Remove any carbon deposits from the glow plug bore – with a reamer if necessary – then clean and inspect the thread in the cylinder head.
6. Screw the glow plug in by hand until it seats in the cylinder head.
7. Set the torque wrench to the correct tightening torque.
8. Ensure that the socket of the torque wrench is correctly in line with the tightening nut of the glow plug and secure it.
9. Refit the electrical supply connection.

Spark plugs – Questions & Answers (Corona stain)

Q. What is the function of the corrugations on the insulator?

A. They are what we call current creep barriers and prevent flash-over. Flash-over is when there is a voltage discharge between the top terminal nut and the metal shell of the plug (as shown in the picture, left) and is highly undesirable because it weakens or prevents the spark occurring within the combustion chamber.

This will lead to misfiring and poor performance and to prevent this phenomenon taking place corrugations (ribs) are provided on the insulator which in effect extend the surface distance between the terminal and the metal shell. This design enhances the insulation needed for preventing flash-over.

Note: Always ensure that the spark plug insulator and the covers/caps are clean and in good condition as worn, perished or dirty covers/caps significantly increase the chances of flash-over occurring.

 

 

Q. Is a stain between the insulator and metal shell caused by gas leakage?

A. On occasions, when a spark plug is removed, a brownish stain that looks like a sign of combustion gas flow can be seen on the insulator just above the caulked portion ofthe metal shell. This discolouration, known as Corona stain, is the result of oil particles suspended in the air adjacent to the plug becoming attached to the surface of the insulator. It does not affect spark plug performance.

 

 

 

Q. Why does Corona stain occur?

A. Spark plugs have very high voltages applied to them in order to create a spark at the electrode gap. Under certain conditions this high voltage creates a phenomenon called Corona discharge (pictured, left) which occurs over the insulator just above the metal shell. It is formed due to the ionization of the gases around the plug. The oil particles are attracted by this discharge and adhere to the insulator causing the discolouration. In low light conditions this event may be observed as a pale blue glow around the high tension leads and plugs.

Zirconia switching Lambda sensor – function and operation

There are basically three different, non-interchangeable types of Lambda sensor. The zirconium dioxide and titanium dioxide Lambda sensors are also called switching, voltage jump or ‘binary’ sensors, because their output signal varies back and forth between two values, depending on whether the fuelling is in a rich or lean state. The third type is the broadband Lambda sensor.

Method of operation of the zirconium dioxide sensor
This sensor element has a hollow, thimble shaped design. The inside surface is in contact with ambient air. The outside surface is situated such that it lies in the stream of the exhaust gas. Both surfaces are covered with a thin, porous platinum layer which acts as electrodes.

There will always be a difference in the concentration of oxygen between the exhaust gas and ambient air. When the Lambda sensor reaches operating temperature, oxygen ions start to move through the ceramic electrolyte from the side that has a greater concentration of oxygen towards the side that has a lower oxygen concentration, attempting to reach a state of equilibrium.

As these ions leave one platinum layer and reach the other layer, a potential differential results, giving rise to an electrical voltage. If the mixture is lean, the voltage will be relatively low (approx. 0.1 volts). If the mixture is rich, it will be relatively high (approx 0.9 volts). There is a large characteristic voltage jump as the stoichiometric point (Lambda = 1.0) is passed.

Testing zirconia switching Lambda sensors
Testing with an oscilloscope is the most effective method. It shows minimum and maximum voltage, the response time and the frequency. When performing the test, the manufacturer’s specifications must be observed.

Test procedure
1. Bring the engine to operating temperature at 2,000 rev/min.
2. Connect the oscilloscope to a signal line without disconnecting the sensor from the engine control unit.
3. Set the measurement range to 1-5 volts and time to 5-10 seconds (observe manufacturer’s specifications).
4. If applicable, activate automatic signal recognition. A correctly functioning sensor swings between 0.1 and 0.9 volts with a frequency of 0.5-4 Hz.

Diagnosis tips
A visual inspection often provides the initial clues for a possible malfunction. Inspection points for the workshop are:

Resistance value of the heating element
If it is above 30 ohms then the sensor is defective.

Cables
Are they broken or is the plug broken? Is the cable seal intact? Has moisture penetrated into the plug? Are the plug contacts in good condition? Is the cable routing too tight?

Sensor body
Does the sensor show any visible damage?

Make sure you use the right sensor type
Each vehicle will have a specifically designed sensor type and therefore it is essential that they are only replaced with matching specification sensors. You can use the current NGK/NTK catalogues to identify the correct replacement sensor for each application.

‘Broadband’ Lambda sensor – function and role

With the ever greater demand to reduce fuel consumption and to lower exhaust emission levels, it has become necessary to operate engines away from the stoichiometric fuelling point under certain conditions. An enriched air/fuel mixture (Lambda less than 1.0) may be required during a cold start and under full load conditions.

These modes of engine operation are subject to continuous research into new strategies to reduce fuel consumption. Some more recent engine concepts are designed to work at an air/fuel ratio much leaner than stoichiometric, at least for part of their operation. These ‘lean burn’ engine strategies must be strictly and accurately controlled.

For this purpose, ‘broadband’ oxygen sensors were developed. These sensors can accurately measure and produce an output signal which is proportional to a very wide range of air-fuel ratios. Fuelling can be maintained at any required air/fuel ratio and their operation is both extremely fast and accurate.

Broadband sensors are also used in modern diesel engines, which mostly operate with an excess air factor.

Method of operation
Broadband sensors consist of two cells: one measurement cell and one pump cell. With the help of the measurement cell, the oxygen concentration of the exhaust gas – which flows into the detection chamber – is measured and compared with that of a stoichiometric mixture.

As a stoichiometric value would generate a 450 mV output any deviation will cause the pump cell to transport oxygen ions into or, by reversing the current, out of the detection chamber in an attempt to regain the target value of 450 mV. Measurement of the value and direction of flow of this generated pump current enables precise calculation of the air/fuel ratio. At a stoichiometric air/fuel ratio there is no net current flow, as the residual oxygen concentration within the detection chamber is designed to produce 450 mV at this value.

Signal output
If a stoichiometric mixture is present (Lambda = 1.0), no current flows through the pump cell. If a rich mixture is present there is very little residual oxygen. A negative current is produced at the pump cell and oxygen is pumped into the detection chamber.

If a lean mixture is present there is more residual oxygen and a positive current is produced at the pump cell. Oxygen is pumped out of the detection chamber.

Cable assignment
NTK broadband Lambda sensors have five cable connections. The yellow and blue cables provide the heater power control. The pump signal current flows through the white cable; the measurement cell signal flows through the grey cable. The black cable provides the earth connection for both pump and measurement cells.

NOx sensors – background and function

Due to the need for reducing the delay in response time and the ever-improving accuracy of the control systems of the modern internal combustion engine, some new and very specific sensor technologies are being utilised by VMs. One critical area that has intense scrutiny is, of course, exhaust gas emissions.

Direct injection petrol engines, motorsport applications and even motorcycles place very specific demands on the technologies used for both exhaust gas measurement and its after-treatment, but it’s the DI engine that gives engineers a significant challenge in “keeping it clean” as you will learn as you read on.

Nitric oxide & nitrogen dioxide

In order to make petrol engines more economical and environmentally friendly, vehicle manufacturers are increasingly relying on direct petrol injection engines which can run at considerably leaner air/fuel mixtures under certain conditions, primarily partial load (cruise) conditions. The result of this can be an improvement of 12-20% in fuel consumption but, as with most things in life, there is a penalty to pay for this benefit.

One of the resultant gaseous compounds produced as a result of the combustion process within a spark ignition engine is what is known collectively as NOx. For the automotive industry this term is used to describe the nitric oxide and nitrogen dioxide contained within the exhaust gas. NOx compounds are environmentally damaging by-products of the combustion process and most vehicles deal effectively with this by the function of the three-way catalytic converter.

Spark ignition engines tend to produce greater quantities of these compounds when running at very lean fuelling conditions and the DI engine operates in this region when in stratified mode. The three-way catalyst cannot cope with this due to the excess oxygen contained within the exhaust gas which reforms the NOx, thus additional treatment of the exhaust gases is required.

NOx gas treatment

One counter-measure strategy is to use a NOx storage catalyst, an additional piece of hardware fitted onto the exhaust system, which temporarily stores and, at a predetermined point, chemically reduces the compounds to harmless nitrogen and oxygen. This function of “regeneration” is triggered by a change in the fuelling calibration, causing a temporary fuel rich state within the storage device.

A vital part of the control strategy for this system is the NOx sensor which is used to detect when the limit of storage capacity (saturation point) has been reached and then to instruct the fuelling management system to start the regeneration phase. The frequency of this cycle can be around once every 60 seconds and then the rich regeneration period commences for perhaps two seconds before reverting to lean mode.

The NOx sensor is an evolution of the wide band oxygen sensor and its element is constructed from special ceramics that contain two oxygen density detecting chambers that work together, allowing the determination of NOx concentration. Their function is quite complex and these sensors require dedicated ECUs which are either integrated into the vehicle’s control modules or may be contained within a unit permanently attached to the sensor harness.

It is common knowledge that most spark ignition vehicles must be fitted with a catalyst monitoring diagnostic sensor. However, this may not be the case where a NOx sensor is used.

A quick guide to ignition coils

The operating principle of the ignition coil is essentially the same for all types – whether the classic can-type coil, or in a coil rail system. The device contains two copper wire windings and a laminated iron core, with the copper wires featuring insulating materials to prevent short circuits.

The battery current fed through the primary winding produces a magnetic field whose strength is further increased by the iron core.

When this circuit is opened, the magnetic field collapses, inducing a high voltage pulse in the secondary coil. This pulse is fed through the H.T. connection to the spark plugs. As an integral part of the ignition system, the coil produces the high voltage required to produce the electric spark to ignite the fuel. The relatively low battery voltage, nominally around 12V, is then transformed to up to 45,000V.

How can 12V produce a high-voltage pulse?

The secondary coil consists of a very fine wire with many more windings than the primary coil. The winding ratio is typically between 1:150 and 1:200. This has the effect of multiplying the voltage whilst reducing the current. The voltage output from the device depends upon:

  • The value of primary circuit current
  • The ‘turns ratio’ of the windings
  • The change time of the coil
  • The rate of magnetic field collapse

The different types of ignition coil

The last few decades have seen great improvements in ignition technology. As a consequence, various new ignition coil types have been developed. Depending on the age of the vehicle, the engine design and the ignition system, any of these ignition coil designs might be used:

Can-type ignition coils
In older vehicles and vintage cars, you might still find what is commonly known as a can-type ignition coil. Some older versions of this type are filled with oil, which acts as an insulator and a coolant, but most have a more modern dry insulation design.

Distributor coils
For this type, the induced high voltage reaches the individual spark plugs via a mechanically driven distributor mechanism.

Ignition blocks
Ignition blocks contain several ignition coils, which are connected by H.T. cables to each plug. This ignition coil type is available with single or dual spark technology. In single-spark ignition blocks, each ignition cable supplies the high voltage pulse to one cylinder. In dual-spark blocks, the high voltage pulse is fed simultaneously to two cylinders: one that is on the power stroke, and the other being on the exhaust stroke and, thus, has a “wasted spark”.

Pencil or coil on plug ignition coils
This ignition coil type is mounted directly on top of the spark plug. The high voltage pulse is fed straight to the spark plug, minimising power loss. As pencil ignition coils are mounted in the spark plug tunnel, they do not take up space in the engine compartment. Pencil ignition coils are used in vehicles with electronic ignition systems and are available as single-spark or dual-spark coils.

Ignition coil pack systems
So called ‘coil packs’ combine a number of pencil ignition coils mounted within a single component, known as a ‘rail’. This rail is then placed across a bank of several spark plugs.

The crucial role of NOx sensors

Due to the need for a reduction in response time delays and the ever increased accuracy of the control systems of the modern internal combustion engine, some new and very specific sensor technologies are being utilised by VMs. One critical area that is always under intense scrutiny is, of course, exhaust gas emissions.

Direct Petrol Injection

To make petrol engines more economical and environmentally friendly, VMs are increasingly relying on Direct Petrol Injection engines that can run at considerably leaner air/fuel mixtures under certain conditions – primarily partial load (cruise) conditions.

The result of this can be an improvement of 12-20% in fuel consumption, but, as with most things in life, there is a penalty to pay for this benefit.

One of the resultant gaseous compounds produced as a result of the combustion process within a spark ignition engine is known collectively as NOx. For the automotive industry, this term is used to describe the nitric oxide and nitrogen dioxide contained within the exhaust gas.

NOx compounds are environmentally damaging by-products of the combustion process, and most vehicles deal effectively with this by the use of a three-way catalytic converter. Spark ignition engines tend to produce greater quantities of these compounds when running at very lean fuelling conditions and the DI engine operates in this region when in ‘stratified’ mode.

The three-way catalyst can’t cope with this, due to the excess oxygen contained within the exhaust gas, which reforms the NOx; therefore, additional treatment of the exhaust gases is required.

Control strategy

One counter-measure strategy is to use a NOx storage catalyst – an additional piece of hardware fitted onto the exhaust system, which temporarily stores and, at a predetermined point, chemically reduces the compounds to harmless nitrogen and oxygen. This function of “regeneration” is triggered by a change in the fuelling calibration, causing a temporary fuel rich state within the storage device.

A vital part of the control strategy for this system is the NOx sensor, which is used to detect when the limit of storage capacity (saturation point) has been reached and will then instruct the fuelling management system to start the regeneration phase.

The frequency of this cycle can be around once every 60 seconds, then the rich regeneration period commences for around two seconds, before reverting to lean mode. The NOx sensor is an evolution of the wide band oxygen sensor and its element is constructed from special ceramics that contain two oxygen density detecting chambers that work together, allowing the determination of NOx concentration.

Their function is quite complex and these sensors require dedicated ECUs, which are either integrated into the vehicle’s control modules or are contained within a unit that is permanently attached to the sensor harness. It is common knowledge that most spark ignition vehicles must be fitted with a catalyst monitoring diagnostic sensor; however, this doesn’t have to be the case where a NOx sensor is used.

Lambda sensors explored

Tim Howes, Deputy General Manager – Supply Chain & Technical Service, NGK Spark Plugs (UK), looks at the origins of vehicle Lambda sensors and the various types.

The term Lambda is used to designate the value of the ratio of the mass of air supplied to an engine divided by the theoretical ideal requirement. That sounds very grand but, essentially, it means that if the engine is supplied with a fuel rich mixture it would have a Lambda reading of less than 1.0 Lambda. Alternatively, if it was supplied with a fuel lean mixture it would produce a reading greater than 1.0 Lambda. In most cases the basic function of a Lambda sensor is to ensure that the fuelling system supplies the engine with a mixture as close to 1.0 Lambda as possible.

Why the need for a 1.0 Lambda mixture?

Most engines needs to be supplied with this 1.0 Lambda mixture because it is the ratio of fuel and air that produces the most complete combustion, thereby providing an efficient use of fuel. The resultant exhaust gases can be dealt with effectively by a three way catalytic converter. This theoretically ideal ratio is called a stoichiometric mixture and for a standard petrol engine the air/fuel ratio is 14.7:1 by mass.

Sensors achieve this control by measuring the residual oxygen content of the exhaust gas before it enters the catalyst; this is why Lambda sensors are also (and more correctly) known as exhaust gas oxygen sensors (EGO). An oxygen concentration outside certain limits will result in the sensor signalling the ECU to amend the fuelling system calibration, thus bringing the mixture back into acceptable limits.

Sensor variations

There are several different types of oxygen sensor in use but, for the majority of cars, there are two non-interchangeable sensor types, using a different strategy to detect the oxygen concentration in the exhaust gas.

Zirconia type

This is by far the most popular sensor type. Under the protective metal end cap there is a thimble shaped ceramic element made from sintered zirconium dioxide. This has two thin micro porous platinum layers added: one covering the inside and one covering the outside. These layers are the electrodes to which the signal wires are attached. On top of the outer layer a further porous ceramic layer is added (aluminium and magnesium oxide) which protects the platinum from dissociation and erosion by the hot exhaust gases. The whole package is then fitted into a metal shell, part of which is threaded to allow fitment to the exhaust system.

This element is inserted into a convenient part of the exhaust system up-stream of the catalyst. The heat energy imparted by the exhaust gases will raise the temperature of the sensor. When 300°C is reached the Zirconia ceramic has a special property in that it becomes ‘permeable’ and will allow oxygen ions to pass through it. The centre of the thimble shaped ceramic element is hollow. This is to allow a pocket of ambient air to act as a reference gas.

In theory a stoichiometric combustion gas will have no oxygen present, however, in practice, small levels of oxygen are present. In an attempt to maintain equilibrium, oxygen ions will migrate through the permeable ceramic and platinum layers. The movement of these ions causes a voltage to be generated. Put simply, the sensor behaves like a small battery with the Zirconia acting as the electrolyte. In this way the voltage output is relative to the oxygen concentration in the exhaust gas.

Lean air fuel mixtures result in relatively small amounts of ionic movement due to the oxygen rich environment of the exhaust gas, whereas rich mixtures are deficient in oxygen, resulting in larger ionic movement as the sensor tries to achieve equilibrium across the element.

Around the stoichiometric point (1.0 Lambda) there is an abrupt and dramatic change in oxygen concentration, producing a large differential between exhaust gas and the reference air. This in turn produces a relatively large change in voltage. This voltage is the signal which is sent to the fuelling control system, enabling an adjustment to bring the air/fuel ratio back into the acceptable window around 1.0 Lambda. There is a natural tendency for the fuel system to overshoot the desired window, therefore the voltage output cycles – fuel lean/fuel rich between a minimum and maximum value – nominally between 0.1 V ~ 0.9 V. This occurs with a frequency of 1~2 Hz. If a gas analysis is carried out the reading may fluctuate between 0.9 Lambda and 1.1 Lambda.

Because the sensor has to reach 300°C before it starts to function there is a period after start up which is not controlled by the Lambda sensor. To combat this it is desirable to install the sensor as near to the engine as is practical. Under certain conditions exhaust gas temperatures can drop sufficiently to impair the function of an unheated sensor. A solution to both problems is to use a heater inside the sensor which rapidly brings the ceramic up to temperature. Heated sensors (HEGO) are therefore particularly desirable when trying to reduce noxious gas emissions. Most contemporary engine control systems are designed to work with heated sensors.

Titania type

The less common Titania sensors have a similar appearance but work in a different way. They use a layered titanium dioxide ceramic element with its electrodes sandwiched in between. At a critical point around 1.0 Lambda the Titania ceramic possesses the property whereby its electrical resistance changes substantially. If a small voltage is applied (typically 5 V) by the vehicle’s control system this change in resistance can be used to adjust the fuelling, keeping the exhaust gases within the desired limits. These sensors do not need access to ambient reference air.

Titania sensors are more expensive to produce but reach operating temperature faster, reaction times are faster and they can be made physically smaller. The sensor’s ceramic element requires a high degree of protection. This is provided by the metal end cap which has specially designed holes to allow a good flow of exhaust gas whilst preventing impact damage, water splash and extremes of temperature. Total protection against leaded fuel and some other air borne compounds can’t be provided, however. These unfriendly compounds can poison the sensor, slowing or preventing its operation.

Special types

There are some systems that allow the engine to run on considerably leaner mixtures under certain conditions and these require a special type of oxygen sensor called a ‘wide band’ or ‘broad band’ sensor. These are much more complex in operation with very sophisticated control mechanisms.

In addition, most road vehicles also have a second sensor fitted after the catalyst. This functions in the same way but is used to monitor the effectiveness of the catalyst and is often referred to as the CMS (catalyst monitoring sensor) or diagnostic sensor; this usually plays little part in regulating the fuelling system but can, on some applications, detect catalyst ageing and allow calibration changes to accommodate.