Grab onto the future
Engines are changing, so the clutch and transmission system is being adapted too
Published: 03 December, 2020
Power transmission drive systems have changed over recent years. Dayco’s National Sales Manager, Steve Carolan observed: “The internal combustion engine almost always relies on a mechanically driven primary
drive system.
“Until relatively recently, these would have been either via a chain running inside the engine or a belt mounted externally. However, in 2007, Dayco designed and developed an alternative solution that combined the benefits of both a ‘wet’ chain and ‘dry’ belt, to produce the world’s first belt-in-oil (BIO) drive system.”
Advantages
Steve continued: “BIO technology has brought in a true revolution in synchronous transmission systems because developing a solution that enables a drive belt to work inside the confines of the engine has meant that the best of belt and chain technologies have been brought together.
“As a result, the previous advantages associated with a chain driven system over an external belt system in terms of the size of the engine, have been mitigated and the more evident advantages of a belt transmission have been maintained. These benefits translate into the ability to reduce the weight of the transmission system and therefore reduce its inertia, which combined with the lower friction properties of a flexible belt, delivers the twin environmental benefits of lower fuel consumption and reduced emissions.
“BIO belts are also typically not as wide as dry belts because the need to dissipate the heat that naturally builds up as a result of friction between the belt and the pulleys/tensioners, is counteracted by the fact that the oil both reduces the level of friction between these components and cools the belt. Dayco BIO applications also benefit from the company’s unique use of PTFE on the teeth of its HT belts, which further reduces friction and means that they have a greater load capacity and provide a longer service life.
“However, perhaps the most significant contribution to these savings is the fact that, unlike a chain, a timing belt, whether located on the wet or dry side of the engine, cannot stretch, which prevents the engine from undergoing phase variations due to elongation and therefore actively helps to avoid increased pollution caused by incorrect valve timing.”
Boundaries
Carmakers are being strongly encouraged through worldwide legislation to reduce exhaust emissions and increase fuel efficiency. “Looking at their mainstream power plants,” said Steve, “Ford for example, has made the decision to deploy a range of high performance, small capacity petrol and diesel engines to address the emission/consumption challenge.
“Ford’s EcoBoost family of turbocharged, direct injection petrol engines are designed to deliver levels of power and torque normally associated with larger capacity engines, while at the same time achieving 20% better fuel efficiency and 15% lower emissions. Integral to the EcoBoost design is the revolutionary BIO timing drive system developed by Dayco.”
Steve added: “These original equipment developments are naturally reflected in Dayco’s aftermarket programme, which allows factors to supply independent workshops with these solutions to enable them to offer their customers a like-for-like replacement that provides them with an alternative to the franchised dealer.”
Profit
As they change, clutch systems have a growing reputation for being complicated. “Some workshops avoid clutch work,” observed Schaeffler Marketing Communications Manager Jeff Earl, “preferring instead to send it to a ‘specialist’; however, by following a few simple precautions, every workshop can avoid turning work down and start turning a profit.
“Supplying car parts is becoming increasingly difficult, especially genuine parts from OE suppliers. Finding additional basic vehicle details – preferably directly from the car – will help the motor factor supply the correct part first time. Schaeffler’s REPXPERT online workshop portal is a perfect place to start.
“Technicians can also access REPXPERT direct from their mobile device, with extra functionality such as a barcode scanner that will take you straight to all of the technical documents for the parts you have ordered.”
Equipment
“There is not a great deal of specialised equipment required, but a few essentials will make the job easier; a two-post ramp and a working transmission jack – or two if working on larger vehicles preferably with a tilting head for a trouble-free refit.
“A universal alignment tool will also make gearbox installation easier and prevent damage to the new clutch. While it is essential to use a special tool to fit self-adjusting clutches, Schaeffler’s SAC tool has added value, as it can be used during any clutch installation to help ensure correct fitment, whilst also including special alignment tools to suit all the latest BMW applications.
“A DMF can be checked for wear prior to removal by using a LuK DMF tool in conjunction with the DMF CheckPoint function in the REPXPERT app. If the DMF does need replacing, then the app also informs the technician if new bolts are required and what torque values to use.”
The right parts
“Once the parts have arrived and the gearbox has been removed,” continued Jeff, “it’s always worth conducting some basic comparisons.
“Sliding the drive plate back and forth to distribute a small amount of grease is a good check that the splines are correct – not forgetting to wipe off any excess grease afterwards.
“On many LuK clutches ‘Getriebe Seite’ may be seen, which is German for ‘Gearbox Side’, while ‘Schwungrad’ is translated to ‘Flywheel’.
If something different is identified – or no direction is given – technicians should carefully check the installation instructions, to avoid problems caused by fitting the drive plate incorrectly.
“It is always worth checking the reluctor/sensor ring on the back of a DMF. Even if it’s from a different manufacturer it should still have the same number of teeth and they should be undamaged. OE suppliers, such as Schaeffler, will replace transit damaged goods – if it has been spotted before fitment.
“A modern plastic CSC can obviously look different, especially if the original was metal, but it should have the same number of fixings and the pipe position should be similar. It may sound simple, but technicians should always read the instruction sheet inside the CSC box. It may contain critical information, such as how to find and discard a redundant pipe seal on Vauxhall applications, and some Ford instructions explain that the O-ring should be replaced by sealant.
“Worn or seized cross shaft bushes need to be rectified; bent or damaged forks need to be replaced; technicians need to always replace the ball pivot on BMW applications and check the others; repair leaking gearbox seals and, finally, reset or replace all self-adjusting cables.”
Finishing touches
Jeff concluded: “Technicians should never grease plastic release bearings. On most pull-type clutches, technicians should fit the release bearing to the gearbox, and locate it to the clutch cover after fitting the gearbox. They need to be extremely careful when inserting the gearbox; swinging up and down on the back of a gearbox, to fit it to a poorly aligned clutch, will most probably cause damage and judder.”
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- Highs and Lows
When faced with diagnosing a fault, in order for us to be able to test the system it is crucial we understand the system’s layout, components and function. We recently faced a fault in a system we had little experience on, so it was an ideal opportunity for a bit of studying.
Technical information is readily available from many sources, be it manufacturer or generic information, and does not take too long to find. While Google isn’t really a substitute for diagnostics, in situations like this it can be very useful for generic information. The fault on this vehicle turned out to be something so trivial I won’t bore you with it. What I would like to share is the valuable information I picked up along the way.
Main purpose
Exhaust gas recirculation (EGR) is nothing new, it’s been used on petrol and diesel engines for many years and while layout and control has varied in design the principle has remained the same. It is important to understand that manufacturers use different methods and configureuration, and for this article I’ve studied several and have tried to demonstrate a generic system.
The main purpose of EGR is to reduce the level of harmful Nitrogen Oxide (NOx) gases emitted from the vehicle’s exhaust. NOx is present in exhaust emissions due to high combustion temperatures and pressures. Under light load/cruising conditions the EGR system directs a proportion of the exhaust gas back into the engine’s air intake. This reduces the oxygen levels which in turn reduces combustion temperature resulting in a lower NOx emission. When power is required from the engine the EGR system closes to insure a more efficient combustion (see figure 1).
EGR on/off
This is the conventional system in its closed (off) position. During operation exhaust gases are taken from the exhaust manifold (pre-turbo), passed through a cooler (10) up to the EGR Valve (6). The cooler is a heat exchanger that not only uses the engine coolant to cool the gases to increase the mass but utilises the heat to warm up the coolant faster which helps the interior heater warm-up faster. The EGR Valve (6) can be either electrical of vacuum operated. The powertrain control module (PCM) commands the EGR valve to open by a specified amount dependent on engine conditions (see figure 2).
Some EGR valves have a position sensor that provides feedback to the PCM to ensure the correct position has been achieved. In a system where the EGR valve is not equipped with a position sensor, the PCM monitors the Mass Airflow signal in order to regulate EGR flow. This is achievable due to the fact that as the EGR valve is commanded open and gases start to flow, the air flowing in to the Mass Airflow Sensor will decrease. The calculation is made using tables of data (mapping) within the PCM’s software. Understanding this is crucial when diagnosing running faults as a fault in the Mass Airflow can easily affect the EGR system and vice versa.
Understanding and diagnosing airflow and EGR faults I find can be easier if you look at it pressure differential. If air is flowing through a tube with a restriction in it, the air pressure after the restriction will always be lower than the pressure before the restriction. The difference in pressure will vary depending on the mass or pressure of the air and the size of the restriction.
Air intake/throttle flap
The air intake/throttle flap (see figure 3) generally defaults to the fully open position while the EGR valve defaults to the closed position. The purpose of the flap is to reduce the pressure on the engine side. As the intake flap starts to restrict the airflow, the pressure decreases to a pressure lower than that of the EGR pressure and the EGR gases start to flow into the engine’s air intake. If the exhaust gas pressure was slightly lower than the air pressure entering the engine then the gases would flow in the wrong direction.
When in good working order this system serves its purpose. However, due to the fact that there is particulate matter in the exhaust gases, the system and components will slowly become blocked, causing reduced flow and valves starting to jam or not seal correctly. The air intake system often contains oil residue from the engines breathing system and slight oil loss from the turbo itself. When this oil is mixed with the particulates in the EGR gases it makes a very sticky gunk that starts to block the inlet manifold and intake ports.
When the engine is under load and turbo boost pressure is required, the EGR valve needs to close and seal. If an EGR valve isn’t sealing correctly when closed then boost pressure will be lost into the exhaust system. The lower boost pressure and reduced oxygen level affects the combustion which in turn causes more particulate matter which only adds to the issue. If the EGR valve is stuck wide open then in most cases the engine will barely run.
High pressure system
Euro 6 was introduced in September 2014 which demanded much tighter emissions than previous which required an advance in emission control technology. While the precise control of the fuel side of the engine management system has gained precision with higher fuel pressure and multiple injections within the cycle, the air intake, exhaust and emission control systems have too. Most manufactures use a high and a low pressure EGR system. Prior to this most EGR systems were relatively simple and fell under the ‘High Pressure EGR’ title (see figure 4 and figure 5).
The high pressure system is similar in layout to previous systems but serves a slightly different purpose. The system is only used during the warm-up phase of the engine from cold start. There is a pre-turbo passage from the manifold directly to the high pressure EGR valve (6). As the system is only used in the warm-up phase there is no need for a cooler. In this particular system there is a distribution channel that directs the gases equally into each inlet port. The purpose of this system is to raise the intake air temperature in order to improve combustion and reduce the warm-up time for the catalytic convertor/NOx storage catalyst (7) allowing them to function sooner. Once at operating temperature the system is pretty much redundant.
Low pressure system
The low pressure system (is active under most engine operating conditions and its purpose replaces that of the older systems- to reduce NOx gases (see figure 6). A proportion of the exhaust gas is collected after the Diesel Particulate Filter (8) and passes through a Wire Mesh Filter (9), through the EGR Cooler (10), up to the Low Pressure EGR Valve (11). The EGR valve then controls the flow through a channel up to the intake side of the turbocharger. The wire mesh filter ensures there is no particulate matter entering the system and also in the event of the particulate filter substrate breaking up, it also protects the rest of the system including the turbocharger, air intake and engine internals from damage. The cooler reduces the gas temperature which in turn increases the mass allowing a higher volume of exhaust gas to be recirculated. Due to the exhaust pressure after the particulate filter being quite low and also the air intake pressure before the turbo charger also being low there is and Exhaust Flap (12) fitted. By closing this slightly the exhaust pressure increases which causes the gases to flow back towards the turbocharger.
Key benefits
These systems usually have between three and four exhaust gas temperature sensors each placed at key points of the exhaust system and two pressure differential sensors. The first is measuring pressure before and after the particulate filter (to calculate soot loading) and second between the DPF outlet and the point after the EGR valve, before the turbo. Coupling these six signals with the Mass Airflow sensor, the positions of both EGR valves and the intake flap, the turbo variable-vane position and the intake pressure (MAP), using the mapping within the PCM’s software means it can also make all calculations necessary. This provides an extremely high intake pressure and exhaust after treatment control.
The key benefits of this system are that the exhaust gases are free of any particulate matter which keeps the entire system much cleaner and therefore reliable. The gases are also cooler meaning a greater mass can be used in a more effective way. Finally the gases re-enter the system before the turbocharger, allowing for the increase in boost pressures at lower engine load and RPM.
Does this make diagnosis harder than before? Not if you take the time to study the purpose of each component and how it works. I’ll openly admit it wasn’t that long ago that I would have taken one look at this system and sent it on its way! Nobody likes being beaten by a job but neither should we have to waste too many hours trying to guess what’s wrong with it, worse still start throwing parts at it. It took me half an hour to locate this info, an hour studying it and a further hour planning what tests I was going to conduct and what results I was expecting to see. What was wrong with it in the end? A faulty sensor confirmed with no more than a voltmeter! After replacing the sensor I wanted to confirm the repair and monitor the function of the components using serial data. Something I highly recommend doing is picking five lines of serial data on every car you work on that requires an extended road test and monitoring them to see how they behave and what effect driving style (engine load) has on them. I guarantee after 10 cars you’ll know what to expect and be far more confident in diagnosing related faults. It works for me!
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