Good vibrations

Frank explains the science behind the way-out sounds made by today’s cars that can be the cause of much head-scratching in the workshop

By Frank Massey | Published:  31 December, 2018

In a previous topic I expanded on the availability of focused test tools for independents. It’s not often that we see a technical breakthrough which has real application potential, but there was a breakthrough recently when Pico introduced a new NVH kit. It has come just in time, as noise, vibration and harshness is a challenge that’s not getting any easier, so what is it?

You must first start by accepting that the motor vehicle is a series of mechanical systems in permanent conflict. There are components travelling in different directions, subject to acceleration, deceleration, changing direction, and of considerable mass differential.

What I have just described there is the internal combustion engine. adding chassis and body systems to the mix. I think you will agree the problem we have is in identifying noise and vibration.

 The difference between noise and vibration is based on frequency and amplitude. Noise is a single event with a diminishing synodal pattern. It looks like a trumpet. Vibration however has a repetitive frequency and amplitude. Both of which will change with speed and a whole host of influences, resonance, beating, and mass differential are just some.  

So why has it become more difficult for us techs to bend our ear and diagnose an issue with confidence? The answer is due to the technical innovations of today’s vehicles. These include the dual mass flywheel, active engine mounts, cylinder cancellation, Audi anc system, infinite computer control of chassis dynamics, and the most obvious of all-  lack of accessibility.

Let’s begin with the basics. As we have seen, Vibration is classified by frequency and amplitude. A large mass will by nature have a lower frequency and a greater mass, while  a small mass will present the exact opposite. Two or more mass that converge with the same frequency combine their mass value increasing the amplitude. This is called resonance. Mass that have a similar but close frequency differential, within say 10hz, cause beating; “wo, wo, wo, wo.” An example of this would be a worn wheel bearing.
Vibration has three elements: Cause, transfer path, and respondent. In almost all cases we experience the respondent. Let’s think about the vibrating ash tray, wedged with paper to stop the noise! Vibration also falls into three other simple categories, vibration we feel, vibration we see, and vibration we hear. We humans can only hear noise between 25hz/22,000hz.

The next consideration is how many events per rotation frequency is experienced these are called, first, second, third, orders etc.
Now let’s do some simple maths. It’s getting interesting now isn’t it? We must convert everything into frequency, the unit is hertz, or cycles per second. For simplicity, a four-cylinder engine revolving at 3000rpm, in top gear 1:1, differential ratio 4:1.
3000/60=50hz divided by final drive ratio 4:1=12.5hz.

Therefore crankshaft vibration will be @50hz and tyres, rim, brake disc, and drive shafts will be at 12.5hz. So, you will now appreciate is a simple matter of separating the various operating frequencies.

Well not quite, but by now I’m hoping you view vibration in a more clinical way and not just based on experience or opinion. Vibration can have different direction or vectors, something tyre fitters more often or not get wrong.

Bring on the technology. The kit which can have an infinite flexibility of accessory options, uses a three-dimensional accelerometer, for vector differential, measuring mass, and a microphone recording sound, together with 1+3 channel interfaces, and bnc connection leads. The engine speed data is collected via the serial port with a drew tech mongoose serial interface. This can also be achieved optically if preferred. The accelerometer has a magnetic base and is directional sensitive, fore/aft, vertical, and lateral. Its initial position should be on the driver’s seat frame. After all that’s where the complaints start! The microphone could be positioned close to a known noise source or in the cabin.

Navigating through the software wizard is straightforward, you will need to select number of cylinders and configuration, in line, opposed, v config, and direction of mounting. You will then need to establish the various gear and final drive ratios, with tyre size data.

The software will then gather data over an infinite timeframe and scaling which is of course adjustable. The most challenging aspect in my opinion is control of the style of driving technique, speed, gearing, direction, braking and the influence of the road surface. The vehicle may have selectable drivetrain and suspension options, which will affect the potential effects of noise and vibration.

Did you remember not to omit the obvious or obscure effects? Has the vehicle been modified in any way whatsoever? Wheel size, spring rates, power output, etc, etc. Record your driving technique and environmental influences into the microphone. After all it is recording sound, all sound!

There are several options in the display menu, from bar chart, frequency, and 3D. you will quickly establish exactly which one of three vehicle systems the problem originates based on visual evidence. Engine, transmission or tyres.
You can then reposition the sensors to further locate the position of the source. Vibration will increase in amplitude, as will noise the closer you are to the source. This is due to the reduction in the length of the transfer path, and any devices that may absorb it.  
I can confidently monitor discrete combustion anomalies based on the transfer of mass energy from the pistons to crankshaft orders, simplifying connectivity issues with coil on plug multi-cylinder engines. I could show you images from a test I conducted recently, but a simple static image does not fully demonstrate the effects of vibration.



Related Articles

  • Part two The good and THE GREAT  

    In part one, we looked at the start of the ‘diagnostic process.’ The first steps were customer questioning, confirming the fault and knowing the system and its function. These help the technician to build the ‘big picture’ necessary to repair the vehicle correctly.
    In this article we will look at the next four steps.

    Step 4: Gather evidence
    It is easy to overlook this step as many technicians think of it as the overall ‘diagnosis.’ However, once the technician understands the system, gathering evidence will provide key information. This step is normally best carried out with the use of test equipment that does not mean the dismantling of systems and components.

    Many technicians have their own favourite tools and equipment but this list can include (but not limited to)
    the following:
    Scan tool – It is always best practice to record the fault codes present, erase the codes, and then recheck. This means codes which reappear are still current. Remember that a fault code will only indicate a fault with a circuit or its function. It is not always the component listed in the fault code that is at fault

    Oscilloscope – An oscilloscope can be used for a multitude of testing/initial measuring without being intrusive. Some oscilloscope equipment suppliers are looking at systems within high voltages hybrid/electric vehicle technology. The waveforms produced by the test equipment can be used when analysing the evidence and may indicate that a fault exists within a system. An understanding of the system being tested will be necessary to understand the information. This may even include performing sums so all those missed maths lessons at school may come back to haunt you. It may take time to become confident analysing the waveforms, so be patient

    Temperature measuring equipment – This can include the use of thermal imaging cameras. Most systems that produce energy/work will also produce some heat. The temperatures produced vary from system to system. Examples include everything from engine misfires to electrical components, as well as air conditioning system components and mechanical components such as brake and hub assemblies. The possibilities are endless and results can be thought provoking.

    Emission equipment – By measuring the end result, an exhaust gas analyser can show you if the engine is functioning correctly. The incorrect emissions emitted from the exhaust help indicate a system fault or a mechanical fault with the engine

    Technical service bulletins – Many vehicle manufacturers produce technical service bulletins (TSBs) that are generated by a central point (usually a technical department) from the information that is gathered from their network of dealers. Some of these may be available to the independent sector either through the VM or through a third party – It’s always worth checking if these exist. They may indicate a common fault that has been reported similar to that the technician is facing. Some test equipment suppliers may provide TSBs as part of a diagnostic tool package

    Software updates – Many vehicle systems are controlled by a ECU. Most vehicle manufacturers are constantly updating system software to overcome various faults/  customer concerns. Simply by updating the software can fix the vehicles problem without any other intervention of repairing a possible fault. This is where having a link to a vehicle manufacturer is vital in repairing the vehicle

    Hints & tips – Most technicians will have a link or access to a vehicle repair forum where they can ask various questions on vehicle faults and may get some indication of which system components are likely to cause a vehicle fault

    Functional checks – Vehicle systems are interlinked and typically share information using a vehicle network. The fault may cause another system to function incorrectly, so it is vitally important that the technician carries out a functional check to see if the reported fault has an effect on another system. By carrying out this check the technician again is building the big picture

    Actuator checks – Most systems today are capable of performing actuator tests. The technician can perform various checks to components to check its operation and if the system ECU can control the component, often reducing the time to the diagnosis, by performing this task the technician can identify whether it is the control signal, wiring or component or it is sensor wiring. This function can be used in conjunction with serial data to see how the system reacts as the component functions

    Serial (live) data – The technician can typically review a vehicle system serial data through a scan tool. Having live data readings to refer to can help you review the data captured. Using actuator checks and viewing the serial data can also help the technician to identify a system fault

    Remember to record all the evidence gathered so it can be analysed during the next step in the diagnosis. We can’t remember everything. If the technician needs to contact a technical helpline they will ask for the actual readings obtained recoding the data gathered will help.

    Step 5: Analyse the evidence
    Analysing evidence gathered during the previous steps can take time. The technician needs to build the big picture from all the evidence gathered during the first few steps. You need to analyse the information gathered, and decide on what information is right and wrong.

    This step may rely on experience as well as knowledge on the product. You should take your time – don’t be hurried. Time spent in the thinking stages of the diagnosis can save time later. Putting pressure on the technician can lead to errors being made. It may be necessary to ask the opinion of other technicians. If the evidence is documented it may be easier to analyse or share between others.

    Step 6: Plan the test routine
    After analysing the evidence gathered it’s now time to start to ‘plan’ the best way to approach to the task or tasks in hand.

    The technician should plan their test routine, decide on what test equipment should they use, what results are they expecting, if the result is good or bad  and which component should they test next.

    Document the plan – this enables you to review decisions made at this stage in the next step. The technician may not always get it right as there may be various routes to test systems/components. The test routine may have to be revisited depending on the results gathered during testing. Documenting the test routine will provide a map.  Also, don’t forget to list the stages, as this is something that could be incorporated into an invoicing structure later.

    The technician should indicate on the routine what readings they expect when they carry out the system testing. This can be generated by their own knowledge/skill or the expected readings may come from vehicle information which they have already sourced. If the information is not known at the time the test routine is planned, then the test routine may highlight what information is required and what test equipment is needed. You shouldn’t be afraid to revisit the plan at any time and ask further questions on which direction the tests should take. If the plan is well documented and the technician becomes stuck at any point, they can pause the process and revisit later. Also the information can then be shared with various helplines that support workshop networks.

    Step 7: System testing
    The technician then follows their pre-determined plan, if it is documented they can record the results of the test(s) as they follow the routine.

    Many technicians tend to go a little off-piste when they get frustrated. Having the routine documented can keep the technician on track and focused on the result. If the routine is followed and the fault cannot be found the technician may have to go back to the analysing the evidence or planning the test routine. The technician shouldn’t be scared of going back a few steps, as I said previously analysing the evidence takes practice and can be time consuming, not to be rushed.
        
    Summing up
    Remember to follow the process. It is easy to be led off track by various distractions but don’t try to short circuit the process. Some steps may take longer than first thought to accomplish than others. Some distractions may be outside of your control, and it may be necessary to educate others. Practice, practice, practice. Refine the process to fit in with your business and its practices, the business could align its estimating/cost modelling to the process, being able to charge effectively and keeping the customer informed at each stage of the process.

    Coming up...
    In the next article I will be looking at the next four steps which are; Step 8: Conclusion (the root cause), Step 9: Rectify the fault and Step 10: Recheck the system(s). The last article in this series will indicate the final three steps and how to fit them all together in order to become a great technician and perhaps succeed in Top Technician or Top Garage in 2018.



  • Blast it! How to disinfect air con systems  

    With cars having been using their air con in full during the warmer months, Helen Robinson, Marketing Director at Euro Car Parts, wants to remind garages that cleaning air conditioning systems remains a good opportunity into the autumn and beyond.
      
    “We’ve all done it – you turn on the air con after not using it for a few months, only to be greeted by a terrible smell. The reason behind this, however, is quite simple. Stagnant water droplets trapped in your dormant system are blasted out, leaving behind a foul odour and some nasty bacteria. While this is a common driver complaint, not every garage is taking the opportunity to upsell and provide a thorough cleaning and disinfection service. Fortunately, you can take three essential steps using products from Normfest that have been specifically designed and formulated to help these troubled drivers.
        
    “The first step is to ‘bomb’ the system with Viro Dry Shot Plus, a powerful anti-bacterial cleaning agent. Using the product is simple – spray it directly into the air intake nozzles that are usually located in the passenger footwell. The spray then disperses throughout the air conditioning system for a thorough, quick and hygienic clean. Viro One Shot Plus eliminates microorganisms, prevents allergic reactions and leaves a lasting pleasant smell. A single can is enough for one application.  
        
    “In the second step, Viro Air Fresh Plus is sprayed directly into the air vents and gets to work on the air conditioner’s piping. Over time, a layer of dirt collects in the ventilation ducts and becomes a perfect breeding ground for bacteria and mould. Viro Air Fresh Plus eliminates these odour-causing particles with direct application, enabled by the included tube nozzle. It provides a long-lasting disinfection and leaves a pleasant citrus fragrance. One can contains enough spray for three applications.
        
    “For the third and final step don’t forget the evaporator. For a complete clean, it is recommended that garages also use Viro Vaporizer to disinfect the air conditioner’s evaporator. A layer of dirt can accumulate on the evaporator fins over time, which provides ideal conditions for microorganisms to reproduce. The product cleans with high-pressure flushing, acting across the evaporator’s entire surface. It quickly kills bacteria and fungi and prevents their resettlement. The product is supplied with a 60-centimetre long tube with a rotary nozzle, helping the user to reach all corners of the evaporator. Viro Vaporizer contains enough spray for one air conditioning system. This final step completes the process, providing comprehensive protection against bacteria and bad odours.”
        
    In conclusion, Helen added: “Disinfecting a vehicle’s air conditioning is not just about removing bad smells. It is important to periodically remove the build-up of bacteria, dirt and dust within the system to avoid discomfort, allergies and health complications. This simple three-step process could be combined with a re-gas and a new cabin filter for a complete system rejuvenation. It presents a great opportunity for garages to upsell and provides a service that directly benefits customers – solving a common driver complaint.”  


  • New ADAS seminar from Snap-on 

    Snap-on is offering a new seminar about ADAS. The event is accredited by the Institute of the Motor Industry (IMI) and gives attendees an overview of ADAS and how the various systems must now be considered part of their everyday work.

  • Keep cool as air con heats up 

    As we move towards through summer, motorists are dropping the dial across the spectrum on their climate control systems.
        
    According to Adam White, Workshop Solutions Director at Euro Car Parts, repairers can make the most of the opportunity if they are properly equipped: “The key to profitability is offering the right services and performing them efficiently, in terms of both time and cost. By those measures, air conditioning is one of the most profitable service areas a workshop can be involved in – given the right expertise and equipment. Unfortunately, air con work is sometimes overlooked by garages who fail to see the potential profits it could bring to their business. With summer here, there are lucrative opportunities for those who are prepared.
      
    “Air con is a key growth area for UK garages. A lot of customers that visit a workshop have some form of issue with their air con system and the average job takes just five minutes. It’s easy to see why air conditioning remains one of the most profitable services that workshops can offer. If you want to make the most of the summer rush, now is the perfect time of year to invest in quality equipment.”
        
    As many workshops will know, automotive air conditioning systems use one of two specific gas types; either R134A or 1234YF. Adam observed: “Perhaps the most important decision for a workshop is whether to use a dual gas or double single gas setup. This will likely be dictated by the size of the business or the amount of air con servicing undertaken. The primary advantage of a dual gas machine is that you only require one unit to cater for both R134A and 1234YF, meaning less occupied space and reduce costs. The alternative is two separate machines, one for each gas. Having two machines is more expensive but it allows you to service two vehicles at once and offers greater opportunity for revenue-generation.
      
    “Workshops should ideally have the capability to cover both 1234yf and R134a systems. We aim to support the independent aftermarket in any way we can. Our latest Workshop Solutions brochure outlines the profitability of air con servicing and is well worth a read. New machines only require a hands-on time of around five minutes, with the total air-con service time taking between 45 minutes to an hour. This effectively gives you an additional pair of hands in the workshop – an hour of labour that can be used and charged elsewhere.”
        
    Adam continued: “Autoclimate’s products cover most of the UK market and it offers a support service that can fix 72% of the issues workshops encounter over the phone, minimising downtime. For the remaining problems, the company has 18 dedicated air con repair specialists committed to performing on-site repairs within three working days. For peace-of-mind, all its air con machines are eligible for a five-year warranty package with included annual servicing.”
        
    Adam concluded: “Whether you are considering investing in your workshop’s first air con machine or a seasoned veteran looking to upgrade, make sure that you evaluate the market to find one that best suits your requirements. The Workshop Solutions brochure is a great source of information and advice on how to maximise workshop profitability. The latest issue provides interesting insights into air-conditioning, including comparisons of popular models and useful finance examples.”

  • Illegal Refrigerants: Why risk it?  

    Honeywell is urging garages to make sure they don’t source illegal refrigerants when dealing with air con systems this summer.
        
    “Air conditioning is by far the most popular at-cost optional extra for UK car owners and drivers, “said Lee Hermitage, Marketing Director, Honeywell Fluorine Products Europe, Middle East and Africa. “It is not only a comfort perk – it is more often considered a safety feature, too. And rightfully so, since air conditioning can prevent drowsiness and help keep drivers alert. That all is good news for UK garages, because the more air conditioning units are in cars on British roads, the more maintenance they will require.For air conditioning to work, the system has to use a refrigerant and these refrigerants are subject to some pretty tough environmental requirements policed by the Environment Agency to limit emissions from air conditioning units in cars.”
        
    Since January 2017, all new vehicles must be equipped with a low global-warming-potential refrigerant. In most cases this is R-1234yf. However, older vehicles are still equipped with R-134a.
        
    Lee continued: “The first step when servicing car’s air conditioning system, is therefore to understand which refrigerant it contains, since it is illegal to service R-1234yf systems with R-134a.”
        
    It is also essential to check if the product has been legitimately placed on the market: “Counterfeiting or smuggling are not words usually used when talking about refrigeration,” said Lee. “However, they became a reality of the industry lately. In the European Union, illegal products are estimated to make up 20% of the refrigeration market and create 20 million MT of CO2 a year – equivalent to the emissions of four million cars. According to the Environmental Investigation Agency’s study, 72% of users have been offered refrigerant in non-returnable containers, a clear sign of the refrigerant being illegal.
        
    “With illegal products, users do not know what refrigerant really is in the container. Such unknown mixtures can represent a health hazard for technicians working with these refrigerants. An illegal product can also impact the performance of the air-conditioning system, ranging from increasing the fuel consumption to damaging the air-conditioning compressor.
        
    There are consequences: “Being found to be in possession of these illegal products may mean fines are imposed and it may result in custodial sentences. While there is a lot of risk associated with illegal refrigerants, there are steps a business can take to make sure they never use these products.”

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