Micro Hybrid & Hybrid Vehicles Explained

Background

As a result of current increasing global warming issues, the environmental pressures on vehicle manufacturers to reduce their vehicle exhaust Carbon Dioxide (CO₂) emissions and improve fuel economy has now been reinforced with EU Legislation. This new EU legislation on emissions targets passed in 2009 commits vehicle manufacturers to cut the average CO₂ emissions from new vehicles to 130g/km by 2015 and 95g/km by 2020.

Various methods are being used to influence the vehicle manufacturers to reduce CO₂ emissions from their vehicles which include:

• Increased costs of vehicle duty
• Increased fuel taxation
• Increased frequency of inner city road toll charges

Other costs to be introduced on high emission vehicles include a government “Showroom tax” on new vehicles which is proposed to be increased over forthcoming years based on fleet average emissions of vehicles made by a particular manufacturer.

Legislation discussions have stated figures of up to 250€/gram of CO₂/km may be charged based on the manufacturer’s average fleet emissions which exceed the legislative level for the time period between emissions reduction targets This charge will be applied to every vehicle sold by that manufacturer.

Based on figures published by the Department of Energy and Climate Change DECC (2012), in 2009 motor vehicles contributed 69.7 million tons of CO₂ to the UK atmosphere which is 13.8% of the total published CO₂ emissions in the UK. The UK average new car CO₂ emissions in 2004 was 171.4 grams of CO₂/km compared to the 2011 reduction target of 138.1grams of CO₂/km which equates to a 19% reduction.

Eco–Initiatives

To meet the growing environmental challenges posed by the introduction of emissions legislation, vehicle manufacturers have developed various eco-solutions to help drivers save fuel and reduce vehicle CO₂ emissions. Some initiatives are related to changes in the battery technology and requirements and some are not, for example:

• Tyre Pressure Monitoring System (TPMS)
  • Indicated to the driver via dashboard warning lamp that tyre pressure(s) are low resulting in reduced fuel economy

• Low rolling resistance tyres
  • Fitted to increase vehicle fuel economy by minimising the loss of the energy caused by the repeated cycles of deformation and recovery of the tyre which is dissipated from the tyre in the form of heat

• Gear Shift Indicator
  • Indicates to the driver the optimum time to change gear in order to maximise fuel economy
  • New radical technologies being introduced include electronic camshafts or electronic valve timing systems which allow the engine tune to be optimised to driving style, improving fuel efficiency and reducing emissions

• Increased volume of Full Hybrid and Electric Vehicles into vehicle manufacturers ranges in order to meet increased market demand for improved fuel economy and emissions reduction

Looking at the effect on volume vehicle sales, the following initiatives require changes in battery technology to support their implementation:

Stop/Start Technologies & Functionality (Micro hybrid 1)

• Initially a manual system now becoming fully automatic, switches off the engine when the vehicle is stationary. The engine is restarted automatically by releasing the brake and depressing the accelerator pedal or clutch pedal dependent on transmission type. Initial Stop/Start systems could be manually switched off, but on next generation vehicles this option is disabled
• Increases the number engine starts the battery has to deliver as well as supporting all of the electrical loads on the vehicle whilst the engine is stopped and the vehicle charging system is not operating
• Requires new electronic methods of monitoring the battery status including State of Charge (SOC) and State of Health (SOH). As the number of Stop/Start cycles required are increased, the vehicle must be able to determine if the engine can restart when the vehicle comes to rest and the engine is switched off
• Initial Stop/Start systems would function if the ambient temperature was below 3^°C whereas the latest systems are projected to operate at -10°C. This reduction in system operating temperature increases the demand on the battery to supply minimum voltages to the electronic circuits and control modules on the vehicle when cranking the engine
• Various vehicle manufacturers state that, on their standard European drive cycles a typical fuel saving of up to 8% can be achieved by the installation of a Stop/Start system. This in current terms of electronics technology means a relatively low cost solution to reduce exhaust emissions
• New technologies such as the Enhanced Flooded Battery (EFB) and AGM (Absorbed Glass Mat) battery have been developed to achieve the new higher duty cycle requirements placed on the battery by particular OEM vehicle manufacturers

The introduction of Stop/Start technology has resulted in a new band of battery failure modes not previously experienced by vehicle manufacturers. This is based on evidence collected from a recent time dependent driving experiment. The experiment featured a journey across London which produced 87 Stop/Start cycles which when compared with a comparable timed motorway journey produced zero Stop/Start events as the feature was not activated

Charge Management & Regenerative Braking (Micro hybrid 2)

Charge Management

• It is likely that vehicle owners would not be aware of the installation of this technology as its operation is seamless, unlike Stop/Start which is clearly detectable as the engine stops if all system operating conditions are fulfilled when the vehicle comes to rest
• When the alternator is running it can typically consume up to 10% of the power produced by the engine. The charge management system effectively switches off the charging system by disconnecting the alternators drive from the engine. This increases the loads placed on the battery but significantly improves the fuel economy of the vehicle
  • The major fuel economy benefits of a charge management system are achieved on longer distance journeys. The use of this system shows that one technology alone is not the solution to every drive cycle but is important as part of an overall package of emission reduction and economy initiatives
  • The life expectations of the battery are greatly increased as it is supporting all of the electrical loads on the vehicle when the charge management system is operating
  • The introduction of charge management systems has resulted in the development of new battery technologies and designs with increased performance. These include EFB and AGM battery types which have a significantly better cyclic life and improved operation in low states of charge

Regenerative Braking

• Regenerative Braking systems recover the energy normally converted into and lost as heat during vehicle braking. When available the recovered energy is fed back into the charging system to recharge the battery
• A conventional technology battery is very inefficient when utilized in in a regenerative braking system. This type of battery is only able to reuse approximately 5 to 15% of the recovered energy due to its relatively high internal resistance. New battery technology developments such as EFB and AGM with reduced internal resistances provide more efficient use of the recovered energy.

Starter/Generator (Micro hybrid 3)

• Starter/generator technology replaces the conventional alternator and starter motor with a combined starter/generator unit installed between the engine and the transmission. The vehicle features both Stop/Start and regenerative braking systems that operate in the same way as for Micro hybrid 1 and 2 vehicles but utilises the starter generator for both start/stop and regenerative braking functions.
• An AGM battery is therefore installed on the vehicle to support the stop/start and regenerative braking systems

Passive Boost (Mild hybrid)

• Future new technologies being introduced to the next generation of vehicles include a solution known as “Passive boost” .Passive Boost is a simpler more cost effective system related to the Kinetic Energy Recovery System (KERS) recently introduced into the Formula 1 race series
• Passive boost technology replaces the conventional alternator and starter motor with a combined starter/generator unit installed between the engine and the transmission. The passive boost function reverses the generator polarity to convert the generator into a motor and utilise a high voltage battery to assist with the acceleration of the vehicle. The starter generator is only used to supplement the power produced by the internal combustion engine therefore the vehicle is not capable of full electric drive
• An AGM battery is therefore only installed on the vehicle to support the electrically operated ancillary components only

Full hybrid

• The full hybrid vehicle features a higher power starter generator and an additional clutch between the internal combustion engine and transmission. This allows the decoupling of the engine and starter generator.
• The internal combustion engine features both stop start and regenerative braking functions, however this system only utilises the internal combustion engine when required which allows the vehicle to be driven on electric power only
• An AGM battery is therefore only installed on the vehicle to support the electrically operated ancillary components only

These new requirements clearly expect significantly more from the battery and the technology has to be improved to match the further increase in demands.

Review of Requirements

It is clear from the developments in vehicle technology that the battery is becoming a critical component in ensuring that the new ECO initiatives will deliver the increases in fuel economy and reductions in CO₂ emissions required by legislation.

It is impossible to expect the current day conventional flooded Lead Acid battery to meet the requirements of Stop/Start and Micro hybrid 2 and 3 vehicles. New battery technologies have therefore been developed over recent years to meet the increasing demands of the vehicles now entering the aftermarket. It is therefore essential to replace the OEM specified battery with that of the same or increased technology and specification in the aftermarket.

The installation of a conventional flooded Lead Acid battery to a Stop/Start only vehicle will result in a significantly reduced battery life and increase the likelihood that the battery will go flat in service. The battery will also be unable to recover sufficiently during its residual drive cycles.

The installation of a conventional flooded Lead Acid battery to a vehicle fitted with a charge management and regenerative braking system will also lead to a significant reduction in expected battery life and an even greater likelihood of the battery repeatedly going flat in service. The charge acceptance of the battery is therefore even more critical in order to ensure that the battery can efficiently accept the available current produced by the alternator and the regenerative braking system.

Battery Technologies

The constant requirement for more efficient, cleaner and technologically advanced vehicles means that the introduction and development of vehicles featuring these systems will have increased to approximately 70-80% of all vehicles produced in Europe by 2015. This equates to over 30 million vehicles within the EU alone. The enforcement of EU emission reduction legislation will affect vehicle manufacturers sales against competitors who have invested and gained the fuel and emission savings.

For high volume production vehicles beginning in 2008/09, two advanced development modifications of the conventional flooded Lead Acid battery are currently being installed. The first generation of these vehicles is now starting to enter the aftermarket. These are:

• AGM technology installed on high performance vehicles featuring advanced Stop/Start and charge management/regenerative braking systems
• EFB technology installed on entry level Start/Stop vehicles, usually where fuel economy and CO₂ reduction requirements are reduced. EFB provides a more cost effective solution over AGM as the design is based a conventional flooded Lead Acid battery but with improved specification and performance.

YBX9000 AGM (Absorbed Glass Mat) Battery

The AGM battery has been designed to fulfill the very special requirements of modern day vehicles which feature high levels of electrical equipment and emission target driven Carbon Dioxide (CO₂) reduction control systems such as:

• Micro hybrid 1 Idle Stop/Start (ISS)
• Micro hybrid 2 Charge Management (Alternator control) and Regenerative Braking
• Micro hybrid 3 Passive boost (Battery powered starter/generator boosted engine allowing engine downsizing with no reduction in performance)

The AGM battery shares a number of design features with the conventional flooded Lead Acid battery but with additional technologies from Industrial and Motorcycle batteries, such as:

• Fully sealed and leak proof
• VRLA (Valve Regulated Lead Acid) “recombinant” technology
• Calcium calcium plates

The AGM battery has unique features that differentiate it from traditional conventional flooded Lead Acid batteries and dramatically increase its all-round performance in an automotive application. These include:

• AGM separators between positive and negative plates retain the electrolyte solution in the ideal position for the discharge and recharge chemical reaction to take place
• Battery cells are electrolyte starved with no free reservoir of acid above the level of the plate pack
• Anti-spill with no possibility of electrolyte leakage even if the battery case is damaged
• Extremely low self-discharge rates when compared to conventional flooded Lead Acid battery type
• High levels of vibration resistance and durability due to the high pack pressures in each cell of the battery
• Increased plate numbers per cell, larger plates, increased operating pressures and higher levels of purer Lead in each plate when compared to conventional flooded Lead Acid batteries give a low internal resistance and greatly reduced battery discharge and recharge times
• The ability to operate the battery at high pack pressures which significantly improves its cyclic durability. (High pack pressures in a conventional flooded Lead Acid battery lead to the electrolyte being forced out from between the plates and the battery and battery failure due to the lack of acid required to maintain the chemical charge/discharge reaction)
• The entire volume of the electrolyte in the battery is held and equally distributed over the entire surface area between the plates. Therefore the AGM battery is not greatly affected by acid corrosion when charging from very low states of charge. Higher acid concentrations between the plates of a conventional flooded Lead Acid battery resulting from charging when in a low state of charge, coupled with lower acid concentrations above and below the plate pack can lead to increased rates of plate corrosion greatly reducing the life of the battery

Benefits of AGM over Conventional Flooded Batteries

• Typically a 30 – 40% increase in cold cranking power (CCA) over conventional flooded Lead Acid battery resulting in increased engine cranking speeds, shorter engine start times and reduced CO₂ emissions during the engine start cycle
• Cyclic durability endurance at deep discharge levels of approximately 50% Depth of Discharge (DOD) is typically 3 – 6 times that of a standard aftermarket conventional flooded Lead Acid battery
• The cyclic operation in a partial state of charge of approximately 50% for original fitment AGM battery is approximately 3 – 5 times that of aftermarket battery. From 2013 Model Year vehicles this increases to approximately 8 – 12 times that of conventional flooded Lead Acid battery
• Maintenance of the ability to accept charge immediately after starting the engine and from energy produced by a Regenerative Braking system, known as Dynamic Charge Acceptance (DCA) is currently up to 3 times that of a conventional flooded Lead Acid battery

YBX7000 EFB (Enhanced Flooded Battery)

The EFB is based on a conventional flooded Lead Acid battery design but with improved specification and performance. Featuring increased cyclic durability and an improved ability to accept charge current by various changes to battery construction and materials.

EFB technology offers a cost effective solution for low specification entry level vehicles, where the battery is not operating across such a low range of State of Charge (SOC) as an AGM battery. This is due to the vehicle manufacturer having to reduce vehicle CO₂ emissions by a lower amount to meet EU reduction targets as base line vehicles already have a lower CO₂ emission level than the high performance and specification vehicles where an AGM battery is required.

Benefits of EFB over Conventional Flooded Batteries

• Typically a 15 – 20% increase in cold cranking power (CCA) over conventional flooded Lead Acid battery resulting in increased engine cranking speeds, shorter engine start times and reduced CO₂ emissions during the engine start cycle
• Cyclic durability endurance at deep discharge levels of approximately 50% Depth of Discharge (DOD) is typically 2 – 4 times that of a standard aftermarket conventional flooded Lead Acid battery
• The cyclic operation in a partial state of charge of approximately 50% is approximately 2 – 3 times that of conventional flooded Lead Acid battery
• Maintenance of the ability to accept charge immediately after starting the engine and from energy produced by a Regenerative Braking system, known as Dynamic Charge Acceptance (DCA) is currently twice that of a conventional flooded Lead Acid battery

Cost Implications & dangers

Due to the increase in performance, higher production costs and unique characteristics of AGM batteries battery care, replacement battery sales, controlling battery warranty claims and enhancing customer satisfaction becomes more important.

Battery care & charging

When installed on the vehicle, AGM battery charging voltages are the same as for any standard battery with no need for any special adjustments to the charging system. This is due to the extremely low internal resistance of the AGM battery resulting in almost no heating of the battery even under conditions requiring high charge and discharge currents.

Due to the extremely low internal resistance of AGM batteries, the acid starved design and reduced charging and discharge time it is essential when charging off the vehicle that the correct type of equipment is used.

Constant current or boost chargers must not be used as this will result in:

• Heating of the battery
• Boiling of the electrolyte
• Increased internal battery pressure
• Loss of recombinant gases to the atmosphere through the PRV (Pressure Relief Valve)
• Drying out of the battery

All of these factors will greatly reduce the lifespan and performance of the battery and cannot be rectified due to the sealed VRLA design.

Replacement battery sales

Due to the high retail cost of replacement AGM batteries retailers will encounter customer resistance to the compulsory purchase of an AGM battery over conventional flooded Lead Acid or EFB battery types based on the level of technology on their vehicle.

If the battery application guide stipulates that the only battery type specified for the vehicle is an AGM then an AGM type is the only battery that is fit for purpose on that vehicle. The following examples illustrate the importance of correct battery application with regard to AGM and EFB batteries:

• Fuel savings based on an Original Equipment Manufacturer (OEM) AGM battery installed on a “Micro hybrid 2” vehicle over a distance of 30000 miles would equate to an average fuel saving of approximately £670 (subject to driving style and cycle)
• Fuel savings based on an Original Equipment Manufacturer (OEM) EFB battery installed on a “Micro hybrid 1” vehicle over a distance of 30000 miles would equate to an average fuel saving of approximately £280 (subject to driving style and cycle)

Installation of a conventional flooded Lead Acid or EFB type over an AGM battery will result in premature battery failure caused by the following:

• Excessive battery cycling as conventional flooded Lead Acid and EFB type batteries have significantly lower cycling specifications
• Excessive plate damage caused by high depths of discharge (DOD) which conventional flooded Lead Acid or EFB batteries are not designed to support
• Accelerated loss of battery plate surface area and resultant capacity (CCA) which can be as much as 16% in the first week of battery service

Conclusion 

To achieve the levels of CO₂ emission reduction and fuel economy improvements designed into the vehicle by the OEM, it is essential that a vehicle originally fitted with an AGM battery should be replaced with an AGM battery of equivalent quality and design and specification.

The installation of a more attractively priced conventional flooded Lead Acid or EFB type battery instead of the specified AGM battery will quickly lead to the loss of Micro hybrid functionality on the vehicle. Inoperative Micro hybrid systems will increase emissions of CO₂, reduce fuel economy and result in the premature failure of the battery. Indications of premature battery failure are battery going flat or being over cycled.

The installation of a more attractively priced conventional flooded Lead Acid battery instead of the specified EFB battery will quickly lead to the loss of Micro hybrid functionality on the vehicle. Inoperative Micro hybrid systems will increase emissions of CO₂, reduce fuel economy and result in the premature failure of the battery. It is essential that the battery is replaced with an equivalent quality EFB battery or higher specification AGM battery if recommended by battery manufacturer.

A conventional flooded Lead Acid battery should not be installed to OEM equipped AGM or EFB vehicles.

General 

It is becoming increasingly common that installing new batteries to “Micro hybrid” equipped vehicles requires the European On-Board Diagnostics (EOBD) error codes to be reset and the replacement battery registered to the vehicle. This is so that the charging control system can be reset and full vehicle functionality regained.

Whether the vehicle requires system resets or battery registration/coding should be advised by the retailer of the battery at the time purchase. The battery retailer should be required to advise the customer how and where the reprograming of the vehicle can be carried out. This gives the customer the information to find their own reprogramming option.

The retailer must also note that the battery was clearly sold with advice only and the vehicle was not reprogrammed by the retailer. This is not the recommended supply option by the battery manufacturer.

Warranty & Customer Satisfaction

• The higher numbers of Micro hybrid vehicle types on our roads will mean an increase in AGM and EFB battery sales and conversely a reduction in the sale of conventional flooded Lead Acid types. It therefore becomes very important for battery retailers to understand the technology behind AGM, the special requirements placed on the battery and the consequences of supplying batteries unsuitable for application.
• If EFB or conventional flooded Lead Acid type batteries are supplied in place of specified AGM types they will almost certainly fail a short time after the start of the battery warranty period. This situation will result in increased false warranty claims and dramatic loss of customer satisfaction.
• It is therefore essential that battery retailers understand the technological reasons for the correct application of AGM batteries and the consequences of installing batteries such as EFB or conventional flooded Lead Acid that are not fit for purpose.
• Using this information, battery retailers can make customers fully aware of the reasons for the high cost of AGM batteries and the technological and performance limits of other battery types. Customers must understand that the installation of other battery types will affect the performance of their vehicle and potentially result in expensive recovery or repair costs.