The inductive charging of smartphones in the car is becoming increasingly popular. That is why more and more OEMs are installing inductive charging stations. This article shows what challenges there are in the development of this technology and what the future of smartphone use in vehicles will look like.
Smartphones have become an integral part of everyday life for many people. According to a study by Ericsson, there will be around 6.1 billion smartphone users worldwide by next year. That corresponds to about 75 percent of today’s world population. In Germany there were around 57 million smartphone users in 2018, and they are particularly popular in the 14 to 49 age group with a user share of over 95 percent.
The way we use mobile phones has also changed: While the first mobile phones were only suitable for making calls, smartphones are now important communication devices in everyday life. Whether for video calls, text messages, apps, listening to music or surfing the Internet – the smartphone is touched an average of 2,617 times a day, as a study by the US market research institute dscout found.
Power-intensive apps drain the battery life
Many smartphone users always have their device with them and want to use it everywhere – even in the car. Studies show that 70 percent of car occupants use their smartphones while driving. They not only make calls, but also use power-intensive apps such as GPS navigation, infotainment options (podcasts, internet radio and playlists), voice-controlled text input, adjustments to vehicle settings (air conditioning and seat positions) or data exchange with the cloud.
All of these applications reduce the battery life of smartphones. Fifteen years ago, a full charge on a cell phone would take about a week. Today the average battery life is only one day.
This does not even take into account the expansion of LTE and LTE Advanced networks, which will consume more energy. Charging the smartphone in the vehicle is therefore all the more important for increasing the comfort of the vehicle occupants. Charging the smartphone via USB in the car is usually an inconvenient procedure – plugs do not fit, an adapter is often missing, connecting while driving is a dangerous, traffic-endangering undertaking, and the charging capacity at the USB port is often too low for fast charging. This can be remedied by charging via “wireless charging”, which more and more OEMs are integrating into their vehicles.
Structure of the wireless charging units
The technology behind wireless charging is based on an invention by the visionary Nikola Tesla, which he made back in 1891: the wireless, “inductive” transmission of energy to operate incandescent lamps. With inductive charging – that is, the wireless energy transfer like an electric toothbrush and its base station – an input voltage is converted into a constant output voltage, similar to a standard switched-mode power supply. The decisive difference to the power supply unit is that the coils used in the power supply unit are installed separately in the transmitter and receiver during wireless charging. A magnetic field with a frequency between 105 kHz and 205 kHz is built up via the alternating current in the coils in the transmitter module. This magnetic field transfers energy to the receiving device, in which a voltage is generated.
Challenges in wireless charging
The development and introduction of wireless charging systems poses a number of design challenges. One concerns electromagnetic compatibility (EMC). Strict requirements are rightly placed on these in automotive applications. EMC refers to the inadvertent generation, emission and absorption of electromagnetic energy that can cause undesirable effects on an electrical system, such as electromagnetic interference (EMI). Wireless charging can also adversely affect the keyless entry system (keyfob) by creating unwanted electromagnetic fields.
The function of the keyfob must under no circumstances interfere with a wireless charging system through electromagnetic radiation. The construction challenge becomes even more apparent when the driver places the keyfob on or near the wireless charging station. For example, if the keyfob is on the wireless charging station / platform while charging, the key might not recognize the vehicle’s request and then not respond. The car would not start. The development of advanced EMC shielding techniques is a necessary prerequisite to ensure the coexistence of the wireless charging system with the keyfob.
Another challenge for wireless charging concerns heat sensitivity. Extreme temperatures not only have a negative effect on a mobile device, but also on the charging station. The typical operating temperature for a mobile phone is between 0 and 35° C. In summer, however, the interior of a vehicle that is parked in a sunny parking lot, for example, can heat up to well over 35° C. If the charging system is not appropriately designed and protected, such drastic temperature increases can cause damage that makes it inoperable.
With wireless energy transfer, heat is generated in the smartphone, which can extend the charging process. That is why optimized thermal management plays an important role in reducing charging times.
When transmitting from the charging station to the phone, part of the energy is naturally lost. Many wireless charging systems can only achieve a maximum efficiency of 65% even under perfect conditions. However, Molex Wireless Chargers can boast an efficiency of 72% (measured from the car battery to the cell phone battery).
Current units are designed to be able to bridge distances of up to 4mm. Greater distances are possible, but require higher transmission energy, which in turn has a negative effect on the critical EMC in the closed vehicle.
Competing communication protocols
The wireless charging system must work with every telephone with inductive charging technology, regardless of the position of the telephone on the charging station. In addition, each vehicle interior has its own special characteristics, including ergonomic design and electronic functionality. What is needed is a uniform platform that can be easily and inexpensively integrated into the design requirements of all vehicles.
In order to achieve maximum device coverage, wireless charging units should be equipped with hardware that meets the broadest possible range of requirements. In the past, however, the possible uses were limited by different standards. The “Qi” standard (pronounced “Tschi”) of the Wireless Power Consortium (WPC), which has been on the market since 2008 and unites over 570 companies including Samsung, Apple, Sony and almost all Android smartphone providers, has prevailed. The Consumer Electronics for Automotive (CE4A) Group, in which leading automobile manufacturers such as BMW, Audi and Daimler are represented, decided to use Qi as the common standard in 2012.
Although the majority of smartphone models are factory-designed for wireless charging, there are still some models that cannot be charged wirelessly. In the near future, a decisive purchase factor for smartphone owners will be which smartphone is Qi-compliant.
Wireless charging with the best reception and transmission properties
A general problem with smartphone use in the car is signal attenuation or signal loss. The car behaves like a Faraday cage and is therefore very well shielded. Telephone calls in the vehicle can be a challenge. Smartphones in the average mid-range car lose around 12 to 15 dB of field strength. This means that only 1/16 to 1/32 of the radio signal from the smartphone gets to the outside, which greatly affects the quality of phone calls and data connections. With the help of an intelligent electronic component (compensator), these losses are balanced out so that reception in the vehicle is just as good as in standard situations. The Compenser can connect to the smartphone via the near field coupling built into the wireless charger and compensates for signal losses in the vehicle, by connecting to the smartphone and the external antenna equally. It thus compensates for the loss of signal and enables optimal voice quality and data connection.
Features for selecting a wireless charging module
It is important that the charger notices when a smartphone is placed on the charging station (only then is a magnetic field generated, before that no energy is absorbed or released), when it is fully charged, and that it then switches itself off automatically. He also has to recognize whether a phone is compatible with the Qi standard at all and – if this is not the case – switch off immediately in order to protect the smartphone from damage or interference. It is also relevant for the OEMs that the modules can be adapted to their needs. This applies to both technical and design-dependent specifications.
For example, there are wireless chargers for vertical installation, but also those that are installed below the center armrest or in front of the gear knob on which the respective smartphone rests safely. It is important that the design of the inductive charging surface matches the car and is user-friendly. This applies to all vehicle occupants, which is why solutions are also available for the rear area of the interior.
Furthermore, the power transmission performance class is an important selection criterion for the vehicle manufacturer. Modern smartphones are able to charge the battery with more than 5 W. Well-known cell phone providers currently charge their phones in Fast Charge mode with approx. 8 W. There are also a few models that charge the battery with approx. 10 W. The Qi standard provides for a power transmission of up to 15 W. In the course of battery development, it will be possible in the future to charge the phones with even higher capacities.
Future wireless charging market
In the foreseeable future, wireless charging will become an everyday feature in the automotive sector. The vehicle is perceived as a living space. And since the smartphone has become a natural companion for 6.1 billion users in most situations in life, it must also work in the car. This results in the requirement for OEMs to make smartphone integration into the automotive environment as convenient as possible. Wireless charging is an answer to this requirement.
But while wireless charging is becoming more and more established in vehicles, developments continue. In the next two to three years, future generations of devices will have the ability to charge multiple devices in parallel and at the same time be backwards compatible with older standard versions. Cameras and wearables like watches are already doing it today. Other end devices will also support this in the future – such as game consoles, children’s toys or tools.
Particularly exciting for the further development of the wireless charging market – especially in the automotive sector – is the integration of the Near Field Communication (NFC) standard, with which further applications that require high data security are possible. By combining it with NFC, the wireless charging technology can also be used for authentication, which enables many other use cases for the connected car. Examples are the automatic termination of a rental process for car sharing, automated payment processes, for example when downloading current, additional maps or augmented reality information.
High-quality wireless charging solutions that offer the OEM the opportunity to develop unique and convenient solutions for the end customer are essential on this path.