Many of you have probably experienced a "shock" of static electricity the moment you step out of your car and touch the door.
This is especially common in winter when the air is dry, and it often leads to questions like:
"Is the car itself accumulating electricity?"
"Since the tires are rubber, does that mean electricity can't escape to the ground?"
"Does static electricity also occur on the body and plastic parts?"
When trying to understand static electricity in cars, it's important to differentiate between:
static electricity that accumulates on the human body
and
charging that occurs on the car body and parts.
Furthermore, cars use a variety of materials with different electrical properties, such as:
metal,
rubber,
plastic,
glass,
fiber,
and paint.
While driving, contact and friction occur in many places, including:
between tires and the road,
between air and the body,
with belts and rotating parts,
and between seats and clothing.
This time, we will provide a clear explanation, from how static electricity is generated in cars, to the charging of tires, metal bodies, and plastic parts, and important safety points you should know.
What exactly is static electricity?
Static electricity is a state where electric charges are unevenly distributed on the surface of an object.
Normally, within a substance, positive and negative charges are balanced to some extent.
However, when:
objects come into contact,
rub together,
or separate,
electron transfer occurs, which can cause one object to become positively charged and the other negatively charged.
Common examples include static electricity felt when:
taking off clothes,
walking across a carpet,
or touching a doorknob.
In cars, charging occurs similarly due to the contact and separation of various materials.
Where does the "shock" come from when you get out of the car?
The most common static electricity experience in a car is the discharge that occurs when you touch the door upon exiting.
This does not necessarily mean that:
"a large amount of static electricity has accumulated on the car's body."
In reality, it's often a case where static electricity has accumulated on the human body.
Nissan also explains that static electricity generated inside the car comes from:
friction between the seat and clothing.
For example, when getting out of a car, a series of actions occur:
clothing rubs against the seat,
the body moves away from the seat,
feet touch the ground,
and then a metal door is touched.
If there is a potential difference between the human body and the car body at this moment, the charge can rapidly transfer, resulting in a "shock."
Why is static electricity more common in winter?
Static electricity tends to accumulate in dry environments.
When there is a lot of moisture in the air or on object surfaces, charges can dissipate gradually.
Conversely, when humidity is low and it's dry, charges are less likely to dissipate, making it easier for a charged state to be maintained.
Therefore, in winter, the chances of experiencing static electricity increase when:
touching a door,
taking off clothes,
or getting out of a car.
Toyota also suggests a method for preventing static electricity when exiting the vehicle: touching a metal part of the car body while placing your feet on the ground.
Charging also occurs in a moving car
Static electricity is not only generated on occupants.
In a moving vehicle, charging can also occur due to external factors.
As a car moves, it undergoes numerous contacts and separations, such as:
tires contacting the road surface,
large volumes of air flowing over the body surface,
plastic and rubber parts vibrating,
and rotating parts moving.
Toyota's patent for a vehicle static eliminator also describes technology based on the premise that the car body becomes charged with static electricity due to external factors like driving.
In other words,
the phenomenon of "static electricity occurring in a moving car"
is not unusual.
Are cars completely insulated from the ground because tires are made of rubber?
A common explanation is that:
"tires are made of rubber, so cars are completely insulated from the ground."
However, this is a bit oversimplified.
Tires are made of various materials, including:
natural rubber,
synthetic rubber,
carbon black,
silica,
steel cords,
and various additives.
Therefore, the electrical resistance of tires varies depending on the materials and structure used.
While common rubber is a poor conductor of electricity,
not "all tires are perfect insulators."
Some tire designs also allow static electricity to escape
Some tires are designed with conductive paths to allow accumulated static charges to dissipate to the road surface.
For example, Bridgestone explains that for some of their two-wheeled vehicle tires with a high silica content, the rubber's conductivity is low. Therefore, they incorporate a highly conductive rubber called "antenna rubber" that extends to the tread surface, making it easier for static electricity accumulated on the vehicle to escape to the road.
In other words,
it's not that "tires are made of rubber, so they absolutely don't conduct electricity,"
but rather,
it's more accurate to understand that "the electrical properties of tires vary depending on their materials and structure."
Does charging occur even with tire-road contact?
When a tire is in motion, it continuously contacts, deforms, and separates from the road surface at high speed.
Such contact and separation are one of the conditions for static electricity generation.
On the other hand, tires also have the role of dissipating charges to the road surface.
Therefore, tires are:
a place involved in charging
and at the same time,
can serve as a path for charge transfer.
This makes them a complex entity.
Consequently, the charging state of a car cannot be explained
"solely by the tires."
Does static electricity accumulate on the metal body?
Car bodies use a lot of metal, such as steel plates and aluminum.
Metals conduct electricity easily, so they are materials where charge can move more readily compared to plastics.
However,
just because it's metal doesn't mean it won't charge.
Since the entire car body is not ideally grounded to the ground, a potential difference can occur on the car body.
In metal parts, charges tend to spread across the conductive area rather than remaining localized.
For this reason, it's important to consider not only
"whether it charges or not,"
but also
"where that charge can move."
Why are plastic parts prone to static electricity?
Modern cars use a large number of plastic parts.
For example:
bumpers,
undercovers,
air cleaner boxes,
intake ducts,
interior panels,
seat surrounds,
door trims,
and various covers.
Since plastic generally does not conduct electricity easily, once a charge appears on its surface, it can be difficult for that charge to move elsewhere.
Therefore, compared to metal parts,
localized charging is more likely to persist.
Toyota's vehicle static electricity removal technology also includes technologies aimed at addressing charging in parts made of insulating materials.
Why are more plastic parts being used in cars?
The reason plastic is used in cars has nothing to do with static electricity.
For example, it's used for:
weight reduction,
design flexibility,
corrosion resistance,
reduction in the number of parts,
crash safety design,
and cost.
Bumpers and undercovers, for instance, are parts that can effectively utilize the properties of plastic.
However, since their electrical properties differ from metal, modern cars, which combine
metal bodies,
paint,
plastic,
rubber,
and glass,
may have varying charging states depending on the location.
Does charging also occur between the air and the body?
When a car is in motion, a large volume of air flows over its body surface.
Air itself contains ions and charges, and there are electrical interactions between these and the charges on the car body.
Toyota has focused on this point and patented several vehicle technologies based on the idea of:
reducing static electricity on the car body surface to change the state of airflow separation around the body.
However, this needs to be understood carefully.
The existence of a patent is not the same as saying that:
"aerodynamic performance will always improve if static electricity is removed from any car."
The actual effect can vary depending on factors such as:
car body shape,
amount of charge,
speed,
weather,
installation location,
and materials.
Therefore, it is not appropriate to generalize and definitively claim improvements in fuel efficiency or driving performance.
Does static electricity on the car body worsen fuel economy?
There are various technological developments and research regarding the relationship between static electricity and vehicle performance.
However,
it cannot be stated as a universal figure for all cars, such as "static electricity on the car causes fuel economy to worsen by X%."
Fuel economy is influenced by numerous factors, including:
engine efficiency,
tires,
vehicle weight,
air resistance,
drivetrain losses,
temperature,
driving style,
and traffic conditions.
While static electricity and charging conditions are subjects of research, it's important not to attribute vehicle performance solely to them.
Car body grounding and "grounding to earth" are different
In automobiles, we use the term:
"body ground."
This is a method of connecting the negative side of electrical components to the car's metal body, using the body itself as a common path for the electrical circuit.
It's important to note here that:
body ground is not the same as grounding to the earth to dissipate electricity.
The role of grounding to the earth used in household electrical installations differs from the body ground in automobiles.
The primary purpose of the car's electrical circuit is to electrically connect:
the battery negative terminal,
the engine,
the body,
and each electrical component.
Therefore,
it's not necessarily true that "because the battery's negative terminal is connected to the body, all static electricity escapes to the ground."
This distinction is also important for understanding "car earthing," which will be covered in the next article.
Are static electricity and battery electricity the same?
This is another point that is often confused.
While the electricity supplied by a car's 12V battery and static electricity both relate to "electricity," their properties differ significantly.
A battery continuously supplies current at a relatively low voltage.
Static electricity accumulated on the human body or other objects, on the other hand, can reach very high voltages, but the amount of charge is small and discharges quickly.
Therefore,
a simple comparison like "if static electricity is several thousand volts, it's more dangerous than a 12V battery"
cannot be made.
It's necessary to consider not only voltage, but also:
current,
amount of charge,
and discharge time.
Can static electricity damage car electronics?
In the world of electronic components, electrostatic discharge is known as ESD and is managed as one of the factors that can damage semiconductors and other devices.
Therefore, strict static electricity countermeasures are implemented in electronic device manufacturing facilities.
On the other hand, electronic devices in commercially available cars are designed assuming real-world vehicle environments.
Normally, there's no need to think that:
"the ECU will break"
just because you experienced a static shock when touching the door.
However, when performing work that involves directly touching electronic components after they have been removed, static electricity countermeasures may become important.
Static electricity countermeasures are important at gas stations
The most safety-critical aspect of static electricity in cars is during refueling.
Gasoline is highly flammable, and there is a risk of its vapors igniting from a static electricity spark.
The Fire and Disaster Management Agency instructs regarding refueling at self-service stations:
to touch the static electricity removal sheet before refueling,
and if there is no static electricity removal sheet, to touch a metal part of the car.
JAF also advises touching the static electricity removal sheet before refueling, regardless of the season.
Static electricity countermeasures during refueling are not something that:
"only need to be concerned about in winter."
Always follow the procedures displayed on the fuel dispenser.
How to reduce the "shock" when getting out of the car
For static shock from the human body, there are relatively simple countermeasures.
The method introduced by Toyota involves:
opening the door,
touching a metal part of the car body,
placing your feet on the ground while still touching the metal part,
and then releasing your hand.
This sequence makes it easier for the accumulated charge in your body to dissipate.
Additionally,
avoiding dryness,
being mindful of clothing materials,
and reducing friction with the seat,
also contribute to reducing the sensation of static electricity.
Are all static electricity removal products effective?
There are various types of static electricity countermeasures available on the market, such as:
keychains,
straps,
seat accessories,
and car body static eliminators.
However,
products that dissipate static electricity from the human body
and
products aimed at changing the charging state of the car body
have different roles.
Furthermore, even for car body products, the conditions vary depending on:
installation location,
conductivity,
materials,
and vehicle model.
Therefore,
it's not advisable to think that "all static electricity countermeasures are the same regardless of where they are attached."
NEXT SCIENCE's concept of "electronic environment"
At NEXT SCIENCE, we position
the electronic environment
as one of our technological research areas.
For cars and machinery, we focus not only on voltage and current, but also on:
the charging of parts and materials,
potential differences,
electrical imbalances,
and the electronic state surrounding metals and plastics.
Technologies such as ORBITRON and Microreactor are being developed in this area.
NEXT SCIENCE has made it a research theme to regulate the static electricity and electronic state that occurs on the car body.
However, perceived experiences and performance changes in vehicles cannot be guaranteed with uniform figures, as conditions vary depending on the vehicle model, state, and usage environment.
It's important not to simplify by saying:
"all static electricity is bad,"
but rather to look at the entire electronic environment, considering:
where on the car body charging occurs,
how the charge moves,
and where it dissipates.
5 key points for understanding static electricity in cars
When considering static electricity in cars, it becomes easier to understand if you separate it into the following five points:
The first is:
Is it static electricity accumulated on the human body?
The second is:
Is it charging of the car body itself?
The third is:
Is it a metal part or a plastic part?
The fourth is:
Is there a path for the charge to escape?
The fifth is:
Is it a safety issue due to static electricity, or a discussion about driving performance?
Specifically,
the "shock" when getting out of the car
and
the charging of the car body during driving
tend to be discussed interchangeably, but they need to be considered separately.
Summary: Static electricity in cars is not generated in just one place
Cars use many materials, such as:
metal,
rubber,
plastic,
glass,
and fiber.
And during driving or getting in and out of the car, contact and separation are repeatedly occurring between:
tires and the road,
air and the body,
seats and clothing,
and various components.
As a result,
the human body,
the car body,
plastic parts,
and areas around the tires,
are all involved in charging.
What's particularly important to remember is that:
"the 'shock' when getting out of the car and the charging of the car body itself are not necessarily the same phenomenon."
Also important are the points that:
tires are not always perfect insulators,
metals are not immune to charging,
charges tend to remain localized on plastics,
and body grounding is different from grounding to the earth.
Static electricity is invisible.
That's why,
instead of judging simply "whether it exists or not,"
considering where it occurs,
where it moves,
and where it dissipates,
is the first step to understanding the electronic environment of a car.