You are here: Home > EV Main Components > Inertia Switch
Inertia Switch

It cannot be stressed hard enough how important an inertia switch is to an EVís complete operations. What an inertia switch mainly does is it kills the main circuit in quick, sudden movement through the help of a magnetized ball-bearing inside it. You can easily reset the inertia switch by simply pressing the top of the device, which works similarly like an airbag sensor. This acts an incredible piece of device during emergencies and will render the lifespan of an EV even longer.

We should add here that the other term for these inertia switches would be acceleration switches. In the event of a crash or other events that generate severe force, these switches could use a mass ball as a sensing element that will open switch contacts. This happens through the help of a mechanical linkage that comes in a variety of acceleration-versus-time curves.

The typical automotive inertia sensors today work in such a way that they connect to the electronics controlling the EVís fuel pump and are positioned to sit somewhere in the dash panel. This mass device is usually a ball that easily moves away from a rest position which, by the time a crash happens, will move from a rest to a setting that has its triggering mechanism open a switch. One example of this system is what is installed in a Toyota inertia switch. What happens in this inertia switch is that it allows the ball to spill from a spring-loaded plunger into a set of switch contact to activate the protection system.

There is usually a cantilever link coming from this plunger towards the engine control that will then signal it to power down during a fuel pump. This enables the EV to read its position to a point where it can avoid accidents and other fuel hazards. Truly, thereís no other mechanism out there that is able to automatically lock the fuel pump and avoid oil leaks towards the engine, preventing fires and lethal risks.

Added to the feature of stopping the fuel pump and unlocking all doors in a crash, an inertia switch is also helpful in preventing electrocution when sheet metal has been ripped off of its insulation and the responders in a car accident need to cut through the vehicle for rescuing trapped occupants. Its other feature would be that it acts as a disabling mechanism for a pack voltage, unless of course you use this as an input to the logic of the controller. However, the simultaneous failure of a controller and its crash is already a probability so high to consider. Itís so unlikely that no technology seems to be developed to address it.

A special tip: you should always remember where you mount these shunts. There are regulatory bodies, such as the Federal Register, that will check if the inertia switches you installed are in proper place and are working according to their standardized status. Also, one way to extend the lifespan of your inertia switches is to check for corrosion and for how long the inertia switch has already been operational.