Automatic start-stop technology

    The mainstream automatic start-stop methods on the market have been questioned due to service life and reliability issues. The setting of the wire-controlled steering system on the Infiniti Q50 is a good example. Even with three sets of ECUs that serve as backup for each other, the engineers still arranged a clutch between the steering column and the steering gear as the last trump card.

    However, in the automotive industry, it is common to follow the crowd, but it is even more common to see weird ones. There are always one or two that do not follow the usual path.

A different approach

    For a general engine, when starting, the onboard battery supplies power to the starter to drive the engine to rotate. For the automatic start-stop system, the engine is required to start faster. The easiest way to achieve this is to use a starter with greater torque and power and a battery with greater power. A more complex and reliable method is to use a fully automatic start-stop mild hybrid method, which adds an additional electric motor and auxiliary battery.

    But in fact, there is more to the process of starting an engine. The most fundamental reason is that the engine needs a starter to start it. This is because the engine needs initial power to allow the piston of one of the cylinders to complete the intake and compression strokes, and then ignite to do work. After that, the engine can start its own cycle and no longer needs the power of the starter.

    The reason why the engine starts slowly is that each start cannot be without the intake and compression process, and the other is that the engagement of the starter and the engine also takes time. Therefore, if the time of these two processes can be shortened or eliminated, the engine restart process time will be accelerated.

Mazda: The secret of micro-control

    It seems that Mazda has been away from the mainstream automaker circle for too long, both in terms of brand awareness and influence. However, this company, known as the "Japanese BMW", is a technology fanatic, like the rotary engine and the second-generation Skyactiv engine that will increase the compression ratio to 18.

    The start-stop technology used by Mazda is called i-stop. The i-stop technology mainly targets the first point mentioned above.

    When the driver steps on the brakes until the vehicle comes to a complete stop, the i-stop system will automatically cut off the fuel supply to make it come to a complete stop, and precisely control the position of the pistons so that the pistons of each cylinder stop at the appropriate position as much as possible each time. Then the most suitable cylinder is selected according to the position of the pistons and fuel is injected. When the brakes are released, the system directly ignites the cylinder that has been injected with fuel, which is equivalent to igniting immediately after the brakes are released. The starter is no longer needed to provide initial power to the engine, and the on-board battery only needs to provide the energy required for ignition, without the need for high current output to drive the starter to operate.

Schematic diagram of engine restart process

   So, the question arises, for gasoline engines, ignition can be carried out immediately, but for diesel engines, it is compression ignition. Can this method also be applied? It is impossible to stop the piston at the critical point of compression ignition, right?

    Of course not. The i-stop system will also accurately control the position of the piston stop, but the diesel engine still needs to perform a compression stroke. However, compared with the two cycles required for the automatic start and stop of a general diesel engine, i-stop only needs one cycle to start the engine.

    According to Mazda's official data, the i-stop system takes 0.35 seconds to restart a gasoline engine and nearly 0.4 seconds for a diesel engine. It can be said to be a seamless restart, so the restart process is also smoother.

    To ensure the service life and performance of the engine, the i-stop system can automatically adjust the idling stop time according to different driving conditions, and can detect the power status of the vehicle battery. When it is found that the voltage is insufficient, it will force the engine to start to charge the vehicle battery.

    In addition, the i-stop system is also equipped with an electric hydraulic pump, which can assist the mechanical hydraulic pump when restarting the engine. The latter will stop working when the oil pressure returns to the working range.

Toyota Denso: Idle stop technology that can be installed later

    Another Japanese automaker, Toyota, chose the second route, and the system was named idle-stop.

    When starting, most starters will push out the pinion gear at the front end to mesh with the engine flywheel, thus driving the engine to start running. After the engine stops supplying fuel, it is still running during the period from when it stops completely. If you restart the engine at this time, the pinion gear of the starter will not be pushed out immediately, but you need to wait until the engine stops completely. Therefore, if the idling time is too short, the restart process of the engine will be relatively slow.

    To solve this problem, Toyota and Japanese auto parts supplier Denso have jointly developed a new type of starter - a permanent mesh starter. As the name suggests, the pinion of this starter is always in mesh with the flywheel of the engine, and a one-way clutch is added between the meshing gear and the engine. After starting, the clutch is disconnected and the engine runs on its own.

    However, this solution also requires the installation of a clutch on the engine, so Denso developed the TS starter based on the permanent mesh starter. The TS starter has two solenoids that independently control the push-out of the pinion and the operation of the starter.

    In other words, it is equivalent to adding a switch to the starter, one switch controls the push of the pinion, and the other switch controls the operation of the starter. When the engine is started for the first time, the starter pushes out the pinion and starts the starter at the same time. After the engine is driven to run, the switch that controls the starter operation is closed, while the switch that controls the pinion remains in the closed state; after the idle stop system starts working, the starter only needs to close the operation switch to directly drive the engine to run without waiting for the engine to stop completely.

    The TS starter does not require modification of the engine, only the starter needs to be replaced, so this technology can be installed later and vehicles that have already left the factory can also enjoy it.

    In addition, a spring is added to the part of the starter that pushes out the pinion to reduce the damage caused by the impact when the pinion meshes with the engine end gear, thereby increasing the service life of the engine.

summary

    Compared with Mazda's i-stop, Toyota's idle stop system has advantages and disadvantages:

    1. Mazda's i-stop system can only work after the engine is completely stopped, while Toyota's idle stop system can restart the engine at any time. With the technical support of Denso, it can be installed in the front or rear at will, and there is no brand restriction.

    2. In terms of the implementation of the starting process, Toyota still uses the on-board battery to power the starter, and the mode in which the starter drives the engine is the same as the light automatic start-stop and semi-automatic start-stop mentioned above. Therefore, the life of the on-board battery is still a test.

    From my point of view, the former is amazing and the latter is stunning. Moreover, with these siege lions with unique thinking, there will surely be more bizarre and more exquisite designs in the future.