A few days ago when I was driving, I accidentally found that when the automatic transmission vehicle was driving in the morning, in the moment when the P gear switched to the D gear, the owner would hear a loud "clucking" sound, I thought that the vehicle was damaged, stepped on the accelerator, the vehicle can still drive normally, there is no abnormality, cut back to the P gear again, re-hang the D gear, and there is no repeated similar sound. In the process of chatting with other car friends, it was found that most vehicles have similar problems, which does not affect normal driving, but it surprises the owner!
P-stop works
Want to understand the above process, we must first figure out the working principle of the transmission P gear: P gear, also known as parking gear, only in the case of vehicle parking, you need to switch to P gear, when the transmission switches to P gear, the parking locking mechanism will lock the output shaft of the transmission, that is, the vehicle's drive wheel lock, its locking mechanism is a ratchet, a ratchet mechanism, by the pawl stuck ratchet, thereby preventing the tire from rotating. The function of the P-stop is the brake after stopping, which prevents the vehicle from moving.
When the P gear is switched to D or R gear, why is there a different sound?
Friends who understand the mechanical structure must know that there will always be gaps between two parts that are in contact with each other and have a tendency to move each other, such as between gears and gears, between gears and racks, and there are gaps between ratchets and pawls, so even in the condition of P gear, when we get off the cart, the vehicle will not move, but it will still shake, and a clear mechanical collision sound can be heard outside the vehicle.
If the vehicle is downhill or uphill, the owner does not pull the handbrake after parking, the vehicle will have a downward sliding trend due to its own gravity, in this case, the ratchet and the ratchet will be tightly stuck, if the owner starts the engine at this time, from the P gear to the D or R gear of the moment, there will be a "cluck" a loud noise, this is the ratchet and the ratchet is dragged away by the sound, the owner does not have to make a fuss.
In addition, when the car hangs up the D gear in the process of driving forward, the owner suddenly steps on the brake to hang the P gear to stop, at this time switch to the R gear, there will also be a corresponding Caton-type abnormal sound, the reason is that in a specific position, the P-stop ratchet and the pawl contact is too close, resulting in a certain residual stress between the ratchet and the pawl, the owner is forcibly dragged by the P gear to the R gear, the ratchet and the pawl suddenly bear the opposite force, due to the residual stress between the ratchet and the pawl, the Caton-type abnormal sound will appear. There is little good solution to this anomaly, which can only be improved by optimizing the structural shape of the ratchet and pawl!
How to reduce the abnormal noise when the P gear switches to D or R gear?
In order to suppress the abnormal noise when the P gear switches to D gear or R gear, the owner can learn some correct parking methods, such as when the car is mainly parked on the ramp, you can first step on the brake, and then hang N gear, while pulling the handbrake, after the handbrake is tightened, then switch from N gear to P gear, and then release the brake pedal; when the owner stops on the flat road, he can consider hanging the P gear first, then loosen the brake, and then pull the handbrake after the residual stress between the ratchet and the ratchet is eliminated. If driving in this way, the owner can minimize the abnormal noise when switching from P gear to D or R gear.
In summary, when driving in the morning, the moment the vehicle switches from P gear to D or R gear, it is normal for the abnormal noise to occur, and the owner does not have to worry about it.