Real shot analytical BYD dual clutch transmission

As a vehicle equipped with BYD's own 6-speed dual clutch transmission developed and manufactured by BYD, BYD's performance is surprising. When you really understand the specific configuration, the dual-clutch transmission technology is even more surprising.

The core technology of this dual-clutch transmission, codenamed 6DT25, such as the dual clutch module, electro-hydraulic control system, and control unit, was all independently developed by BYD. As an independent auto brand without any relevant experience, it is of course not worth mentioning and imitating. The transmission is currently mainly used to match BYD's 1.5T turbocharged engine. Its launch is a good complement to the incompetent competitiveness of autonomous vehicle brands due to the lack of automatic transmission models or due to the relatively backward automatic transmissions purchased.

BYD six-speed dry dual clutch type transmission of the basic information 6DT25 maximum transmission torque 250 Nm number of forward gear / reverse gear number 6/1 by weight and about 70 kg match engine models match BYD 1.5T engine mounted in speed sharp, On the G6 model

Selecting independent research and development on the roads of outsourcing, technical cooperation, etc. is often the most difficult but also the most practical way. Once the technology is successfully mastered, it will no longer be controlled by others, and it will be able to formulate related product strategic plans more easily.

Is it the choice to develop a traditional AT transmission or a dual clutch transmission? In general, AT transmissions have always been known for their technical complexity and high manufacturing difficulty. Dual-clutch transmissions are almost identical to manual transmissions in gear transmission systems. The key points are the aforementioned core technologies. On the whole, the manufacturing difficulty of the dual-clutch transmission is still smaller than that of the conventional AT transmission. Therefore, it is BYD's first choice to use the dual-clutch transmission that is independently researched and developed and is currently fashionable.

Regarding the mechanical structure of the dual-clutch transmission, we do not have much to say this time. Instead, we will focus on the electro-hydraulic control system of the transmission and its control unit. The control unit is equivalent to the human brain and is the core control mechanism of the transmission. After understanding its logic, it is not difficult for us to understand the series of reactions and actions it has made.

● Three stages of clutch engagement This 6DT25 uses an electronic hydraulic system to control the clutch combination and separation and to select gears. Due to the high precision of the automatic transmission, various types of slide valves are also required in the oil system. With its high manufacturing precision, it also imposes high requirements on the oil itself that acts as a lubricant, heat sink, and force transfer in a variety of complex and harsh working environments. BYD's dual-clutch transmission oil and Volkswagen's 7-speed DSG are the same overseas suppliers. According to BYD's technical personnel, they worked with suppliers to solve the problem that oil may be generated under certain conditions. The problem of crystallization, that is, the absence of a gear due to oil is not the case.

Due to the dry dual clutch module, its structure and working principle are similar to those of the manual transmission (MT), except that the MT controls the degree of combination by the human foot, and the dual clutch is controlled by the electronic control unit. Humans can finely operate the clutch through their rich sensing system, clever brain and driving experience to ensure driving comfort. To make this machine do the same, you need a set of control, execution, and feedback systems that are sensitive, accurate, and fast.

The so-called double clutch has two sets of clutch systems, of which the clutch 1 controls the 1st, 3rd, and 5th gears, and the clutch 2 controls 2, 4, 6 and the reverse gear. There is a displacement on each control clutch with the separated piston rod. The sensor, through it, judges the degree of coupling of the clutch and feeds this signal back to the control unit, thereby helping it to judge and issue a command to control the clutch action.

The process of clutch engagement is not simply a matter of approaching each other until full contact, which can only lead to shifting. There are three stages in the execution of specific actions. In simple terms, it is "fast, slow, and fast." The first stage: the clutch and the drive plate (think of a large flywheel in motion) quickly approach until the critical state to be contacted; the second stage: the two slowly contact each other until the speed of the clutch is basically synchronized with the drive plate; The third stage: The two are completely combined, so that the rigid connection state.

In fact, this kind of control logic basically imitates people's movements under the foot during shifting. The whole process is judged by the displacement sensor to determine the stage of integration, so that the shift process of the vehicle can be kept smooth and smooth.

● Control logic when the vehicle is stationary and the transmission is in the D range. In the case of the AT transmission and the D range, a large part of the power of the engine is consumed in the torque converter. The dual clutch transmission does not have such an energy buffer structure. However, it cannot be maintained in a semi-linkage state for a long time, which may cause premature wear of the clutch linings. The control logic designed by BYD's engineers for this purpose is the critical state in which the clutch and the drive plate are to be in contact. This is the first stage mentioned above. This ensures that there is no contact wear between the two.

In order to ensure that the driver lifts the brake pedal, the vehicle can immediately move forward, where there are two important signals designed. One is the brake light signal at the brake pedal and the other is the brake fluid pressure signal. When these two signals are satisfied at the same time, the control unit of the transmission assumes that the driver is ready to start the walking vehicle. At this time, the control unit will send signal control. The piston pushes the clutch to complete the aforementioned second and third phases.

This kind of control logic allows the owner to wait for the red light, without worrying that the transmission is in the D range and slamming on the brake will damage the transmission. The owner can handle it according to his own habits.

● About "overheat protection"

In the previous process of SpeedRui's testing (click here for details), after several catapult starts, the transmissions 1, 3, and 5 have been lost. After that, they communicated with the technicians to confirm that the transmission started overheat protection. The program cuts off clutch 1. Previously, the control logic of the electronic control unit did not limit the engine speed in this abnormal situation in which the brakes and the accelerator were simultaneously depressed, because such operations are hardly performed as ordinary users.

To this end, the technician also modified the control logic to limit the engine speed in this case to 1500 rpm in order to minimize the wear and associated overheating of the relevant components. In addition, there is also a situation that we often encounter, that is, frequent city traffic jams that stop and stop. The frequent combination and separation of clutches often causes premature wear and overheating, which affects normal use.

BYD's technicians also designed a thermal protection program for this situation. This program does not directly monitor the temperature of a certain component. Instead, it determines the clutch indirectly through the signals of various sensors and the coefficient of heat dissipation of clutch friction linings. overheat. If the temperature of the transmission rises to a certain threshold, the driver will be warned first by the alarm of the instrument. If the driver still drives in a bad condition and the temperature increases further, the control unit will order a forced cut-off to protect the transmission. Overheated clutch shaft, but the vehicle can still be operated with the remaining clutch and the gear it controls.

●Reliability Consumers often pay attention to its durability and reliability when purchasing a car, especially large components such as engines and transmissions. We also cast this issue to BYD's technical staff. Their feedback is that the relevant components of the transmission, such as the control unit, dual clutch, etc., can achieve the same lifespan as the entire vehicle, in which the key components have been subjected to a single component and Assembly durability test. Although this sounds a bit official, the long-term use of this product and the ability to accumulate it have to be judged.

Full text summary:

The R&D and manufacturing experience of the core components has been firmly in the hands of BYD, especially the software program integrated into the control unit. Usually it is invisible and intangible, and it is precisely the soul of the entire transmission. Its behavior is controlled by it. It should be said that BYD's experience is not rich enough in the maturity of the dual clutch transmission matching the engine and the vehicle. This may lead to a less satisfying driving experience, but it can be used for such a short period of time. On the basis of this, and it is very good to abandon some of the problems on the object being modeled, and to ensure the reliability of the product, which is worthy of admiration anyway.