Chapter 3 Reducers and Multi-Shift Boxes
3.1 Needs and advantages of multi-gear
The development direction of electric drive, one is higher power, torque density, higher limit output speed, higher system efficiency, lower system cost, higher NVH performance, such a background has given birth to a very diverse segmentation of technical routes, such as high speed, oil cooling, high voltage, disconnecting device, dual motor, SIC, excitation, and so on.
Multiple gears increase the torque while increasing the speed of the vehicle. The increased torque makes the motor a little smaller, which reduces losses while achieving higher efficiency. By having two gears, not only can the maximum torque be increased in the lower gears but also the maximum speed can be increased, optimizing the motor for the best efficiency range while increasing the range.
Multi-gear is a good technical solution, for example, two-speed gearboxes in the low-speed gears to make the speed ratio larger, acceleration time, climbing performance will be better, high-speed gears can be made more efficient, so in some performance cars to do some multi-gear solutions. But as the motor speed gets higher and higher, the speed ratio can be made larger, and with the application of silicon carbide technology, the whole differentiation of multiple gears is not as obvious as we think, so some companies' choice is to use high speed motors or silicon carbide technology to do these performance cars, so that the same effect can be achieved.
From the control point of view, the motor response is fast, multi-gear in the gear switching process there is time loss, after adding a gear and to solve these problems in the process of shifting, how to balance this time, or how to make it faster, this is a factor to consider. With the development of motor performance, now the motor efficiency bandwidth has been made very wide, if we attack the German market, multi-gear is indeed a demand, because he needs to achieve a maximum speed of 250 km or even higher, so that single-gear is difficult to cover the acceleration performance of the lower gears and high-speed fuel consumption, but in China's working conditions under the current motor development, single-gear can already meet the basic needs of Chinese customers. But in the current development of the motor under the conditions of China, single gear can already meet the basic needs of Chinese customers.
Six dimensions summarize the advantages of multi-gear.
First: reduce the performance requirements of the motor, a large transmission ratio of the first gear can reduce the maximum torque and peak power of the motor, a small transmission ratio of the second gear can reduce the maximum speed of the motor, reducing the performance requirements of the drive motor.
Second: improve the overall vehicle dynamics, using the same motor, first gear large ratio can improve the acceleration, climbing performance, second gear small ratio can improve the maximum speed, improve the overall vehicle dynamics performance.
Third: improve the economy of the vehicle, through the optimization of the two speed ratios and the shift rule, can improve the efficiency of the motor operation, improve the economy of the vehicle to increase the range.
Fourth: improve NVH and reliability, the second gear small ratio reduces the maximum speed of the motor, reduces the high frequency whistle and high speed vibration of the drive system, improves the quality of the vehicle, improves NVH performance, and also improves the risk of failure of high-speed rotating parts.
Fifth: Matching oil-cooled flat wire motor. Reduces the peak motor speed requirement, circumvents the high-speed skin effect of flat-wire motors, gives full play to the technical advantages of oil-cooled flat-wire motors, and greatly improves the electric drive system and power density.
Sixth: Reduce system cost. If the same power and economy requirements are maintained, the system cost can be reduced by reducing the motor performance requirements and battery capacity.
3.2 Multi-shift system with clutch and synchronizer
BorgWarner's current two-gear system is divided into two parts in terms of structure. The first-gear system is operated by a multi-mode clutch for gear shifting, and the second-gear system is operated by a wet clutch, while a synchronizer is added to enhance efficiency and realize intelligent disconnection and intelligent parking, and an electronic limited-slip differential can be optionally installed to improve the efficiency of the whole vehicle and the stability of the whole vehicle.
Specifically, the multi-mode clutch can play the purpose of dog teeth + one-way clutch, multi-mode clutch to achieve disconnect mode, will achieve two-way torque through the implementation of the structure, to switch to a one-way clutch mode will fall into the slot, so that it becomes a one-way mode. In addition, integrated disconnect and parking function, through the different clutch mode switching, to disconnect the two gears at the same time this is called intelligent disconnect, which can further improve the efficiency of the whole vehicle.
To achieve disconnection is to simultaneously disconnect and first and second gear this is intelligent disconnection, this process does not require additional execution structure.
Smart park and smart disconnect are reversed first and second gear combined at the same time, so that the smart park function is achieved, all clutches remain in the locked state, this is the smart park mode. The process from first to second gear, the design concept is the design concept of power shifting, the clutch of two gears in first gear, energy recovery can be reversed, in first gear when the multi-mode clutch lock synchronizer disconnected, normally closed clutch disconnected, to open the normally closed clutch, reduce the synchronizer need to shift, the normally closed open when the synchronizer will shift, the synchronizer to shift after the normal Closed clutch returns to the process of shifting to first gear to second gear, and finally to further enhance efficiency, the multi-mode clutch is then switched from single-phase mode to bi-directional to further reduce the loss of multi-mode.
Synchronizer is used with normally closed clutch, there is a scheme of multi-mode clutch with normally open clutch, this time the synchronizer is eliminated. The first is for efficiency considerations, if there is no synchronizer, there is still some internal loss, we will disconnect the synchronizer when the clutch is still closed state, this time is not loss. Add synchronizer to achieve two main functions, one is intelligent disconnection, and another is intelligent parking, without the introduction of additional parking system to achieve the two functions.
3.3 Torque vectoring and disconnection system
BorgWarner's torque vectoring management system has two motives for development: first, to replace the traditional differential with a dual clutch system in electric drive to achieve the role of torque vectoring; second, to integrate the disconnect function, now the application target is electric and hybrid P4 architecture, now this product is still placed on the rear auxiliary drive, so this is why we need the disconnect function for this product. Torque vectoring helps to improve the dynamic stability of the vehicle, integrated disconnect function can improve the efficiency of the vehicle, reduce the vehicle's electricity consumption.
The clutch system inside the electric drive system can also play a role in limiting the torque of the entire transmitter to avoid torque shock.
This system controls the torque distribution between the left rear wheel and the right rear wheel by means of a double clutch, while the traditional rear wheel, the traditional left wheel and the right wheel are realized through a differential, this one is through a clutch, each clutch controls the left and right wheels separately. A series of optimization, the entire disconnect mode dragging torque down to 2NM or less. The maximum torque capacity is 2600NM single side expandable, we are the sixth generation of the actuator and integrated controller, with AUTOSAR, CAN, CANFO and other safety features. About the electric bridge disconnect system, now for the electric 4WD auxiliary drive of this efficiency improvement, auxiliary drive non-working state for the whole vehicle torque or power loss reduction there are two programs, one is to use induction motor, and then is the use of this synchronous motor + dynamic system, the program is synchronous motor + dynamic system.
Through the simulation of the system, including communication with various customers, we now conservatively estimate that the system can save the energy consumption of the whole vehicle by about 1%-5%, and we are now conducting road tests with some customers, and the results we get now are much better than 5%.
3.4 Multi-gear gearbox without clutch and synchronizer
No matter what the motor does, no matter 20,000 rpm or 30,000 rpm, the two-speed gearbox can always widen the torque speed range, which in turn can further improve the driving speed, climbing degree and driving time of the whole vehicle, which are the evaluation indexes of power, and also can change the working point of the motor through gear shifting to make it more efficient.
The speed ratio of the first gear can be made larger, and the maximum torque of the motor can be lowered, thus reducing the total volume and cost of the whole powertrain, and because there is a neutral gear after two gears, it is more convenient for the maintenance of the whole car.
When there is only one gear, the working area is more inclined to the low-efficiency area. If there are two gears, the working point can be moved to the high-efficiency area with equal power, thus improving efficiency.
The range improvement is more than 10% for commercial vehicles and 7% for passenger cars when compared with no gear change.
Commercial vehicles should return to the more mass-produced, more mature parallel shaft mechanical transmission, very high efficiency.
Further is the parallel shaft mechanical transmission without clutch, in electric vehicles, with clutch, motor speed and clutch control are challenges, if the clutch is removed, the clutch of the three roles of the motor can also be completed, the clutch is removed, the cost can be reduced, the structure is more compact, reliability is also greatly improved.
Central drive is a very common configuration in commercial vehicles, that is, the drive motor and mechanical transmission, arranged together to drive our rear axle through the drive shaft. The advantage is that the separation and engagement of the clutch is eliminated, and the motor can be actively synchronized to achieve the control of gear shifting. But there is a problem, the inertia of the motor rotor rotation is really large, and the rotational inertia of the transmission input will increase significantly, which will lead to a longer power interruption, because the synchronization capacity will increase and the synchronizer wear will be more serious, and this time the active synchronization control of the motor has to be used.
In a conventional fuel car AMT inside there is a clutch, when shifting you only need to control the shift force inside the transmission. If there is a synchronizer inside the system, just take the clutch out, this is possible to do active synchronization control, control its relative speed.