Control technology of the hottest hydraulic automa

Control technology of hydraulic automatic transmission

1 Preface

the basic form of automatic hydraulic transmission is that the hydraulic torque converter is connected in series with the rotating shaft mechanical transmission with power shift. Because it has good automatic adjustment and adaptability to external load, it makes the vehicle start smoothly and accelerate evenly. Its damping effect reduces the dynamic load and torsional vibration of the transmission system, extends the service life of the transmission system, and improves the riding comfort, driving safety, trafficability, and the average speed of the vehicle. The efficiency of automatic transmission is lower than that of mechanical transmission, which has been an important reason for its development. In order to solve this problem, the hydraulic automatic transmission has adopted many methods, such as multi-component working wheel hydraulic torque converter, lockup clutch, increasing the gear position of planetary gear transmission, electronic control and so on, so that its comprehensive economic performance has been improved. The most effective one is that in the past decade, a large number of electronic technologies have been applied in control, which has brought the performance of hydraulic automatic transmission to a new level. The main work in this area includes: shift point control, torque converter lockup clutch control, shift quality control, etc

a typical hydraulic automatic transmission control system is shown in Figure 1, which mainly includes input signal sensor and switch, electronic control unit and output actuator. The sensors include engine speed, load and temperature sensors shared with the electronic fuel injection engine control system, sensors for measuring the output speed of the transmission, as well as selector lever position, shift mode, forced low gear switch, etc. The electronic control unit is composed of i/o interface, CPU and memory (ram/rom), and its function is to determine the best gear and whether the torque converter is locked. The realization of the action depends on the electromagnetic hydraulic valve

2. Control of shift point

shift point is a function of transmission output speed, engine load, selector position switch and shift mode switch. For example, if the driver can place the selector lever in the "d" position and select the "E (economy)" mode, the shift point is determined by the shift diagram shown in Figure 2. The abscissa in the figure is the transmission output shaft speed (equivalent to vehicle speed), and the ordinate is the engine throttle opening (equivalent to load). The curve,, in the figure corresponds to the shift point during upshift, and the curve,, 2-L corresponds to the shift point during downshift. When the vehicle speed increases, as long as the operating point determined by the engine load and transmission output speed crosses the corresponding upshift curve to the right, the transmission will automatically upshift by one gear. When the vehicle speed decreases, as long as the operating point determined by the engine load and transmission output speed crosses the corresponding downshift curve to the left, the transmission will automatically downshift by one gear. It can be seen from the curve shape that the higher the engine load, the higher the vehicle speed when upshifting or downshifting, so as to ensure the dynamic performance of the vehicle when driving at a high load and low gear. Due to the limitation of the memory space of the control unit, the upshift and downshift curves in the shift diagram are not continuous and smooth like those in the past hydraulic control methods, but often in a step shape

3. Control of lockup clutch

in order to improve the efficiency of automatic transmission, the hydraulic torque converter can be locked. The locking work is completed by the lockup clutch, which is jointly controlled by engine load, output shaft speed, gear and shift mode

the lockup clutch is electronically controlled, that is, the electromagnetic induction sensor provides the speed signal of the transmission output shaft, the throttle position switch provides the engine load signal, plus the shift lever position and mode switch signal, which are transmitted to the control unit for processing and control. The actuating elements include switch type solenoid valve and pulse type solenoid valve. The latter mainly controls the oil pressure applied by the piston of the lockup clutch to improve the comfort of changing from hydraulic transmission to mechanical transmission. Although the locking of the locking clutch can be carried out in all gears, it is actually limited to the third and fourth gears. 6. Beverage packaging tightening/bursting force test gear. The two groups of dotted lines and dotted lines in Figure 2 are the locking and disengagement curves of the lockup clutch. When the operating point determined by the engine load and transmission output speed crosses the dotted line to the right, the lockup clutch locks up and turns from hydraulic transmission to mechanical transmission. Due to the decrease of vehicle speed or the increase of engine load, when the working point determined by engine load and variable speed output speed crosses the point line to the left, the lockup clutch is separated and the mechanical transmission is changed into hydraulic transmission. However, during the transformation of the two transmission conditions, the change of the speed ratio causes the transmitted torque to produce a step, which causes the dynamic load of the transmission system and affects the ride comfort. Therefore, the selection of locking operating point has become a key problem

this problem can be well solved by using pulse solenoid valve. Pulse solenoid valve is composed of solenoid coil, armature, valve core, etc. its function is to control the oil pressure in the oil circuit. Different from the ordinary switch solenoid valve, the electrical signal controlling the operation of the pulse solenoid valve is not a constant voltage signal, but a pulse electrical signal with a fixed frequency. The solenoid valve opens and closes the oil drain hole repeatedly under the action of pulse electric signal. The computer changes the pulse width, or the time ratio of current on and off in each pulse cycle, that is, the so-called duty cycle (defined as in a pulse cycle, the duration of power on is a, and the duration of power off is B, then the duty cycle =a/(a+b) × 100%, so its variation range is%) to change the time ratio of solenoid valve opening and closing, so as to control the oil circuit pressure. The larger the duty cycle, the more hydraulic oil will be discharged through the solenoid valve, and the lower the oil circuit pressure; On the contrary, the smaller the duty cycle, the higher the oil circuit pressure

in order to take advantage of the soft force transmission characteristics of the hydraulic torque converter, the lockup clutch can also be disengaged for a short time during gear shifting to make the hydraulic torque converter work

4. Control of shift quality

shift quality mainly depends on the smoothness of planetary gear meshing. As shown in the schematic diagram of planetary gear transmission in Figure 3, the second gear is the combination of the high gear of the front planetary row and the first gear of the rear planetary row, and the control elements that need to work are C2, B0 and F2. The third gear is composed of the low gear of the front planetary row and the second gear of the rear planetary row. The control elements that need to work are C0, C1, B2, F0 and F1. When the second gear is shifted to the third gear, the two planetary gears must be synchronized in the opposite direction, that is, when the transmission is shifted from the second gear to the third gear, the front planetary gear must be upshifted, and the rear planetary gear must be downshifted, both of which must be carried out at the same time. The key here is that the release of brake B0 and the combination of B2 should be carried out at the same time, otherwise it will cause gear shift interference or short-term power interruption

three measures are commonly used to improve the shift quality: first, torque reduction control of the engine during shift; The second is the main oil pressure control; The third is to separate the lockup clutch for a short time during gear shifting, so that the hydraulic torque converter works and plays the role of gently transmitting power. The first two measures are mainly introduced below

engine torque reduction control is to reduce the torque generated by the engine. The purpose of controlling the engine torque during the loaded upshift is to reduce the energy dissipated by the friction elements during the shift. It is achieved by reducing the torque generated by the engine during gear shift synchronization, without the need for increasing the need for metal copper in many industries to interrupt power. The purpose of controlling the engine torque when downshifting with load is to suppress the shivering caused by the one-way clutch and friction elements during gear shifting. The usual way to reduce engine torque is to delay the ignition time

change of vehicle longitudinal acceleration during upshift with and without engine torque control. When there is no engine torque control, in order to control the clutch slip time within 500ms, it is necessary to increase the torque during the slip period, which will cause a large torque jump at the end of the shift, causing changes in longitudinal acceleration and affecting comfort. If the maintenance cost is also eliminated, the engine torque is reduced by 50% with the same slip time, and the clutch oil pressure is significantly reduced, the acceleration during the shift is similar to the level before the shift, and the torque jump at the end of the shift is also small, which improves the shift quality and reduces the load of the friction elements within the same time

the purpose of main oil pressure regulation and control is to accurately match the working oil pressure of relevant shift friction elements with the input torque of the transmission. The specific method is to divide the working oil pressure into two parts: one is the fixed foundation pressure; The other part is the pressure that can be adjusted by the electrohydraulic switching valve. The input torque of the transmission can be accurately calculated by parameters such as engine air intake, engine speed, torque converter speed ratio and so on. Thus, in different gears, the pressure parameters can be adjusted according to their working conditions. Another is to adopt closed-loop control for the oil pressure of the shift clutch to make the angular acceleration of the input shaft within the specified range

in order to smoothly shift the planetary gear transmission from second gear to third gear, the shift process of the front and rear planetary rows can be monitored to accurately control the oil pressure of brakes B0 and B2 in real time. For example, the speed of the front planetary sun gear (that is, the speed of brake B0) of Toyota A350 automatic transmission is taken as the speed signal of the input shaft of the automatic transmission and collected by the input speed sensor. In addition, a sensor is added to measure the speed of the rear planetary row sun gear (that is, the speed of brake B2). When changing from second gear to third gear, the cylinder of brake B0 must be pressurized and the cylinder of brake B2 must be depressurized. In the traditional hydraulic control system, the oil cylinders of brakes B0 and B2 are connected to the accumulator, and the oil pressure of the accumulator is adjusted by the pulse solenoid valve controlled by the computer. Therefore, as long as the back pressure of the accumulator changes, the oil pressure of brakes B0 and B2 will change, so they cannot be controlled independently. If the oil circuit is changed appropriately, when the transmission is shifted from second gear to third gear, the accumulator is cut off from the return oil circuit of brake B0, and the oil pressure of brake B0 is controlled by the pulse solenoid valve of torque converter lockup clutch (at this time, the lockup valve of lockup clutch is in the off state, and the lockup clutch does not work), so brakes B0 and B2 can be controlled separately. The oil pressure of B2 begins to rise, and the torque transmission gradually changes from one-way clutch F2 to brake B2. When the effect of F2 on torque transmission is completely lost, the rear planetary row begins to shift, the oil pressure of brake B0 begins to adjust, the front and rear planetary rows shift at the same time, the front planetary row has completed the shift, and the rear planetary row continues to shift. In this way, due to the precise control of the oil pressure, the shift time is short, and the torque dynamic load of the output shaft is small, realizing a smooth shift

5. Application of other control technologies

other control technologies are also applied in modern automatic transmission, mainly including:

A) adaptive control

adaptive control has roughly two kinds: dynamic control and steady-state control

dynamic control is mainly used to monitor the transmission ratio during gear shifting, and as described above, it is used to accurately control the shift oil pressure. The steady-state control mainly considers the influence brought by the change of the friction coefficient of the friction plate material of the actuator. The first is the influence of temperature. This can be done by installing a hydraulic oil temperature sensor in the automatic transmission oil tank, so that the factor that the friction coefficient of the material changes with the increase of oil temperature can be corrected in the computer control program. The second is the influence of the reduction of friction coefficient. There are two reasons for the reduction of the friction coefficient. The first is the possible leakage. The leakage of the clutch will reduce the capacity, causing the friction plate to slip and heat, and then