Research On Gear-shifting Strategy And Key Parameters For Automatic Mechanical Transmission Of Heavy Truck

Automatic transmission can improve driving facilities and reduce driver fatigue.With rapid development of the transportation industries and national economy level in our country,the share of trucks equipped with automatic transmissions is raising.As the key technology of automatic transmission,gear-shifting strategy should be highly intelligent that can adapt to the characteristics of vehicles,meet the requirements of different driving environment and driving intention.The gear-shifting strategy of truck needs to pay more attention to the economic and dynamic characteristics of the vehicle in addition to have the common characteristics of the common gear-shifting strategy.Based on a full investigation of the characteristics of heavy trucks and combined with the development status and future trends of gear-shifting strategy,this research identifies influencing factor to the gear-shifting strategy and designs new gear-shifting for heavy trucks.The contents of this research mainly include:(1)Shift schedule and vehicle simulation model were built up in view of the target vehicle.According to the size parameters,engine torque and fuel characteristics of the target heavy truck,dynamic shift schedule and economical shift schedule were established;Trucksim/Matlab softwares were used to establish simulation model of vehicle powertrain and shifting logic system which could provide the simulation basis and platform for the design and performance verification of the later gear-shifting strategy.(2)In order to solve the problem of power loss caused by the frequent shift of heavy truck which has dozens of gears,a skip gear-shifting strategy was put forward.Firstly,reasonable gear for starting was set up under different loads in order to reduce the number of shift when truck speed increased from zero to a stable value.Then in the process of running,the skip gear number was determined during one shift according to the vehicle acceleration in order to reduce the number of shift action.In order to minimize the number of gear change in the ramp,a skip down shift strategy was designed with estimating the number of gear change and considering the range of engine speed for the truck driving into the ramp with high speed and needing to shift down.(3)As the load of heavy truck often changed and shift cycle was usually occurred when the truck drove on ramp,a kalman filter recognition based on the truck load forecast was used to identify load and road slope.During the period of shift,the power transmission of AMT was interrupted and truck load was estimated.Then the estimated result was set to be as the initial load value in kalman filter to shorten the convergence time.A truck traveling data were used to verify this method offline and the results showed that it can quickly and effectively identify the vehicle load and road slope.(4)In view of using gear-shifting strategy to ensure sufficient power to the truck while keeping low fuel consumption as much as possible,a gear-shifting strategy based on predictive geographic information was put forward.According to the geographical condition of the road in front of the truck within a certain distance,through the power performance and fuel economy performance of building comprehensive optimization index,dynamic programming was used to calculate the optimal shifting strategy.By adjustment of the weight coefficient,an optimized gear-shifting strategy could meet the dynamic demand of road circumstances and as the same time meet the fuel-efficient demand of the truck in the predicted range.(5)In order to solve problems of unexpected up shift for automatic transmission vehicles in cornering driving,a gear shifting strategy using information of bend radius and distance of the vehicle to the curve was proposed.First,vehicle dynamic in curve was analysised and truck modeling in the curve was built.Then through observation of vehicle cornering experiment,security shift gear shift index and physiological index were put forward.Downshift time coefficient which could adjust the shift point in advance was designed based on the physiological index and security index.(6)When the truck was climbing,an anthropomorphic gear-shifting strategy was designed by using predictable geographical information on ramp.According to the characteristics of driving uphill operation,upshift was delayed within a specified range when the driver increased throttle before drove into the ramp.Gear shift was canceled or delayed when the truck was leaving the ramp in order to make the gear shift consistent with the driver's intention,and conducive to vehicle ramp running.In the road conditions of downhill,gear strategy of engine auxiliary brake was studied.Through the vehicle dynamics on downhill,the required brake power was analysised.By bench experiment,the target engine braking ability was obtained.According to the required brake power and the target engine braking ability,the gear position to maintain a steady speed could be calculated.At the same time,braking stability of the truck was analyzed and considered in the shift strategy when the engine auxiliary brake was added to the truck.(7)In the condition of no access to connection of geographic information to the gear shift control system,a test in skid pad with planned traveling track is designed to prove the effectiveness of the shift strategy test based on geographic information.