Shift characteristics analysis and smooth shift for an automatic power transmission

Smooth shift is one of the key issues in automatic power transmission control systems. However, the torque sensors are too expensive to be used in shift controllers on production vehicles. In order to provide a basic strategy for smooth shifting by using RPM sensors only and in order to accomplish the shift within a designated time, this paper studies detailed characteristics of the smooth shift for clutch-to-clutch shift mechanism. A desired trajectory of slip speed is proposed for smooth acceleration shift defined in this paper. Also the clutch torque needed to achieve this trajectory is derived, and it may be used as a open loop shift control law.     

On the instantaneous and average piston friction of swash plate type hydraulic axial piston machines

Piston friction is one of the important but complicated sources of energy loss of a hydraulic axial piston machine. In this paper, two formulas are derived for estimating instantaneous piston friction force and average piston friction moment loss. The derived formula can be applicable for piston guides with or without bushing as well as for axial piston machines of motoring and pumping operations. Through the formula derivation, a typical curve shape of friction force found from several experimental measurements during one revolution of a machine is clearly explained in this paper that it is mainly due to the equivalent friction coefficient dependent on its angular position. Stribeck curve effect can easily be incorporated into the formula by replacing outer and inner friction coefficients at both edges of a piston with the coefficient given by Manring (1999) considering mixed/boundary lubrication effects. Novel feature of the derived formula is that it is represented only by physical dimensions of a machine, hence it allows to estimate the piston friction force and loss moment of a machine without hardworking experimental test.     

Novel torque motor model for performance design and analysis of a servo valve with permanent magnets

Servo valves are widely used for modern hydraulic actuator control. This valve consists of a torque motor with permanent magnets. In present study, a novel torque motor model is derived by considering magnetic flux leakage and demagnetization effect of the permanent magnets involved in the servo valve. The derived model was validated by comparing experimental data with the model calculation represented with physical parameters. Since these two important physical phenomena, missing in the previously well-known model, are considered in the newly derived torque motor model, it can be used for the physical parameter design of a torque motor and the analysis of a servo valve controlling electro-hydraulic servo systems.

     

Friction coefficient, torque estimation, smooth shift control law for an automatic power transmission

For shift quality improvement, torque sensors are currently too expensive to be used on production vehicles. To achieve smooth acceleration shift, the reference trajectory of the clutch slip speed for accomplishing the shift process within a designated shift completion time and its relationship with the clutch actuating torque were suggested by Jeong and Lee (1999). In order to facilitate the proposed algorithm, nonlinear estimators for necessary information such as the axle shaft torque, clutch friction and turbine torque were designed using only speed sensors. Accounting for the modeling error, a control law for this indirect smooth shift was proposed based on the above mentioned suggestions. Simulation results of the proposed estimators and shift controller were presented and further considerations for practical applications are discussed.     

A novel performance model given by the physical dimensions of hydraulic axial piston motors: Experimental analysis

Huhtala (1997) discussed the strength and weakness of some existing models for hydraulic piston machines and unfortunately concluded that any model is not accurate enough for wide operating ranges. As an effort to develop an accurate model applicable for wide operating range, Jeong (2006) proposed a performance coefficient model for a hydraulic axial piston motor of swash plate design, which is given by the physical dimensions. In this paper, validity of the new performance model is addressed through experimental analysis. Estimation process for model parameters is established and thenperformance decision parameters are estimated from efficiency measurement data for a test motor. As the result, maximum and average efficiency estimation error over wide operating ranges of speed 300–2700 RPM and pressure 20–300 bar are just 2.33% and within 0.30%, respectively. Hence, it can be said that this paper opens a door toward developing true performance estimation model.     

A novel performance model given by the physical dimensions of hydraulic axial piston motors: Model derivation

Since Wilson (1948) had firstly developed steady-state flow rate and moment loss model for hydraulic piston machines, several authors tried to make precise performance models. However, Huhtala (1997) discussed the strength and weakness of some existing models comparing with measurement data and concluded unfortunately that any model is not accurate enough for wide operating ranges. For a hydraulic axial piston motor of swash plate design with rotating cylinder, new performance formula is derived in this paper through theoretical study on leakages and friction losses of three facing gaps and other non-negligible losses. And efficiency surface of an example motor is estimated and extension of the formula for hydraulic pumps is discussed. A novel feature of the derived model is that all coefficients are given by the physical dimensions of a motor, hence allowing calculation and analysis of the performance of a motor in mind.