T.W.G.L. Klaassen

ANALYSIS OF SLIP IN A CONTINUOUSLY VARIABLE TRANSMISSION

High clamping force levels reduce the efficiency of the Continuously Variable Transmission (CVT). However, high clamping force level are necessary to prevent slip between the belt and the pulleys. If a small amount of slip is allowed, the clamping force level can be reduced. To achieve this, slip in a CVT is investigated. From measurements on an experimental setup, Traction curve data and efficiency measurements are derived. A model describing slip in a CVT is verified using measurements with a belt with increased play. It is found that small amounts of slip can be controlled in a stable way on the setup. The traction curve was mostly dependent on the CVT ratio. Efficiency is found to be highest for 1 to 2% slip depending on the ratio. The model is in reasonable agreement with the measurements.Copyright

Performance optimisation of the push-belt CVT by variator slip control

Continuously variable transmissions (CVTs) are applied in an increasing number of vehicles. Large ratio coverage allows for reduced engine speeds, which adds to both highway driving comfort and reduced fuel consumption. It becomes increasingly important to further improve the performance in terms of efficiency, robustness and torque capacity of the CVT. This paper describes the possibilities of improving the CVT by minimising variator clamping forces. This is accomplished by using slip control technology. This technique allows for the best possible transmission efficiency, combined with improved robustness for slip damage. This paper first describes the relation between variator slip and functional transmission properties. The conditions for optimum performance regarding efficiency and robustness are identified. This leads to the development of a variator slip controller. The remaining sections describe experimental results on two test rigs and in a production vehicle. The paper concludes with an outlook into further developments.

Nonlinear stabilization of slip in a continuously variable transmission

One way to predict and control the output torque of a geared neutral CVT is to use the relationship between slip in the variator and transmitted belt torque. This relationship is often referred to as the traction curve. For small slip values, the output torque increases almost linearly with slip. However, at approximately 2% slip, the maximum output torque is reached. For larger slip values, the output torque shows even a decline. Hence, measuring the traction curve in open loop is not possible. Stability analysis shows that by modifying the plant with a nonlinear feedback control torque depending on the slip, a stable closed loop plant with two new defined inputs is obtained. An open loop input torque at this plant now uniquely defines the slip in the system. The primary shaft angular velocity is controlled using a robust stabilizing controller. This controller is tuned using measured frequency response functions at different slip values.

Shift dynamics modelling for optimisation of variator slip control in a pushbelt CVT

Efficiency improvement of the pushbelt CVT by reducing variator clamping forces is well established. The increased risk of gross belt slip calls for novel approach, including direct control of belt slip. First attempts led to promising results in steady state conditions, but unacceptable slip occurred during fast shifting events. In this work theoretical variator shift models are validated. Results are used for model optimisation of the variator shift dynamics, leading to an optimised CVT slip controller. Results of the experiments after implementation in a test vehicle are presented. A comparison is made to the results obtained with the previous controller.

Simulated behaviour of a vehicle with V-belt geared neutral transmission with variator slip control

Abstract Combining both launch and reverse drive functions with the ratio change function in a geared neutral continuously variable transmission (GN-CVT), thus making a launch device like a torque converter and a drive-neutral-reverse (DNR) set obsolete, is attracting considerable attention. This paper covers the modelling and simulation of a V-belt geared neutral transmission in and around the geared neutral point. Owing to the specific nature of the geared neutral state, conventional driveline simulation models are shown to be inadequate. Experimental results are presented, allowing a more detailed description of the functional properties of the V-belt variator, especially those related to small amounts of slip between the belt and the pulleys. The measured data will be analysed to obtain grey model fitting parameters, which allow the data to be used in a simulation program based on a dynamic driveline model. It will be shown that, with a GN-CVT, stall and launch performance can be considerably better than that achieved with a driveline with a torque converter (TC).

Modeling and simulation of an electro-mechanically actuated pushbelt type continuously variable transmission

For analysis, control design and testing of an electro-mechanically actuated CVT, a simulation model is built. The model incorporates all major driveline components and a new proposed actuation system with servomotor actuation. The clamping forces in the variator are calculated using an explicit formulation of a model based on Coulomb friction. The model also includes slip and shifting losses based on transient variator models. Results show realistic behavior of the CVT. In comparison with a conventional hydraulically actuated CVT, this electromechanical system consumes very little power and achieves a high actuation performance.

The Empact CVT: modelling, simulation and experiments

This paper shows the implementation of a simulation model for new electromechanically actuated metal V-belt type Continuously Variable Transmission (CVT), referred to as the Empact CVT. An analysis of the dynamics of the actuation system and of the driveline shows that the eigenfrequencies of the system depend on both the CVT ratio and the slip in the variator. An accurate variator model is required to incorporate all characteristic dynamics. The implemented variator model is an explicit formulation of a model which gives an estimation of the tension forces and compression forces in the pushbelt. The simulation model also includes slip, shifting losses based on transient variator models and friction. Simulations are compared to measurements, showing good results.