Cam Lift Research Articles

Design and characteristic analysis of a novel deformation-controllable piezoelectric vibration energy harvester for low frequency

Vibration energy harvesting using the piezoelectric effect is becoming a promising solution to the sustainable green power source for low-power portable and wireless electronics. To harvest low-frequency vibration energy and prevent the damage of piezoelectric vibrator due to the excessive deformation, a novel deformation-controllable piezoelectric vibration energy harvester (D-CPVEH) by using a wedge cam to limit the maximum deformation of the cantilevered piezoelectric vibrator is proposed in this paper. The cam structure can drive the pre-bending piezoelectric vibrator to produce a controllable-amplitude and unidirectional deformation, thereby improving the reliability of the harvester significantly. To verify the feasibility of the proposed principle and design, theoretical analysis and numerical simulation are firstly performed, and then the influences of system parameters on the dynamic response of the D-CPVEH are analyzed in terms of amplitude ratio of the cam and deformation of the vibrator. Afterwards, a prototype is fabricated and tested in terms of frequency response characteristics. The simulation and experimental results show that the maximum deformation of the piezoelectric vibrator can effectively be limited by introducing the cam structure. Besides, it demonstrates that the spring stiffness, additional mass, cam lift, cam angle and excitation frequency exert a significant effect on the amplitude ratio of the cam, the deformation of the piezoelectric vibrator, the output voltage and the maximum voltage of the harvester, and the optimal operating bandwidth. The maximum generated voltage increases while the corresponding optimal operating bandwidth decreases with the increase of the cam lift. It is found that the maximum voltage is basically independent of other structural parameters except for the cam lift. Furthermore, the optimal operating bandwidth can be effectively adjusted by the spring stiffness, additional mass and cam angle to adapt to the broadband low-frequency vibration environments. The testing result shows that the D-CPVEH can achieve the maximum power of 2.58 mW at 5.5 Hz with the optimal load resistance of 30 kΩ.

Design and characterization of an amplitude-limiting rotational piezoelectric energy harvester excited by a radially dragged magnetic force

In order to avoid the damage of piezoelectric vibrator due to excessive deformation during resonance, an amplitude-limiting rotational piezoelectric energy harvester excited by a radially dragged magnetic force was presented in this paper. The amplitude-limiting device consisted of two springs and a wedge cam to limit deformation of the piezoelectric vibrator. Simulation analysis and tests were carried out to obtain the influence of system parameters on the response characteristics of the piezoelectric vibrator. The results showed that the amplitude-limiting device could effectively limit the maximal deformation and output voltage of the piezoelectric vibrator. The maximum generated voltage increases with the increases of the wedge cam lift, but the optimum speed range decreases. The effective speed range increased with the decreasing number ratio of exciting magnets and the rising spring stiffness. Moreover, a combination of a high-stiffness return spring and a low-stiffness buffer spring is helpful to enhance the effective speed range and to decrease the fluctuation of output voltage. Therefore, the energy generation capability and bandwidth of the energy harvester could be effectively improved through reasonable parameter matching. Under the load resistance of 40 kΩ, the maximal output power of 2.3424 mW is achieved at the rotating speed of 183.7 rpm.

A cantilevered piezoelectric energy harvester excited by an axially pushed wedge cam using repulsive magnets for rotary motion

Harvesting energy from the rotary environment to replace the conventional electrochemical batteries has gained considerable interest. Different from the existing rotation-induced energy harvesters based on the bidirectional deformation of piezoelectric vibrators, a novel cantilevered piezoelectric energy harvester excited by an axially pushed wedge cam using repulsive magnets for rotary motion was presented and fabricated in this paper. The new piezoelectric rotary energy harvester (PREH) was characterized by the simultaneous realization of unidirectional deformation and limited amplitude for piezoelectric vibrators. To verify the feasibility of the proposed principle and design, a theoretical model was established based on Fourier series as well as superposition principle. Meanwhile, the influence of the system parameters on the response characteristic of the presented PREH were obtained by simulation. And then, the experiments of rotating speed response were performed to evaluate the energy harvesting performance in terms of the deformation and open-circuit voltage. Both simulation and experimental results showed that the amplitude of the piezo-cantilever could be limited by using the cam mechanism and there were obvious resonance peaks on the amplitude-rotary speeds curves. Thus, the relatively stable output voltage could be maintained over a broad rotating speed range. Also, the stable voltage increased with the increasing of cam lift, but the effective rotating speed range became narrow. With the increasing of the cam angle, the effective rotating speed bandwidth could be increased, whereas the self-locking phenomenon of the piezo-cantilever would occur when the angle was increased to some extent. Besides, the bandwidth could be adjusted by changing the number of exciting magnets and stiffness of cam system. Under the optimum matching parameters, the maximum power 10.88 mW was reached for the presented PREH.

A low-order adaptive engine model for SI–HCCI mode transition control applications with cam switching strategies

This article presents a low-order engine model to support model-based control development for mode transitions between spark ignition (SI) and homogeneous charge compression ignition (HCCI) combustion modes in gasoline engines. The modeling methodology focuses on cam switching mode transition strategies wherein the mode is abruptly changed between SI and recompression HCCI via a switch of the cam lift and phasing. The model is parameterized to a wide range of steady-state data which are selected to include conditions pertinent to cam switching mode transitions. An additional HCCI combustion model parameter is augmented and tuned based on transient data from SI to HCCI mode transitions where the conditions can be significantly outside any contained in the baseline steady-state parameterization. An adaptation routine is given which allows transient data be assimilated in online operation to update the augmented parameter and improve SI–HCCI transition predictions. With the baseline steady-state parameterization and augmented mode transition parameter, the model is shown to reproduce both steady-state data and transient performance output time histories from SI–HCCI transitions with considerable accuracy.

Design of a variable valve hydraulic lift system for diesel engine

A continuous variable valve lift (VVL) mechanism for a diesel engine is proposed in this research. The hydraulic mechanism, which consists of a driving plunger, a driven plunger, a hydraulic cylinder, and a hydraulic oil tank, is the key part of the VVL mechanism. Simulation is conducted to study the relationship between maximum valve lift and rotation angle of driving plunger. Calculation results indicate that the maximum valve lift decreases with increasing rotation angle. A prototype was manufactured and successfully tested in a single-cylinder diesel engine. The experiments, which were conducted at different rotation angles of the driving plunger, validate the accuracy of the calculation results. The difference between experimental valve lift curve and cam lift curve is considered the result of oil leakage. Rotating the driving plunger is an effective method to regulate valve lift. Working stability of the VVL mechanism is validated through a multi-cycle operation. Experimental results indicate that the VVL mechanism is effective and reliable for realizing continuous VVL in engines.

COMPUTATIONAL TOOL FOR SIMULATION OF THE DYNAMIC RESPONSE OF VALVE TRAIN

This paper presents the development of the MOTORI 2004 computing tool that calculates the distance, speed and acceleration of a car engine valve train’s oscillating mass m, which is reduced to the valve axis. Distance diagrams, speed and accelerations are provided in dependence on the camshaft twist angle at a constant rotational speed in several consecutive revolutions. The computing tool implements a mathematical description and numerical solution for the motion of mass m of a valve gear dynamic model. Valve lift h is given numerically using a series of equidistant points in the period of one camshaft revolution. The variabilities of camshaft rotation and spring thread vibration as a result of cam lift harmonic excitation. The computing solutions were tested at valve opening points and in imaginary extreme operating conditions - soft/hard spring, low/high damping, low/high rotational speed and increased clearance.

Development of Variable Valve Actuation Mechanism for Multi-cylinder SI Engine

Engine designers are prompted to consider Variable Valve Actuation system because of the inherent compromises with fixed valve events. The major goal of a VVA mechanism is to control the amount of air inducted into the engine. In this paper, a novel two-step VVA mechanism is presented to facilitate the variation in valve timing and lift of base engine. This mechanism helps the engine breathe effectively by changing the valve timing and lift after the set switch-over engine speed by dividing the operating range of engine in two zones viz, low speed and high speed zone. A simple, cost effective and feasible option to incorporate both low lift cam and high lift cam is presented in order to vary intake valve timing for improving engine breathing during low-speed low-load operation, and high-speed full-load operation. The engine is simulated in 1D simulation software GT suite to identify the potentials of variable valve actuation. The software is used to find suitable valve timings and lifts for low and high speed zone and the switch-over point engine speed. The simulation model has shown an average improvement in volumetric efficiency by 2.8%.

DYNAMICAL SIMULATION OF A VALVETRAIN MECHANISM: AN ENGINEERING EDUCATION APPROACH

The present work aims to present a valvetrain model considering the dynamics functioning aspects of an Otto’s engine. The model will be constructed using Adams/View® software, which is a powerful modeling and simulating environment of dynamic systems. It allows building, simulating, refining and optimizing any mechanical system. In fact, the model will help engineering students to understand how the mechanism works, in terms of displacement, velocity and acceleration of the valve as a function of the time. It is also possible to know the behavior of the force in the spring as a function of the time and, finally, the torque applied in the cam due to a angular velocity input. Relative to spring force, during the Otto engine cycle, the cam lobe must be able to open and close the valve as fast and as smoothly as possible. The force responsible to close the valve is applied by the valve spring, which is also responsible for keeping contact between the cam lobe and the valve. Dynamic forces impose limits on cam and valve lift. Thus, the simulation model allows determining these forces and displacements through the cam rotation. As main objectives the authors wish to make available a model which is capable to show in 3D the animation of a valvetrain mechanism of an Otto engine, obtaining the main curves for analysis and evaluation of this mechanism performance.

Application of Cam Lift Fitting Method Based on Alternative-point Interpolation in Grinding Process

On the basis of previously study on optimization of cam lift fitting,based on the cubic spline curve fitting method,a new method using the odd-even alternative-point interpolation for the lift fitting of cam curve is proposed.The method requires several cycles of interpolation fitting process.Through setting fitting accuracy threshold and importing maximum cycle times,lift fitting error controlling and algorithm's termination are realized.Numerical analysis comparison between new methods and parametric cubic spline curve fitting method is conducted by using Matlab programming.The results show that the new method can significantly improve the smoothing degree of the original lift curve and its first order,second order differential.In NC cam grinding process,the continuity of the grinding carriage feed rate and acceleration are improved,meanwhile,the feed shaft flexible impact and the tracking error are reduced.Experiments are accomplished using the results of the approach on TKM120 CNC camshaft grinder.Compared to the process result of cubic parameter spline curve lift fitting,the experimental results show that the new approach can significantly improve the surface quality and the contour accuracy.

Cam Grinding Interpolation Research Based on Cubic Non-Uniform Rational B-Splines

With the development of auto industry and aviation industry,the cam quality requirements higher and higher. The NURBS curve has excellent natures that can smooth the cam grinding path and improve its processing quality. Combined with existing CAD software and CNC systems, respectively, from reverse and forward two aspects of NURBS curve to illustrate the non-uniform B-spline principle and given the relevant formulas. Choosing X-C coordinates points of the cam grinding as the research object, adopt reverse and forward NURBS curve interpolation to fit the cam grinding path. Analysed the fitting error caused by line segment fit NURBS curve and cam lift error caused by NURBS interpolation. Summarized the advantages and disadvantages of two ways Nurbs interpolation discussed the method to improve NURBS interpolation for cam grinding.

Mechanical Spring Replacement With Pneumatic Return Device in a Valve Train: Effects on Dynamics and Preload Tuning

The paper presents a comparison of performance for a cam transmission of an engine valve train operating with a mechanical spring and with a return spring device that uses a pneumatic spring. Dynamic analysis of the cam mechanism is performed in the frequency and time domains employing a combined lumped-distributed parameter model capable of predicting the effects of the higher harmonics of the cam lift profile on system performance, in particular of the return spring device. Dynamic stiffness of the transmission in the frequency domain and time history of the contact force between cam and follower are evaluated. The limits of the traditional mechanical spring-closing system at high-speed camshaft operations are investigated, highlighting that they are mainly imposed by the internal resonances of the spring. The pneumatic spring is an improved replacement of the steel spring because of better dynamic behavior. Furthermore, the pneumatic return device allows preload tuning of the spring, which may increase transmission efficiency through proper control of the fluid pressure. Study of the pressure control circuit is also presented.

Vane Pump Theory for Mechanical Efficiency

This paper describes the theoretical analysis on the mechanical efficiency of a hydraulic-balanced vane pump and presents a design concept to decide values such as vane thickness and cam lift to improve its mechanical efficiency. In this paper, the friction torque characteristics of the balanced vane pump, especially the friction torque caused by the friction between a cam contour and vane tips are both experimentally and theoretically investigated. Although the friction force increases with vane thickness increase due to increase in the vane force, the mechanical efficiency of the vane pump does not decrease when the cam lift becomes large as the vane thickness is increased. An important parameter ∊ defined as the ratio to be obtained by dividing the cam lift by the vane thickness determines essentially the mechanical efficiency of the vane pump. The pumps with the same ∊ have the same mechanical efficiencies, even if the cam lift or the vane thickness varies. A larger value of ∊ leads the vane pump to obtain a higher mechanical efficiency although the limit of vane strength governs the upper limit for ∊. Additionally, reducing the friction coefficient of the vane tip contributes to improvement of the mechanical efficiency.

Engine Valve Lift and Phase Control System

A new type engine valve control system has been presented, in which both valve lift and phase are controlled directly by electric motors. A mechanism of the phase control system is made of planetary gears. The outer gear is the timing pulley which has timing belt driven by the crank of an engine. Two planetary gears are inside of the pulley. The gears engage in inner gear of the pulley. The center of the disc which has centers of the planetary gear is connected to the camshaft. Then, the crank rotation is transmitted to the cam shaft, and rotation of sun gear is added to the rotation of cam shaft. This means that when rotation angle of the sun gear is controlled, phase of the cam can be controlled. The lift control system is made of linear slider and ball screw. The cam shape of this system is three-dimensional. The height of the cam varies along the axis of the shaft. Hence, when the ball screw rotates, the cam shaft slides in the axial direction, so that the lift of the cam varies. Experimental tests have been carried out for the system. lt is ascertained that both cam lift and phase can be controlled continuously.

Calculation of Cam-Form Errors

In the grinding process for a cam, the dynamics of the grinding machine causes a systematic error. The deviation from the desired cam lift recorded on a survey sheet is approximated and smoothed for a typical example. Thereby, displacement, velocity, and acceleration of the error curve can be determined and superposed to the theoretical (desired) values; as a result, one obtains the actual values. Besides, the error-perturbed radii of curvature and Hertzian pressure are calculated. From these data, the impact of the manufacturing error on the dynamic behavior and stress can be determined.

Tappet Rotation and Friction Reduction in a Center Pivot Rocker Arm Contact

The instantaneous tappet rotation velocity and instantaneous friction torque were measured simultaneously for the CVH center pivot rocker arm geometry. The measurements were made in a cam/tappet friction apparatus equipped with a laser reflectance tappet rotation monitor capable of following rapid changes in tappet rotation velocity. The data showed that more rapid tappet rotation resulted in lower friction. The effect was greatest in the region of maximum cam lift. Several tappets were modified to produce higher rotation rates than production tappets. The best results were obtained with tappets incorporating an internal squeeze film bearing to reduce resistance to rotation. The data were analyzed to elucidate the cause for the friction reduction effect. The analysis showed that most important effect was the partial rolling motion between the surfaces, rather than enhancement of the oil film thickness. A model based on that conclusion agreed reasonably well with the experimental data.

Coulomb Friction and Optimal Rocker Arm Ratio for High-Speed Cam Systems

The operating speed of a high-speed cam system can be maximized by the proper choice of both kinematic and dynamic parameters of a lumped model. Considering rocker arm ratio as an unconstrained kinematic parameter and Coulomb friction as an unconstrained dynamic parameter, it was found that the camshaft speed at which toss occurred was characterized by several local extrema, all of which were sensitive to the presence of Coulomb friction. For a particular cam system and two separate cam lift curves, design charts have been developed to aid in the choice of optimal rocker arm ratio for maximum operating speed in the presence of Coulomb friction.

An Experimental and Analytical Investigation of the Dynamic Response of a High-Speed Cam-Follower System. Part 2: A Combined, Lumped/Distributed Parameter Dynamic Model

Part 2 describes the development of a dynamic model of a high-speed cam-follower system in which the return spring is modeled as a distributed-parameter element. The dynamic response requires the solution of a coupled set of differential equations, one ordinary and one partial. The dynamic model has the unique capability of faithfully reproducing the effect of the higher harmonics of the cam lift curve on system performance. The model, which has been refined and verified with the aid of the results described in Part 1, is capable of accurately predicting both normal system response as well as pathological behavior associated with the onset of toss, bounce, and spring surge. In comparison, a lumped-parameter dynamic model (differing only in the modeling of the valve spring) does not adequately predict the onset of pathological behavior.