Prototype for Engine Tests

To demonstrate the functioning of the various air stroke valve methods, a prototype was designed and built that allows the system to be tested with an engine. The primary interest was to investigate the dynamic supercharging of the engine.

Parameters and Design. Very short operating times for the air stroke valve are required for dynamic supercharging. Extensive preliminary investigations using one-dimensional charge cycle calculations from the program GT-Power clearly show that valve operating times (the opening and closing process) of ∆t_s = 2 ms are necessary to completely exploit the available potential. For this reason, a spring-mass oscillator was selected to be used as a direct valve drive that acts on the valve shaft. The movement of the oscillating system is controlled by two reverse solenoids that can be independently actuated, between which a hinged armature pivots supported by a spring.

This has the advantage that oscillation can occur at the system resonance frequency upon starting. The energy required for valve actuation is then saved as spring energy and is immediately available for acceleration. In the actual polarity reversing process, only part of the loss arising during movement must be compensated, which means that the drive requires less energy. Another advantage is that the direction of the hinged armature can be reversed immediately after contact, which further increases the flexibility of the air stroke valve drive in regard to the crankshaft angle for the operating times.

Implemented Prototype. A Rotax BMW F650 single-cylinder engine with a stroke volume of 650 cm³ was selected as a test engine. The engine had two symmetrical intake ports and was equipped with Otto direct injection, which allows unhindered access to the intake line and easy adaptation of the air stroke valve drive. For measuring, the engine was equipped with a very short induction pipe (280 mm). The air stroke valve (see Fig. 10-88), a symmetrical butterfly valve in a rectangular channel cross section of 30 mm X 60 mm, is in the two individual channels before the intake line branches.

Fig. 10-88. Air stroke valve prototype for testing in a single-cylinder engine

Because of the very long tubular section in the cylinder head, the ratio between the sum of all clearance volumes (combustion chamber, channels in the cylinder head, induction pipe up to the valve) and the stroke volume is

The natural frequency of the oscillated spring-mass system is determined by the torsion spring in the armature shaft and the moment of inertia of the hinged armature and valve. Since, in particular, the dynamic supercharging was to be investigated in detail at the required fast operating times, a design was created that permitted opening and closing times of ∆t_s = 2.1 ms. The switching time can be varied by changing the moment of inertia by adding weight. An angular resolver was on the free end of the shaft to determine the current valve position.

The magnets to control the switching processes are designed as U-shaped magnets that are aligned with each other at an angle of 45°. The alternating control of the actuator is carried out with the power electronics developed for this drive that controls the sequence of the output and holding current to the magnets. When the polarity of the armature is reversed, the holding magnet is switched off, and a high output current is initially fed to the opposite magnet. If the armature is lying on the holding magnet, the current is reduced over time to a lower holding current. The required output for this prototype is between 20 and 30 W, depending on the engine speed. If valve actuation is not desired, the armature can be held in open valve position.

In operating the air stroke valve, it is important to have a low amount of leakage from the induction pipe to the space between the air stroke valve and intake valve in closed valve position. The seal was attained by creating a 2-mm-deep cutout in the induction pipe wall (see Fig. 10-88) into which the valve swings with a small gap and then contacts. By correspondingly adjusting the drive, the valve edges lie on the contact edges in the induction pipe with a slight amount of force from the elasticity of the valve when in the closed position.

In the drive design, particular attention was paid to achieving very short operating times to especially reveal the effects of dynamic supercharging and hot charging. Other issues involving the durability of the overall system and noise emissions of the drive were largely left untouched in the development of this prototype.