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2006-01-0223
Improvements to a Four Cylinder
Gasoline Engine Through the Fully Variable
Valve Lift and Timing System UniValve®
Rudolf Flierl and Daniel Gollasch
Technical University of Kairslautern值得阅读的书
Andreas Knecht
Hilite International / Hydraulik-Ring GmbH
Wilhelm Hannibal
enT ec CONSULTING GmbH
Reprinted From: Variable Valve Actuation 2006
(SP-2007)习惯
2006 SAE World Congress
Detroit, Michigan
多动症的表现
April 3-6, 2006
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ABSTRACT
In addition to first test results from a one single-cylinder engine with the UniValve fully variable valve
lift and timing system - prented at the 2005 SAE Congress - this paper contains the results of a fired 2.0 I four cylinder gasoline engine [1], [2]. The cylinder head has been replaced with a new cylinder head concept that includes the fully variable valve lift and timing system (VVTL system) UniValve. The other engines parameters and components have not been changed. The intention was to investigate the engine behavior only by exchanging the standard inlet valve train with for the UniValve fully variable valve train. The VVT engine load can be controlled either with a standard throttle or unthrottled, only through the fully variable variation of the valve lift and the valve opening period. The engine has been installed on a dynamic test bench. The torque behavior, the power output, the raw emissions and the fuel consumption have been measured for the standard ries production engine directly in comparison with the VVT engine. The VVT engine was driven with both load control options. With different valve lift heights of two adjacent inlet valves the flow turbulence can be incread. This influence of this inlet valve phasing on the fuel consumption and on the emissions at part load will be measured on the UniValve engine too in 2006 too. With a special design of the turnable eccentric control shaft the engine can be driven with different loads for defined cylinder groups, so that for example for a specific engine load point a cylinder group runs with low load while the other cylinder group works with higher load. This load control strategy is called “Cylinder Up Loading”. The target therefore is to get still a higher efficiency and a better fuel consumption at higher part loads. INTRODUCTION对酒当歌的当
The worldwide trend towards more stringent laws on exhaust emissions is continuing and, at the same time, increasing prices of fossil fuels on the world market are putting pressure on the automotive industry to develop internal combustion engines that posss distinct fuel consumption saving potential for the future. This situation is confronting the international automotive industry with increasingly greater challenges, which it has to meet by developing innovative technologies. Engine management in particular is taking on greater
importance.
Fig. 1: Design and functionality of the UniValve
fully variable valve timing system
2006-01-0223
Improvements to a Four Cylinder Gasoline
Engine Through the Fully Variable Valve Lift
and Timing System UniValve®
Rudolf Flierl and Daniel Gollasch
Technical University of Kairslautern
Andreas Knecht
Hilite International / Hydraulik-Ring GmbH
Wilhelm Hannibal
enTec CONSULTING GmbH Copyright © 2006 SAE International
For the valve train, this means that innovative, extendable solutions are being implemented for engine management. Fully variable valve control systems that can vary both valve lift as well as valve opening duration, are to be expected to come out in future in on ries production engines in addition to systems [3] to [8] of BMW. Practicable solutions available for high-volume production engines operate according to a mechanical principle. Hydraulic or electromechanical solutions are not ud. With the combination of camshaft adjustment mechanisms, modern IC engines have considerable potential for improving all engine target values.
The contents of this article give an idea which potentials can be realized with fully variable mechanical valve control systems. The engine ud for the system comparison is a 2.0 l four-cylinder engine with two double overhead camshafts and a camshaft phar on the intake camshaft. Tests were conducted on mechanical and fired test beds. The basic engine is of modular design, making it suitable for basic tests in order to illustrate, fully variable valve control concepts in combination with turbocharging or direct injection. The tests will be done in 2006. To compare the
standard throttled engine with the only through the inlet valve closing time throttled engine, only the inlet valve train was changed to the UniValve system. The combustion chamber, the piston and the intake manifold of the ba engine were ud.
FUNCTIONAL PRINCIPLE
The functional principle of the valve control system ud can best be explained by means of a drawing. Between the cam and the standard roller cam follower, a rocker arm with a working curve is ud. This rocker arm has a variable pivot or anchorage location in order to achieve the desired variability. When a standard rocker arm is ud, the pivot or anchorage location is not variable, so that the valve lift pattern is not variable either, (Fig. 2,
left).
Fig. 2: UniValve basis functionality with a rocker arm
Changing the rocker arm anchorage location with, for example by means of an eccentric contour on an eccentric control shaft (Fig. 2, right) allows the desired variable change in the valve lift cluster as shown in the example in Fig. 7. In the vertical direction, a guide takes over the control of the rocker arm. For this, an additional roller is in contact to the guide. The design on the inlet side as well as the functional principle of the solution for the four-cylinder engine are explained below in detail in Figs. 1 to 8.
The UniValve system is bad on a standard roller rocker finger design for a constant valve lift as in modern ries-production gasoline and diel engines, [9] to [11]. With an additional transmission element, the rocker arm (5) or (13), as well as an actuator of the eccentric shaft (9), step less variability of valve lift and valve opening time is achieved (Figs. 2 and 7). Here, the roller rocker fingers (10) are no longer driven directly by the camshaft (4) but via the rocker arms (13) which are mounted in pairs to form a forked lever (e Fig. 4). The camshaft (4) thus moves out the forked levers which are supported on a rotary eccentric shaft (9) via a roller as in Fig. 8 or a sliding contact
surface (14), as in Fig. 4. From this support geometry, the rocker arm acquires its rocking movement. As a result of this rocker movement of the forked lever over the central roller (8) within a locally fixed guide (7), the roller rocker fingers (10) are in turn actuated and the inlet valves (11) thus opened. During this process the rollers of the roller rocker fingers are in direct contact with the working curve of the forked lever, (Fig. 4
).
Fig. 3: Curvature plot of the lever working curve
Valve lift is steplessly adjusted via the eccentric control shaft (9) which is swivel-mounted in the cylinder head. As a result of this, the working curve (15) of the rocker arms (13) is traverd progressively, which leads to an increa in valve lift. The further the roller rocker finger can move along the working curve (15), the greater is the resulting valve lift. The anchorage location on the rocker arm is shifted over a total distance of 3.2 mm in the direction of the camshaft (4). All valve lifts in the range 0 to 9.3 mm full-lift can thus be realized, (Fig. 6). The ability of this valve control system to perform zero lift is due to the subdivision of the working curve on the
rocker arm into three ctions as well as the circular shape of the bearing surface in the guide (7). In Fig. 3, the original contour of the working curve for one version is scaled up and shown darker to make it clearer. The curvature over the length of the working curve is also marked for the individual ctions. Among other things, this provides information for evaluating the dynamic stability of the valve gear.
The guide radius has its centre point on the axis of the cam follower roller. The first ction of the working curve (15) is described by a radius R0 in Fig. 4 with the midpoint in the centre of the cam follower (2), and is responsible for zero lift. As a result of the two conditions, the valves do not open even at full deflection of the cam followers (2). To make it this easier to understand, the arrow lines in Fig. 1 mark the degrees
of freedom of the valve gear.
Fig. 4: Forked lever with sliding contact surface
The forked lever asmbly is shown in symmetrical construction in Fig. 4. The pair of intermediate levers are connected by a rigid axis or shaft (16), on which all the rollers are located. In order to minimize friction of in the system, rollers (8) and (2) have needle bearings.
The spring slider rollers (12), however, only have plain bearings, as the do not perform any major relative movements in guiding the spring arms. In the partial lift movement, the cam follower roller automatically follows a ction of the zero-lift area along the working curve of lever (13). During this time, the valve spring pretensioning force is not yet active.
For this reason, additional springs (1) and (3) are provided for the lift adjustments in order to ensure a zero-play between of the rocker arm and its contact partner. Fig. 5 shows how the lever asmbly is installed in the cylinder head. It was possible to install the UniValve
system within the outline of the basic cylinder head.
Fig. 5: UniValve package situation
TEST RESULTS FROM MECHANICAL TEST BED Investigations on the component test bed are ud to determine mechanical parameters of the valve gear. Valve lifts are measured in relation to th
e angle position of the eccentric shaft and are summarized as one a single control characteristic line, (Fig. 6
).
Fig. 6: Eccentric shaft characteristic
Fig. 7 shows the valve lift curves measured at a speed of 1000 rpm. The control time of the maximum lift of 9.3 mm extends over 250 °CA; that of the idling valve lift of approx. 0.3 mm is 90 °CA. This results in a significant reduction in control time. The inlet valves are clod at the preci moment in which the required charge amount is in the cylinder. As a result, it is possible to
