CHEMICAL ENGINEERING TRANSACTIONS
VOL. 51, 2016
A publication of
The Italian Association
of Chemical Engineering
Online at www.aidic.it/cet
Guest Editors: Tichun Wang, Hongyang Zhang, Lei Tian
Copyright © 2016, AIDIC Servizi S.r.l.,
ISBN 978-88-95608-43-3; ISSN 2283-9216
Adjustment Performance of a Novel Continuous Variable
Valve Timing and Lift System
Jiadui Chen*, Yongming Wu, Yuling Xu, Ziqin Wang, Fengguo Tian
Key Laboratory of Advanced Manufacturing, Ministry of Education, Guizhou University, Guiyang 550018, Guizhou, China
chjd97@163.com
A new variable valve technology that is named continuous variable valve timing and lift system by hydraulic
volume adjustable is presented in the paper. The AMESim simulation model of continuous variable valve
timing and lift system by hydraulic volume adjustable is established. The adjustment performance of the
system is studied deeply by the simulation model. The results show that both the valve timing and valve lift of
the system can be adjusted independently and continuously, the valve advance angle, the valve retard angle
and the valve duration angle increase with the increase of engine speed, and the valve lift increases with the
increase of engine speed or load, decreases with the increase of engine speed or load. The novel continuous
variable valve timing and lift system would more meet the distribution requirements of engine.
1. Introduction
The variable valve technology can change the timing, duration angle and lift of valve in line with the changes
of engine working conditions, making the engine gain reasonable gas distribution under every working
condition, so as to improve the engine idling speed stability, promote the external characteristic torque at low
speed, enhance the thermal efficiency, increase the fuel economy, reduce emission and improve the vehicle
driving comfort, and so on (Chen, 2014). Since the British Dugald Clerk obtained the first variable valve
technology patent in 1880(Thomas, 1989), the variable valve technology has been studied by many people for
a long time, and a lot of variable valve systems have been presented, some of them have been applied to the
car (Allen et al., 2002; Qu et al., 2012), such as Honda’s VTEC, BMW’s Valvetronic (Flierl et al., 2000) and
Fiat’s Multiair (Lucio et al, 2010). However, there are a few disadvantages such as complex structure, complex
control process, high cost, limiting to improve the engine valve in these technologies. These disadvantages
restrict the application of variable valve technology in practical engineering (Hu et al., 2015). At present,
though many different variable valve technologies have been commercial, it has not yet to find out the
integrated solution that is excellent in various aspects, such as performance, structure, applicability, economy
and so on.
A continuous variable valve timing and lift system by hydraulic volume adjustable (CVVTL) that can realize the
independent and continuous adjustment of valve timing and lift, satisfy the reasonable gas distribution
demands of engine in all working conditions is presented. The AMESim simulation model of CVVTL is
established to study the adjustment performance of CVVTL, and the simulation results are analysed in detail.
2. The CVVTL system
The structure of CVVTL is shown in figure 1. The CVVTL is composed of cam, cam cylinder, valve cylinder,
valve assembly, phase regulator, lift regulator, seating buffer and oil supply system, and so on. The valve
phase regulator and lift regulator mainly consists of cylinder, piston, spring, gag lever post, and adjusting
device. The oil supply system consists of oil tank, oil pump, check valve, relief valve and pipeline. The CVVTL
system realizes the continuous adjustment of the valve advance angle and the valve retard angle by
controlling the time that the oil flows into and flow out from the valve cylinder, which by fairly adjusting the
position of gag lever post of phase regulators. And the system can realize the continuous adjustment of valve
DOI: 10.3303/CET1651220
Please cite this article as: Chen J.D., Wu Y.M., Xu Y.L., Wang Z.Q., Tian F.G., 2016, Adjustment performance of a novel continuous variable
valve timing and lift system, Chemical Engineering Transactions, 51, 1315-1320 DOI:10.3303/CET1651220
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lift by controlling the liquid volume flows into the valve cylinder and lift regulator, which can control by fairly
adjusting the position of gag lever post of lift regulator.
Figure 1: Schematic diagram of CVVTL
3. Simulation Model
Figure 2 is the AMESim simulation model of CVVTL. The compressibility of hydraulic oil and pressure loss
existing in the physical system are fully considered in the simulation model. And hydraulic pipelines of
simulation model have similar parameters with physical system. The switchover of oil circuit from cam cylinder
to valve cylinder at different time in physical system is simulated by the controlling subsystem in the model.
The electromotor is used to simulate the engine rotation driving the rotation of cam to bring about the
reciprocating movement of cam cylinder piston, and then generate the oil pressure to drive the motion of the
valve cylinder piston, phase regulator piston, and lift regulator piston. The displacement sensor is used to
detect the displacement of valve oil cylinder piston. The speed sensor is used to detect the direction of
reciprocating motion of cam cylinder piston. It can realize the simulation of valve cylinder and seating
cushioning mechanism by using the signal of displacement sensor, the signal of speed sensor and control
system cooperatively and the combination of variable throttle, mass block, spring, spool with hole section
orifice of HCD. The phase regulator and lift regulator are simulated by the combination of one-way cylinder
and mass block. The parameters setting of simulation model should be refer to the physical system, the
simulation parameters are shown in table 1.
(a) simulation model (b) Cam profile
Figure 2: The AMESim simulation model of CVVTL
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Table 1: Simulation parameters
Item Parameter
Cross-section area of check valve(mm2) 10
Discharge coefficient 0.6
Diameter of cam oil cylinder piston (mm) 16
Diameter of phase regulator piston (mm) 10
Diameter of valve oil cylinder piston (mm) 10
Diameter of lift regulator piston (mm) 16
Diameter of pipeline (mm) 8
Pre-tightening force of phase regulator spring (N) 10
Pre-tightening force of valve spring (N) 120
Pre-tightening force of lift regulator spring (N) 157
Gap height between valve oil cylinder and its piston(mm) 0.225
Stiffness of phase regulator spring (N/mm) 1.25
Stiffness of lift regulator spring(N/mm) 1
Stiffness of valve spring(N/mm) 40
Buffer length (mm) 1.5
Length of the pipe connects the cam oil cylinder and phase regulator (mm) 400
Length of the pipe connects the cam oil cylinder and lift regulator (mm) 450
Length of the pipe connects the cam oil cylinder and valve oil cylinder (mm) 600
Equivalent quality of valve assembly(kg) 0.08
Equivalent quality of phase regulator piston assembly(kg) 0.005
Equivalent quality of lift regulator piston assembly(kg) 0.02
Density of hydraulic medium(kg/mm3) 870×10-9
4. Simulation Results and Analysis
Define the cam angle 0° the same as the crank angle 0°.
4.1 Timing adjustment
When adjusting the valve timing, the displacement of lift regulator piston should be set to 0mm, and the
displacement of phase regulator piston will be adjusted according to the engine speed. Figure 3 and figure 4
are the simulation results of valve timing adjustment. The values in the legend of figure 3 are the adjustments
of phase regulator. From the figure 3, it can be known that:
(1) In the displacement adjustment range of phase regulator piston, the valve advance angle, the valve retard
angle and the valve lift gradually decrease with the increase of the adjustment of phase regulator piston. The
greater of the adjustment of phase regulator piston, the more liquid volume flows into the phase regulator
cylinder, the slower system oil pressure goes up, and the longer system to get the oil pressure value to open
the valve. Therefore, the valve advance angle, the valve retard angle and the valve lift decrease
correspondingly. The decrease of valve lift in the timing adjustment accord with the tendency of gas
distribution requirement at the engine speed decreases and the load decreases as well. If the engine load is
constant or increases, it can be compensated by increasing the adjustment of valve lift.
(2) The relationship between the adjustment of phase regulator piston and adjustment of the valve advance
angle is nonlinear. The relationship between the adjustment of phase regulator piston and adjustment of the
valve retard angle also is nonlinear. For the same increment of adjustment of phase regulator piston, the
closer phase regulator piston to the zero position, the larger valve advance angle and valve retard angle will
be changed. From the cam profile shown in figure 2(b), it can be seen that the closer to the starting point of
cam lift, the lift of cam rise more slowly, the longer system oil pressure rises to the pressure point that can
open the valve. The cam’s fall curve is similar with the lift of cam. So the smaller adjustment of phase
regulator piston, the larger changes of the valve advance angle and the valve retard angle.
(3) The CVVTL system can realize the continuous adjustment of the valve advance angle from 0°CA to 36°CA
and the continuous adjustment of the valve retard angle from 0°CA to 54°CA by changing the adjustment of
phase regulator piston at 800r/min.
Figure 4 presents the simulation results of different adjustments of phase regulator at different speeds. The
adjustment is 0 mm at 4000r/min, the adjustment is 1mm at 3000r/min, the adjustment is 4mm at 1500r/min,
and the adjustment is 6.4mm at 800r/min. From figure 4, it can be known that CVVTL can realize the valve
advance angle and the valve retard angle increase with the increase of engine speed at the same time, and
decrease with the decrease of engine speed at the same time, by adjusting the displacement of phase
regulator piston according to the change of engine speed. The adjustment range of valve advance angle is
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0°CA～37°CA, and the adjustment range of retard angle is 0°CA～61°CA. The simulation results indicate that
the CVVTL system can realize the function of continuous adjustment of valve timing.
(a) 800 r/min (b) 1500 r/min
Figure 3: Valve lift curves of different adjustments of phase regulator
Figure 4: Simulation results of different adjustments of phase regulator at different speeds
4.2 Lift adjustment
When adjusting the valve lift, the displacement of phase regulator piston should be set to 0mm, and the
displacement of lift regulator piston will be adjusted according to the engine speed or load. Figure 5 and figure
6 are the simulation results of lift adjustment. The values in the legend of figure 5 are the adjustments of lift
regulator. From the figure 5, it can be known that:
(1) The system can realize the continuous variable of valve lift by changing the adjustment of lift regulator
piston. The oil total volume that flows into the lift regulator oil cylinder would be changed while changing the
adjustment of lift regulator piston, and the oil total volume that flows into the valve cylinder would also be
changed. So the continuous variable of valve lift is realized.
(2) All the starting point of curve at the same engine speed is the same point, all the end point of curves also is
the same point. It is to say that the lift adjustment does not influence the valve timing. Since the design value
of pre-tightening force of lift regulator spring is bigger than that of valve spring, when the force that system oil
pressure acts on the lift regulator piston reaches the pre-tightening force of lift regulator spring, the valve has
opened for a moment. So the lift adjustment always occurs behind the valve opening. This not only effectively
avoids the false operation of lift regulator, but also ensures that valve timing is not influenced by the lift
adjustment.
(3) Within the adjustment range of lift regulator piston, the valve lift gradually decreases with the increase of
adjustment range of lift regulator piston. Since the stiffness of lift regulator spring is far less than that of valve
spring, when system oil pressure reaches up to the oil pressure that corresponds to the working point of lift
regulator spring, oil pumped from cam cylinder mainly flows into the lift regulator cylinder, and less oil flows
into the valve oil cylinder. So, the change of valve lift is slowly. However, when the lift regulator piston reaches
its adjustment position, oil pumped from cam cylinder mainly flows into the valve cylinder, the valve lift up
sharply. The situation is opposite in the valve return. The bigger adjustment of lift regulator piston, the more oil
flows into lift regulator cylinder. Accordingly, the less oil flows into valve cylinder. And the maximum valve lift is
smaller.
(4) When engine speed reaches up to 4000r/min, the system still has good lift adjustment performance. The
maximum valve lift is less than 4mm at 6mm of adjustment of lift regulator piston. Surely, this working
condition is rare in practical engine running.
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(5) This system can realize 0.6mm of the maximum valve lift at 800r/min. This will beneficial to the engine idle
gas distribution, reducing oil consumption and emission.
(6) Compared with figure 5(a) and figure 5(b), it can be found that the higher the engine speed, the greater the
maximum lift at the same adjustment. The increase of engine speed brings about the increase of hydraulic
shock and oil movement inertia, eventually raises the oil pressure. And furthermore, the system pressure
fluctuations and shocks will be further intensified with the increase of engine speed. So, it is necessary to
adopt corresponding technical measures to control the pressure impact and fluctuation of system into
reasonable range, to ensure the reliability of system in the high speed working conditions.
(a) 800 r/min (b) 4000r/min
Figure 5: Valve lift curves of different adjustments of lift regulator
Figure 6 presents the simulation results of different adjustment of lift regulator at different engine speeds. The
adjustment of lift regulator is 0mm at 5500r/min., the adjustment of lift regulator is 2mm at 4000r/min, the
adjustment of lift regulator is 4mm at 3000r/min ant the adjustment of lift regulator is 11mm at 800r/min. From
figure 11, it can be known that the valve lift adjustment is not influence the valve timing. The system can
realize the continuous adjustment of lift according to the engine speed by adjusting the lift regulator piston
continuously, and get very small valve lift under the condition of low speed. The adjustment range of valve lift
is 0.6mm to 11.25mm when the speeds of engine from 800r/min to 5500r/min.
Figure 6: Valve lift curves of lift adjustment at different speeds
4.3 Both timing and lift adjustment
The simulation parameters of both valve timing and lift adjustment at different speeds are in table 2, and figure
7 is the simulation result. As shown in figure 7, the system can realize the continuous variable of valve timing
and lift by adjusting the phase regulator and lift regulator at the same time according to the engine speed, the
adjustment range of valve advance angle is 0～36°CA, the adjustment range of valve advance angle is
0～54°CA, and the adjustment range of valve lift is 0.6 mm ～11.25mm when the speeds of engine from
800r/min to 5500r/min.
Table 2: Simulation parameters at different speeds
Curve 1 Curve 2 Curve 3 Curve 4
Engine Speed（r/min） 5500 4000 1500 800
Adjustment of Phase Regulator（mm） 0 0.4 2.4 5.6
Adjustment of Lift Regulator（mm） 0 1 5 6.5
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Figure 7: Valve lift curves of both timing and lift adjustment at different speeds
5. Conclusions
There are various realization approaches of variable valve technology. So far many of them have realized
commercialization, but they cannot satisfy the gas distribution requirement of various working conditions of
engine very well. This paper presents a novel variable valve system, namely the continuous variable valve
timing and lift system by hydraulic volume adjustable which realizes the adjustment of valve timing by
controlling the time that the oil flows in and out the valve cylinder, and realizes the adjustment of valve lift by
controlling the volume of oil flows in the valve cylinder. Compared with the existing technologies, the CVVTL
system has obvious advantages.
The AMESim simulation model of CVVTL is established. The adjustment performance of the system is studied
deeply using the simulation model. The results show that both the valve timing and valve lift of the system can
be adjusted independently and continuously. The valve advance angle, the valve retard angle and the valve
duration angle increase with the increase of engine speed at the same time, and decrease with the decrease
of engine speed at the same time. The valve lift increases with the increase of engine speed or engine load,
decreases with the increase of engine speed or engine load. Adjusting both valve timing and lift, the
adjustment range of valve advance angle is 0～36°CA, the adjustment range of valve advance angle is
0～54°CA, and the adjustment range of valve lift is 0.6 mm ～11.25mm when the speeds of engine from
800r/min to 5500r/min.
Acknowledgments
This work was supported by Guizhou province science and technology fund (no.LH[2014]7626) and Guizhou
University talent fund(no. 2015-50).
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