U.S. patent application number 13/339832 was filed with the patent office on 2013-01-03 for continuously variable valve timing system and method for controlling the same.
This patent application is currently assigned to Kia Motors Corporation. Invention is credited to Jong Bum Park.
Application Number | 20130000575 13/339832 |
Document ID | / |
Family ID | 46146655 |
Filed Date | 2013-01-03 |
United States Patent
Application |
20130000575 |
Kind Code |
A1 |
Park; Jong Bum |
January 3, 2013 |
CONTINUOUSLY VARIABLE VALVE TIMING SYSTEM AND METHOD FOR
CONTROLLING THE SAME
Abstract
A continuously variable valve timing (CVVT) system which may be
operated in cooperation with a continuously variable valve lift
(CVVL) engine may be included. A reference position of a suction
CVVT may be set by a spring. In addition, a method for controlling
a continuously variable valve timing (CVVT) system may be included.
The method includes setting a reference position of a suction CVVT
to a most advanced angle position, and controlling a delayed angle
amount at the reference position of the most advanced angle.
Inventors: |
Park; Jong Bum; (Anyang-si,
KR) |
Assignee: |
Kia Motors Corporation
Seoul
KR
Hyundai Motor Company
Seoul
KR
|
Family ID: |
46146655 |
Appl. No.: |
13/339832 |
Filed: |
December 29, 2011 |
Current U.S.
Class: |
123/90.15 |
Current CPC
Class: |
F01L 2001/34483
20130101; F01L 13/0026 20130101; F01L 13/0015 20130101; F01L
2013/0073 20130101; F01L 1/3442 20130101; F01L 2013/0068
20130101 |
Class at
Publication: |
123/90.15 |
International
Class: |
F01L 1/344 20060101
F01L001/344 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 28, 2011 |
KR |
10-2011-0063011 |
Claims
1. A continuously variable valve timing (CVVT) system which is
operated in cooperation with a continuously variable valve lift
(CVVL) engine, wherein a reference position of a suction CVVT is
set by a spring.
2. The continuously variable valve timing (CVVT) system of claim 1,
wherein the spring is adapted such that a suction cam timing is
shifted in an advanced angle direction when an oil control valve
installed in the CVVT system does not operate.
3. A method for controlling a continuously variable valve timing
(CVVT) system which is operated in cooperation with a continuously
variable valve lift (CVVL) engine, comprising the steps of: setting
a reference position of a suction CVVT to a most advanced angle
position; and controlling a delayed angle amount at the reference
position of the most advanced angle.
4. The method according to claim 3, wherein when an oil control
valve installed in the CVVT system does not operate, a suction cam
timing is shift in an advanced angle direction by a bias spring
which is installed in the CVVT system.
5. The method according to claim 3, wherein when the oil control
valve installed in the CVVT system operates to the max, the oil
control valve changes an oil pressure passage connected to the CVVT
system.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority to Korean Patent
Application No. 10-2011-0063011, filed on Jun. 28, 2011 in the
Korean Intellectual Property Office, the entire contents of which
is incorporated herein for all purposes by this reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a continuously variable
valve timing system and a method for controlling the same, and more
particularly, to a continuously variable valve timing system and a
method for controlling the same which can improve a fuel efficiency
by controlling a reference position when a general hydraulic CVVT
(continuously variable valve timing) system is employed in a
continuously variable valve lift (CVVL) engine having no
self-advanced/delayed angle function.
[0004] 2. Description of Related Art
[0005] In general, it is known in CVVL engines that a valve lift
and valve opening duration is directly controlled by an electronic
control unit (ECU) to improve fuel efficiency, performance and
responsibility, and reduce emissions.
[0006] A valve lift changing property of the CVVL system is varied
depending upon the structure of the variable lift mechanism of the
CVVL engine. In view of the engine control, the valve lift changing
property can be divided into two types described below, depending
upon whether the maximum opening point (MOP) is varied or not when
the valve lift is changed.
[0007] FIG. 1 is a view illustrating a lift changing property of a
CVVL system having no self-advanced/delayed angle function. FIG. 2
is a view illustrating a lift changing property of a CVVL system
having a self-advanced/delayed angle function. FIGS. 1 and 2 show
the change in suction valve lift profile at a valve lift variation
according to the presence or absence of the self-advanced/delayed
angle function.
[0008] The CVVL system having no self-advanced/delayed angle
function is a system in which the MOP is not changed by the
operation of the CVVL mechanism when the valve lift is changed. The
structure thereof is relatively simple, which is preferable to CVVL
embodiment, but the cam timing is controlled by a separate CVVT
system. The CVVL system having the self-advanced/delayed angle
function is a system in which the MOP is changed by the operation
of the CVVL mechanism when the valve lift is changed. If the
advanced/delayed angle property of the CVVL mechanism is utilized,
it can share a portion of separate CVVT operating necessity.
[0009] In addition, it is necessary to perform a cam timing control
by monitoring a separate CVVT system to the CVVL engine having no
self-advanced/delayed angle function. A conventional hydraulic CVVT
system which is generally employed in a common Non-CVVL engine is
used.
[0010] In the hydraulic CVVT system for the Non-CVVL engine, since
a fixed suction value lift is used in the Non-CVVL engine, a
suction/exhaust cam timing is controlled to minimize a fuel
consuming amount under driving conditions. In the case of the
general Non-CVVL engine, a reference position is selected on the
basis of the optimum cam timing in a low-speed and low-load region
including start and idle, and generally corresponds to a
suction/exhaust timing at which the value overlap is minimized.
[0011] That is, the reference position of the suction cam timing is
the most delayed angle position, while the reference position of
the exhaust cam timing is the most advanced angle position. The
reference position should be maintained under a condition in which
the oil pressure sufficient for driving the CVVT is not generated
at start and low-speed driving.
[0012] In the CVVT, as shown in FIG. 3, if an outer sprocket
rotates, an inner rotor rotates slower than the outer sprocket due
to cam frictional torque, and thus the timing is always shifted to
the most delayed angle position. In the case of the suction CVVT,
the shifted position becomes the reference position, but in the
case of the exhaust CVVT, a bias spring is installed between the
sprocket and the inner rotor to forcefully shift the timing to the
most advanced angle position, so that the most advanced angle
position is maintained through the resilient force. If RMP is
increased or the idle is increased as compared with the idle
driving condition, the optimum cam timing should be shifted in such
a manner that the suction is shifted to the advanced angle
direction and the exhaust timing is shifted to the delayed angle
direction, in relation to the idle cam timing. In this instance,
the oil pressure created in a head oil gallery is respectively
applied to the advanced angle chamber and the delayed angle chamber
in the CVVT apparatus by an oil control valve (OCV) through two oil
circuits (advanced angle oil passage and delayed angle oil
passage). In the case of the cam frictional torque and the exhaust
CVVT, the CVVT is operated against the resilient force of the bias
spring by the pressure difference between the advanced angle
chamber and the delayed angle chamber.
[0013] In the case of the hydraulic CVVT employed in general
Non-CVVL engines, an oil pressure of a predetermined level or more
should be obtained to operate the CVVT. Accordingly, since the
stability and responsibility in the CVVT control is significantly
deteriorated at the low speed (usually idle RPM) which cannot
create the sufficient oil pressure in the Non-CVVL engine, the cam
timing of the reference position (suction the most delayed angle
position and the exhaust most advanced angle position) should be
used as it is. Therefore, the cam timing is selected as the
reference position, and the cam timing is controlled in such a
manner that the suction is shifted in the advanced angle direction
and the exhaust is shifted in the delayed angle direction, rather
than the reference position, in the engine driving region except
for the low-speed and low-load duration.
[0014] However, in the case where the CVVT system for the Non-CVVL
engine is employed in the CVVL engine having no
self-advanced/delayed angle function, it is not possible to control
the optimum cam liming, and thus there are some problems of
reducing the fuel efficiency, generating knocking, decreasing
vehicle responsibility, and vibrating the vehicle.
[0015] That is, only when the RPM is increased to create the oil
pressure sufficient to operate the CVVT, the suction/exhaust cam
timing can be varied. However, in the low-speed duration the CVVT
is not operated due to the lack of the oil pressure, and the
suction/exhaust CVVT should be operated in the reference position
(suction most delayed angle and exhaust most advanced angle). In
the case of using the lowest delayed lift, there is another problem
in that the fuel efficiency is deteriorated due to the increased
pumping loss and the increased effective compression ratio.
[0016] The information disclosed in this Background of the
Invention section is only for enhancement of understanding of the
general background of the invention and should not be taken as an
acknowledgement or any form of suggestion that this information
forms the prior art already known to a person skilled in the
art.
BRIEF SUMMARY
[0017] Various aspects of the present invention are directed to
providing a continuously variable valve timing system and a method
for controlling the same, which improves a method for controlling
selection of a reference position of a CVVT (continuously variable
valve timing) in a general Non-CVVL engine and a CVVL (continuously
variable valve lift) engine when a general hydraulic CVVL system is
employed in the CVVL engine having no self-advanced/delayed angle
function, thereby reducing a pumping loss and thus improving a fuel
efficiency and an effective compression ratio to improve a knock
property and reduce variations of RPM in a cycle.
[0018] In one aspect of the present invention, there is provided a
method for controlling a continuously variable valve timing (CVVT)
system which is operated in cooperation with a continuously
variable valve lift (CVVL) engine, including the steps of, setting
a reference position of a suction CVVT to a most advanced angle
position. controlling a delayed angle amount at the reference
position of the most advanced angle.
[0019] With the above configuration, the present invention can set
a low valve lift and optimum cam timing, which is necessary for the
same in a low RPM region including an idle condition, as a
reference position. Therefore, the optimum valve lift can be used
in the region without employing the CVVT control, thereby improving
the fuel efficiency in the idle and low-speed region. In addition,
a proper effective compression ratio is maintained to suppress
generation of knock and decrease variations of RPM. When the valve
lift is changed, it is possible to improve the fuel efficiency at
the low speed, without complicating the mechanism required to
employ the CVVL mechanism having the self-advanced/delayed angle
function and increasing rotational inertial and friction, as well
as a cost. Furthermore, as compared with the CVVL mechanism having
the self-advanced/delayed angle function, when a temperature of
cooling water is low or atmosphere is low, the combination of the
valve lift and the cam timing optimized for various driving
conditions, such as full-load driving and costing driving, can be
achieved by using the general hydraulic CVVT module to improve a
merchantable quality.
[0020] The methods and apparatuses of the present invention have
other features and advantages which will be apparent from or are
set forth in more detail in the accompanying drawings, which are
incorporated herein, and the following Detailed Description, which
together serve to explain certain principles of the present
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a view illustrating a lift changing property of a
CVVL system having no self-advanced/delayed angle function.
[0022] FIG. 2 is a view illustrating a lift changing property of a
CVVL system having a self-advanced/delayed angle function.
[0023] FIG. 3 is a view illustrating the structure of a hydraulic
CVVT system in the related art.
[0024] FIG. 4 is a view illustrating the structure of a hydraulic
CVVT system according to an exemplary embodiment of the present
invention.
[0025] FIG. 5 is a graph illustrating the efficiency based on a
valve lift and a suction cam timing.
[0026] FIG. 6 is a view illustrating an optimum valve lift and a
suction timing in a continuously variable valve lift engine.
[0027] FIG. 7 is a view illustrating the optimum valve lift and the
suction timing for each driving condition.
[0028] FIG. 8 is a view illustrating properties of the optimum
valve lift and the suction timing.
[0029] FIG. 9 is a view illustrating an effective compression ratio
and a RAM variation according to a lift/suction cam.
[0030] It should be understood that the appended drawings are not
necessarily to scale, presenting a somewhat simplified
representation of various features illustrative of the basic
principles of the invention. The specific design features of the
present invention as disclosed herein, including, for example,
specific dimensions, orientations, locations, and shapes will be
determined in part by the particular intended application and use
environment.
[0031] In the figures, reference numbers refer to the same or
equivalent parts of the present invention throughout the several
figures of the drawing.
DETAILED DESCRIPTION
[0032] Reference will now be made in detail to various embodiments
of the present invention(s), examples of which are illustrated in
the accompanying drawings and described below. While the
invention(s) will be described in conjunction with exemplary
embodiments, it will be understood that the present description is
not intended to limit the invention(s) to those exemplary
embodiments. On the contrary, the invention(s) is/are intended to
cover not only the exemplary embodiments, but also various
alternatives, modifications, equivalents and other embodiments,
which may be included within the spirit and scope of the invention
as defined by the appended claims.
[0033] Hereinafter, a preferred embodiment of the present invention
will be described with reference to the accompanying drawings. In
the entire description of the present invention, the same drawing
reference numerals are used for the same elements across various
figures.
[0034] FIGS. 4 to 9 are views illustrating a continuously variable
valve timing system and a method of controlling the same according
to an exemplary embodiment of the present invention. FIG. 4 is a
view illustrating the structure of a hydraulic CVVT system
according to an exemplary embodiment of the present invention. FIG.
5 is a graph illustrating the efficiency based on a valve lift and
a suction cam timing. FIG. 6 is a view illustrating an optimum
valve lift and a suction timing in a continuously variable valve
lift engine.
[0035] In addition, FIG. 7 is a view illustrating the optimum valve
lift and the suction timing for each driving condition. FIG. 8 is a
view illustrating properties of the optimum valve lift and the
suction timing. FIG. 9 is a view illustrating an effective
compression ratio and a RAM variation according to a lift/suction
cam.
[0036] In a CVVL engine, controlling a dimension of a valve lift
continuously and variably is to minimize a pumping loss and thus
improve a fuel efficiency. Since the valve lift and a valve opening
duration can be variably controlled in the CVVL engine, the engine
can be operated by selecting a suction valve opening position and a
suction valve closing position to have an optimum value in
cooperation with a CVVT mechanism.
[0037] As shown in FIGS. 5 and 6, if the suction valve closing
timing is significantly shifted to an advanced angle, the air
confined in a combustion chamber is adiabatically expanded to a
bottom dead center (BDC), and then is subjected to adiabatic
compression as a piston is raised.
[0038] In this instance, since the pumping loss is theoretically
zero to a piston position during a suction valve closing timing,
the pumping loss is minimized by suctioning an air volume
corresponding to a volume of a combustion chamber for the suction
valve closing duration. Meanwhile, in the case where the suction
valve closing position is significantly shifted to an advanced
angle in the general Non-CVVL engine having a constant valve lift
and valve closing direction, the suction valve opening timing is
significantly shifted to the advanced angle, and thus the valve
overlap becomes excessively large, so that misfire occurs due to
unstable combustion, which is a condition which cannot drive a
vehicle.
[0039] Meanwhile, in FIG. 5, a first diagram indicates a combustion
pressure and a volume at a maximum lift (valve lift which is equal
to MP1), and a second diagram indicates a combustion pressure and a
volume at a minimum lift (throttle minimizing lift by a throttle
body).
[0040] In comparison to the pumping loss (area of a border portion
of the first diagram) in the case of using the maximum lift, the
pumping loss (area of red border portion) in the case of using the
minimum lift is varied depending upon the minimum lift, but when
the minimum lift is 1 mm, the pumping loss can be reduced by 1/3 of
the Non-CVVL (or the maximum lift). It can reduce an indicated mean
effective pressure (IMEP) and fuel consumption, thereby improving
the fuel efficiency.
[0041] FIGS. 7 and 8 show the optimum valve lift and a suction
timing property, in which the below engine driving property is
obtained according to the lift and the suction cam.
[0042] First, if the lift is minimum and the suction cam is the
most advanced angle, the pumping loss is minimized and the fuel
efficiency is improved. If the lift is minimum and the suction cam
is at the most delayed angle, the effective compression ratio is
excessive, knocking occurs, and an RPM variation in the cycle is
excessive. If the lift is maximum and the suction cam is the most
advanced angle, the inner EGR is excessive, and the combustion
stability is deteriorated. If the lift is maximum and the suction
cam is at the most delayed angle, the high-speed output is
increased.
[0043] The properties of the continuously variable valve timing for
each load region will now be described.
[0044] Since the fuel efficiency is important in the idle region
including a low speed and a low load, the minimum lift and the most
advanced angle suction cam timing should be used. In the engine
equipped with the oil pump and the CVVT system for a general
Non-CVVL, since the oil pressure sufficient to operate the CVVT is
not created due to the low RPM, the suction cam timing is fixed to
the most delayed angle condition. In this instance, the pumping
loss can be reduced by using the maximum lift instead of the
minimum lift, but the fuel efficiency is deteriorated in comparison
with the minimum lift and the most advanced angle suction cam.
[0045] With reference to the idle silence, a torque difference
required for the compression process according to the effective
compression ratio occurs, and thus there is a difference in the RPM
variation properties within a cycle. In general, if the effective
compression ratio is lowered at the idle driving, the RPM variation
is decreased to improve the idle silence. Accordingly, as shown in
FIG. 9, it can be known that the minimum lift and the most advanced
angle condition which lowers the effective compression ratio are
advantageous in order to reduce the idle RPM variation.
[0046] The minimum lift and the most advanced angle suction cam
timing are required in a partial-load region which is an important
region, as well as the idle region. In this instance, as the load
is increased, the lift is increased and the suction cam timing is
slightly delayed.
[0047] In the full-load region, it is important to improve a torque
by suction the maximum air volume at the full load, and thus a lift
capable of obtaining the maximum air volume, and a cam timing at
that time are selected. In general, 60% to 80T of the maximum lift
at low and middle speed is used, and the maximum lift is used at
the high speed.
[0048] Since there are the suction valve lift and the suction valve
timing which can maximize the fuel efficiency and the combustion
stability depending upon the driving condition, the CVVL engine
having a self-advanced angle function has an effect of obtaining
the advanced angle of the opening/closing timing and a valve
profile through reduction of the lift, but the CVVL engine having
no self-advanced angle function should have the optimum cam timing
by the control and operation of the CVVT.
[0049] The CVVT system capable of obtaining the optimum cam timing
in the CVVL engine according to an exemplary embodiment of the
present invention, and the method for controlling the same will be
described.
[0050] As described above, the optimum fuel efficiency, drivability
and performance can be satisfied by simultaneously obtaining the
optimum lift and cam timing for every engine driving region. It can
be seen that CVVT requirements at the low speed are different from
those of the general Non-CVVL engine.
[0051] Therefore, the present invention relates to the hydraulic
control CVVT for driving the optimum cam timing for every valve
lift in the CVVL engine having no self-advanced/delayed angle
function or remarkably insufficient advanced/delayed angle amount,
as compared with the necessary advanced/delayed angle amount, when
the valve lift is varied. A reference position of the suction CVVT
is set to the most advanced angle position, and a CVVT assembly
with a bias spring to control the delayed angle amount at the
reference position of the most advanced angle.
[0052] According to an exemplary embodiment of the present
invention, the reference position of the suction CVVT in the CVVT
system which operates in cooperation with the CVVL engine is set by
the spring.
[0053] In order to set the reference position of the suction CVVT
to the most advanced angle position and control the delayed angle
of the CVVT, the CVVT system is provided with the bias spring so
that the suction cam timing is shifted in an advanced angle
direction when an oil control valve installed in the CVVT system
does not operate (when PWM is zero). In the case where the oil
control valve installed in the CVVT system operates to the max
(when PWM is applied), it is preferable that the oil control valve
changes an oil pressure passage connected to the CVVT system to
change an oil circuit in a head or an oil passage in a cam
shaft.
[0054] As described above, in the state in which the oil control
valve does not operate or the head oil pressure is not sufficient
at the low speed, since the oil pressure is not applied to the
advanced angle chamber and the delayed angle chamber in the CVVT
module, the cam timing is shifted to the advanced angle position by
the resilience force of the bias spring.
[0055] The position of the CVVT can be fixed by using a lock pin,
like a general CVVT module. If the oil control valve is operated
after the oil pressure is created, the oil pressure is applied to
the delayed angle chamber of the CVVT module through the oil
control valve and the oil circuit. The delayed angle chamber is
connected to a drain passage through the oil control valve, and
thus the cam timing is shifted in the advanced angle direction by
the oil pressure difference in the advanced angle chamber and the
delayed angle chamber.
[0056] With the continuously variable valve timing system and the
control method according to an exemplary embodiment of the present
invention, the reference position of the suction CVVT is set to the
most advanced angle position in the CVVT system which is operated
in cooperation with the CVVL engine. After that, the delayed angle
amount is controlled at the reference position of the advanced
angle to improve the fuel efficiency at the low speed and increase
the merchantable quality.
[0057] The foregoing descriptions of specific exemplary embodiments
of the present invention have been presented for purposes of
illustration and description. They are not intended to be
exhaustive or to limit the invention to the precise forms
disclosed, and obviously many modifications and variations are
possible in light of the above teachings. The exemplary embodiments
were chosen and described in order to explain certain principles of
the invention and their practical application, to thereby enable
others skilled in the art to make and utilize various exemplary
embodiments of the present invention, as well as various
alternatives and modifications thereof. It is intended that the
scope of the invention be defined by the Claims appended hereto and
their equivalents.
* * * * *