JPH11287111A - Internal combustion engine - Google Patents

Abstract

(57) Abstract: At least one intake valve having an intake passage guided in a cylinder and an exhaust passage guided out of the cylinder, and controlling an intake cross section in the intake passage. Is provided to control an exhaust cross section in the exhaust passage,
At least one exhaust valve is provided, the at least one intake valve and the at least one exhaust valve being controlled in relation to the working cycle of the internal combustion engine by at least one camshaft driven by the crankshaft of the internal combustion engine. An improvement of this type of internal combustion engine is provided in which a device for reducing throttling losses with a correspondingly adapted valve control time can be integrated as easily as possible into existing structures. A tension side of at least one tension means is provided.
And the unloaded side 9 are each provided with at least one adjustable tensioning device 27,
Control can be performed so that the rotation speed ratio between the camshaft 8 and the crankshaft 2 can be changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The invention relates to an internal combustion engine, in particular a four-stroke internal combustion engine, comprising at least one cylinder and at least one intake passage guided in the cylinder and having a controllable intake cross section. At least one exhaust passage having a controllable exhaust cross section guided out of the cylinder;
At least one intake valve for controlling an intake cross section is provided, and at least one exhaust valve for controlling an exhaust cross section is provided in an exhaust passage.
One intake valve and at least one exhaust valve are controlled in relation to the working cycle of the internal combustion engine by at least one camshaft via at least one pulling means driven by the crankshaft of the internal combustion engine. About things.

[0002]

2. Description of the Related Art Known four-stroke internal combustion engines have a valve drive for controlling gas exchange, the valve drive comprising intake and exhaust valves, valve springs for closing these valves,
It consists of a cam drive and a transmission member. One or more camshafts, typically driven by a crankshaft via a chain or belt, provide a constant intake and exhaust valve lift curve for controlling gas exchange in a conventional four-stroke internal combustion engine. Have. The valve opening time and the valve closing time, the valve opening time and the valve stroke are periodically constant in each working cycle of each cylinder. These valve control parameters are given in advance by structurally defined cam profiles and cam heights, and are between the optimal gas supply at full demand power and as little loss as possible, i.e. the partial load of the internal combustion engine. A compromise is made between good engine efficiency during operation and as little harmful emissions as possible. However, such a compromise is inconvenient, and it is necessary to obtain good maximum power while at the same time obtaining good efficiency within the partial load range. The high engine power at high revolutions requires long valve opening times and large valve strokes in order to allow as much fresh gas as possible to flow into the combustion chamber during each intake cycle. Such a design of the valve control has the disadvantage that throttling losses occur at low rotational speeds and partial load ranges. Because, for this type of operation of the internal combustion engine, especially the opening time and the valve stroke of the intake valve,
It is too long or too large for the required intake air volume. Moreover, in order to be able to adjust the correct filling of the combustion chamber, the intake pipe cross-section is reduced by means of a throttle valve, which causes throttle losses during gas exchange. Here too, the valve overlap, i.e. the opening of the exhaust valve before the intake valve is completely closed, lengthens the scavenging losses and leaves too much residual gas in the cylinder at many operating points. become.

[0003] Different systems are known in which the valve lift curve is variable or in phase shift from the intake lift curve to the exhaust lift curve. This can have a positive effect on the torque of the internal combustion engine and the amount of residual gas in the full load curve. The change parameters of the influence of the valve lift curve basically provide the valve stroke, the valve opening time and the valve opening time. It is known to affect the closing time of the intake valve, in particular to reduce throttle losses.

For example, it is known to combine a variable stroke of the intake valve with a stepless phase shift of the intake opening time. For this purpose, an additional eccentric shaft is provided, which is adjusted, for example, by an electric motor.

[0005] It is further known that the system for changing the valve stroke is closely related to the opening time.
In this case, an additional second intake camshaft is used, which rotates at the same speed as the already existing first camshaft. A special transmission allows the two camshafts to rotate with respect to each other via an electric motor. Systems for changing the valve stroke and the valve control time are also known, which are realized via an axially variable cam profile of the camshaft. In this case, the individual cams controlling the respective intake or exhaust valves have cam profiles which are variable in the axial direction of the camshaft. Thereby, the valve stroke time and the valve control time are changed by the axial adjustment of the camshaft during the operation of the internal combustion engine. A disadvantage of this type of structurally relatively expensive solution is that additional components require costly modifications in the cylinder head.

[0006] Systems are also known in which the throttle loss is reduced immediately before the intake valve by means of an additional valve. For example, a rotary slider incorporated in an intake pipe has been proposed.
In this case, the air flows through the hollow rollers and passes through the slits into the intake passage. The rollers are driven by an intake camshaft via a belt and are thus variable in a phase arrangement by means of an additional adjustable tension member. as a result,
Similarly, a reduction in throttling loss is obtained. It is not necessary to change the cylinder head structure and the small volume of the intake passage still has a small negative pressure, which is taken into account for a good mixture formation of the injected fuel quantity. However, such systems have the disadvantage of limited variability.

[0007] Furthermore, a motor-type control device for intake and exhaust valves of an internal combustion engine is known. In this case, the valves are not operated via one or more mechanical camshafts driven by crankshafts, but via respective motors assigned to each valve. Such an electric motor has in each case a unique camshaft on its motor shaft, which camshaft controls the valve in a known manner. In such a simple configuration, the valve stroke is not variable. However, if desired, the valve control time can be varied within other ranges by controlling the electric motor in such a way as to take into account the engine speed as well as various operating parameters of the internal combustion engine. The disadvantage of this system, however, is that the construction costs are additionally very high due to the large number of motors integrated in the cylinder head. These motors cannot be designed weakly on the basis of the high forces generated. Furthermore, relatively expensive sensors that are less susceptible to interference are needed. This is because incorrect control of the valve will cause the valve head to contact the piston head and thus damage the engine.

[0008]

The object of the invention is to provide an internal combustion engine in which a device for reducing throttle losses with a correspondingly adjusted valve control time can be integrated as easily as possible into existing structures. It is to be.

[0009]

According to the present invention, at least one adjustable tensioning device is provided on each of the tension side and the unloaded side of at least one tensioning means. The tensioning device is controllable so that the speed ratio between the camshaft and the crankshaft can be varied.

[0010]

According to the present invention, the opening and closing times of the valves and the opening time of the valves, and also the opening and closing of the intake and exhaust valves of the internal combustion engine, are simple. The advantage is that the speed can also be influenced and controlled independently of each other. With a controllable tensioning device for the tensioning means for driving the at least one camshaft, the camshaft, which rotates at half the camshaft speed, in a conventional manner in a four-stroke internal combustion engine, relative to the crankshaft. Rotation can be varied, and thus the valve opening parameters can be effectively influenced.
With this type of dynamically variable valve control, a number of valve opening curves for intake and exhaust valves of any such type can be realized. In an internal combustion engine with a large number of camshafts, these camshafts are each provided with a separate pulling means and a separate A tensioning device is provided for independently controlling the tensioning means. However, it is likewise possible to provide a tensioning device for this pulling means, for example when driving two camshafts via a common pulling means. This tensioning device can exert the same effect on the two camshafts via a common tensioning means.

Furthermore, the control of the tensioning device, which is designed as a linear adjusting element, is controlled by an engine electronic control unit (Motron) in connection with the already existing characteristic fields.
It is advantageous to perform ic). For this purpose, a speed sensor is preferably provided directly on the camshaft. This rotational speed sensor enables real-time signal processing of the engine electronic control unit. The control of the linear adjustment device can advantageously be realized in digital technology, for example by means of a PID characteristic curve. This is because, in this manner, the microcontroller present in the control device of the internal combustion engine performs all control functions. Therefore, the valve opening control is based on
No additional components of the control device of the internal combustion engine are required.

It is further advantageous if the dynamically variable valve control of the valve opening time for controlling the valve stroke is assisted by a suitable valve stroke control device. This significantly increases the possibility of affecting the combustion course of the internal combustion engine. Moreover,
Valve stroke control involves the complete closing of the intake valve, whereby the throttle valve previously required for controlling the intake air volume can be omitted entirely.
This is because this function is performed by the intake valve.

[0013] Further advantageous embodiments of the invention are described in the dependent claims.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a schematic side view of a drive for a camshaft 8 via a crankshaft 2 of an internal combustion engine, not shown. The crankshaft 2 has a drive wheel (crankshaft wheel) 4 on the end face side. The drive wheel 4 cannot rotate relative to the camshaft 8 via the pulling means 6 (that is, rotate together). Drive wheel (camshaft wheel) 10 coupled to the drive shaft. The camshaft 8, which is located on the upper side, i.e. at the level of the valve in the cylinder head, is supported in the illustrated embodiment in the cylinder head of the internal combustion engine via a number of bearings 30, preferably sliding bearings. ing. The camshaft 8 has a number of cams 31, 32, 33
And 34, these cams can be operated directly or via suitable known pivoting and / or lever devices (not shown) of the intake and exhaust valves 35, 3 of the internal combustion engine.
6, 37 and 38 are controlled in relation to the working cycle of the internal combustion engine. In the embodiment shown, for example, only four valves are shown. However, internal combustion engines have at least one intake valve and one exhaust valve for each cylinder. The cams 31, 32, 33 and 34 each have a non-circular, preferably semi-elliptical, profile and are defined structurally invariant with respect to valve stroke and valve control time.
The pulling means 6 for making the correct working connection in relation to the phase of the camshaft 8 and the crankshaft 2 may be a link chain or a pin chain, a V-belt or a toothed belt.
FIG. 1 further shows two tensioning rollers 1 facing each other.
4 and 16, these tensioning rollers being the linear adjustment member 1 fixed to the engine casing 22.
Via 8 and 20, it is pressed against the pulling means 6. These linear adjusting members 18 and 20 are provided on the tension rollers 14 rotatably supported by these adjusting members.
And 16 allow for permanent tensioning of the pulling means 6 and, in a corresponding reversing control, extend or shorten or stagger the opening time of the intake and exhaust valves as the camshaft 8 rotates respectively. The camshaft 8 is accelerated or braked, depending on the situation. Although only one camshaft 8 is shown in the illustrated embodiment, in a known multi-cylinder four-stroke internal combustion engine in which a number of camshafts are provided for each cylinder row, each camshaft 8 is The pulling means 6 to be driven may be provided with at least two linear adjusting members 18 and 29. Thus, in an internal combustion engine with cylinders arranged in a so-called V-shape or boxer-shape in a row (each having one unique camshaft for controlling the intake and exhaust valves of each cylinder row) With a corresponding effect on the camshaft rotation by means of two linear adjusting members 18 and 20, respectively, a sufficient change in the valve opening time is realized for both intake and exhaust valves.

FIG. 2 is a plan view schematically showing the arrangement of the pulling means 6 in the drive unit on the end face side of the camshaft 8 by the crankshaft 2. The same parts as those shown in FIG. 1 are denoted by the same reference numerals, and are not repeatedly described. Further, the drive wheel 4 is coupled to a crankshaft (not shown) of the internal combustion engine at the end face side so as to be relatively non-rotatable, and is relatively non-rotatably coupled to an end face side of a cam shaft (not shown). Shown are the drive wheel 10 and the tensioning means 6 (which may be a chain or a belt) necessary to transmit the rotational movement. The effective diameter of the drive wheel 10 is twice the effective diameter of the drive wheel 4. Because, in a four-stroke engine, the valve is operated every two revolutions of the crankshaft, and accordingly, at least one camshaft must rotate at half the revolution of the crankshaft. It is. Furthermore, two freely rotatable tensioning rollers 14 and 16 are shown, which tensioning rollers 14 and 16 are connected via two linear adjusting members 18 and 20 to the engine casing 2.
2 and supports the pulling means and applies tension to the pulling means to provide a camshaft wheel (drive wheel) 1
0 is slightly rotatable with respect to the crankshaft wheel (drive wheel) 4. The directions of rotation of the crankshaft and camshaft are indicated by arrows 24. It is important that the two linear adjustment members 18 and 20 be properly controlled in order to accurately maintain the precise control times of the intake and exhaust valves of the internal combustion engine. At high rotational speeds, the friction and thus the efficiency loss of the overall valve actuation are increased, so that the two linear adjusting members 18 and 20 are configured to be very elastic and the tension roller 14 is pulled by the tension means 6 The pressing force of the linear adjusting member 18 pressing against the side 7 is gradually increased, and the linear adjusting member 20 pressing the tension roller 16 against the no-load side 9 of the pulling means 6.
It is preferable that the pressing force is gradually weakened so as to obtain a shift in the valve control time. The adjustment of the linear adjustment members 18 and 20 accelerates the camshaft 8 briefly within one revolution, thereby causing it to rotate in the direction of rotation (indicated by the arrow 24), whereby the tension side 7 Is strongly pushed by the tension roller 14 and the linear adjusting member 18. At the same time, the unloaded side 9 pushes back the tensioning roller 16 and the linear adjustment member 20 (which must be flexible only over a corresponding path), so that the pulling means 6
Is always completely nervous. By the reverse control, that is, the linear adjustment member 20 is caused to retreat and the linear adjustment member 18 is caused to enter and travel, so that the camshaft 8 is moved.
Is reduced by a predetermined amount, so that the camshaft 8 is rotated in a direction opposite to its rotational direction. This process of acceleration and deceleration is repeated a plurality of times during one rotation of the camshaft. This is because in a four-cylinder internal combustion engine, eight intake and exhaust valves must be controlled in the above-described manner by only two valves per cylinder and one camshaft located above. If a large number of valves are provided for each cylinder, a correspondingly large number of control cycles is required for each rotation of the camshaft.

At high rotational speeds of known internal combustion engines, the high dynamics of control of the linear drive members 18 and 20 (Dyn)
amik), these adjusting members 18, 20
Is preferably controlled by the associated control electronics. The characteristic curve of the valve-opening cam is taken, for example, from a target value characteristic field stored in the central engine control unit. This target value characteristic field contains various operating parameters of the internal combustion engine, such as crankshaft speed, load,
Can be taken from temperature and others. Individual target value characteristic fields of this type are defined and optimized for each internal combustion engine. The actual value of the rotational speed of the camshaft 8 is determined by a suitable angle increment system (Winkelinkrementsyste
m), for example, by contacting an inductive sensor system or a Hall sensor system (Hallgebersystem) for permanent removal in real time.

If two camshafts are provided for each cylinder row, preferably for controlling intake and exhaust valves, each having a unique camshaft, these camshafts have a common tension. It is driven by the crankshaft of the internal combustion engine via the means. In this case, the change in the valve control time is selectively
The adjustment can be performed by two linear adjusting members 18 and 20. This is because the two camshafts always rotate in the same phase via the pulling means connection. When each camshaft is driven by its own corresponding pulling means, each camshaft is accordingly assigned a unique tensioning device, which tensions all intake valves and all exhaust valves. The control times can be varied independently of each other. However, it is advantageous if the control time of the intake valves only is affected and the exhaust control time is kept constant, in order to make the whole control device even simpler. Because, when affecting the intake control time, a relatively large effect can be obtained to obtain good partial load efficiency,
This is because good full load characteristics can also be obtained.

The control of the linear adjusting members 18 and 20 is as follows.
It can be done in different formats. For example, it can be operated hydraulically and / or electro-hydraulically using engine oil as hydraulic fluid. Similarly, permanent or electromagnetic operation is also possible. Furthermore, it is also possible to use, for example, an electric linear motor.

The relative rotational movement of the camshaft 8 with respect to the crankshaft 2 is controlled on the pulling side 7 of the pulling means or on the no-load side 9.
Instead of using two linear tensioning devices 18 and 20, it is also possible to perform this selectively by means of a motor-driven adjusting element. For this purpose, an electric motor is advantageously fixed to the engine housing, the motor shaft of which drives the centrifugal disc. One tensioning roller 14 and 16 for variably tensioning the tensioning means 6 is mounted on the centrifugal disk. The drive device for driving the motors acting as servomotors together fulfills the same function as the linear adjustment members 18 and 20.

FIGS. 3a to 3d show qualitative shapes of the respective valve lift curves of the respective intake and exhaust valves.
The different control characteristics of the variable valve control are thus clear. The horizontal axis in the drawing is the time t
There have been described, the maximum value respectively in the vertical axis 57 is shown a valve stroke H _v is unchanged. Additionally, the d of a through 3 in FIG. 3, there is shown a line 56 of the one-dot chain line extending in the vertical direction, the line 56, the maximum valve stroke time of Hv t ₄ normal curve 40 and , for the time _{t 4,} is intended to clarify the deviation of the curve 42, 44, 46, 48 that have changed with respect to the normal of the curve 40. 3a to 3d vertical axis 57
Shows a time limit of the valve open time t ₀ obtained earlier. Furthermore, the vertical dashed line 58 shown in FIGS. 3 a to 3 d indicates the latest valve closing time t ₇ .

[0022] a in FIG. 3, the valve advantageously shows a valve stroke H _v over the opening time of the intake valve. Normal curve 4 not adjusted by linear adjustment members 18, 20
0 corresponds to the conventional setting of the valve control time. This valve is
It opened at time _{t 7,} the maximum valve stroke H at time _{t 4
v} reached, to close at time _{t 6.} The same drawing shows a compressed curve 42, which is preferably used for the partial load range of the internal combustion engine. Curve 42
Is achieved by the camshaft wheel (drive wheel) 10 being slightly decelerated by the adjusting members 18, 20 during the opening movement of the valve. From the time point t _4, i.e. the maximum valve stroke H _v, the cam shaft is accelerated such valve is rapidly closed totally shortened valve opening time is thereby achieved.

FIG. 3b shows a curve 44 shifted to the left, in which the valve opens completely early relative to the normal curve 40 (t _0). ), the maximum stroke is obtained at an early stage, it closes again early (t _5). This curve 44 shows that the linear adjustment members 18 and 20 are fully open, that is to say at time t _0.
From to time t _5, the cam shaft wheel 10 by being accelerated relative to the crank shaft wheel 4, is realized.

FIG. 3c further shows a curve 46 shifted to the right, in which the valve opens totally lagging behind the normal curve 40 (t ₃ ). , Its maximum stroke is obtained late and closes late (t ₇ ). This curve 46 shows that the linear adjusting members 18 and 20 are fully open, ie at time t _3.
From to time t _7, the cam shaft wheel 10 by delayed with respect to the crankshaft wheel 4, it is realized.

FIG. 3d shows a number of curve groups 50, 52,
Reference numeral 54 is shown, and these curves show the possibility of adjusting the valve opening time. Furthermore, a curve 48 is shown which is maximally widened, which curve shows the limit value of the valve opening time in an internal combustion engine at full load operation. In curve 48, the valve is already open at the time _{t 0,}
To obtain the maximum stroke at the time t _4, closed at time t _7. Curves 50 shows a common open time t0, the maximum value shifted to the left side of the valve stroke H _v relative to normal of the curve 40, the different valve opening characteristics and a different closing times. Curves 52 contrast, different valve opening having a common closure time t _7, the maximum value of the valve stroke H _v which are offset in the right direction with respect to the normal of the curve 40, and a different open times The characteristics are shown. The curves 54 is provided with the common vertex t _4, having a different valve opening times and the valve closing time, shows a broadened curve or compressed curve.

[Brief description of the drawings]

FIG. 1 is a schematic view of a drive device for a camshaft over a crankshaft of an internal combustion engine.

FIG. 2 is a plan view of the drive device on the end face side of the camshaft over the pulling means of the crankshaft.

3a is a diagram showing the valve stroke over the opening time of the intake and exhaust valves, b is a diagram showing a shifted curve with an advanced valve opening time, and c is a diagram showing the delayed valve opening time. FIG. 7 d shows a diagram with shifted curves, and FIG. 7 d shows all the possibilities of adjusting the valve opening time in a group of curves.

[Explanation of symbols]

2 crankshaft, 4 drive wheel (crankshaft wheel), 6 pulling means, 7 pulling side, 8 camshaft, 9 no load side, 10 drive wheel (camshaft wheel), 12 electric machine, 13 casing,
14,16 tension roller, 18,20 coil spring,
22 engine casing, 24 arrow, 30
Bearing, 31, 32, 33, 34 Cam, 35, 3
6, 37, 38 intake and exhaust valves, 40 normal curves, 4
2, 44, 46, 48 curves, 50, 52, 54 curves, 56 dashed line, 57 vertical axis, 58 dashed line

Continued on the front page (72) Inventor Hans-Dieter Schlein Germany Mark Groningen Enzstraße 12 (72) Inventor Reiner Walter Germany Federalheim Ludwig-Hofer-Strasse 2

Claims (18)

[Claims] 1. An internal combustion engine, in particular a four-stroke internal combustion engine, comprising at least one cylinder and at least one cylinder having a controllable intake cross section guided in said cylinder.
One intake passage and at least one exhaust passage having a controllable exhaust cross section guided out of the cylinder and controlling the intake cross section in the intake passage;
At least one intake valve is provided, and at least one exhaust valve for controlling an exhaust cross section is provided in an exhaust passage. The at least one intake valve and the at least one exhaust valve are connected to an internal combustion engine. At least one driven by at least one pulling means by a crankshaft of
In the form controlled by one camshaft in relation to the working cycle of the internal combustion engine, at least one pulling means (6) on at least one pulling side (7) and at least one unloading side (9). An adjustable tensioning device (27) is provided, said tensioning device (2).
7) The internal combustion engine, wherein the internal combustion engine is controllable so that the rotation speed ratio between the camshaft (8) and the crankshaft (2) can be changed. 2. The at least two tensioning devices (27)
2. The rotating camshafts (8) are mutually controllable such that they are periodically braked or accelerated in relation to the working cycle of the internal combustion engine and different operating parameters. 3.
An internal combustion engine as described. 3. The at least two adjustable tensioning devices (27) are such that the pulling side (7) of the pulling means (6) is strongly deflected whereas the unloading side (9) of the pulling means (6) Is weakly diverted or vice versa,
Mutually controllable, with the crankshaft (2)
3. The internal combustion engine according to claim 2, wherein the tensioning means (6) is fully tensioned on both the tension side (7) and the no-load side (9) at each rotational speed. 4. At least two controllable tensioning devices (27) are supported on the casing (22) of the internal combustion engine, and on the tension side (7) and the unloaded side (9) of the tensioning means (6), 4. The internal combustion engine according to claim 3, which has at least one tensioning roller (14, 16), which is rotatably mounted and rotates with the tensioning means (6). 5. The at least two controllable tensioning devices (27) are each provided with a linear adjustment member (18, 2).
0), and these adjusting members (18,
5. The internal combustion engine as claimed in claim 4, wherein the one end is fixed to the casing and the other end is provided with tensioning rollers pressed against the tensioning means. 6. The linear adjustment member (18, 20) is operable hydraulically and / or electrohydraulically.
An internal combustion engine as described. 7. A linear adjusting member (18, 20),
The internal combustion engine of claim 5 operable pneumatically. 8. The internal combustion engine according to claim 5, wherein the linear adjustment members (18, 20) can be operated electromagnetically. 9. The internal combustion engine as claimed in claim 5, wherein each of the linear adjusting members (18, 20) is motor-operable via one linear motor. 10. The at least one intake valve and the at least one exhaust valve of at least one cylinder are each assigned a unique intake or exhaust camshaft. 2. The internal combustion engine according to claim 1. 11. The internal combustion engine according to claim 10, wherein the intake camshaft and the exhaust camshaft are commonly driven by a camshaft (2) via a pulling means (6). 12. The internal combustion engine according to claim 10, wherein the intake camshaft and the exhaust camshaft are each driven by a crankshaft (2) via one separate pulling means (6). 13. A tensioning means (6) for driving an intake camshaft and an exhaust camshaft, wherein each of said linear adjustment members (18, 20) has an influence on the rotational speed ratio of said tensioning means to said crankshaft (2). 13. The internal combustion engine according to claim 12, comprising: 14. The method according to claim 1, wherein the control of the at least two linear control elements is effected via an engine electronic control unit in connection with different operating parameters of the internal combustion engine. An internal combustion engine according to any one of the preceding claims. 15. The method according to claim 1, wherein the control of the at least two linear adjustment members is effected via a digital regulator having PID characteristics. Internal combustion engine. 16. The control of at least two linear control elements (18, 20) for influencing the valve opening time is combined with the control of intake and / or exhaust valves of an internal combustion engine. Item 16. The internal combustion engine according to any one of Items 1 to 15. 17. The internal combustion engine according to claim 16, wherein the valve stroke (H _v ) of the intake valve can be reduced periodically and / or permanently to zero independently of the working cycle of the internal combustion engine. 18. The internal combustion engine according to claim 17, wherein the amount of the combustion gas supplied to the internal combustion engine is controlled exclusively by controlling an intake valve.