Patent Application
20050092271
This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application Nos. 2003-326790 and 2003-326791 filed in Japan on Sep. 18, 2003, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a valve gear with a cylinder suspending mechanism of an internal combustion engine (hereinafter referred to as engine).
2. Description of the Related Art
To realize the most suitable engine output characteristics according to an operation area, various types of engines, which perform the switching of the opening period or the lift amount of intake and exhaust valves, and the like, have been suggested (for instance, refer to Unexamined Japanese Patent Publication Nos. 2001-41017 and 2002-227624).
In the engine disclosed in Publication No. 2001-41017, a driven rocker arm supported by a rocker shaft is oscillated by a first cam to drive an intake valve to be open or close, and a drive rocker arm formed adjacent to the driven rocker arm and supported by the rocker shaft is oscillated by a second cam. A piston is fitted into a cylinder formed in the driven rocker arm so as to be slidable by hydraulic pressure, while in the drive rocker arm, an engaging projection that is engageable with the piston along with the oscillation is formed.
In a low revolution area of the engine, for instance, the piston of the driven rocker arm is switched to its lower position to cause the engaging projection of the drive rocker arm to strike at the air, to thereby open and close the intake valve along the shape of the first cam by using the driven rocker arm. In a high revolution area of the engine, on the contrary, the piston of the driven rocker arm is switched to its upper position to be pressed by the engaging projection of the drive rocker arm to oscillate the driven rocker arm with the drive rocker arm, to thereby open and close the intake valve along the shape of the second cam.
In the engine disclosed in Publication No. 2002-227624, a first rocker arm corresponding to a low-speed cam, a second rocker arm corresponding to a high-speed cam, and a third rocker arm corresponding to a suspension cam are supported in an intake-side rocker shaft, and a pair of intake valves is driven to open or close in liaison with the first and third rocker arms. There is provided a switch pin in each rocker arm to be slidable by hydraulic pressure in the axial direction of the rocker shaft. The rocker arms are connected with or disconnected from one another according to the sliding position of the switch pins.
In the low revolution area of the engine, for example, the connections of the rocker arms are released by the switch pins. One of the intake valves is driven to be open or close along the low-speed cam through the first rocker arm, and the other intake valve is practically kept closed by the suspension cam through the third rocker arm. In the high revolution area of the engine, the rocker arms are connected by the switch pins, and all the rocker arms are integrally oscillated by the high-speed cam to drive both the intake valves to be open or close along the high-speed cam.
As described above, in the engine disclosed in Publication No. 2001-41017, the switching is carried out in two operation states in each of which the intake valve is driven to be open or close by means of a corresponding one of the first and second cams. In the engine disclosed in Publication No. 2002-227624, the switching is performed in two operation states in one of which the intake valves are driven to be open or close by the low-speed cam and the suspension cam and in the other of which the intake valves are driven to be open or close by the high-speed cam. It has been desired to provide a cylinder suspending function for suspending certain cylinders in addition to the above-stated functions.
To add the cylinder suspending function, however, it is required to add a mechanism for stopping the oscillation of the rocker arms connected to the intake valves (namely the driven rocker arm in Publication No. 2001-41017 and the first and third rocker arms in Publication No. 2002-227624). This generates a problem that, with technologies disclosed in Publication Nos. 2001-41017 and 2002-227624, the entire valve gear would be enlarged in size as the configuration thereof becomes complicated.
A valve gear with a cylinder suspending mechanism requires that intake and exhaust valves of suspending cylinders be kept closed. For instance, as for an SOHC-type engine in which intake and exhaust valves are driven to open or close by a single camshaft, a circular suspension cam is provided on the camshaft, and intake and exhaust rocker arms are brought into contact with the suspension cam when cylinders are inoperative, to thereby hold the intake and exhaust valves closed. It is required in such an engine to form as many suspension cams as rocker arms on the camshaft. This causes problems, however, that the camshaft has to be long in its entire length, that the manhours of processing the camshaft are increased, and so on. Therefore, countermeasures against these problems have been suggested (refer to Unexamined Japanese Patent Publication No. 2002-201921 (
Publication No. 2002-201921 discloses an engine in which intake-side and exhaust-side rocker shafts each support a pair of drive rocker arms corresponding to a pair of intake and exhaust valves. According to the sliding movement of switch pins, the drive rocker arms are connected with or disconnected from their respective free rocker arms that are each oscillated by an intake cam, real suspension cam, and exhaust cam of a camshaft, to thereby arbitrarily open and close the intake and exhaust valves. The intake-side and exhaust-side drive rocker arms are located such that the intake-side drive rocker arms substantially correspond to their respective exhaust-side drive rocker arms in the axial direction of the rocker shaft, and a pair of suspension cams is formed on the camshaft so as to be located in between the corresponding intake and exhaust drive rocker arms. At the time of cylinder suspension, the corresponding intake and exhaust drive rocker arms are brought into contact with the common suspension cam, to thereby keep the intake and exhaust valves closed.
In an engine disclosed in Unexamined Japanese Patent Publication No. 2002-201921, suspension cams are reduced in number by half by providing a common suspension cam to intake and exhaust drive rocker arms. On the other hand, however, a pair of suspension cams is indispensable per cylinder due to constraints on layout of a cylinder suspending mechanism.
More specifically, as illustrated in
Accordingly, the engine disclosed in the publication requires that a pair of suspension cams be formed on the camshaft per cylinder, which discourages full achievement of reduction of a camshaft's entire length and a reduction in manhours of processing the camshaft.
An object of the present invention consists in providing a valve gear with a cylinder suspending mechanism of an internal combustion engine, whose entire valve gear mechanism is downsized by efficiently arranging the configuration of the valve gear including the cylinder suspending mechanism.
The valve gear with a cylinder suspending mechanism of an internal combustion engine according to the present invention comprises a first rocker arm having a tip end connected to either one of intake and exhaust valves and pivotably supported on a first rocker shaft, a second rocker arm located at one side of the first rocker arm, pivotably supported on the first rocker shaft, and driven by a first cam formed in a camshaft, a third rocker arm located at the other side of the first rocker arm, pivotably supported on the first rocker shaft, and driven by a second cam formed in the cam shaft and having a cam shape different from the first cam, a first switching mechanism for switching connection and disconnection of the first rocker arm with respect to the second or third rocker arm, and control means for controlling the switching of the first switching mechanism, in which the first switching mechanism includes a first piston slidably fitted into a first cylinder formed in the first rocker arm, a second piston slidably fitted into a second cylinder formed in the first rocker arm, a first engaging projection extending from the second rocker arm and formed to be engageable with the first piston, and a second engaging projection extending from the third rocker arm and formed to be engageable with the second piston, and the first and second pistons are switched between an engaging position and a non-engaging position with respect to the first and second engaging projections.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitative of the present invention, and wherein:
A valve gear with a cylinder suspending mechanism of an engine according to an embodiment of the present invention will be described below.
The engine according to the present embodiment is constructed as a V-six cylinder gasoline engine having four valves per cylinder, and is designed to be capable of switching a high-speed mode for realizing particularly high engine output, a low-speed mode for dealing with normal engine output, and a cylinder suspending mode for suspending cylinders located on one of two banks. Therefore, valve gears of both banks each have a switching mechanism for switching the low-speed mode and the high-speed mode, and one of the banks is provided with a cylinder suspending mechanism. First of all, an explanation will be provided about a configuration of the bank having the cylinder suspending mechanism (hereinafter referred to as a suspension cylinder bank, and the opposite one as a non-suspension cylinder bank).
As illustrated in
Cylinders are arranged in a row along the camshaft 2 in the longitudinal direction. The valve gear for one of the cylinders will be described below, and it should be noted that the valve gears for the other cylinders each have the identical configuration. As shown in
As illustrated in
Referring to
As illustrated in
Disposed in the lower cylinder 16a is a lower piston 18a (a second portion of a first piston). The lower piston 18a can slide in the lower cylinder 16a in the vertical direction while being restricted in rotation around the axis of the lower cylinder 16a by a restriction pin, not shown. In the upper cylinders 16b, there is located an upper piston 18b (a first portion of the first piston), which is also slidable in the upper cylinder 16b in the vertical direction. The upper piston 18b is made of a material having higher rigidity than a material used for making the lower piston 18a.
A cap 19 is pressed into an opening of the upper cylinder 16b and prevented by a snap ring 20 from being detached therefrom. In the upper cylinder 16b, there is interposed a compression spring 21 between the cap 19 and the upper piston 18b. As shown in
An operation window 22 is formed in a left surface of the low-speed cylinder portion 16, that is, in a side facing the camshaft 2, and a run-off 23 is formed as a recess in a left surface of the lower piston 18a. When the pistons 18a and 18b are in the upper positions shown in
Referring to
As is the case with the low-speed cylinder portion 16, a cap 27 is fitted in an opening of the cylinder 17a with a snap ring 26, and a compression spring 28 is interposed between the cap 27 and the piston 25. As illustrated in
There is formed an operation window 29 in a left surface of the high-speed cylinder portion 17, and also a run-off 30 as a recess in a left surface of the piston 25. When the piston 25 is located in the lower position shown in
As illustrated in
An operation arm portion 36 (first engaging projection) extends from an upper-side position of the roller 35 of the low-speed drive rocker arm 32 in a rearward direction along the axis of the camshaft 2. The operation arm portion 36 has a tip end that is bent into an L-shape toward the intake driven rocker arm 11 located in the right side thereof, to thereby face the operation window 22 of the low-speed cylinder portion 16. The low-speed drive rocker arm 32 is oscillated along the shape of the low-speed cam 6 while rotating the roller 35 on the low-speed cam 6 that is in rotation. In a base circular zone (zone in which a lift amount is 0) of the low-speed cam 6, the low-speed drive rocker arm 32 is oscillated in the valve-closing direction to separate the tip end of the operation arm portion 36 from the operation window 22 in the leftward direction as shown by a solid line in
There is formed a boss portion 39 in the high-speed drive rocker arm 38 (third rocker arm), the boss portion 39 being located at the rear of the intake driven rocker arm 11 on the intake rocker shaft 3 and pivotably supported on the intake rocker shaft 3. As is the case with the low-speed drive rocker arm 32, the high-speed drive rocker arm 38 is biased by a bias spring, not shown, in the valve-closing direction through a bias portion 39a, to thereby bring a roller 40, which is provided in the left side, into contact with the high-speed cam 9 as illustrated in
An operation arm portion 41 (second engaging projection) extends from an upper-side position of the roller 40 of the high-speed drive rocker arm 38 in a frontward direction along the axis of the camshaft 2. The operation arm portion 41 has a tip end that is bent into an L-shape toward the intake driven rocker arm 11 located in the right side thereof, to thereby face the operation window 29 of the high-speed cylinder portion 17. Like the low-speed drive rocker arm 32, the high-speed drive rocker arm 38 is oscillated along a shape of the high-speed cam 9 while rotating the roller 40 on the high-speed cam 9. In a base circular zone of the high-speed cam 9, the high-speed drive rocker arm 38 is oscillated in the valve-closing direction to separate the tip end of the operation arm portion 41 from the operation window 29 in the leftward direction as shown by a solid line in
According to the present embodiment, a first switching mechanism M1 is constituted by the lower and upper pistons 18a and 18b of the low-speed cylinder portion 16, the piston 25 of the high-seed cylinder portion 17, the operation arm portion 36 of the low-speed drive rocker arm 32, and the operation arm portion 41 of the high-speed drive rocker arm 38.
Contrary to the intake-side valve gear, the exhaust-side valve gear does not include the high-speed cylinder portion 17 of the intake driven rocker arm 11 and the high-speed drive rocker arm 38 corresponding thereto. A configuration of the exhaust-side valve gear will be described below.
As illustrated in
Referring to
In the above-described state, if the exhaust driven rocker arm 43 is oscillated counterclockwise, the exhaust valves are opened against the valve springs through the adjust bolts 46 of the valve-side arm portions 45. Hereinafter, an oscillating direction of members constructing the exhaust-side valve gear, including the exhaust driven rocker arm 43, an after-mentioned exhaust drive rocker arm 49 and the like, is defined as a valve-opening direction if the oscillating direction is counterclockwise, and a valve-closing direction if clockwise.
As illustrated in
The cylinder portion 48 will be roughly described below with the same reference numerals as those for the low-speed cylinder portion 16. The lower piston 18a (a second portion of a third piston) and the upper piston 18b (a first portion of the third piston) are fitted in the lower cylinder 16a (one half of a third cylinder) and the upper cylinder 16b (another half of the third cylinder) of the cylinder portion 48, respectively, to be slidable in the vertical direction. The pistons 18a and 18b are downwardly biased by the compression spring 21. When the pistons 18a and 18b are in the lower positions as shown in
The members including the lower piston 18a, the upper piston 18b, the cap 19, the compression spring 21 and the like are commonly used to be accommodated in the exhaust-side cylinder portion 48 and in the intake-side low-speed cylinder portion 16.
As illustrated in
The exhaust drive rocker arm 49 will be roughly described with the same reference numerals as those for the low-speed drive rocker arm 32. The exhaust drive rocker arm 49 is biased by a bias spring, not shown, in the valve-closing direction through the bias portion 33a, to thereby bring the roller 35, which is provided in the right side thereof, into contact with the exhaust cam 7. Extending from the exhaust drive rocker arm 49 in the rear direction is the operation arm portion 36. The operation arm portion 36 has the tip end that is bent leftward to have an L-shape, to thereby face the operation window 22 of the cylinder portion 48 of the exhaust driven rocker arm 43. The exhaust drive rocker arm 49 is oscillated along the shape of the exhaust cam 7 while rotating the roller 35. In the base circular zone of the exhaust cam 7, the exhaust drive rocker arm 49 is oscillated in the valve-closing direction to separate the tip end of the operation arm portion 36 from the operation window 22 in the rightward direction as shown by a solid line in
According to the present embodiment, a second switching mechanism M2 is constituted by the lower and upper pistons 18a and 18b of the cylinder portion 48, and the operation arm portion 36 of the exhaust drive rocker arm 49.
Descriptions about the valve gear for one cylinder of the suspension cylinder bank have been completed. The other cylinders each have a configuration identical to the aforementioned one.
Referring to
In the exhaust rocker shaft 4, an oil path 57 for cylinder suspending mode is formed along the axial direction of the shaft 4. The oil path 57 has front and rear ends that are open in front and rear end surfaces of the exhaust rocker shaft 4, respectively. The front end of the oil path 57 is connected to an OCV 58 for cylinder suspending mode via an oil supply path, not shown, formed in the cylinder head 1. One end of an L-shaped metal pipe 59 is pressed and fixed into the rear end of the oil path 57. The other ends of the intake-side and exhaust-side metal pipes 54 and 59 face each other with a prescribed distance therebetween and interfitted with respective ends of a rubber hose 60 to be connected to each other.
The OCV 55 for high-speed mode and the OCV 58 for cylinder suspending mode receive oil supply from a lubricating oil pump, not shown, provided to the engine, and are switching-controlled by an ECU 61 (which serves as control means and is an abbreviation for “engine control unit”) that is mounted on the vehicle, to thereby appropriately supply oil to the oil path 52 for high-speed mode and the oil path 57 for cylinder suspending mode.
As illustrated in
Referring to
As is clear from
A valve gear of a non-suspension cylinder bank has no cylinder suspending mechanism and has only a switching mechanism for switching between the low-speed mode and the high-speed mode. A concrete configuration of the valve gear of a non-suspension cylinder bank will be described hereinafter. In the intake side, the low-speed cylinder portions 16 of the intake driven rocker arm 11 and the low-speed drive rocker arm 32 are not provided (the high-speed cylinder portions 17 and the high-speed drive rocker arm 38 are maintained). The intake driven rocker arm 11 is oscillated directly by the low-speed cam 6 without the medium of the low-speed drive rocker arm 32, to thereby open and close the intake valve all the time.
In the exhaust side, the cylinder portion 48 of the exhaust driven rocker arm 43 and the exhaust drive rocker arm 49 do not exist. Therefore, the exhaust driven rocker arm 43 is oscillated directly by the exhaust cam 7 without the medium of the exhaust drive rocker arm 49, to thereby open and close the exhaust valve all the time. Since the intake and exhaust driven rocker arms 11 and 43 are constantly oscillated as stated, the suspension cam 8 of the camshaft 2 is not provided, either. Furthermore, the lack of the cylinder suspending mechanism entails the absence of the oil paths 51 and 57 for cylinder suspending mode, which are to be located in the intake and exhaust rocker shafts 3 and 4.
The following description is about an operating state of the valve gear with a cylinder suspending mechanism of the engine, which is configured in the aforementioned manner.
Switching control of the OCVs 55 and 58 is carried out by the ECU 61, based on engine speed Ne. For instance, the cylinder suspending mode (third mode) is activated in a rotation range where the engine speed Ne is less than a first threshold value Ne1, and an output demand to the engine is adequately low. The low-speed mode (first mode) is activated in a rotation range where the engine speed Ne falls in the range of from the first threshold value Ne1 to a second threshold value Ne2 (>Ne1), and ordinary engine output is required. The high-speed mode (second mode) is activated in a rotation range where the engine speed Ne is equal to or more than the second threshold value Ne2, and particularly high engine output is required. Hereinafter, the operating state of the valve gear will be described with respect to each mode.
In the suspension cylinder bank, the ECU 61 switching-controls the OCV 55 for high-speed mode and the OCV 58 for cylinder suspending mode and discontinues the oil supply to the oil path 51 for cylinder suspending mode and the oil path 52 for high-speed mode.
As a result, in the low-speed cylinder portion 16 of the intake driven rocker arm 11 and the cylinder portion 48 of the exhaust driven rocker arm 43, the lower pistons 18a and the upper pistons 18b are held in the lower positions by a biasing force of the respective compression springs 21, and the outer circumferential surfaces of the upper pistons 18b are exposed through the respective operation windows 22, as shown in
During the operation of the engine, the low-speed drive rocker arm 32, the high-speed drive rocker arm 38, and the exhaust drive rocker arm 49 are constantly oscillated along the shapes of the corresponding cams 6, 7 and 9. Along with the oscillation, the tip ends of the operation arm portions 36 and 41 are inserted into and separated from the operation windows 22 and 29 of the driven rocker arms 11 and 43.
The high-speed drive rocker arm 38 independently strikes at the air with the tip end thereof inserted into and separated from the run-off 30 that is exposed through the operation window 29 of the high-speed cylinder portion 17. The high-speed drive rocker arm 38 does not oscillate the driven rocker arms 11 and 43 as the after-mentioned low-speed drive rocker arm 32 and exhaust drive rocker arm 49 do.
The low-speed drive rocker arm 32 and the exhaust drive rocker arm 49 press the outer circumferential surfaces of the upper pistons 18b exposed through the operation windows 22 of the low-speed cylinder portion 16 and the cylinder portion 48 when being oscillated in the valve-opening direction. By so doing, the drive rocker arms 32 and 49 oscillate the corresponding driven rocker arms 11 and 43 in the valve-opening direction, to thereby open the intake and exhaust valves. When the low-speed drive rocker arm 32 and the exhaust drive rocker arm 49 are oscillated in the valve-closing direction, the corresponding driven rocker arms 11 and 43 receive the biasing force of the valve springs, which is produced along with the closing of the intake and exhaust valves, and are then oscillated in the valve-closing direction.
Consequently, the intake driven rocker arm 11 is oscillated with the low-speed drive rocker arm 32 to open and close the intake valves along the shape of the low-speed cam. The exhaust driven rocker arm 43 is oscillated with the exhaust drive rocker arm 49 to open and close the exhaust valves along the shape of the exhaust cam.
In the non-suspension cylinder bank, since the ECU 61 discontinues the oil supply to the oil path 52 for high-speed mode from the OCV 55 for high-speed mode, the high-speed drive rocker arm 38 strikes at the air as is the case with the suspension cylinder bank. Thus, the intake valves are driven to open and close along the shape of the low-speed cam 6, and the exhaust valves along the shape of the exhaust cam 7. As a consequence,. in the low-speed mode, the engine output required within the ordinary rotation range is realized by using the low-speed cam 6 and the exhaust cam 7.
While stopping the oil supply to the oil path 52 for high-speed mode in the suspension cylinder bank and the non-suspension cylinder bank, the ECU 61 supplies oil from the OCV 58 for cylinder suspending mode in the suspension cylinder bank.
The oil running from the OCV 58 flows through the oil path 57 of the exhaust rocker shaft 4 from the front side to the rear side to be supplied into the lower cylinder 16a of the exhaust driven rocker arm 43 via each communication path 65. The oil subsequently passes through the metal pipes 54 and 59 and the hose 60, and then flows through the oil path 51 of the intake rocker shaft 3 from the rear side to the front side. Eventually the oil is supplied into the lower cylinder 16a of the intake driven rocker arm 11 via each communication path 63.
In the lower cylinders 16a and the upper cylinders 16b of the intake driven rocker arm 11 and the exhaust driven rocker arm 43, the lower pistons 18a and the upper pistons 18b slide upward in response to hydraulic pressure of the supplied oil, resisting the compression spring 21, to be switched to the respective upper positions. This movement exposes the run-offs 23 of the lower pistons 18a through the respective operation windows 22. Therefore, the low-speed drive rocker arm 32 and the exhaust drive rocker arm 49 independently strike at the air with the respective tip ends inserted into and separated from the run-offs 23 exposed through the operation windows 22 of the corresponding driven rocker arms 11 and 43, to thereby halt the oscillating operation with respect to the driven rocker arms 11 and 43.
Since the high-speed drive rocker arm 38 also strikes at the air, in each cylinder of the suspension cylinder bank, the intake and exhaust valves are kept closed due to the biasing force of the valve springs, and the intake driven rocker arm 11 and the exhaust driven rocker arm 43 are held at valve-closing positions while the sliding-contact portions 15a and 47a of the cam-side arms 15 and 47 are in contact with the suspension cam 8.
In the non-suspension cylinder bank, the operation of each cylinder is continued as in the low-speed mode, and the vehicle is operated by torque generated in the non-suspension cylinder bank. At the same time, the suspension of each cylinder in the suspension cylinder bank makes it possible to cut back on fuel consumption.
In the suspension cylinder bank, the ECU 61 discontinues the oil supply to the oil path 51 for cylinder suspending mode from the OCV 58 for cylinder suspending mode, and on the other hand supplies oil to the oil path 52 for high-speed mode from the OCV 55 for high-speed mode.
In consequence, as in the low-speed mode, the outer circumferential surfaces of the upper pistons 18b are exposed through the respective operation windows 22 in the low-speed cylinder portion 16 of the intake driven rocker arm 11 and the cylinder portion 48 of the exhaust driven rocker arm 43.
The oil flowing in the oil path 52 is supplied through the communication path 64 into the cylinder 17a of the high-speed cylinder portion 17 in the intake driven rocker arm 11 of each cylinder. In the cylinder 17a, the piston 25 slides upward in response to the hydraulic pressure of the supplied oil, resisting the compression spring 28, to be switched to the upper position. The outer circumferential surface of the piston 25 is then exposed through the operation window 29.
As a result, in the exhaust side, the exhaust driven rocker arm 43 is oscillated with the exhaust drive rocker arm 49 along the shape of the exhaust cam 7, and the exhaust valve is driven to be open and close along the shape of the exhaust cam 7 as in the low-speed mode.
In the intake side, the pistons 18b and 25 of the low-cylinder portion 16 and the high-speed cylinder portion 17 are both exposed, and therefore can be pressed by the corresponding drive rocker arms 32 and 38. However, only the high-speed drive rocker arm 38 actually performs the pressing operation, and the low-speed drive rocker arm 32 strikes the air. This is because the high-speed cam 9 has a wider lift zone (or operation angle) and a greater lift amount, compared to the low-speed cam 6. In short, the intake valve is driven to be open and close along the shape of the high-speed cam 9 in the high-speed mode.
In the non-suspension cylinder bank as well as the suspension cylinder bank, oil is supplied to the oil path 52, and the intake valves are driven to be open and close along the shape of the high-speed cam 9. Consequently, in the high-speed mode, high engine output required in the high rotation range is realized by extending an opening period of the intake valves or by increasing the lift amount thereof, compared to the low-speed mode.
The valve gear with a cylinder suspending mechanism of the engine according to the present embodiment operates as stated above. According to the present embodiment, the low-speed drive rocker arm 32 and the high-speed drive rocker arm 38 are arranged in front and at the rear of the intake driven rocker arm 11 as stated, and the low-speed cylinder portion 16 and the high-speed cylinder portion 17 are disposed side by side in the intake driven rocker arm 11. Moreover, according to the sliding positions of the lower piston 18a and the upper piston 18b slidably fitted into the low-speed cylinder portion 16 and the piston 25 slidably fitted into the high-speed cylinder portion 17, the operation arm portions 36 and 41 extending from the low-speed drive rocker arm 32 and the high-speed drive rocker arm 38 are caused to perform pressing operation or to strike at the air.
The exhaust drive rocker arm 49 is located in front of the exhaust driven rocker arm 43, and the cylinder portion 48 is provided in the exhaust driven rocker arm 43. According to the sliding positions of the lower piston 18a and the upper piston 18b slidably fitted into the cylinder portion 48, the operation arm portion 36 extending from the exhaust drive rocker arm 49 is caused to perform the pressing operation or to strike at the air.
As a consequence, in the intake side, the members, such as the low-speed cylinder portion 16, the high-speed cylinder portion 17, the low-speed drive rocker arm 32, and the high-speed drive rocker arm 38, are efficiently arranged around the intake driven rocker arm 11 to gather in one place. In the exhaust side, the members including the exhaust drive rocker arm 49 and the like are efficiently arranged around the exhaust driven rocker arm 43 to gather in one place. Therefore, the configuration of the valve gear including the cylinder suspending mechanism can be well-organized in the cylinder head 1, which makes it possible to achieve not only the downsizing of an entire valve gear mechanism but also the downsizing of the engine.
Furthermore, with the result that the members of the valve gear mechanism are arranged to gather in one place, the cylinder portions 16, 17 and 48 of the driven rocker arms 11 and 43 and the drive rocker arms 32, 38 and 49 are inevitably made closer to one another, and the tip ends of the operation arm portions 36 and 41 extending from the drive rocker arms 32, 38 and 49 then face the cylinder portions 16, 17 and 48 at the substantially shortest distance. Therefore, the operation arm portions 36 and 41 can be reduced to the minimum in length. Consequently, it is possible to lessen the weight of the drive rocker arms 32, 38 and 49 while ensuring enough strength by forming these arms into efficient shapes, which encourages a reduction in inertial weight of the entire valve gear.
According to the present embodiment, the sliding-contact portions 15a and 47a of the cam-side arm portions 15 and 47 of the intake driven rocker arm 11 and the exhaust driven rocker arm 43 are brought into contact with the common suspension cam 8 in the cylinder suspending mode. Factors in achievement of the above configuration, and operation and advantages obtained due to the configuration will be described below in detail.
As is obvious from
Since the exhaust cam 7 is so located as to substantially correspond to the exhaust drive rocker arm 49 in the axial direction of the camshaft 2, there is formed a dead space on the camshaft 2 at the position corresponding to the exhaust driven rocker arm 43, and the suspension cam 8 is disposed in the dead space.
In consequence of the application of the above layout, it is possible to open and close the intake and exhaust valves according to the mode switches by means of the driven rocker arms 11 and 43 that individually function. Furthermore, it is also possible-to bring the sliding-contact portions 15a and 47a of the cam-side arm portions 15 and 47 extending from the intake and exhaust driven rocker arms 11 and 43 into contact with the common suspension cam 8. As a result, there simply has to be provided the single suspension cam 8 per cylinder on the camshaft 2. This makes it possible to shorten the entire length of the camshaft 2 and to reduce man-hours required to manufacture the camshaft 2, thereby lowering the cost of production, in comparison with the engine disclosed in Japanese provisional patent publication No. 2002-201921, which requires a pair of suspension cams per cylinder.
The suspension cam 8 may be narrow in view of the function if it simply serves to control the oscillation of the driven rocker arms 11 and 43. Due to restrictions for the processing of a cam, however, the suspension cam 8 needs to be located at some distance from an adjacent cam. To be concrete, in order to avoid interference of a grindstone with the adjacent cam when the suspension cam 8 is polished or in order to facilitate the work of removing burr of the polished cam, there needs to be a space between the suspension cam 8 and the adjacent cam. Therefore, each of the suspension cams 8 requires a considerable occupied space in the axial direction of the camshaft 2, and moreover as many occupied spaces as cylinders are required. Unlike the valve gear disclosed in the above Publication No. 2002-201921 which requires a pair of suspension cams per cylinder, the valve gear of the present embodiment functions by using the single suspension cam 8, and therefore, the entire length of the camshaft 2 can be shortened to a large degree.
Furthermore, not only the cams 6 through 9 located on the camshaft 2 but also the intake and exhaust driven rocker arms 11 and 43 and the intake and exhaust drive rocker arms 32, 38 and 49 can be efficiently arranged without waste. This makes it possible to achieve the downsizing of the entire valve gear and therefore to accomplish the downsizing of the engine as well.
Additionally, in the layout of the above-described valve gear, the boss portion 12 of the intake driven rocker arm 11 and the boss portion 44 of the exhaust driven rocker arm 43 partly overlap each other as shown in
The operation arm portions 36 and 41 of the low-speed drive rocker arm 32, the high-speed drive rocker arm 38 and the exhaust drive rocker arm 49 are so formed as to extend along the axial direction of the camshaft 2. The operation arm portions 36 and 41 have the respective tip ends bent into an L-shape toward the corresponding cylinder portions 16, 17 and 48, to thereby face the operation windows 22 and 29. Accordingly, as is the case with the cam-side arm portions 15 and 47 of the driven rocker arms 11 and 43, the operation arm portions 36 and 41 of the drive rocker arms 32, 38 and 49 have the respective tip ends facing the operation windows 22 and 29 of the cylinder portions 16, 17 and 48 at the substantially shortest distance. This lessens the weight of the drive rocker arms 32, 38 and 49 while ensuring enough strength by forming these arms into efficient shapes, which encourages a reduction in the inertial weight of the entire valve gear.
Although the explanation of the embodiment has been completed, the form of the present invention is not limited to the above embodiment. For instance, the invention is applied to the V-six cylinder gasoline engine having four valves per cylinder in the above embodiment. As long as the engine is one having a valve gear with a cylinder suspending mechanism, however, the engine does not have to be a V-six cylinder gasoline engine in terms of category and type. On the contrary, the invention may be applied to for example a diesel engine or an in-line four-cylinder engine having two valves per cylinder.
According to the embodiment, the cylinder suspending mechanism is provided to not only the intake side but also the exhaust side in the suspension cylinder bank, and the exhaust valve is kept closed while the cylinder suspending mode is activated. For instance, however, the exhaust driven rocker arm 43 may be oscillated directly by the exhaust cam 7 without the cylinder suspending mechanism of the exhaust side.
In the embodiment, not only the piston 25 of the high-speed cylinder portion 17 but also the upper piston 18b of the low-speed cylinder portion 16 is exposed to enable the pressing operation in the high-speed mode. However, only the piston 25 of the high-speed cylinder portion 17 is actually pressed. Therefore, it is not necessary to expose the upper piston 18b of the low-speed cylinder portion 16, and the upper piston 18b may be maintained in the upper position which exposes the run-off 23.
According to the embodiment, the exhaust drive rocker arm 49 is supported in front of the exhaust driven rocker arm 43, and the exhaust cam 7 and the suspension cam 8 are disposed on the camshaft 2 to correspond to the rocker arms 43 and 49. However, the rocker arms 43 and 49, and also the cams 7 and 8, may be located the other way around in the longitudinal direction. In this case, too, it is still possible to achieve exactly the same operation and advantages as in the layout of the valve gear described in the embodiment.
Furthermore, in the embodiment, the pistons 18a, 18b and 25 provided to the intake and exhaust driven rocker arms 11 and 43 are pressed or not pressed by using the operation arms 36 and 41 of the drive rocker arms 32, 38 and 49, to thereby oscillate the driven rocker arms 11 and 43 according to the mode switches. The configurations of the first and second switching mechanisms, however, are not limited to the above-mentioned configuration. For instance, like the engine disclosed in the above Publication No. 2002-201921, the drive rocker arms 32, 38 and 49 and the driven rocker arms 11 and 43 may be connected with or disconnected from one another with switch pins that slide in the axial direction of the camshaft 2.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-326791 | Sep 2003 | JP | national |
| 2003-326790 | Sep 2003 | JP | national |
