JP7106933B2 - valve gear for internal combustion engine - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to a valve train for an internal combustion engine, and more particularly to a valve train for opening and closing intake valves or exhaust valves (collectively referred to as engine valves) of an internal combustion engine.

In such a valve gear, a camshaft is rotationally driven by a crankshaft, and a cam provided on the camshaft opens an engine valve against the biasing force of a valve spring.

When the engine valve opens and closes, the camshaft is subjected to a valve opening torque (positive torque) that pushes the camshaft back in the opposite direction of rotation, i.e., in the reverse direction, due to the biasing force of the valve spring, and the camshaft is generated alternately with a closing torque (this is referred to as a negative torque) that pushes forward in the rotational direction, that is, in the forward rotation direction. Due to this torque fluctuation, a rotation fluctuation of the camshaft occurs. There is a problem such as rattle sound (cracking noise) occurring between

Conventionally, therefore, a camshaft is provided with a cancel cam for generating an anti-phase cancel torque that cancels out the fluctuating torque.

JP 2008-180214 A JP 2010-84526 A JP 2010-281221 A

By the way, there is a case where a variable mechanism is provided to change the valve timing of the engine valve. In this case, the fluid pressure supplied to the variable mechanism is controlled for valve timing control.

SUMMARY OF THE INVENTION Accordingly, an object of the present disclosure is to provide a valve gear for an internal combustion engine that can simplify fluid pressure control for a variable mechanism.

According to one aspect of the present disclosure,
a camshaft rotationally driven by a crankshaft of an internal combustion engine, the camshaft having a cam that opens an engine valve against the biasing force of a valve spring;
a variable mechanism configured to vary valve timing of the engine valve with respect to crank phase;
a cancel cam that is provided on the camshaft and causes the camshaft to generate cancel torque that cancels fluctuation torque generated in the camshaft by opening and closing the engine valve;
with
The cancel cam is constructed and arranged so that the total torque, which is the sum of the fluctuating torque and the cancel torque, is always a positive torque that tends to push back the camshaft in the reverse direction. A valve train for an internal combustion engine is provided.

Preferably, the valve gear further comprises a fluid pressure control device configured to control fluid pressure supplied to the variable mechanism,
The fluid pressure control device stops supplying fluid pressure to the variable mechanism when retarding the valve timing.

Preferably, a plurality of the cancel cams are provided.

According to the present disclosure, fluid pressure control for the variable mechanism can be simplified.

It is a schematic longitudinal cross-sectional view of a valve train. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1; 1 is a schematic plan view of a valve train; FIG. FIG. 4 is a valve lift diagram showing how valve timing changes. FIG. 10 is a diagram showing the profile of a cancel cam; 4 is a cam lift diagram of a cancel cam; FIG. 4 is a graph showing fluctuating torque (cam torque) for each cylinder and total cam torque; 5 is a graph showing cancel torque for each cancel cam and total cancel torque; 4 is a graph showing total cam torque, total cancel torque and total torque; FIG. 5 is a diagram showing the states of the variable mechanism and the hydraulic control device when advancing the valve timing; FIG. 10 is a diagram showing states of the variable mechanism and the hydraulic control device when the valve timing is retarded; FIG. 4 is a diagram showing states of a variable mechanism and a hydraulic control device when valve timing is held;

Embodiments of the present disclosure will be described below with reference to the accompanying drawings.

1 to 3 show the valve operating system of this embodiment. 1 is a schematic vertical cross-sectional view of the valve train, FIG. 2 is a cross-sectional view taken along line II--II of FIG. 1, and FIG. 3 is a schematic plan view of the valve train.

The internal combustion engine (engine) of the present embodiment is a multi-cylinder diesel engine mounted on large vehicles such as trucks and buses, and specifically is an in-line six-cylinder diesel engine. However, the application, type, etc. of the vehicle and engine are not limited and are arbitrary.

A rotational driving force from a crankshaft (not shown) is transmitted to the camshaft 1 through a power transmission mechanism (not shown) consisting of a gear mechanism. The engine of this embodiment is a DOHC engine, and the camshaft 1 is an intake camshaft for opening and closing an intake valve. However, additionally or alternatively, the present disclosure may be applied to an exhaust camshaft for driving an exhaust valve (not shown). Intake valves and exhaust valves are collectively called engine valves.

For convenience, one end side (left side in FIG. 1) in the direction (axial direction) of the central axis C1 of the camshaft 1 is referred to as front, and the other end side (right side in FIG. 1) is referred to as rear. These longitudinal directions coincide with the longitudinal directions of the engine and the vehicle (the engine is vertically installed). However, they do not necessarily have to match. #1 cylinder to #6 cylinder are arranged in order from the front. 1 and 3 show the configuration of one cylinder (#6 cylinder).

The valve train includes a camshaft 1 having a cam 4 for opening the intake valve 3 against the biasing force of a valve spring 2, and a variable valve timing valve configured to vary the valve timing of the intake valve 3 with respect to the crank phase. A mechanism 5 and cancel cams 6A and 6B provided on the camshaft 1 for generating cancel torque in the camshaft 1 for canceling fluctuating torque generated in the camshaft 1 by opening and closing the intake valve 3.

Two intake valves 3 are provided for each cylinder, and these two intake valves 3 are opened and closed simultaneously by a valve bridge 8 . When the intake valve 3 is opened, the cam 4 and the rocker arm 9 push the valve bridge 8 downward (toward the back in the thickness direction of FIG. 3) against the biasing force of the valve spring 2 . On the other hand, when the intake valve 3 is closed, the biasing force of the valve spring 2 pushes the valve bridge 8 upward (toward the front side in the thickness direction of the paper surface of FIG. 3).

The camshaft 1 is held between a cam carrier 12 on the lower side and a cylinder head 13 on the upper side so as to be radially rotatable. The camshaft 1 is provided with flanges 14 and 15 that axially sandwich the cam carrier 12 and the cylinder head 13 and position the camshaft 1 in the thrust direction.

A rear end portion of the camshaft 1 positioned behind the cam carrier 12 and the cylinder head 13 is rotatably accommodated in a housing 30 of the variable mechanism 5 . The housing 30 is provided with an input gear 17 with which the final gear 16 of the power transmission mechanism is meshed. The camshaft 1 receives rotational driving force from the crankshaft through the input gear 17 .

The cam 4 is fixed on the outer peripheral portion of the camshaft 1 . The rocker arm 9 is rotatably supported by the rocker shaft 18 . C2 indicates the central axis of the rocker shaft 18; A rocker roller 19 is rotatably provided on the rocker arm 9 , and the rocker roller 19 is always in contact with the cam 4 . The rocker arm 9 is provided with an extension 20 that engages the upper surface of the valve bridge 8 .

The variable mechanism 5 is configured to steplessly and continuously change the valve timing of the intake valve 3 between the most advanced position S1 and the most retarded position S2 as shown in FIG. Here, the valve timing includes both the opening timing at which the engine valve starts opening and the closing timing at which the engine valve finishes closing. A crank phase period or a cam phase period during which the engine valve is open (that is, the valve lift amount VL is greater than zero) is called a working angle. In this embodiment, the working angle Δαs and the maximum valve lift VLmax are kept constant, while the opening timing and the closing timing are continuously changed by the variable width Δαh.

As shown in FIGS. 1 and 2, the variable mechanism 5 has a rotor 31 formed at the rear end of the camshaft 1 and the above-described housing 30 accommodating the rotor 31 in a relatively rotatable manner.

As shown in FIG. 2, the housing 30 has a plurality of (four) housing vanes 32 protruding radially inward at equal intervals in the circumferential direction, and hydraulic chambers 33 are formed between these housing vanes 32 . On the other hand, a plurality of (four) rotor vanes 34 protruding radially outward are formed on the rotor 31 at regular intervals in the circumferential direction. Of the partitioned hydraulic chambers 33 , the advancing chamber 35 is positioned rearward in the rotational direction, and the retarding chamber 36 is positioned forward in the rotational direction.

An advance oil passage 37 communicating with an advance chamber 35 and a retard oil passage 38 communicating with a retard chamber 36 are formed inside the camshaft 1 . An advance oil supply hole 39 for communicating the advance oil passage 37 with the oil gallery 41 is formed inside the cylinder head 13 . A retarding oil supply hole 40 for communicating the retarding oil passage 38 with an oil gallery 41 is formed inside the cam carrier 12 . The oil gallery 41 is a space as an oil reservoir that is formed inside the cylinder block and stores high-pressure oil (pressure oil as pressure fluid).

The advance chamber 35, the advance oil passage 37, and the advance oil supply hole 39 constitute an advance passage. The retardation chamber 36, the retardation oil passage 38, and the retardation oil supply hole 40 constitute a retardation passage. A hydraulic control device is provided in order to control the hydraulic pressure supplied to the advance channel and the retard channel and, in turn, to control the hydraulic pressure supplied to the variable mechanism 5 .

The hydraulic control device includes an oil gallery 41 as a hydraulic pressure source, an oil pan 43 as an oil tank for storing oil at normal pressure, these oil gallery 41, oil pan 43, advance oil supply hole 39 and retard oil supply hole 39. A switching valve (referred to as OCV) 42 for switching the communication state of the oil supply hole 40, and an electronic control unit (referred to as ECU) 100 as a control unit, circuitry, or controller configured to control the OCV 42. . The ECU 100 controls the engine and includes a CPU, ROM, RAM, input/output ports, storage devices, and the like. The OCV 42 is composed of a solenoid valve.

As shown in FIG. 10, the OCV 42 has a plurality of (specifically, four) ports forming the inlet and outlet of oil, that is, a first switching port Q1, a second switching port Q2, a third switching port Q3 and a fourth switching port. has Q4. The first switching port Q1 is connected to the oil gallery 41 . The second switching port Q 2 is connected to the advance oil supply hole 39 and communicates with the advance chamber 35 . The third switching port Q3 is connected to the oil supply hole 40 for retardation, and is communicated with the retardation chamber 36 . A fourth switching port Q4 is connected to the oil pan 43 .

An oil pump (not shown) sucks the normal pressure oil from the oil pan 43 and supplies it to the oil gallery 41 as high pressure oil. Instead of the oil gallery 41, an oil pump may be used directly as a hydraulic source.

As shown in FIGS. 1 and 3, in this embodiment, a plurality of cancel cams are provided. Specifically, two cancel cams, that is, a first rear cancel cam 6A and a second front cancel cam 6B are provided. be provided. These first and second cancel cams 6A and 6B are fixed to the outer peripheral portion of the camshaft 1 in close proximity to each other.

Similar to the cam 4, these cancel cams 6A and 6B push down springs 27A and 27B through rocker arms 25A and 25B and valve bridges 26A and 26B, respectively, which are for canceling, when the camshaft 1 rotates. 1 is generated. Such a torque canceling mechanism is configured substantially in the same manner as the intake valve driving mechanism described above, the only difference being that the intake valve 3 is not provided. Therefore, the parts of the intake valve driving mechanism can be used to manufacture the torque canceling mechanism at low cost.

The first and second canceling rocker arms 25A and 25B are configured in the same manner as the rocker arm 9 described above, have rocker rollers 19 and extensions 20, and are rotatably supported by a common rocker shaft 18. . These rocker arms 25A and 25B are not connected to each other and operate independently. Two canceling first and second springs 27A, 27B are provided for each of the canceling cams 6A, 6B. These springs 27A and 27B are sandwiched between the first and second canceling valve bridges 26A and 26B and the upper surface of the cam carrier 12 and installed. The external dimensions of the springs 27A and 27B are substantially the same as the external dimensions of the valve spring 2, and the structure of the valve bridges 26A and 26B is the same as that of the valve bridge 8 described above. Therefore, it is possible to reduce costs by sharing parts. The cancel cams 6A and 6B compress the springs 27A and 27B, and positive torque is applied to the camshaft 1 when the springs 27A and 27B push back in the reverse direction. Further, the cancel cams 6A and 6B extend the springs 27A and 27B, and negative torque is applied to the camshaft 1 when the springs 27A and 27B push forward in the forward rotation direction.

In the case of this embodiment, cylinders #1 to #6 are arranged in order from the front. Periodically fluctuating torque occurs six times (=N times, where N is the number of cylinders). In principle, the camshaft 1 should be provided with one cancel cam having six (N) cam lobes because it is sufficient to generate the cancel torque of the opposite phase to cancel this fluctuation torque six times.

However, in this case, it is necessary to machine as many as six cam lobes on the short circumference of the cancel cam, which makes it difficult or practically impossible to machine the cam lobes. Therefore, in this embodiment, a plurality of cancel cams, specifically two (n=2), are provided for one camshaft 1, and cancel torque is generated three times (=N/n times) for each cancel cam. I am trying to let As a result, the number of cam lobes to be machined into one cancel cam can be halved (3=N/n), and the machining of the cam lobes can be facilitated.

FIG. 5 shows the cam profile of the first cancel cam 6A. Also, FIG. 6 shows a cam lift diagram of the first cancel cam 6A. The first cancel cam 6A has three cam lobes 29 of the same shape at equal intervals in the circumferential direction (cam phase intervals of 120°=360/(N/2)°) projecting radially outward from the base circle 28. have. The first cancel cam 6A generates a positive cancel torque each time the cam lobe portion 29 pushes down the spring 27A. The second cancel cam 6B also has the same cam profile as the first cancel cam 6A. The first cancel cam 6A and the second cancel cam 6B are fixed to the inner camshaft 11 with a cam phase difference of 60° (=360/(N/2)/2°) from each other. A canceling torque is generated at a 60° cam phase interval, that is, at a 120° crank phase interval.

In FIG. 7, the line a indicates the fluctuating torque (referred to as cam torque) generated in the camshaft 1 each time the intake valves of cylinders #1 to #6 are opened and closed. Regarding each cam torque, when the intake valve 3 is opened, when the cam 4 pushes down the intake valve 3 against the urging force of the valve spring 2, the camshaft 1 has a rotation direction R and a rotation direction R to push it back. A positive torque in the opposite direction (ie, reverse direction) is generated. Conversely, when the intake valve 3 is closed, the valve spring 2 tends to push the cam 4A and the camshaft 1 in the rotation direction R (that is, the forward rotation direction). is generated.

When these cam torques for each cylinder are added together, the total cam torque shown by line b in FIG. 7 is obtained. The total cam torque b is a fluctuating torque that fluctuates in a crank phase cycle of 120° (=720/N°) symmetrically on the positive side and the negative side around the zero torque position. Here, it is assumed that the variable mechanism 5 is controlled to the most advanced position S1.

On the other hand, in FIG. 8, lines c and d indicate fluctuating torques (called cancel torques) generated in the camshaft 1 by the first and second cancel cams 6A and 6B, respectively. The positive/negative of cancel torque is the same as the positive/negative of cam torque, as described above. Adding these canceling torques c and d gives a total canceling torque as indicated by line e in FIG.

Unlike the total cam torque b, the total cancel torque e fluctuates at a crank phase cycle of 120° (=720/N°) symmetrically on the positive side and negative side around the torque position of the predetermined positive value Tc. is the fluctuating torque. It is characteristic that the torque center position of the total cancel torque e is shifted from zero to the positive side. The first cancel cam 6A and the second cancel cam 6B are constructed and arranged so as to obtain such a total cancel torque e.

FIG. 9 shows total cam torque b, total cancel torque e, and total torque f, which is the sum of the total cam torque b and total cancel torque e.

The total cancel torque e is out of phase with the total cam torque b by 60° (=720/N/2°) in crank phase. Therefore, the total cam torque b can be canceled by the total cancel torque e, and the torque fluctuation of the camshaft 1 caused by the opening and closing of the intake valve 3 can be suppressed.

Actually, the amount of torque fluctuation of the total torque f (upper and lower width of torque fluctuation waveform) is greatly reduced from the total cam torque b before cancellation, and the torque fluctuation of the camshaft 1 is greatly suppressed.

In addition, by suppressing the torque fluctuation of the camshaft 1, the rotation fluctuation of the camshaft 1 can be suppressed. Further, it is possible to reduce the rattle noise (tooth rattle) generated between the input gear 17 provided on the camshaft 1 and the final gear 16 meshed therewith. In general, a scissors gear is provided to reduce the rattle noise, but in this embodiment, the scissors gear can also be omitted, thereby reducing the manufacturing cost.

By the way, as shown in the figure, the total torque f is always a positive torque. It's becoming The first cancel cam 6A and the second cancel cam 6B are constructed and arranged so as to obtain such a total torque f.

The phase difference between the cam 4 and the first and second cancel cams 6A, 6B remains constant. Therefore, even if the variable mechanism 5 changes the cam phase with respect to the crank phase, the phase difference between the total cam torque b and the total cancel torque e does not change. Therefore, regardless of changes in valve timing, the total torque f is always positive. Even if the valve timing is changed, all of the lines b, e, and f shown in FIG. 9 simply move in the horizontal direction.

Assuming that the total torque f is always positive torque in this way, the camshaft 1 always receives a reverse torque that pushes it back in the reverse direction. As a result, it is possible to greatly simplify the hydraulic control performed on the variable mechanism 5 by the hydraulic control device, as described below.

FIG. 10 shows the states of the variable mechanism 5 and the hydraulic control device when the valve timing is changed to the advance side (at the time of advance). Similarly, FIG. 11 shows the states of the variable mechanism 5 and the hydraulic control device when the valve timing is retarded (during retardation). FIG. 12 shows the states of the variable mechanism 5 and the hydraulic control device when the valve timing is held at the same phase (when the phase is held).

As shown in FIG. 10, the camshaft 1 is constantly applied with a reverse torque Tr resulting from the above-described positive total torque f. This reverse torque Tr acts like a spring that urges the camshaft 1 in the reverse direction. Assuming the existence of this reverse torque Tr, the variable mechanism 5 is controlled as follows.

As shown in FIG. 10, when the valve timing is advanced, the OCV 42 is switched to the advance position by the ECU 100, the first switching port Q1 and the second switching port Q2 are brought into communication, and the third switching port Q3 and the third switching port Q3 are switched to the advanced position. 4 The switching port Q4 is brought into communication. Then, the high-pressure oil stored in the oil gallery 41 is introduced into the advance chamber 35 through the first switching port Q1 and the second switching port Q2 in order. The high-pressure oil in the retardation chamber 36 is discharged to the oil pan 43 through the third switching port Q3 and the fourth switching port Q4 in this order. Then, the torque in the forward rotation direction applied to the rotor 31 and thus the camshaft 1 by the oil pressure in the advance chamber 35 exceeds the reverse torque Tr. Advance angle operation is performed.

On the other hand, as shown in FIG. 11, when the valve timing is retarded, the OCV 42 is switched to the retarded position by the ECU 100, the first switching port Q1 is not communicated with any of the switching ports, and the second switching port Q2 and the second switching port Q2 are connected. The third switching port Q3 is in communication with the fourth switching port Q4.

Then, the supply of hydraulic pressure to the variable mechanism 5 is stopped, and hydraulic pressure is not supplied to either the advance chamber 35 or the retard chamber 36 . The high-pressure oil in the advance chamber 35 is discharged to the oil pan 43 through the second switching port Q2 and the fourth switching port Q4 in this order. The high-pressure oil in the retardation chamber 36 is discharged to the oil pan 43 through the third switching port Q3 and the fourth switching port Q4 in this order.

Thus, hydraulic pressure is discharged from both the advance chamber 35 and the retard chamber 36, and the camshaft 1 is retarded with respect to the housing 30 only by the reverse torque Tr, as indicated by the arrow h.

Generally, as indicated by the imaginary line i in FIG. 11, the first switching port Q1 is communicated with the third switching port Q3, and hydraulic pressure is supplied to the retard chamber 36 to retard the camshaft 1. be done. However, in this embodiment, when the camshaft 1 is retarded, it is not necessary to supply hydraulic pressure to the retard chamber 36 and thus the variable mechanism 5 . Therefore, it is possible to greatly simplify the hydraulic control during the retarding operation.

In addition, by stopping the supply of hydraulic pressure, the driving load of the oil pump can be reduced, which is advantageous in terms of improving fuel efficiency. Moreover, there is a possibility that the structure of the oil passage and the OCV 42 can also be simplified.

Since the volume of the retard chamber 36 increases when the camshaft 1 is retarded, it is necessary to replenish the retard chamber 36 with normal pressure oil. Therefore, the tip of the oil passage extending from the fourth switching port Q4 to the oil pan 43 is immersed in the oil of the oil pan 43. As shown in FIG. As a result, the normal pressure oil in the oil pan 43 can be sucked in accordance with the increase in the volume of the retardation chamber 36, and the retardation chamber 36 can be replenished with the normal pressure oil.

When the phase of the valve timing is held, for example, the OCV 42 is switched by the ECU 100 to a holding position as shown in FIG. are not connected to any switching port. Then, the supply of hydraulic pressure to the variable mechanism 5 is stopped, and the camshaft is moved to a phase position where the sum of the forward torque due to the hydraulic pressure in the advance chamber 35 and the sum of the reverse torque and the reverse torque Tr due to the hydraulic pressure in the retard chamber 36 is balanced. 1 is retained.

By the way, when torque fluctuations occur in the camshaft 1 due to the opening and closing of the intake valve, the hydraulic pressure in at least one of the advance chamber 35 and the retard chamber 36 fluctuates due to this, and the hydraulic pressure pulsation in phase with the torque fluctuation is It is also transmitted to another oil supply (not shown) connected to it via the oil gallery 41, and can affect the other oil supply.

However, according to the present embodiment, since the cancel cams 6A and 6B can suppress torque fluctuations based on the opening and closing of the intake valves, it is possible to suppress such hydraulic pulsations and reduce the influence on other oil supply units. .

Although the embodiments of the present disclosure have been described above in detail, the present disclosure can be practiced with other embodiments and modifications.

(1) The configuration of the variable mechanism can be changed arbitrarily, and the valve timing may be changed stepwise. Further, the fluid pressure for operating the variable mechanism may be fluid pressure other than hydraulic pressure, such as air pressure.

(2) In the above embodiment, the two cancel cams 6A and 6B are provided immediately before the cam 4 of the #6 cylinder, which is located at the rearmost position, or between the cams 4 of the #5 and #6 cylinders. However, the number of cancel cams is arbitrary, and if there are no restrictions such as machining of cam lobes without problems, the number of cancel cams may be one. Conversely, the number of cancel cams may be three or more. Also, the cancel cam should have a total number of cam lobes equal to the number of cylinders of the camshaft on which it is installed. should have The installation positions of the cancel cams can also be changed arbitrarily. For example, the two cancel cams 6A and 6B may be installed separated by one or more cylinders.

(3) In the above embodiment, a torque canceling mechanism including rocker arms 25A, 25B, valve bridges 26A, 26B, and springs 27A, 27B is used to generate canceling torque by canceling cams 6A, 6B. However, the mechanism can be changed as appropriate.

(4) In the above embodiment, both the opening timing and closing timing of the engine valve (intake valve 3) are variable, but only one of them may be variable. Also, the operating angle may be variable, and the valve lift amount may be variable.

Embodiments of the present disclosure are not limited to the above-described embodiments, and include all modifications, applications, and equivalents encompassed by the concept of the present disclosure defined by the claims. Accordingly, the present disclosure should not be construed in a restrictive manner, and can be applied to any other technology that falls within the spirit of the present disclosure.

1 camshaft 2 valve spring 3 intake valve 4 cam 5 variable mechanism 6A, 6B cancel cam 41 oil gallery 42 switching valve (OCV)
43 oil pan 100 electronic control unit

Claims (2)

a camshaft rotationally driven by a crankshaft of an internal combustion engine, the camshaft having a cam that opens an engine valve against the biasing force of a valve spring;
a variable mechanism configured to vary valve timing of the engine valve with respect to crank phase;
a cancel cam that is provided on the camshaft and causes the camshaft to generate cancel torque that cancels fluctuation torque generated in the camshaft by opening and closing the engine valve;
a fluid pressure control device configured to control fluid pressure supplied to the variable mechanism;
with
The cancel cam is constructed and arranged so that the total torque, which is the sum of the fluctuating torque and the cancel torque, is always a positive torque that tends to push back the camshaft in the reverse direction ,
The fluid pressure control device stops supply of fluid pressure to the variable mechanism when retarding the valve timing.
A valve gear for an internal combustion engine, characterized by: 2. The valve gear for an internal combustion engine according to claim 1 , wherein a plurality of said cancel cams are provided.

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