Internal combustion engine

Abstract

An exhaust-side variable valve mechanism (21) is set so that, when an engine is stopped, the valve timing of an exhaust valve is at the latest angle state, resulting in the maximum valve overlap. Therefore, the exhaust-side variable valve mechanism 21 has the maximum valve overlap amount at the start of the internal combustion engine. In the exhaust-side variable valve mechanism (21), the initial position of the valve timing of the exhaust valve is set to the latest angle position. Therefore, the internal combustion engine can secure intended internal EGR immediately after starting, and can reduce HCs in exhaust at the time of starting.

Description

internal combustion engine

[0001] The present invention relates to an internal combustion engine equipped with a variable valve mechanism that can change the valve timing of an exhaust valve.

[0002] For example, Patent Document 1 discloses a technology for increasing the amount of valve overlap by selecting either the most advanced control of an intake valve side variable valve timing mechanism or the most retarded control of an exhaust valve side variable valve timing mechanism depending on the cooling water temperature at start-up.

[0003] In Patent Document 1, even when the viscosity of the valve timing control oil is high and valve timing control is difficult, the internal EGR remaining in the combustion chamber can be varied to suppress the generation of black smoke and stabilize the combustion state.

[0004] However, the most advanced and most retarded control in Patent Document 1 displaces the intake valve side variable valve timing mechanism or the exhaust valve side variable valve timing mechanism to a hard limit position that determines the most advanced or retarded position, and it is not possible to quickly change the valve timing to the hard limit position, which may result in a deterioration in exhaust performance due to an increase in HC (hydrocarbons).

[0005] That is, there is room for further improvement in terms of improving exhaust performance at the start of an internal combustion engine.

[0006] Japanese Patent Application Laid-Open No. 2003-328789

[0007] The internal combustion engine has a variable valve mechanism that can change the valve timing of an exhaust valve, and a control unit that changes the valve timing of the variable valve mechanism to control a valve overlap amount, which is a period during which an intake valve opening period and an exhaust valve opening period overlap. The variable valve mechanism is set so that the valve timing of the exhaust valve is in a fully retarded state when the engine is stopped, and the valve overlap amount is maximized when the engine is started.

[0008] The internal combustion engine can ensure a desired internal RGR immediately after starting, and can reduce HC (hydrocarbons) in the exhaust gas when the internal combustion engine is started.

[0009] 1 is a schematic explanatory diagram showing an outline of a drive system for a vehicle equipped with an internal combustion engine according to the present invention; 2 is a characteristic diagram showing the operating ranges of the internal combustion engine according to the present invention; 3 is an explanatory diagram showing an example of the schematic configuration of an exhaust-side variable valve mechanism; 4 is an explanatory diagram showing the locking mechanism of the exhaust-side variable valve mechanism, where (a) is an explanatory diagram showing the locked state and (b) is an explanatory diagram showing the unlocked state; 5 is an explanatory diagram showing the valve timing of the intake and exhaust valves for each operating range of the internal combustion engine, where (a) is an explanatory diagram showing the valve timing in a first operating range A, (b) is an explanatory diagram showing the valve timing in a second operating range B, and (c) is an explanatory diagram showing the valve timing in a third operating range C.

[0010] An embodiment of the present invention will now be described in detail with reference to the drawings. Figure 1 is an explanatory diagram showing a schematic overview of a drive system of a vehicle 1 equipped with an internal combustion engine 10 according to the present invention. The vehicle 1 has a drive unit 3 that drives drive wheels 2 and a power generation unit 4 that generates electric power for driving the drive wheels 2.

[0011] The drive unit 3 has a drive motor 5 as a second electric motor that drives and rotates the drive wheels 2, and a first gear train 6 and a differential gear 7 that transmit the driving force of the drive motor 5 to the drive wheels 2. The drive motor 5 is supplied with power from a battery 8 that is charged with electricity generated by the power generation unit 4, etc.

[0012] The power generation unit 4 has a generator 9 as a first electric motor that generates electricity to be supplied to the drive motor 5, an internal combustion engine 10 that can drive the generator 9, and a second gear train 11 that transmits the rotation of the internal combustion engine 10 to the generator 9.

[0013] The vehicle 1 is a so-called series hybrid vehicle that does not use the internal combustion engine 10 as a power source. In other words, the internal combustion engine 10 is installed on the vehicle for the purpose of generating electricity. For example, when the remaining battery charge of the battery 8 becomes low, the vehicle 1 drives the internal combustion engine 10 to generate electricity with the generator 9 in order to charge the battery 8.

[0014] Explaining in more detail using FIG. 2, the internal combustion engine 10 secures the electric power required for traveling through highly efficient power generation, and is basically operated, for example, at an operating point within a narrow operating region along the optimum fuel economy line α so as to obtain the desired output (torque) with minimal fuel consumption.

[0015] More specifically, when the internal combustion engine 10 drives the generator 9 to generate electricity, it basically operates at an operating point within a predetermined first operating region A, which includes the best fuel economy point. Furthermore, when the vehicle 1 requires a large amount of power generation, the internal combustion engine 10 operates at an operating point within a predetermined second operating region B for high-output power generation, which is set at a higher rotation speed and a higher load than the first operating region A. Furthermore, the internal combustion engine 10 operates at an operating point within a third operating region C, which is set at a lower rotation speed and a lower load than the first operating region A, during startup, while warming up after a cold start, and during catalyst warm-up until the temperature of an exhaust purification catalyst disposed in the exhaust passage reaches a predetermined temperature. The minimum rotation speed within the third operating region C is set to a rotation speed higher than the so-called normal idle rotation speed. In other words, the operating point within the third operating region C is an operating point for fast idle.

[0016] Since the internal combustion engine 10 is mounted on a vehicle to generate electricity by driving the generator 9, it is operated within a limited operating range, i.e., a narrow (long) operating range along the best fuel economy line α, as described above, compared to an internal combustion engine that transmits the rotation of a crankshaft to drive wheels to drive the drive wheels. Furthermore, since the internal combustion engine 10 is for generating electricity, it is not operated in an operating range with a lower rotation speed than the third operating range C. When starting the internal combustion engine 10, the engine speed is increased to the rotation speed of the third operating range C by cranking. Specifically, the internal combustion engine 10 increases the rotation speed in one go to the minimum rotation speed in the third operating range C by cranking.

[0017] Fig. 2 is a characteristic diagram that schematically shows the operating ranges of the internal combustion engine 10. In Fig. 2, a first operating range A is continuous with a second operating range B and a third operating range C. A characteristic line S in Fig. 2 represents the torque characteristic when the throttle is fully open.

[0018] The traction motor 5 is a direct drive source for the vehicle 1, and is driven by AC power from, for example, a battery 8. The traction motor 5 also functions as a generator when the vehicle 1 is decelerating.

[0019] The generator 9 converts rotational energy generated in the internal combustion engine 10 into electrical energy and charges, for example, the battery 8. The generator 9 also functions as an electric motor that drives the internal combustion engine 10, enabling motoring of the internal combustion engine 10. The generator 9 may also function as a starter motor for the internal combustion engine 10. Note that the electric power generated by the generator 9 may not be charged into the battery 8, but may be supplied directly to the drive motor 5 depending on the operating state, for example.

[0020] The internal combustion engine 10 has a valve operating mechanism for an intake valve (not shown) and an exhaust valve (not shown), and a control unit 12 as a control section that controls the valve overlap amount of the intake valve and the exhaust valve.

[0021] The intake valve mechanism is, for example, a general direct acting valve mechanism, which means that the lift angle and the phase of the lift central angle of the intake valve in the internal combustion engine 10 are always constant.

[0022] The exhaust valve mechanism is an exhaust-side variable valve mechanism 21 that can change the valve timing of the exhaust valve. The exhaust-side variable valve mechanism 21 is a phase variable mechanism that continuously advances or retards the phase of the central angle of the exhaust valve lift (phase relative to the crankshaft). The phase variable mechanism is already known, for example, from Japanese Patent Application Laid-Open No. 2002-89303, and retards the phase of an exhaust camshaft (not shown), which drives the exhaust valve to open and close, relative to the crankshaft (not shown).

[0023] 3 is an explanatory diagram showing an example of the schematic configuration of the exhaust-side variable valve mechanism 21. The exhaust-side variable valve mechanism 21 is hydraulically driven and includes an inner rotor 22 (first rotor) and an outer rotor 23 (second rotor) fitted to the inner rotor 22 so as to be rotatable relative to the inner rotor 22.

[0024] The inner rotor 22 is fixed to the tip of an exhaust camshaft (not shown) and rotates integrally with the exhaust camshaft. When the exhaust camshaft rotates together with the inner rotor 22, a cam (not shown) provided on the exhaust camshaft drives the exhaust valves to open and close. Four vanes 24 are provided radially on the outer periphery of the inner rotor 22.

[0025] The outer rotor 23 is disposed coaxially on the outer peripheral side of the inner rotor 22. The outer rotor 23 is fixed to an exhaust cam sprocket 26 by a plurality of mounting bolts 25. The exhaust cam sprocket 26 is linked to the crankshaft via a timing chain (or timing belt) (not shown).

[0026] The inner circumference of the outer rotor 23 is formed with the same number (four) of protrusions 27 as the number of vanes 24 of the inner rotor 22, and each vane 24 is housed in a recess 28 formed between adjacent protrusions 27.

[0027] The tip of the vane 24 is in sliding contact with the inner periphery of the recess 28 via a first seal member 29, and the tip of the protrusion 27 is in sliding contact with the outer periphery of the inner rotor 22 via a second seal member 30. As a result, the inner rotor 22 and the exhaust camshaft, and the exhaust cam sprocket 26 and the outer rotor 23 are able to rotate relative to each other around the same axis.

[0028] The recess 28 is partitioned by the vane 24 to form two liquid-tight spaces 31, 32. Of these two spaces 31, 32, the space 32 on the rotational direction of the exhaust camshaft (the direction of arrow P1) relative to the vane 24 is a retard-side hydraulic chamber, and the space 31 on the opposite side (the direction of arrow P2) is an advance-side hydraulic chamber.

[0029] An advance angle side oil passage 33 that supplies hydraulic oil to the advance angle side hydraulic chamber 31 and a retard angle side oil passage 34 that supplies hydraulic oil to the retard angle side hydraulic chamber 32 are formed in the inner rotor 22 .

[0030] In this embodiment, when hydraulic oil is supplied to the advance hydraulic chamber 31 via the oil control valve 35 (see FIG. 4), the valve timing of the exhaust valve is advanced, and when hydraulic oil is supplied to the retard hydraulic chamber 32 via the oil control valve 35, the valve timing of the exhaust valve is retarded. The oil control valve 35 is a solenoid valve that controls the hydraulic oil supplied to the exhaust variable valve mechanism 21 to control the valve timing.

[0031] The exhaust-side variable valve mechanism 21 also has a lock mechanism 41 that can mechanically hold the valve timing of the exhaust valve at a position where the valve timing is most retarded (maximum retarded position).

[0032] 4A and 4B are explanatory diagrams that schematically show the lock mechanism 41 of the exhaust-side variable valve mechanism 21, where FIG. 4A shows the locked state and FIG. 4B shows the unlocked state.

[0033] 4, the lock mechanism 41 is generally composed of a lock pin 42 as an elongated position-retaining member that can advance and retreat parallel to the rotation axes of the inner rotor 22 and the outer rotor 23, a lock pin accommodating chamber 43 formed in the inner rotor 22 that accommodates the lock pin 42, a coil spring 44 disposed in the lock pin accommodating chamber 43 that constantly urges the lock pin 42 toward the outer rotor 23, and an accommodating recess 45 formed in the outer rotor 23 that can accommodate the tip of the lock pin 42 when the valve timing of the exhaust valve is at the most retarded position. The accommodating recess 45 is formed to be continuous with one of the multiple advance-side hydraulic chambers 31. The same hydraulic pressure as that of the advance-side hydraulic chamber 31 acts on the accommodating recess 45.

[0034] When the valve timing of the exhaust valve is at the most retarded position and hydraulic oil is not supplied to the advance-side hydraulic chamber 31, the locking mechanism 41 presses the locking pin 42 toward the accommodating recess 45 by the spring force of the coil spring 44, and the tip of the locking pin 42 is accommodated in the accommodating recess 45, thereby entering a locked state ( FIG. 4( a) ). In the locked state, the tip of the locking pin 42 is caught in the accommodating recess 45, mechanically holding the valve timing of the exhaust valve at the most retarded position. When in the locked state, the locking mechanism 41 restricts the valve timing of the exhaust valve from changing to the advance side.

[0035] When the valve timing of the exhaust valve is not at the most retarded position, the locking mechanism 41 is in an unlocked state (FIG. 4B) with the entire locking pin 42 housed in the locking pin housing 43. In the unlocked state, the locking mechanism 41 does not mechanically hold the valve timing of the exhaust valve.

[0036] When the valve timing of the exhaust valve transitions to the most retarded position due to, for example, the hydraulic pressure of the hydraulic oil supplied to the retard-side hydraulic chamber 32 or the cam torque acting on the exhaust camshaft, the spring force of the coil spring 44 accommodates the tip of the lock pin 42 in the accommodating recess 45. If no hydraulic oil is supplied to the advance-side hydraulic chamber 31 when the valve timing of the exhaust valve is at the most retarded position, the spring force of the coil spring 44 accommodates the tip of the lock pin 42 in the accommodating recess 45, and the lock mechanism 41 is in a locked state.

[0037] When the internal combustion engine 10 stops and the supply of hydraulic oil is stopped, the exhaust-side variable valve mechanism 21 shifts the valve timing of the exhaust valve to the retard side due to the cam torque caused by the force of the valve spring of the exhaust camshaft. In other words, when the internal combustion engine 10 stops, the exhaust-side variable valve mechanism 21 shifts to the most retarded position without control, and the lock mechanism 41 mechanically restrains (locks) the valve timing of the exhaust valve at the most retarded position.

[0038] The control unit 12 is capable of controlling the valve timing of the exhaust valve by controlling the oil control valve 35. In other words, the control unit 12 changes the valve timing of the exhaust valve to control the valve overlap amount, which is the period during which the intake valve opening period and the exhaust valve opening period overlap.

[0039] FIG. 5 is an explanatory diagram showing the valve timing of the intake and exhaust valves for each operating region of the internal combustion engine 10, where (a) shows the valve timing of the intake and exhaust valves in the first operating region A, (b) shows the valve timing of the intake and exhaust valves in the second operating region B, and (c) shows the valve timing of the intake and exhaust valves in the third operating region C.

[0040] In the first operating region A, the internal combustion engine 10 is set to a first exhaust valve timing in which the exhaust valve closing timing is near top dead center, and the valve overlap amount is small.

[0041] In the second operating region B, the internal combustion engine 10 is set to a second exhaust valve timing in which the closing timing of the exhaust valve is retarded from near top dead center, and the valve overlap amount is greater than that at the first exhaust valve timing.

[0042] In the third operating region C, the internal combustion engine 10 is set to a third exhaust valve timing in which the exhaust valve closing timing is significantly retarded from near top dead center, and the valve overlap amount is greater than that at the second exhaust valve timing.

[0043] The internal combustion engine 10 has a maximum valve overlap amount when it is started (at startup), and thereafter the valve timing of the exhaust valve is controlled to the advance side to reduce the valve overlap. In other words, the valve overlap amount during operation of the internal combustion engine 10 never becomes larger than the valve overlap amount at startup.

[0044] In addition, since the control unit 12 operates at an operating point within the third operating region C while the internal combustion engine is warming up after a cold start or while the exhaust purification catalyst is warming up, the control unit 12 controls the exhaust side variable valve mechanism 21 so that the valve timing of the exhaust valve is at the most retarded position at this time.

[0045] Here, the exhaust-side variable valve mechanism 21 is set so that the valve timing of the exhaust valve is at its most retarded position when the internal combustion engine 10 stops. In other words, the exhaust-side variable valve mechanism 21 is set so that when the engine is stopped, the valve timing of the exhaust valve is at its most retarded position, and the valve overlap amount is maximized.

[0046] Therefore, the exhaust-side variable valve mechanism 21 is already in a state where the valve timing of the exhaust valve is fully retarded so that the valve overlap amount is maximized when the internal combustion engine 10 is started. In other words, the exhaust-side variable valve mechanism 21 has the initial position of the valve timing of the exhaust valve set to the fully retarded position. In other words, the exhaust-side variable valve mechanism 21 is in a state where the valve overlap amount is maximized when the internal combustion engine 10 is started. The exhaust-side variable valve mechanism 21 has the initial position of the valve timing of the exhaust valve set to the fully retarded position.

[0047] Therefore, the internal combustion engine 10 can ensure the desired internal EGR (residual gas) immediately after starting the internal combustion engine 10, and can reduce HC (hydrocarbons) in the exhaust gas at the time of starting.

[0048] Furthermore, the exhaust-side variable valve mechanism 21 does not need to retard the valve timing of the exhaust valve at start-up, so the control amount (operation amount) of the oil control valve 35 of the internal combustion engine 10 is smaller at start-up than in a system that retards the valve timing of the exhaust valve at start-up to increase the valve overlap amount, and overall system costs (power consumption) can be reduced.

[0049] When the internal combustion engine 10 is started, the engine speed is increased in one go to the speed within the third operating region C, so even if the valve overlap amount at the time of starting is at its maximum, the engine does not stall at the time of starting.

[0050] The internal combustion engine 10 is mounted on a vehicle for generating electricity, and its operating range is limited (narrower) than the operating range of an internal combustion engine that transmits rotation of a crankshaft to drive the drive wheels of the vehicle.

[0051] Therefore, since the exhaust side variable valve mechanism 21 only needs to be able to accommodate a relatively limited operating range, it is possible to make the range of change in the valve timing of the exhaust valve relatively small (narrow), thereby reducing costs.

[0052] If the lock mechanism 41 of the exhaust-side variable valve mechanism 21 is a lock mechanism (intermediate lock mechanism) that holds the exhaust valve timing at an intermediate position between the most retarded and most advanced positions, the exhaust valve timing may be changed from the intermediate position to the advanced or retarded side. Therefore, such an intermediate lock mechanism requires a separate oil control valve dedicated to controlling the lock pin that restricts the relative rotation of the inner rotor and outer rotor at the intermediate position.

[0053] However, in the internal combustion engine 10 of the present application, the exhaust-side variable valve mechanism 21 has a lock mechanism 41 that holds the exhaust valve timing at the most retarded position, so the direction in which the exhaust valve timing can be changed from the state where it is held at the most retarded position is limited to the advance side. Therefore, the internal combustion engine 10 of the present application can use the oil control valve 35 that controls the valve timing to release the locked state by the lock pin 42 of the lock mechanism 41 in the exhaust-side variable valve mechanism 21. In other words, the exhaust-side variable valve mechanism 21 provided in the internal combustion engine 10 of the present application can be made less expensive than a variable valve mechanism that has an intermediate lock mechanism.

[0054] Although specific embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention.

[0055] For example, the internal combustion engine 10 may use a variable valve mechanism that can change the valve timing of the intake valve, rather than a direct acting valve mechanism. In this case, the internal combustion engine 10 can suppress (decompress) the in-cylinder pressure during cranking, enabling smooth starting with less vibration.

Claims

1. An internal combustion engine comprising: a variable valve mechanism capable of changing the valve timing of an exhaust valve; and a control unit that changes the valve timing of the variable valve mechanism to control the amount of valve overlap, which is the period during which the intake valve opening period and the exhaust valve opening period overlap, wherein the variable valve mechanism is set so that the valve timing of the exhaust valve is in a fully retarded state when the engine is stopped, maximizing the amount of valve overlap, and the amount of valve overlap is maximized when the engine is started.

2. The internal combustion engine according to claim 1, wherein the control unit controls the variable valve mechanism so that the valve timing of the exhaust valve is at the most retarded position while the internal combustion engine is warming up after a cold start and while a catalyst for exhaust purification is warming up.

3. The internal combustion engine according to claim 1, which is mounted on a vehicle for generating electricity.

4. An internal combustion engine according to claim 3, wherein said variable valve mechanism has a mechanical locking mechanism capable of holding the valve timing of said exhaust valve at a most retarded position.

5. An internal combustion engine according to claim 1, wherein the variable valve mechanism changes the valve timing of the exhaust valve by continuously retarding the phase of the lift central angle of the exhaust valve.

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