The present invention relates to a two-wheeled motor vehicle provided with a noise-reduction device.
As in ordinary vehicles, two-wheeled motor vehicles have a silencer or muffler provided in an exhaust passage. The muffler can offer certain reduction in noise produced by the exhaust on the motor vehicle. However, while traveling in a densely populated urban area, the two-wheeled motor vehicle is required to achieve a further noise reduction than as it achieves during the travel in a sparsely populated suburban area.
In general, the length and flow-passage area of an exhaust passage are determined based on the rated output of an engine. Accordingly, it may occur that when the two-wheeled motor vehicle is traveling at a low speed with low engine output, the length or the flow-passage area of the exhaust passage becomes excessively large and the engine efficiency is reduced. To avoid this problem, a prior technology relying on the use of an exhaust valve has been proposed. The exhaust valve is disposed in an exhaust passage and operable to reduce the flow-passage area or the length of the exhaust passage when the engine power output is small, thereby preventing a reduction in the engine efficiency.
An exhaust valve so configured as to reduce the cross-sectional area of a flow passage promises a certain level of noise reduction effect, as will be discussed below.
Exhaust noise produced by the engine is emitted along an exhaust passage. When the exhaust valve closes the exhaust passage, part of the exhaust noise is blocked from escaping to the outside by the exhaust valve. A certain level of noise reduction effect can thus be attained.
Such exhaust valve is disclosed in, for example, Japanese Patent Publication (JP-B2) No. 3242240. The exhaust valve disclosed in JP 3242240 B2 is disposed in an intermediate part of the exhaust passage of a two-wheeled motor vehicle. The degree of opening of the exhaust valve is proportional to the rotation angle of a throttle grip of the two-wheeled motor vehicle.
The relation between the rotation angle of the throttle grip and the degree of opening of the exhaust valve is that when the rotation angle of the throttle grip increase from zero to a predetermined angle, the degree of opening of the exhaust valve is approximately proportional to the rotation angle of the throttle grip. Due to such proportional relation, the exhaust valve begins to open simultaneously with the start of rotation of the throttle grip. With this arrangement, the noise becomes large even when the two-wheeled motor vehicle is traveling at a low constant speed.
In view of the travel in a closely populated urban area, it is highly desirable that the noise produced from an engine of the two-wheeled motor vehicle during the travel at a low constant speed is as low as possible.
It is an object of the present invention to provide a technique which is capable of reducing the noise produced from an engine when a two-wheeled motor vehicle is traveling at a low constant speed.
According to an aspect of the present invention, as recited in claim 1, there is provided a two-wheeled motor vehicle, comprising: a body frame; an engine mounted to the body frame for driving a rear wheel; an exhaust passage extending from the engine for discharging exhaust gas from the engine; a muffler provided at an outlet of the exhaust passage for reducing exhaust noise; an intake passage connected to the engine for supplying intake air into the engine; a throttle valve disposed in the intake passage for adjusting the amount of fuel gas to be supplied to the engine; a throttle grip rotatable by the driver to change the degree of opening of the throttle valve; and a noise-reduction device which, when a throttle ratio which is a ratio of the angle of operation of the throttle valve to a maximum rotation angle of the throttle grip is between zero and a predetermined value, reduces noise emitted from the engine.
According to the invention as recited in claim 2, the noise-reduction device comprises an exhaust valve which is configured to change a cross-sectional area of the exhaust passage and also to reduce the noise most efficiently when the exhaust valve has a minimum degree of opening.
According to the invention as recited in claim 3, the noise-reduction device comprises an intake valve which is configured to change a cross-sectional area of the intake passage and also to reduce the noise most efficiently when the degree of opening of the intake valve is minimal.
According to the invention as recited in claim 4, the noise-reduction device comprises an ignition device which is configured to advance ignition timing when the throttle ratio is between zero and the predetermined value.
According to the invention as recited in claim 5, the ignition timing of the ignition device is advanced when the predetermined value of the throttle ratio is 5 to 25%.
According to the invention as recited in claim 6, the minimum degree of opening of the exhaust valve is a degree of opening corresponding to a valve-opening area which is 15 to 35% of a valve-opening area achieved when the exhaust valve is fully opened.
According to the invention as recited in claim 7, the minimum degree of opening of the intake valve is a degree of opening corresponding to a valve-opening area which is 30 to 60% of a valve-opening area achieved when the intake valve is fully opened.
According to the invention as recited in claim 1, when the throttle ratio of the throttle grip is between zero and the predetermined value, the noise-reduction device operates to reduce the noise. When the two-wheeled motor vehicle is traveling at a low constant speed, the throttle ratio is between zero and the predetermined value, and the noise-reduction device operates.
According to the invention, there is provided a technique which is capable of reducing the noise produced from an engine when a two-wheeled motor vehicle is traveling at a low constant speed.
According to the invention as recited in claim 2, the exhaust valve is kept with a minimum degree of opening so as to reduce the noise. The exhaust valve also serves to improve the engine efficiency. The exhaust valve is thus able to achieve an effect to improve the engine efficiency and an effect to reduce the noise.
According to the invention as recited in claim 3, the intake valve is kept with a minimum degree of opening so as to reduce the noise. The intake valve also serves to improve the engine efficiency. The intake valve is thus able to achieve an effect to improve the engine efficiency and an effect to reduce the noise.
According to the invention as recited in claim 4, the ignition timing is advanced. When the two-wheeled motor vehicle is not in an accelerated condition, the engine load is low and, hence, the degree of opening of the throttle valve is small and the amount of fuel gas supplied to the combustion chamber is reduced accordingly. In this instance, if the ignition timing is advanced, a smaller amount of fuel gas will be subjected to combustion for a longer time than as usual. As a consequence, only a reduced amount of unburned gas is produced, which can eliminate combustion in the exhaust passage and does not pose any risk to increase the noise.
According to the invention, it is possible to reduce the noise by advancing the ignition timing.
Adjustment of the ignition timing can easily be achieved by using a permanently-installed ignition device. This means that noise reduction cab be achieved without incurring additional cost.
According to the invention as recited in claim 5, the predetermined value of the throttle ratio is 5 to 25%. When the two-wheeled motor vehicle is traveling at a low constant speed, the rotation angle of the throttle grip corresponds to a throttle ratio of 5 to 25%. With this throttle ratio, the noise-reduction device is prompted to operate with the result that the noise can be reduced.
According to the invention as recited in claim 6, the minimum degree of opening of the exhaust valve is set to a degree of opening corresponding to a valve-opening area which is 15 to 35% of a valve-opening area achieved when the exhaust valve is fully opened. By thus setting the valve-opening area of the exhaust valve, the noise is blocked from propagating to the outside and, hence, the noise produced by the engine can be efficiently reduced.
According to the invention as recited in claim 7, the minimum degree of opening of the intake valve is set to a degree of opening corresponding to a valve-opening area which is 30 to 60% of a valve-opening area achieved when the intake valve is fully opened. By thus setting the valve-opening area of the intake valve, the noise is blocked from propagating to the outside and, hence, the noise produced by the engine can be efficiently reduced.
Certain preferred embodiments of the present invention will be discussed below with reference to the accompanying drawings.
A first embodiment of the present invention will be described below with reference to the accompanying drawings.
As shown in
A fuel tank 21 is disposed on the body frame 11, and an air cleaner 22 is disposed between the fuel tank 21 and the engine 15 for taking in and filtering fresh air. An intake passage 23 extends from the air cleaner 22 and is connected to the engine 15 at a front end thereof.
A description will next be made about a throttle grip, which is gripped and rotated by the driver and has a throttle cable extending therefrom. As shown in
A throttle valve 31 is disposed in an intermediate portion of the intake passage 23 for adjusting the amount of fuel gas to be supplied to the engine 15. The first cable 28 is connected to the throttle valve 31.
The air cleaner 23 has a built-in air-cleaner element 32 for removing foreign substances from the fresh air, and is provided with an intake valve 33 for variably changing the cross-sectional area of the intake passage 23. The intake valve 33 may be built in the air cleaner 22, or alternatively, it may be disposed in the intake passage 23 extending from the air cleaner 22. The second cable 29 is connected to the intake valve 33.
The muffler 17 is provided with an exhaust valve 34 for variably changing the cross-sectional area of the exhaust passage 16. The exhaust valve 34 may be built-in the muffler 34, or alternatively, it may be disposed in an intermediate portion of the exhaust passage 16. The third cable 30 is connected to the exhaust valve 34.
The throttle ratio of the throttle grip 25 during low speed traveling will next be described with reference to
A curve “A” shown in
A curve “B” shown in
The two-wheeled motor vehicle with small-capacity engine performs driving at a low constant speed when the throttle ratio of the throttle grip is between zero and 25%. Alternatively, the two-wheeled motor vehicle with large-capacity engine performs driving at a low constant speed when the throttle ratio is between zero and 5%.
Next, the configuration of the exhaust valve 34 will be described below with reference to
A lever 39 is mounted to one end of the valve shaft 36, and a front end of the third cable 30 is connected to the lever 39. When the third cable 30 is pulled, the lever 39 turns the valve shaft 36 in a valve-opening direction. The valve shaft 36 is provided with a return spring 41 so that when a pull on the third cable 30 is released, the valve shaft 36 is automatically turned in a valve-closing direction by the force of the return spring 41.
The return spring 41 and the lever 39 are received in a protective case 42, and the protective case 42 is attached to the valve housing 35 by means of a plurality of screw fasteners 43. A lid 44 is attached by a screw fastener 45 to the protective case 42 so as to close an open end of the protective case 42. With the lid 44 thus attached, the protective case 42 is substantially protected against inversion by foreign substances.
A description will next be made about the principle of a lost motion mechanism which is configured to block transmission of the movement of a driving member to a driven member for a given time period at the initial stage of the movement of the driving member.
As shown in
In
As shown in
The behavior of the exhaust valve 34 will next be described with reference to
The throttle ratio value b2 is set, for example, in the range of 5 to 25% with respect the maximum rotation angle of the throttle grip.
While the throttle ratio of the throttle grip is between zero and the b2 value, the exhaust valve is kept to exhibit a minimum degree of opening. The minimum degree of opening of the exhaust valve is such a degree of opening, which corresponds to a valve-opening area that is 15 to 35% of a valve-opening area achieved when the exhaust valve is fully opened.
As shown in
While the throttle ratio of the throttle grip is between zero and the b2 value, a sufficient noise reduction effect can be attained by keeping the degree of opening of the exhaust valve at a value corresponding to a valve-opening area, which is 15 to 35% of the entire valve-opening area. If the valve-opening area of the exhaust valve exceeds 35%, only a limited noise reduction effect can be obtained. Alternatively, if the valve-opening area of the exhaust valve is less than 15%, the engine output will be negatively affected. It is therefore desirable that the degree of opening of the exhaust valve should preferably be maintained at a value corresponding to a valve-opening area, which is in the range of 15 to 35% of the entire valve-opening area of the exhaust valve.
The above-mentioned advantageous effects can be also expected for the intake valve.
As shown in
While the throttle ratio of the throttle grip is between zero to the b2 value, a sufficient noise reduction effect can be attained by maintaining the degree of opening of the intake valve at a value corresponding to a valve-opening area, which is 30 to 60% of the entire valve-opening area of the intake valve. If the valve-opening area exceeds 60%, only a limited noise reduction effect can be achieved. Alternatively, if the valve-opening area is less than 30%, the engine output will be negatively affected. It is therefore desirable that the degree of opening of the intake valve should preferably be maintained at a value corresponding to a valve-opening area, which is 30 to 30% of the entire valve-opening area of the intake valve.
A description will be made about another form of lost motion mechanism, which requires less number of structural components than that of the lost motion mechanism 47 shown in
As shown in
With the eccentric cam (pulley drum) 55 thus configured, when the third cable 30 is pulled at a constant speed, the valve shaft 36 turns slowly in early stages of turning motion of the eccentric cam 55 and, as shown in
As shown in
A second embodiment of the present invention will next be described with reference to the drawings. As shown in
The control unit 57 obtains information about a vehicle speed from a vehicle speed sensor 58. The control unit 57, on the basis of the throttle ratio information and the vehicle speed information, switches a lost motion mechanism 54 between an operating state and a disabled or inoperative state.
As shown in
The flowchart shown in
As shown in
If it is determined that the travel speed of the two-wheeled motor vehicle is in the range of a1 to a2, the process advances to ST12. Alternatively, if it is determined that the travel speed of the two-wheeled motor vehicle is not in the range of a1 to a2, the process jumps to ST19.
When an affirmation determination is made (“YES”) at ST11, the control unit places the lost motion mechanism shown in
The affirmative determination (“YES”) at ST 11 is followed by a further determination as to whether the two-wheeled motor vehicle is now in an accelerated condition (or in a decelerated condition). As for the two-wheeled motor vehicles while being accelerated (or decelerated), the power output is given priority over other factors and, hence, no action will be taken to reduce noise during acceleration (or deceleration) of the two-wheeled motor vehicles. The determination as to whether the two-wheeled motor vehicle is now being accelerated (or decelerated) relies on the largeness of a difference between an initial speed V1 and a speed (final speed) V2 after the elapse of a certain period of time T.
Thus, an initial speed V1 of the two-wheeled motor vehicle is recorded at ST12, and a timer is started at ST13. The timer continues to count down until a preset time t0 elapses (ST14).
The preset time t0 is determined by, for example, a graph shown in
When the preset time t0 elapses, ST15 records a final speed V2. Subsequently, at ST16, a difference between the initial speed V1 and the final speed V2 is calculated. If (V1-V2) is a negative value, this means that the two-wheeled motor vehicle is in an accelerated condition. Alternatively, if (V1-V2) is a positive value, this means that the two-wheeled motor vehicle is in a decelerated condition. Furthermore, if the absolute value of (V1-V2) is equal to or smaller than a predetermined value V, it is determined that the two-wheeled motor vehicle is not in an accelerated condition (or in a decelerated condition) at ST16. The predetermined value V is, for example, 1.5 km/h.
If a negative determination is made (“NO”) at ST16, this means that the two-wheeled motor vehicle is in an accelerated condition (or in a decelerated condition). Thus, the noise-reduction device is not operated. This state of operation is called “normal travel mode” (ST19).
Alternatively, if an affirmative determination is made (“YES”) at ST16, this means that the two-wheeled motor vehicle is not in an accelerated condition (or in a decelerated condition). Then the process goes on to ST17, which determines as to whether the throttle ratio 2 of the throttle grip is in the range of b1 to b2 where b1 corresponds to zero and b2 corresponds to a predetermined value.
If a negative determination is made (“NO”) at ST17, the noise-reduction device is not operated (ST19).
Alternatively, if an affirmative determination is made (“YES”) at ST17, the noise-reduction device is operated. This mode of operation is called “low-noise travel mode” (ST18).
A single cycle of operations of the noise-reduction device has thus been completed.
A noise control unit 80 is configured to achieve a noise reduction effect most efficiently when the following three conditions are fulfilled: (a) the vehicle speed is within a predetermined speed range (a1 to a2), (b) a variation in speed is equal to or smaller than a predetermined value (v), and (c) the throttle ratio is within a predetermined range (b1 to b2).
The main cable 26, junction box 27, first to third cables 28-30, and lost-motion mechanisms 54 that are shown in
The control unit 57, on the basis of throttle ratio information from the throttle ratio detection sensor 56, operates the throttle valve actuator 66 to adjust the degree of opening of the throttle valve.
Furthermore, the control unit 57, based on vehicle speed information from the vehicle speed sensor 58 and the throttle ration information from the throttle ratio detection sensor 56, operates the intake valve actuator 64 and the throttle valve actuator 66 so as to execute the low-noise travel mode (ST18 shown in
The control unit 57 sends a signal to an ignition device 67 so as to control ignition timing of the engine.
The reason for such lower noise level may be considered as follows. When the two-wheeled motor vehicle is not in an accelerated condition, the engine load is low and, hence, the degree of opening of the throttle valve is small, thereby reducing the amount of fuel gas supplied to the combustion chamber. In this instance, if the ignition timing is advanced, a smaller amount of fuel gas will be subjected to combustion for a longer time than as usual. As a consequence, only a reduced amount of unburned gas is produced, which can eliminate combustion in the exhaust passage, thereby lowering the noise.
The present invention is particularly suitable for application in a two-wheeled motor vehicle designed for the travel in an urban area.
Number | Date | Country | Kind |
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2008-171900 | Jun 2008 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2009/061476 | 6/24/2009 | WO | 00 | 12/29/2010 |