JPH04237635A - Muffling device for engine type industrial vehicle - Google Patents

Abstract

PURPOSE:To enable the efficient muffling of noise generated in an engine type industrial vehicle with simple structure. CONSTITUTION:A head guard 91 formed to be hollow is provided with an intake air inlet 93 and an intake air outlet 94. A first intake air path 11 and a second intake air path 12 are provided between the intake air inlet 93 and the intake air outlet 94. Both intake air paths 11, 12 are formed in such a way that the difference between the path lengths L1, L2 of both intake air paths 11, 12 is odd times larger than the half-wavelength of noise. The noises propagated respectively through both intake air paths 11, 12 from the intake air inlet 93 are merged at the intake air outlet 94 in the state of being shifted in phase by the half-wavelength part of the noise. As a result, both noises interfere with each other to be muffled.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine-powered industrial vehicle such as a forklift that utilizes a head guard as an air intake pipe to the engine, and specifically relates to a muffling device for muffling noise generated by intake air.

0002

2. Description of the Related Art Some engine-powered industrial vehicles such as forklift trucks utilize a head guard as an air intake pipe to the engine. That is, as shown in FIGS. 6 and 7, in the forklift 9 as an engine-driven industrial vehicle, the pillar 921 of the head guard 91 is formed in a hollow shape, and the pillar 921 has an intake inlet 93 at the top and bottom. and an intake outlet 94. The intake outlet 94 is connected to an air cleaner 96 through an air introduction pipe 95, and air is supplied to the engine 9 through the air cleaner 96.
7. In addition, in FIGS. 6 and 7, 922 is the roof frame of the head guard 91, 9
Reference numeral 23 indicates a guard portion provided on the ceiling of the head guard 91.

0003

[Problem to be Solved] However, in conventional noise reduction devices for engine-powered industrial vehicles, when air is taken in through the intake inlet provided in the head guard, louder noise is generated from the intake inlet. This is because air pulsation occurs due to intake air. Therefore, the above-mentioned noise gives an unpleasant feeling to the operator of the industrial vehicle. One way to solve the above problem is to install a silencer in the pillar of the head guard (for example, in the Japanese Utility Model Application No. 62-1
Publication No. 20025). The muffling device includes the air inlet pipe inserted upward into a pillar, and a movable plate in contact with the inner periphery of the pillar and the outer periphery of the air inlet pipe arranged vertically movably to form a muffler chamber. There is. A spring member that normally biases the movable plate downward is arranged within the pillar, and the downward force exerted by the spring member is balanced with the negative suction pressure generated in the muffling chamber corresponding to the engine rotation speed. Accordingly, the capacity of the silencing chamber can be changed by moving the movable plate up and down. However, in the above-mentioned silencer, the structure of the pillar is complicated. This makes it difficult to manufacture the pillars, leading to increased costs. SUMMARY OF THE INVENTION In view of these conventional problems, it is an object of the present invention to provide a noise reduction device for an engine-powered industrial vehicle that has a simple structure and can perform noise reduction at low cost.

0004

[Means for Solving the Problems] The present invention provides an engine-driven industrial vehicle in which a hollow head guard is provided with an intake inlet and an intake outlet, and the intake outlet is connected to the engine side. A first intake path and a second intake path having different path lengths are provided up to the outlet,
A noise reduction device for an engine-powered industrial vehicle is characterized in that the difference in path length between the two intake paths is an odd number multiple of a half wavelength of noise. The most noteworthy feature of the present invention is that two intake paths are provided within the head guard, and the propagation noises of both intake paths are shifted in phase by half a wavelength at the intake outlet, merge together, and interfere with each other. This is because the lengths of both intake paths are different. In the present invention,
The first intake passage and the second intake passage are provided in the head guard. As a means for this, there is a method (see FIG. 1) in which the pillars of the head guard and the roof frame are each formed into hollow shapes, and these are communicated with each other to form a first intake passage and a second intake passage. Further, there is a method of forming a first intake passage and a second intake passage using a pillar of a head guard, a roof frame, and a guard portion (see FIG. 3). In addition, in the present invention, the path length of the first intake path and the second
The length of the intake path is made different. The difference in path length between both intake paths is 1/2, 3/2, 5/2, etc. of the noise wavelength.
Make it so that That is, the difference is made to be an odd number multiple of the half wavelength of the noise.

[0005]

[Operations and Effects] In the present invention, air taken into the head guard from the intake inlet flows through the first intake path and the second intake path.
It is supplied from the intake outlet to the engine side via the intake path. The noise generated by the intake air is separated into a first intake path and a second intake path, and propagates from the intake inlet to the intake outlet. At this time, at the intake outlet, the noise that has propagated through the first intake path and the noise that has propagated through the second intake path merge with the phase shifted by a half wavelength of the noise. Therefore, both noises interfere with each other and cancel each other out (see Figure 2). Therefore, noise can be muffled with a simple structure in which two intake paths having the above-mentioned path length relationship are formed in the head guard. Therefore, the cost is also low. Therefore, according to the present invention, the structure is simple and
It is possible to provide a low-cost silencer for engine-powered industrial vehicles.

[0006]

Embodiment Embodiment 1 A silencer for an engine-powered industrial vehicle according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. As shown in Fig. 1, the device 1 of this example is a forklift head guard 9.
1, a first intake path 11 and a second intake path 1 having different path lengths are connected from the intake inlet 93 to the intake outlet 94.
2 is provided, and the path length L1 of both intake paths 11 and 12 is
, L2 is an odd number times the half wavelength of the noise. In this example, two left and right pillars 921 at the rear of the head guard 91 and a roof frame 922 are communicated with each other. In addition, the intake pipe 1 is connected between the lower parts of both the left and right pillars 921.
It is connected by 0. And, in the intake pipe 10,
A suction outlet 94 is provided. The first intake path 11 is
It is formed by the left pillar 921 and the intake pipe 10, and the path length of the first intake path 11 is L1. The second intake path 12 is formed by the upper part of the left pillar 921, the roof frame 922, the right pillar 921, and the intake pipe 10, and the length of the second intake path 12 is L2. There is. The path length L2 of the second intake path 12 is made longer than the path length L1 of the first intake path 11 by an odd number times a half wavelength of the noise. Other than that,
This is the same as the conventional example. Since the device of this example is configured as described above, it exhibits the following effects. That is, when the engine 97 is operated, air taken into the head guard 91 from the intake inlet 93 is supplied to the air cleaner 96 from the intake outlet 94 via the first intake path 11 and the second intake path 12, and then The air is supplied from the air cleaner 96 to the engine 97. At this time, noise is generated at the intake inlet 93 due to the intake air. As shown in FIG. 1, this noise is separated into the first intake path 11 and the second intake path 12 and propagates from the intake inlet 93 to the intake outlet 94. Then, at the intake outlet 94, the noise N1 that has propagated through the first intake path 11 and the noise N2 that has propagated through the second intake path 12 merge. Here, noise N1,
Assuming that the wavelength of N2 is λ, the intake outlet 9 as shown in Fig. 2
4, the phase of both nozzles N1 and N2 is half a wavelength λ
It is off by /2. This is the first intake path 11 and the second intake path 11.
The difference in path length (L2-L1) with the intake path 12 is half the wavelength λ
This is because it is an odd multiple of /2. Therefore, at the intake outlet 94, both noises N1 and N2 interfere with each other. As a result, the sound is muted. In this way, according to this example, the head guard 1 has two intake paths 11 and 12.
With a simple structure that only requires the formation of

Embodiment 2 A silencer 2 of this embodiment will be explained using FIG. 3. In this example, the pillar 921 of the head guard 91, the roof frame 922, and the guard part 923 provided on the ceiling provide
A first intake path 21 and a second intake path 22 are formed. That is, the pillar 921, the roof frame 922, and the guard portion 923 are formed in a hollow shape. And head guard 9
An intake inlet 93 is provided in the front pillar 921 of the vehicle. Further, the pillar 921 and the roof frame 922 are communicated with each other. Further, the roof frame 922 and one end of the guard portion 923 are communicated with each other. A first intake path 21 is formed by the pillar 921 and the roof frame 922. Further, the pillar 921, the roof frame 922, and the guard portion 923 form a second intake path 22. The path lengths of both intake paths 21 and 22 are provided so that the difference therebetween is an odd number times a half wavelength of the noise. Therefore, the same effects as in the first embodiment can be obtained. Next, a specific example will be explained. Generally, in engine-powered industrial vehicles such as forklifts, large noises are generated at frequencies of 100 Hz, 200 Hz, and 1 KHz, as shown in FIG. This noise of 100 Hz and 200 Hz is generated as intake noise from the intake inlet 93 provided in the pillar 921, for example. Further, the noise of 1 kHz is generated from the engine 97, for example, as combustion noise. And 1
For example, the noise of 00Hz is generated when a 4-cylinder engine 97
Occurs when rotating at 000 rpm. Here, if the speed of sound is 340 m, and the frequency of noise is 100 Hz, the wavelength of noise is 3.4 m, and the half wavelength of noise is 1.7 m.
becomes. Further, when the frequency of the noise is 200 Hz, the wavelength of the noise is 1.7 m, and the half wavelength of the noise is 0.85 m. Therefore, for example, when trying to muffle noise with a frequency of 200 Hz, the difference between the path length of the first intake path and the path length of the second intake path is an odd multiple of 0.85 m, that is, 0.85 m. The first intake route and the second intake route are formed to have a length of 2.55 m, 4.25 m, . . . . That is, the first and second intake paths are set by various methods such as those shown in the first and second embodiments so as to obtain the difference in path length. Further, the relationship between the above noise reduction amount and frequency is as shown in FIG. 5.

[Brief explanation of the drawing]

FIG. 1 is a rear sectional view of a silencer for an engine-powered industrial vehicle according to a first embodiment.

FIG. 2 is a diagram of a noise waveform showing a state of noise interference caused by the silencer of the first embodiment.

FIG. 3 is a perspective view of a silencer according to a second embodiment.

FIG. 4 is a diagram showing the relationship between noise magnitude and frequency before muting in a specific example.

FIG. 5 is a diagram showing the relationship between the amount of noise reduction after silencing and frequency in a specific example.

FIG. 6 is a perspective view of a conventional engine-powered industrial vehicle.

FIG. 7 is a rear sectional view of a head guard of a conventional engine-powered industrial vehicle.

[Explanation of symbols]

1. ．． ．． silencer, 11. ．． ．． first intake path, 12. ．． ．． second intake path, 2. ．． ．． silencer, 21. ．． ．． first intake path, 22. ．． ．． second intake path, 91. ．． ．． head guard, 93. ．． ．． intake inlet, 94. ．． ．． intake outlet, 97. ．． ．． engine,

Claims (1)

[Claims] Claim 1: In an engine-powered industrial vehicle in which a hollow head guard is provided with an intake inlet and an intake outlet, and the intake outlet is connected to the engine side, the head guard has a space between the intake inlet and the intake outlet. , the first path with different path lengths
1. A silencer for an engine-powered industrial vehicle, comprising an intake path and a second intake path, the difference in path length between the two intake paths being an odd number multiple of a half wavelength of noise.