RU2254985C1 - Gasoline-powered saw - Google Patents

Abstract

FIELD: timber and woodworking industries; production of gasoline-powered saws.

SUBSTANCE: the invention is pertaining to timber and woodworking industries and may be used in production of gasoline-powered saws. The saw contains a gasoline engine; a sawing device; a supporting frame with a tubular section, fixed to engine body through springs; a front and a rear handles and a stop. The mean diameter of springs makes 5-7 diameters of the springs wire. At that the space between the supporting frame and the engine body in places of the springs fixation ensures their preliminary strain equal to 0.4-0.6 of a working stroke of a spring. The technical result is effective damping of vibration in octava bands of operating frequencies 31.5; 63; 125; 250; 500 and 1000 Hz.

EFFECT: the invention ensures the effective damping of vibrations in octava bands of operating frequencies.

3 dwg

Description

The invention relates to the forestry and woodworking industries and can be used in enterprises for the design and manufacture of gasoline-powered saws.

In the present invention, a gasoline-powered saw is developed in which an effective vibration protection of the operator’s hands is provided in a wide frequency range (30-1000 Hz).

A gasoline-powered saw is a powerful source of dynamic loads, which, depending on the operating mode, are fully or partially perceived by the operator.

In this regard, one of the most important tasks when creating hand-held gasoline-powered saws is to achieve the maximum reduction in the level of vibration on the outer surfaces of the control handles covered by the operator's hands when working with the saw. The complexity of solving this problem lies in the fact that, depending on the operating mode (idling on the bucking, bucking, felling), the operator’s hands are affected by vibration loads in a wide frequency range (30-1000 Hz). In accordance with patent information studies, a fairly large number of mechanical damping devices have been developed over the past years, providing partial damping of vibration on the control handles of gasoline-powered saws.

A portable motor saw is known (see, for example, USSR application No. 2031894 for class B 27 B 17/00 for 1974), in which the control handles are rigidly connected to cages having elastic elements in the form of an outer and inner ring connected to the inside with jumpers. The vibration transmitted from the engine and the saw apparatus is damped during transmission to the handles due to the absorbing properties of the elastic material of the elastic elements that are mounted on the engine. As the authors note, the presence of elastic elements reduces vibration, provides good vibration resistance and control of the saw in any position. The main disadvantage of this design is that effective vibration isolation of the control levers is provided in a limited range of vibration frequencies. The limitation of the frequency range for vibration is due to the specifically specified rigid properties of the elastic elements. In addition, the saw itself has a rather complex structure and increased weight due to the presence of clips.

Known portable saws (see application of the USSR No. 2331564 for class B 27 V 17/00 for 1976, patent Germany 2043708 for class B 27 B 17/02 for 1977, patent Germany 2525116 for class B 27 V 17 / 02, US patent 3,698,455 for class B 27 B 17/02 for 1972, US patent 3,945,119 for class B 27 B 17/02 for 1976, US patent 4,141,143 for class B 27 B 17/02 for 1979) in which the support frame with control handles is directly attached to the motor housing through elastic elements that provide effective damping of vibration in the high-frequency region. To reduce the level of vibration in the low-frequency spectrum, various designs of rigid dampers are used.

The fastening of the support frame with control handles to the saw engine through flexible elastic elements significantly affects the controllability of the saw, which is unsafe for the operator during his work.

A portable motor saw is also known (see application of the USSR No. 3249074 for class B 27 B 17/00 for 1981), adopted by the authors as a prototype. It includes an engine with a saw apparatus, a support frame with front and rear control levers, attached to the engine housing through three rigid springs, partially acting as shock absorbers at high frequencies (500-1000 Hz).

Rigid springs provide good controllability of the saw, while in order to reduce vibration on the control handles, the emphasis is connected to the engine housing by means of shock absorbers. When sawing, the emphasis is pressed against the wood and the shock absorbers act as vibration dampers.

The main disadvantage of the prototype saw is the ineffective vibration isolation of the control levers at low operating frequencies, the most dangerous for the human body. Measured at the stand of vibration velocity of the control levers in octave strips of operating frequencies: 31.5 Hz; 63 Hz; 125 Hz; 250 Hz exceed by 3-5 dB the permissible vibration levels according to GOST 17770-72 “Manual machines, Permissible vibration levels”. The limitation of the frequency range for effective vibration damping is due to the given severity of the shock absorbers.

In the prototype saw, the support frame with the control levers is attached to the engine housing through three rigid springs. The stiffness of the spring is determined by the numerical value of the index “C”.

C = To / d, where

To = D-d - the average diameter of the spring;

D is the outer diameter of the spring;

d is the diameter of the spring wire.

In accordance with the reference data (see V.I. Anuryev, “The Handbook of a Mechanical Engineering Designer, Volume 3, M .: Mashinostroenie, 1979, p. 96), for cylindrical helical compression and tension springs made of circular steel, the index“ C ”has values from 4 to 12. The smaller the numerical value of the “C” index, the greater the spring stiffness.

In the prototype saw, the bolt fastening of the support frame with the motor housing is carried out through hard springs (C = 4.0) with virtually no prior loading. With such a rigid fastening of the support frame with control handles to the engine casing (vibration source) when operating in the “idle running on the bucking” mode, the operator’s hands in the low frequency range (31-250 Hz) are exposed to vibration loads exceeding 3-5 dB permissible vibration levels. And only in sawing under load at frequencies of 500-1000 Hz do springs act as vibration dampers.

The technical task of the present invention is to remedy these disadvantages and create a gasoline-powered saw design, which provides vibration damping in the entire frequency range 31-1000 Hz.

The technical result of the invention lies in the fact that the mounting of the support frame to the motor housing is carried out through pliable non-rigid springs, the average diameter of which is 5-7 diameters of the spring wire, while the distance between the supporting frame and the saw motor housing at the points of attachment of the springs provides their preload the value of 0.4-0.6 working stroke of the spring.

In Fig.1 shows a gasoline-powered saw, General view. It contains an engine 1, a saw apparatus 2, a support frame 3 with a tubular part 4, fixed to the engine housing 1 through springs 5, a front handle 6 located on the tubular part 4 of the support frame 3, a rear handle 7 and an abutment 8. Two mounting points of the support frame 3 to the housing of the engine 1 through the springs 5 is shown in figure 1. The third place of attachment of the tubular part 4 of the support frame 3 to the engine housing 1 through the spring 5 is shown in figure 2 - view along A in figure 1.

The operation of a gasoline-powered saw is as follows. The engine 1 with the saw apparatus 2 generates a spatial vibration transmitted through the support frame 3 to the control handles 6, 7. Placing the springs 5 between the engine casing 1 and the support frame 3 with a preload of 0.4-0.6 of the spring travel allows to exclude direct vibration transmission in the low frequency range 31-250 Hz from the engine 1 with the saw apparatus 2 to the support frame 3 with the control handles 6, 7. This ensures good controllability of the saw.

The vibration damping in the saw design proposed by the authors is carried out due to the elastic deformation of the springs:

- at idle due to the preload of the springs;

- in sawing due to the compression and torsion springs.

Based on numerous experimental data (sawing at a stand in idle mode, bucking and roll with measuring vibration levels on the outer surface of the handles), the authors found that the ratio of the average spring diameter to the diameter of the wire, of which the spring is made, and the amount of spring preload. With an average spring diameter equal to more than seven diameters of its wire, in combination with a preload of less than 0.4 working stroke, the springs have large bending movements. As a result of this, vibration loads on the operator’s hands in idle mode increase. In this mode of operation, the saw is in limbo in the hands of the operator and represents a certain mass with a vibration source (saw engine idling). The operator’s hands, compressing the control handles and holding the saw, represent a certain attached mass to the saw through the springs. A dynamic system is formed in which the attached mass (operator’s hands) and springs with large bending movements become a dynamic damper for a chainsaw, as a result of which there is a powerful selection of energy from a vibration source (saw engine) and its transfer to the operator’s hands. In addition, due to the great flexibility of the springs, the controllability of the saw apparatus 2 is deteriorated. With an average spring diameter of less than five diameters of its wire, in combination with a preload of more than 0.6 working springs, the springs are very stiff. As a result, the damping efficiency is sharply reduced vibration at low frequencies of 31-250 Hz in idle mode on the bucking, and when felling and bucking, it is possible to close the coil of springs and vibration without damping is directly transmitted to the hands of the operator.

Thus, only with an average spring diameter equal to 5-7 diameters of the spring wire, and preloading it by a value of 0.4-0.6 working stroke, an effective damping of vibration in the working frequency range is provided.

At present, bench and full-scale (in the timber industry enterprises of Russia) tests of the proposed saw design have been carried out. Achieved practical damping of vibration on the control levers in octave bands of operating frequencies of 31.5; 63; 125; 250; 500 and 1000 Hz.

Claims (1)

A gasoline-powered saw, including an engine with a saw apparatus, a support frame with a tubular part, attached to the engine housing through springs, an emphasis, front and rear control handles, characterized in that the support frame is attached to the engine housing through springs, the average diameter of which is 5- 7 diameters of the spring wire, while the distance between the supporting frame and the saw motor housing at the points of attachment of the springs ensures their preload by a value of 0.4-0.6 spring travel.

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