ENGINE START FACILITATING VALVE

Abstract: To facilitate start of a 2-cycle engine, for instance, compression pressure at the first compression stroke is released through the valve to reduce reaction force applied to an engine starter; once the mixture is ignited, explosion pressure at the first explosion stroke and after is accumulated in the accumulator space through the check valve member to keep the valve member closed against the valve spring, so that the engine is operated under the ordinary conditions; when the engine is at halt, accumulator pressure is released through the openable check valve member and the valve member opened by the valve spring to its original conditions.

Description: Field of the Invention The present invention relates to an engine start facilitating valve, and more specifically a valve for facilitating start of a two-cycle engine started by a recoil starter or a small starting motor. Description of the Prior Art Conventionally, a small two-cycle (e.g. single cylinder) engine is started by use of a mechanical recoil starter or a small starting motor. At engine start, however, since a reaction force due to cylinder pressure developed at piston compression stroke is applied to the recoil starter or the starting motor in addition to engine starting force, there exists a problem in that a large engine starting power is inevitably required for two-cycle engine start, and therefore the size of the recoil starter or the starting motor inevitably increases. In order to relieve the engine compression at engine start, the prior document EP-A-0024871 proposes an automatic compression release mechanism. In such mechanism two independently operating flexible plate valves control serially connected inlet and outlet ports, respectively, of a valve chamber forming a part of a compression release passageway connecting the combustion chamber of the engine with a zone of lower pressure. The plate valve controlling the outlet port is normally in an open position and remains open at engine start (engine compression stroke), relieving the engine compression; such outlet valve is then flexed to a closed position in response to a rapid pressure build-up in the chamber caused by ignition of the mixture in the engine combustion chamber (engine explosion stroke and after), thereby sealing the compression release passage after the engine starts. When the engine is stopped, such outlet valve shall return to the original open condition to permit the engine compression relief at the subsequent engine start. However, it may happen that such kind of outlet valve, for various reasons, remains in the closed position so that the compression release mechanism becomes ineffective. The automatic compression release mechanism proposed in the aforesaid prior document is therefore not reliable. SUMMARY OF THE INVENTION It is the primary object of the present. invention to provide a highly reliable engine start facilitating valve, particularly for allowing a two-cycle engine to be started by means of a small-sized recoil starter or starting motor. Such an object is achieved by an engine start facilitating valve, comprising: a valve housing attached to the engine; a spacer member disposed within the valve housing and formed with at least one accumulator space for accumulating engine explosion pressure; a check valve member disposed within the valve housing, for opening/closing communication between an engine combustion chamber and the accumulator space; a further valve member disposed within the valve housing, for opening/closing communication between the accumulator space and atmospheric pressure, so that, at engine compression stroke, cylinder pressure is released to atmospheric pressure through the opened check valve member and the opened further valve member, and so that, at engine explosion stroke and aster, cylinder pressure is accumulated in the accumulator space by closing of the further valve member; characterized in that the engine start facilitating valve further comprises: a valve rod for elastically urging the further valve member to open condition by a valve spring, so that, at engine stop, accumulated pressure is released through the valve member by pushing the valve rod to return the valve member. The valve rod and the valve spring ensure high reliability of the engine start facilitating valve. BRIEF DESCRIPTION OF THE DRAWINGS The features and advantages of the engine start facilitating valve according to the present invention will be more clearly appreciated from the following description taken in conjunction with the accompanying drawings in which like reference numerals designate corresponding elements and in which: Fig. 1 is a longitudinal cross-sectional view showing an embodiment of the engine start facilitating valve according to the present invention, which illustrates a state before engine start; Fig. 2 is a similar cross-sectional view showing the same, which illustrates another state after engine start; and Fig. 3 is a cross-sectional view taken along the line III-III in Fig. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the engine start facilitating valve according to the present invention will be described in detail hereinbelow with reference to the attached drawings: In Fig. 1 an engine cylinder 1 is formed with a combustion chamber 2, and a piston 3 is fitted to the combustion chamber 2 so as to be movable therein reciprocably. To the top head of the engine cylinder 1, an ignition plug 4 and an engine start facilitating valve 10 according to the present invention are fixed by screwing threaded portions thereof into threaded holes formed on the cylinder head. The engine start facilitating valve 10 comprises a valve housing 11, a valve rod 12, a valve spring 13, a cylindrical check valve member 14, a cylindrical valve member 15, and a triangular spacer member 16. The valve housing 11 is composed of a main valve housing 11A fixed to the cylinder head at a threaded portion 11a thereof with a washer 22 interposed therebetween, a valve rod support housing 11B fixed to the main valve housing 11A at a threaded portion 11b thereof with the triangular spacer 16 and a spacer support member 11C interposed therebetween, and a cap housing 11D fixed to the valve rod support housing 11B at a threaded portion 11d thereof. The main valve housing 11A is formed with a central hollow portion 18 and three different diameter shoulder portions. The central hollow portion 18 communicates with the combustion chamber 2. The cylindrical check valve member 14 is disposed at the smallest inner diameter shoulder portion; the triangular spacer member 16, the cylindrical valve member 15, and the spacer support member 11C are disposed at the medium inner diameter shoulder portion; and the valve rod support housing 11B is screwed into the largest inner diameter shoulder portion. The valve rod support housing 11B is formed with a central longitudinal hollow portion or passage 19 through which the valve rod 12 is loosely fitted and a radial passage 17 open to the atmospheric pressure. The valve rod 12 is formed with a flange portion 12a and a head portion 12b. The valve spring 13 is disposed between the flange portion 12a of the valve rod 12 and the inner surface of the cap housing 11D. Further, since the triangular spacer member 16 is fitted to the medium inner diameter shoulder portion, three accumulator spaces 16a are formed between the outer side surfaces of the spacer member 16 and the inner wall of the main valve housing 11A, as shown in Fig. 3. Further, the check valve member 14 is radially and axially loosely fitted to the smallest inner diameter shoulder portion of the main valve housing 11A, and the valve member 15 is also radially and axially loosely fitted between the triangular spacer member 16 and the valve rod support housing 11B, being usually urged against the spacer member 16 by the valve rod 12 biased by the valve spring 13. Therefore, the accumulator space 16a communicates with the combustion chamber 2 via the check valve member 14 and the axial passage 18, and further with the atmospheric pressure via the valve member 15 and the axial passage 19 and the radial passage 17 formed in the valve rod support housing 11B. The operation of the engine start facilitating valve according to the present invention will be described hereinbelow. Before the engine is started, the valve is in the state as shown in Fig. 1. Under these conditions, when the engine is started by a recoil starter (not shown) or a starting motor, since the valve member 15 is kept open by the valve rod 12 urged by the valve spring 13, a mixture introduced into the engine cylinder 1 and compressed by the piston 3 is partially released to the atmosphere via the check valve member 14, the accumulator space 16a, the valve member 15, the axial passage 19 and the radial passage 17 formed in the valve rod support housing 11B. Therefore, it is possible to reduce a reaction force due to cylinder pressure developed at piston compression stroke and simultaneously applied to the recoil starter or the starting motor, thus facilitating engine start operation. However, once the compressed mixture is ignited within the engine cylinder 1, since an explosion pressure (higher than the compression stroke pressure) is introduced to the accumulator space 16a via the check valve member 14, the valve member 15 is closed against the valve spring 13, so that the axial passage 19 and the radial passage 17 are kept closed as shown in Fig. 2. Under these conditions, since the valve member 15 is kept closed by a high explosion pressure introduced into the accumulator space 16a, the engine can be operated under the ordinary conditions. Under these conditions, the check valve member 14 is also kept closed by the accumulated pressure. Further, when the engine is stopped, since the pressure within the accumulator space 16a is released through a small gap of the check valve member 14 (since the axial length of the smallest shoulder portion of the main valve housing 11A is wider than the thickness of the check valve member 14), the accumulator pressure drops, so that the valve member 15 returns by the elastic force of the valve spring 13 to its original position as shown in Fig. 1. Furthermore, in case the valve member 15 sticks to the valve seat (the lower end surface of the valve rod support housing 11B), it is possible to readily return the valve member 15 to its original open position by pushing the head 12b of the valve rod 12 by the hand. As described above, in the engine start facilitating valve according to the present invention, since pressure developed within the engine cylinder and applied to the recoil starter or the starting motor can be released open at a first engine compression stroke to reduce the compression pressure, it is possible to facilitate engine start. After the engine has been started, since pressure generated within the engine cylinder at explosion stroke and after is accumulated in the accumulator space between the valve member and the check valve member to keep the valve closed against the elastic force of the valve spring, the engine can be operated under the ordinary conditions. At engine stop, the accumulated pressure is released through the check valve member and the valve member. Further, in case the valve member sticks to the valve seat by foreign matters such as lubricant, carbon, etc., it is possible to easily return the valve member to its normal open position by simply pushing the head of the valve rod by the hand. Further, since no elastic spring member is used for the check valve member contacting with a high temperature gas, it is possible to prevent the malfunction of the check valve member due to a weak spring member annealed by heat. Furthermore, since the check valve member is not of piston type, it is possible to prevent the malfunction of the check valve member due to carbon accumulation.

Claims: An engine start facilitating valve (10), comprising: a valve housing (11) attached to the engine; a spacer member (16) disposed within the valve housing (11) and formed with at least one accumulator space (16a) for accumulating engine explosion pressure; a check valve member (14) disposed within the valve housing (11), for opening/closing communication between an engine combustion chamber (2) and the accumulator space (16a); a further valve member (15) disposed within the valve housing (11), for opening/closing communication between the accumulator space (16a) and atmospheric pressure, so that, at engine compression stroke, cylinder pressure is released to atmospheric pressure through the opened check valve member (14) and the opened further valve member (15), and so that, at engine explosion stroke and after, cylinder pressure is accumulated in the accumulator space (16a) by closing of the further valve member (15); characterized in that the engine start facilitating valve (10) further comprises: a valve rod (12) for elastically urging the further valve member (15) to open condition by a valve spring (13), so that, at engine stop, accumulated pressure is released through the valve member (15) by pushing the valve rod (12) to return the valve member (15). An engine start facilitating valve according to claim 1, wherein the valve rod (12) is formed with a valve head (12b) projecting from the valve housing (11), in case the further valve member (15) sticks to a valve seat the further valve member (15) being readily released open when the valve head (12b) is pushed. An engine start facilitating valve according to claim 1, further comprising rod means (12) for enforcingly opening the further valve member (15) against the pressure inside the accumulator space (16a). An engine start facilitating valve according to claim 1, wherein the space member (16) has a triangular shape, three accumulator spaces (16a) being formed between three end surfaces of the space member (16) and a inner wall of the valve housing (11). An engine start facilitating valve according to claim 1, wherein the check valve member (14) is loosely fitted within the valve housing (11), so that, when the engine is stopped, the accumulator pressure drops and the further valve member (15) is pushed by the valve spring (13) to the open condition. An engine start facilitating valve according to claim 1 or 5, wherein the further valve member (15) is loosely fitted within the valve housing (11). An engine start facilitating valve according to claim 1 or 5, wherein the check valve member (14) is planar. An engine start facilitating valve according to any one of the claims 1,2,3,5,6,7 wherein the further valve member (15) is planar. An engine start facilitating valve according to claim 1 or 2, wherein the valve housing (11) includes a main valve housing (11A), a support housing (11B) supporting the valve rod (12) and housing the valve spring (13), and a cap housing (11D) on the support housing (11B), said main valve housing (11A), support housing (11B), and a cap housing (11D) being removably fixed to each other by threaded engagement. An engine start facilitating valve according to any one of the claims 1,2 or 9, wherein the valve housing (11) is removably fitted on the upper portion of a cylinder (1) of the engine by a threaded engagement (11a). An engine start facilitating valve according to one or more of the preceding claims, applied to a two-stroke engine.

Inventors: NOMOTO, SHIGEKI
Applicants: KOMATSU ZENOAH CO., LTD.
Application year: 1989
Main classification: F02N17
IPC codes: F02N17, F02N15, F01L13, F02D15