EP0076348B1

EP0076348B1 - Exhaust valve casing

Info

Publication number: EP0076348B1
Application number: EP19810304727
Authority: EP
Inventors: Keijiro C/O Diesel Engine Engineering S. Tayama; Hiroaki C/O Diesel Engine Res. & Dev. Miyano
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Ltd
Priority date: 1981-10-12
Filing date: 1981-10-12
Publication date: 1985-07-31
Also published as: EP0076348A1; DE3171601D1

Description

The present invention relates to exhaust valve casings for an internal combustion engine of the kind which provides an exhaust passage independently of the cylinder head.
Such exhaust valve casings are known and are frequently used in relatively large 2-stroke internal combustion engines.
A known construction of exhaust valve and its valve casing is shown in Figure 1. Thus, in the valve casing 1 are assembled a valve seat 2 and a valve 3 by the intermediary of a valve spring 4 and a spring cap 5; it will be noted that the periphery of the valve seat 2 is formed independently of the cylinder head. In the known construction shown there is also provided a valve guide bush 7 made of a material that is favourable for lubrication in order to obtain smooth sliding movement of the valve 3. It will also be noted that the valve casing 1 is fastened jointly with the valve seat 2 in a pressure-tight manner to a cylinder head 6 at a contact surface 2a between said valve seat 2 and cylinder head by means of bolts (not shown).
Provision is made such that the valve 3 may be opened and closed at predetermined timing by means of an exhaust valve driving apparatus (not shown) so that exhaust gas within the cylinder 8 can flow out, to be replaced by a fresh charge flowing in through a scavenging port (not shown), or the like.
When the valve 3 is opened, high-temperature exhaust gas from the cylinder 8 flows out as shown by the arrows a, and passes through an exhaust passage 1a and thence through an exhaust pipe, supercharger, or exhaust economizer or the like (not shown) to atmosphere. Since the exhaust passage 1 a is exposed to high-temperature exhaust gas, for the purpose of preventing a temperature rise in the material of the valve casing 1 and maintaining sufficient lubrication between the stem of the valve 3 and the valve guide bush 7, the exhaust passage 1 a is cooled by a coolant such as fresh water, and the valve seat 2 is constructed such that it is also cooled by a coolant, thereby enhancing its durability.
More particularly, as shown by arrows b coolant flows continuously through a coolant inlet 1 b provided in the valve casing 1 into cooling chambers 1c and 1d in said valve casing and, after it has cooled the valve casing and valve seat, it flows out through a coolant outlet 1e.
However, in the above-described known valve casing, since the wall of the exhaust passage 1a in the valve casing is also positively cooled by the coolant, exhaust gas discharged through said passage also tends to be cooled. Hence, the energy possessed by the exhaust gas is subjected to a cooling loss by a corresponding amount, and so, the exhaust gas energy that can be utilized in a supercharger, or an exhaust gas economizer is reduced. Consequently, the heat transfer area of an exhaust gas economizer must be enlarged; in some cases it may even happen that a turbogenerator making use of the exhaust gas becomes inoperable, and so, such a construction of valve casing is unfavourable from the viewpoint of energy saving.
In addition, since the valve casing is formed as a casting, due to casting difficulties, the coolant chambers 1c and 1d cannot be made as small as desired. Consequently, the height of the valve casing 1 must be made greater than desired.
Another construction of such an exhaust valve casing is known from CH-A-429 304 in which cooling chambers (14, 18) are provided around the valve guide (19) and around the valve seat. The chambers are connected by a coolant duct (11) extending through the wall of the casing and, a further coolant duct (16) extends through the length of the casing wall to the valve seat chamber (14). A wall (10) of the valve casing defining the valve guide cooling chamber (18) extends downwardly around the valve into the exhaust gas passageway so that, in use, the effect of coolant flowing through that chamber is to cool the gas exhaust passageway as well as the valve guide.
It will be appreciated also that, in this construction, the said coolant ducts, running alongside the exhaust gas passageway, will further tend to cool exhaust gas passing through the casing to the exhaust outlets (11a, 11b).
One object of the present invention is to provide an exhaust valve casing of the kind discussed above, in which thermal loss in the exhaust gas is reduced, whilst ensuring adequate cooling of the valve guide, and valve seat.
Another object of the present invention is to provide such an exhaust valve casing, in which the height of the casing, and thus a length of the exhaust valve stem, can be reduced, with resultant saving in weight and manufacturing costs.
According to the present invention, there is provided an exhaust valve casing for an internal combustion engine, of the kind which is intended to be fastened to the cylinder head to provide a valve seat and exhaust gas passage and to support the exhaust valve and a valve guide therefor independently of the cylinder head, and in which said casing is provided with annular cooling chambers at two locations, one disposed around the periphery of said valve guide, and the other disposed around said valve seat, characterised in that the two cooling chambers and ducts through said valve casing for supplying coolant to and from said chambers are arranged with respect to, and spaced sufficiently away from, the exhaust gas passage such that, in use, coolant flowing therethrough cools respectively the valve guide and valve seat without substantially any cooling effect on said exhaust passage.
The valve casing may include respective independent coolant inlet and outlet ducts through the wall of said casing to the two chambers, and in that said coolant inlet and outlet ducts of the valve seat are in the proximity of said valve seat. It will be appreciated that the independent coolant ducts to the two chambers can, nevertheless, be connected externally of the casing to a common source of coolant.
In the exhaust valve casing according to the present invention, since no coolant chambers or ducts are provided in the vicinity of the exhaust passage, no positive cooling can take place in this region. Thus, thermal loss from the exhaust gas is reduced to a minimum, and hence more energy is available from the exhaust gas for use in a supercharger, exhaust gas economizer, or the like.
In addition, since the exhaust valve casing according to the present invention lacks a cooling chamber in the vicinity of the exhaust passage, the height of the valve casing, as well as the length of the valve stem can be reduced, with a consequent saving in weight and manufacturing costs. Also, such a reduced height and configuration of the exhaust valve can be advantageous for space utilisation in an engine room.
Conveniently, the casing wall around the gas exhaust passage may be lagged externally to further reduce thermal losses in the exhaust gas.
In order that the invention may be readily understood, and further features and advantages made more apparent, one preferred construction of exhaust valve, and casing therefor, will now be described by way of example, with reference to the accompanying drawings, in which:-

Figure 1 is a longitudinal cross-sectional view of a known construction of exhaust valve,
Figure 2 is a longitudinal cross-sectional view, similar to Figure 1, showing the preferred construction according to the present invention, and
Figure 3 is a transverse cross-sectional view taken along line III-III of Figure 2.

Referring now to Figures 2 and 3 of the drawings, the exhaust valve casing 11 is provided at its inner end with a wall part defining a valve seat 12 and a valve 13 is supported in the casing by the intermediary of a valve spring 14 and a spring cap 15. The exhaust valve thus provides an exhaust gas passage and valve assembly which is independent of the cylinder head 16. The stem of the valve 13 is slidably mounted in a valve guide bush 17. The valve casing 11 is fastened jointly with the valve seat 12 to the cylinder head 16 in a pressure-tight manner by means of bolts 19 (see Figure 3). In this figure, reference numeral 20 designates ribs provided for enabling transmission of a uniform stress in a circumferential direction through a contact surface 12a (see Figure 2) between the valve seat and cylinder head.
An annular cooling chamber 11c is formed along an outer periphery of the valve guide bush 17, and coolant is introduced thereto through a coolant inlet duct 11b and discharged through a coolant outlet duct 11d. To prevent coolant from leaking out of the cooling chamber 11c, seals 21 are provided in the valve guide bush 17.
A second annular cooling chamber 12b, is formed within the wall part defining the valve seat 12, and coolant is introduced to this chamber through a coolant inlet duct 11 and discharged through a coolant outlet duct (not shown).
In this preferred construction of exhaust valve, in order to reduce thermal loss from the exhaust gas caused by heat transfer to the coolant, cooling of a peripheral wall 11f around the exhaust passage 11 a by means of coolant, is practiced in the known construction discussed above, is abolished. Furthermore the cooling arrangement is constructed in such a manner that only the two locations described above are cooled by the coolant.
More particularly, through the temperature of the valve casing is raised as a whole due to the abolition of cooling of the peripheral wall 11f around the exhaust passage 11a, in order to prevent degradation of the lubricating capability of the valve guide bush 17 due to increased temperature in the material of the valve casing, the outer periphery of the valve guide bush 17 is positively cooled by means of the coolant. In addition, in a similar manner to the known construction, the valve seat 12 is positively cooled by coolant. Furthermore, the peripheral wall 11f around the exhaust passage 11 of the exhaust valve casing 11 is lagged externally by a heat-insulating materia) 11g (see Figure 3) such as, for example, asbestos.
In the cooling arrangement described coolant is introduced through the coolant inlet duct 11 for valve seat cooling as shown by arrow B, and flows into the cooling chamber 12b, and thereafter, around the cooling chamber, to be discharged externally through the coolant outlet duct. Coolant is also introduced through the coolant inlet duct 11 b for the valve guide bush 17 as shown by an arrow A, to flow into the cooling chamber 11c along the outer periphery of the bush 17 and to be discharged externally through the coolant outlet duct 11d.

Claims

1. An exhaust valve casing for an internal combustion engine, of the kind which is intended to be fastened to the cylinder head to provide a valve seat (12) and exhaust gas passage (11a) and to support the exhaust valve (13) and a valve guide (17) therefor independently of the cylinder head, and in which said casing is provided with annular cooling chambers at two locations, one (11c) disposed around the periphery of said valve guide, and the other (12b) disposed around said valve seat, characterised in that the two cooling chambers (11c and 12b) and ducts through said valve casing for supplying coolant to and from said chambers are arranged with respect to, and spaced sufficiently away from, the exhaust gas passage (11a) such that, in use, coolant flowing therethrough cools respectively the valve guide (17) and valve seat (12) without substantially any cooling effect on said exhaust passage (11a).

2. An exhaust valve casing according to Claim 1, characterised in that independent coolant inlet and outlet ducts (11b, 11d, 11e, -) are respectively n < inE (1: : t th provided through the wall of said casing to the chambers, and in that said coolant inlet and outlet ducts of the valve seat are in the proximity of said valve seat.

3. An exhaust valve casing according to Claim 1 or Claim 2, characterised in that the casing wall (11f) around the exhaust gas passage (11a) is lagged externally by heat-insulating material (11g).