Camshaft drive for engine

Details Camshaft drive for engine Camshaft drive for engine

1998-10-02

2001-03-13

Lo, Weilun (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

Camshaft drive means

C123S090270

Reexamination Certificate

active

06199525

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a camshaft drive for an engine and more particularly to an improved camshaft drive arrangement for an overhead camshaft that permits a compact engine construction.
In substantially all engine applications, there is a large demand for more compact engine constructions. This is particularly true in connection with automotive applications. One particularly demanding situation in an automotive application is when the engine is positioned transversely in the chassis. Such transverse placement normally substantially limits the number of cylinders that can be used because of the length constraints.
Where overhead camshafts are employed, the camshafts are normally driven off of the crankshaft by a timing mechanism that is generally provided at one end of the crankshaft. Such arrangements have a number of difficulties, not the least of which is the fact that this type of a drive generally adds to the overall length of the engine.
There has been proposed, therefore, a type of camshaft drive where the camshaft is driven from an intermediate shaft which is in turn driven from the crankshaft. By doing this, it is possible to shorten the length of the crankshaft and, accordingly, the entire engine. In addition, since there are several stages in the drive from the crankshaft to the camshaft, it is possible to utilize smaller driving sprockets or pulleys in order to achieve the necessary two-to-one speed reduction between the speed rotation of the crankshaft and the camshaft. This further facilitates the formation of compact engine constructions.
An example of an engine having this type of construction may be found in U.S. Pat. No. 5,154,144 issued Oct. 13, 1992, and assigned to the assignee hereof.
Although this type of structure is quite advantageous, the intermediate shaft is mounted in the cylinder head and this tends to give rise to a rather bulky cylinder head arrangement. This may be best understood by reference to
FIG. 1
, which is a view showing this prior art type of engine camshaft driving arrangement. The arrangement shown in
FIG. 1
is not exactly the same as that shown in the aforenoted issued United States Letters Patent, but the problems presented by it are evident from this figure.
As seen in this figure, an engine, shown partially with portions removed and other portions broken away, indicated generally by the reference numeral
11
, is comprised of a cylinder block assembly
12
to which a cylinder head assembly
13
is detachably affixed in a known manner. The cylinder head assembly
13
includes a main cylinder head member
14
.
In the illustrated prior art example, the engine
11
is of a live-cylinder, inline type and thus the cylinder block
12
is formed with five, inline cylinder bores. Pistons, which are not shown, are slidably supported in the cylinder bores and are connected to a crankshaft that is rotatably journaled in a crankcase assembly by connecting rods, none of which structure is illustrated inasmuch as it is well known.
A first intermediate shaft
15
is journaled within a chamber formed at one side of the cylinder block and which has an exterior surface
16
that receives a closure plate so as to enclose this chamber. This first intermediate shaft has a gear
17
formed on it that is in mesh with a gear formed on the crankshaft at the throw between the first and second cylinders. This gear arrangement preferably drives the first intermediate shaft
15
at the same speed as the crankshaft. However, because of the gear drive arrangement, the first intermediate shaft
15
will rotate in an opposite direction from that of the crankshaft. Therefore, there are balance masses
18
and
19
formed on this first intermediate shaft
15
so as to balance some of the unbalanced forces in the engine.
The first intermediate shaft
15
is journaled by bearing surfaces formed in web portions
21
of the surface
16
and by the cover plate attached thereto.
A driving sprocket
22
is affixed on the first intermediate shaft
15
adjacent the gear
17
. A chain
23
or other flexible transmitter drive extends upwardly from the sprocket
22
and is entrained with a further sprocket
24
affixed to one end of a second intermediate shaft
25
. This second intermediate shaft
25
is journaled in the cylinder head member
14
by suitable bearing surfaces. It should be noted that the sprocket
24
is disposed between the intake port openings
26
of the number
1
and number
2
cylinders.
At least one overhead camshaft
27
is journaled in the cylinder head assembly
13
and has cam lobes
28
for operating valves associated with the respective cylinders. This camshaft has a sprocket
29
affixed to its forward end and which is driven by a sprocket
31
affixed to the forward end of the second intermediate shaft
25
through a flexible transmitter such as a chain
32
.
The combined ratio between the sprockets
22
and
24
and
31
and
29
is two-to-one so that the camshaft
27
will be driven at one-half crankshaft speed. Because the reduction need not take place in a single stage, the sprockets
22
,
24
,
31
and
29
can be smaller than if the reduction was made in a single stage. This permits a more compact engine and since the drive sprocket for the camshaft need not be formed at an end of the crankshaft, the engine can be made shorter in an overall length.
In spite of these advantages, because of the necessity of mounting the second intermediate shaft
25
in the cylinder head, the cylinder head construction becomes rather complicated and costly. This makes the upper portion of the engine more difficult to position in an engine compartment. This is particularly true when low, sloping hood lines are desired.
Therefore, it is the principal object of this invention to provide an improved camshaft driving arrangement that permits the formation of the compact engine but which nevertheless can be simple and use a more conventional type of cylinder head construction.
It is a still further object of this invention to provide an improved and compact cylinder head, cylinder block and camshaft drive arrangement for an internal combustion engine when the camshafts are driven through a pair of intermediate shafts, but neither of them need be mounted in the cylinder head assembly.
SUMMARY OF THE INVENTION
This invention is adapted to be embodied in a camshaft drive arrangement for an engine having a cylinder block having at least one cylinder bore closed by a cylinder head. A crankshaft is driven by a piston contained within the one cylinder bore and which crankshaft rotates about a first axis within the cylinder block. A first intermediate shaft is journaled for rotation by the cylinder block about a second axis that is parallel to the first axis and which is disposed at one side of the crankshaft. First drive means drive the first intermediate shaft from the crankshaft. A second intermediate shaft is journaled for rotation by the cylinder block about a third axis that is parallel to the first and second axes and at a position that is contiguous to the cylinder head. Second drive means drive the second intermediate shaft from the first intermediate shaft. At least one camshaft is journaled for rotation by the cylinder head about a fourth axis which is parallel to the first, second and third axes for operating at least one valve associated with the cylinder head. A third drive means drives the camshaft from the second intermediate shaft.


REFERENCES:
patent: 4841789 (1989-06-01), Ochiai
patent: 4993374 (1991-02-01), Okui
patent: 5024287 (1991-06-01), Okui et al.
patent: 5113807 (1992-05-01), Kobayashi
patent: 5724930 (1998-03-01), Sakurai et al.
patent: 5740768 (1998-04-01), Sakurai et al.
patent: 0335246 (1989-04-01), None
patent: 0415022 (1991-03-01), None
Patent Abstracts of Japan, vol. 10, No. 261, Sep. 5, 1986 & JP A 61 085510 A (Honda Motor Co Ltd), May 1, 1986.

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