Tool for loosening or tightening spark plug

A tool is provided for loosening or tightening a spark plug while interposing a gasket and a pressure sensor between the spark plug and a cylinder head. The tool consists of concentric, relatively rotatable inner and outer cylinders. The inner cylinder is engageable with the spark plug for rotation together therewith and for loosening or tightening the same. The outer cylinder is lockingly engageable with a cylinder head by means of an axial projection of the outer cylinder and a groove of the cylinder head. The outer cylinder is further lockingly engageable with the gasket by means of a locking leg of the outer cylinder and a peripheral cut of the gasket. The gasket is thus lockingly engageable with the cylinder head by way of the outer cylinder for preventing the pressure sensor from rotating relative to the cylinder head when the spark plug is loosened or tightened.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates in general to a tool for loosening or 
tightening a spark plug on a cylinder head of an internal combustion 
engine and more particularly to an improved socket wrench for a spark 
plug. 
2. Description of the Prior Art 
A socket for an impact wrench is well known in the art and used for 
loosening or tightening a spark plug. This socket is in the form of a 
hollow cylinder having a hexagonal opening adapted for fitting a hexagonal 
portion of a spark plug. 
In some instances, a ring-shaped pressure sensor is installed between a 
spark plug and a cylinder head. This pressure sensor is used for measuring 
the pressure within an engine cylinder and thereby detecting a combustion 
condition of an engine. The pressure sensor is fixed to the cylinder head 
when the spark plug is tightened and is operable to convert a cylinder 
pressure to an electric signal by means of a built-in piezoelectric 
ceramic element, which electrical signal is taken out to the outside 
through a lead wire of the pressure sensor. 
Since the automobile engine compartment is jammed with a number of engine 
accessories or automotive parts, a lead wire that is too long may possibly 
interfere with other parts or may possibly contact the same to be damaged 
or broken. For this reason, the lead wires of each part are usually 
designed to be of a minimum possible length. The pressure sensor is no 
exception to this. Accordingly, unless the pressure sensor is arranged to 
point in a predetermined direction, the lead wire may be too short to 
reach a part to be connected. For this reason, the pressure sensor needs 
to be arranged in a position of pointing in a predetermined direction. 
Further, rotation of the pressure sensor may possibly cause a twist of the 
lead wire and a breakage of the same or the joint between the pressure 
sensor body and the lead wire may be pressed against the wire receiving 
groove to cause a crack at the joint. 
However, with the conventional wrench socket for a spark plug, the pressure 
sensor remains rotatable until the spark plug is tightened and is thus 
driven to rotate in response to the tightening of the spark plug. 
Accordingly, it has been difficult to fix the pressure sensor while 
holding it in a position of pointing in a predetermined direction. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is provided a tool for 
loosening or tightening a spark plug while interposing a pressure sensor 
between the spark plug and a cylinder head. 
The tool comprises concentric, relatively rotatable inner and outer 
cylinders. The inner cylinder has engaging means for engaging the spark 
plug and is thereby rotatable together therewith for loosening or 
tightening the spark plug. The outer cylinder has preventing means for 
preventing the pressure sensor from being driven to rotate relative to the 
cylinder head when the spark plug is driven for its loosening or 
tightening. 
The above structure is effective for solving the above noted problems 
inherent in the prior art device. 
It is accordingly an object of the present invention to provide a novel and 
improved tool for loosening or tightening a spark plug, which spark plug 
is installed on a cylinder head by interposing therebetween a pressure 
sensor, which can assuredly hold the pressure sensor in a position of 
pointing in a predetermined direction without being affected by rotation 
of the spark plug for its loosening or tightening. 
It is a further object of the present invention of the above described 
character to prevent the pressure sensor from being damaged at the time of 
loosening and tightening of the spark plug. 
It is a further object of the present invention to provide a novel and 
improved tool of the above described character which can be readily used 
in the current internal combustion engines.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIGS. 1 and 2, a spark plug loosening or tightening tool 
1 of the present invention is in the form of a wrench socket consisting of 
a hollow, outer cylinder 2 and an inner cylinder 3 concentrically and 
rotatably installed in the outer cylinder 2. 
The outer cylinder 2 has on an outer circumferential surface an axially 
elongated projection 4 of a generally semi-circular cross section and 
having at its top end an axially elongated groove 5 for receiving therein 
a lead wire 14b of a pressure sensor 14. The outer diameter of the outer 
cylinder 2 is a little smaller than the inner diameter of a spark plug 
attaching hole 7 of a cylinder head 6. A wall defining the spark plug 
attaching hole 7 is partly recessed to define an axially elongated wire 
receiving groove 8 of a generally semi-circular cross section, so that the 
axial projection 4 of the outer cylinder 2 is engageable with the wire 
receiving groove 8. Accordingly, when the tool 1 is inserted into the 
spark plug attaching hole 7 in such a way that the axial projection 4 is 
engaged with the wire receiving groove 8, the outer cylinder 2 cannot 
rotate relative to the cylinder head 6 although the former is axially 
movable relative to the latter. 
The inner cylinder 3 is rotatable on the inner circumferential surface of 
the outer cylinder 2 by the effect of a plurality of small balls 9 running 
in grooves formed in the mating surfaces of the inner and outer cylinders 
3 and 2. The inner cylinder 3 has at an upper end portion thereof an 
attaching hole 10 of a square cross section in which a correspondingly 
shaped drive shaft of an impact wrench (not shown) is fitted and at a 
lower end portion thereof a hexagonal hole 13 for fitting a hexagonal 
portion 12 of a spark plug 11. 
A pressure sensor 14 for installation between the spark plug 11 and 
cylinder head 6 is of the known type and consists of an annular sensor 
body 14a and a lead wire 14b connected thereto. A threaded portion 15 of 
the spark plug 11 passes through a central opening 14c of the pressure 
sensor 14. A gasket 16 formed from a copper plate is disposed between the 
pressure sensor 14 and the spark plug 11. 
The outer cylinder 2 is provided with a locking means "A" for preventing 
rotation of the pressure sensor 14 relative to the cylinder head 6 at the 
time of loosening or tightening of the spark plug 11. The locking means 
"A" includes the axial projection 4 and the lead wire receiving groove 8 
which are engageable with each other for preventing relative rotation 
between the outer cylinder 2 and the cylinder head 6. The locking means 
"A" further includes a peripheral cut 16a of the gasket 16 and a lower end 
locking leg 2a of the outer cylinder 2 which are engageable with each 
other for preventing relative rotation between the outer cylinder 2 and 
the gasket 16. More specifically, the peripheral cut 16a of the gasket 16 
is semi-circularly shaped and is sized so as to make the peripherally cut 
half of the outer periphery of the gasket 16 of substantially the same 
diameter as the inner diameter of the outer cylinder 2. The locking leg 2a 
is shaped correspondingly to the peripheral cut 16a of the gasket 16 and 
has a length substantially equal to the thickness of the gasket 16 so that 
the locking leg 2a is fittingly engageable with the peripheral cut 16a. 
Therefore, the outer cylinder 2 and the gasket 16 are directly engageable 
to prevent rotation of the gasket 16 even if the gasket 16 receives a 
driving force from the spark plug 11 at the time of loosening or 
tightening of the spark plug 11. While the pressure sensor 14 is pressed 
against the lower surface of the gasket at the time of installation of the 
spark plug 11, it will not rotate since the gasket, 16 is held stationary. 
While the present invention has been described and shown as above, it is 
not for the purpose of limitation. For example, as shown in FIG. 3, the 
locking means "A" may be constituted by a peripheral projection or finger 
16b of the gasket 16 and a cut or recess 2b of the outer cylinder 2. 
Further, the locking means "A" may be constituted by a projection and 
recess provided on the outer cylinder 2 and the pressure sensor 14 so that 
both are directly engaged to prevent relative rotation therebetween. 
The spark plug 11 and pressure sensor 14 are installed on the cylinder head 
6 by using the tool 1 of this invention as follows. 
As seen from FIG. 1, the spark plug 11, gasket 16 and pressure sensor 14 
are joined in such a manner that the threaded portion 15 passes through 
the gasket 16 and the pressure sensor 14. The spark plug 11, gasket 16 and 
pressure sensor 14 are then installed in the spark plug attaching hole 7 
of the cylinder head 6 in such a manner that the lead wire 14b of the 
pressure sensor 14 is received in the groove 8 of the cylinder head 6. The 
tool 1 is then fitted on the spark plug 11 in such a manner that the axial 
projection 4 is engaged in the groove 8 and the lead wire 11 is received 
by the groove 5, the hexagonal portion 12 of the spark plug 11 and the 
hexagonal portion 13 of the inner cylinder 3 are engaged with each other, 
and the locking leg 2a of the outer cylinder 2 is engaged in the 
peripheral cut 16a of the gasket 16. 
Under this condition, the inner cylinder 3 is rotated by means of a tool 
handle or wrench handle (not shown) thereby causing the spark plug 11 to 
be screwed into the cylinder head 6. In this instance, the spark plug 11 
rotates relative to the gasket 16 while being strongly pressed against the 
same, thus causing the gasket 16 to be subjected to a driving force. 
However, by the effect of locating engagement with the outer cylinder 2, 
the gasket does is not rotate but is held stationary relative to the outer 
cylinder 2. Accordingly, no driving force is transferred from the gasket 
16 to the pressure sensor 14, thus making it possible to attain the 
tightening of the spark plug 11 without causing any rotation of the 
pressure sensor 14. 
From the foregoing, it will be understood that a tool or wrench socket of 
this invention has a two-part structure consisting of an outer cylinder 
for providing locking engagement between a gasket and a cylinder head and 
an inner cylinder rotatable on the outer cylinder for loosening or 
tightening a spark plug, whereby rotation of the pressure sensor otherwise 
caused at the time of loosening and tightening of the spark plug is 
prevented by the outer cylinder. Accordingly, it becomes possible to 
loosen or tighten the spark plug while holding the pressure sensor in a 
correctly directed position, and therefore there is not any problem such 
as breakage of a lead wire of the pressure sensor or a crack at the joint 
between the pressure sensor body and the lead wire, which may otherwise be 
caused at the time of tightening of the spark plug. Furthermore, since the 
spark plug loosening or tightening tool of this invention does not require 
any particular design change of the cylinder head, it can be readily used 
in the current engines.