Diaphragm-type vacuum pump device

A diaphragm-type vacuum pump device which includes a diaphragm, a pumping chamber the volume of which is changed by reciprocating motion of the diaphragm, a check valve for drawing air into the pumping chamber, a check valve for discharging air from the pumping chamber and an orifice or relief valve disposed in the pumping chamber so that the pumping chamber communicates with atmosphere.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to diaphragm-type vacuum pump devices for generating 
a required vacuum by a displacement of a diaphram operated by a motor and, 
more particularly, to diaphragm-type vacuum pump devices used in, for 
example, a vacuum-actuated speed control system or a vacuum-actuated brake 
booster in a motor vehicle, as a vacuum source to supply vacuum under a 
condition where insufficient engine vacuum is generated at an engine 
intake manifold. 
2. Discussion of the Background 
In a conventional diaphragm-type vacuum pump device such as shown in 
Japanese Utility Model Laid-open Application No. 50 (1975)-155610 or 
Japanese Utility model Publication No. 58(1983)-36867, the diaphragm-type 
vacuum pump device generates a required vacuum by reciprocating motion of 
a diaphragm when the vacuum at the engine intake manifold decreases and is 
less than a predetermined value. 
Such diaphragm-type vacuum pump device uses, for example, a vacuum-type 
speed control system as shown in FIG. 3 in which the actual speed of the 
motor vehicle is controlled automatically and is automatically maintained 
at a set speed without depressing an accelerator pedal. 
In the vacuum-type speed control system, an engine intake manifold 1 is 
connected to a chamber 10a of a vacuum pump via a pipe 2. As a result, a 
valve 11 is changed to an open condition by the vacuum existing in the 
engine intake manifold 1. Then the vacuum at the engine manifold 1 is 
communicated with an actuator 5 via the valve 11, a chamber 10b 
(communicable with the chamber 10a through the valve 11) and a pipe 4. The 
actuator 5 pulls an accelerator link by the force of the atmospheric 
pressure caused by the vacuum at the engine intake manifold 1. In order to 
pull an accelerator link by the actuator 5, the vacuum level at the engine 
intake manifold 1 is higher than a predetermined required level, (i.e., a 
mm Hg) as represented in FIG. 4. The actuator 5 is operated by a 
controller 6 and controls the degree of opening of a throttle valve 7. 
When the vacuum at the engine intake manifold decreases and reaches the 
predetermined level, a vacuum responsive switch 8 operates and supplies a 
detecting signal to the controller 6. Then the controller 6 supplies a 
current to a motor 12 which drives the vacuum pump 10. The motor 12 
operates to rotate a crank shaft of vacuum pump 10. A diaphragm 13 
reciprocates vertically in response to the movement of the crank shaft. 
Therefore valves 14 and 15 are respectively alternately changed to 
opposite conditions. Thus the vacuum at the chamber 10b is increased. 
The vacuum pump 10 is required to generate a vacuum higher than the 
determined pressure (a mm Hg) even when flow consumption is at a maximum 
value. Therefore, the vacuum pump having pumping characteristics as shown 
in FIG. 4 is used. 
However, in the conventional diaphragm-type vacuum pump 10, when flow 
consumption in the actuator 5 is less, the generating vacuum in the vacuum 
pump 10 is increased as shown in FIG. 4. Furthermore, in starting the 
vacuum pump 10, a heavy load is applied to the motor 12. Therefore, a 
large starting torque in the motor 12 as a driving power source of the 
vacuum pump 10 is required. Consequently, in the conventional vacuum pump, 
the motor for driving the vacuum pump is required to be more powerful and 
must be more durable. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to avoid the 
disadvantages of the prior art diaphragm-type vacuum pump devices noted 
above. 
More particularly, it is an object of the present invention to provide an 
improved diaphragm-type vacuum pump device which is operable with a 
smaller driving torque of the diaphragm during starting. 
It is another object of the present invention to provide an improved 
diaphragm-type vacuum pump device which is prevented from generating an 
excessive vacuum. 
These and other objects are achieved or facilitated in accordance with the 
present invention by providing a new and improved diaphragm-type vacuum 
pump which includes a diaphragm, a pumping chamber for operating a check 
valve for drawing air thereinto and a check valve for discharging air 
therefrom disposed therein by the change of volume thereof due to 
reciprocating motion of the diaphragm and an orifice disposed in the 
pumping chamber so as to communicate the pumping chamber with atmospheric 
pressure existing outside the pumping chamber. 
Accordingly, the atmospheric pressure is introduced into the pumping 
chamber during starting whereby the starting torque of the vacuum pump can 
be decreased. 
According to another aspect of the present invention, the diaphragm-type 
vacuum pump includes a diaphragm, a pumping chamber for operating a check 
valve for drawing air thereinto and a check valve for discharging air 
therefrom by the change of volume of the pumping chamber due to 
reciprocating motion of the diaphragm and a relief valve disposed in the 
pumping chamber so as to change the open condition thereof when the level 
of vacuum at the pumping chamber exceeds the predetermined value. 
Accordingly, when the level of vacuum at the pumping chamber exceeds the 
predetermined value due to the movement of diaphragm, the relief valve 
introduces atmospheric air into the pumping chamber, whereby an excessive 
vacuum condition in the pumping chamber can be prevented.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, there is illustrated in FIG. 1 a 
diaphragm-type vacuum pump which includes a pumping chamber A formed 
between a diaphragm 23 of elastic material such as rubber, etc. and a 
second housing 26 disposed within a first housing 28. The entire outer 
circumferential portions of diaphragm 23 is clamped between the second 
housing 26 and a third housing 27. The clamping force on diaphragm 23 is 
obtained by tightening screws (not shown) of housings 28 and 27, but may 
be obtained by tightening screws of housings 28, 26 and 27 or by other 
fixing means. 
A first end portion of a connecting rod 29 is fixed to the center portion 
of the diaphragm 23, and a second end portion of the connecting rod 29 is 
rotatably mounted on a crank shaft 37. The crank shaft 37 is connected to 
a rotational shaft (not shown) of a motor 22 and generates reciprocating 
vertical movement of the connecting rod 29. 
Connection of the connecting rod 29 and the diaphragm 23 is accomplished 
not only by connection of one end portion of the connecting rod 29 with 
the diaphragm 23 but also by use of a connecting member which prevents 
damage to the diaphragm 23 caused by an oscillatory motion of the fixing 
portion between one end portion of the connecting rod 29 and the diaphragm 
23. The motor 22 may be an electromagnetically operated reciprocating 
motor. 
A check valve 24 for drawing air into the pumping chamber A and a check 
valve 25 for discharging air from the pumping chamber A are disposed in 
the second housing 26. An orifice 31 for communicating the pumping chamber 
A with atmospheric pressure and having a predetermined ventilation 
resistance is formed in the second housing 26 at the side of check valve 
25. 
An intake port 32 communicated with an actuator and an exhaust port 33 
communicated with an engine intake manifold are disposed in the first 
housing 28. An exhaust check valve 21 is mounted on a valve supporting 
member 34 disposed between the intake port 32 and the exhaust port 33. An 
exhaust chamber B for introducing vacuum from the engine intake manifold 
via the exhaust port 33 is formed between the exhaust port 33 and the 
check valve 21. An intake chamber C for introducing vacuum to the actuator 
via the intake port 32 is located between valve supporting member 34 and 
second housing 26. An air filter 35 is disposed between the exhaust port 
33 and the check valve 21. The vacuum generated at the engine intake 
manifold is introduced into the actuator via intake port 32, intake 
chamber C, check valve 21 for exhausting the exhaust chamber B, air filter 
35 and exhaust port 33. 
An O-ring 36 is disposed between first housing 28 and second housing 26 so 
as to maintain the intake chamber C airtight. The check valves 21, 24 and 
25 are of an umbrella-type which are well known. 
The operation of a diaphragm-type vacuum pump device as shown in FIG. 1 is 
as follows: the vacuum is introduced to the exhausting chamber B from the 
engine intake manifold via the exhaust port 33 serves to open the check 
valve 21 whereby the vacuum is introduced into the actuator via the check 
valve 21 and the intake port 32. In general, the vacuum at the engine 
intake manifold is directly introduced into the actuator and is used to 
control a throttle valve. 
When the vacuum at the engine intake manifold is lessened, the motor 22 is 
operated, whereby the diaphragm 23 is reciprocated and the level of vacuum 
in the inhalant chamber C is then increased by operation of the pumping 
chamber A. For example, when the pumping chamber A is expanded, the check 
valve 24 assumes an open condition, air is sucked into the pumping chamber 
A via the check valve 24 and, therefore, the level of vacuum in the 
inhalant chamber C increases. In turn, when the pumping chamber A is 
contracted, the check valve 25 for discharging air assumes an open 
condition, whereby air within the pumping chamber A is discharged to 
atmosphere. 
However, in the situation where the diaphragm-type vacuum pump is used in a 
speed control system of a motor vehicle, when a resumption switch is 
operated to return actual vehicle speed to the predetermined speed after 
braking operation during operation of the speed control system, a 
situation occurs whereby the level of the vacuum at the intake chamber C 
is high due to the flow consumption in the actuator being less. In such 
situation, the vacuum pump starts to operate, but the check valve 24 
cannot assume an open condition until the level of vacuum in the pumping 
chamber A is changed so as to be higher than that of the intake chamber C 
and, therefore, the starting torque of the motor 22 is large. 
On the other hand, when a rotational angle .theta. at the point of 
connection of the motor shaft 37 and the connecting rod 29 is 90.degree., 
the torque of the motor 22 is at its maximum as shown in FIG. 2. 
The characteristics of a vacuum pump with the orifice 31 is shown by the 
broken line in the graph in FIG. 2, and the characteristics of a vacuum 
pump without the orifice 31 is shown by the solid line in the graph in 
FIG. 2. The torque of the vacuum pump with the orifice 31 is lower than 
that of the vacuum pump without the orifice 31 due to atmospheric pressure 
being continuously introduced into the pumping chamber A via the orifice 
31, whereby the pressure at the pumping chamber A is maintained at or near 
atmospheric pressure during a stopping condition of the vacuum pump. 
Therefore, in the vacuum pump with the orifice 31, even if the motor 22 is 
started from the condition that the rotational angle .theta. is 
90.degree., the starting torque of the motor 22 can be reduced. 
In the first embodiment according to the present invention, although the 
orifice 31 is shown as being disposed in the second housing 26, the 
orifice 31 can be replaced by an orifice 31a disposed within the 
connecting rod 29 as shown in the broken line in FIG. 1 for communicating 
the pumping chamber A with atmospheric pressure. 
FIG. 5 and FIG. 6 show a second embodiment according to the present 
invention. In FIG. 5, the same reference numerals indicate the same 
members in accordance with the first embodiment of the present invention. 
Relief valve means 40 are disposed in the second housing 26. A valve 
member 44 is biased to a closed position by a spring 42 so as to contact a 
relief port 41. The relief port 41 communicates the pumping chamber A to 
atmosphere when the valve member 44 is opened and maintains the pressure 
within chamber A when the valve member is closed. When the level of vacuum 
within the pumping chamber A increases and reaches the prescribed value, 
the valve member 44 moves downwardly against the biasing force of spring 
42, whereby atmospheric pressure is introduced into the pumping chamber A 
via the relief valve 40. Therefore, the level of the vacuum within the 
pumping chamber A does not exceed the prescribed value by the operation of 
the relief valve 40. As a result, the characteristics of the vacuum pump 
are as shown by the solid line in FIG. 11. 
Furthermore, the relationship between the torque T of the motor 22 and the 
rotational angle .theta. of the connecting rod 29 and between the level P 
of the vacuum at the pumping chamber A and the rotational angle .theta. of 
the connecting rod 29 of the motor 22 are as shown in FIG. 7 and FIG. 8. 
The rotational angle .theta. in FIG. 7 and FIG. 8 are similar to the 
rotational angle .theta. as shown in FIG. 2. 
As shown by broken lines in FIG. 7 and FIG. 8, the peaks of the torque T 
and the level P of the vacuum at the pumping chamber A of the vacuum pump 
in accordance with the second embodiment of the present invention are 
lower than that of the conventional vacuum pump which is not equipped with 
the relief valve 40. The torque T and the level P of the vacuum at the 
pumping chamber in the conventional vacuum pump are as shown in solid 
lines in FIG. 7 and FIG. 8. 
Furthermore, in the second embodiment of the vacuum pump according to the 
present invention, the orifice 31 is also disposed in the second housing 
26 as shown in FIG. 5. Therefore, the starting torque of motor 22 can be 
reduced in a manner similar to that of the first embodiment of the vacuum 
pump according to the present invention. 
FIG. 9 shows a third embodiment according to the present invention which is 
a modification of the second embodiment and in which an orifice 31a is 
similar to the orifice 31 as shown in FIG. 1 and FIG. 5 is disposed in the 
valve member 44 of the relief valve 40. 
FIG. 10 shows a fourth embodiment according to the present invention which 
is a modification of the second embodiment and in which the relief valve 
40 is disposed in the connecting rod 29. Namely, a valve member 44b of the 
relief valve 40 is biased in a closing direction thereof by a spring 42b. 
A relief port 41b of the relief valve 40 is disposed in the connecting rod 
29 and is communicated with atmospheric pressure via a hole 46 and the 
third housing 27. The biasing force of the spring 42b is adjustable by 
positioning an adjustable screw 45 which is movable in an axial direction 
with respect to and engageable with the connecting rod 29 as shown in FIG. 
10. 
Obviously, many modifications and variations of the present invention are 
possible in light of the above teachings. It is therefore to be understood 
that within the scope of the appended claims, the invention may be 
practiced otherwise than as specifically described herein.