Device for controlling the pressure in the bearings of a roots blower supercharger

A pressure controlling device for controlling pressure acting on end faces of bearings in a Roots blower type supercharger. An end portion of a shaft having an impeller projects through an inner wall of a housing of the supercharger, and is rotatably supported by a bearing provided outside of the inner wall. An annular space is formed the bearing and the inner wall. The annular space is communicated with the atmosphere through an air passage which is connected to a control valve. The control valve closes for a predetermined period after the engine load becomes higher than a predetermined value.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a pressure controlling device for 
controlling pressure acting on bearings provided in a Roots blower type 
supercharger mounted on an internal combustion engine. 
2. Description of the Related Art 
A Roots blower type supercharger of an internal combustion engine has two 
mating lobed impellers fixed on two rotary shafts, respectively, so that 
these impellers rotate in opposite directions to each other to carry out a 
pumping operation. There are usually clearances between the two impellers 
and between the impellers and an inner surface of a housing in which the 
impellers are housed, and accordingly, a part of the highly pressurized 
air discharged by the impellers may leak to a low pressure part in the 
housing through these clearances. As a result, pressure of the leaked air 
acts on one end face of bearings which rotatably support the rotary 
shafts, so that a pressure difference occurs at the end faces of each 
bearing. This high pressure causes grease lubricating the bearings to flow 
to the low pressure side of the bearing. In other words, the grease 
holding ability of the bearings is reduced. To prevent such a reduction of 
the grease holding ability caused by this pressure difference, a 
construction by which air pressure acting on the bearings is reduced has 
been proposed. That is, this construciton comprises a labyrinth formed on 
an inner surface of a hole through which the shaft extends, and a portion 
between the bearing and the labyrinth is communicated with the atmosphere, 
so that the above pressure difference is reduced. 
In the above construction, a clearance between the labyrinth and the shaft 
must be rather large, to prevent contact between the labyrinth and the 
shaft, and an opening for connecting the portion between the bearing and 
the labyrinth to the atmosphere also must be large to fully reduce the air 
pressure acting on the bearings. With a construction having such a large 
clearance and opening, however, in an engine state in which the amount of 
intake air is considerably reduced, such as idle running, a problem occurs 
in that the atmospheric air is sucked into the intake passage of the 
engine through the labyrinth so that the amount of intake air is 
increased, that is, the number of revolutions of the engine is increased 
even though the throttle valve is closed. 
To resolve this problem, in Japanese Unexamined Patent Publication No. 
61-16232, the applicant has already proposed a construction in which an 
annular space is formed around the shaft and between the bearing and the 
labyrinth, and this space can be communicated with the atmosphere. The 
annular space is communicated with the atmosphere when supercharging 
occurs, and is shut off from the atmosphere when the amount of intake air 
is reduced to a minimum. 
In the above proposed device, however, since the annular space is 
communicated with the atmosphere, during a sudden increase in the engine 
load a part of the boost pressure generated in the supercharger is 
released to the atmosphere through the annular space. As a result, the 
desired output torque of the engine is not fully realized during this 
sudden increase in engine load, so that the resultant acceleration of the 
vehicle is poor. 
SUMMARY OF THE INVENTION 
Therefore, an object of the present invention is to provide a pressure 
controlling device by which, upon a sudden increase in engine load, a part 
of boost pressure generated in the supercharger does not leak outside of 
the housing so that an output torque of the engine is sufficient to obtain 
a good acceleration of the vehicle. 
According to the present invention, there is provided a pressure 
controlling device comprising a control valve connected to a passage 
formed in a housing of the supercharger to communicate with the 
atmosphere, means for sensing an increase in load of the internal 
combustion engine, and means for controlling the control valve to vary a 
flow passage area of the passage to the atmosphere according to the engine 
load. The controlling means closes the valve to reduce the flow passage 
area for a predetermined period after the sensing means senses an engine 
load which is higher than a predetermined value.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described with reference to the attached 
drawings. 
FIG. 1 shows a general construction of an internal combustion engine having 
a supercharger provided with a pressure controlling device of an 
embodiment of the present invention. A Roots blower type supercharger 4 is 
provided in an intake tube 5 connected to a main body 6 of an internal 
combustion engine. An air filter 1 is disposed in the inlet portion of the 
inlet tube 5, and an air flow meter 2 is provided downstream of the air 
filter 1. The specific volume of intake air flowing in the intake tube 5 
is measured by the air flow meter 2 and adjusted by a throttle valve 3 
provided between the air flow meter 2 and the supercharger 4 and connected 
to an accelerating pedal (not shown). A pressure sensor 64 is provided in 
the intake tube 5 and between the supercharger 6 and the main body 6 to 
sense an intake air pressure. A first air passage 7 is connected to a 
housing of the supercharger 4, as described later, and a second air 
passage 8 is connected to an upstream portion of the throttle valve 3. A 
control valve 9 is connected to the first and second air passages 7 and 8 
to open or close the passages 7 and 8, through control by an electronic 
control unit (ECU) 13 having a microcomputer. 
The ECU 13 has a micro processing unit (MPU) 13a, a memory 13b, an output 
port 13c, and input port 13d, and a bus 13e which interconnects those 
elements. The ECU 13 opens or closes the control valve 9 according to a 
signal sent from an idle switch 61, a clutch sensor 62 of the supercharger 
4, the air flow meter 2, a revolution sensor 63, or the pressure sensor 
64. The idle switch 61 turns ON when an opening degree of the valve 9 is 
less than a predetermined value, to output a signal denoting an idle 
running of the engine. The clutch sensor 62 outputs a signal denoting a 
supercharging state of the supercharger 4 when a clutch of the 
supercharger 4 is connected. The air flow meter 2 outputs a signal 
corresponding to a specific volume of intake air Q. The revolution sensor 
63 is provided in a distributor (not shown) to output a signal denoting 
the number of engine revolutions. The pressure sensor 64 outputs a signal 
corresponding to a pressure in the intake tube 5. 
The control valve 9 has a housing 9a which communicates with the first and 
second air passages 7 and 8, and houses a valve body 9b, a spring 9c, and 
a solenoid 9d. The valve body 9b opens or closes the opening portions of 
the first and second air passages 7 and 8 to connect them or shut them 
off. The spring 9c urges the valve body 9b in a direction in which the 
valve body 9b will close the air passages 7 and 8. The solenoid 9d urges 
the valve body 9b against the spring 9c to open the air passages 7 and 8 
when the solenoid 9d is energized. 
FIG. 2 shows a construction of the supercharger 4. A body 20 is formed as a 
cylinder having a closed end and an open end, which open end is closed by 
a rear plate 21; namely, a housing is formed by the body 20 and the rear 
plate 21. The body 20 has an inner wall 22 at the end opposite to the rear 
plate 21, so that a chamber 23 (FIG. 3) is defined between the inner wall 
22 and the rear plate 21. Ball bearings 24 are provided in the body 20 and 
outside of the inner wall 22, and ball bearings 25 are provided in the 
outer portion of the rear plate 21. Two rotary shafts 26, 27 extend 
through the inner wall 22 and the rear plate 21, and are rotatably 
supported by the bearings 24 and 25. Lobed impellers 28 and 29 are fixed 
to the rotary shafts 26 and 27 by pins 31 and 32, respectively. The 
impellers 28 and 29 are housed in the chamber 23 and mated with each 
other. A pulley 33 is fixed to an end portion of the shaft 27 which 
projects through the inner wall 22. The pulley is connected to a crank 
shaft (not shown) of the engine by an endless belt, and is rotated when 
the engine is driven. A clutch (not shown) is housed in the pulley 33 to 
transmit the rotation of the pulley 33 to the shaft 27. Gears 35 and 36 
are fixed on the other end portions of the shafts 26 and 27 by screws 41 
and washers 42, and are meshed with each other so that rotation of the 
shaft 27 is transmitted to the shaft 26. Thus, the impellers 28 and 29 
rotate in opposite directions to draw in air through an inlet port 37 of 
the housing and to compress and discharge the air through an outlet port 
38 of the housing. A cover 43 is provided on an outer surface of the rear 
plate 21 to cover the gears 35 and 36 and the rear plate 21, and to form 
an oil chamber 44, and lubricating oil is reserved in the chamber 44 to 
lubricate the gears 35 and 36. A cap 45 is fixed on an outer surface of 
the inner wall 22 to cover the projecting portion of the shaft 26. 
The four bearing portions supporting the rotary shafts 26 and 27 have 
basically the same construction, and therefore, only the bearing portion 
at the upper left side in FIG. 2 is described in detail. The ball bearing 
24 is an oil lubricating type bearing, and therefore, an oil seal ring 50 
is provided on the inner side of the inner race of the bearing 24. A hole 
formed in the inner wall 22 through which the shaft 27 passes has a large 
diameter portion near the seal ring 50 and a small diameter portion near 
the impeller 28. An annular space 51 is formed between the seal ring 50 
and the inner wall 22. As previously known, a labyrinth portion 52 is 
formed on the inner surface of the small diameter portion to restrict air 
flow from the chamber 23 to the annular space 51, and an air passage 53 is 
formed in the inner wall 22 to connect the annular space 51 to the 
atmosphere. The air passage 53 is communicated with the air passage 7 
which is connected to the control valve 9. An annular space formed in the 
left side bearing portion of the shaft 27 is communicated with the annular 
space 51 through an air passage 54 formed in the inner wall 22. The right 
side bearing portions have the same construction as the left side bearing 
portions. That is, annular spaces 51 are provided between the bearings 25 
and rear plate 21, and are communicated with the air passage 7 through air 
passages 53 and 54 to connect to the atmosphere. 
FIG. 4 shows a flowchart of a program for controlling the control valve 9 
by the ECU 13. This program is carried out by an interrupt signal output 
at predetermined periods. In step 101, it is judged whether or not the 
idle switch 62 is turned ON, that is, whether or not the engine is in an 
idle running state. When the engine is in the idle running state, the 
process proceeds to step 102 and the solenoid 9d is deenergized so that 
the control valve 9 is closed. Conversely, if the engine is not in the 
idle running state, the process proceeds to step 103, where it is 
determined whether or not the engine is running in a supercharging state, 
that is, whether or not the engine load has been suddenly increased. This 
determination of the supercharging state may be carried out by calculating 
the Q/N (Q; specific volume of intake air, N; the number of engine 
revolutions); by determining whether or not a pressure in the intake tube 
5 is higher than a predetermined value; or by determining a connection 
state of the clutch of the supercharger 4. Thus, if the engine condition 
is determined to be in a supercharging state, the process proceeds to step 
104 and the solenoid 9b is deenergized for a predetermined period, so that 
the control valve 9 is closed for the same period. That is, the valve body 
9b closes the openings of the passages 7 and 8 for a predetermined period 
after the idle switch 61, for example, is turned OFF (the throttle valve 3 
is open). A timer (not shown) is used for restricting the period for which 
the solenoid 9d is deenergized. On the other hand, in step 103, if the 
engine condition is determined as not being in a supercharging state, step 
105 is carried out and the solenoid 9d is energized to open the control 
valve 9. 
Thus, when the engine is started and is in the idle running condition, the 
program of steps 101 and 102 is carried out in that order, to keep the 
control valve 9 closed. Conversely, if the engine is in a normal running 
condition, the program of steps 101, 103, and 105 is carried in that 
order, to keep the control valve 9 open. If the engine is in the 
supercharging condition, so that the vehicle is suddenly accelerated, the 
program of steps 101, 103, and 104 is carried out in that order, to close 
the control valve 9 for a predetermined period and then again open it. 
Therefore, whenever the supercharging state occurs, the control valve 9 
closes for a predetermined period and then again opens. 
The end surface of the bearing 24 is subjected to an intake air pressure in 
the chamber 23 through the labyrinth 52 and the annular space 51. In a 
normal running condition of the engine, an electric current is applied to 
the control valve 9, and the valve body 9d is drawn against the spring 9c 
by an electromagnetic force generated in the solenoid 9d, to open the 
passages 7 and 8. Therefore, the passages 7 and 8 are communicated with 
each other, and accordingly the annular space 51 is communicated with the 
upstream portion of the throttle valve 3 where the pressure is 
approximately the atmospheric pressure, because that portion is 
communicated with the atmosphere through the air filter 1. This means that 
the air in the annular space 51 is bled to the upstream portion. That is, 
the pressure in the annular space 51 is reduced, and thus the pressure 
difference between both end surfaces of the bearing 24 becomes a very 
small value. Therefore, grease confined in the bearing 24 is prevented 
from flowing toward the outside of the bearing 24. 
On the other hand, in an idle running condition, the ECU 13 cuts the 
electric current to the control valve 9, so that the valve body 9b of the 
control valve 9 closes the openings of the passages 7 and 8, by force of 
the spring 9c, and the ECU 13 cuts out the clutch of the supercharger 4. 
As a result, the end face of the bearing 24 is subjected to a negative 
pressure from the downstream portion of the intake tube 5 through the 
chamber 23 and the seal ring 50. But, since the impellers 28 and 29 are 
not rotating, the lubricating oil in the bearing does not substantially 
leak to the inside of the bearing 24. That is, the function of the seal 
ring 50 is not affected. Further, since the control valve 9 is closed, the 
atmospheric air is barred by the valve 9 from entering the annular space 
51 through the air passage 7. That is, the atmospheric air is not led to 
the downstream portion of the supercharger 4 in the intake tube 5 through 
the labyrinth portion 52 and the chamber 23, so that the specific volume 
of intake air is not increased to prevent an increase in the engine load. 
When the engine load is higher than a predetermined value, so that the 
supercharger 4 is driven, the control valve 9 is closed for a 
predetermined period. Therefore, highly pressurized air generated in the 
chamber 23 is not released to the atmosphere through the annular chamber 
51 and the air passage 53, and any reduction in the boost pressure is 
prevented. As a result, a required boost pressure of the intake air is 
supplied into a combustion chamber of the engine, so that the acceleration 
performance of the vehicle is improved. Such a operation in which the 
control valve 9 is closed after the start of a supercharging operation is 
restricted to a predetermined period, and therefore, the temperature of 
the grease in the bearing does not become high during that period, so that 
the viscosity of the grease is not reduced, and thus the grease does not 
flow out from the bearing. 
Note that, although the above embodiment has a construction in which the 
control valve 9 is closed when the supercharger 4 starts to operate, the 
control valve 9 may not close fully, but the control valve 9 may be closed 
to a predetermined opening to reduce the flow passage area to be lower 
than a predetermined value. Further, the control valve 9 need not be an 
electromagnetic valve, as in the above embodiment, but may be a diaphragm 
device which has a diaphragm moved by a negative pressure to open and 
close a valve. 
As described above, according to the present invention, during normal 
running of the engine, even if an intake pressure acts on a bearing, a 
part of the pressurized air is bled away so that the pressure difference 
acting on both end faces of the bearing is reduced, and therefore, grease 
lubricating the bearing is fully retained by an oil seal ring provided on 
the end face of the bearing. In an idle running condition, an increase of 
a specific volume of intake air and the engine load are prevented. 
Further, upon a sudden increase in the engine load, a boost pressure is 
accordingly increased without harming the durability of the supercharger, 
so that the acceleration performance of the vehicle is improved. 
Although embodiments of the present invention have been described herein 
with reference to the attached drawings, many modifications and changes 
may be made by those skilled in this art without departing from the scope 
of the invention.