1. An air cleaner for an engine for purifying air to be introduced into the engine, said air cleaner comprising:
a cleaner housing;
a cleaner element made of a urethane foam and formed in a tubular form having an endless wall and operable to pass the air therethrough in a direction across a thickness of the cleaner element to purify the air, said cleaner element, when viewed in a direction conforming to a heightwise direction of the wall, representing a heteromorphic shape and having upper and lower end faces opposite to each other;
first and second retainer plates each made of an elastic material and bonded respectively to the upper and lower end faces of the wall to retain the heteromorphic shape of the wall; and
a holder assembly including a first holder member having a first seat element for holding the upper end face of the cleaner element through the first retainer plate and a second holder member having a second seat element for holding the lower end face of the cleaner element through the second retainer plate;
said cleaner element and said first and second retainer plates being carried by the holder assembly and accommodated within the cleaner housing together with the holder assembly.
2. The air cleaner for an engine as claimed in claim 1, wherein the first holder integrally includes a tubular body onto which the cleaner element is externally mounted.
3. The air cleaner for an engine as claimed in claim 2, further comprising a sealing member sandwiched between the second seat element of the second holder and the second retainer plate.
4. The air cleaner for an engine as claimed in claim 3, each of the first and second retainer plates and the sealing member is made of a rubber material.
5. The air cleaner for an engine as claimed in claim 3, wherein the sealing member is disposed in the second seat element of the second holder at a location confronting a lower end face of the tubular body of the first holder through the second retainer plate.
6. The air cleaner for an engine as claimed in claim 5, wherein the second seat element of the second holder has a circumferentially extending groove defined therein and said sealing member is engaged in the circumferentially extending groove.
7. The air cleaner for an engine as claimed in claim 1, wherein the holder assembly includes a tubular body onto which the cleaner element is externally mounted and further comprising a first sealing member sandwiched between the first seat element of the first holder and the first retainer plate and a second sealing member sandwiched between the second seat element of the second holder and the second retainer plate, said tubular body intervening between the first and second retainer plates.
8. The air cleaner for an engine as claimed in claim 7, wherein the first sealing member is disposed in the first seat element of the first holder at a location confronting an upper end face of the tubular body through the first retainer plate and the second sealing member is disposed in the second seat element of the second holder at a location confronting a lower end face of the tubular body through the second retainer plate.
9. An air cleaner for an engine for purifying air to be introduced into the engine, said air cleaner comprising:
a cleaner housing;
a cleaner element formed in a tubular form having an endless wall and operable to pass the air therethrough in a direction across a thickness of the cleaner element to purify the air, said cleaner element having upper and lower end faces opposite to each other;
a retainer plate made of an elastic material and bonded to at least one of the upper and lower end faces of the wall;
a holder assembly for holding the cleaner element, the holder assembly having a seat element which holds said at least one of the upper and lower end faces of the cleaner element through the retainer plate and being accommodated within the cleaner housing together with the cleaner element; and
a sealing member disposed in the holder assembly and sandwiched between the retainer plate and the seat element.
10. The air cleaner for an engine as claimed in claim 9, wherein each of the retainer plate and the sealing member is made of a rubber material.
11. The air cleaner for an engine as claimed in claim 9, wherein the holder assembly includes a first holder having a tubular body formed integrally therewith and a second holder cooperable with the first holder for holding the cleaner element between it and the first holder and wherein the cleaner element is externally mounted on the tubular body.
12. The air cleaner for an engine as claimed in claim 11, wherein the second holder has the seat element defined therein and wherein the sealing member is disposed in the seat element of the second holder at a location confronting a lower end face of the tubular body of the first holder through the retainer plate.
13. The air cleaner for an engine as claimed in claim 12, wherein the seat element of the second holder has a circumferentially extending groove defined therein and the sealing member is engaged in the circumferentially extending groove.
14. The air cleaner for an engine as claimed in claim 9, wherein the cleaner element is made of an urethane foam.
15. The air cleaner for an engine as claimed in claim 9, wherein first and second retainer plates are bonded respectively to the upper and lower end faces of the cleaner element; wherein the holder assembly includes a first holder having a first seat element defined therein for holding the upper end face of the cleaner element through the first retainer plate and a second holder having a second seat element defined therein for holding the lower end face of the cleaner element through the second retainer plate and also includes a tubular body onto which the cleaner element is externally mounted; wherein first and second sealing members are sandwiched between the first seat element of the first holder and the first retainer plate and between the second seat element of the second holder and the second retainer plate, respectively: and wherein the tubular body intervenes between the first and second retainer plates.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
What is claimed is:
1. An improved three-order sigma-delta modulator, comprising:
an analog-to-digital converter, to output a digital modulation signal;
a digital-to-analog converter, to convert the digital modulation signal into an analog signal and generate a feedback signal;
a first integrating network, to receive an external signal and the feedback signal and generate a first output signal with a first gain factor;
a second integrating network, connected in series with the first integrating network, to receive the first output signal and a feedback gain signal with a feedback gain factor that is generated by increasing the gain of the feedback signal by the feedback gain factor, and to generate a second output signal with a second gain factor;
a third integrating network, connected in series with the second integrating network, to receive the second output signal and generate a third output signal with a third gain factor; and
an adder, connected in series with the third integrating network, to combine a feedforward output signal with a feedforward gain factor that is generated by increasing the gain of the first output signal by the feedforward gain factor and a modulation output signal with a modulation gain factor that is generated by increasing the gain of the third output signal by the modulation gain factor, and to generate a desired noise transfer function.
2. The improved three-order sigma-delta modulator of claim 1, wherein the first, second, third, feedforward, feedback and the modulation gain factors have a relationship with the desired noise transfer function as the following equation:
2
N
T
F
=
(
Z
–
1
)
3
Z
3
+
Z
2
(
–
3
+
B
1
C
1
+
A
1
B
2
B
3
C
3
)
+
Z
(
3
–
2
B
1
C
1
+
B
1
B
2
B
3
C
3
–
A
1
B
2
B
3
C
3
)
+
(
B
1
C
1
–
1
)
where
NTF is the desired noise transfer function in Z domain; Al is the feedback gain factor of the second integrator; B1, B2, B3 are the first, second, third integrator’s gain factors; C1 is the feedforward gain factor; and C3 is the feedback gain factor.
3. The improved three-order sigma-delta modulator of claim 2, wherein any analog three-order sigma-delta modulator with the desired noise transfer function comprises a switched capacitor.
4. The improved three-order sigma-delta modulator of claim 2, wherein any digital three-order sigma-delta modulator with the desired noise transfer function comprises a digital logic circuit.
5. An improved three-order sigma-delta modulator, comprising:
a first adder, having a first input terminal, a second input terminal and an output terminal, the first input terminal connected to an external signal;
a first gain unit, having an input terminal and an output terminal, the input terminal connected to the output terminal of the first adder;
a second adder, having a first input terminal, a second input terminal and an output terminal, the first input terminal connected to the output terminal of the first gain unit;
a first delay unit, having an input terminal and an output terminal, the input terminal connected to the output terminal of the second adder, the output terminal connected to the second input terminal of the second adder;
a feedforward gain unit, having an input terminal and an output terminal, the input terminal connected to the output terminal of the first delay unit;
a third adder, having a first input, a second input and an output terminal, the first input terminal connected to the output terminal of the first delay unit;
a second gain unit, having an input terminal and an output terminal, the input terminal connected to the output terminal of the third adder;
a fourth adder, having a first input terminal, a second input terminal and an output terminal, the first input terminal connected to the output terminal of the second gain unit;
a second delay unit, having an input terminal and an output terminal, the input terminal connected to the output terminal of the fourth adder, the output terminal connected to the second input terminal of the fourth adder;
a third gain unit, having an input terminal and an output terminal, the input terminal connected to the output terminal of the fourth adder;
a fifth adder, having a first input terminal, a second input terminal and an output terminal, the first input terminal connected to the output terminal of the third gain unit;
a third delay unit, having an input terminal and an output terminal, the input terminal connected to the output terminal of the fifth adder, the output terminal connected to the second input terminal of the fifth adder;
a modulation gain unit, having an input terminal and an output terminal, the input terminal connected to the output terminal of the third delay unit;
a sixth adder, having a first input terminal, a second input terminal and an output terminal, the first input terminal connected to the output terminal of the modulation gain unit, the second input terminal connected to the output terminal of the feedforward gain unit;
an N-bit analog-to-digital converter, having an input terminal and an output terminal, the input terminal connected to the output terminal of the sixth adder, the output terminal connected to the external;
an N-bit digital-to-analog converter, having an input terminal and an output terminal, the input terminal connected to the output terminal of the N-bit analog-to-digital converter, the output terminal connected to the second input terminal of the first adder; and
a feedback gain unit, having an input terminal and an output terminal, the input terminal connected to the output terminal of the N-bit digital-to-analog converter, the output terminal connected to the second input terminal of the third adder.
6. The improved three-order sigma-delta modulator of claim 5, wherein N is any integer greater than zero.
7. The improved three-order sigma-delta modulator of claim 5, wherein the first, second and third gain units, belonging to first, second and third integrators, and the feedforward, feedback and modulation gain units have a first, second, third, feedforward, feedback and modulation gain factors, respectively.
8. The improved three-order sigma-delta modulator of claim 7, wherein the first, second, third, feedforward, feedback and modulation gain factors have the following relationship to the integrators
3
N
T
F
=
(
Z
–
1
)
3
Z
3
+
Z
2
(
–
3
+
B
1
C
1
+
A
1
B
2
B
3
C
3
)
+
Z
(
3
–
2
B
1
C
1
+
B
1
B
2
B
3
C
3
–
A
1
B
2
B
3
C
3
)
+
(
B
1
C
1
–
1
)
where
NTF is desired noise transfer function in Z domain; A1 is the feedback gain factor; B1, B2, B3 are the first, second, third gain factors; C1 is the feedforward gain factor; and C3 is the feedback gain factor.
9. The improved three-order sigma-delta modulator of claim 8, wherein any analog three-order sigma-delta modulator with the desired noise transfer function comprises a switched capacitor.
10. The improved three-order sigma-delta modulator of claim 82, wherein any digital three-order sigma-delta modulator with the desired noise transfer function comprises a digital logic circuit.