Patent Application
20080121480
1. Field of the Invention
The present invention relates to an ejector for generating a negative pressure and a negative pressure supply apparatus using the ejector. More particularly, the present invention relates to an ejector arranged to rapidly generate a target negative pressure and a negative pressure supply apparatus for brake booster, using the ejector.
2. Description of Related Art
Heretofore, an ejector has been utilized for generating a negative pressure. This ejector is arranged to generate a negative pressure by air ejected from a nozzle. To improve performance of the ejector, various techniques have been proposed. One of the techniques is for example to design a throat with a diameter larger at a predetermined ratio than a diameter of the nozzle and set a predetermined distance between the nozzle and the throat, thereby improving the ejector performance (Japanese Unexamined Utility Model Publication No. 62-112000(1987).
As a negative pressure supply apparatus using the ejector, for example, there is a negative pressure supply apparatus for brake booster arranged to supply a negative pressure to a brake booster attached to a brake master cylinder constituting a braking system of a vehicle. This type of negative pressure supply apparatus includes a nozzle connected to an air inlet port, a diffuser connected to of an air outlet, and a decompression chamber located between the nozzle and diffuser. A negative pressure generated by air ejected from the nozzle is allowed to flow from the decompression chamber into the brake booster (Japanese Unexamined Patent Publication No. 2005-171925).
However, the aforementioned ejector and negative pressure supply apparatus for brake booster have no clear specifications or data for allowing a predetermined large (high) negative pressure to be generated in a short operating time (with high response). In other words, the above publication has no disclosure about the ejector and the negative pressure supply apparatus capable of generating a predetermined large negative pressure in a short operating time. Thus, the above ejector and the negative pressure supply apparatus for brake booster could not generate a predetermined large negative pressure in a short operating time.
In particular, there is an increasing demand for the negative pressure supply apparatus for brake booster capable of setting as large (high) a target negative pressure as possible and shortening the time required to obtain the target negative pressure.
The present invention has an object to provide an ejector capable of generating a predetermined large (high) negative pressure in a short operating time and a negative pressure supply apparatus for brake booster using the ejector.
To achieve the above object, the present invention according to one aspect provides an ejector for generating a negative pressure, including: a nozzle communicating with a fluid inlet; a diffuser communicating with a fluid outlet; and a decompression chamber placed between the nozzle and the diffuser; wherein the ejector is arranged to generate the negative pressure in the decompression chamber by a fluid ejected from the nozzle, a target pressure P in the decompression chamber is set in a range of “40 kPa<P≦50 kPa”, and an SD/Sd ratio between a sectional area SD of an inlet of the diffuser and a sectional area Sd of an outlet of the nozzle is determined to satisfy a relation:
“1.20≦SD/Sd≦4.08−0.047P”.
According to another aspect, the present invention provides an ejector for generating a negative pressure, including: a nozzle communicating with a fluid inlet; a diffuser communicating with a fluid outlet; and a decompression chamber placed between the nozzle and the diffuser; wherein the ejector is arranged to generate the negative pressure in the decompression chamber by a fluid ejected from the nozzle, a target pressure P in the decompression chamber is set in a range of “40 kPa<P≦50 kPa”, and an SD/Sd ratio between a sectional area SD of an inlet of the diffuser and a sectional area Sd of an outlet of the nozzle is determined to satisfy a relation:
“1.25≦SD/Sd≦4.2−0.05P”.
Further, according to another aspect, the present invention provides an ejector for generating a negative pressure, including: a nozzle communicating with a fluid inlet; a diffuser communicating with a fluid outlet; and a decompression chamber placed between the nozzle and the diffuser; wherein the ejector is arranged to generate the negative pressure in the decompression chamber by a fluid ejected from the nozzle, a target pressure P in the decompression chamber is set to 40 kPa or lower, and an SD/Sd ratio between a sectional area SD of an inlet of the diffuser and a sectional area Sd of an outlet of the nozzle is determined to satisfy a relation: “1.25≦SD/Sd≦2.2”.
According to another aspect, furthermore, the present invention provided a negative pressure supply apparatus for brake booster for supplying a negative pressure to a brake booster mounted in a vehicle, wherein the supply apparatus includes the aforementioned ejector, and the decompression chamber can be communicated with the brake booster.
In the drawings,
A detailed description of a preferred embodiment of an ejector embodying the present invention will now be given referring to the accompanying drawings. This ejector of the present embodiment will be explained referring to
Referring to
The nozzle 15 is configured to communicate with the inlet port 11 and have a tapered inner wall so that a cross sectional area gradually decreases in a direction opposite the inlet port 11 to raise the velocity of flow flowing in the nozzle 15 trough the inlet port 11. This nozzle 15 communicates with one end of the diffuser 17 via the decompression chamber 16.
The diffuser 17 is configured to have a tapered inner wall, but tapered reversely from the nozzle 15, so that a passage sectional area gradually increases in a direction toward the outlet port 12 to reduce flow loss of fluid ejected from the nozzle 15 for preventing a decrease in flow velocity of the fluid in the nozzle 15. The other end of this diffuser 17 communicates with the outlet port 12. The fluid flowing in the ejector 10 through the inlet port 11 is allowed to pass through the nozzle 15, part of the decompression chamber 16 (a communicating portion between the nozzle 15 and the diffuser 17), and the diffuser 17 to flow out through the outlet port 12.
The decompression chamber 16 communicates with the nozzle 15 and the diffuser 17, while it is connected to the suction chamber 19 via a first check valve 21. The suction chamber 19 is also connected to the communication passage 18 via a second check valve 22. This suction chamber 19 communicates with the joint port 13.
In the above ejector 10, when a fluid flows therein through the inlet port 11, the flow of this fluid passing through the nozzle 15 generates a negative pressure in the decompression chamber 16, causing the first check valve 21 to open. Accordingly, the negative pressure generated in the decompression chamber 16 is introduced from the decompression chamber 16, via the suction chamber 19 and the joint port 13, to an object to be supplied with the negative pressure.
To shorten the time required to reach a target negative pressure (herein, referred to as a “time-to-target negative pressure”), the inventors of the present invention have found out through experiment that a relation (SD/Sd) between a sectional area SD of an entrance of the diffuser and a sectional area Sd of an outlet of the nozzle has only to be adjusted to an optimum ratio. The ejector 10 of the present embodiment is therefore arranged to satisfy a relation that an SD/Sd ratio of the inlet sectional area SD (inlet diameter D) of the diffuser to the outlet sectional area Sd (outlet diameter d) of the nozzle 15 in
Here,
As can be seen from
As is evident from
As shown in
As can be seen from
Since the target negative pressure P in the decompression chamber 16 is set in the range of “40 kPa≦P≦50 kPa”, focusing attention to
As for the upper limit of the SD/Sd ratio, on the other hand, the SD/Sd ratio is “2.2”, “2.0”, and “1.75” which are smaller with respect to the target negative pressure larger in the range of “40 kPa<P≦50 kPa” as shown in
A preferable range of the SD/SD is “1.25≦SD/Sd≦4.2−0.05P”, because the ejector designed with such a numerical SD/Sd range can further shorten the time-to-target negative pressure.
As above, the ejector is designed with the SD/Sd ratio set in the range of “1.20≦SD/Sd≦4.08−0.047P”, so that the target negative pressure can be generated in a short time even where the target negative pressure P to be generated in the decompression chamber is as large as “40 kPa<P≦50 kPa”.
If the target negative pressure P to be generated in the decompression chamber is set to be 40 kPa or lower (P≦40 kPa), as shown in
Moreover, to shorten the time-to-target negative pressure, the inventors of the present invention also have found out through experiment that it is necessary to optimize a ratio L/d of the distance L between the outlet of the nozzle 15 and the inlet of the diffuser 17 to the outlet diameter d of the nozzle 15. The ejector 10 of the present embodiment is therefore designed with the L/d ratio satisfying the relation “0.50≦L/d≦1.50”.
Here,
Hence, the optimum range of the L/d ratio will be studied below referring to
As is evident from
Further, as can be seen from
The above results show that the ejector 10 with the target negative pressure P in the decompression chamber 16 set in the range of “40 kPa≦P≦50 kPa” has to be designed to have the L/d ratio satisfying the relation of “0.50≦L/d≦1.50”, thereby further shortening the time-to-target negative pressure.
Here, preferably, the L/d ratio is set to satisfy the relation of “0.75≦L/d≦1.20”. By setting the L/d ratio in such a numerical range, the time-to-target negative pressure can be minimized as shown in
Successively, the negative pressure supply apparatus for brake booster using the ejector 10 mentioned above will be explained referring to
A negative pressure supply apparatus for brake booster 30 (hereinafter, simply referred to as a “negative pressure supply apparatus 30”) is arranged to supply a negative pressure (“intake pipe negative pressure”) generated in an intake pipe 34 constituting an air intake system of an engine 33 to a brake booster 32 attached to a brake master cylinder 31 equipped in a vehicle, as shown in
Here, the bypass passage 40 is connected to communication passages 37a and 37b formed in a throttle body 37 and communicates with the intake pipe 34. That is, the passage including the bypass passage 40 and communication passages 37a and 37b corresponds to a “bypass passage” of the present invention. An entrance (the communication passage 37a) of the bypass passage 40 is located between an air cleaner 35 fixed to an end of the intake pipe 34 and a throttle valve 36 placed at some position in the intake pipe 34. On the other hand, an exit (the communication passage 37b) of the bypass passage 40 is located between the throttle valve 36 and the engine 33.
Further, an opening and closing valve 50 is placed between an inlet port of the ejector 10 and the communication passage 37a (on the upstream side of the ejector 10) to open and close the bypass passage 40 for executing ON-OFF control of the operation of the ejector 10, thereby making the ejector 10 active or inactive. This opening and closing valve 50 is configured to perform valve opening and closing operations by a temperature sensitive medium. In the present embodiment, a bimetal is used for the temperature sensitive medium.
The opening and closing valve 50 includes a valve chamber 52 having a bottom formed with a plurality of protrusions 52a (eight protrusions in the present embodiment) arranged at predetermined intervals as shown in
As shown in
The bimetal 51 is configured to become curved in the following manner depending on the temperature in the throttle body 37. Specifically, the bimetal 51 is convex in an upstream direction, separating from the valve seat 53, as shown in
Opening and closing of the bypass passage 40 may be conducted by a solenoid valve or a diaphragm valve. However, the aforementioned opening and closing valve 50 is constituted of the bimetal 51 provided in the valve chamber 52 and the spring 54 supporting the bimetal 51, so that this valve 50 is a very simple structure needing only a small number of components as compared with the solenoid valve or diaphragm valve. Accordingly, the opening and closing valve 50 can be small in size and light in weight, and low in manufacturing cost.
As shown in
Since the negative pressure supply apparatus 30 is integrally assembled with the throttle body 37 as mentioned above, the operation of the opening and closing valve 50 can be controlled by heat transmission from a hot-water pipe provided in the throttle body 37. Thus, the opening/closing control of the opening and closing valve 50 can be executed accurately according to the state of the engine 33 (during the cold period or during the warm-up period).
The negative pressure supply apparatus 30 does not have to be placed singly, unlike the conventional apparatus, and therefore needs no fixing tool that would be required for the conventional apparatus. This makes it possible to eliminate the need for a pipe for connecting the negative pressure supply apparatus to the intake pipe. Thus, the negative pressure supply apparatus 30 can be provided with reduced total weight and in lowered cost. Since the need for providing a pipe to the negative pressure supply apparatus 30 is eliminated, achieving shortening of the length of the bypass passage 40 and accordingly lowering pressure loss, the performance of the negative pressure supply apparatus 30 can be enhanced.
The following explanation is made on the operation of the negative pressure supply apparatus 30 configured as above. During the cold period of the engine 33, firstly, the bimetal 51 placed in the opening and closing valve 50 is held in a convex shape protruding in the upstream direction, separating from the valve seat 53, thereby allowing the bypass passage 40 to open. Hence, the air flowing from the air cleaner 35 into the intake pipe 34 toward the throttle valve 36 is partly allowed to pass through the bypass passage 40 and flow into part of the intake pipe 34 downstream from the throttle valve 36. The ejector 10 is thus made active, increasing an intake pipe negative pressure.
At this time, the increased intake pipe negative pressure acts on the first check valve 21 to open the valve 21. The increased intake pipe negative pressure is therefore supplied from the decompression chamber 16, via the suction chamber 19 and the pipe 41, to the brake booster 32. The ejector 10 can generate the target negative pressure P in a short operating time, thereby supplying the increased negative pressure to the brake booster 32 with good response.
As mentioned above, the negative pressure supply apparatus 30 can supply the increased intake pipe negative pressure to the brake booster 32 during the engine cold period. Consequently, even where the intake pipe negative pressure is low because of delaying of an ignition timing during the cold period for inducing activation of a catalyst, it is possible to supply, with good response (rapidly), an intake pipe negative pressure sufficient to activate the brake booster 32.
During the warm-up period, the bimetal 51 provided in the opening and closing valve 50 is recurved to be convex in the downstream direction, coming into contact with the valve seat 53. Thus, the opening and closing valve 50 closes off the bypass passage 40. As a result, the air flowing from the air cleaner 35 into the intake pipe 34 toward the throttle valve 36 is checked, or prevented from flowing in the bypass passage 40. The ejector 10 is made inactive. At this time, the intake pipe negative pressure acts on the second check valve 22 to open the second check valve 22. The intake pipe negative pressure is accordingly supplied directly to the brake booster 32 via the suction chamber 19 and the pipe 41. Consequently, an excess amount of air flow to the engine 33 in the warm-up state can be prevented, thereby avoiding a decrease in accuracy of air flow control in the control of fuel-air ratio of the engine 33.
As described above, the ejector 10 of the present embodiment is arranged such that the SD/Sd ratio between the inlet sectional area SD of the diffuser 17 and the outlet sectional area Sd of the nozzle 15 is set in the range of “1.20≦SD/Sd≦4.08−0.047P”. Accordingly, even where the target negative pressure P in the decompression chamber 16 is as large (high) as a value set in a range of “40 kPa<P≦50 kPa”, the target negative pressure P can be obtained in a short operating time. The ejector 10 is also configured such that the L/d ratio of the distance L between the outlet of the nozzle 15 and the inlet of the diffuser 17 with respect to the outlet diameter d of the nozzle 15 is set in the range of “0.50≦L/d≦1.50”, so that the time-to-target negative pressure can further be shortened.
According to the negative pressure supply apparatus 30 for brake booster using the above ejector 10, during the cold period of the engine 33, the ejector 10 can be made active to increase the intake pipe negative pressure to the target negative pressure in a short time and supply such an increased negative pressure to the brake booster 32. During the warm-up time of the engine 33, on the other hand, the ejector 10 can be made inactive, checking the excess air flow to the engine 33, thereby preventing a decrease in accuracy of air flow control in the control of fuel-air ratio of the engine 33.
The aforementioned embodiment is merely an example, and the present invention may be embodied in other specific forms without departing from the essential characteristics thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-316382 | Nov 2006 | JP | national |
