JPH068103B2 - Hydraulic booster - Google Patents

Description

Detailed Description of the Invention A. OBJECTS OF THE INVENTION (1) Field of Industrial Application The present invention relates to a hydraulic booster used for boosting a master cylinder for an automobile, in particular, a booster cylinder; A booster piston that divides the interior into a front input hydraulic chamber and a rear output hydraulic chamber that are connected to a hydraulic source, and that is connected to a master piston of a master cylinder; and an input that is slidably movable in the axial direction with respect to this booster piston. A rod; an inlet valve provided in an inlet oil passage formed between the input and output hydraulic chambers formed in the booster piston, the inlet valve interlocking with the input rod so that the valve is closed when the input rod retracts and opened when the input rod moves forward; The present invention relates to an improvement of an outlet valve which is provided in an outlet oil passage connecting between an output hydraulic chamber and an oil tank, and which is opened when the input rod moves backward and is closed when the input rod moves forward;

(2) Conventional Technology This type of booster is already known, as disclosed in, for example, Japanese Patent Laid-Open No. 61-44064.

Conventionally, in order to filter the hydraulic oil supplied to such a booster, an oil filter is installed in an oil tank for supplying the hydraulic oil to the hydraulic source.

(3) Problems to be solved by the invention With the oil filter installed in the oil tank as described above, foreign matter can be separated from the hydraulic oil supplied to the oil tank, but it remains in the booster cylinder during manufacture. The processing waste cannot be separated, and the processing waste etc. may cause clogging of the inlet valve and the outlet valve.

The present invention has been made in view of the above circumstances, and the hydraulic booster prevents the inlet valve and the outlet valve from being clogged even if machining waste or the like remains in the booster cylinder. The purpose is to provide.

B. Configuration of the Invention (1) Means for Solving the Problems In order to achieve the above-mentioned object, an annular groove on the outer periphery of the booster piston, which opens to the input hydraulic chamber, and the annular groove communicates with the inlet oil passage. And an oil filter is attached to the annular groove.

(2) Operation According to the above configuration, the oil filter is always located at the closest distance to the inlet valve regardless of the operating position of the booster piston. Therefore, even if foreign matter such as machining waste remains in the booster cylinder, it can be reliably separated from the hydraulic oil and prevented from entering the inlet valve side.

(3) Embodiment Hereinafter, one embodiment of the present invention will be described with reference to the drawings. First, in FIG. 1, M indicates a tandem master cylinder for a two-system hydraulic brake of an automobile, which is located above the cylinder body 1. oil tank 2 is formed, the inside thereof is partitioned into a front oil reservoir 2 ₁ and the rear oil sump 2 ₂ by a partition wall 2a of the lower half.

The cylinder hole 3 of the cylinder body 1 has a small diameter hole 3a passing directly below the oil tank 2 and a large diameter hole 3b connected to the rear end of the small diameter hole 3a.
And more stepped. Front oil reservoir _{2 1} The small diameter hole 3a
The front hydraulic chamber (not shown) to be refueled from the cylinder hole 3
Rear master piston 5 defining between the overall and the front master piston 4, the rear hydraulic chamber 6 which is oil from the rear oil sump 2 ₂ and front master piston 4 defined between the front end wall of the
Of the rear master piston 5 is slidably engaged with the large-diameter hole 3b. Therefore, the rear master piston 5 is composed of a small-diameter piston portion 5a and a large-diameter piston portion 5b having a larger diameter.

Both piston portion 5a, the large-diameter hole 3b defined replenishment oil chamber 7 by 5b, the oil chamber 7 is communicated with the rear oil sump 2 ₂ through an oil passage 8.

An elastic piston cup 9 is provided on the front surface of the small-diameter piston portion 5a.
Is mounted, a relief port 10 is opened in front of the piston cup 9 in the retreat limit of the rear master piston 5 to communicate between the rear hydraulic chamber 6 and the oil passage 8, and a small-diameter piston is provided. The portion 5a is formed with a through hole 11 which allows the replenishment oil chamber 7 to communicate with the back portion of the piston cup 9.

In the front hydraulic chamber (not shown) and the rear hydraulic chamber 6,
A return spring 12 is housed for biasing the front and rear master pistons 4 and 5 in the backward direction.

When the rear master piston 5 is pushed forward and the piston cup 9 crosses the opening of the relief port 10, hydraulic pressure is generated in the rear hydraulic chamber 6, and the hydraulic pressure is generated in the rear hydraulic chamber 6.
Is supplied to a brake hydraulic circuit (not shown) that communicates with the brake hydraulic circuit.

When the rear master piston 5 retreats from the forward position and the rear hydraulic chamber 6 is depressurized, the outer peripheral portion of the piston cup 9 bends forward due to the pressure difference between the front and rear of the piston cup 9, and a gap is created between the outer peripheral portion and the inner surface of the cylinder hole 3. result, the rear oil reservoir 2 ₂ oils oil passage 8,
It flows into the rear hydraulic chamber 6 through the supply oil chamber 7 and the through hole 11,
When the hydraulic oil is replenished, and at the same time, when the excessive replenishment is performed, the excessive amount is supplied from the relief port 10 to the rear oil reservoir 2
Returned to ₂ .

The front master piston 4 moves forward as the pressure in the rear hydraulic chamber 6 is increased, generates hydraulic pressure in the front hydraulic chamber, and supplies this to the corresponding brake hydraulic circuit. Substantially the same Although during retraction of the piston 4 in which the front oil reservoir 2 ₁ oil is supplied to the front hydraulic chamber, replenishing mechanism of generation mechanism and oil of such a hydraulic pressure and the rear hydraulic chamber 6 side Therefore, detailed description thereof will be omitted.

As clearly shown in FIG. 2, at the rear end of the cylinder body 1 of the master cylinder M, a booster cylinder 16 of the hydraulic booster B of the present invention is continuously provided with an annular body 15 sandwiched between the cylinder body 1 and the booster cylinder 16. The cylinder 16 is connected by a bolt 17.

Here, the small diameter hole 3a of the cylinder hole 3 of the master cylinder M
_{D 1} the diameter of, university-diameter hole and 3b diameter of _{D 2,} the annular body 15
Has an inner diameter of D ₃ , and a cylinder hole 18 of the booster cylinder 16.
Let D ₄ be the diameter of (see FIG. 1), these dimensions are set to the relationship of the following equation.

D ₁ <D ₃ <D ₄ <D _{2 The} booster piston 19 is a small-diameter piston portion 19 a at the front.
And the large-diameter piston portion 19b at the rear and the large-diameter piston portion 1
9b and a rod portion 19c protruding from the rear end surface,
The small-diameter piston portion 19a and the large-diameter piston portion 19b are oil-tightly fitted in the inner hole of the annular body 15 and the cylinder hole 18 of the booster cylinder 16, respectively, and the rod portion 19c is oil-tight in the rear end wall of the booster cylinder 16. It penetrates and projects to the outside. An annular step portion 18a capable of supporting the rear end surface of the large-diameter piston portion 19b is formed at the rear end portion of the cylinder hole 18 in order to define the retreat limit of the booster piston 19.

Thus, the annular body 15 supports the rear end of the rear master piston 5 at its front end surface to define the retracting limit thereof. Further, in the cylinder hole 18, the annular body 15 and the large-diameter piston portion 19b define an input hydraulic chamber 20 therebetween, and the large-diameter piston portion 19b and the rear end wall of the booster cylinder 16 define an output hydraulic chamber 21 therebetween. To achieve. This output hydraulic chamber 2
In No. 1, the pressure receiving area is naturally formed larger than that of the input hydraulic chamber 20. Further, the large-diameter piston portion 5b of the rear master piston 5 of the master cylinder M and the small-diameter piston portion 19a of the booster piston 19 define an outlet chamber 22 therebetween.

Referring again to FIG. 1, the input hydraulic chamber 20 is connected to the oil tank 2 by a supply oil passage 23, and the oil passage 23 is provided with a hydraulic pump 24 as a hydraulic pressure source for pumping the stored oil in the oil tank 2 to the input hydraulic chamber 20. And a pressure accumulator 25 is connected to the downstream side of the pump 24.

In FIG. 2, the booster piston 19 is provided with ball-type first and second inlet valves 26 ₁ and 26 ₂ and one spool-type outlet valve 27 in parallel.

The first inlet valve 26 ₁ is a tubular valve chamber 29 ₁ formed along the axial direction of the booster cylinder 19 in the middle of an inlet oil passage 28 ₁ that communicates between the input and output hydraulic chambers 20 and 21, and its valve. the oil passage 28 in cooperation with chamber 29 ₁ of the rear end wall to form a valve seat ₁
Ball valve element 30 for opening and closing the _first and a valve spring 31 ₁ biases close the valve element 30 ₁ in the valve chamber 29 inside _1, the ball valve element 30 ₁ against the force of the valve spring 31 ₁ And an operating rod 32 ₁ capable of opening. Actuating rod 32 ₁ is the booster piston 19 is fitted in a freely axially slidable, the rear end portion thereof protrudes into the output hydraulic chamber 21.

The second inlet valve 26 ₂ is arranged symmetrically to the first inlet valve 26 ₁ with respect to the axis of the booster piston 19, and its configuration is the first except for the difference in the lengths of the operating rods 32 ₁ and 32 ₂ . It is the same as the inlet valve 26 ₁ , and in the figure, the first inlet valve 26 ₁
In the part corresponding to
Add ₂ ".

Thus, the opening timing of the first inlet valve 26 ₁ is set to the second inlet valve 26 1.
_In order to make it earlier than that of ₂ , the operating rod 3 of the first inlet valve 26 ₁
2 ₁ and longer than operating rod 32 ₂ of the second inlet valve 26 _2, when the valve is closed, opposing gap _{L 1} of the rear end of the actuating rod 32 ₁ and the interlocking ring 48 front below the actuating lever 32 ₂ Rear end and interlocking ring 4
8 is set to be smaller than the facing gap L ₂ with the front surface. That is L
₁ <L ₂ .

An oil filter 61 is mounted on the small-diameter piston portion 19a of the booster piston 19 in the vicinity of both the inlet valves 26 ₁ and 26 ₂ . As shown in FIGS. 2 and 5, the oil filter 61 comprises an annular filter body 62 made of an elastic material such as rubber having oil resistance and four filter nets 63. The filter main body 62 has four U-shaped grooves 64 extending in the axial direction on the outer circumference.
Is formed with four windows 65 reaching the inner peripheral surface of the filter body 62, and the filter mesh 63 is provided on the peripheral walls of these windows 65.
The peripheral edge of the is embedded and bonded. In this way, each filter net 63 is stretched around the corresponding 65.

The elastic filter body 62 is tightly attached while extending into an annular groove 66 provided on the outer circumference of the small-diameter piston portion 19a, and slidably fitted on the inner peripheral surface of the cylinder hole 18 of the booster cylinder 16. A small annular groove 67 is further formed on the bottom surface of the annular groove 66, and the upstream ends of the inlet oil passages 28 ₁ and 28 ₂ are opened at the groove bottom. Therefore, the hydraulic oil in the input hydraulic chamber 20 can flow into the inlet valves 28 ₁ and 28 ₂ through the U-shaped groove 64, the window 65 and the small annular groove 67.

The outlet valve 27 includes a valve cylinder 33 fitted to the piston 19 on the axis of the booster piston 19, and a valve piston 35 slidably fitted in an inner hole of the valve cylinder 33, that is, a valve hole 34.

The valve piston 35 has a rear end protruding from the valve cylinder 33 and is also used as an input rod, and a brake pedal 37 is connected to the rear end via a push rod 36.

The valve cylinder 33 has an outlet port 38 that communicates with the output hydraulic chamber 21, and the valve piston 35 has an annular groove 39 that shuts off and communicates with the outlet port 38 in accordance with its advance / retreat, and the annular groove 3
9 and an outlet oil passage 40 continuous with 9. This outlet oil passage 40
Are communicated with the outlet chamber 22 through an outlet oil passage 41 formed in the booster piston 19, and the outlet chamber 22 includes a radial groove 42 (see FIG. 4) provided in the front end surface of the annular body 15, a cylinder. An annular oil passage 43 formed at the rear end of the main body 1
And a return oil passage 44 connected to the oil passage 43 to communicate with the oil tank 2.

In the output hydraulic chamber 21, a pin 45 is fitted on the valve piston 35 at right angles to its axis. Both ends of the pin 45 are connected to the valve cylinder 33 and the rod portion 19 of the booster piston 19.
Each of the projecting end portions 45a and 45a is formed into a truncated cone shape by penetrating through axially elongated holes 46 and 47 respectively formed in c and projecting to the outer peripheral surface of the rod portion 19c. As shown in FIG. 3, connecting holes 49, 49 of a split interlocking ring 48 slidably fitted on the outer peripheral surface of the rod portion 19c are fitted into the projecting end portions 45a, 45a. Interlocking ring 48
A coil spring 50 is wound around the outer periphery of the interlocking ring 48 in order to maintain the connection state with the. And Thus, interlocking ring 48 so as to push the inlet valve ₂₆ 1, 26 ₂ of the actuating rod ₃₂ 1, 32 ₂ forwardly by receiving the advancement of the valve piston 35 is disposed to face the rear end.

A return spring 52 is interposed between the valve piston 35 and the valve cylinder 33 to elastically repel them in the axial direction. Therefore, the spring 52 has the function of holding the valve cylinder 33 on the booster piston 19 in addition to the function of returning the valve piston 35 to the backward direction.

The first stopper may support the rear surface of the valve piston 35 and the pin 45 integral in order to restrict the retraction source of the valve piston (i.e. the input rod) 35 in backward course of the booster piston 19 60 ₁
Is constituted by the rear end surface of the long hole 47.

Further, when the booster piston 19 is in the retreat limit, in order to restrict the retraction source of the valve piston 35, the second stopper 60 _second annular rear end surface may support the interlocking ring 48 is engaged with the inner wall of the booster cylinder 16 It

Thus, when the valve piston 35 is retracted, the outlet valve 27 is opened, that is, the outlet port 38 is communicated with the annular groove 39.
Its opening becomes the maximum opening when the valve piston 35 in the retracted course of the booster piston 19 has been received by the first stopper 60 ₁ via the pin 45, the booster piston 1
The valve piston 35 moves to the second position via the interlocking ring 48 at the backward limit of 9
It is set to be the minimum opening when it is received by the stopper 60 _2.

Moreover, the booster piston 19 is positioned at the retracted source, and when the valve piston 35 is restricted to retreat source with the second stopper 60 _2, opposite the first inlet valve 26 ₁ of the actuating rod 32 ₁ and the interlocking ring 48 The gap is set to be slightly larger than the minimum opening of the outlet valve 27.

The booster piston 19 is provided with a large-diameter hole 53 opening on the front surface thereof and a small-diameter hole 54 extending from the large-diameter hole 53 to the valve hole 34. The large-diameter hole 53 is made of rubber in order from the back. The elastic piston 55 and the pressure-receiving piston 56 having the same diameter as that of the elastic piston 55 are slid together, and the small-diameter hole 54 is slidably fitted with the reaction piston 57 whose both ends are in contact with the facing surfaces of the valve piston 35 and the elastic piston 55.

An output rod 58 is integrally provided on the front surface of the pressure receiving piston 56, and the output rod 58 deeply penetrates into a recess 59 on the rear surface of the rear master piston 5 and abuts against the piston 5, whereby the rear piston 5 And the booster pistons 19 are arranged as close as possible.

The depth of the recess 59 is selected to be equal to or larger than the radius of the large-diameter piston portion 5b of the rear master piston 5. With this arrangement, when the rear master piston 5 is pushed by the output rod 58, an aligning action can be given to the piston 5.

In the above, the pressure receiving piston 56, the elastic piston 55, and the reaction piston 57 constitute a reaction force mechanism R that transmits the operation reaction force of the master cylinder M to the valve piston 35.

Next, the operation of this embodiment will be described.

In the inoperative condition of the brake pedal 37, since the valve piston 35, as shown in Figure 2 is held by the elastic force of the spring 52 back to the backward limit is restricted by the second stopper 60 ₂ via the interlocking ring 48 The outlet valve 27 is opened with the minimum opening. On the other hand, the first and second inlet valves 26 ₁ , 26 ₂
In, actuating rod ₃₂ 1, 32 ₂ have been released from interlocking ring 48, the valve element ₃₀ 1, 30 ₂ is seated on the valve spring ₃₁ 1, 31 ₂ with power valve chamber ₂₉ 1, 29 ₂ of the valve seat Therefore, the valve is closed. Thus input, while the output hydraulic pressure chamber 20, 21 while being blocked by both inlet valves ₂₆ 1, 26 _2, the output hydraulic pressure chamber 21, outlet port 38, annular groove 39, the outlet passage 40 and 41, the outlet chamber 22, radially Groove 4
2, the front and rear master pistons 4 and 5 and the booster piston 19 are connected to the oil tank 2 through the annular oil passage 43 and the return oil passage 44 and are in the atmospheric pressure state. It is held in the retreat limit by force.

Further, in this case, the hydraulic pressure from the hydraulic pump 24 or the pressure accumulator 25 is introduced into the input hydraulic chamber 20, and since this hydraulic pressure acts on the front surface of the large diameter piston portion 19b of the booster piston 19, this also causes the booster piston 19 is kept in the retracted source. The ball valve elements 30 ₁ and 30
_Since No. ₂ has a high closing property, it is possible to reliably prevent the pressure oil from leaking from the input hydraulic chamber 20 to the output hydraulic chamber 21.

Now, when the brake pedal 37 is depressed to brake the automobile, the valve piston 35 and the interlocking ring 48 are pushed forward from the brake pedal 37 via the push rod 36,
From the relationship of L ₂ <L _3, the annular groove 39 is first blocked from the outlet port 38, that is, the outlet valve 27 is closed. Next, the interlocking ring 48 abuts against the rear end of the operating rod 32 ₁ of the first inlet valve 26 ₁ and pushes it forward, whereby the ball valve body 30
₁ away from its valve seat and then the interlocking ring 48
The operating rod 32 ₂ of the rear end of the inlet valve 26 ₂ in contact pushes it forward, thereby to separate the ball valve element 30 ₂ from its seat. Thus, the first and second inlet valves 26 ₁ , 2
6 ₂ are sequentially opened.

Incidentally, the outlet valve 27 is closed, the first step in the first inlet valve 26 ₁ is opened, the output hydraulic pressure chamber 21 is cut off the communication between the oil tank 2, the input hydraulic pressure chamber from the hydraulic pump 24 or the accumulator 25 The oil pressure introduced in 20 is changed to the oil filter 6
1, the oil is supplied to the output hydraulic chamber 21 through the inlet oil passage 28 ₁ and the valve chamber 29 ₁ , so that the hydraulic chambers 20 and 21 have substantially the same pressure.
Therefore, the second inlet valve 26 ₂ in the ball valve element 3 before opening
0 ₂ will receive a substantially equal hydraulic pressure to front and rear hydraulic closing force of the ball valve element 30 ₂ by the input hydraulic pressure chamber 20 is canceled or significantly reduced by opening valve force by the hydraulic pressure of the output hydraulic pressure chamber 21 Since the valve opening resistance of the ball valve element 30 ₂ becomes extremely small, when the interlocking ring 48 pushes the operating rod 32 ₂ in the next stage, it substantially resists the force of the valve spring 31 _2. in it is possible to open the ball valve body 30 ₂ lightly.

Then, when the both inlet valves 26 ₁ and 26 ₂ are opened, the pressure oil in the input hydraulic chamber 20 is smoothly supplied to the output hydraulic chamber 21 through the oil filter 61 and both oil passages 28 ₁ and 28 ₂ , so that the hydraulic pressure is increased. The booster piston 19 can be promptly advanced.

At that time, the oil filter 61 is moved together with the booster piston 19, always so located close range of both the inlet valves 6 _1, 26 _2, even if the foreign matter processing refuse such an input hydraulic chamber 20 is left , It is separated from the hydraulic oil by the filter net 63 of the oil filter 61, and the foreign matter inlet valves 26 ₁ , 2
Entry into 6 ₂ side can be reliably prevented. Further, since the filter body 62 slides on the inner peripheral surface of the booster cylinder 16 as the booster piston 19 moves, it contributes to stabilizing the operation of the booster piston 19.

The forward booster piston 19 advances the rear master piston 5 via the reaction force mechanism R and the output rod 58. In this way, the master cylinder M is boosted.

When the booster piston 19 moves forward, its front end portion enters the large diameter hole 3b of the master cylinder M. Thus, the large-diameter hole 3b serves not only to guide the large-diameter piston portion 5b of the rear master piston 5 but also to receive the front end portion of the booster piston 19 that moves forward, thereby increasing the length of the booster cylinder 16. Can be shortened.

While the booster piston 19 is pushing the rear master piston 5, the pressure receiving piston 56 operates so as to receive the reaction reaction force of the master cylinder M from the rear master piston 5 to compress the elastic piston 55, and the compression force thereof. Is fed back to the valve piston 35 via the reaction piston 57 and further to the brake pedal 37 via the push rod 36, so that the operator can sense the magnitude of the braking force.

Brake pedal 3 to release the operation of master cylinder M
When 7 is released, the valve piston 35 retracts together with the interlocking ring 48 due to the elastic force of the return spring 52, and accordingly, the interlocking ring 48 is first separated from the operating rods 32 ₂ and 32 _{1 in} order and the inlet valve 2 is released.
6 ₂ , 26 ₁ close in that order, and then the valve piston 35
Of the annular groove 39 communicates with the outlet port 38, that is, the outlet valve 2
7 is opened, the opening valve piston 35 upon reaching the maximum opening degree is restricted to retreat source by the first stopper 60 ₁ via the pin 45.

In this way, since the opening degree of the outlet valve 27 is set to the maximum opening degree, the hydraulic pressure that has been in the output hydraulic chamber 21 is quickly discharged from the outlet port 38 to the annular groove 39, and thus to the oil tank 2 through the return oil passage 44. So booster piston 1
9 can be swiftly retracted by the returning force of the return spring 12 of the master cylinder M.

Then, receiving if reaching the retracted source booster piston 19 abuts against the annular step 18a, the valve piston 35 is regulated by the second stopper 60 _2, the first regulation stopper 60 ₁ against the booster piston 19 The valve is stopped at a position slightly advanced as compared with the above case, whereby the opening of the outlet valve 27 is closed to the initial minimum opening.

In the illustrated example, the oil tank 2 of the master cylinder M is shared as the oil tank of the hydraulic booster B, but an oil tank dedicated to the hydraulic booster B may be provided.

C. EFFECTS OF THE INVENTION As described above, according to the present invention, the booster piston is provided with the annular groove on the outer circumference thereof which opens to the input hydraulic chamber, and the through hole which communicates the annular groove with the inlet oil passage. Since the oil filter is installed in the groove, the oil filter can always occupy a position close to the inlet valve regardless of the operating position of the booster piston, and therefore foreign matter such as machining waste remaining in the booster cylinder can be kept. It can be reliably separated from the hydraulic oil to prevent clogging of the inlet valve and the outlet valve.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention, FIG. 2 is an enlarged view of a main part thereof, FIG. 3 is an enlarged sectional view taken along line III-III of FIG. 1, and FIG. 4 is FIG. IV-IV line sectional view of FIG. 5, FIG. 5 is a perspective view of an oil filter. B ... Hydraulic booster 16 ... Booster cylinder, 19 ... Booster piston, 2
0 ... Input hydraulic chamber, 21 ... Output hydraulic chamber, 24 ... Hydraulic pump as a hydraulic source, 26 ₁ , 26 ₂ ... Inlet valve, 27 ... Outlet valve, 28 ₁ , 28 ₂ ... Inlet oil passage, 40, 41 ... Outlet Oil passage, 61 ... Oil filter, 62 ... Filter body, 63
... filter mesh, 65 ... window, 66 ... annular groove

Claims (2)

[Claims] 1. A booster cylinder, which is divided into a front input hydraulic chamber and a rear output hydraulic chamber which are slidably engaged in the booster cylinder and communicate with a hydraulic source, and are connected to a master piston of a master cylinder. Booster piston;
An input rod slidably and axially slidably fitted on the booster piston; provided in an inlet oil passage connecting the input and output hydraulic chambers formed in the booster piston, and closed when the input rod retracts and opened when advanced. An inlet valve interlocked with the input rod; an outlet oil passage connecting the output hydraulic chamber and the oil tank,
Open the valve when the input rod moves backward, and close it when moving the input rod forward.
In a hydraulic booster including an outlet valve interlocked with the input rod; an annular groove on the outer periphery of the booster piston, which opens to the input hydraulic chamber, and a through hole which communicates the annular groove with the inlet oil passage. And a hydraulic booster having an oil filter attached to the annular groove. 2. The oil filter according to claim 1, wherein the oil filter is elastically mounted in the annular groove and is slidably fitted on the inner peripheral surface of the booster cylinder. A hydraulic booster comprising a hydraulic chamber and a filter mesh stretched over a plurality of windows provided in the filter body so as to connect the through holes.