JP2006322479A - Band brake servo device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a band brake servo device for reducing shock during fastening a rotor to a brake band. <P>SOLUTION: The band brake servo device 1 comprises a servo stem 3 for slidably holding a 3-4 piston 2 during 3-4 shift to generate the fastening of the brake band B to a rotary drum with the displacement of the 3-4 piston 2. Besides, an accumulation piston 5 is provided in an internal space of a cover C consisting of a housing 101 and a cover 102. It has a pressure receiving face 2f1 which has a 3-4 hydraulic pressure chamber R3 formed between the 3-4 piston 2 and itself for 3-4 operating hydraulic pressure to be supplied thereto and a supported face 5f2 which is supported on the cover 102 located on the opposite side of the 3-4 hydraulic pressure chamber via an elastic member E3 and which has a pressure accumulating chamber Ra formed between the cover 102 and itself for sliding to the direction of increasing the volume of the 3-4 shifting hydraulic pressure chamber R3 against the energizing force of the elastic member E3 with the rise of hydraulic pressure in the 3-4 hydraulic pressure chamber R3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a band brake servo device that operates a brake band for controlling braking of a rotating body.

  The automatic transmission is performed by engaging / disengaging various friction elements such as a clutch and a brake, and one of the brakes is a band brake including a rotating drum and a brake band surrounding the rotating drum. The band brake performs braking of the rotating body by fastening the rotating body and the brake band, and the fastening and releasing of the rotating body and the brake band are performed by a servo device controlled by hydraulic pressure.

  For example, in the case of a servo device used in a forward four-speed automatic transmission, a servo stem that causes fastening of a brake band and the rotating body is engaged with two servo pistons arranged in the internal space of the case. The brake band and the rotating body are engaged / released by supplying each servo piston with an appropriate combination of 1-2 shift pressure, 2-3 shift pressure, and 3-4 shift pressure.

On the other hand, in the automatic transmission, in order to reduce the shock generated when the rotating body and the brake band are engaged and to achieve smooth engagement, the 1-2 shift pressure and the 2-3 shift pressure are respectively stored in the control valve unit. It is configured so that a shelf pressure is once generated in the 1-2 shift pressure and the 2-3 shift pressure at an initial stage when the accumulator for 1-2 shift pressure and the 2-3 shift pressure accumulator are arranged and supplied to each servo piston. (For example, refer to Patent Document 1).
Japanese Unexamined Patent Publication No. 01116349

  However, conventionally, the control valve unit has a 1-2 shift pressure control valve that controls the 1-2 shift pressure, a 2-3 shift pressure control valve that controls the 2-3 shift pressure, and a 3-4 shift pressure. 3-4 shift pressure control valve, ND select pressure control valve for controlling ND select pressure, ND select pressure accumulator, etc. are arranged, so there is a space for placing 3-4 shift pressure accumulator. It cannot be secured. For this reason, in the conventional forward four-speed automatic transmission, a shelf pressure cannot be generated in the 3-4 shift pressure, and a shock is generated during the 3-4 shift.

  The problem to be solved by the present invention has been made on the basis of the fact recognition described above, and without significantly changing the layout of peripheral devices necessary for operating the band brake, the rotating body and the brake band can be It is an object of the present invention to provide a band brake servo device capable of reducing a shock at the time of fastening.

  According to the first aspect of the present invention, there is provided a case having an internal space that is connected to a housing that houses a brake band that controls braking of the rotating body and communicates with the inside of the housing, and is slidably held in the internal space of the case. A band comprising: a servo piston that is displaced by receiving a hydraulic pressure by liquid; and a servo stem that slidably holds the servo piston and causes fastening of the brake band and the rotating body by displacement of the servo piston. In the brake servo apparatus, a pressure receiving surface that forms a variable capacity chamber to which the hydraulic fluid is supplied between the servo piston and an inner space of the case, and a back surface of the pressure receiving surface via an elastic member. And a support surface that forms a pressure accumulating chamber between the case and the case. It is characterized in the provision of the accumulation piston sliding in the direction of expansion of volume of the variable capacity chamber against the force.

  According to a second aspect of the present invention, in the first aspect of the present invention, the brake band is displaced in a direction approaching the servo piston and is slidably held in the internal space of the case to cause release of the brake band and the rotating body. A second servo piston is provided, and a control pressure supply circuit is provided for supplying the hydraulic fluid of the second servo piston to the accumulator as the control pressure of the accumulator piston.

  According to a third aspect of the present invention, in the second aspect, the control pressure supply circuit is an internal passage formed in the servo stem.

  According to a fourth aspect of the present invention, in the second or third aspect, the drain means for discharging the liquid or air that has entered the space formed between the servo piston and the second servo piston is provided. It is a feature.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, a drain means for discharging excess liquid or air in the pressure accumulating chamber is provided.

  According to the first aspect of the present invention, in the internal space of the case constituting the servo device for the band brake, a variable capacity chamber in which hydraulic fluid is supplied between the rotating piston and the servo piston that causes fastening of the brake band is provided. A rotating body and a brake band are provided by providing an accumulator piston having a pressure receiving surface to be formed and a support surface that is supported by an elastic member as a back surface of the pressure receiving surface and forms a pressure accumulating chamber between the pressure receiving surface and the case. When the hydraulic pressure in the variable capacity chamber is increased so as to be fastened, the accumulator piston slides in a direction to increase the volume of the variable capacity chamber against the biasing force of the elastic member. The hydraulic pressure received from the hydraulic fluid at the pressure receiving surface once becomes a shelf pressure corresponding to the urging force of the elastic member in the servo device.

  Therefore, according to the first aspect of the present invention, there is no need to separately provide an accumulator device for generating a shelf pressure in the hydraulic pressure received from the hydraulic fluid, so that the periphery necessary for operating the band brake is not necessary. The shock can be reduced when the rotating body and the brake band are fastened without significantly changing the layout of the device.

  The invention according to claim 2 includes a second servo piston that is slidably held in the internal space of the case and is displaced in a direction approaching the servo piston to cause release of the brake band and the rotating body. A control pressure supply circuit for supplying the hydraulic fluid of the second servo piston as the control pressure of the accumulator piston to the pressure accumulating chamber is provided, so that the combination of the control pressure supplied from the control pressure supply circuit and the elastic member Thus, the shelf pressure can be easily controlled to a desired hydraulic pressure.

  According to the third aspect of the present invention, since the control pressure supply circuit is an internal passage formed inside the servo stem, the servo device can be made compact without increasing its size.

  Since the invention according to claim 4 is provided with drain means for discharging the liquid or air that has entered the space formed between the servo piston and the second servo piston, the servo piston and the Even if liquid or the like leaks into the space formed between the second servo piston by mistake, the liquid does not remain in the space, so that the operation of the servo piston is not delayed. The shelf pressure can be easily controlled to a desired hydraulic pressure.

  Since the invention according to claim 5 is provided with drain means for discharging excess liquid or air in the pressure accumulating chamber, even if excessive liquid is supplied into the pressure accumulating chamber or air is mixed, Since excess liquid or the like in the pressure accumulating chamber is drained to the outside, the shelf pressure can be easily controlled to a desired fluid pressure without destabilizing the pressure accumulating function for keeping the shelf pressure constant. it can.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  1 to 3 are sectional views showing a band brake servo apparatus 1 according to a first embodiment of the present invention. FIG. 4 is a longitudinal sectional view showing a power train equipped with a forward four-speed stepped automatic transmission. The servo device 1 of this embodiment is employed in the stepped automatic transmission.

  First, the power train 100 shown in FIG. 4 is configured such that respective elements are arranged in parallel on three axes of a drive axis O1, an intermediate axis O2, and a driven axis O3. On the drive axis O 1, a lockup type torque converter 110 to which power from an engine (not shown) is input, an oil pump P drivingly coupled to the pump impeller 111 of the torque converter 110, and a turbine runner of the torque converter 110 112 and an automatic transmission 130 that is drive-coupled via an input shaft S1, and an idler shaft S2 having a first idler gear G2 that meshes with an output gear G1 of the automatic transmission 130 on an intermediate axis O2. Arrange. The idler shaft S2 has a second idler gear G3 at a position opposite to the first idler gear G2, and is drive-coupled to a differential gear 140 disposed on the driven axis O3 via a final gear G4 meshing with the second idler gear G3. .

  The automatic transmission 130 is a high gear that fastens and opens between the two planetary gear mechanisms 131 and 132 that are arranged forward and backward along the drive axis O1 and the sun gear 131s of the front planetary gear mechanism 131 and the input shaft S1. The clutch C1, the reverse clutch C2 for fastening / releasing the input shaft S1 and the rotating drum 133, the brake band B for fastening / releasing the rotating drum 133 to / from the power train housing 101, and the front planetary gear mechanism 131 A low one-way clutch OWC1 for attaching the carrier 131c to the power train housing 101, and a forward clutch C3 for fastening and releasing between the ring gear 132r of the rear planetary gear mechanism 132 and the rotary drum 134 fixed to the output gear G1. , Fastening between the carrier 132c of the rear planetary gear mechanism 32 and the rotating drum 134 via a one-way clutch OWC2 Having an overrun clutch C4 to open, and a low and reverse brake C5 to engagement and disengagement of the rotary drum 134 relative to the power train housing 101.

  Next, the servo device 1 of the band brake B will be described with reference to FIGS. 1 to 3 show 1 → 2 shift, 2 → 3 shift, and 3 → 4 shift, respectively.

  The servo device 1 includes a power train housing 101 and a cover 102 fastened to the housing 101 by bolts so as to form a case C having an internal space communicating with the internal space of the housing 101 through an opening A. In the inner space of the case C, annular cylinder forming members 103 and 104 are fitted.

  Reference numeral 2 is held slidably on the inner peripheral wall 103f1 of the cylinder forming member 103 constituting the inner wall of the case C via an annular seal member S, and is used as 3-4 shift hydraulic fluid (first hydraulic fluid). It is an annular 3-4 speed change piston (first servo piston) that is displaced in response. The 3-4 speed change piston 2 is also slidably held by the servo stem 3 slidably held by the opening A of the case C. Therefore, a snap ring 3s is attached to the servo stem 3, and the sliding toward the opening A of the 3-4 speed change piston 2 is restricted by the 3-4 speed change piston 2 coming into contact with the snap ring 3s. To do.

  Reference numeral 4 denotes an annular 1-2 speed change piston that is slidably held via an annular seal member S on the inner peripheral wall 101f1 of the housing 101 constituting the inner wall of the case C and the inner peripheral wall 104f of the cylinder forming member 104. (Second servo piston) and an annular 1-2 speed change hydraulic chamber (variable capacity chamber) to which 1-2 speed change hydraulic fluid (second hydraulic fluid) is supplied together with the housing 101 and the cylinder forming member 104 It has annular pressure receiving surfaces 4f1 and 4f2 forming R1. The 1-2 shifting hydraulic fluid is supplied to the 1-2 shifting hydraulic chamber R1 through a supply passage 12 provided by cutting out a cylinder forming member 104 from a supply hole 11 provided in the housing 101.

  The 1-2 speed change piston 4 includes an elastic member (spring) E1 supported by the case C (housing 101), and a spring E2 supported by a servo stem 3 via a washer w held by a snap ring 3s. And slidably held by the servo stem 3. The servo stem 3 is integrally provided with an annular protrusion 3p. When the 1-2 speed change piston 4 abuts on the protrusion 3p, the sliding toward the opening A of the 1-2 speed change piston 4 is restricted. To do. As a result, the surfaces 4f3 and 4f4 of the 1-2 speed change piston 4 facing the housing 101 are arranged between the housing 101 and the annular 2-3 speed change hydraulic chamber (variable capacity chamber) to which 2-3 speed change hydraulic fluid is supplied. ) Constructs a pressure-receiving surface that forms R2. The 2-3 speed hydraulic fluid is supplied from a supply hole 13 provided in the housing 101 to the 2-3 speed change hydraulic chamber R2.

  In the case C, between the 3-4 speed change piston 2 and the 1-2 speed change piston 4 is a space Ro in which hydraulic fluid is not supplied in order to smoothly perform the respective operations. For this reason, this embodiment is provided with drain means for discharging hydraulic oil or air that has entered the space Ro, and the space Ro is a drain path formed between the cylinder forming member 103 and the cylinder forming member 104. It passes through a drain hole Ad provided in the housing 101 via r1 and an annular storage chamber Rd connected to the drain path r1. As a result, even if hydraulic oil or air leaks into the space Ro by mistake, the hydraulic oil or the like flows from the drain hole Ad through the drain path r1 and the storage chamber Rd, as indicated by reference numeral D1 in FIGS. Discharged.

  Reference numeral 5 denotes an annular accumulator piston that is slidably held via an annular seal member S on the inner peripheral wall 102f of the cover 102 that constitutes the inner wall of the case C and the inner peripheral wall 103f2 of the cylinder forming member 103. The servo stem 3 is slidably held and is arranged in tandem so as to face the pressure receiving surface 2f1 of the 3-4 speed change piston 2. The accumulator piston 5 also receives a pressure receiving surface 5f1 that forms an annular 3-4 shift hydraulic chamber (variable capacity chamber) R3 to which the 3-4 shift hydraulic pressure 4A is supplied between the accumulator piston 5 and the 3-4 shift piston 2. And a support surface 5f2 which is supported on the cover 102 via a spring E3 as a back surface of the pressure receiving surface 5f1 and forms an accumulation chamber (pressure accumulating chamber) Ra between the cover 102 and the cover 102.

  The hydraulic fluid for 3-4 speed is supplied from a supply hole 14 provided in the housing 101. The supply hole 14 includes an annular expansion chamber 15 formed on a mating surface with the housing 101 by a circumferential groove provided in the cylinder forming member 103, and a supply path provided in the cylinder forming member 103 connected to the expansion chamber 15. 16 to the 3-4 shift hydraulic chamber R3.

  Furthermore, since the accumulator piston 5 performs a smooth operation, a circumferential groove that does not contact the inner peripheral wall 103f2 of the cylinder forming member and the inner peripheral wall 102f of the cover 102 is provided between the pressure receiving surface 5f1 and the support surface 5f2 of the accumulator piston 5. 5n, and an annular space R4 is formed between the inner peripheral wall 103f2 of the cylinder forming member.

  Further, in this embodiment, a drain means for discharging excess hydraulic oil or air in the accumulation chamber Ra is provided. This drain means includes a drain path r2 for connecting the accumulator chamber Ra provided in the cover 102 to the space R4 and a cylinder forming member 103 for connecting the space R4 to the storage chamber Rd, as indicated by reference numeral D2 in FIG. A drain passage r3 penetrating therethrough, and excess hydraulic oil or air in the accumulation chamber Ra is discharged from the storage chamber Rd through the drain hole Ad. Further, the drain means is provided with a recess communicating with the drain path r3 in the cylinder forming member 103 as shown by reference numeral D3 in FIG. 3, and returned to the expansion chamber 15 from the drain path r4 formed between the recess and the cover 102. May be. According to such a configuration, hydraulic oil or the like that erroneously enters the space R4 can be discharged by the drain circuits indicated by the symbols D2 and D3.

  The servo stem 3 has a stem pin 3a attached to the tip of the servo stem 3 so as to be swingable, and the stem pin 3a presses the bracket Ba fixed to the brake band B. Thereby, the brake band B contacts the rotating drum 133 with a tightening force corresponding to the pressing force of the stem pin 3a to generate a desired braking force. Further, the servo stem 3 is provided with an internal passage 6 for supplying a part of the hydraulic oil for 2-3 shift from the 2-3 shift hydraulic chamber R2 to the accumulator chamber R3. The hydraulic pressure due to the shifting hydraulic fluid acts as the control pressure Ps of the accumulator piston 5.

  Next, the operation of the servo device 1 will be described with reference to FIGS.

  First, during the 1-2 shift, as shown by reference numeral 2A in FIG. 1, the 1-2 shift pressure 2A is supplied to the 1-2 hydraulic chamber R1, and the 1-2 shift piston 4 resists the urging force of the spring E1. Then, the servo stem 3 is slid toward the brake band B. As a result, the servo stem 3 presses the brake band B via the stem pin 3a and the bracket Ba to cause the rotary drum 133 and the brake band B to be fastened, thereby stopping the rotary drum 133. At this time, the 1-2 shifting hydraulic fluid supplied to the 1-2 hydraulic chamber R1 passes through the existing 1-2 shifting pressure accumulator disposed in the control valve unit (not shown) as in the prior art. A shelf pressure is supplied as the 1-2 shift pressure 2A. Thus, during the 1 → 2 shift, the stem pin 3a does not press the band bracket Bb all at once, but gradually reduces it in a stepwise manner, thereby reducing the shock generated when the rotary drum 133 and the band brake are engaged. be able to.

  Next, at the time of 2 → 3 shift, as indicated by reference numeral 3R in FIG. 2, the 2-3 shift pressure 3R is supplied to the 2-3 hydraulic chamber R2, and the urging force by the 2-3 shift pressure 3R and the spring E1 is supplied. Slid the servo stem 3 away from the brake band B together with the 1-2 piston 4 against the urging force of the spring E1 and the 1-2 speed change pressure 2A. As a result, the stem pin 3a is separated from the band bracket Ba, and the fastening between the rotating drum 133 and the brake band B is released, and the rotation of the rotating drum 133 is restored. At this time, the 2-3 shifting hydraulic fluid supplied to the 2-3 hydraulic chamber R2 also passes through the existing 2-3 shifting pressure accumulator disposed in the control valve unit (not shown). Although shelf pressure is also generated in the transmission pressure 3R, in this embodiment, a part of the 2-3 shifting hydraulic fluid supplied to the 2-3 hydraulic chamber R2 is accumulated in the accumulator chamber Ra via the internal passage 6 of the servo stem 3. Therefore, the shelf pressure supplied as the 2-3 shift pressure 3R can be suppressed to be lower than when the existing 2-3 shift pressure accumulator is used. As a result, the stem pin 3a is gradually separated from the band bracket Bb stepwise even at the time of the 2 → 3 shift, so that the shock that occurs when the rotary drum 133 and the band brake are released can be reduced.

  Further, at the time of 3 → 4 shift, as indicated by reference numeral 4A in FIG. 3, 3-4 shift pressure 4A is supplied to the 3-4 hydraulic chamber R3, and this 3-4 shift pressure 4A and 1-2 shift pressure 2A The urging force caused by is caused to slide the servo stem 3 toward the brake band B together with the 3-4 speed change piston 2 against the urging force caused by the springs E1, E2 and the 2-3 speed change pressure 3R. Thus, the servo stem 3 presses the brake band B via the stem pin 3a and the bracket Ba to stop the rotating drum 133. At this time, the hydraulic fluid for 3-4 shift supplied to the 3-4 hydraulic chamber R3 is essentially 3-4 shift pressure 4A because there is no 3-4 shift pressure accumulator in the control valve unit (not shown). There is no shelf pressure formed.

  However, in this embodiment, when the hydraulic pressure in the 3-4 hydraulic chamber R3 rises, the accumulator piston 5 moves away from the 3-4 speed change piston 2 against the biasing force of the spring E3, as shown in FIG. That is, in order to slide in the direction of increasing the volume of the 3-4 shift hydraulic chamber R3, the 3-4 shift pressure 4A received from the 3-4 shift hydraulic fluid at the pressure receiving surface 2f1 of the 3-4 shift piston 2 is In the servo device 1, the shelf pressure is temporarily set according to the urging force of the spring E3. That is, according to the present servo device 1, the stem pin 3a can be gently and gradually pressed against the band bracket Ba without providing a separate 3-4 shift accumulator during 3 → 4 shift.

  Accordingly, since the servo device 1 includes the accumulator piston 5 inside, it is not necessary to separately provide a 3-4 shift accumulator for generating a shelf pressure in the 3-4 shift hydraulic pressure. A shock can be reduced when the rotating drum 133 and the brake band B are fastened without significantly changing the layout of peripheral devices such as a control valve unit required for operation.

  In particular, in this embodiment, it is slidably held in the internal space of the case C and receives a 2-3 shift pressure 3R by 2-3 shifting hydraulic fluid, and is displaced toward the 3-4 shift piston 2. A control pressure supply circuit including a 2-3 piston 4 for causing the brake band B and the rotary drum 133 to be released, and supplying a part of the 2-3 shifting hydraulic oil to the accumulator chamber Ra as a control pressure of the accumulator piston 5. 6 is generated in the 3-4 shift pressure 4A of the 3-4 hydraulic chamber R3 by the combination of the control pressure by the 2-3 shift pressure 3R supplied from the control pressure supply circuit 6 and the elastic member E3. The shelf pressure can be easily controlled to a desired oil pressure. Furthermore, in this embodiment, since the control pressure supply circuit 6 is an internal passage formed inside the servo stem 3, the servo device 1 can be made compact without increasing its size.

  In addition, in this embodiment, a circumferential groove 5n that does not contact the inner peripheral wall 103f2 of the cylinder forming member and the inner peripheral wall 102f of the cover 102 is provided between the pressure receiving surface 5f1 and the support surface 5f2 of the accumulator piston 5. Since the sliding of 5 is performed smoothly, the responsiveness when the shelf pressure is generated in the 2-3 shift pressure 4A of the 3-4 hydraulic chamber R3 is improved. In particular, as shown in FIG. 3, this embodiment is provided with drain means (r3, r4, Rd, Ad) for discharging the liquid or air that has entered the circumferential groove 5n. Even if hydraulic oil or the like leaks from the chamber Ra by mistake, the leaked hydraulic fluid or the like does not remain in the circumferential groove 5n, so that there is no delay in the operation of the accumulator piston 5 and 2 in the 3-4 hydraulic chamber R3. -3 The shelf pressure generated in the transmission pressure 4A can be easily controlled to a desired hydraulic pressure.

  In this embodiment, drain means (r1, Rd, Ad) for discharging hydraulic oil or air that has entered a space Ro formed between the 3-4 speed change piston 2 and the 1-2 speed change piston 4 are provided. 2 and 3, even if hydraulic oil or air leaks into the space Ro from the accumulator chamber Ra or the 3-4 hydraulic chamber R3 through the space between the servo stem 3 and the operation, Since oil or the like does not remain in the space Ro, the 2-3 shift pressure in the 3-4 hydraulic chamber R3 is maintained without causing a delay in the operation of the 3-4 shift piston 2, the 1-2 shift piston 4, or the accumulator piston 5. The shelf pressure generated in 4A can be easily controlled to a desired hydraulic pressure.

  Furthermore, since this embodiment is provided with drain means (r2, r3, Rd, D1) or drain means (r2, r3, r4, 15) for discharging excess hydraulic oil or air in the accumulation chamber Ra. Even when excessive hydraulic oil is supplied into the accumulator Ra or air is mixed, the hydraulic oil (control pressure) in the accumulator Ra remains outside as indicated by the symbol D1 in FIG. 2 or the symbol D2 in FIG. Since the drain is drained, the pressure accumulation function for keeping the shelf pressure formed as the 3-4 shift pressure 4A constant is generated in the 3-4 shift pressure 4A of the 3-4 hydraulic chamber R3 without becoming unstable. The shelf pressure can be easily controlled to a desired hydraulic pressure.

  FIG. 5 is a cross-sectional view of a main part comparing a servo device 1 which is a modification of the present embodiment and a conventional servo device. In the drawing, the upper half with respect to the alternate long and short dash line XX is a conventional servo device, and the lower half with respect to the alternate long and short dash line XX is the servo device 1 of the present embodiment. However, in the conventional servo device, elements having substantially the same function as those of the servo device 1 of the present embodiment are denoted by the same reference numerals as those of the servo device 1 of the present embodiment, and description thereof is omitted.

  As shown in FIG. 5, the servo device 1 of the present embodiment uses the snap ring 3s to prevent the servo stem 3 from coming off, but the other parts are the same as those shown in FIGS. . In the conventional servo device, since there is no accumulator piston 5 that once forms a shelf pressure in the 3-4 transmission pressure 4A applied to the 3-4 transmission piston, when the shelf pressure is generated in the 3-4 transmission pressure 4A, A 3-4 shift accumulator for generating a shelf pressure in the 3-4 shift pressure 4A must be separately provided in the circuit for supplying the 3-4 shift hydraulic fluid 4A arranged around the servo device. it is obvious.

  FIG. 6 is a cross-sectional view of a principal part in which a modified example of the servo device 1 is compared with a conventional servo device. Also in this figure, the upper half with respect to the alternate long and short dash line XX is a conventional servo device, and the lower half with respect to the alternate long and short dash line XX is another embodiment of the present invention. However, also in FIG. 6, portions having the same functions as those of the servo device 1 of the present embodiment are denoted by the same reference numerals as those in FIGS.

  In the case of the other form shown in FIG. 6, as shown in the figure, the shelf pressure generated in the 3-4 transmission hydraulic pressure 4A can be set low by securing a large accumulator chamber Ra. A shock when starting to press the band bracket Bb can be greatly reduced.

  The above shows preferred forms of the present invention, but those skilled in the art can make various modifications within the scope of the claims. For example, the retaining protrusion 3p of the servo stem 3 may be combined with the washer W or the snap ring 3s, and the holding of the spring E2 and the snap ring 3s and the washer W may be combined with the snap ring 3s or the washer W or the servo stem 3. An integral protrusion 3p may be used. That is, the parts constituting the above-described embodiments can be appropriately combined depending on the application.

  The present invention is not limited to the band brake employed in an automatic transmission mounted on a vehicle or the like, and may be applied to various mechanisms or devices as long as the band brake is employed as one fastening element of a power transmission mechanism. Can do.

It is sectional drawing which shows the time of 1-> 2 gear shifting of the servo apparatus of the band brake which is the 1st form of this invention. It is sectional drawing which shows the time of 2-> 3 speed change of the servo apparatus of the form. It is sectional drawing which shows the time of 3-> 4 gear shifting of the servo apparatus of the form. It is a longitudinal cross-sectional view which shows the power train carrying the step-speed automatic transmission of 4 speeds which employ | adopted the servo apparatus of the form. It is principal part sectional drawing which compared the servo apparatus of the same form with the conventional servo apparatus. It is principal part sectional drawing which compared the servo apparatus which is the other form of this invention, and the conventional servo apparatus.

Explanation of symbols

1 Servo device 2 3-4 speed change piston (first servo piston)
3 Servo stem 4 1-2 speed change piston (second servo piston)
5 Accumulation piston E Spring (elastic member)
R1 1-2 hydraulic chamber (variable capacity chamber)
R2 2-3 Hydraulic chamber (variable capacity chamber)
R3 3-4 Hydraulic chamber (variable capacity chamber)
R4, Ro space

Claims (5)

A case having an internal space that is connected to a housing that houses a brake band that controls braking of the rotating body and communicates with the inside of the housing, and is slidably held in the internal space of the case and is displaced by receiving the hydraulic pressure from the hydraulic fluid. In a servo device for a band brake comprising a servo piston, and a servo stem that slidably holds the servo piston and causes the brake band and the rotating body to be fastened by displacement of the servo piston,
In the internal space of the case, a pressure receiving surface that forms a variable capacity chamber to which the hydraulic fluid is supplied between the servo piston and the back surface of the pressure receiving surface is supported by the case via an elastic member. And an accumulator that slides in a direction to increase the volume of the variable capacity chamber against the urging force of the elastic member due to an increase in hydraulic pressure in the variable capacity chamber. A band brake servo device comprising a piston. A second servo piston that is slidably held in the internal space of the case and is displaced in a direction approaching the servo piston to cause release of the brake band and the rotating body;
2. The band brake servo device according to claim 1, further comprising a control pressure supply circuit that supplies hydraulic fluid of the second servo piston to the pressure accumulating chamber as control pressure of the accumulator piston.   3. The band brake servo device according to claim 2, wherein the control pressure supply circuit is an internal passage formed in the servo stem.   4. The band brake servo device according to claim 2, further comprising drain means for discharging liquid or air that has entered a space formed between the servo piston and the second servo piston.   The band brake servo device according to any one of claims 1 to 4, further comprising drain means for discharging excess liquid or air in the pressure accumulating chamber.

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