GB1603849A - Piston and cylinder units - Google Patents

Piston and cylinder units Download PDF

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Publication number
GB1603849A
GB1603849A GB3951377A GB3951377A GB1603849A GB 1603849 A GB1603849 A GB 1603849A GB 3951377 A GB3951377 A GB 3951377A GB 3951377 A GB3951377 A GB 3951377A GB 1603849 A GB1603849 A GB 1603849A
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GB
United Kingdom
Prior art keywords
piston
diameter portion
sealing element
bearing element
face
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB3951377A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
MOTAPRODUCTS AUTOMOTIVE Ltd
Original Assignee
MOTAPRODUCTS AUTOMOTIVE Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by MOTAPRODUCTS AUTOMOTIVE Ltd filed Critical MOTAPRODUCTS AUTOMOTIVE Ltd
Priority to GB3951377A priority Critical patent/GB1603849A/en
Publication of GB1603849A publication Critical patent/GB1603849A/en
Expired legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T11/00—Transmitting braking action from initiating means to ultimate brake actuator without power assistance or drive or where such assistance or drive is irrelevant
    • B60T11/10—Transmitting braking action from initiating means to ultimate brake actuator without power assistance or drive or where such assistance or drive is irrelevant transmitting by fluid means, e.g. hydraulic
    • B60T11/16—Master control, e.g. master cylinders
    • B60T11/236—Piston sealing arrangements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16J—PISTONS; CYLINDERS; SEALINGS
    • F16J15/00—Sealings
    • F16J15/16—Sealings between relatively-moving surfaces
    • F16J15/166—Sealings between relatively-moving surfaces with means to prevent the extrusion of the packing

Description

(54) IMPROVEMENTS IN AND RELATING TO PISTON AND CYLINDER UNITS (71) We, MOTAPRODUCTS AUTO MOTIVE LIMITED, a British Company, of Moprod House, 251 Melchett Road, Birmingham Factory Centre, Kings Norton, Birmingham, West Midlands, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to piston and cylinder units.
In particular, the invention is concerned with piston and cylinder units of the kind, hereinafter referred to as the kind specified, wherein the piston includes a generally cylindrical larger diameter portion which is a close sliding fit in a cylindrical bore of the cylinder, and a generally cylindrical smaller diameter portion coaxial with the larger diameter portion and which carries, adjacent to the latter, an annular sealing element the outer peripheral part of which is in sealing engagement with the face of the cylinder bore.
The invention has been devised in connection with hydraulic brake master cylinders for motor vehicles and for convenience the following description will be confined to this application of the invention.
However, it is to be understood that there is no limitation in this regard since the invention is applicable to hydraulic piston and cylinder units of the kind specified for other uses and also to pneumatic units of the kind specified.
A brake master cylinder is mounted in, for example, a motor car with a part-spherical end of a brake pedal operated push rod seated in a part-spherical cavity formed in the end face of the larger diameter portion of the piston remote from the smaller diameter portion and the sealing element, the push rod extending longitudinally of the cylinder through the adjacent end thereof. The other end of the cylinder remote from the push rod is connected to a hydraulic fluid reservoir through a normally open valve and the interior of the cylinder between said end thereof and the sealing element is connected via brake pipes to the brake-operating cylinders of the vehicle wheels.The arrangement is that, on depression of the brake pedal, the push rod moves longitudinally and pushes the piston axially along the cylinder bore towards said other end of the cylinder with the result that, the said valve having been closed, fluid is forced from the interior of the bore into the brake pipes and the brakes are thereby operated. When the pedal is released the piston is returned to its original position by a spring and fluid flow back into the interior of the bore. The valve having been opened, fluid can also flow into the cylinder from the reservoir.
A problem which arises with piston and cylinder units of the kind specified designed for use as brake master cylinders is that because the push rod has no directional guidance in its piston-actuating movement, it frequently applies off centre forces to the piston so that the piston is not moved in a truly axial direction but 'tilts' slightly in the cylinder bore, with the result that the circumferential corners of its larger diameter portion contact the face of the bore and damage it usually by wearing it away or even scoring it. We have realised that this problem could be overcome, or at least minimised, by rounding the said corners.
In one known form of unit of the kind specified the sealing element is of rubber and its inner part is located in a circumferentially extending recess formed in the smaller diameter portion of the piston immediately adjacent to the larger diameter portion, the side face of the recess adjacent to the larger diameter portion being a continuation of the adjacent end face of the latter. We have found with a unit of this form that it is not possible, as proposed by us, to round the corner of larger diameter portion of the piston adjacent to the sealing element since the circumferential outer corner of the sealing element adjacent to the small gap which is formed between the larger diameter piston portion and the cylinder bore, extrudes into said gap and the seal between the sealing element and the bore is impaired after many cycles of operation.
The object of the present invention is to provide an improved form of piston and cylinder unit.
A particular aim of the invention is to provide a form of unit which enables the above problem of brake master cylinders to be over come without the effectiveness of the seal being impaired.
According to the invention we provide a piston and cylinder unit of the kind specified wherein the circumferential corner of the larger diameter portion of the piston adjacent to the sealing element is rounded or chamfered and an annular bearing element is provided around the smaller diameter portion of the piston and between the opposed end faces of the sealing element and the larger diameter portion of the pistion, the bearing element being arranged to support axially the adjacent outer circumferential corner of the sealing element.
The provision of the bearing element makes it possible to round or chamber the circumferential corner of the larger diameter portion of the piston adjacent to the sealing element thereby to prevent the corner damaging the cylinder bore as described above in relation to brake master cylinders, without the seal between the sealing element and the bore being impaired.
Thus, since the bearing element is disposed between the sealing element and the gap which is formed at the rounded or chamfered comer between the larger diameter piston portion and the bore, and the adjacent outer circumferential corner of the sealing element which is the part thereof most susceptible to extrusion, is supported axially by the bearing element, the said corner of the sealing element is prevented from extruding into the gap and distorting the sealing element. It will be appreciated that on movement of the piston'in a direction from the larger diameter portion towards the smaller diameter portion, the sealing element is moved axially with the piston by an axial force applied to it by the opposed end face of the bearing element which in turn has an axial force applied to it by the adjacent end face of the larger diameter portion.
Preferably, the circumferential corner of the larger diameter portion of the piston remote from the sealing element is also rounded or chamfered.
Preferably, there is a small clearance between the inner cylindrical face of the annular bearing element and the opposed cylindrical face of the smaller diameter portion of the piston and the element is a sliding clearance fit in the bore of the cylinder so that the element is capable of slight lateral floating movement. The element, being a sliding fit in the cylinder bore, also assists in guiding the piston for axial movement in the bore.
The sealing element is preferably so formed that its outer circumferential corner adjacent to the bearing element is spaced inwardly from the outer periphery of the bearing element. For example, the outer peripheral face of the sealing element may be tapered in a direction towards the bearing element.
Preferably, the inner part of the sealing element is disposed in a circumferentially extending groove formed in the smaller diameter portion of the piston at a spacing from the adjacent end face of the larger diameter portion which corresponds to the thickness of the bearing element.
The invention also provides, for incorporation in a piston and cylinder unit of the kind specified, a piston having a generally cylindrical larger diameter portion and a generally cylindrical smaller diameter portion which is coaxial with the larger diameter portion and carries an annular sealing element and an annular bearing element, the bearing element being disposed between opposed end faces of the sealing element and the larger diameter portion and being arranged to support axially the adjacent outer circumferential corner of the sealing element, and the circumferential corner of the larger diameter portion adjacent to the bearing element being rounded or chamfered.
The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through one form of piston and cylinder unit embodying the invention, Figure 2 is a longitudinal section showing the piston of the unit in detail, and Figure 3 shows the bearing element in detail.
The piston and cylinder unit illustrated in the drawings is designed for use as a brake master cylinder in a motor car and comprises a metal cylinder 10 having a cylindrical bore 11, and a metal piston 12 comprising a generally cylindrical smaller diameter portion 13 and a cylindrical larger diameter portion 14 which is coaxial with the portion 13 and is a close sliding fit in the cylinder bore 11.
The end of the larger diameter portion 14 of the piston remote from the smaller diameter portion 13 is formed with a central part-spherical cavity 15 to cooperate with a part-spherical end of a brake pedaloperated push rod (not shown) which extends longitudinally into the cylinder through one end thereof.
The smaller diameter portion 13 is formed with a blind bore 16 which extends into the larger diameter portion 14, and a cap (not shown) is retained on the smaller diameter portion by means of internal formations thereof engaged in a circumferential groove 17 formed in said portion. The end of the cylinder 10 remote from the push rod is connected by a normally open valve (not shown) to a hydraulic fluid reservoir. The interior of the cylinder is connected by brake pipes (not shown) to the brake cylinders of the wheels of a vehicle. The arrangement is that on depression of the brake pedal the push rod moves longitudinally and moves the piston axially in the cylinder thereby closing the valve and forcing fluid from the cylinder into the brake pipes to operate the brakes.A spring (not shown) is interposed between the cap and the end of the cylinder remote from the push rod to return the piston to its original position when the brake pedal is released, the valve thereby being opened so that fluid can flow into the interior of the cylinder not only from the brake pipes thereby releasing the brakes, but also from the reservoir.
The smaller diameter portion 13 of the piston 12 is provided with a generally annular sealing element 18 of rubber or other appropriate material and an annular bearing element 19 of a suitable plastics material, for example Nylon 11 or Nylon 66. The inner part of the sealing element 18 is disposed in a circumferentially extending groove 20 formed in the smaller diameter portion 13 at a spacing from the adjacent end face 21 of the larger diameter portion 14 which corresponds to the thickness of the bearing element 19.
The bearing element 19 is interposed between the said end face 21 of the larger diameter portion of the piston and the opposed end face 22 of the sealing element. There is a smaller clearance between the inner cylindrical face of the bearing element and the opposed cylindrical face of the smaller diameter portion of the piston, and the element is a sliding fit in the cylinder bore 11, so that it is capable of lateral floating movement between the opposed end faces of the larger diameter portion and the sealing element.
The outer peripheral face of the sealing element 18 tapers slightly inwardly in a direction towards the bearing element 19, and it will be seen that the outer circumferential corner 23 of the sealing element therefore bears against and is supported axially by the opposed end face of the bearing element. This prevents extrusion of the said corner of the sealing element as the bearing element applies an axial force to it under the axial force in turn applied to the bearing element by the larger diameter portion of the piston on axial movement of the latter under the action of the push rod.
Extrusion of the inner circumferential corner of the sealing element adjacent to the bearing element is prevented by the corner defined by the adjacent side face of the recess 20 and the bottom face of the recess.
The circumferential corners 24 and 25 of the larger diameter portion 14 of the piston are considerably rounded to prevent said corners damaging the cylinder bore 11 should the piston 'tilt' in the cylinder, and it will be noted that rounding of the corner 24 adjacent to the sealing element does not cause any extrusion of the element.
The circumferential groove 20 is provided with an inclined side face 26 to guide the sealing element into position in the groove as it is slid over the piston on assembly.
In a modification the recess 20 is omitted and the sealing element surrounds a plain cylindrical face extending through the bearing element right up to the end face 21 of the larger diameter portion of the pistion. In this case the cap may be arranged to abut the outer end face of the sealing element to retain it in position on the piston.
WHAT WE CLAIM IS: 1. A piston and cylinder unit of the kind specified wherein the circumferential corner of the larger diameter portion of the piston adjacent to the sealing element is rounded or chamfered and an annular bearing element is provided around the smaller diameter portion of the piston and between the opposed end faces of the sealing element and the larger diameter portion of the piston, the bearing element being arranged to support axially the adjacent outer circumferential corner of the sealing element.
2. A piston and cylinder unit as claimed in claim 1 wherein the circumferential corner of the larger diameter portion of the piston remote from the sealing element is also rounded or chamfered.
3. A piston and cylinder unit as claimed in claim 1 or 2 wherein there is a small clearance between the inner cylindrical face of the annular bearing element and the opposed cylindrical face of the small diameter portion of the piston and the element is a sliding clearance fit in the bore of the cylinder so that the element is capable of slight lateral floating movement.
4. A piston and cylinder unit as claimed in claim 1, 2 or 3 wherein the sealing element is so formed that its outer circumferential corner adjacent to the bearing element is spaced inwardly from the outer periphery of the bearing element.
5. A piston and cylinder unit as claimed in claim 4 wherein the other peripheral face of the sealing element is tapered in a direction towards the bearing element.
6. A piston and cylinder unit as claimed in any one of the preceding claims wherein the inner part of the sealing element is disposed in a circumferentially extending groove formed in the smaller diameter portion of the piston at a spacing from the adjacent end face of the larger diameter portion which corresponds to the thickness of the bearing element.
7. For incorporation in a piston and cylinder unit of the kind specified, a piston having a generally cylindrical larger diameter portion and a generally cylindrical smaller diameter portion which is coaxial with the larger diameter portion and carries and annular sealing element and an annular bearing element, the bearing element being disposed between opposed end faces of the sealing element and the larger diameter portion and being arranged to support axially the adjacent outer circumferential corner of the sealing element, and the circumferential corner of the larger diameter portion adjacent to the bearing element being
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. into the brake pipes to operate the brakes. A spring (not shown) is interposed between the cap and the end of the cylinder remote from the push rod to return the piston to its original position when the brake pedal is released, the valve thereby being opened so that fluid can flow into the interior of the cylinder not only from the brake pipes thereby releasing the brakes, but also from the reservoir. The smaller diameter portion 13 of the piston 12 is provided with a generally annular sealing element 18 of rubber or other appropriate material and an annular bearing element 19 of a suitable plastics material, for example Nylon 11 or Nylon 66. The inner part of the sealing element 18 is disposed in a circumferentially extending groove 20 formed in the smaller diameter portion 13 at a spacing from the adjacent end face 21 of the larger diameter portion 14 which corresponds to the thickness of the bearing element 19. The bearing element 19 is interposed between the said end face 21 of the larger diameter portion of the piston and the opposed end face 22 of the sealing element. There is a smaller clearance between the inner cylindrical face of the bearing element and the opposed cylindrical face of the smaller diameter portion of the piston, and the element is a sliding fit in the cylinder bore 11, so that it is capable of lateral floating movement between the opposed end faces of the larger diameter portion and the sealing element. The outer peripheral face of the sealing element 18 tapers slightly inwardly in a direction towards the bearing element 19, and it will be seen that the outer circumferential corner 23 of the sealing element therefore bears against and is supported axially by the opposed end face of the bearing element. This prevents extrusion of the said corner of the sealing element as the bearing element applies an axial force to it under the axial force in turn applied to the bearing element by the larger diameter portion of the piston on axial movement of the latter under the action of the push rod. Extrusion of the inner circumferential corner of the sealing element adjacent to the bearing element is prevented by the corner defined by the adjacent side face of the recess 20 and the bottom face of the recess. The circumferential corners 24 and 25 of the larger diameter portion 14 of the piston are considerably rounded to prevent said corners damaging the cylinder bore 11 should the piston 'tilt' in the cylinder, and it will be noted that rounding of the corner 24 adjacent to the sealing element does not cause any extrusion of the element. The circumferential groove 20 is provided with an inclined side face 26 to guide the sealing element into position in the groove as it is slid over the piston on assembly. In a modification the recess 20 is omitted and the sealing element surrounds a plain cylindrical face extending through the bearing element right up to the end face 21 of the larger diameter portion of the pistion. In this case the cap may be arranged to abut the outer end face of the sealing element to retain it in position on the piston. WHAT WE CLAIM IS:
1. A piston and cylinder unit of the kind specified wherein the circumferential corner of the larger diameter portion of the piston adjacent to the sealing element is rounded or chamfered and an annular bearing element is provided around the smaller diameter portion of the piston and between the opposed end faces of the sealing element and the larger diameter portion of the piston, the bearing element being arranged to support axially the adjacent outer circumferential corner of the sealing element.
2. A piston and cylinder unit as claimed in claim 1 wherein the circumferential corner of the larger diameter portion of the piston remote from the sealing element is also rounded or chamfered.
3. A piston and cylinder unit as claimed in claim 1 or 2 wherein there is a small clearance between the inner cylindrical face of the annular bearing element and the opposed cylindrical face of the small diameter portion of the piston and the element is a sliding clearance fit in the bore of the cylinder so that the element is capable of slight lateral floating movement.
4. A piston and cylinder unit as claimed in claim 1, 2 or 3 wherein the sealing element is so formed that its outer circumferential corner adjacent to the bearing element is spaced inwardly from the outer periphery of the bearing element.
5. A piston and cylinder unit as claimed in claim 4 wherein the other peripheral face of the sealing element is tapered in a direction towards the bearing element.
6. A piston and cylinder unit as claimed in any one of the preceding claims wherein the inner part of the sealing element is disposed in a circumferentially extending groove formed in the smaller diameter portion of the piston at a spacing from the adjacent end face of the larger diameter portion which corresponds to the thickness of the bearing element.
7. For incorporation in a piston and cylinder unit of the kind specified, a piston having a generally cylindrical larger diameter portion and a generally cylindrical smaller diameter portion which is coaxial with the larger diameter portion and carries and annular sealing element and an annular bearing element, the bearing element being disposed between opposed end faces of the sealing element and the larger diameter portion and being arranged to support axially the adjacent outer circumferential corner of the sealing element, and the circumferential corner of the larger diameter portion adjacent to the bearing element being
rounded or chamfered.
8. A piston as claimed in claim 7 wherein the circumferential corner of the larger diameter portion remote from the bearing element is also rounded or chamfered.
9. A piston as claimed in claim 7 or 8 wherein there is a smaller clearance between the inner cylindrical face of the annular bearing element and the opposed cylindrical face of the small diameter portion.
10. A piston as claimed in claim 7,8 or 9 wherein the outer peripheral face of the sealing element is tapered in a direction towards the bearing element so that the outer circumferential corner of the sealing element adjacent to the bearing element is spaced inwardly from the outer periphery of the bearing element.
11. A piston as claimed in claim 7,8,9 or 10 wherein the inner part of the sealing element is disposed in a circumferentially extending groove formed in the smaller diameter portion at a spacing from the adjacent end face of the larger diameter portion which corresponds to the thickness of the bearing element.
12. A piston and cylinder unit substantially as herein described with reference to and as illustrated in Figures 1, 2 and 3 of the accompanying drawings.
13. For a piston and cylinder unit of the kind specified, a piston substantially as herein described with reference to and as illustrated in Figures 1,2 and 3 of the accompanying drawings.
GB3951377A 1978-05-26 1978-05-26 Piston and cylinder units Expired GB1603849A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB3951377A GB1603849A (en) 1978-05-26 1978-05-26 Piston and cylinder units

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB3951377A GB1603849A (en) 1978-05-26 1978-05-26 Piston and cylinder units

Publications (1)

Publication Number Publication Date
GB1603849A true GB1603849A (en) 1981-12-02

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GB3951377A Expired GB1603849A (en) 1978-05-26 1978-05-26 Piston and cylinder units

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0441476A2 (en) * 1990-01-06 1991-08-14 Lucas Industries Public Limited Company Master cylinder apparatus
WO1999035401A1 (en) * 1998-01-09 1999-07-15 Robert Bosch Gmbh Reciprocating pump
WO2019108852A1 (en) 2017-12-01 2019-06-06 Hb Performance Systems, Inc. Brake master cylinder with curved lands

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0441476A2 (en) * 1990-01-06 1991-08-14 Lucas Industries Public Limited Company Master cylinder apparatus
EP0441476A3 (en) * 1990-01-06 1992-05-27 Lucas Industries Public Limited Company Master cylinder apparatus
WO1999035401A1 (en) * 1998-01-09 1999-07-15 Robert Bosch Gmbh Reciprocating pump
US6327964B1 (en) * 1998-01-09 2001-12-11 Robert Bosch Gmbh Reciprocating pump
WO2019108852A1 (en) 2017-12-01 2019-06-06 Hb Performance Systems, Inc. Brake master cylinder with curved lands
US10518759B2 (en) 2017-12-01 2019-12-31 Hb Performance Systems, Inc. Brake master cylinder with curved lands

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Legal Events

Date Code Title Description
PS Patent sealed
PCNP Patent ceased through non-payment of renewal fee