Spring Brake Cylinder for a Vehicle Brake

A spring brake cylinder for a vehicle brake, comprising:

• a) a cylinder housing with a casing wall and a cylinder-bottom;
• b) a spring brake piston running in said cylinder housing for activation of the vehicle brake;
• c) a pressure spring positioned between the spring brake piston and the cylinder-bottom for activating a parking brake by mechanically influencing the spring brake piston;
• d) a hollow release screw with a first throughbore, axially locked against movement relative to the cylinder-bottom for the mechanical release of the parking brake, which at a first end is rotatably mounted in the cylinder-bottom and which has a screw head on the outside of the cylinder-bottom and which at a second end runs freely in a bore of the spring brake piston;
• e) a rotationally locked, running nut threaded onto said release screw, where said running nut has an outer end position at a set distance from said cylinder-bottom and is arranged to, through contact against the spring brake piston, bring the spring brake piston in the axial direction of the release screw when turning the release screw by manipulation of the screw head;
• and
• f) an axially displaceable, relative to the release screw, pin indicator arranged in the first throughbore of the release screw;
• and
• g) a locking piece that has a second throughbore, and a first thread which is threaded with a second thread of the release screw, where the pin indicator extends through the second throughbore, wherein
• h) the pin indicator at a first end, located within the cylinder housing, is axially fixed to a position sensor which is provided with a contact surface for contact against the running nut;
• and wherein
• i) the pin indicator at a second end has an indication body arranged to visibly protrude out of the screw head of the release screw in case of axial displacement of the pin indicator caused by axial displacement of the running nut from its outer end position, and of the contact surface of the position sensor, which contact surface is in contact with the running nut, during rotation of the release screw for mechanical release of the parking brake, where
• j) the position sensor includes an indicator cap with a central opening, where the indicator cap and the locking piece are axially displacable to each other,
• k) the first end of the pin indicator is configured to snap fit with a central opening of the indicator cap,
• l) at least one first spring is arranged between the indicator cap and a bottom of the bore of the spring brake piston, and
• m) the second throughbore of the locking piece is provided with a tool engagement surface which is configured for a rotationally fixed engagement of a rotation tool.

A method for manufacturing a spring brake cylinder having:

• a cylinder housing with a casing wall and a cylinder-bottom;
• a spring brake piston running in said cylinder housing for activation of the vehicle brake;
• a pressure spring positioned between the spring brake piston and the cylinder-bottom for activating a parking brake by mechanically influencing the spring brake piston;
• a hollow release screw with a first throughbore, axially locked against movement relative to the cylinder-bottom for the mechanical release of the parking brake, which at a first end is rotatably mounted in the cylinder-bottom and which has a screw head on the outside of the cylinder-bottom and which at a second end runs freely in a bore of the spring brake piston;
• a rotationally locked, running nut threaded onto said release screw, where said running nut has an outer end position at a set distance from said cylinder-bottom and is arranged to, through contact against the spring brake piston, bring the spring brake piston in the axial direction of the release screw when turning the release screw by manipulation of the screw head;
• an axially displaceable, a relative to the release screw, pin indicator arranged in the first throughbore of the release screw;
• and
• a locking piece that has a second throughbore, and a first thread which is threaded with a second thread of the release screw, where the pin indicator extends through the second throughbore, wherein
• the pin indicator at a first end, located within the cylinder housing, is axially fixed to a position sensor which is provided with a contact surface for contact against the running nut;
• and wherein
• the pin indicator at a second end has an indication body arranged to visibly protrude out of the screw head of the release screw in case of axial displacement of the pin indicator caused by axial displacement of the running nut from its outer end position, and of the contact surface of the position sensor, which contact surface is in contact with the running nut, during rotation of the release screw for mechanical release of the parking brake, where
• the position sensor includes an indicator cap with a central opening, where the indicator cap and the locking piece are axially displacable to each other,
• the first end of the pin indicator is configured to snap fit with a central opening of the indicator cap,
• at least one first spring is arranged between the indicator cap and a bottom of the bore of the spring brake piston, and
• the second throughbore of the locking piece is provided with a tool engagement surface which is configured for a rotationally fixed engagement of a rotation tool,
• the method comprising the steps of:
• a) positioning the first spring in the bore of the spring brake piston at the bottom of the bore;
• b) providing a pre-assembled unit of the indicator cap and the locking piece within the bore of the spring brake piston, so that the preassembled unit can contact the first spring;
• c) positioning the release screw together with the running nut screwed on in the cylinder housing and in the bore of the spring brake piston;
• d) inserting a rotation tool into the first throughbore of the release screw until it engages the tool engagement surface in the second throughbore of the locking piece;
• e) turning the rotation tool in such a way that the first thread of the locking piece is threaded with the second thread of the release screw, where the locking piece is held in a coaxial position with the release screw by the indicator cap, which is axially preloaded by the first spring;
• f) removing the rotation tool out of the first throughbore of the release screw;
• and
• g) inserting the pin indicator into the first throughbore of the release screw until the first end of the pin indicator axially snap fits with the central opening of the indicator cap, where the indicator cap is axially supported by the first spring.