DESC:Field of the invention
The present invention relates to testing of shock absorbers on automobiles and more particularly, to a piston testing system for a shock absorber and still more particularly to the piston band testing system.
Background of the invention
Prior art shock absorber/ damper traditionally use PTFE banded piston. The drawback of those dampers is that in numerous incidences a molded band over the piston of the shock absorber dislodges and causes failure of the product prematurely. The testing products are observed to be of poor durability and result in higher costs for warranty.
Generally, the shock absorber piston has a blunt side and a skirt side or lip side. Piston seals maintain sealing contact between piston and cylinder bore. The pressure acting on the piston seal increases contact forces between piston seal and cylinder surface. The lip seal is used to wipe the oil while it is functioning and also provide an effective seal between two pressure zones. It has been found that the friction or drag of a lip seal against the inside of the cylinder wall can dislodge the band. This phenomenon can be observed in the working condition only. Hence in order to validate the product, the working condition of the shock absorber has to be simulated inside a factory setup.
Accordingly, there is a need of improved testing system to test the product for its acceptance to be used in field by overcoming the above mentioned drawbacks of the prior art.

Objects of the invention
An object of the present invention is to provide a testing system for a banded piston for its acceptance to be used in field.
Another object of the present invention is to provide method for testing the banded piston for its acceptance to be used in the field.
Summary of the invention
The present invention provides a piston testing system for a banded piston of a shock absorber. In order to validate the banded piston, working condition of the shock absorber is simulated piston testing system. The change of pressure, temperature and side load is carried out in a cyclic order as determined in an auto cycle of the piston testing system. The present invention successfully achieves challenge of increasing the pressure to set pressure in a second and to reduce the pressure to zero in a second.
Brief description of the drawings
The objectives and advantages of the present invention will become apparent from the following description read in accordance with the accompanying drawings wherein,
Figure 1 shows a piston testing system for a banded piston in a shock absorber, in accordance with the present invention,
Figure 2 shows the flow chart for testing of a banded piston in a piston testing system, in low pressure and low temperature conditions, in accordance with the present invention,
Figure 3 shows the flow chart for testing of a banded piston in a piston testing system, in high pressure and low temperature conditions, in accordance with the present invention, and
Figure 4 shows the flow chart for testing of a banded piston in a piston testing system, in high pressure and high temperature conditions, in accordance with the present invention.
Detailed description of the invention
The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiments.
The present invention provides a piston testing system for a banded piston of a shock absorber. In order to validate the product, working condition of the shock absorber is simulated inside a factory setup. The change of pressure, temperature and side load is carried out in a cyclic order as determined in an auto cycle of the piston testing system. The present invention successfully achieves challenge of increasing the pressure to set pressure in a second and to reduce the pressure to zero in a second.
This present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures. These reference numbers are shown in bracket in the following description.
Referring now to figure 1, a piston testing system (100) [hereinafter, “the system (100)] for a shock absorber, in accordance with the present invention is shown. The piston testing system comprises of a side load cylinder (40), a shox oil supply source (not shown), a fixture (35) for holding a banded piston assembly (50), system safety guards (not shown), and a machine MMI display (not shown). The banded piston assembly (50) comprises of a piston (5) and a spacer (10) mounted on a piston rod (15). The fixture (35) includes a cylindrical pressure chamber (20) with a pressurized oil inlet (30) at one side and a leak oil outlet (25) at the other side such that when a banded piston assembly (50) is mounted therein, the leak oil outlet (25) is at the spacer (10) side thereof. The side load cylinder (40) provides a side load upto 600 N on the banded piston assembly (50) mounted in the fixture (35). The shox oil supply (not shown) pressurizes the pressure chamber (20) with pressurized shox oil with pressure ranging from 0 to 400 bar. The temperature of the shox oil can be varied from room temperature to 120°C. The banded pistons (50) moves to and fro in the cylindrical pressure chamber (20) during test cycles, under the influence of the side load and the pressurized oil. During the movement, lip of the piston (5) wipes the oil from the side walls of the pressure chamber (20) and also provides the effective seal between the two pressure zones. If the band is dislodged or peeled off from the piston, there will be some amount of oil remained adhering to the side walls of the pressure chamber (20), leaks off from the leak oil outlet (25). The leakage of oil is correlated to the defect in the piston band.
The banded piston (50) is fixed in the fixture (35) of the system (100) and the system safety guards are closed. System (100) is put in auto mode and testing cycle option is selected. The system (100) operating in auto mode provides three different test cycles for testing the banded piston (50):
• low pressure and low temperature test cycle (200) [hereinafter, “test cycle (200)],
• high pressure and low temperature test cycle (300) [hereinafter, “test cycle (300)], and
• high pressure and high temperature test cycle (400) [hereinafter, “test cycle (400)]
Test cycles (200), (300) and (400) are selected one after another in a sequence to test the banded piston under different working conditions.
Referring to figure 2, a flow chart for test cycle (200) in accordance with the present invention is shown. When test cycle (200) is selected and started, at step (115) of the test cycle (200), the system (100) actuates the side load cylinder (40) to provide side load of 200 N on the banded piston (50). At step (120), the pressure chamber (20) of the fixture (35) is pressurized with shox oil at 6 bar pressure for 1 sec. At step (125), the pressure chamber (20) gets depressurized for 1 sec. At step (130), the pressure chamber (20) gets pressurized with the shox oil at 16 bar pressure for 1 sec and again at step (135) the pressure chamber depressurizes for 1 sec. Pressure chamber is pressurized with the shox oil at 20 bar pressure for 1 sec at step (140) and depressurized for 1 sec at step (145). Next, the pressure chamber (20) is pressurized with the shox oil at 24 bar pressure for 1 sec at step (150) and depressurized for 1 sec at step (155). The whole sequence of steps from step (120) to (155) is repeated 1000 times automatically on the system (100). Completion of the cycle is displayed on the MMI screen and test cycle (200) is complete.
The banded piston (50) is then tested for high pressure and low temperature conditions in test cycle (300). Referring to figure 3, a flow chart for test cycle (300) in accordance with the present invention is shown. The pressure chamber (20) is pressurized with pressurized shox oil at 400 bar pressure for 1 sec at step (220) and depressurized for 1 sec at step (225). Sequence of steps (220) and (225) is repeated 1000 times automatically on the system (100) and completion of 1000 cycles is indicated on the MMI screen.
In next test cycle (400), the banded piston (50) is tested for high pressure and high temperature conditions. Referring to figure 4, a flow chart for test cycle (400) in accordance with the present invention is shown. At step (315), the test cycle (400) involves actuation of the side load cylinder (40) to provide a side load of 200 N on the banded piston (50). The pressure chamber (20) is pressurized with pressurized shox oil at 120oC to 200 bar pressure for 1 sec at step (320) and depressurized for 1 sec at step (325). Next, the pressure chamber (20) is pressurized with pressurized shox oil at 120oC to 300 bar pressure for 1 sec at step (330) and depressurized for 1 sec at step (335). Again at step (340), the pressure chamber (20) is pressurized with pressurized shox oil at 120oC to 400 bar pressure for 1 sec and depressurized for 1 sec at step (345). The sequence of steps (320) to (345) is repeated 1000 times automatically on the system (100) and completion of 1000 cycles is indicated on the MMI screen.
After completing test cycles (200), (300) and (400), oil leaked from the leak oil outlet (25) is measured and quality of piston band is validated.
Advantages of the invention
• The system (100) facilitates to test the product for its acceptance to be used in field.
• The system (100) enables changing of pressure within a second.
• The system (100) facilitates to test working condition of the shock absorber simulated inside a factory setup.
The foregoing objects of the invention are accomplished and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention described in the present embodiment. Detailed descriptions of the preferred embodiment are provided herein; however, it is to be understood that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure, or matter. The embodiments of the invention as described above and the methods disclosed herein will suggest further modification and alterations to those skilled in the art. Such further modifications and alterations may be made without departing from the spirit and scope of the invention
,CLAIMS:1. A piston testing system (100) for testing a banded piston assembly (50) having a piston (5) and a spacer (10) mounted on a piston rod (15); the piston testing system (100) comprising:
a fixture (35) for holding the banded piston assembly (50), the fixture (35) having a cylindrical pressure chamber (20) with a pressurized oil inlet (30) at one side thereof and a leak oil outlet (25) at the other side thereof, such that when a banded piston assembly (50) is held therein, the leak oil outlet (25) is at the spacer (10) side of the banded piston assembly (50);
a side load cylinder (40) capable of providing a side load up to 600 N on the banded piston assembly (50) mounted in the fixture (35);
a shox oil supply (not shown) capable of supplying the pressurized shox oil having temperature in the range of 25°C to 200°C, to the cylindrical pressure chamber (20) through the pressurized oil inlet (30), with a pressure between 0 bar to 400 bar such that the cylindrical pressure chamber (20) is pressurized to high pressure within a second and depressurized to low pressure within a second;
a multimedia interface display (not shown) operably connected to the piston testing system (100);
wherein, the piston (5) of the banded piston assembly (50) moves to and fro within the cylindrical pressure chamber (20) under the influence of the side load provided by the side load cylinder (40) and the pressurized oil in the cylindrical pressure chamber (20); the moving piston (5) wipes the oil from the side walls of the pressure chamber (20) and the oil adhering to the side walls of the pressure chamber (20) is collected through the leak oil outlet (30); and the banded piston assembly (50) is tested by changing the pressure, temperature and side load in a cyclic order.
2. A method of piston testing for testing a banded piston assembly (50) having piston (5) and a spacer (10) mounted on a piston rod (15), the piston testing system comprising:
holding the banded piston assembly (50) in a fixture (35) having a cylindrical pressure chamber (20) with a pressurized oil inlet (30) at one side thereof and a leak oil outlet (25) at the other side thereof, such that the leak oil outlet (25) is at the spacer (10) side of the banded piston assembly (50);
starting a low pressure and low temperature test cycle (200) in auto mode;
starting a high pressure and low temperature test cycle (300) in auto mode after completion of the low pressure and low temperature test cycle (200);
starting a high pressure and high temperature test cycle (400) in auto mode after completion of the high pressure and low temperature test cycle (300); and
validating the banded piston assembly (50) by measuring the shox oil leaked from the leak oil outlet (30);
wherein
the test cycle (200) includes actuation of side load cylinder (40) to provide side load up to 600 N on the banded piston (50); pressurization of the cylindrical pressure chamber (20) with shox oil to low range pressure; successive depressurization at the regular intervals of one second and repetition of pressurization and successive depressurization steps;
the test cycle (300) includes pressurization of cylindrical pressure chamber (20) to a high pressure and successive depressurization at the regular intervals of one second and repetition of pressurization and successive depressurization steps; and
the test cycle (400) including actuation of side load cylinder (40) to provide side load upto 600 N on the banded piston (50); pressurization of the cylindrical pressure chamber (20) with high temperature shox oil to high range pressure; successive depressurization at the regular intervals of one second and repetition of successive pressurization and depressurization steps.
3. The method of piston testing as claimed in claim 2 wherein the cylindrical pressure chamber (20) is pressurized up to 50 bar pressure in test cycle (200)
4. The method of piston testing as claimed in claim 2 wherein the cylindrical pressure chamber (20) is pressurized up to 500 bar pressure in test cycle (300)
5. The method of piston testing as claimed in claim 2 wherein the cylindrical pressure chamber (20) is pressurized up to 500 bar pressure in test cycle (400)
6. The method of piston testing as claimed in claim 2 wherein the temperature of the shox oil is in the range of 100oC to 150oC.