Cam measurement probe conversion and equivalent lift table calculation method

1 Overview The camshaft is a key component that affects the working quality of the engine distribution mechanism. Its function is to ensure that the engine valve group has an accurate and stable good movement pattern. The measurement of the cam mainly provides a basis for assessing the geometric accuracy of the cams on the camshaft and the dynamic characteristics after installation. Therefore, when measuring the cams, the cam follower (tapped pin) should be selected according to the design requirements. The form and shape of the probe, according to the design requirements given by the rotation - lift table to measure, in order to correctly reflect the movement of the cam mechanism. 2 Probe conversion The conversion of probes does not mean simply changing one probe to another probe, but refers to the conversion of measurement parameters when using a probe that does not meet the design requirements and shape for cam measurement. In the measurement, a set of operation that removes a probe head that does not conform to the design requirements and form and installs a probe head that meets the design requirements form and shape is called probe tip replacement. Probe conversion and probe replacement are two very different concepts. Whether it is to determine the detection position of the cam or the lift of the measurement cam, the probe head of the same form and shape as the cam follower (tapped pin) should be used. For example, the follower of the valve cam of the S195 diesel engine is a flat tappet. A flat probe must be used for measurement. The follower of the oil supply cam is a roller tappet. The diameter of the tappet should be the same as that of the roller tappet. Roller probes. However, when the design requirements of the followers of the cams on the same camshaft are different, the measurement heads of different forms and shapes that meet the design requirements are supposed to be used for measurement. However, some measurers need to save the measurement process. The trouble of replacing the probe, even with the same probe to measure the cam on the camshaft, which caused a probe conversion problem for a certain cam, especially in the automatic measurement of the cam, this conversion probe form and The phenomenon of shape is more common.

Fig. 1 Different cam angles of the probe at the same cam inspection point

Fig. 2 Solution of Equivalent Rotation and Equivalent Lift when Converting a Plane Probe to a Roll Probe

After the conversion of the probe form and shape, the equivalent lift table was used instead. There was no problem in principle. However, the current equivalent lift tables are generally calculated based on the design angle instead of on the basis of design inspection points. In other words, if the probe is converted to the same angle as the one before the conversion, the cam inspection point will be different: If the inspection point is the same before and after the probe conversion, the cam rotation angle is different. For example, for the "sensitive point" m of the S195 diesel engine's gas distribution cam, when measured with a flat probe designed for design, the cam angle ap = 46°07'16" (Fig. 1a): when using a 15mm roller probe, the cam Corner angle aG=16° 53' (Fig. 1b): When using the knife edge probe, the cam angle aD = 6° 52'28" (Fig. 1c). That is, the ap≠aG≠aD of the same inspection point of the cam. It can be seen that after conversion of the probe form and shape, if the equivalent lift is still calculated according to the design angle, the position of the cam design test point is tampered with, and the cam shape error at the inspection point before and after the probe conversion will occur. Differently, the accuracy of the cam measurement data may be affected, and even the judgment of the cam conformity may be wrong (wrong or invalid). 3 Equivalent Lift Table When a probe with a form and shape that meets the design requirements cannot be used due to measurement process conditions, for example, an overhead camshaft cam with a motorcycle engine, the rocker arm and the cam type must be used. The valve lift of the face-to-face oscillating cylinder is converted into the cam lift of the center-to-center moving flat probe. (For conversion calculation, see Yang Guangxing et al., “Principles and Design of Motorcycle Engines” (Wuhan Institute of Surveying and Mapping, 1993) Page 297) The use of flat probes is beneficial to the machining and measurement of the cams. For example, for the S195 diesel engine camshafts, the design requires that the cams (intake and exhaust) be measured with a flat probe, and the cams with a 15 mm roller For probe measurement, if the 15mm roller probe is adopted uniformly, the measurement of the valve is changed by the valve cam measurement, and each cam on the same camshaft adopts a single probe measurement, which is conducive to the automatic measurement of the cam. - Calculation of lift: Suppose the cam angle is zero when the maximum lift of the cam (thorn) is reached. When the cam turns over a certain angle, the cam comes into point contact with the probe i (i is the inspection point), and the flat probe comes Say cam The angle is ap, and the corresponding lift is hp: for the roller probe, the cam angle is aG, and the corresponding lift is hG. Assuming that OOi=Li,OiO1=ri+rc in FIG.2, the OA in OO1A =OOi+OiA=Li+(ri+rc)cosapO1A=(ri+rc)sinap aG=tg-1{(ri+rc)sinap/[Li+(ri+rc)cosap]} Considering the formula for each segment of the cam profile, Rewrite the above equation as aG=tg-1{(ri+rc)sinf(ap)/[Li+(ri+rc)cosf(ap)]} (1) <In OOoO1, get the cosine theorem (ri +rc)2=(ro+hG+rc)2+Li2-2Li( ro+hG+rc)cosaG Expand Simplify the above equation and consider adapting to each segment, get hG=(ri+rc)cossin-1[Lisinf( aG)/(ri+rc)]+Licosf(aG)-( ro+rc) (2)
Schedule equivalent corner - lift table
(S195 Diesel Engine Gas Cam) Inspection Point Design Lift Table
(with flat probe) Equivalent lift table
(with 15mm roller probe)
(i) Corner
(ap) lift
(hp) Corner
(aG) Lift
(hG) 1 0° 7.5500 0° 7.5500 Top Round Segment 2 1° 7.5472 0°22' 7.5490 Top Round Segment 3 2° 7.5387 0°44' 7.5459 Top Round Segment 6 5° 7.4795 1°50' 7.5246 Top Round Segment 11 10° 7.2690 3°40' 7.4483 Top round section 21 20° 6.4343 7°20' 7.1422 Top round section 31 30° 5.0716 11° 6.6283 Top round section 41 40° 3.2217 14°40' 5.9000 Top round section 46 45° 2.1315 16 °30' 5.4521 Top round section 47 46°07'16" 1.8731 16°53' 5.3512 Sensitive point 48 47° 1.6748 19°58' 4.2962 Round section 49 48° 1.4647 23°03' 3.6002 Round section 50 49° 1.2712 26°07' 2.9822 Complex segment 51 50° 1.0944 29°12' 2.4304 Complex segment 56 55° 0.4618 44°36' 0.5785 Complex segment 61 60° 0.0000 60° 0.0000 Contact 62 61° 0.2476 60°02' 0.2321 Transition Section 63 62° 0.2410 60°04' 0.2150 Transition section 64 63° 0.2298 60°06' 0.1986 Transition section 65 64° 0.2140 60°08' 0.1828 Transition section 66 64°00'53" 0.2139 60°08'08" 0.1827 Contact point 67 65° 0.1965 65° 0.1765 Buffer section 71 70° 0.1195 70° 0.1071 Buffer section 76 75° ​​0.0612 75° 0.0548 Buffer section 81 80° 0.0221 80° 0.0198 Buffer section 88 87°30' 0.0000 87°30' 0.0000 Buffer section