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Cams are used in motorbike engines, like the one shown in the 3D graphic on the right - Leaving Cert DCG - Question C-4 - 2013
Question C-4
Cams are used in motorbike engines, like the one shown in the 3D graphic on the right. Fig. C-4 below shows the outline of such a cam. The cam imparts this motion ... show full transcript
Worked Solution & Example Answer:Cams are used in motorbike engines, like the one shown in the 3D graphic on the right - Leaving Cert DCG - Question C-4 - 2013
Step 1
Draw the displacement diagram for the cam.
Answer
To draw the displacement diagram for the cam, we follow these steps:
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360° Division: Create a horizontal axis representing the full 360° rotation of the cam. Divide this axis into segments: 0°-90°, 90°-180°, and 180°-360°.
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Height for Uniform Velocity: From 0° to 90°, the follower rises uniformly to a height of 50mm. Hence, during this interval, draw a straight line from the origin (0,0) to (90,50).
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Dwell Section: From 90° to 180°, the cam dwells, meaning a lack of vertical displacement. Thus, draw a horizontal line from (90,50) to (180,50).
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Uniform Acceleration and Retardation: From 180° to 360°, the follower falls back to its original position. For this segment, we need to represent this motion with UAR. Starting at (180,50), the line drops to (360,0). The fall of 50mm over a 180° arc can be represented with a curve falling faster towards the endpoint.
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Complete Diagram: Ensure the plot covers all segments, highlighting that 0° to 90° represents an increase with uniform velocity, 90° to 180° a static position, and 180° to 360° indicates a decrease with acceleration and deceleration.
Finalizing the displacement diagram clearly illustrates each phase of the cam's movement.
Step 2
Draw the cam profile given the following:
Answer
To draw the cam profile, we need to consider:
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Cam Centre and Nearest Approach: Start by marking the centre of the cam. Given the nearest approach of the follower to the centre is 30mm, determine the radius.
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Camshaft: The diameter of the camshaft is 20mm, so the radius will be 10mm. Make sure to include this in the drawing.
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Angular Divisions: Based on the displacement diagram, divide the circle into angular sections of 0°-90°, 90°-180°, and 180°-360°.
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Direction of Rotation: Remember that the cam rotates in an anti-clockwise direction. This is critical for establishing the angle of the cam profile accurately.
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Identify Points on the Profile: Utilize the heights noted in the displacement diagram to mark key points on the cam profile. For 0° to 90°, the highest point (50mm).
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Draw the Cam Profile: Finally, sketch the profile. For the upward rise, make a smooth curve from 0° to 90° reaching up to 50mm. Then, maintain that height until 180°. From 180° to 360°, draw the descending profile keeping in mind UAR to represent the curve accurately back to the base level.
This methodical approach ensures a clear and precise representation of the cam profile based on the displacement diagram and given parameters.