Upgrading the Engine Mounts

Over past few weeks the engine mount team has focused on solving the vibration issues of vehicle and has made some good headway. Both Manny and Sherj spent time in the school’s Plastics lab to cast samples of polyurethane with varying durometer ratings. This durometer rating dictates the hardness of the polyurethane, which in turn affects other key properties of the polymer. The plan for this polyurethane is to insert it between the engine and the mount so it can act as an isolator, hence damp vibrations.

engine mount polymers
These different samples of polyurethane will undergo tests to determine specific properties, such as flexural strength and toughness. The data these tests provide will help the engine mount team to decide which sample of polyurethane will best suit the vehicle.

Once a desired durometer rating for the polyurethane is selected, it will be cast and machined into the desired geometry and installed on the vehicle.

 

Background Research

With these generic multi use engines, the possibility of mounting is quite large. For this particular example we took a look at everything from, compressors, water pumps and generators to ATV’s, UTV’s and racing karts to see if any particular method used could solve or help solve the particular issues we have isolated for this redesign.

The research into tools with similar motors mounted, didn’t really provide anything of use as most were just solid mounted with a simple design, due to it being a stationery design. The research into what we consider similar vehicles gave us an idea of how vibration is dealt with but not really anything in particular to help with our specific design. Most of these similar vehicles do not use solid mounts like our original, but rather have some kinds of anti-vibration materials added, (ie polyurethane or rubbers of different kinds). These ideas are great for those applications but rubber due to the excessively minimal slack allowed by the CVT is not really feasible for us, the polyurethane is something we may look into more due to its lack of flex.

Design wise there aren’t any mass market products that could be directly used or referenced. The most detailed and engineered design on the market currently would be used for racing shifter karts. These karts have similar issue as the Baja Buggy in that vibration and mounting point stress are very key in design.

 

The current car has competed in the 2015 Collegiate Design Series in Oregon. Aside from several components failing, there were other apparent issues. One of these issues were the members holding the engine. These members were unsupported for their entire length, causing the members to deflect a relatively large distance. Allowing the engine run in such a state for prolonged periods of time could lead to a catastrophic failure of the members and possibly damaging other valuable components. There were no calculations or simulations done to examine the unsupported member and whether or not it could fail through fatigue.

engine mounts
Figure 2: The Current V1 Engine Mounts

To solve this issue, the unsupported member can be braced using the engine mount and the frame members surrounding the transmission. This can be accomplished in a multitude of ways. The most simple of these is to weld the unsupported member to any adjacent frame member. The major advantage to this would be the amount of time and resources saved to fix the problem. The major downside is the welds would cause major restrictions. Currently, the engine can freely slide the entire length of the member it is supported by, allowing for easy tensioning of the CVT belt as well as a simple removal process for the engine. An engine mount that would allow for this freedom could involve a clamping system. This system would look very similar to what is currently being used but it would have an additional extrusion in contact with an adjacent member to act as the clamp. This extrusion would also consist of another piece placed on the other side of the member and bolts to hold these two pieces together. This design would allows for free movement after the bolts are removed, but would still provide support. Optimizing this design could also save weight as no simulations were done to test if material could be removed.

 

Vibration

 

Another issue with current engine mount is they are currently hard mounted to the frame. This causes a severe transfer of vibration to the member supporting the engine as well as throughout the entire car. This vibration has the potential to cause failure in a multitude of components such as the electronics, so it must be looked in to. There were no calculations or simulations done previously to determine the exact impact of the vibrations.

A solution to this problem could be the use of shims. The shims would be inserted where the engine mount clamps onto the frame. The shims could be made of rubber and would isolate the engine from the engine mounts. It is this isolation that would damp vibrations. A downside to these rubber shims is they may affect the tension in the CVT belt.

Other teams had varying views on the subject of engine vibration. Some teams had no need for vibration damping; they left the engine hard mount to the frame. There were other teams who had severe vibration and used either flexible or solid inserts to damp vibration.

 

 

Casting

Currently, the engine mount is stock 2×2 aluminum that has notches cut out with a ball mill. Holes were then drilled to bolt the engine to the mount, and then the mount to the frame. Instead of using stock aluminum, the casting of aluminum parts could be done. This has the major advantage of confirming the viability of casting future parts. This will allow future teams to create part geometries that would otherwise be very difficult to machine.

The new engine mount could be casted from a different aluminum alloy to maximise the desired qualities such as castability and machinability. A composition that would do this is Aluminum 319, which is an alloy containing 6% silicon and 3.5% copper. This type of aluminum alloy is commonly used for engine parts, which makes it a prime candidate for an engine mount.

Another aluminum alloy that meets the required machinability and castability properties is Aluminum 356. Aluminum 356 contains 7% silicon and 0.3% magnesium. It is also used for flywheel castings, automotive transmission bodies and pump bodies.

with the faculty at BCIT, casting different alloys is possible. This will involve using an uncontaminated crucible and sourcing the correct materials to achieve the desired composition.