Download - Log #2 Hydraulic Brake
The most common type of braking system used in automobiles and other machines today
is hydraulic brakes. Prior to the advent of hydraulic brake systems, cars used mechanical brakes.
Hydraulic brakes apply more pressure to break pads than mechanical brakes because they use
compressed fluids. This helps the vehicle to stop with more force, without requiring the driver to
apply more force (Haverdink). I decided to research this topic because I have hydraulic brakes on
my mountain bike which help me to brake safely when traveling down slopes. This log will
specifically focus on hydraulic presses, how they are implemented into the hydraulic braking
system on a car, and the advantages of hydraulic brakes compared to mechanical brakes.
To begin, a hydraulic braking system is similar to a hydraulic press. A simple hydraulic
press consists of a cylinder that contains two pistons, one smaller than the other (Chalupnik). The
cylinder is filled with a liquid called brake fluid that has a low freezing point, a high boiling, and
the ability to absorb water (Kelsey). A force applied to the smaller piston is transferred through
this brake fluid to the larger piston (Chalupnik). The effect this causes can be explained by
Pascal's law which states that when there is an increase in pressure at any point in a confined
fluid, there is an equal increase in pressure at every other point in the container (Hodanbosi)
Therefore, if pressure is applied to the smaller piston, the pressure is increased throughout the
cylinder and affects the pressure of liquid on the large piston creating more force in the
movement of the large piston (refer to figure 1 in the Appendix). The reason the force generated
by the large piston is higher, even though the pressure is the same, is because the pressure is
being applied to a larger area in the large piston. The extra force this system creates is why it is
present in the brakes on cars.
The hydraulic system used for brakes on a vehicle has the same properties as a hydraulic
press in that it increases force (Chalupnik). However, instead of having a single cylinder with
two pistons, hydraulic brakes have a five cylinder system with each cylinder containing one
piston. This is because there is one master cylinder located near the brake pedal and a cylinder
for each wheel of the car. In this system, the master cylinder contains a small piston and the
wheel cylinders contain larger pistons. Brake lines connect the master cylinder to each wheel
cylinder allowing brake fluid to flow evenly from the master cylinder into each wheel cylinder.
The master cylinder is mechanically connected to the brake pedal so that when the pedal is
pressed, the piston slides forward through the chamber exerting pressure on the brake fluid. The
fluid transmits this pressure through the brake lines, forcing the pistons in the wheel cylinders to
slide forward. As the wheel cylinders move forward, they apply break pressure to pads or shoes
which either close around a disk, or push against a drum in the wheel depending on which kind
of brakes are used in the wheels of the vehicle (Haverdink).
Another type of brakes are mechanical brakes that uses levers or cables which connect
the brake pedal directly to the braking pads. For the car to stop faster, the driver has to apply
more force to the brake pedal. On hydraulic brakes, the extra force is applied through the brake
fluid (Haverdink). This makes hydraulic brakes safer because the driver does not need to apply a
lot more extra force in order to stop more quickly. As mentioned earlier, when there is an
increase in pressure at any given point in a confined fluid, there is an equal increase in pressure
at every point in the container(Hodanbosi). In the case of hydraulic brakes, this means that the
force applied to a brake pedal increases through the other pistons present in a hydraulic braking
system and therefore applies a greater amount of force to the brake pads than the original force
of the drivers foot against the brake pedal. Therefore, vehicles are able to slow down faster
because of the increased pressure on the brake pads, and drivers do not need to apply as much
force on the brake pedal as they would have to with mechanical brakes. This is why hydraulic
brakes are both safer and more effective than mechanical brakes.
Living in mountainous Colorado, I really enjoy mountain biking with my father. Without
my bike’s various hydraulic systems I would not be able to do this as well. I decided to research
hydraulic brakes because I use them on my mountain bike and wanted to learn more about the
scientific processes they perform that allow me to stop easier on my bike. While I did focus on
researching the hydraulic brakes present in automobiles for my topic section, mountain bikes
also have similar hydraulic systems that carry the same properties as the hydraulic press. The
brakes on mountain bikes use a hydraulic system because the rider needs to stop suddenly when
facing difficult obstacles. The extra force that hydraulic brakes provide in stopping the bike is
also needed to counteract the force of gravity that pulls the bike down the hill. The mountain
bike has other hydraulic systems such as front and rear suspension shocks which are similar to a
hydraulic press and help to make the bike ride smoother over rocks and ledges in the trail. In
addition, many newer bikes have an adjustable seat post that use a hydraulic system that raises
and lowers the seat while riding. This seat post system allows the rider to get his weight lower
on the bike for steep descents, but also allows full leg extension during climbs and level riding.
The hydraulics present on mountain bikes help me and bikers all over the world to traverse
mountains and enjoy the outdoors.
Another part of hydraulics that interests me is their many uses in society because of the
mechanical advantage they provide. Hydraulic presses and pumps are examples of mechanical
advantage which is the ratio of the force that performs the work of a machine to the force that is
applied to a machine ("Mechanical Advantage"). In this case, the force applied to a hydraulic
pump (eg. the brake pedal) is far less than the force it performs in doing it’s task (e.g. applying
the brake pads to the disk) and therefore hydraulics give us mechanical advantage. This very
principle allows us to construct tall buildings, build bridges, and dig huge tunnels with hydraulic
systems. The construction of taller buildings allows for more condensed populations which
means that a city can support more people and also more businesses. The digging of tunnels has
helped with the transportation of goods through mountains, and has also helped with mining for
resources. Lastly, the construction of bridges has helped to make travel over bodies of water
easier. These are all example of how mechanical advantage from hydraulics and other systems of
mechanical advantage help our society.
Another interesting part about hydraulics is its use in civil engineering. The machines
built with hydraulics explain the mechanical side of hydraulic engineering, but civil engineers
use hydraulics to study the flow of water in rivers and pipes. Understanding the forces of a
hydraulic system helps people in this field to design embankments and levees that provide flood
control along rivers. It also helps in the creation of irrigation systems and water supply systems
for cities (Chalupnik). This would have been very important in Colorado last year when many
rivers flooded because of heavy rains. More and better levees along the rivers and creeks may
have reduced the flooding, damage to many homes, and loss of life.
For my further development, I decided to address problems associated with bunk beds
using a hydraulic system. While bunk beds are convenient for maximizing space in a bedroom,
they are very dangerous. Between 1990 and 2005, almost 573,000 kids from infants to age 21
suffered injuries significant enough to warrant a visit to the emergency room (Aleccia). These
injuries were most likely caused by the height of bunk beds and climbing of a ladder in order to
reach the top bed. Climbing down from the ladder can also be quite dangerous to young children.
With the safety of children in mind, I came up with an idea to solve this problem.
My idea is that there could be a hydraulic piston system within the legs of the bunk bed.
The pistons in the legs would change the height of the top bed while the bottom bed would
remain a normal height from the floor. The force to raise the pistons could be applied similarly to
that of a car jack. A lever could be connected to the bottom of a cylinder positioned next to one
of the bed legs. For now this will be called the master cylinder. The master cylinder would
contain a piston smaller than the pistons in the cylinders in each bed leg and would be filled with
hydraulic fluid. It would be connected to the cylinders present in each of the bed legs using
piping similar to brake lines. When it's time to go to sleep, a kid could easily climb into bed, and
then his parents could simply step on this pump lever to pump fluid into the bed legs. Stepping
on the lever would cause the small piston in the master cylinder to pump the hydraulic fluid from
the master cylinder evenly into each bed leg cylinder through the lines connecting them. The
pressure applied to this liquid by the small piston would in turn raise the height of the larger
pistons in each of the bed legs. This would cause the top bunk of the bed to raise gradually until
it was an acceptable height above the bottom bed. Once the height is met, the lever would be
pressed down once more and secured with a metal rod connected to the cylinder. Once the lever
is secured, a valve would close off the lines connecting the bed leg cylinders and the master
cylinder. This would keep the hydraulic fluid from seeping back into the master cylinder under
the weight of the bed and therefore keep the bed from falling back down. At this point, with the
top bed secured, another kid could climb into the bottom bunk. Then in the morning, the kid
could climb out of the bottom bunk and the system could be lowered gradually by releasing the
lever. Under the weight of the bed and the kid laying on it, the hydraulic fluid in the bed leg
cylinders should return through the piping to the master cylinder and therefore the bed should
gradually lower until it returns to its down position. A more advanced system could use an
electric hydraulic pump with activation switches located on the headboard of the top bed. This
system would allow a kid to raise and lower the bed themselves while laying on the bed.
This idea helps to keep kids safe around bunk beds as they do not have to climb a ladder
to get in and out of bed. Another advantage is that while the bed is in the down position, it will
be easier to change the sheets. While these advantages do help families who want a bunk bed
because it saves space, the cost of this bed would be much more expensive than a normal bunk
bed. Another problem is the safety pieces implemented to keep the top bed from falling back
down once it has been pumped up to its top height. Developing this would require further
research on the durability of pistons over extended periods of time, as the pistons in each of the
cylinders would need to remain working for multiple years. Developing this would require
further research on hydraulic lock systems similar to the ones used on an elevator to prevent the
bed from falling in the case of a hydraulic failure. Once these problems are addressed, I think
this idea could help to decrease the number of injuries caused by bunk beds.
In my topic section I discussed the use of pistons and hydraulic fluid to apply a greater
amount of force to brakes. To further my understanding of how hydraulic systems can be used to
apply force to lifting objects instead of applying force to brakes, I decided to build a simple
hydraulic crane model. This model was constructed out of wood cubes, crafting sticks, two
plastic syringes, and vinyl piping (refer to figure 2 in the Appendix). I started by creating a base
for the crane, so that it would stand upright, and then created a tower that provided a starting
height for the crane's arm. The arm was then attached using cable ties between two blocks with
holes through them. These tied blocks at the base of the arm acted as the fulcrum for the crane.
Next I attached another block with a hole through it to the top of one of the syringes. The syringe
was connected to another syringe with vinyl piping and both were filled half way with vegetable
oil. The syringe with the block attached to it was then taped to the crane's tower and the block
was cable tied to the arm of the crane. This completed the construction of the model.
With the model completed, I started to test its movement. The two syringe plungers acted
as pistons. I held one of the syringes and applied force to it by pushing down the plunger. This
force compressed the oil in the syringe and caused it to flow through the vinyl piping into the
syringe attached to the crane's tower. The increase in fluid in the syringe connected to the crane
caused its plunger to lift up and therefore lift the arm of the crane (refer to video 1, linked in the
appendix). This was a hydraulic system because the force was applied to liquid which then
applied the force to the crane's arm. However, this system did not offer any mechanical
advantage because the two pistons were the same size. If the piston I was holding was smaller
and the piston attached to the crane was larger, than a greater amount of force would be applied
to the crane's arm with less force applied to the syringe I was holding. To test this further, I could
remake the model with different sized syringes, and attach a string to the arm to lift different
weights.
I did notice a problem with my model after performing a few tests. When I pulled out the
plunger of the syringe I was holding, the other syringe still lowered, but it didn't lower as
smoothly as it had when it lifted. I found that the source of this error was that there was air inside
the syringes. The air would compress more than the liquid would and so it would cause the
plunger to fall in sudden stops instead of lowering smoothly (refer to video 1). From this
problem, I learned that if air is present in a hydraulic system, it will cause the system to fail or
prevent it from completing its objective. Therefore, if air is somehow let into a hydraulic braking
system, it may cause the brakes to stop working. This means that there must be certain seals in
place to keep the system contained and keep contaminants out.
Upon doing my application, I faced a problem. As mentioned above, I noticed that there
was air present in the hydraulic system I had created and this caused the system to not work
correctly. This led me to thinking that hydraulics may not be as safe as I had thought. If air
happens to contaminate the system, then it will fail. This means that there must be seals in place
to prevent this from happening. If these seals fail and air is let into the system, is there a way to
remove air from the system or does it have to be rebuilt? During my research, I came across
articles explaining what happens when hydraulics fail in planes, but many of them mentioned the
system leaking, as if hydraulic fluid from the cylinders had seeped out of the cylinders. Though,
this is not what I am trying to address. Since my system failed because of air, I wanted to look
into other times when systems have failed because of air contamination, but I could find none.
Finding a solution to this could help me to fix my hydraulic system without having to reset the
syringes with new oil. While I couldn't find articles explaining this kind of contamination, I
figure it could still happen. There must be a solution to it because if a person is to build a
hydraulic system for a car, then they don't want to have to fix it when air contaminates it. There
could be some sort of scrubber that can be used to release air without releasing the fluid from the
system. If there isn't a solution to this problem, than there must be a lot of different materials in
place in order to keep air from permeating the cylinders and disabling the hydraulic system .
Further research may suggest that they use certain manufacturing processes in order to make sure
air never enters a hydraulic system during its use. This may be a topic that I will pursue in a later
log because it will help me to better understand the removal of air present in a hydraulic system.
Appendix
Figure 1: Shows that a small force applied to a small piston creates a greater amount of force on the big piston because of pressure created in the fluids between them.
Figure 2: Shows the model hydraulic crane I created.
Video 1: https://www.youtube.com/watch?v=plkWmxNc82Y
Works Cited
Aleccia, JoNel. Bunk beds cause boo-boos -- and serious injury. 2 June 2008. 7 October 2014. <http://www.nbcnews.com/id/24895552/ns/health-childrens_health/t/bunk-beds-cause-boo-boos-serious-injury/#.VDYOx_ldUuQ>.
Chalupnik, James D. "Hydraulics." World Book Advanced. World Book, 2014. Web. 9 Oct. 2014.
Easy Hydraulic Machines. n.d. 8 October 2014. <http://www.instructables.com/id/Easy-Hydraulic-Machines/>.
Haverdink, William H. "Brake." World Book Advanced. World Book, 2014. Web. 9 Oct. 2014.
Hodanbosi, Carol. Pascal's Principle and Hydraulics. August 1996. 7 October 2014. <http://www.grc.nasa.gov/WWW/k-12/WindTunnel/Activities/Pascals_principle.html>.
How Hydraulic Jacks Work. n.d. 8 October 2014. <http://www.thomasnet.com/articles/materials-handling/how-hydraulic-jacks-work>.
Kelsey. What is Hydraulic Fluid? 1 October 2014. 7 October 2014. <http://www.wisegeek.com/what-is-hydraulic-fluid.htm>.
Mechanical Advantage. n.d. 8 October 2014. <http://www.merriam-webster.com/dictionary/mechanical%20advantage>.
"Pressure." n.d. revision world. Picture. 8 October 2014.
Reverb:SRAM. n.d. 8 October 2014. <https://www.sram.com/rockshox/products/reverb>.