Electric motors

Introduction for Hydraulic braking for The electric motor technology vs. hydraulic braking

The hydraulic braking system using the concept of a four-wheel brake system was proposed in the year 1918 by Malcolm Loughead. The system capitalized on the use of fluids to make it possible to transfer a large force to the brake shoe when pressing the pedal with much less force. Most vehicles adopted this braking system in their cars.  Since then many developments have been made to improve brakes, one of which is regenerative braking.  A common regenerative braking method, called Generator Braking (GB) in this report, is used in electric cars and utilizes a motor that also acts as generator when the brakes are applied to conserve energy.  Another regenerative braking system developed by The Ford Motor Company and the Eaton Corporation in the late 1920’s for a typical gasoline or diesel combustion engine that stores brake energy in the form of a compressed gas is called Hydraulic Power Assist Braking  (HPA)  (Baharom, Hussain, & Day, 2013).

HPA is used in gasoline and diesel combustion engines.  HPA works by using the kinetic energy of the vehicle to power a reversible pump.  This pump is triggered once the driver steps on the brake pedal and causes the hydraulic fluid, Nitrogen gas in the case for HPA, to be sent from low-pressure accumulator to a high-pressure accumulator inside the vehicle. This takes the kinetic energy of the car and stores it as pressure inside the accumulator which can be used again (Kumar, 2012).The vehicle is slowed down, until it finally stops and roughly 80 percent of the cars original kinetic energy is stored as pressure (Ohnishi, Saito, Oshima, & Higashihara, 2013) (Kumar 2012).  The nitrogen gas stays under pressure until the accelerator is pressed by the driver, in which case, the pump reverses and releases the pressure and spins the drive shaft thus accelerating the car forward (Kumar 2012).  

HPA performs best in city driving where there is a lot of traffic because of the constant starts and stops. HPA is better than the conventional braking systems because the excess kinetic energy is converted into a storable form of energy, namely pressure,  that can be used to accelerate the car back up to speed.  HPA has a long life span due to the reusable parts that do not take much wear and tear and is rather efficient (Kepner 2002).  Conventionally excess kinetic energy is converted to heat by friction in the brakes, which is undesirable . Consequently, HPA has reduced the cost of driving because the cost of replacement of brake parts is minimized and the level of fuel consumption has been reduced since the pressurized nitrogen gas is doing most of the work to accelerate the car.

Generator Braking also conserves useful energy but is used on electric vehicles.  These are vehicles that rely on an electric motors powered by a battery to propel the engine. Vehicles that utilize this technology do not have gasoline tanks but obtain energy by charging a battery from electrical sockets and recharging if the batteries have been depleted.

The electric motor technology has been in place for more a century and has had many advances including GB. Although it is difficult to exactly pinpoint the first inventor of an electric motor driven vehicle, innovators in America, Netherlands and Hungary can be attributed to the first innovation. For instance in USA, William Morrison invented the first vehicle that had a capacity of six passengers (Nykvist et al., 329-332).  The electric motor car has had major impacts on the car industry. First, since they do not use fossil fuels, the cars do not directly pollute environment which is very important in the control of greenhouse gases emissions and global warming. This can be achieved if the cars use electricity produced from renewable energy resources, thus eliminating air pollution. Secondly, the electric motors technology has affected the consumer price in fueling or recharging their vehicles these vehicles have convenience of lasting anywhere between 100 and 200 miles on a single charge. Lastly, the electric motors produce an constant torque as opposed to that of combustion engines that increase depending on the revolution speed of the engine (Helmers et al., 1-15).

Although the technology of Generator Braking seems relatively new, it has been used for over one hundred years.  The first real beneficial use was in the early 1900’s on trams (Raworth).  Trams incorporated a regenerative braking system that used the engine to help slow down the tram on declining slopes (Raworth).  A system very similar to the one used on trams in the early 1900’s is used in electric cars today.

The use of technology such as GB has even further improved the efficiency of the electric cars. GB improves the efficiency of the vehicle by reducing the amount of friction created between the brake pad and disk and converting it into electrical energy which can be used to recharge the battery of the car.  The key to GB lies in the engine of the car.  When electricity is applied to the engine, it accelerates the drive shaft and propels the car forward.  However, when the car begins to stop, instead of the brake pad being pressed against the brake disk, the drive shaft rotates the opposite direction and the engines starts to produce electricity, effectively becoming a generator (Bosch). This means as the car stops, the battery powering the engine of the car is slowly recharged.  This ultimately reduces the total amount of energy loss due to friction on the brake pad and uses it to power the engine of the car.

Analysis for hydraulic braking

The HPA was analyzed under several different conditions such as hydraulic driving condition, cruise condition, accelerating/climbing condition, and regenerative braking condition (Kumar). These conditions vary by the amount of torque that is produced by the engine and how much torque is used for actually powering the hydraulic pump. All the torque equations used by Kumar are detailed in the appendix (Equation #, #, # and #). The most important is the force of the hydraulic pump/motor increasing the pressure of the nitrogen gas is:

Where is the force of the hydraulic pump or motor, is the torque of the hydraulic pump or motor, is the final ratio of the differential, is the ratio of the hydraulic pump or motor, is the efficiency of the hydraulic pump or motor, and r is the radius at which the force is being applied (Kumar). This equation helps determine how much force is being done to compress the nitrogen gas and relates to how much energy is saved during braking. It was found that nearly 70 percent of the energy used in braking was able to be recovered (Kumar).

Another study conducted by Liu et al. found that the addition of a HPA system led to a 25 percent reduction in fuel consumption. This evidence is supported by Figure #, #, and # (in Appendix) which show the difference between a HPA system and a non HPA system comparing: acceleration, velocity, and fuel consumption. The acceleration and velocity lines for both look nearly the same while the fuel consumption shows a clear drop for the HPA system.

One design issue that the HPA system has to address is the placement of the hydraulic pump on the car and what order it should be in relative to the engine, clutch, transmission, and differential. A diagram of the HPA system installed is given in the appendix (Figure #) (Liu et al.). The HPA system should come after the engine, clutch, and transmission. Kumar took this one step farther and saw that the front axle becomes more loaded when braking is applied in a front wheel drive system and the HPA preforms best when in front of the differential (Figure #) (Kumar).

The experimental data shows ample opportunity for this technology to grow and improve as it is already producing tremendous results such as 25 percent fuel reduction and recovering 70 percent of the kinetic energy without much optimization in place (Liu et al.).

The energy flow for the HPA system is shown in the appendix by Figure #. The energy flow for a car without an HPA system allows the kinetic energy of the car to be dissipated through heat with the break pad pressing against the rotor. The HPA system changes this energy loss by changing the kinetic energy of the car into shaft work for the compressor/pump. With shaft work being put into the compressor/pump, it will act like a compressor. This compression stores the shaft work in the nitrogen gas a pressure differential. This energy is stored in the accumulator until the car is ready to accelerate in which the process is reversed. The pressure difference allows rotational energy to be created in the pump shaft, which is then translated to the drive train and wheels. This accelerated the car forward and changes the shaft work back into kinetic energy.

Appendix

Torque calculation of low-speed cruise conditions (Kumar)

Torque calculation of middle/high speed cruise conditions (Kumar)

Torque calculation of accelerating/climbing conditions (Kumar)

Figure #. Acceleration from 0-50 km/h (Liu et al.)

Figure #. Cycle Run History of Velocity km/h (Liu et al.)

Figure #. Fuel Consumption

Figure #. Orientation (Lui et al.)

Figure #. Detailed Orientation (Kumar)

Kinetic Energy

Compressed Nitrogen

Shaft Rotation

Heat Loss

Drive Shaft Rotation

Non-HPA System Brake Energy Flow

HPA System Reversible Brake Energy Flow

Figure #. Energy Flow for Conventional Versus HPA

Baharom, M. B., Hussain, K., & Day, A. J. (2013). Design of full electric power steering with enhanced performance over that of hydraulic power-assisted steering. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 0954407012468413.

Bosch, Robert. Chassis Systems Control (n.d.): n. pag. Reduce Consumption. Protect the Environment. Regenerative Braking System. Bosch Automotive Technology. Web. 25 Mar. 2016.

Gilles, T. (2005). Automotive Chassis: Brakes, suspension, and steering. Clifton Park, N.Y:   Thomson Delmar Learning.

Heissing, B., & Ersoy, M. (2011). Chassis Handbook and Fundamentals, driving dynamics, components, mechatronics, perspectives. Wiesbaden: Vieweg Teubner.

Helmers, Eckard, and Patrick Marx. "Electric cars: technical characteristics and environmental impacts." Environmental Sciences Europe 24.1 (2012): 1-15.

Kepner, R. "Hydraulic Power Assist − A Demonstration of Hydraulic Hybrid Vehicle Regenerative Braking in a Road Vehicle Application." SAE International. SAE International, n.d. Web. Feb. 2016. <http://papers.sae.org/2002-01-3128/>.

Kumar, Amitesh. "Hydraulic Regenerative Braking System." International Journal of Scientific & Engineering Research 3.4 (2012): n. pag. International Journal of Scientific & Engineering Research. International Journal of Scientific & Engineering Research. Web. Feb. 2016. < http://www.ijser.org/researchpaper/hydraulic-regenerative-braking-system.pdf >.

Marks, G. C. M. (1905). The Hydraulic power engineering: A practical manual on the concentration and transmission of power by hydraulic machinery. London: Lockwood.

Nunney, M. J. (1992). Light and heavy vehicle technology. Oxford: Newnes.

Nykvist, Björn, and Måns Nilsson. "Rapidly falling costs of battery packs for electric vehicles." Nature Climate Change 5.4 (2015): 329-332.

Ohnishi, K., Saito, Y., Oshima, T., & Higashihara, T. (2013, July). Powered orthosis and attachable power-assist device with Hydraulic Bilateral Servo System. In Engineering in Medicine and Biology Society (EMBC), 2013 35th Annual International Conference of the IEEE (pp. 2850-2853). IEEE.

Raworth, Alfred. "Proceedings of the Institution of Electrical Engineers." Google Books. N.p., n.d.Web.25Mar.2016.