Monthly Archives: March 2017

Electric Car

An electric car is an automobile that is propelled by one or more electric motors, using electrical energy stored in rechargeable batteries. The first practical electric cars were produced in the 1880s. Electric cars were popular in the late 19th century and early 20th century, until advances in internal combustion engines, electric starters in particular, and mass production of cheaper gasoline vehicles led to a decline in the use of electric drive vehicles.

Since 2008, a renaissance in electric vehicle manufacturing has occurred due to advances in batteries, concerns about increasing oil prices, and the desire to reduce greenhouse gas emissions. Several national and local governments have established tax credits, subsidies, and other incentives to promote the introduction and now adoption in the mass market of new electric vehicles depending on battery size and their all-electric range.

Compared with cars with internal combustion (IC) engines, electric cars are quieter and have no tailpipe emissions. When recharged by low-emission electrical power sources, electric vehicles can reduce greenhouse gas emissions compared to IC engines. Where oil is imported, use of electric vehicles can reduce imports.

Recharging can take a long time and in many places there is a patchy recharging infrastructure. Battery cost limits range and increases purchase cost over IC vehicles, but battery costs are decreasing. Drivers can also sometimes suffer from range anxiety- the fear that the batteries will be depleted before reaching their destination.

Electric cars are a variety of electric vehicle (EV). The term “electric vehicle” refers to any vehicle that uses electric motors for propulsion, while “electric car” generally refers to highway-capable automobiles powered by electricity. Low-speed electric vehicles, classified as neighborhood electric vehicles (NEVs) in the United States, and as electric motorised quadricycles in Europe, are plug-in electric-powered microcars or city cars with limitations in terms of weight, power and maximum speed that are allowed to travel on public roads and city streets up to a certain posted speed limit, which varies by country.

While an electric car’s power source is not explicitly an on-board battery, electric cars with motors powered by other energy sources are generally referred to by a different name: an electric car carrying solar panels to power it is a solar car, and an electric car powered by a gasoline generator is a form of hybrid car. Thus, an electric car that derives its power from an on-board battery pack is a form of battery electric vehicle (BEV). Most often, the term “electric car” is used to refer to battery electric vehicles.

Much of the mileage-related cost of an electric vehicle is depreciation of the battery pack. To calculate the cost per kilometer of an electric vehicle it is therefore necessary to assign a monetary value to the wear incurred on the battery.

The Tesla Roadster’s battery pack is expected to last seven years with typical driving and costs US$12,000 when pre-purchased today. Driving 40 miles (64 km) per day for seven years or 102,200 miles (164,500 km) leads to a battery consumption cost of US$0.1174 per 1 mile (1.6 km) or US$4.70 per 40 miles (64 km).

The cost of charging the battery depends on the cost of electricity. As of November 2012, a Nissan Leaf driving 500 miles (800 km) per week is estimated to cost US$600 per year in charging costs in Illinois, U.S., as compared to US$2,300 per year in fuel costs for an average new car using regular gasoline.

According to Nissan, the operating electricity cost of the Leaf in the UK is 1.75 pence per mile (1.09 p/km) when charging at an off-peak electricity rate, while a conventional petrol-powered car costs more than 10 pence per mile (6.21 p/km). These estimates are based on a national average of British Petrol Economy 7 rates as of January 2012, and assumed 7 hours of charging overnight at the night rate and one hour in the daytime charged at the Tier-2 daytime rate.

Great effort is taken to keep the mass of an electric vehicle as low as possible to improve its range and endurance. However, the weight and bulk of the batteries themselves usually makes an EV heavier than a comparable gasoline vehicle, reducing range and leading to longer braking distances. However, in a collision, the occupants of a heavy vehicle will, on average, suffer fewer and less serious injuries than the occupants of a lighter vehicle; therefore, the additional weight brings safety benefits despite having a negative effect on the car’s performance. They also use up interior space if packaged ineffectively. If stored under the passenger cell, not only is this not the case, they also lower the vehicles’s center of gravity, increasing driving stability, thereby lowering the risk of an accident through loss of control. An accident in a 2,000 lb (900 kg) vehicle will on average cause about 50% more injuries to its occupants than a 3,000 lb (1,400 kg) vehicle. In a single car accident, and for the other car in a two car accident, the increased mass causes an increase in accelerations and hence an increase in the severity of the accident.

Some electric cars use low rolling resistance tires, which typically offer less grip than normal tires. Many electric cars have a small, light and fragile body, though, and therefore offer inadequate safety protection. The Insurance Institute for Highway Safety in America had condemned the use of low speed vehicles and “mini trucks,” referred to as neighborhood electric vehicles (NEVs) when powered by electric motors, on public roads. Mindful of this, several companies (Tesla Motors, BMW, Uniti) have succeeded in keeping the body light, while making it very strong.

F-N-R gearbox with spur-gear differential

A differential is a gear train with three shafts that has the property that the angular velocity of one shaft is the average of the angular velocities of the others, or a fixed multiple of that average. In automobiles and other wheeled vehicles, the differential allows the outer drive wheel to rotate faster than the inner drive wheel during a turn. This is necessary when the vehicle turns, making the wheel that is traveling around the outside of the turning curve roll farther and faster than the other. The average of the rotational speed of the two driving wheels equals the input rotational speed of the drive shaft. An increase in the speed of one wheel is balanced by a decrease in the speed of the other. When used in this way, a differential couples the input shaft (or prop shaft) to the pinion, which in turn runs on the ring gear of the differential. This also works as reduction gearing. On rear wheel drive vehicles the differential may connect to half-shafts inside an axle housing, or drive shafts that connect to the rear driving wheels. Front wheel drive vehicles tend to have the pinion on the end of the main-shaft of the gearbox and the differential is enclosed in the same housing as the gearbox. There are individual drive-shafts to each wheel.

A differential consists of one input, the drive shaft, and two outputs which are the two drive wheels, however the rotation of the drive wheels are coupled to each other by their connection to the roadway. Under normal conditions, with small tire slip, the ratio of the speeds of the two driving wheels is defined by the ratio of the radii of the paths around which the two wheels are rolling, which in turn is determined by the track-width of the vehicle (the distance between the driving wheels) and the radius of the turn. Non-automotive uses of differentials include performing analog arithmetic. Two of the differential’s three shafts are made to rotate through angles that represent (are proportional to) two numbers, and the angle of the third shaft’s rotation represents the sum or difference of the two input numbers. The earliest known use of a differential gear is in the Antikythera mechanism, circa 80 BCE, which used a differential gear to control a small sphere representing the moon from the difference between the sun and moon position pointers. The ball was painted black and white in hemispheres, and graphically showed the phase of the moon at a particular point in time. See also the Chinese South-pointing chariot. An equation clock that used a differential for addition was made in 1720. In the 20th Century, large assemblies of many differentials were used as analog computers, calculating, for example, the direction in which a gun should be aimed. However, the development of electronic digital computers has made these uses of differentials obsolete. Military uses may still exist, for example, for a hypothetical computer designed to survive an electromagnetic pulse. Practically all the differentials that are now made are used in automobiles and similar vehicles.

Power transmission is an inevitable part in any automobile. The power from the prime mover (engine/motor) is transferred to the wheels using a suitable transmission system. Various designs of gearbox have been developed in the past. In this paper, an F-N-R (forward-neutral-reverse) gearbox with a compact spur-gear differential is designed by following the design parameters for spur gear, for the required output torque of a vehicle. All the gears and casing for the gearbox is modeled using Solidworks tool. A simple and user-friendly shifting mechanism is designed for the gearbox, adding to comfort. A new spur-gear differential is designed, having spur gears to accomplish differential action, which is more compact and light-weight compared to a conventional differential, since the heavy bevel gear assembly is omitted. Different analyses such as static, dynamic (time-dependent), contact, modal and fatigue analyses are done using ANSYS software. The main objective is to design and fabricate a light-weight, efficient and compact F-N-R gearbox as a replacement to current models.

In this study, an in-wheel motor torque control strategy was proposed for a 4-wheel drive in-wheel type electric vehicle by considering the rollover risk, vehicle driving and handling performance. LTR (lateral load transfer ratio), which is the rollover index, is significantly relevant to the vehicle lateral acceleration. For reducing the rollover risk, the vehicle lateral acceleration must be decreased. Lateral acceleration depends on the vehicle speed and turning radius. These factors can be controlled by the in-wheel motor torque control. To develop the in-wheel motor torque control strategy, the LTR was calculated from the vehicle dynamics to estimate the rollover. Threshold of LTR was introduced using the vehicle specifiations. LTR error which is the difference between the threshold of LTR and actual LTR was used to control the front and rear motor torques. Motor control strategy was composed of two parts: First, to reduce the vehicle velocity, output torque of the in-wheel motors at all wheels were reduced depending on the amount of the LTR error. In addition, co-operative braking control was performed using the electro-hydraulic braking system. Second, to improve the handling performance, additional output torque control of the front in-wheel motors were carried out. Through the simulation results, it was found that the rollover risk was decreased as much as 30% by the in-wheel motor torque control compared to that of no control

Pedestrian Headforms

Used for pedestrian safety testing, Diversified Technical Systems’ (Seal Beach, CA) pedestrian headforms (which emulate a human head) embedded data acquisition solution are instrumented with a triaxial accelerometer and miniature SLICE NANO data recorder inside and then launched at a vehicle’s hood and windshield to test for potential injuries that may be sustained by pedestrians. DTS’ three-channel SLICE NANO miniature data recorder with 16 GB flash memory offers a cable-free solution for both the 4.5 kg (9.9 lb) “adult” and the 3.5 kg (7.7 lb) “child” headform. The mounting block also houses a DTS ACC3 PRO triaxial accelerometer, which has a mass of 2000 g (70 oz), that measures the linear acceleration and impact forces. Options are also available for other sensor models. “The DAS and sensors are all inside so there are no cables to get tangled up when it’s launched at the car. That also helps with repeatability—something that’s especially important for regulation testing,” said Scott Pruitt, DTS president and co-founder.

Features pedestrian facility include:

  • Equipment and software developed in-house for targeting and aligning the headform which ensures every impact is exactly where it is supposed to be, well within the permitted tolerance.
  • An accurate independent measurement of the headform velocity before impact, for every test, using a laser-based system.
  • Lower-leg tests conducted using a long acceleration distance to ensure the foam at the rear of the leg is not compressed before the impact on the vehicle

A complete suite of impactors, gives capability to perform any type of testing:

  • Headforms Adult (4.8kg) Small Adult (3.5kg) and Child (2.5kg)
  • Euro NCAP / Japan / GTR 4.5kg Adult headform
  • Upper Leg WG17 / EC / Euro NCAP
  • Lower Leg WG17 / EC / Euro NCAP

The WG17 Headform impactors from Humanetics were developed with the Netherlands Organisation for Applied Scientific Research (TNO) in Delft and partners in the Working Group 17 from the European Enhanced Vehicle-safety Committee (EEVC). These headform impactors have been incorporated in a EEVC proposal for a Directive for Pedestrian Safety Tests of passenger cars for the European Commission. The design of the headform is based on the current WG10 headforms, which are currently used as the tool in pedestrian safety evaluations in the European New Car Assessment Program (EuroNCAP).

In June 1997, the European Enhanced Vehicle-safety Committee (EEVC) decided to set up a Pedestrian Safety working group: WG17. The main task of EEVC Working Group 17 was to review EEVC Working Group 10 pedestrian protection test methods from 1994 and to propose possible revisions, taking into account new data in the field of accident statistics, biomechanics and test results. The EEVC WG17 report has been finalized in December 1998. Several improvements in test conditions, requirements and tools (i.e. impactors) have been included. The new EEVC pedestrian protection test methods will be used by the European Commission for further development of regulations in this field.

Since 1994, the subsystem impactors described in the EEVC test methods have been further evaluated and improved. EEVC WG17 has included new impactor specifications in the EEVC test methods:

  • Improvement of the leg-form impactor with a damper in order to avoid vibrations.
  • Alteration of headform impactor material to improve production and durability.
  • Improvement of the dynamic certification procedure of the leg-form and headform impactors in order to better reflect actual use in bumper and bonnet tests.
  • Enhanced durability and repeatability of the headform impactors.
To improve durability and repeatability EEVC WG17 decided to change to a more Hybrid-like head- form, i.e. an aluminium sphere covered with a PVC skin. The headform specifications have been updated in this respect. The outer diameter and mass of the headforms are unchanged. The Humanetics WG17 Headform impactors meet the original certification requirement, which was developed on the basis of a drop test. Meeting this biofidelity requirement meant that the EEVC WG17 subsequently approved the Humanetics WG17 Headform impactor design.
The original headform certification speed obtained from a drop test was only 20-25% of the impact speed on the car bonnet. EEVC WG17 has now developed a new dynamic certification procedure, which better reflects the actual use of headform impactors in bonnet tests.
In 2009 Euro NCAP has introduced a new overall vehicle rating that will put growing emphasis on pedestrian protection in the years to come.  This new rating system was implemented in February 2010.  At the same time, a new European Commission regulation on the pedestrian protection, (EC) No. 78/2009, has been published, which repeals and replaces the previous EC directives 2003/102/EEC and 2005/66/EC.

Vehicle Connectivity

Automotive suppliers and companies from other fields are jockeying to team up with the right group of partners to provide services for connected vehicles and smart cities. The collaborations cross boundaries to include insurance companies, app providers and public services as well as a range technology suppliers. Connected vehicles are rapidly moving into the mainstream, putting pressure on companies to figure out what services and features they want to offer. App companies, cellular and satellite providers, insurance companies, data centers and service providers are all struggling to cash in on the connected car boom. Communication companies like Ericsson are attempting to help vehicle owners find the apps and services they need. Ericsson created a center for app and service providers.

Automakers also detailed the need for multiple partnerships, which are often called an “ecosystem,” during the 2017 TU-Automotive Detroit conference. These ecosystems build upon alliances that have been established in recent years. Consumers who spend much of their time connected to the Web are pressing automakers to provide far-ranging amenities. Today’s technology lets service providers offer a broad range of offerings, making it difficult to determine what users might want and how they can earn revenue. For example, insurance companies that use connectivity to track mileage must decide what else they want to do.

The challenge facing automotive suppliers extends to the public sector. More urban planners are exploring ways to use connectivity to reduce congestion by using vehicle data to adjust stoplights and help drivers quickly find parking, among many other tasks. However, creating the digital infrastructure needed to support various services won’t be cheap, so private companies may be asked to help pay for equipment. This infrastructure will probably include V2V and V2I (vehicle-to-vehicle and vehicle-to-infrastructure) communications. That is expected to reduce accidents, which cost communities and drivers millions of dollars and copious time. When vehicles communicate in this fashion, security is paramount. Green Hills Softwareis addressing this security by partnering with Autotalks and Commsignia to address the huge volume of certificates that will be needed to limit communication to authorized transponders.

Many conference speakers noted that innovative offerings will often come from startups, which can pose challenges for large companies that aren’t used to finding and working with tiny companies. OEMs and Tier 1s will have to devise strategies that let them work with many different partners without spending getting bogged down. While cellular communications will play a central role in connected services, these links may not be the most effective technology for OEMs to transmit over the air (OTA) updates, monitor vehicles’ diagnostic and other tasks. Satellite provider Inmarsat has partnered with Continental to offer OEMs a global network. Handling all this data brings management services and big data analysis into the fray. Rush-hour traffic may tax the data handling capabilities of infrastructure equipment that’s sending infotainment files to vehicles while collecting traffic and safety information. The amount of data created by vehicles will soar even higher when autonomy becomes real. That will impact processing requirements on vehicles and off.