When your vehicle is stopped but has its engine running, the fuel used is not contributing towards moving the vehicle. This contributes to fuel use inefficiency of the vehicle.
Situations where you may have the engine running but not moving the vehicle include when the car has just been started and getting warmed up, when you are waiting for passengers, at the stop sign, or when you are waiting for the traffic lights to turn green. Of course it may not make sense to do this all the time because, for example, your idling at the stop sign is only until you have room to maneuver yourself onto the road that you are turning into. In this case, the length of idling time is unpredictable. However if this idling time is predictable, then it makes it easier for the decision to turn the engine off.
Traffic lights are cases when the idling period is much more predictable. Cars stopped at the lights will have no recourse but to wait for the light to turn green before they can move forward. The wait for the green light is not consistent but can vary from traffic light to traffic light depending on the implementation, time of day, the traffic situation and the sensor data used by the traffic light system to control the frequency of the lights changing and the wait duration for the lights to change.
Drivers can decide to turn off their vehicles when stopped at the red light to save fuel. However, this means constant monitoring and guessing when they should turn off and on the engines, and contributes to another decision that burdens the vehicle operator. A faulty decision here probably will not contribute to a traffic accident, but certainly make for more irate drivers, and potentially adds to traffic congestion.
Certain parts of Europe and Asia have traffic lights that use visible displays that show the wait time before the red light changes to green. This could be used by the drivers to get ready going from a stopped position, or decide when they should turn the engine off and on again if they choose to do that to save fuel. However, this is not be effective all the time as the display may be blocked by other vehicles, or visibility could be obscured by distance or weather conditions.
The solution proposed here, called the Smart Driving Manager, provides a means to provide the necessary information to the vehicle operator that is effective and reliable. It makes it much easier for the driver to decide on when he should turn the engine off and on again, or it can even be used to achieve the engine shutoff in a more automated and controlled manner using an automatic engine start-stop system.
From the driver’s perspective, the Smart Driving Manager appears as a module that can be attached to a convenient location near the dashboard or the vehicle’s driver’s display area.
In its simplest form, the Smart Driving Manager will indicate the red light timer countdown value when the driver has stopped at the traffic lights. Depending on what that value is the driver can decide to stop or start the engine. For example if the countdown value is higher than 30 seconds, turn the engine off. As the value goes down to 5 seconds, start the vehicle and put it in gear to prepare for the green light.
Benefits or Usefulness To Consumers
According to the US Department of Energy, less than about 13% of the energy from the fuel you put in your tank gets used to move your car down the road in urban driving. This number goes up to 20% for more rural driving dues to the reduced congestion, and traffic stops.
The rest of the energy is used for accessories such as air-conditioning, or lost to engine and driveline inefficiencies and idling. It is clear that there still exists significant potential to improve fuel efficiency with advanced technologies (Fig. 1).
In urban driving, standby/idling alone contributes to up to 17% of the energy lost, a number that actually exceeds the fuel energy used to move the vehicle. Being able to accurately predict and use the wait period information correctly at traffic lights and turning off the engine instead of idling at traffic lights will contribute to reducing this standby/idling loss.
There may be some concerns that stopping and restarting the vehicle will consume more fuel and have a negative impact on the vehicle, but modern vehicles that use fuel injection technology instead of carburetors do not have these issues. The typical rule of thumb is if you are going to idle for more than 60 seconds or even 30 seconds, it is more fuel efficient to turn the engine off.
Having a system such as the Smart Driving Manager will offload and automate the much of the decision making process and monitoring required of the driver for the traffic lights changing. This will make the idling shut off technique be more practical and dependable.
Other important benefits include less noise pollution with more engines off and the emission of CO2 into the atmosphere is reduced.
Detailed Description Of The Design
As mentioned before the device will appear as an appliance to the driver. This appliance will provide the red light timer countdown value for the driver to make his decision to turn off the engine and when to turn it on again. The Smart Driving Manager can also support vehicles that have automatic engine start-stop system module.
There are several challenges addressed by this Smart Driving Manager solution. It is important to be able to direct the timer data to the appropriate vehicles. This is solved by using data packets from the SDM_TX that contain direction information that can be used to match the direction information provided by SDM_RX installed in the vehicle.
Noise and interference from traffic lights for intersections in close proximity can also be another problem. This is taken care of by using a receiver system that will lock in to the strongest signals that are transmitted from the closest SDM_TX transmitter.
The solution includes the following two sub-systems:
- Smart Driving Manager Transmitter (SDM_TX)
- A traffic light system that has the capability to provide and communicate this red light timer countdown information to the vehicle.
- The SDM_TX obtains the traffic light data from the existing traffic lights control system. The data from the existing traffic control computer provide the data for the SDM_TX to generate the necessary timing information for the traffic lights that are controlled for that particular intersection.
- The traffic timer data is broadcast at regular intervals to the vehicles with a radio transmitter and antenna system that is tunable to several channels. Each SDM_TX uses only one frequency channel. The frequencies of multiple SDM_TX’s in close proximity must be different from each other in order for the receiver to recognize that data is from different SDM_TX’s. This provides sufficient separation of transmitted signals between traffic lights that are in close proximity and allows the signals to be picked up by the SDM_RX in the targeted vehicles.
- The SDM_TX should be able to cover a range of 250meters. The transmitter’s signal strength can be configured for optimum coverage but at the same time it should not be too strong to overwhelm the next SDM_TX located nearby.
- Smart Driving Manager Receiver (SDM_RX)
- The SDM_RX system is able to identify and accept the data that is meant for the vehicle and to provide the red light timer countdown information to the driver and the automatic start-stop system.
- The SDM_RX system has a signal reception system that is capable of locking in to the strongest signal among several channels that it is scanning for. This allows the SDM_RX in the vehicle to lock in to the traffic control signals from the traffic light system or SDM_TX meant for the vehicle.
- On receiving the signal from the SDM_TX, the SDM_RX system will provide the timer information for the decision to turn the vehicle’s engine off and on again.
- The vehicle’s engine turn off can be a manual or an automated operation. The SDM_RX can prompt the driver to turn off and on the engine with a set of prerecorded audio commands or visually with a display. In the automated mode, the SDM_RX can turn off and on the engines by controlling the vehicles’ Integrated Starter Generator/Auto Start Stop System.
The SDM_TX transmits information to the vehicles stopped at the intersection where the traffic light is located. It has to be able to transmit the timer data to the vehicles stopped at each part of the 4 ways. The transmitted information needs to be for the appropriate red light and the SDM_RX, the receiver system in the vehicle, must be able to understand and accept only the timer data meant for those vehicles waiting at the particular red light (Fig. 2). Therefore, the SDM_RX has to know the direction the vehicle is facing, and the data transmitted by the SDM_TX has to include this orientation or direction information of the vehicles at the particular red light.
In order to send the data packets and have these packets be received by the specific groups of vehicles at the different red lights, the format of the packet needs to have the vehicle orientation information, in addition to the timer data. A SDM_TX packet can look like the below (Fig. 3).
The data telegram or packet consists of the following fields:
- The Start of SDM Frame header identifies the packet as the type used for Smart Driving Manager. The SDM_RX receiver can use this header id to filter out non-SDM transmission and only accept SDM packets. (8 bits)
- The Source Info1,2 of the packet that can include the particular traffic light installed, the city and the state, or the SDM device the sent the RF signal. (16 bits)
- The Direction or orientation of the vehicles being targeted by the data. This is equivalent to a multicast address for the vehicles at a particular red light. The received packet’s SDM Direction data will be compared to the direction/orientation data obtained from the built-in compass in the SDM_RX. If they match, the packet will be forwarded to the SDM_RX for processing and utilization. The ‘-L’ packets are for the lights for vehicles in the ‘turn Left’ lane. Thus, there are potentially two sets of timer data that have to be discerned. The driver can decide this manually when given the two sets of timer values, or if automated, this can be gated by the turn indicator signal. (3 bits)
- The Timer Data contained in the packet is the timer countdown value. The units for this can be in seconds or tens of seconds, depending on the required precision, and the need to reduce the size of the packets. (5 bits)
- The CRC field ensures the integrity of the received packet. (16 bits)
We take an example of a typical 4-way intersection with separate lights for left turns (Fig. 4).
The two parts of the solution comprise of the Smart Driving Manager Red-Light Timer Transmitter (SDM_TX) and the Smart Driving Manager Receiver (SDM_RX).
Smart Driving Manager Red-Light Timer Transmitter (SDM_TX)
The SDM_TX is integrated or coupled to the existing traffic light control system at the intersection. The SDM_TX obtains the traffic lights data from the existing traffic lights control system. The data from the existing traffic control computer provide the data for the SDM_TX to generate the necessary timing information for the traffic lights that are controlled for that particular intersection (Fig. 5).
The primary component of the SDM_TX is the Infineon PMA7110, a device with an RF transmitter integrated with an embedded 8051 microcontroller. The Infineon PMA7110 is used for the main control functions of the SDM_TX to read the traffic lights data from the existing traffic control system, generate packets with CRC, and transmit these packets to the SDM_RX located inside the vehicles approaching or stopped at the traffic lights. The PMA7110 has 4 independent 16-bit built-in timers for the red lights countdown data, up to 32kbps, with on-chip tuning of the crystal oscillator.
The unidirectional communication between from the SDM_TX and the SDM_RX system is achieved with radio frequency signals operating at 865-870MHz. Other frequencies can be used, but 865-870MHz was chosen as a convenient band to use for the application to match the receiver device’s operational frequency.
The PMA7110 contains a Multi-band (315/434/868/915MHz) ASK/FSK UHF transmitter with selectable RF transmission output power 5/8/10dBm on 50 H load with fully integrated VCO and PLL synthesizer. This allows the SDM_TX to be configured for optimum transmitter output and coverage but at the same time not too strong to overwhelm the next SDM_TX, and for tuning the RF transmitter frequency to the desired value within the band (Fig. 6).
Each of the SDM_TX located at the traffic control system at the traffic lights intersection will have to be set up with the proper orientation and compass data for the different red lights at the intersection. This can be done with a configuration utility for the information to be entered and stored into the SDM_TX’s non-volatile memory. The information will be tagged to the packet transmitted to the SDM_RX and serves as the destination address for the vehicles targeted by this transmission.
Smart Driving Manager Receiver (SDM_RX)
The SDM_RX resides in the vehicle. The following describes the main components of the SDM_RX.
- Infineon XC866 microcontroller.
- a. This 8-bit 8051 based microcontroller serves as the processing engine of the SDM_RX.
- b. The XC866 also has enhanced communications supporting the Control Area Networking (CAN) bus and Synchronous Serial Communications (SSC) that support Serial Peripheral Interface (SPI). These communication technologies are well suited and have been deployed for automobile applications.
- c. In the case where the SDM_RX includes automated engine stop start, the XC866 can be used to control the vehicle’s engine starter mechanism.
- Infineon TLE 5011 - GMR Based Angular Sensor, Compass/Magnetic Sensor
- a. This is the GMR angular sensor and provide the ability to determine orientation of the device relative to the Earths magnetic field, essentially providing compass information.
- b. The TLE 5011 can be interfaced to the XC866 using SSC.
- c. Calibration information can be stored in the XC866’s non-volatile FLASH memory.
- d. The full 16-bit resolution of the TLE5011 is not needed since the vehicle needs to only be pointing in the general direction and does not need to be fully aligned with 16-bit precision. Using all 16-bits can cause non-matching of the SDR_TX packet with vehicles that are not precisely lined up, and these packets will be filtered out. 3-bit precision may be sufficient, but the optimum precision can be determined through further studies.
- e. The XC866 communicates with the TLE 5011 using SSC, and with the TDA523x using SPI.
- Infineon TDA523x Series ASK/FSK Autonomous Receiver
- a. This ASK/FSK receiver works for the frequency bands 302 – 320 MHz, 433 – 450 MHz, and 865 – 870 MHz. It contains a fully integrated RF-synthesizer and offers multi-channel capability. The SDM application uses the frequencies from 865-870MHz.
- b. The TDA523x has a multi-channel PLL receiver that can support up to 17 subchannels. This allows the SDM_RX to detect signals from different SDM_TX.
- c. The TDA523x receiver is configured to lock in to the strongest signal within the operating band, thus ensuring that it is receiving signals from the SDM_TX at the closest traffic intersection. The TDA523x device has a Receive Signal Strength Indicator (RSSI) generator that can be used to determine the relative input signal power of the received signal. The RSSI value can be read from the peak detector registers. The XC866 device can then determine from the RSSI input and the associated channel, the correct frequency to lock on to.
- d. The XC866 communicates with the TDA523x using SPI.
- The SDM_RX system can be powered by the vehicle’s 12V supply.
- The vehicle operator or driver can receive the timer and status information either through a set of audio messages and/or have this information be displayed through a variety of display devices. The complexity and quality of the user interface capability can be decided upon and designed depending on the cost performance requirements.
- The display can be a simple display with digital output displaying the countdown values. Controls can be implemented with switches to reset the SDM_RX, or run the calibration routine for the TLE5011 compass functionality.
- The audio function is implemented with a set of pre-recorded messages stored on the XC866. A Sigma Delta modulator DAC is used for inexpensive, good quality audio output generation.
The TDA523x is set up work in the self-polling mode to autonomously poll for incoming RF signals. The receiver switches off and goes to sleep in between scans to save power. If a incoming signal meets the wake requirements such as an ID match, then the device is configured to generate an interrupt to the XC866 when a new packet has been received. The TDA523x support multiple channels and configurations. This allows not only signals from different SDM_TX’s using different frequency channels to be recognized by the SDM_RX, but the SDM_RX can be enhanced to monitor other sensors as well such as tire pressure monitoring (Fig. 7 and Fig. 8).
Summary and Conclusions
The Smart Driving Manager is a system that can assist the drivers to stop and start their vehicles at traffic lights. The Department of Transportation estimates that 17 billion gallons of gasoline are wasted every year due to vehicles idling while motionless. The ability to intelligently stop and start your vehicles will drastically reduce this enormous waste. Even if we just estimate the waste at 10%, the savings from the SDM solution can potentially contribute to over 1.7 billion gallons of gasoline.
In addition to the engine start and stop feature, this Smart Driving Manager can be used to monitor various items that can affect the fuel economy of the vehicle, the safety of the occupants and enhance the driving experience. Air pressure in the tires, excessive fuel consumption due to excess weight or driving behavior, can be monitored and reported to the driver. The built-in compass functionality of the SDM_RX can provide an additional navigational data checkpoint and further assist the driver. Remote engine start can also be implemented.
Today, there are start/stop solutions designed into smarter vehicles to improve their fuel efficiency. Vehicles that use these start/stop solutions are reaping the benefits of not wasting fuel in running the engine of a non-moving vehicle. However, these existing start/stop solutions are costly and not that easily added on to vehicles that are already on the road.
The SDM solution allows the implementation of a solution that is relatively inexpensive, modular, and scalable, both in the installation of the SDM_TX or the SDM_RX. The SDM_TX can be deployed first for intersections that are busier to get the most benefit from the higher traffic flow at these intersections. The SDM_RX can be as simple as a dashboard device that prompts and provides audio and visual cues to the driver to assist in the manual operation of the vehicle. More advanced versions of the SDM_RX can be implemented to interface to the vehicle’s engine’s on off mechanisms.
From a usage point of view, the SDM solution does not require a complete re-installation of existing traffic light systems nor is it a solution that can be only installed in new vehicles. The SDM_TX and SDM_RX are units that can be retrofitted to existing traffic light systems and vehicles that are already on the road. In its simplest form, the SDM_RX will provide information to the driver to assist the driver to manually operate the vehicle. In its more sophisticated version, the SDM can be integrated with the vehicle’s control system to provide automated optimizations in the vehicle’s operation to enhance fuel economy, safety and the overall driving experience.
- Example energy flows for a late-model midsize passenger car: (a) urban driving; (b) highway driving. Source: U.S. Department of Energy. http://en.wikipedia.org/wiki/Image:Energy_flows_in_car.png
- PMA7110 Product Documentation - RF Transmitter IC with embedded 8051 Microcontroller, LF 125kHz ASK Receiver and FSK/ASK 315/434/868/915 MHz Transmitter
- XC866 - 800MHz Receiver Documentation
- TLE 5011 Product Documentation - GMR Based Angular Sensor, Compass/Magnetic Sensor
- TDA523x Series Product Documentation- ASK/FSK Autonomous Receiver Family