Tractor Design & Testing 3(2+1)

Lesson 20. Electronics and guidance system of tractor

2. Electronics and instrumentation in tractors can be used for:

1. Continuous monitoring and tracking  of tractor

2. Advanced Mechanized Farming

3. Continuous monitoring and tracking  of tractor

The instrument panel of a tractor is placed so that the instruments and gauges can easily be read by the operator. They inform the operator about the vehicle speed, engine temperature, oil pressure, rate of charge or discharge of the battery, amount of fuel in the fuel tank, and distance travelled. Vehicle accessories, such as windshield wipers and horns, provide the operator with much needed safety devices. Now a days all these gauges and meters are of electronic types.

An electronic tachometer obtains a pulse signal from the ignition distributor, as it switches the coil on and off. The pulse speed at this point will change proportionally with engine speed. This is the most popular signal source for a tachometer that is used. Electronic speedometers and tachometers are self contained units that use an electric signal from the engine or transmission. They differ from the electric unit in that they use a generated signal as the driving force. The gauge is transistorized and will supply information through a magnetic, Analog or light emitting diode (LED)

Continuous monitoring of engine and location of tractor operation is very important especially when tractor is working at remote areas. Recently New Holland Fiat (I) ltd. has started a system called “Sky watch system” in India for the proper engine monitoring and tracking of its working. Alerts are sent through SMS or online detail of following parameters to the owner. 

• Engine oil pressure

• Water temperature

• Engine hours

• Tractor location

• Fuel level

• Service reminders

Potential Customers of Sky Watch Tractor may be;

• Tractor Fleet Owner

• Custom hiring operators,

• Cooperative service providers

• Tractors Used at Remote Location, like forests, hills etc.

• Tractors used in commercial Applications like Loader, Dozer, Combine, Long Haulage etc.

4. Advanced mechanized farming

World over, various devices or instruments are being introduced for advanced mechanized farming. These includes communication between tractor and implement, navigators, Sensors for soil and plant parameters etc. Some of these are explained below 
 
i. CAN-based tractor – agricultural implement communication ISO 11783 (CANBUS)

The standard forms the backbone of the autonomous agricultural machine system. A logical consequence of the observed trend toward increased use of electronics in tractors and implements is the networking of these components. The supplemental costs of networking represent just a small portion of the overall electronic development costs. Yet they have the potential of significantly enhancing performance of the total system. Only by networking is it possible to move toward the goal of achieving autonomous agricultural machines.as shown in Fig. 20.1. CANBUS have four wire system, including CAN high (yellow), CAN low (green), CAN power (red), and CAN ground (black). Also, CANBUS contains an electric power supply, also referred to as the “active terminator”, with battery power and battery ground to keep CANBUS level at the desired Voltage.

 
Fig. 20.1 Tractor with CANBUS and its wiring diagram (Anon, 2013)

Standardized networking permits multiple utilization of individual components in the network and this reduces development costs. Automatic interventions into the tractor controller, e.g. to modify the operating speed or rounds per minute, permits more effective use of implements. For the farmer and user of the total system standardization also opens up the possibility of combining implements produced by different manufacturers with different tractors. Hence a standard protocol has been introduced in tractors for communication and networking. The standard in the agricultural area for communications between a tractor and an implement (add-on equipment such as a thresher or a mower) is called ISO 11783 or Isobus in short. The international standard consists of the transmission medium (Physical Layer) to application of the entire spectrum of serial communications based on CAN.

Data communication

The ISO 11783 standard is based on CAN, which has been used for a long time in the agricultural industry. This is a passive two-wire bus terminated at the bus ends by a characteristic impedance. Each node must be capable of being connected or disconnected during network operation. An active termination is used to achieve these plug-and-play properties. This means that the node at the end of the bus must automatically terminate it with the characteristic impedance to prevent reflections. The data rate is 250 kbit/s with a sample point of 80 %. Furthermore the entire implement - or at least the electronics - may be supplied with voltage over the bus. Voltages of 12 V or 24 V are permitted. The maximum total length of the bus is 40 m, whereby the length of possible branch lines is limited to 0.3 m. The number of nodes on a bus segment is limited to 30. The wiring used is a 4-conductor, unshielded, and twisted cable for the CAN network and the voltage supply to the controllers and to the active termination. Various types of connectors are defined with different functions: Implement connectors (Breakaway Connector), bus extensions (Bus Extension Connector) and diagnostics (Diagnostic Connector). The entire Isobus is subdivided into at least two segments. The Tractor Bus is a segment, which permits communication within the tractor, e.g. powertrain, valves, etc. The second segment is the Implement Bus. This segment is available for communication between implement and tractor as well as between implements themselves. At least one Tractor ECU (electronic control unit) serves as the interface between the two segments. Communication on the Tractor Bus does not need to be ISO 11783-compatible.

ii. Navigation System

Automated guidance of agricultural vehicles (tractors, combines, sprayers, spreaders) has been motivated by a number of factors—most important is to relieve the operator from continuously making steering adjustments while trying to maintain field equipment or implement performance at an acceptable level. Global positioning system (GPS) guidance systems and auto-steer technology make use of the most efficient routes around a field, eliminating overlaps and skip. Precision Agriculture practices are energy savers. Site specific farming using equipment guidance (autosteer) systems, yield monitoring systems, field mapping and precision crop input application provides many economic and environmental benefits in addition to energy savings. These systems are useful particularly in applying pesticides, lime, and fertilizers and in tracking wide planters/drills or large grain-harvesting platforms. Navigation systems help operators reduce skips and overlaps, especially when using methods that rely on visual estimation of swath distance and/or counting rows. This technology reduces the chance of misapplication of agrochemicals and has the potential to safeguard water quality. Also, GPS navigation can be used to keep implements in the same traffic pattern year-to-year (controlled traffic), thus minimizing adverse effects of implement traffic (Fig. 20.2).

Relatively inexpensive navigation aids known as parallel-tracking devices assist the operators to visualize their position with respect to previous passes and to recognize the need for steering adjustments. These aids are commercially available in several configurations. One system is a lightbar, which consists of a horizontal series of Light Emitting Diodes (LEDs) in a plastic case 12 to 18 inches long. This system is linked to a GPS receiver and a microprocessor. The lightbar is usually positioned in front of the operator, so he or she can see the accuracy indicator display without taking their eyes off the field. The lightbar can be mounted inside or outside of the cab, and the operator watches the “bar of light.” If the light is on the centerline, the machine is on target. If a bar of light extends to the left, the machine is off the path to the left and needs to be corrected. In like manner, if a bar of light extends to the right, the machine is off to the right.

Guidance systems are rapidly growing in popularity as savings permit a very short pay-back time.

Manual guidance – here a display tells the operator where to drive but the operator does the steering. This type of guidance will generally eliminate half the overlap, reducing it from an average of 5-10%.

 
Fig. 20.2: Tractor with satellite navigator (ARAG, Italy)

Automatic guidance – these systems steer the tractor for you and are available in various accuracies. As steering is done for you it is possible to reduce overlap from 10% down to about 1%. All guidance systems use commercially available satellites. for basic vehicle positioning but require a correction signal – there are alternatives with differing degrees of accuracy but the RTK offering 2cm accuracy is