Claims:We Claim:
1. A communications system for a work vehicle, comprising:
a. a data bus supported by the work vehicle for communicating messages;
b. a plurality of control units coupled to the data bus; each control unit configured to control a function of the work vehicle;
c. each of the first messages transmitted by each control unit being assigned a transmission update rate, and the processor of each control unit being also configured to schedule the transmission of the first messages to meet the respective assigned update rates; and
d. the processor of each control unit further being configured to perform a request to transmit a scheduled operation
2. The communications system of claim 1, wherein the assigned update rate of one of the first messages can differ from the assigned update rate of another of the first messages.
3. The communications system of claim 1, wherein the data bus includes a controller area network (CAN) data bus.
4. The communications system of claim 1, wherein the predefined number of first messages which can be transmitted on the data bus by each control unit during the predefined time period is one.
5. The communications system of claim 1, wherein the predefined time period corresponds to a control cycle time period of the respective control unit
, Description:Technical Field of the Invention
The present invention relates generally to a communication system in a work vehicle for managing communications between control units that control various functions of the vehicle. More particularly, the invention relates to controlling the transmission and reception of messages between the control units on a work vehicle over a data bus wherein only a predefined number of messages are scheduled for transmission during a predefined time period and wherein received messages are sorted using lookup tables into a set of desired messages for storage
Background of the Invention
Work vehicles including, but not limited to, agricultural work vehicles (e.g., tractors and combines) and construction work vehicles (e.g., dozers and loader-backhoes), perform certain functions based on the interaction of several control units which communicate with each other over a data bus. Each control unit may perform certain functions in conjunction with a particular device coupled to the control unit. For example, a transmission control unit connected to a work vehicle's transmission can direct the transmission to downshift, upshift or maintain a constant gear ratio based upon inputs received from a gear shift lever operated by the vehicle operator, and also based upon data received from other control units via the data bus. The transmission control unit may also receive feedback signals from the transmission. Further, the transmission control unit may itself transmit data (e.g., status and fault data for the transmission) over the bus to other control units. Thus, the transmission control unit may be capable of both transmitting and receiving data via the data bus.
In a typical work vehicle having a data bus populated by multiple control units (e.g., an armrest control unit, the transmission control unit, etc.), each control unit may be required to transmit and receive messages over the same data bus. For example, to properly execute its respective control functions, each control unit on the bus may need to receive certain sensed or calculated input data from other control units at predefined update rates, and may also be required to transmit certain output data for use by the other control units, also at predefined update rates. Further, upon detection of certain events or conditions (e.g., upon detection of a malfunction such as a transmission fault or upon detection of a change in status such as the actuation of an operator input device), the control units may be required to provide a “flag” signal on the bus indicative of the event or condition for use by the other control units. Some of the “flag” signals, such as those indicating a change in an important system input or fault, may need to be transmitted over the bus to the other control units immediately.
As work vehicles become increasingly sophisticated, additional control units continue to be coupled to the data bus and incorporated into the communications system. With each additional control unit, the scheduling of messages on the data bus becomes more complex. In some cases, all of the messages cannot be transmitted as quickly as desired under all conditions without exceeding the bandwidth of the bus. For example, the operator of a work vehicle expects the vehicle to respond quickly to actuations of an operator input device (e.g., actuation of a four-wheel drive switch). Thus, when the input device is actuated, the change in status must be transmitted to the appropriate control unit relatively quickly to avoid a sluggish response. However, in some communications systems, the status of infrequently changing inputs such as operator input devices are transmitted at relatively slow periodic update rates (e.g., every 500 m sec), such that the response time to a change in status is correspondingly slow. In other communications systems, the status of infrequently changing inputs such as switches is transmitted only when a transition is detected, and there is no scheduled periodic update. While not performing periodic updates of these inputs decreases loading on the bus and increases the bus bandwidth available for other signals, the communications system may miss signals due to failures or transients, thereby causing a loss of system functionality. In existing vehicle communications systems, thus, the system designer must often select an appropriate balance between vehicle responsiveness, bus loading, and the ability to gracefully handle transients.
Object of the Invention
The present invention relates to a communications system for a work vehicle. The communications system includes a data bus supported by the work vehicle for communicating messages along with multiple control units coupled to the data bus.
Summary of the Invention
Each control unit controls a function of the work vehicle and includes a processor for controlling communications with at least one other control unit on the data bus. The communications include transmitting first messages onto the data bus and receiving second messages from the data bus. The processor of each control unit schedules the transmission of only a predefined number of the first messages on the bus during a predefined time period. The predefined number is selected so that each control unit can transmit its scheduled messages within the predefined time period.
The present invention further relates to a communications system for a work vehicle. The communications system includes a data bus supported by the work vehicle for communicating messages and multiple control units coupled to the bus. Each control unit controls a function of the work vehicle and includes a processor for controlling communications with at least one other control unit on the data bus. The communications include transmission of first messages onto the bus and reception of second messages from the bus. The second messages include undesired messages and a set of desired messages. The processor of each control unit also sorts the second messages in reference to a plurality of lookup tables to distinguish between the undesired messages and the set of desired messages and saves each of the desired messages in a memory location defined to store the respective message.
Brief Description of Drawings
FIG. 1 is a flow diagram illustrating an exemplary message scheduling process executed by each control unit in accordance with the present invention.
Detailed Description of Invention
In step a request-only message with high priority can be transmitted immediately upon request by another control unit by storing the request-only message at the beginning of the array indexed by i such that the request-only message will be transmitted even if the particular time slot is not open. This will, however, result in delaying any previously scheduled message by one control cycle. An expedited message is transmitted if there is an open slot (or lower priority message slot) prior to the normal transmit time of the selected message. For example, if an event or condition occurs at time .such that the transmission of message M2 is expedited, the timer corresponding to M2 is set to 0 and the message will be transmitted on data bus 40 in time slot 9 according to the message scheduling program illustrated in FIG. 1. Thereafter, M2 will be realigned to be normally transmitted again in time slots 14, 19, 24, etc.
In addition to scheduling the transmission of messages on data bus, microprocessor of each control unit sorts all incoming messages transmitted on data bus into a set of predefined desired messages and saves each of the desired messages to either a shared or a unique memory location. the transmit messaging program of FIG. 1 can also handle the transmission of both expedited and request-only messages. Assume a message M1 has been assigned a predetermined periodic update rate. Also assume the communication system is defined such that the transmission of M1 will be expedited on the occurrence of an event or condition. In this case, the value of the timer corresponding to message M1 will normally be decremented at step during each control cycle until for message M1 reaches 0, at which point M1 will be transmitted at step, and the timer value will be reset to the periodic update rate at step to prepare for the next transmission of M1. However, when the occurrence of the event or condition is detected by microprocessor, the corresponding timer is simply set to 0, and message M1 will be transmitted on the next control cycle (assuming that a time slot is open). Thus, the transmission of message M1 will have been expedited due to the occurrence of the event or condition.
For example, assume message M1 includes the status of a slow-changing operator input device such as a switch. Normally, M1 may be assigned a relatively slow update rate (e.g., 500 msec). However, the system may be defined so that, upon the detection of a change in status of the switch, microprocessor 60 will set the timer for M1 to 0, and the changed status of the switch will be transmitted on an expedited basis.
Now, assume that a message M2 has been defined as a request-only message. In this case, the timer value associated with M2 will be initialized with the value of (FF hex). Normally, message M2 will not be transmitted at any update rate since the timer for message M2 (i.e., the TX_UPDATE_CNTR value for M2) will not be decremented by microprocessor 60 at step due to the test at step (i.e., the value represents “do not decrement timer”). However, upon request for the transmission of message M2, microprocessor will simply set the timer for M2 to 0, and message M2 will be transmitted on the next control cycle (if a time slot is open). Thus, the transmission of message M2 will have occurred on a request-only basis. The request may have been presented to microprocessor from another control unit on bus 40 using an appropriate message. Alternatively, microprocessor may be programmed to transmit a request-only message only upon the detection of a particular event or condition (similar to the expedited transmission mode, except that the request-only message is not normally transmitted at any rate). The timer for M2 will then be reset to at step to await the next transmission request.