Patent Publication Number: US-7722243-B2

Title: Automatic drum rotation control concrete transit mixer truck

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to concrete transit mixing trucks. In particular, the invention relates to a control system for controlling rotation of the drum of the mixer truck while the truck is in motion. 
   Concrete transit mixer trucks are used to transport concrete to a worksite while mixing or agitating the payload of cement, aggregate, sand and water. Fins within the drum mix the payload as the drum rotates. 
   As the concrete constituents are initially loaded into the drum, and as the truck moves to the worksite, the drum is rotated in a first or charge direction, so that the payload tends to move away from discharge opening of the drum. At the worksite, the rotation of the drum is reversed so that it rotates in a second or discharge direction. The fins move the payload toward the discharge opening. A chute attached below the discharge opening delivers the concrete from the drum to the worksite. 
   The drum is rotated by a hydraulic drive. A hydraulic motor in the hydraulic drive is driven by the truck engine through a power takeoff connection. As a result, the speed of the hydraulic motor driving the drum will vary with engine speed. 
   The constantly moving concrete within the drum contacts the interior of the drum and fins. Over time, the fins and the interior lining of the drum will be worn to an extent that they require replacement. The replacement of the drum and the fins is an expensive repair. 
   On average, the drum and fins of a concrete transit mixer truck will require replacement about every 1.5 million revolutions of the drum. Thus, the faster the drum is rotated on average, the sooner the drum and fins will require replacement. 
   Some concrete transit mixer trucks have been provided with a constant drum speed feature, in which the hydraulic motor is operated at a constant speed, rather than at a variable speed that is a function of the truck engine speed. By using the constant drum speed feature while the truck is traveling to the worksite, the constant rotational speed of the drum will generally be less than the average rotational speed of the drum if the hydraulic motor were allowed to vary with engine speed. A 30 to 40 percent reduction in the number of revolutions can be achieved if constant drum speed is used whenever the truck is traveling to or from a worksite. This can yield significant benefits in maintenance costs for the truck. In addition, it can result in significant savings in fuel and a gain in effective horsepower, because the drum is not accelerated whenever the engine accelerates. 
   Despite the benefits of a constant drum speed feature, it has not achieved widespread usage, even among businesses owning the trucks with the constant drum speed feature. Because the driver must turn on the constant drum speed feature when traveling, the use of the constant speed feature is dependent upon the driver remembering to activate the system. In addition, many drivers believe that they can control the truck and the drum better themselves manually, and therefore choose not to use the constant speed feature. 
   BRIEF SUMMARY OF THE INVENTION 
   A control system for transit mixer truck automatically controls the drum drive system based upon sensed vehicle speed. When the speed of the transit mixer truck exceeds a threshold, the control system causes the drum drive system to rotate the drum at a constant speed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a side view of a concrete transit mixer truck. 
       FIG. 2  is a block diagram of a control system for automatically controlling drum rotation at a constant speed whenever the truck is traveling. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a side view of concrete mixing truck  10 , which includes cab  12 , chassis  14 , wheels  20 ,  22 ,  24  and  26 , drum  28 , front pedestal  30 , rear pedestal  32 , hydraulic drive  34 , discharge opening  36 , and chute  38 . Mixer drum  28  holds and mixes concrete, and is supported by chassis  14  between front pedestal  30  and rear pedestal  32 . Rear pedestal  30  has a greater height than front pedestal  32 , so that the rear of drum  28  is elevated. 
   Hydraulic drive  34  rotates drum  28  in a charge direction to mix the concrete while truck  10  is traveling to the work site. When truck  10  is in position at the work site to deliver the concrete, the driver causes hydraulic drive  34  to reverse the rotation of drum  28  so that it rotates in the discharge direction. As the drum rotates, the fins within drum  28  move the concrete toward discharge opening  36 . The concrete is delivered out of drum  28  through discharge opening  36  and down chute  38 . 
   Hydraulic drive  34  is driven by a power take-off from the engine of truck  10 . As engine speed varies, the input drive to hydraulic drive  34  changes speed, which will result in a change in the speed of rotation of drum  28 . With the present invention, a control system automatically engages hydraulic system  34  to operate at a constant speed whenever truck  10  is in motion. The control system receives a signal representative of sensed vehicle speed, and compares that speed to a threshold value. When the sensed vehicle speed is greater than the threshold, the control system engages hydraulic drive  34  to operate at a constant speed. The speed of rotation of drum  28  in the constant drum speed mode is preferably high enough to keep the payload within drum  28  in motion, but low enough to extend the usable life of the drum and fins, as well as saving energy costs and reducing the amount of horsepower of the truck engine that is used for drum rotation. The rotational speed in the constant drum speed mode is less than about 2 revolutions per minute, and preferably about 1 revolution per minute. 
     FIG. 2  is a block diagram showing control system  50 , which automatically controls drum rotation based upon sensed vehicle speed. As shown in  FIG. 2 , control system  50  includes mixer control  52 , user interface  54 , vehicle motion sensor  56 , hydraulic interface  58 , drum control  60 , hydraulic system  62 , drum speed sensor  64 , remote monitoring transmitter  66 , GPS system  68  and engine control system  70 . 
   Mixer control  52  controls the operation of hydraulic system  62  through hydraulic interface  58  and drum control  60 . Based upon control signals supplied by mixer control  52  through hydraulic interface  58 , drum control  60  provides charge, discharge and speed control signals to hydraulic system  62 . The charge and discharge signals control the direction of rotation of hydraulic system  62 . The speed control signal controls the speed at which hydraulic system  62  drives drum  28 . Hydraulic system  62  receives its input power from the power take off (PTO) output of the truck engine. 
   Drum speed sensor  64  provides a drum speed signal as feedback to drum control  60  or mixer control  52 , or both, as shown in  FIG. 2 . The drum speed sensor signal allows closed loop control by either mixer control  52  or drum control  60  when system  50  is operating in a constant drum speed mode. 
   Mixer control  52  receives a signal from vehicle in motion sensor  56  which indicates to mixer control  52  whether truck  10  is in motion. If truck  10  is moving at greater than a threshold speed (such as 10 mph), mixer control  52  provides control signals through hydraulic interface  58  to drum control  60  to cause hydraulic system  62  to operate in the charge direction at a constant speed of, for example, 1 revolution per minute. 
   Once the constant drum speed mode has been initiated, mixer control  52  will maintain hydraulic system  62  in the constant drum speed mode until mixer control  52  receives an input from user interface  54  that either selects manual operation, or selects a discharge mode. Mixer control  52  provides signals to user interface  54  to operate indicators or displays so that the driver can determine what mode system  62  is currently operated in. 
   Vehicle motion sensor  56  can take a number of different forms to provide a signal representative of vehicle speed. For example, in one embodiment vehicle motion sensor  56  is a magnetic sensor positioned adjacent the drive shaft of truck  10 . A magnet is mounted on the drive shaft, so that each time the drive shaft goes through a full revolution, the magnet passes the magnetic sensor, and a pulse is generated. Based upon the pulses generated by the magnet sensor, a vehicle speed signal can be generated. 
   In another embodiment, vehicle motion sensor  56  is a part of GPS system  58 , and makes use of a speed over ground signal derived by GPS system  68 . The vehicle motion signal can also be derived from the speedometer of truck  10 , or from any other location or device where a signal representative of vehicle speed can be derived. 
   Mixer control  52  also communicates with remote monitoring transmitter  66 , which can communicate wirelessly with a remote monitoring system to provide information about operation of truck  10  while it is at the job site or traveling to or from the job site. Remote monitoring transmitter  66  receives information from GPS system  68 , so that the location of truck  10  can be remotely monitored, and information from engine control system  70  so that the operation of truck  10  can be monitored remotely. 
   The signal from mixer control  52  to remote monitoring transmitter  66  provides an indication of when drum  28  is being rotated in the constant drum speed mode. If the driver chooses to override the automatic constant drum speed feature, that information is reported to the remote monitoring system. The information allows management to determine whether its drivers are deliberately overriding the automatic constant drum speed feature, and thus impacting the savings in maintenance and fuel costs that can be gained if the automatic constant drum speed feature is used. 
   The information provided to the remote monitoring system from mixer control  52  can also include information on drum speed, based upon feedback from drum speed sensor  64 . This can allow management to show the driver the variations in drum speed that occur when the driver overrides the automatic constant drum speed feature. 
   The data relating to operation in constant drum speed mode, and driver overrides of that mode, as well as drum speed data, can also be stored in memory by mixer control  52 . The memory can later be interrogated in order to evaluate the performance of control system  50  and the driver. Storage of data in memory carried on truck  10  may be an alternative for those trucks that do not have a remote monitoring capability. 
   The automatic constant drum speed feature eliminates the need for the driver to remember to use the feature. Since the initiation of the constant drum speed mode is triggered by vehicle speed exceeding a threshold, the use of the feature can be maximized. As a result, significant savings in maintenance and fuel costs can be achieved. 
   Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.