Abstract:
An engine control system for changing engine speed on an agricultural vehicle. The system includes a vehicle control unit for controlling an engine and a transmission mounted within the vehicle, and a tire control unit for detecting the pressure of at least one tire and wherein the engine speed is automatically changed upon detection of an adjustment of the tire pressure.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to an engine control system for changing the engine speed on an agricultural vehicle in response to a change in tyre pressure. More specifically the invention relates to such an engine control system on an agricultural tractor. 
     2. Description of Related Art 
     An agricultural tractor is used both on roads and in fields. The tyre pressure necessitated for work on a field is low, roughly 0.8 bar. The tyre pressure required on road is higher, roughly 2 bar. 
     Some agricultural tractors are fitted with an automatic control system which allows the driver to set the vehicle speed (that is the speed over ground) and other parameters associated with the vehicle whilst the control system automatically changes the engine speed and the transmission ratio simultaneously to reach the desired vehicle speed. Such a system reduces fuel consumption. 
     Field work may require high power and therefore the engine speed may be high, for example 2100 rpm. If the driver then returns to the road, with the automatic control system activated, the system would decrease the engine speed to roughly 1750 rpm. Since the tractor has moved from the field to the road, it is necessary to increase the tyre pressure. Since the air for the tyre pressure control is supplied by an on board compressor which is driven directly by the engine, the performance of the compressor is decreased and as a result it takes longer to inflate the tyres than if the engine speed was the same as that on the field. The driver must therefore remember to deactivate the automatic control system when inflating the tyres and re-activate it when inflation has finished. Often this can be forgotten. 
     It as an aim of the invention to provide an engine control system which overcomes the aforementioned problems. 
     OVERVIEW OF THE INVENTION 
     According to the invention there is provided an engine control system as set out in claim  1 . Preferred features of the invention are set out in the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described, by way of example only with reference to  FIG. 1  which is a circuit diagram showing a driveline on an agricultural tractor provided with an engine control system in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a driveline of a tractor  1  having steerable front wheels  2 , rear wheels  3 , a combustion engine  4 , a transmission  5  and a rear wheel driveline  6 . The rear wheel driveline  6  comprises a rear differential  7  and brakes  8 . A front wheel driveline  9  comprises an all wheel drive clutch  10 , a cardan driveline  11  and a front differential  12 . A steering cylinder  13  pivots front wheels  2 . 
     An air compressor  14  supplies air to an air supply system  15 . The air supply system  15  may comprise an air dryer, air reservoir and other components as described in the applicant&#39;s previous patent applications GB 0911309.3 and GB 0922016.1. Air compressor  14  is directly driven by engine  4  with a constant ratio. A brake system  16  is supplied by air supply system  15 . 
     Combustion engine  4  and transmission  5  are controlled by a tractor or vehicle control unit  20 . The control unit  20  is connected to a tractor main display  21  for input and display of information. To reduce fuel consumption, the driver can select TMS (Tractor Management System) which is an automated mode which means that the vehicle control unit  20  reduces the speed of the engine  4  and simultaneously adapts the ratio of the transmission  5  to keep the ground vehicle speed constant. As the driveline of the front wheels is connected with the driveline of the rear wheels by a fixed gear ratio, consideration of the rear wheel driveline is sufficient to explain how TMS works. 
     If the speed over ground of the vehicle v v  is desired to be 50 km/h and the effective perimeter U w  of the rear wheel is about 5,555 meters, the rear wheel rotation speed n w  must be about 150 rpm:
 
 n   w   =v   v   /U   w =50 000 m/h 5,555 m 60=150 rpm
 
     The drive torque of the combustion engine  4  is transmitted via the transmission  5  (of a CVT type) to the front wheel  2  and rear wheels  3 . 
     Between the transmission  5  and the rear wheels  3  the overall ratio is constant and can be taken as i G =32.97. 
     The output rotation speed n T  of the transmission  5  is calculated by the formula:
 
 n   T   =i   G   ×v   v   /U   w =4.956 rpm
 
and must be kept constant to achieve a constant speed over ground of 50 km/h.
 
     Presuming that engine speed of the combustion engine  4  is equal to the input speed into transmission  5  and is at its maximum of n Emax =2.200 rpm, the current value of the variable gear ratio of transmission i T1 5 is:
 
 i   T1   =n   Emax   /n   T =0.44
 
     If TMS reduces engine speed to a minimum value n Emin =1750 rpm, the gear ratio of transmission  5  must be adjusted to:
 
 i   T2   =n   Emin   /n   T =0.35
 
to keep vehicle speed constant. This adjustment is especially advantageous when having a CVT type transmission but may also be realised by a stepped, automatically shifted transmission used in tractors or trucks.
 
     As air compressor  14  is drivingly connected to the engine  4  with a ratio of i c =1,116, performance of the air compressor  14  varies with engine speed:
         At maximum engine speed n Emax =2200 rpm, compressor speed is n c1 =2.200×1,116=2.455 rpm resulting in an air delivery of 490 l/min.   At minimum engine speed n Emin =1.750 rpm, compressor speed is n c1 =1.750×1,116=1953 rpm resulting in an air delivery of 415 l/min. So a reduction of engine speed caused by TMS reduces the rate of air delivery by compressor  14  by about 15%.       

     To adjust the tyre pressure, the vehicle is equipped with a tyre pressure control system (TPCS) which comprises steerable front wheels  2  and non steerable rear wheels  3 . Wheels  2 ,  3  are equipped with a rotary feed through arrangement  30  to guide air from the chassis to the wheels  2 ,  3  and then into tyre volumes  2   a ,  3   a . The figure shows a feed through arrangement  30  where a supply system and tyre volume  2   a ,  3   a  are connected all the time. Alternative feed through arrangements are described in the applicant&#39;s patent application Nos. GB 1016662.7, GB. 0 1016661.9, GB 1021928.5, GB 1021929.3, GB1016662.7. 
     Each wheel has a respective control valve  31  to inflate or deflate tyre volumes  2   a ,  3   a . For deflation, air is discharged from tyre volume  2   a ,  3   a  to the outside via discharge outlet  31   a  of each valve. Inflation is provided by connecting supply system  15  to the tyre volumes  2   a ,  3   a.    
     Each control valve  31  is controlled by a tyre TPCS control unit  32 . TPCS tyre control unit  32  is connected to vehicle control unit  20  or alternatively may be integrated in vehicle control  20 . 
     TPCS control unit  32  is connected to a TPCS display  21  for the input of, for example, a set tyre pressure value and for the display of information. TPCS display  21  may also be integrated in tractor main display  21  as described in the applicant&#39;s patent application No. GB 0916233.3. 
     The tractor maybe operated under various different modes which affects how the engine control system of the present invention functions. These modes are explained below: 
     Mode 1: Tractor Management System (TMS) 
     The tractor may be driven in TMS mode for low fuel consumption. On the field, the tractor may operate with a tyre pressure of, for example, 0.8 bar. After field operation, the operator (or an automatic system) will want to increase tyre pressure to about 2 bar. As the TMS setting has reduced engine speed to around 1750 rpm, the air compressor has a reduced speed of 1953 rpm resulting in an air delivery of 415 l/min. The operator may recognise this and deactivate TMS and manually increase engine speed by using an electronic hand throttle. This is uncomfortable and may result in the driver forgetting to re-activate TMS again after inflation. 
     The engine control system of the present invention will preferably automatically de-activate the TMS function and increase engine speed, to 2200 rpm for example, which will result in a higher air compressor speed of around 2455 rpm and an air delivery of 490 l/min. This will save about 15% of the tyre inflation time due to the approximate linear relation between compressor speed/air delivery and the tyre inflation time. After reaching the set tyre pressure value, TMS is activated again and the engine speed will return to the speed it was before TMS was de-activated. 
     The tractor may have other automatic driveline controls which need to be taken into account if the engine control system of the present invention is used which are for example: 
     Mode 2: Engine Overloading 
     In vehicles with automatically shifted, stepped transmissions, and CVT transmissions, the operator can set up engine overloading. In this mode the engine speed is allowed to be reduced by load until a specified speed is reached before shifting to the next gear/or adjusting gear ratio. When the engine control system of the present invention is used whilst the tractor is in this mode, the engine control system preferably deactivates operation of the tractor in this mode. 
     As with TMS mode, when the set tyre pressure is reached the engine speed will return to the speed it was before the engine overloading mode was deactivated. 
     There are also vehicle operating modes wherein an automatic increase of the engine speed may cause undesirable operation of the vehicle or damage for components. Among these modes are: 
     Mode 3: Constant PTO 
     If an implement is attached to the PTO (power take off shaft) the PTO will require a constant power. In this case if an increase in tyre pressure is made, the automated engine control system of the present invention may not result in an increase in engine speed. For the TPCS this may result in lower performance but ensure tractor operation. So, when the PTO mode is in use the engine control system of the present invention will preferably be de-activated. 
     Mode 4: Coast Operation 
     When a vehicle is going downhill, the vehicle weight keeps the engine in rotational movement. This is known as a coast or pull mode and may result in an increase in engine speed. This mode is detected by, for example, an increase in engine speed without an increase in fuel injection, or alternatively by means associated with the CVT transmission as described in applicant&#39;s patent application No GB 0800613.2. 
     To protect the engine from obtaining a high engine speed (for example 2600 rpm) which could cause damage, the transmission is downshifted/adjusted to brake the vehicle. The higher the engine speed in coast operation, the earlier the driver must manually decelerate the vehicle by using the service brake/park system or engine brake. In this mode an automatic increase of the engine speed by the engine control system in accordance with the invention may cause an unexpected vehicle acceleration. 
     So in this mode, it is not desirable that the engine control system increases the engine speed to improve tyre inflation as this would then require action by the operator to reduce the engine speed. Instead, the engine control system according the present invention will preferably be de-activated under coast operation mode. 
     The engine control system of the present invention preferably checks the mode the tractor is operating in before it changes the engine speed. The tractor mode is registered with the vehicle control unit and the TCPS control unit checks the mode with the vehicle control unit before increasing engine speed. 
     The engine control system may advantageously reduce engine speed to a default setting after a tyre pressure limit is reached. 
     It is envisaged that there may be other modes beside those already described which require an automatic increase of the engine speed whilst adjusting tyre pressure. Further, there may be additional modes of vehicle operation which prohibit an engine speed increase which lie within the scope of the present invention. 
     In the shown embodiment, the transmission is a stepless hydrostatic-mechanical power split drive. It is envisaged that any other kind of transmission system may be used, such as:
         a combustion engine and a stepped shift transmission with hydraulic/electric shift means;   an electric drive system having a combustion engine and an electrical-mechanical power split drive;   an electric drive system having a combustion engine and an electric motor replacing a central transmission;   an electric drive system having a combustion engine and an electric motor related to at least two wheel hubs.       

     As all these transmission systems are capable of adjusting engine speed and accordingly the speed of the drive/wheels to reduce fuel consumption they all fall within the scope of the invention.