Patent Publication Number: US-2021163064-A1

Title: Utility vehicle braking

Description:
The present invention relates to braking systems for utility vehicles, particularly self-propelled four-wheel drive agricultural machines, and more particularly to such systems where controlled braking is applied to the inner wheels of a turning vehicle in order to reduce turning radius. 
     With the growing size of agricultural machinery, the net power of agricultural machines such as tractors is also increasing. This also results in an increase in tyre size to transfer the power to the ground. The increasing tyre size also helps to reduce soil compaction which has negative impact on crop growth. However, the increased tyre size has the result that, when the vehicle is turning, parts of the tyres move towards the area where the engine is installed (engine periphery). Therefore there is a limitation in steering angle which impacts the steering capability in terms of turning radius, but the minimum turning radius is very important for manoeuvrability (e.g. when turning on a headland in a field). In addition, stricter exhaust gas emission requirements result in more installation space being required in the front area (e.g. for cooling systems or exhaust emission treatment systems), especially in the engine periphery penetrated by the tyres during steering. Enlarging the installation space in this area, especially the width transverse to driving direction, limits the steering angle of the tractor. A narrow track width also limits the steering angle which is an issue for e.g. the US market which has a strong demand for narrow-tracked tractors so that the tyres are able to move along narrow crop rows. 
     To mitigate the aforementioned problems it is known to have steering brake system. An example of a brake arrangement for steering braking of a utility vehicle is described in commonly-assigned European patent application EP-A-2896540. The vehicle has a cardan brake acting on the front axle, and separate left and right service brakes on the rear wheels. The left rear service brake is activated by movement of a first brake lever and the right rear service brake is activated by movement of a second brake lever. The left and right rear service brakes and the cardan brake are activated together by movement of both brake levers. To apply steering braking, only one of the brake levers is applied. 
     Utility vehicles intended for operation at relatively higher speeds are normally provided with two separate braking circuits and service brakes on each axle, whereby each circuit is assigned to one axle (in cars, the split is more commonly transverse). In consequence, for a utility vehicle the service brake force ratio for front and rear axle is thereby  50 / 50  which means that each axle is provided with only 50% of the total available braking force under normal operation. In the case of steering braking only with the rear axle (as in EP-A-2896540 above), the braking of only one side results in only half of the rear axle capacity being used, so only 25% of the total available braking force is applied. Compared to vehicles without front service brakes (which provide 100% of the steering force on the rear axle and 50% on one side during steering braking) this results in a major disadvantage of insufficient steering brake capability. 
     The main effect used during steering braking is that the braking of the rear axle on one side results in that the vehicle being virtually rotated about a vertical axis towards the inner curve side (similar to a track type tractor during differential steering). The front of the tractor is thereby moved out of the track which is given by the Ackermann-steering-track. The high weight of modern high horse power tractors is also present at the front and increases the front axle load. In combination, with the bigger wheel sizes on ail axles, it is getting increasingly difficult to move the inner front wheel inwards during steering braking. 
     In accordance with a first aspect of the invention there is provided a method of brake steering in a four-wheel drive utility vehicle having a driven front axle carrying at least two front wheels, a driven rear axle carrying at least two rear wheels, a powertrain delivering torque to the front and rear axles via a connecting shaft, a controlled clutch arrangement in the connecting shaft operable to vary the distribution of delivered torque between the front and rear axles, and independently operable service brakes on each of the front and rear wheels, the method comprising;
         on the vehicle entering a turn, applying the service brakes of the front and rear wheels on the inside of the turn and adjusting the clutch arrangement to adapt the share of the available torque between the front and rear axles.       

     In addition to facilitating tighter turning in e.g. headland turns for big tractors, the controlled adaption of the torque transfer during steering braking results in more efficient curve driving, with reduced scrubbing leading to a reduction in soil damage. Furthermore, power is better transferred to the ground for better efficiency. 
     Where the vehicle is additionally provided with independently-operable parking brakes on each of the rear wheels the method may further comprise, on entering a turn applying also, and to a predetermined level of braking force, the parking brake on the rear wheel on the inside of the turn. Suitably, the level of parking brake braking force applied to a rear wheel on entering a turn is substantially proportional to the level of service brake braking force applied to the same wheel. 
     Preferably, the level of service brake braking force applied during a turn may be determined by the level of pressure exerted by a user of the vehicle on a brake control of the vehicle. 
     Preferably, on entering a turn, the share of the available torque delivered to the front axle is approximately 30% higher than that delivered before entering a turn, or the share may be controllably varied based on one or more of the following factors:
         gross weight of the vehicle;   amount of front and/or rear ballasting carried by the vehicle;   weighting information pertaining to a towed or carried implement;   extent of measured wheel-slip for one or more wheels of the vehicle;   tyre pressure in one or more tyres on respective wheels of the vehicle;   angle of turn directed by a user of the vehicle;   current speed of the vehicle;   ambient conditions external to the vehicle.       

     Also in accordance with the present invention there is provided a driveline or a four-wheel drive utility vehicle comprising:
         a driven front axle carrying at least two front wheels;   a driven rear axle carrying at least two rear wheels;   a powertrain delivering torque to the front and rear axles via a connecting shaft;   a controlled clutch arrangement in the connecting shaft operable to vary the distribution of delivered torque between the front and rear axles;   independently operable service brakes on each of the front and rear wheels; and   a control system coupled with the powertrain, clutch arrangement and service brakes, and configured to detect when the vehicle enters a turn, apply the service brakes of the front and rear wheels on the inside of the turn, and adjust the clutch arrangement to adapt the share of the available torque between the front and rear axles.       

     Preferably the driveline further comprises independently-operable parking brakes on the rear wheels, with the control system being configured on detecting that the vehicle is entering a turn to apply also, and to a predetermined level of braking force, the parking brake on the rear wheel on the inside of the turn, suitably with a level of parking brake braking force that is substantially proportional to the level of service brake braking force applied to the same wheel. 
     Further features of the driveline are recited in the attached claims, to which attention is now directed, and the disclosures of which are incorporated herein by reference. 
     Further in accordance with the present invention there is provided a utility vehicle including a driveline as set forth above. The utility vehicle may further comprise a geographical positioning system coupled with the control system, with the control system being configured to not implement the above-recited method of brake steering on determination that the vehicle is outside of a predetermined geographical area. 
    
    
     
       Further advantages of the invention will become apparent from reading the following description of specific embodiments with reference to the appended drawings in which:— 
         FIG. 1  is a representation of a utility vehicle, in the form of a tractor, suitably provided with a braking system embodying the present invention; 
         FIG. 2  is a schematic representation of the driveline arrangement of the tractor of  FIG. 1 ; 
         FIG. 3  is a schematic circuit diagram of a first embodiment of a pneumatically operable brake system for the tractor of  FIG. 1 ; 
         FIG. 4  is a schematic circuit diagram of a further embodiment of a pneumatically operable brake system for the tractor of  FIG. 1 ; 
         FIG. 5  represents a method of brake steering as may be effected by the tractor of  FIG. 1 ; and 
         FIG. 6  represents a relationship between applied service and park brake forces. 
     
    
    
     Referring to  FIG. 1 , a utility vehicle in the form of a tractor  10  is shown having a cab  12  and an engine compartment  14 . A chassis  16  which is partly visible connects a front wheel suspension and steering assembly (indicated generally at  18 ) and a rear axle assembly (indicated generally at  20 ). A vehicle control system (represented schematically at  62 ) is coupled to receive data from a number of sensors  11 : such data may include (but is not limited to):
         gross weight of the vehicle;   amount of front and/or rear ballasting carried by the vehicle;   weighting information pertaining to a towed or carried implement;   extent of measured wheel-slip for one or more wheels of the vehicle;   tyre pressure in one or more tyres on respective wheels of the vehicle;   angle of turn directed by a user of the vehicle;   current speed of the vehicle;   ambient conditions external to the vehicle.       

     Further inputs to the control system  62  may come from a user-operable input device such as a touchscreen display and input device  13  positioned in the vehicle cab  12 , and a geographical positioning system for the vehicle. 
     Referring additionally to the driveline arrangement of  FIG. 2 , a prime mover such as an internal combustion engine  22  drives an input shaft  24  of a gearbox/transmission unit  26  via a flywheel  28 . The transmission unit  26  may be configured to adapt gear ratios in a stepped or continuously variable mode to drive first  30  and second  32  output shafts. 
     Output shaft  30  drives the vehicle rear axle left and right driveshafts  34 L,  34 R via rear axle differential  36 . Note the designations “front”, “rear”, “left” and “right” as used herein are taken from the point of view of a user/driver sat facing forward in the cab  12 . The rear axle assembly  20  further comprises left and right rear axle service brakes  38 L,  38 R (with respective park brakes  40 L,  40 R), left and right rear axle final drives  42 L,  42 R, and left and right rear wheels  44 L,  44 R. As shown, the service and park brakes may share a common set of brake disks  39 L,  39 R, with the service brake being spring-biased to the open position and the park brake spring-biased to the closed position. Such an arrangement is described in e.g. German utility model DE9204417U1. 
     In like manner, output shaft  32  drives the vehicle front axle left and right driveshafts  46 L,  46 R via cardan shaft  48  and front axle differential  50 . The front axle assembly  18  further comprises left and right front axle service brakes  52 L,  52 R, left and right front axle final drives  54 L,  54 R, and left and right front wheels  56 L,  56 R. Between the output shaft  32  and front axle differential  50  there is provided an all-wheel drive (AWD) clutch mechanism  60  by operation of which, under the direction of a vehicle control system  62  (described further below), the drive to the vehicle front wheels  56 L,  56 R may be selectively engaged or disengaged, or engaged with a controllably variable degree of clutch slippage to enable the engine output torque delivered to the front axle assembly  18  to be controllably varied such that the share of output torque between front and rear axles may be adapted. 
     A further output shaft  64  of the transmission unit  26  may be provided to drive a power take-off (PTO) shaft in conventional manner. 
       FIG. 3  shows a schematic circuit diagram of a pneumatically operable brake system for the tractor  10  of  FIG. 1 . A first brake circuit C 1  is provided for activating left and right rear service brakes  38 L,  38 R individually for application to left and right rear wheels  44 L,  44 R respectively. This first brake circuit C 1  comprises a first pressure control valve  70  and supply lines L 3 , L 3   a , L 3   b , L 4 , L 4   a  and L 4   b . Left and right rear service brakes  38 L,  38 R are operated by respective left and right associated brake relay valves  72 L,  72 R. Lines L 3   a  and L 3   b  are linked by a shuttle valve  74  which passes the greater pressure in either of the lines to proportional valve  76  in the control circuit for rear park brakes  40 L,  40 R (described below). 
     A second brake circuit C 2  is provided for activating left and right front service brakes  52 L,  52 R individually for application to left and right front wheels  56 L,  56 R respectively. This second brake circuit C 2  comprises a second pressure control valve  78  and supply lines L 1 , L 1   a , L 1   b , L 2 , L 2   a  and L 2   b . Left and right front service brakes  52 L,  52 R are operated by respective left and right associated brake relay valves  80 L,  80 R. 
     The service brakes  38 L,  38 R,  52 L,  52 R are activated by the driver by two levers, such as two foot pedals  82 L,  82 R. Left or first foot pedal  82 L, when pressed opens a left rear brake valve  84 L and a left front brake valve  86 L. Right or second foot pedal  82 R when pressed opens a right rear brake valve  84 R and a right front brake valve  86 R. Pedals  82 L,  82 R will activate a piston or pistons  88  of a cylinder or cylinders (not shown) which activate the first and second pressure control valves  70 ,  78 . Movement of either or both of the pedals  82 L,  82 R will activate both of the first and second pressure control valves  70 ,  78 . 
     The service brakes  38 L,  38 R,  52 L,  52 R are connected to a fluid supply  90  such as a compressor, or air chamber via their respective brake relay valves  72 L,  72 R,  80 L,  80 R. When neither pedal  82 L nor pedal  82 R is pressed, the brake relay valves  72 L,  72 R, SOL,  80 R are in a closed position which means that the brakes  38 L,  38 R,  52 L,  52 R are not activated. Each brake circuit C 1 , C 2  is connected to a separate fluid reservoir of the fluid supply  90 . The first brake circuit C 1  including first control valve  70  is connected to fluid supply  90   a , and the second brake circuit C 2  including second control valve  78  is connected to fluid supply  90   b.    
     The first control valve  70  switches left associated rear brake valve  72 L, or right associated rear brake valve  72 R, or both of them, to an open position via left and/or right brake valves  84 L,  84 R. When the associated rear brake valve  84 L,  84 R is open, the respective rear service brake  38 L,  38 R is activated. Associated rear brake valves  84 L,  84 R are connected in parallel. 
     The second control valve  78  switches left associated front brake valve SOL, or right associated front brake valve  80 R, or both of them, to an open position via left and/or right brake valves  86 L,  86 R. When the associated front brake valve  86 L,  86 R is open, the respective front service brake  52 L,  52 R is activated. Associated front brake valves  86 L,  86 R are connected in parallel. 
     When neither of the pedals  82 L,  82 R is moved, the front and rear brake valves  86 L,  86 R,  84 L,  84 R are biased to a closed position. When both foot pedals  82 L,  82 R are pressed together, piston  88  activates first and second control valves  70 ,  78  and at the same time the front and rear brake valves  86 L,  86 R,  84 L,  84 R are opened. Air flows from the fluid supply  90   b , along line L 1 , through second control valve  78 , along line L 2  through the front brake valves  86 L,  86 R and through to the respective front brake valves  80 L,  80 R which switches valves  80 L,  80 R to an open position. Air can then flow from the fluid supply  90   b  along line L 1  and parallel lines L 1   a  and L 1   b  to the respective front service brakes  52 L,  52 R. At the same time, air also flows from the fluid supply  90   a , along line L 4  through first control valve  70 , along line L 3  through left and right brake valves  84 L,  84 R and along lines Lia, L 3   b  through to associated brake relay valves  72 L,  72 R which switch valves  72 L,  72 R to an open position. Air can then flow from air supply  90   a  through line L 4 , through lines L 4   a  and L 4   b  to activate rear service brakes  38 L,  38 R. If the driver wishes to apply the brakes on one side only, for example the left front service brake  52 L and left rear service brake  38 L to help him steer left around a bend, the driver pushes the left foot pedal  82 L only. 
     The rear park brakes  40 L,  40 R are controlled by a park brake control circuit C 3  connected to a further separate reservoir  90   c  of fluid supply  90 . In conventional operation, a park brake control valve  92 , activated by a hand brake lever, is operable to connect the fluid supply, via a relay valve  94  and respective left and right rear solenoid valves  96 L,  96 R, to release the park brakes  40 L,  40 R. The solenoid valves  96 L,  96 R are spring biased to the operating position shown in which the output of relay valve  94  is connected to the park brakes  40 L,  40 R. 
     To enhance the brake steering operation, the park brakes  40 L,  40 R are used to supplement the braking pressure applied by the rear service brakes  38 L,  38 R. The fluid supply  90  from reservoir  90   c  is connected as a further input to proportional valve  76  (along with the output from shuttle valve  74  in circuit C 1 ) with the proportional valve out put on line L 5  being connected to the left and right rear solenoid valves  96 L,  96 R. Operating one of the rear solenoid valves (e.g. left rear solenoid valve  96 L) disconnects the respective park brake  40 L from the output of relay valve  94  and instead connects it to the output of proportional valve  76  on line L 5 . The effect of the proportional valve  76  is to reduce the opening pressure applied to the park brake  40 L as the closure pressure on the corresponding service brake  38 L is increased (so fluid pressure applied on the park brake is substantially inversely proportional to that applied on the service brake) such that the braking force applied by the park brake is substantially proportional to that applied by the service brake. This proportional application of the park brake during brake steering reduces the ground damage that may otherwise occur if maximum park brake force were applied regardless of service braking force (as would be the case with the above-mentioned combined park and service brake arrangement of DE9204417U1). 
       FIG. 4  shows an alternative embodiment of the invention in which the pedal-operated front brake valves  86 L,  86 R are replaced by solenoid-operated valves  98 L,  98 R connected between the line L 2  output of second control valve  78  and the respective front brake valves  80 L,  80 R operating left and right front service brakes  52 L,  52 R. Other components of the arrangement of  FIG. 4  are the same as in  FIG. 3 , are denoted by the same reference numerals, and will not be further described. 
     The brake circuit shown in  FIG. 4  may be adapted to a full electronic braking system (brake by wire) wherein the left rear brake valve  84 L and the right rear brake valve  84 R are not directly connected to two foot pedals  82 L,  82 R. Instead, solenoid valves are used to activate the rear service brakes  38 L,  38 R. The movement of the two foot pedals  82 L,  82 R may then be measured by sensors and forwarded to control unit  62 , which in turn controls the solenoid valves. Furthermore, such a brake system may be provided with only one foot pedal. A further activation means may be provided so that the driver can activate steering brake operation or the system may automatically activate steering brake depending on sensed parameters (vehicle speed, field/road operation, etc.). Furthermore the park brake control valve  92  may be also solenoid valves (connected with control system  62 ) which is operable to connect the fluid supply, via a relay valve  94  and respective left and right rear solenoid valves  96 L,  96 R, to release or activate the park brakes  40 L,  40 R. In such an arrangement, the brake force of the park brake under normal operating condition, cannot be controlled by the driver, only ON/OFF condition is possible. 
     Whilst the above arrangement described is intended for use as a pneumatic circuit, it is envisaged that the above described brake arrangement can also be operated hydraulically. 
       FIG. 5  represents a method of brake steering as may be effected by the tractor  10  of  FIG. 1  under the direction of the control system  62 . On the vehicle entering a turn at  100 , the service brakes of the front and rear wheels on the inside of the turn are applied by the user at  102  and at the same time at  104  the clutch arrangement ( 60 ;  FIG. 2 ) is controllably varied to adapt the share of the available torque between the front and rear axles. Also on entering a turn, at  106  the parking brake on the rear wheel on the inside of the turn is applied. 
     As described above and represented in  FIG. 6  (with the pedal stroke of pedals  82 L or  82 R depicted on the horizontal axis while the brake forces/fluid pressures are depicted on the vertical axis), the controllably varied level of braking force applied by the parking brake (as depicted with graph G 1 ) is preferably substantially proportional to the level of applied service brake force (as depicted with graph G 2 ) while the fluid pressure applied on the park brake (as depicted with graph G 3 ) is substantially inversely proportional to that applied on the service brake (as depicted with graph G 4 ). The graphs G 1  and G 2  may show equal values but are depicted with a small offset for clarity reasons. The pedal stroke shown on the horizontal axis starts with 20% which means that before, no brakes are actuated but e.g. the brake lights are anyway switched on, e.g. at a stroke of 10% before the vehicle is braked. 
     Referring back to  FIG. 5 , with the adaption at  104 , the share of the available torque delivered to the front axle may be altered by a fixed amount, e.g. to be approximately 30% higher than that delivered before entering a turn. Alternatively, at  108  an optional step prior to adjusting the clutch (at  102 ) comprises adjusting the degree of variation based on external factors identified by the sensors  11 , such as:
         gross weight of the vehicle;   amount of front and/or rear ballasting carried by the vehicle;   weighting information pertaining to a towed or carried implement;   extent of measured wheel-slip for one or more wheels of the vehicle;   tyre pressure in one or more tyres on respective wheels of the vehicle;   angle of turn directed by a user of the vehicle;   current speed of the vehicle;   ambient conditions external to the vehicle.       

     If sensor input indicates the vehicle is heavier at the rear, the control system  62  may not activate the front service brake, while when the vehicle is heavier at the front, the system may not activate the additional brake force supplied by park brake. This situative brake control enables an efficient operation avoid excessive brake force to reduce soil damages. An ABS sensor giving wheel speeds to determine tyre slip may then be used for control of brakes and clutch. 
     As brake steering should only be used in field conditions, and not on the road, a further determination may be made at  110  prior to the start of a turn at  100  as to whether the vehicle is in a “safe” geographical location, namely a field. This determination may be made automatically in control system  62  on the basis of input from the geographical positioning system  15  ( FIG. 1 ). 
     In the foregoing the applicants have described A method of brake steering in a four-wheel drive utility vehicle having a driven front axle carrying at least two front wheels, a driven rear axle carrying at least two rear wheels, a powertrain delivering torque to the front and rear axles via a connecting shaft, a controlled clutch arrangement in the connecting shaft operable to vary the distribution of delivered torque between the front and rear axles, and independently operable service brakes on each of the front and rear wheels. The method comprises, on the vehicle entering a turn, applying the service brakes of the front and rear wheels on the inside of the turn and adjusting the clutch arrangement to adapt the share of the available torque between the front and rear axles. Additional braking force may be applied from independently operable park brakes on the rear wheels in inverse relationship to the level of service brake force applied. 
     From reading of the present disclosure, other modifications will be apparent to those skilled in the art. Such modifications may involve other features which are already known in the field of vehicle driveline and braking systems and component parts therefore and which may be used instead of or in addition to features described herein.