Technical field

The present invention generally relates to a hydraulic braking control system for agricultural vehicles or the like, such as agricultural tractors, earth-moving machines, operating machines, etc.

More particularly, the invention relates to a hydraulic braking equipment or system for one such vehicle, which system is equipped with safety functions arranged to act on the braking members of the vehicle.

Prior Art

As known, in agricultural vehicles, which will be preferably referred to hereinafter for the sake of convenience of the description, two braking pedals are generally provided. Each pedal acts on a respective master cylinder and, if individually actuated, performs braking on a rear wheel of the vehicle located in a position corresponding to the position of the pedal having been actuated. As it can be easily understood, such an individual actuation has the effect of assisting in steering the vehicle, which pivots about the wheel being braked (pivot braking or SBF, Steer-by-Braking Function).

In accordance with the prior art, if the pedals are jointly actuated, braking takes place at least on both rear wheels.

Joint actuation of the pedals is generally achieved by coupling the pedals by means of a suitable lock and by operating on the respective master cylinders connected to the pedals. In this way, actuation of one pedal also actuates the other one and, consequently, both master cylinders, thereby allowing performing braking at least on both rear wheels.

In accordance with the prior art, in vehicles with two pedals and two braking cylinders, the joint actuation of the pedals also allows performing braking on all vehicle wheels, on the front and rear wheels and/or on a trailer, if any.

For instance, document EP 1415878 A2 discloses a hydraulic braking system for earth-moving machines having two braking circuits and two braking pedals.

From document EP 0650877 A1 a braking system for rear wheels of tractors is instead known where a single braking circuit controlled by a single braking pedal is provided.

In accordance with such a prior art, a single pedal is actuatable for obtaining steer- by-braking on one of the two rear wheels of a tractor. Steer-by-braking is performed with the assistance of devices located on the front wheels of the tractor and arranged to detect whether the front wheels of the tractor have exceeded a given steering radius.

In accordance with the prior art, the determination of the steering radius is independent of the tractor speed so that, in order to avoid steer-by-braking in situations where the front wheels have exceeded a given steering radius but the speed is too high, the braking system necessarily entails the provision of a speed sensor.

From document EP 20931 18 A1, a device for tractors is known allowing the steer- by-braking function by using a pair of pedals arranged to actuate a single master cylinder. From document EP 20931 1 1 A1, a pedal to be used on tractors for performing steer-by- braking is known.

The pedal disclosed in document EP 20931 1 1 A1 includes two side pads, used for performing steer-by-braking, and a central pad used for performing braking with both rear brakes.

The known pedal requires, in all conditions, the provision of a control circuit interpreting which of the three pads is being used, and of a speed sensor disabling the accidental use of one of the two side pads when a given speed is exceeded.

A first problem of the prior art is that using two pedals either requires the provision of two master cylinders or, in case of a single pedal, two pedals and three pads and a single master cylinder, requires the provision at least of a speed sensor and possibly of an electrical apparatus and a very complex electronic control circuit, the operation of which is necessary in order the braking system can operate.

It is also known that braking on a single wheel is convenient when the vehicle is to move along working ways, such as those envisaged for ploughing fields, moving earth, etc., whereas joint braking on two or four wheels is convenient when the vehicle moves along road stretches or ways.

In general, a problem of the prior art is that the driver of the vehicle, when passing from working ways to road ways, often forgets coupling together the pedals through the lock.

As it can be easily understood, if the pedals are not coupled, should one of the pedals be actuated while the vehicle is moving along a road way, the vehicle will pivot about the braked wheel with a serious danger for both the vehicle driver and other drivers or vehicles present on the road way.

Such a problem is solved in part by document EP 20931 18 A1, which however requires that the vehicle electrical system is perfectly operating.

Generally speaking, the Applicant has noticed that the prior art fails effectively and safely solving the problems mentioned above and ensuring safety functions capable of operating both when the electrical system is operating and when it is not operating, while ensuring that the agricultural vehicles can operate, along the working ways, with the braking modalities typical of those vehicles.

Description of the invention

It is an object of the present invention to obviate the problems mentioned above.

The object is achieved through the hydraulic braking control system for agricultural vehicles or the like as claimed herein.

The present invention also relates to a braking control method for agricultural vehicles or the like.

The claims are integral part of the technical teaching provided herein in respect of the invention.

The following synthetic description of the invention is given in order to provide a basic understanding of some aspects of the invention.

This synthetic description is not an exhaustive description and, as such, it is not to be intended as being suitable for identifying key or critical elements of the invention, or for defining the object of the invention. It only aims at setting forth some concepts of the invention in simplified form, as an anticipation of the detailed description included below.

In accordance with a feature of the present invention, the braking system includes a single brake pump that is actuatable by means of one pedal in order to control the selective braking of at least a right rear brake or a left rear brake.

More particularly, the connection of the pump to the brakes is achieved through valves of normally open type controlled by a control unit.

In accordance with another feature of the present invention, a speed sensor is provided, which is associated with at least one of the rear brakes and is connected to the control unit so that the latter can disable the selective braking when the vehicle speed exceeds a predetermined value.

In accordance with a further feature of the present invention, the pump of the system is actuatable by means of a pair of pads that are articulated on a rocker arm fastened to the pedal so that each pad can actuate the pedal independently of the other pad.

Brief Description of the Figures

The above and other features and advantages of the invention will become apparent from the following description of preferred embodiments made by way of non limiting example with reference to the accompanying Figures, in which elements denoted by a same or similar reference numeral correspond to components having the same or similar function and construction, and in which:

- Fig. 1 is a diagram of an embodiment of the equipment or system; and

- Fig. 2 schematically shows a detail of the system shown in Fig. 1.

Detailed Description of a Preferred Embodiment

Referring to Fig. 1, a hydraulic braking control equipment or system (system) 10 for agricultural vehicles or the like in accordance with the present invention includes a control pedal (pedal) 101, a brake pump (pump) 102, for instance a tandem pump of known type, a pair of pressure amplifiers (amplifiers) 105 and 106, for instance of the type with differential area and predetermined intervention point, as described for instance in French Patent FR 1380403, a respective pair of hydraulic valves 15 and 16, for instance electrically controlled valves, and a pair of respective rear brakes 25 and 26 of the type with hydraulic control.

Pedal 101 is arranged to operate pump 102, which is connected, through a main outlet or first outlet 104 and a branch, to each of the two amplifiers 105 and 106, respectively. Each amplifier 105 and 106 has its outlet connected to a respective hydraulic valve (electrically controlled valve) 15 and 16, which in the preferred embodiment is of the normally open type and allows independently controlling left and right rear brakes 25 and 26, respectively, depending on commands transmitted to electrically controlled valves 15 and 16 by an electronic control unit (control unit) 30.

In accordance with the embodiment shown in Fig. 1, pump 102 also has a second outlet 107 arranged to control a pair of front brakes 28 and a trailer brake 29.

In accordance with such an embodiment, outlet 107 is connected to both a front brake valve 18, for instance of the normally open type and preferably electrically controlled by control unit 30, and a trailer brake valve 19, of known type.

Front brake valve 18 allows fluidically connecting pump 102 to left and right front brakes 28, under the control of control unit 30.

In accordance with other embodiments, for instance when front brakes are not provided, the second outlet can be dispensed with and connection to trailer brake valve 19 can take place through the first outlet 104.

In such case, pump 102 is not a tandem pump, but a single-circuit pump, known per se. In accordance with yet other embodiments, the pair of front brakes 28, if it is provided, can also be controlled through a logic unit (logic head), of known type, located downstream electrically controlled valves 15 and 16 controlling the left and right rear brakes 25 and 26. In this case the brake pump is, for instance, a known single-circuit pump.

Of course, in other embodiments, system 10 may lack the front brakes and the trailer brake.

In accordance with the preferred embodiment, pedal 101 includes a pedal body 1 14 (Fig. 1 and Fig. 2) ending with an articulation bushing 1 15 articulated on an axis 1 16. Preferably, pedal 101 is driven by two pads, a right pad 109 and a left pad 1 10, respectively, articulated on a rocker arm 1 11 fastened to pedal body 1 14.

Each of the right and left pads, if individually actuated, is arranged to operate a respective right or left switch 1 12 or 1 13, connected to control unit 30.

Preferably, each pad 109 and 1 10, if actuated, besides operating the respective switch 1 12 or 1 13, rests on a pad stop arranged to make the pad integral with body 1 14 of pedal 101, so as to actuate the pedal itself.

Operation of right or left switch 1 12 or 1 13, respectively, causes control unit 30 to close electrically controlled left or right valve 15 or 16, respectively.

Thanks to the commands from control unit 30 causing the closing of the electrically controlled valve opposed to the pad having been actuated, it is possible to keep the fluidic connection between pump 102 and the brake corresponding to the pad having been actuated open, thereby causing braking of that brake, and to close the fluidic connection between the pump and the brake in position opposed to the pad having been actuated, thereby preventing braking of that brake.

In accordance with such an embodiment, pads 109 and 1 10 can also be coupled to each other, in known manner, through a lock 1 17, even if this is not necessary, as it will be disclosed in detail below. Preferably in such case the pads, fastened to each other, do not operate switches 1 12 or 1 13, so that electrically controlled valves 15 and 16 remain open and allow braking at least by means of both rear brakes.

As the skilled in the art can easily understand, the above configurations are operative for instance also in case of electrical blackout on the vehicle.

Actually, in case of electrical blackout on the vehicle, actuation even of a single pad actuates the pedal, the brake pump and the brakes, since rear brake valves 15 and 16, being of the normally open type, allow in any case actuating both rear brakes, thereby avoiding possible safety problems on road ways.

Of course, in case of electrical blackout during working ways, steer-by-brake SBF is no longer impossible, so that it is presumable that an electrical blackout, if any, is to be suitably signalled, for instance through a warning light supplied with power independently of the electric circuit of the vehicle.

In the preferred embodiment, a speed sensor 27 connected to control unit 30 is provided, the sensor being associated with at least one out of the left and/or right rear brakes 25, 26.

In accordance with such an embodiment, if only one of the two pads 109 or 1 10 is actuated and control unit 30 detects, through the at least one sensor 27, a speed higher than a predetermined speed, for instance 12 Km/h, control unit 30 keeps rear brake valves 15 and 16 open, without need for further checks, so as to allow simultaneous braking by means of at least both rear brakes 25 and 26, even if only one pad is actuated.

Of course, if electrically controlled valve 18 controlling front brakes 28 is provided, control unit 30 will keep this electrically controlled valve open, so as to cause also braking of the front brakes.

In accordance with a second embodiment, pump 102 as shown in Fig. 1, for instance of the tandem type, is replaced by a differential pump (Brake Differential Master Cylinder or MCD), connected through a branch to respective electrically controlled valves located downstream the MCD.

In such case, the differential pump also operates as pressure amplifier.

A system made in accordance with such a second embodiment allows attaining the equivalence, being the force applied, the pressure and the stroke the same, both to pads connected through a lock and to a single pad actuated with the vehicle having a speed higher than the predetermined speed.

In case of actuation of a single pad at a speed lower than or equal to the predetermined speed in order to brake only one of the rear brakes, being the force applied the same, a stroke reduction is achieved by means of the differential pump, jointly with the halving of the outlet pressure,.

Hereinafter a comparison is made by way of example between what is provided for by the prior art and what is provided for, e.g., in accordance with the first embodiment.

In accordance with the prior art, two differential pumps are provided, each having for instance:

- primary diameter: 35 mm (9.62 cm ² ); - amplifying diameter: 23 mm (4.15 cm ² );

- pedal ratio: 5.6

- useful stroke: 35 mm.

In case of actuation of a single pedal of one of the two pumps, by applying a load of 50 Kg to the pedal, a pressure

- 50 Kg (at the pedal) x 5.6 (pedal ratio) = 280 kg (at the pump push rod) / 9.62 cm ² = 29.1 bars

is achieved.

Such a pressure corresponds to the maximum pressure at the primary piston of the differential pump.

At the intervention pressure of the differential pump, the following pressure is achieved:

- 280 kg (at the pump push rod) / 4.15 cm ² = 67.47 bars.

Such a pressure corresponds to the maximum braking pressure on one of the two brakes when 50 Kg are applied to one of the two pedals.

Of course, when the two pedals are coupled through a lock and under the same conditions (50 Kg applied to the coupled pedals), the following pressures are achieved:

- 14.55 bars (maximum pressure at the primary piston of each of the two pumps); and

- 33.73 bars (maximum braking pressure at the primary piston of each of the two pumps, at the intervention pressure of the differential pump).

In accordance for instance with the first embodiment of the present invention, and assuming:

- diameter of the master cylinder: 49.2 mm (19 cm ² );

- hydraulic amplification ratio of each pressure amplifier: 4.69;

- pedal ratio: 5.6

- useful stroke: 35 mm,

in case of actuation of a single pad, by applying a load of 50 Kg to the pad, there is obtained:

- 50 Kg (at the pad) x 5.6 (pedal ratio) = 280 kg (at the pump push rod) / 19 cm ² = 14.74 bars (maximum pressure at the pump primary piston)

and, at the intervention pressure of one of the two amplifiers:

- 14.74 x 4.69 = 69.13 bars, corresponding to the maximum braking pressure when a load of 50 Kg is applied to the pad and hence to the pedal.

If the two pads are coupled through a lock, under the same conditions there is still obtained:

- 14.74 bars (maximum pressure at the primary piston) and

- 69.13 bars (maximum braking pressure, when 50 Kg are applied to the coupled pads).

As it can be readily understood, if the load on the pads does not change, also the maximum braking pressure does not change.

Such a condition does not change even in case the vehicle speed exceeds a predetermined speed, for instance 12 Km/h, and a single pad is actuated.

The example applied to one of the embodiments described clearly shows that the system in accordance with the present invention allows attaining, by means of a single pedal and two pads, results corresponding to those attainable by means of two pedals and two pumps, for instance differential pumps, as usually provided for in agricultural vehicles and the like.

The operation of the system described hitherto is as follows.

In case of working ways, in which the vehicle speed is presumably lower than a speed possible in case of road ways, actuation of one of the two pads 109 or 1 10 enables braking of one of rear brakes 25 or 26 located in a position corresponding to that of the pad having been actuated, thanks to the intervention of control unit 30 which cuts off the fluidic connection between pump 102 and valve 15 or 16 opposed to the pad having been actuated.

If front brake valve 18 controlled by control unit 30 is provided, in case of actuation of a single pad during working ways the control unit provides for cutting off the fluidic connection between pedal 101 and front brakes 28, so that the latter are not blocked.

In case of road ways, since control unit 30 is configured so as to keep the vehicle speed under control through sensor 27, if the vehicle speed exceeds a predetermined speed actuation of only one pad 109 or 110 is handled as the actuation of both pads, so that pump 102 actuates at least both rear brakes and also front brakes 28, if the latter are provided.

The above description makes it apparent that the system allows controlling the behaviour of the vehicle brakes, while utilising only one brake pedal, by taking into account the vehicle speed, independently of whether or not the brake actuation pads are coupled together through lock 1 17.

The above description makes it also apparent that the system does not require valves for balancing the pressures at the rear wheels, since the braking actuation pressure always comes from a single source, both in case of a conventional pump with single or double circuit, and in case of a differential pump with single or double circuit.

Of course, obvious modifications and/or variations to the above description in respect of the size, the shapes, the materials and the components, as well as in respect of the details of the illustrated construction and the operating manner, are possible without departing from the invention as defined in the following claims.