BRAKE AND STEER-BY-BRAKING (SFB) PEDAL ARRANGEMENT FOR TRACTORS

The present invention relates to a brake and steer- by-braking pedal arrangement for tractors .

As is known, conventional tractors are equipped with a brake and steer-by-braking pedal arrangement, normally comprising two brake pedals enabling a so- called steer-by-braking function (SBF) .

In this type of brake pedal arrangement, if the driver presses the left (or right) pedal only, the brake system only brakes the rear left (or right) wheel, thus reducing the turn radius of the tractor, especially during headland manoeuvres.

At present, the two brake pedals simply have a driver-operated mechanical lock device for integrally connecting the pedals for on-road use or when the SBF is not required. The mechanical lock should always be used when running on-road, to safeguard against the driver inadvertently pressing only one of the two pedals when the tractor is running at high speed, thus resulting in sharp swerving and possible capsizing of the vehicle. When running on-road, the two brake pedals are connected integrally by the lock device, and can only be pressed simultaneously to slow down or stop the vehicle as a whole.

This long-standing solution, however, has two main drawbacks :

(1) the driver may neglect to activate the lock device to connect the two brake pedals integrally before the vehicle gets up to speed, thus resulting, as stated, in highly dangerous situations in the event of emergency braking (swerving of the vehicle at high speed, if only one pedal is pressed) ;

(2) using current systems, the steer-by-braking function (SBF) cannot be applied effectively to electronic (e.g. ABS) brake systems.

Moreover, in current SBF systems, each pedal has a respective master cylinder, so the hydraulic circuits of the two master cylinders must be connected by a compensating valve to compensate any difference in pressure between the two hydraulic circuits when braking the tractor normally; all of which seriously complicates the hydraulic circuits of the tractor brake system.

It is therefore the main object of the present invention to provide a tractor pedal arrangement designed to eliminate the aforementioned drawbacks, and which at the same time is cheap and easy to produce.

It is a further object of the present invention to provide an electronically controlled, in particular ABS, brake system comprising at least one innovative tractor pedal arrangement.

According to the present invention, there is provided a tractor pedal arrangement as claimed in the

accompanying Claims.

A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a longitudinal section of a pedal arrangement in accordance with the present invention in a first rest position;

Figure 2 shows a longitudinal section of the Figure 1 pedal arrangement in a second normal-brake position; Figure 3 shows a longitudinal section of the Figure 1 and 2 pedal arrangement in a third position with the steer-by-braking function (SBF) engaged.

As shown in Figure 1, the pedal arrangement 10 according to the present invention comprises a right pedal 11 and a left pedal 12, which act (synchronously or diachronically) on a single master cylinder 13 housed in sliding manner inside a cylindrical guide 14.

Pedals 11, 12 are located on opposite sides of a longitudinal axis of symmetry (AX) of pedal arrangement 10 as a whole.

Right pedal 11 is connected mechanically to master cylinder 13 by a respective push-rod 15 guided at least partly, and also in sliding manner, inside cylindrical guide 14 of master cylinder 13. In the rest position shown in Figure 1, the bottom surface 15a of push-rod 15 rests on the top surface 13a of master cylinder 13.

In the Figure 1 rest position, the top surface 13a

of master cylinder 13 is also aligned with a fixed reference line LV.

Right pedal 11 is fitted with a control rod 16 for controlling a respective right potentiometer 17. In actual use, control rod 16 controlling potentiometer 17 slides inside a sleeve 16a fitted integrally to potentiometer 17 by two supports 16b, 16c with holes. A first end 16* of control rod 16 is fixed to pedal 11, and a second end 16** is fitted, by known means not shown, with a retaining washer RD.

Control rod 16 is inserted inside a respective helical spring SPl located between pedal 11 and support

16b, and which restores pedal 11 to the Figure 1 position when foot pressure is applied by the driver and then released from pedal 11.

Similarly, left pedal 12 is connected mechanically to master cylinder 13 by a respective push-rod 18 also guided at least partly inside cylindrical guide 14.

In the rest position shown in Figure 1, the bottom surface 18a of push-rod 18 rests on the top surface 13a of master cylinder 13.

A gap SP is left, along axis (AX) , between the two pedals 11, 12.

Left pedal 12 is fitted with a control rod 19 for controlling a respective left potentiometer 20.

In actual use, control rod 19 controlling potentiometer 20 slides inside a sleeve 19a fitted integrally to potentiometer 20 by two supports 19b, 19c

with holes. A first end 19* of control rod 19 is fixed to pedal 12, and a second end 19** is fitted, by known means not shown, with a retaining washer RD.

Control rod 19 is inserted inside a respective helical spring SP2 located between pedal 12 and support

19b, and which restores pedal 12 to the Figure 1 position when foot pressure is applied by the driver and then released from pedal 12.

In the embodiment shown in the attached drawings, the two potentiometers 17, 20 are fixed to the outer surface of cylindrical guide 14.

As will be clear to anyone skilled in the art, potentiometers 17 and 20 may be replaced by any other mechanical, electromechanical or electronic device capable of determining the instantaneous position of pedals 11 and 12, or the distance between them, or the distance between them and fixed reference line LV.

As stated, potentiometers 17 and 20 provide for determining the distance (X) of right pedal 11 and the distance (Y) of left pedal 12 from fixed reference line LV respectively.

The values of distances (X) and (Y) are transmitted in signal form to an electronic central control unit CL, which processes the incoming data and implements control strategies by which to control the hydraulic circuit (not shown) of master cylinder 13 (see below) .

As shown in Figure 2, master cylinder 13 may be activated by both pedals 11, 12 of pedal arrangement 10;

in which case, only normal braking, e.g. of the four drive wheels (not shown) of the tractor, is effected. In the Figure 2 position, the SBF function is therefore idle. As shown in Figure 2, when braking normally (i.e. when the SBF function, as stated, is idle) , the distances between pedals 11, 12 and fixed reference line LV are altered (now (X*) and (Y*) respectively) but not to the same degree. In other words, since it is practically impossible for the driver to press both pedals 11, 12 in the same way and with the same force, the value of (X*), when braking the tractor normally, will normally never be exactly equal to (Y*) . The electronic control system (connected to electronic central control unit CL) , however, allows a small difference (Z*) between the two distances (Y*) and (X*), and still interprets the signal as indicating the driver's intention to brake normally (i.e. with the SBF function deactivated) .

As shown in Figure 3, if the difference, however, between distances (X**) and (Y**) increases over and above a given threshold value, the electronic system interprets this as the driver's intention to turn right, for example, as shown in fact in Figure 3. (The difference may be positive or negative; in the Figure 3 configuration, it is negative, since the value of (Y**) is greater than (X**) .

The same also applies when the driver turns left; in which case, the difference between the value of (X) and (Y) is positive.

To improve steering safety, a pedal requisite may advantageously, though not necessarily, be introduced, in the sense that, to activate the steer-by-braking

(SBF) function, not only must the distance between pedals 11 and 12 exceed a given threshold value, but the pedal not involved in the steering operation must also be in the rest position shown in Figure 1.

Another function may also be implemented, whereby the SBF function is disabled automatically when the speed of the tractor exceeds a given predetermined threshold value. The main advantages of the present invention are as follows :

- it solves the problem of the driver neglecting to connect the two brake pedals integrally prior to the vehicle reaching high speed; - it provides for applying the steer-by-braking function (SBF) to electronic (e.g. ABS) brake systems; and

- one master cylinder serves both brake/steer-by- braking pedals.