Parking brake for a tractor

A parking brake for a motor vehicle includes: a manual operating lever; a braking device designed to act on brake disks applied on a bevel pinion for transmission of the motion to the wheels of the motor vehicle; and a cable for transmission of the command imposed via the lever on the braking device. The brake is activated either automatically by a hydraulic actuator when the engine of the motor vehicle is turned off, or alternatively, by a manual command imposed by the operator through the lever whether or not the engine of the motor vehicle is running.

BACKGROUND OF THE INVENTION

The present invention relates to a parking brake for a motor vehicle, in particular for a tractor.

As is known, a parking brake, referred to commonly as “hand brake,” enables parking of the motor vehicle just by acting on the brake lever located in the cab. Consequently, the operator, even in the case where the engine of the motor vehicle is turned off, must engage the parking brake manually.

It has thus appeared desirable to provide a parking brake that may be activated automatically whenever the engine of the motor vehicle is turned off, and which, in any case, may be able to function as a traditional hand brake, and hence can be engaged manually by the operator, even when the engine of the motor vehicle is on. In the latter case, the motor vehicle should not have any gear engaged and, hence, be in neutral.

Consequently, a purpose of the present invention is to provide a parking brake that will carry out the aforesaid functions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1shows a parking brake100according to the preferred embodiment. The parking brake100comprises a manual operating lever10which is pivoted on a fulcrum11and is located in a control cab (not illustrated) of a motor vehicle (not illustrated).

The parking brake100has the purpose of braking a bevel pinion12, which meshes with a fitted crown wheel13, which transfers the motion to two axle shafts14(FIG. 1shows only one of them) on which are mounted two drive wheels W (only one shown inFIG. 1) of the motor vehicle.

A spindle15, unitary connected with the pinion12, carries a plurality of brake disks16actuated by a braking device50, the constructional elements of which will be described in greater detail hereinafter with particular reference to the other annexed figures. In order to operate the braking device50, a cable17(preferably of a Bowden type, although other cables or even other types of linkages may be used) is disposed between the lever10and the braking device50.

More in particular, the cable17(FIG. 1) is connected, on one side, to an eyelet18made on the lever10, whilst, on the other side, it is connected to an eyelet51provided on a relay lever52, which forms an integral part of the aforementioned braking device50(see further).

It is to be understood that in the ensuing description only the items present in the attached drawings that are essential for an understanding of the present invention will be numbered and described.

Referring now toFIGS. 2 and 3, the braking device50comprises a main body53, which provides, preferably as a single unit, a plate53afor fixation to the frame (not shown) of the motor vehicle, a cylinder53b,and projecting portions53c,which are designed to support the brake disks16(visible only inFIG. 1). Furthermore, the plate53acomprises six through holes54, each of which is provided with a respective bolt55for fixing to the rear transmission case (not illustrated) of the motor vehicle. The cylinder53bis closed at its bottom end by a disk56fixed thereto with means known and not described.

As shown inFIG. 3, defined within the cylinder53bis a chamber57designed to house a piston58, on which an adjustment pin59rests. One end59aof the adjustment pin59is in turn screwed to an internal threaded portion of a bushing60provided with a terminal flange61. The bushing60is housed partially in a through hole60amade in the disk56and can slide freely in said through hole60a.

Between the terminal flange61and the disk56, a pack of Belleville washers62are tightly fitted; the washers62carrying out an indirect elastic action on the piston58via the bushing60and the adjustment pin59screwed thereto. Connected to the piston58on the other side of the adjustment pin59is a stem64terminating with a fork65.

Also the other end59bof the adjustment pin59is threaded. Screwed to this end59bis an adjustment detent63awhich is variably tightened for reasons that will be explained in greater detail hereinafter. As best shown inFIGS. 2 and 3, the aforesaid adjustment detent63ais set between a nut63screwed onto the lower end of the adjustment pin59and the bottom surface of the disk56.

To return to the chamber57, it may be noted that a portion57ais designed to receive pressurized oil coming from a hydraulic circuit (not shown) of the motor vehicle. More particularly, with reference toFIGS. 2 and 3, it will be seen that the pressurized oil is brought to the portion57aby means of a hydraulic line66, inflow of oil being controlled by a solenoid valve67(FIG. 2). In addition, the oil contained in the portion57ais discharged, when needed (see later), through a port68, visible inFIG. 3, connected directly to the rear-transmission case (not illustrated) of the tractor.

The fork65connects the stem64via a pin69to a crank70provided with a circular cavity71(FIG. 2) coupled to a shaft72(seeFIGS. 2 and 5). The coupling of the circular cavity71to the shaft72is such as to enable free rotation of the crank70with respect to the shaft72. Between the pin69and the shaft72, the crank70has a seat73designed to receive a pawl74for the purposes that will be described more fully hereinafter. The pawl74is idle with respect to its own seat73.

As shown in particular inFIGS. 5–8, the shaft72is coupled to a cam76(FIG. 8, and shown in greater detail inFIG. 9) by means of splines75(FIG. 7). In its central part, the cam76comprises a toothed seat77(FIG. 9) that is coupled to the splines75provided on the shaft72in such a way that said cam76is angularly fixed with respect to the shaft72. Furthermore, on the periphery of the cam76, as shown again inFIG. 9, there are provided two shaped cavities78,79, which have substantially the same shape and are obtained by removing part of the material constituting the periphery of the cam76or by casting the cam76with the shaped cavities78,79formed in the periphery.

The shaped cavity79has a length L much greater than the diameter D1of the pawl74(seeFIG. 8). In fact, the pawl74, in use, is located within the shaped cavity79, as shown inFIG. 9.

The shaft72(seeFIGS. 7 and 8) is in turn elastically stressed, via the cavities of the cam76, by a spring80wound in a spiral about the longitudinal axis of symmetry (a) of the shaft72. A first end80aof the spring80rests on an abutment element unitary provided on the main body53(not shown), whilst a second end80bis fixed to a small pin81fitted into a seat81a(FIG. 9) made in the cam76. The reasons for the presence of the spring80will be explained hereinafter.

Provided at one end of the shaft72is a shaped element82(seeFIGS. 4–8), rotation of which, as will be seen more clearly hereinafter, packs together the brake disks16so as to brake the wheels W.

As regards the relay lever52, at the end opposite to the one where the eyelet51is located, there is provided a circular seat (not visible in the figures) engaged by the shaft72. More particularly, the relay lever52can rotate freely with respect to the shaft72. The cam76is thus located between the crank70and the relay lever52, as shown inFIGS. 4 and 5.

The relay lever52in turn has a pawl83(resting idle in its seat83ain the lever52), which, in use, is located within the shaped cavity78. The pawl83has a diameter D2(FIG. 5) smaller than the length L of the shaped cavity78so as to enable its free displacement within the shaped cavity78.

Consequently, two commands can reach the cam76.

The first command can be imparted by the piston58, which, to all effects, forms an integral part of a hydraulic actuator84comprising, the elements already described in relation to the cylinder53b(see above).

Conversely, the second command can reach the cam76via the relay lever52operated manually by the operator using, for this purpose, the lever10(seeFIG. 1).

In use, when the engine (not shown) of the motor vehicle is running, also the hydraulic circuit is pressurized. Consequently, from said circuit a certain amount of oil under pressure is deviated, which, through the hydraulic line66and the control of the solenoid valve67(FIG. 2), fills the portion57aof the chamber57. Consequently, the piston58moves down, compressing at the same time the pack of Belleville washers62. Driven by the stem64, by the fork65and by the crank70, the pawl74will be positioned closely to the side79aof the shaped cavity79(seeFIGS. 5,7, and9), so that the only way for the user to engage the parking brake remains the traditional one of acting manually on the relay lever52with the modalities referred to previously. Under the condition where the engine is running, the pawl83is located closely to the side78aof the shaped cavity78. For simplicity reasons,FIG. 9shows both pawls74and83in a middle position of their respective cavities78,79although this does not correspond to an operating position.

Consequently, in the case where the engine is on, the only way to apply the parking brake of the motor vehicle is to rotate the relay lever52, and hence the cam76, in the direction indicated by the arrow F1(see, for example,FIG. 2). In this case, the pawl83, which is already in the proximity of the side portion78aof the shaped cavity78, is immediately pushed against the wall78aof the shaped cavity78, causing rotation in the direction of the arrow F1of the shaft72and of the shaped element82, which, as has been said, actuates the brake disks16. Such a rotation is enabled because pawl74is close to wall portion79aand thus there is a considerable gap between said pawl74and the wall portion79b.

In other words, when the engine is on, each of the pawls74and83is located in an almost extreme upward position of its own shaped cavity79and78, respectively. In this condition, when the brake is operated manually, the pawl83will immediately contact the top portion78aand will cause rotation of the cam76in the direction of the arrow F1. This is possible because there is a sufficient amount of space between the other pawl74and the bottom portion79bof the shaped cavity79. When the engine is off and the handbrake is not operated, the pawl74will move upward and immediately contact the top portion79a(on account of the pressure drop in the cylinder) and will set the cam76again in rotation in the direction of the arrow F1. This is again rendered possible by the fact that there is a sufficient space between the pawl83and the bottom portion78bof the shaped cavity78, since at the instant when the engine is still on, the pawl83is located close to the wall portion78a.

If the operator so desires, he can have both systems active at the same time. With the engine off, and consequently the brake on by the action of the pawl74. the operator is still able to also put the handbrake on, by pulling the lever51lever52in the direction of an arrow F1and thereby moving pawl83towards and in contact with wall portion78a. At this instance, both pawls74and83are in contact with the respective wall portions79aand78aand braking is thus ensured both by the hydraulic system and the mechanical system. Should the engine be switched on again, the pawl74will release wall portion79aand move in the direction of wall portion79b. the cam76however will not rotate because it is prevented from doing so by pawl83still pressing against wall portion78a. The brake therefore will remain on until the handbrake lever10also has been released.

As appears again fromFIG. 9, the bottom ends of the shaped cavities78,79are slightly curved because said cavities78,79are preferably made with a ball-end two-fluted mill with a circular path. In so far as the path of the two pawls83and74, respectively, is circular, there consequently is no need for the bottom ends to be rectilinear, as long as the pawls74and83do not interfere with the slightly raised middle portion of the respective cavities78and79during their circular movement therethrough.

When the operator wants to disengage the hand brake (once again with the engine on) all he has to do is to release the lever10(FIG. 1), and the system will return to the initial position thanks to the elastic action exerted by the spring80on the cam76. In this case, both the relay lever52and the cam76will rotate in the direction identified by the arrow F2(see for exampleFIG. 2).

Conversely, in the case where the engine is turned off, the hydraulic circuit is connected to the discharge. Consequently, also the pressurized oil present in the portion57ais discharged through the port68. Hence, the pack of Belleville washers62is allowed to push the bushing60upwards, as well as the adjustment pin59, the piston58, the stem64, the fork65, the crank70, and the pawl74, which will exert a thrust on the wall of the top portion79aof the shaped cavity79(FIG. 9). Also in this case, the cam76will turn in the direction of the arrow F1and will engage the brake according to what has been said previously. It is to be noted that the action of the Belleville washers62overcomes the oppositely directed action of the spring80.

A further function of the parking brake100is the park-lock function. Acting on the solenoid valve positioned in point67, it is possible to discharge the pressurized oil present in the portion57athrough the port68obtaining the same result as in the case described previously. This is a particular function that is required from the motor vehicle with the engine running when the driver wants to be certain that the vehicle will remain still in particular conditions of maneuver without having to operate the lever10in the cab.

In the park-lock situation, to disengage the parking brake, it is sufficient to re-supply the solenoid valve with electrical current in order to send pressurized oil again into the portion57a.

Consequently, it may be stated that, with the parking brake100forming the subject of the present invention, the system for blocking the wheels W will be activated automatically whenever the engine of the motor vehicle is turned off or else when the signal to the control solenoid valve of the device is intentionally interrupted, whilst there will always be the possibility of engaging the hand brake manually both with the engine off and with the engine on. In addition, it should be noted that, both when the actuator84goes into action and when the relay lever52is pulled manually, the same cam76provided with the two shaped cavities78,79is used.

If there were a breakdown such as to cause the engine to be turned off, or some fault of the hydraulic circuit, or else a failure of a signal to arrive to the solenoid valve for control of the braking device, the oil would be discharged by the portion57athrough the port68, and the hand brake would remain engaged owing to the action of the actuator84.

However, in this case, to enable the towing of the motor vehicle, the hand brake can be disengaged by resorting to an emergency device85, which basically comprises the nut63and the adjustment detent63a(see for exampleFIG. 3). If the adjustment detent63ais screwed on the threading provided on the end59buntil it presses against the bottom of the disk56, the emergency pin59will be pulled down, allowing the other elements connected thereto to move downwards, including the cam76, which will rotate in the direction of the arrow F2. In this connection, it should be noted that the permanent contact of the tip of the adjustment pin59with the bottom wall of the piston58is ensured by the presence of the return spring80which will cause a return action on respectively the cam76, the pawl74, the fork65, the stem64, and ultimately the piston58, which, consequently, will always remain pressed against the tip of the adjustment pin59.

Advantages of the present parking brake are the following:

assurance that, when the engine is off, the motor vehicle will, in all cases, have its parking brake automatically engaged; and

commands unified in a single cam, both in the case of automatic engagement of the parking brake and in the case of manual operation via a lever rotated by the operator in the cab.