BRAKE DEVICE FOR SYNCHRONIZING GEARWHEELS IN A GEARBOX AND A GEARBOX PROVIDED THEREWITH

TECHNICAL FIELD

The present invention relates to a brake device for a stepped gearbox and intended to brake in a controlled manner the rotation speed of a countershaft . The brake device is particularly intended for vehicles with manual gearboxes such as trucks, passenger cars, buses etc. The invention also relates to a brake device which occupies little space in the gearbox and comprises at least one lever which applies friction to a component in the gearbox. The invention also comprises a gearbox provided with said brake device.

BACKGROUND

Stepped gearboxes for vehicles may have up to 15-16 gears and 5-6 synchronisation devices and usually comprise a mainshaft with a number of freely supported shift gearwheels which are in engagement with a corresponding number of fixed gearwheels arranged on a countershaft. During a gearchange operation, before one of the freely supported shift gearwheels can be engaged with the mainshaft, the rotation speed of the shift gearwheel is adjusted to (synchronised with) the rotation speed of the mainshaft by means of a mechanical synchronisation device which serves as a brake for the shift gearwheel. These synchronisation devices, one for each shift gearwheel, are expensive and occupy space and are now increasingly being replaced by a single shaft brake controlled, for example,

electronically which brakes the speed of the layshaft so that the rotation speed of the shift gearwheel which is to be engaged is synchronised with the rotation speed of the mainshaft. Eliminating the synchronisation package makes it possible for the gearbox to be shorter and less expensive to manufacture.

Shaft brakes are previously known but comprise relatively complicated units with a plurality of parts, which makes them expensive and time-consuming to manufacture and fit. They also occupy a relatively large amount of space in the gearbox and entail encroachment upon and modifications to the configuration of the gearbox.

Volvo patent application SE524354 refers to a shaft brake in which a brake element is integrated with and forms part of the shaft which is to be braked. The brake acts upon a conically shaped surface at the end of the respective shaft. That brake has a number of disadvantages. It involves substantial modifications to the internal configuration of the gearbox. The brake is difficult to change and maintain, e.g. if the linings need changing because of wear. The braking effect is reduced in that the lever from the centre of the shaft to the action point of the brake linings is short and it may be difficult to lead away quickly enough the friction heat arising from frequent or closely spaced gearchanges .

Scania patent application SE527267 refers to a synchronisation brake with an annular brake element, with the braking force directed axially towards the gearbox component .

Other examples of shaft brakes are referred to in US-A- 4211313, US-A-4727764 and DE-A-19652916.

SUMMARY OF THE INVENTION

An object of the invention is to solve said problems and provide a synchronisation brake which is inexpensive to manufacture and fit and occupies minimum space in the gearbox. The synchronisation brake has also to be easy to maintain and be fittable to existing gearboxes. The invention eliminates the need for synchronisation rings in the gearbox.

The abovementioned and further objects are achieved according to the invention by a device according to the features indicated in the characterising part of claim 1.

The invention also relates to a brake device which by electromechanical, hydraulic or pneumatic means, e.g. via vehicle's own existing compressed air system, can act upon a layshaft in a gearbox in such a way that it is braked in a controlled manner during gearchanges . The brake device may take the form of a unit fittable on existing gearboxes close to an outside of the gearbox where it is readily accessible for fitting and maintenance work and situated in such a way that the brake does not encroach upon spaces intended for other vehicle components within or outside the gearbox and does not entail modifications to the configuration of the gearbox.

A control system, not further described here, activates the brake by allowing a flow, e.g. via solenoid valves, of a pressure fluid such as compressed air into ducts to cause a piston to move in such a way that the two levers articulated on a common spindle are used to rotate at least one oval element which, as a result of such rotation, expands sideways and presses on brake linings situated in the immediate vicinity. The brake linings are moved somewhat and press themselves against surfaces arranged on the reverse gearwheel and, by friction, brake the reverse gearwheel and lower the speed of the layshaft to a desired rotation speed.

Further features and advantages of the invention are indicated by the more detailed description set out below and the attached drawings and claims .

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described below in a preferred embodiment example with reference to the attached drawings.

Figure 1 depicts a perspective view of a known type of stepped gearbox, in this case a manual stepped gearbox intended for a truck, with the reverse gearwheel partly visible.

Figure 2 depicts the housing of the gearbox as seen from in front, with only the reverse gearwheel and the brake device fitted. Figure 3 depicts a side view of the service aperture of the gearbox at the region of the location of the reverse gearwheel, with the brake device fitted.

Figure 4 depicts in more detail, in a view as seen from in front, the brake device fitted to the reverse gearwheel. Figure 5 depicts in a view as seen from in front the brake device in Figure 4 with a protective and guide plate fitted.

Figure 6 depicts a perspective view of the brake device in Figure 5.

DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 depicts a side view of a stepped gearbox 1. A service aperture 2 which is normally covered by a hatch fitted over it makes it possible for a gearbox component such as a reverse gearwheel 3 to be accessible, e.g. for replacement, inspection or maintenance. The function of the reverse gearwheel 3 in the gearbox 1 is to change the direction of rotation. The brake device 4 according to the invention is only partly depicted in the figure.

Figure 2 depicts the housing of the gearbox 1 as seen from in front, with only the reverse gearwheel 3 and the brake device 4 fitted, for the sake of clarity. The reverse gearwheel 3 is mounted on a reverse shaft 5 supported in the housing of the gearbox 1. An actuating means, e.g. a hydraulic or pneumatic cylinder 6 with a piston, is arranged in such a way that when the cylinder 6 is activated a rod 7 coupled mechanically to the piston is caused to move forward/back substantially in its axial direction. The rod 7 itself acts upon one or more levers 8 connected articulatedly to it. A pipe 10 is connected to the cylinder 6 to supply pressurised hydraulic oil or air in a conventional manner. The cylinder 6 may with

advantage be fitted to, or be an integral part of, the cover (not depicted) which normally closes the service aperture 2. The rod 7 is suitably supported in the housing of the gearbox 1 in such a way that said axial movement is effected. The brake device 4 occupies so little space and is so configured that it may be situated in or adjacent to an existing gearbox component 3 without entailing any constructional or geometric modifications or adaptations to the existing gearbox 1 or its housing.

For the brake device 4 to function, it requires an electronic control system including sensors, electric cables and, where applicable, pipelines for compressed air or hydraulic fluid. These are not described in more detail, since a suitable control system is already known and is described, inter alia, in patent specification SE527267C2 filed by the same applicant.

Figure 3 depicts the service aperture 2 as seen from directly in front. As previously mentioned, the service aperture 2 is normally covered by a hatch (not depicted) fitted by means of purpose-made threaded holes 11 in the housing of the gearbox 1. The figure shows the reverse gearwheel 3 situated centrally in the service aperture 2. The cylinder 6, which may also be larger than as here depicted, appears on the left side of the reverse gearwheel 3.

Figure 4 depicts in more detail the reverse gearwheel 3 with the constituent parts of the brake device 4. The pipe 10 leads to the cylinder 6, and the latter 's internal piston and shaft cause the rod 7 to move in its axial

direction. Levers 8a, b are movable relative to the rod 7 via articulations 9a, b. At the end regions of the levers 8a, b there are oval or ellipsoid elements 14a, b respectively situated between a pair of brake bands 15a, b and 16a, b which are adapted to pressing against brake surfaces or inside surfaces 17a, b of the reverse gearwheel 3. The brake bands 15a, b and 16a, b have curved shapes and are adapted to the curved surfaces 17a, b of the reverse gearwheel 3. A first surface 17a is constituted by the shaft hub 18 of the reverse gearwheel 3, and a second surface 17b by the inside of the toothed rim 19 of the reverse gearwheel 3. The brake bands 15a, b and 16a, b are held in place, inter alia, by spigots 20 which run through holes or along grooves arranged in the brake bands 15a, b and 16a, b. The brake bands 15a, b and 16a, b are adapted to exerting the braking force in the radial direction of the reverse gearwheel 3 in order to minimise mechanical loading sideways. The brake bands 15a, b and 16a, b and the elements 14a, b are in principle fitted within the reverse gearwheel 3.

When the rod 7 is pressed inwards by the cylinder 6, i.e. towards the left in Figure 4, the elements 14a, b rotate somewhat under the action of the levers 8a, b and, owing to their oval shape, they expand in the transverse or horizontal direction and press the respective brake bands 15a, b and 16a, b outwards, to the sides, so that they come into engagement with the inside surfaces 17a, b of the reverse gearwheel 3. The reverse gearwheel 3 is thus subjected to a selectable braking force.

Figure 5 depicts substantially the same parts as Figure 4 except that a cover plate 21 provided with holes 22 for the spigots 20 and the elements 14a, b is arranged beside the reverse gearwheel 3 and intended to hold the brake bands in place during operation.

Figure 6 depicts the reverse gearwheel 3 and its brake device 4 in perspective view, showing the positions of some of the components more clearly. It illustrates, for example, how the spigots 20 extend through the cover plate 21.

In the embodiment described, the toothed rim 19 of the reverse gearwheel 3 engages in a conventional manner by constant tooth engagement both with a toothed rim on a layshaft in the gearbox and with a freely rotatable reverse shift gearwheel on the mainshaft of the gearbox, which can for reverse gear function be engaged with the mainshaft. In a conventional manner, there are on the mainshaft, for respective gear steps, other freely rotatable shift gearwheels which are capable of being coupled with the mainshaft and are in constant tooth engagement with fixed gearwheels on the countershaft of the gearbox 1.

As previously mentioned, the cylinder of the brake device is operated by means of a suitable pressure fluid. In the example described, compressed air from a source such as a compressor in the vehicle in which the gearbox is installed may be used. Such a compressed air source is commonly in standard use in most of the vehicles here referred to. The compressed air is fed via control

devices and pipelines connected to the brake device. The pressure level of the compressed air is controlled by a regulating or solenoid valve which is itself controlled by an electronic control unit. The control unit may also be an integral part of the computer's own computer.

The control unit also receives, as previously mentioned and in a conventional manner, signals from various sensors, e.g. a speed sensor detecting the speed of the reverse gearwheel, a speed sensor detecting the speed of the mainshaft, a gear selector sensor detecting the chosen gear step etc. The control unit calculates thereafter for the speed of the reverse gearwheel a set-value to which its rotation speed is braked during gearchanging .

The invention is described above with reference to a preferred embodiment. The invention is of course is not limited thereto, since other variants of the invention are also possible within the protective scope of the claims.

The brake device may for example be so configured that the direct braking effect is exerted on other components of the gearbox. Instead of the pneumatic or hydraulic means mentioned, it is also possible to use an electromechanical action upon the lever or levers . This may be an electric motor or a solenoid.