BRAKE DEVICE FOR SYNCHRONIZING OF GEARS IN A GEAR BOX AND GEAR BOX PROVIDED THEREWITH

TECHNICAL FIELD

The present invention relates to a brake device for a stepped gear box which is adapted to brake the speed of rotation of a lay shaft in a controlled manner. The brake device is especially arranged for vehicles with manual gear boxes such as trucks, passenger cars, buses etc. The invention also relates to a brake device which occupies a small space in the gear box and comprises at least one lever that exerts friction against a component in the gear box. The invention also relates to a gear box provided with said brake device.

BACKGROUND

Stepped gear boxes for vehicles may have up to 15-16 gears and 5-6 synchronizing devices and usually comprise a main shaft with a number of freely journalled gear change gears that are engaging a corresponding number of fixed gears arranged on a lay shaft. During a gear change operation, before one of the freely journalled gear change gears may be engaged with the main shaft, the speed of rotation of the gear change gear is synchronized, the speed is adapted, to the speed of rotation of the main shaft using a mechanical synchronizing device, which serves as brake for the gear change gear. These synchronizing devices, one for each gear change gear, are expensive and take up space and are today replaced more and more often by a single, e.g. electronically controlled, shaft brake which brakes the speed of rotation of the lay shaft so that the speed of rotation of the gear change gear which is to be engaged, is synchronized with the speed of rotation of the main shaft. By that the synchronizing packs are removed, the length of the gear box may be shortened and manufactured at lower cost.

Shaft brakes are previously known but comprise relatively complicated units with several separate parts that make them costly and time consuming to manufacture and assemble. They furthermore still take up a relatively large space in the gear box and demand interference in and changes of the design of the gear box.

In the patent SE524354, applied for by Volvo, a shaft brake is shown where a brake element is integrated with, and constitutes a part of, the shaft that is to be braked. The brake acts on a conically shaped surface at the end of the shaft in question. This brake is associated with a number of drawbacks. Among other things, it requires substantial changes of the internal design of the gear box. The brake is difficult to replace and to maintain, e.g. if the linings have to be replaced due to wear. The braking effect is reduced as the lever from the center of the shaft to the point of engagement of the brake linings is short and it can be difficult to sufficiently fast conduct away the friction heat which arises at frequent or frequently occurring gear changes .

In the patent SE527267, applied for by Scania, a synchronizing brake with a ring shaped brake element is also shown. The drawbacks are to a large extent the same as for the brake according to the patent SE524354.

Other examples of shaft brakes are shown in the patent documents US-A-4 211313, US-A-4727764 and DE-A-19652916.

SUMMARY OF THE INVENTION

An object of the invention is to solve the mentioned problem and to supply a synchronizing brake that has few parts, is inexpensive to manufacture and assemble and that requires a minimum of space in the gear box. The synchronizing brake

shall also be easy to assemble and to maintain. By the invention the need for synchronizing rings in the gear box is eliminated.

The above mentioned and further objects are achieved according to the invention by a device according to the, in the characterizing portion of claim 1, mentioned features. The invention thus relates to a brake device which, by means of e.g. pneumatics via the own existing pressure air system on the vehicle, may actuate a lay shaft in a gear box so that the lay shaft is braked in a controlled manner during gear change. The brake may be designed as a separate unit or module, with an own casted house, which may be assembled on existing gear boxes close to an outer side of the gear box where it is easily accessible for assembly work and maintenance work and placed in such a way that the brake does not intrude on spaces intended for other vehicle components outside of the gear box and without the need for changes of the internal design of the gear box.

A control system, not shown in more detail, activates the brake by letting in, e.g. via magnetic valves, pressurized air into the channels which makes the both pistons to move in a direction towards each other and will press against the two levers, journalled on a common axis, which in turn is pressed with its outer ends against the side surfaces of the reverse gear and thereby brakes the reverse gear by friction and decreases the speed of rotation of the lay shaft to the required speed of rotation.

Further features and advantages of the invention are evident from the subsequent detailed description and from the attached drawings and claims .

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 shows a perspective view of a known type of stepped gear box, in this case a manually shifted box intended for a truck.

Figure 2 shows a part of the gear box with assembled brake module,

Figure 3 shows a cross-section seen from above through a gear box according to figure 1 and with an assembled brake.

Figure 4 shows in more detail a part of the section in figure

3 and where the assembly of a brake module according to the invention is evident.

Figure 5 shows a cross-section through the brake module in more detail.

Figure 6 shows a section right through the gear box and how the brake according to the invention is assembled in relation to the reverse gear which is to be braked.

DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 shows a side view of a stepped gear box 1 of known type. In the figure the whole gear box is shown together with a casing which in assembled state usually encloses a coupling device. Through a maintenance cover, here removed, a reverse gear 2 assembled on a lay shaft in the gear box may be made accessible, e.g. for assembly, inspection or replacement.

Figure 2 shows a part of the gear box 1 in figure 1 with a brake device 3 according to the invention in the form of a separate unit or module assembled in the same attachments 4 as for the said maintenance cover. The outer shape of the brake device 3 is evident from here. A plate, with a rectangular shape which corresponds to the maintenance cover, forms a casted base element on which the other parts of the housing are arranged. Thus appears e.g. the housing part 5 which

contains the different active components of the brake, one of the two connections 6 for pressure fluid and a cover shaped part 7 which covers the reverse gear 2.

The brake device 3 requires for its function an electronic control system with sensors, electrical cables and piping for pressurized air. These are not shown in more detail in the figure as a suitable control system is earlier known and described in among others the patent document SE527267C2, filed by the same applicant.

Figure 3 shows a cross-section from above through the gear box 1 according to figure 1. From here are evident the different parts that a standard stepped gear box comprises. From the cross-section is also evident the lay shaft 8 in question, reverse shaft 9 with the reverse gear 2 and the braking device 3 with its levers 10a, b.

Figure 4 shows, in more detail, a part of the cross-section in figure 3. The reverse shaft unit 11 shown in the figure comprises a lay shaft 8 and a reverse shaft 9 with a reverse gear 2. The reverse shaft 9 is assembled torsionally fixed in a pair of opposed wall sections 11a, b in the housing of the gear box 1. The reverse gear 2 is in turn journalled freely rotatable on the reverse shaft 9 via roller bearings 12. Axial washers 13a, b are arranged as liners on both sides of the reverse gear 2.

In the described embodiment the tooth track 14 of the reverse gear 2 engages in a known way with constant engagement of teeth on one hand with a tooth track 15 on the lay shaft 8 in the gear box 1, on the other hand with a freely rotatable reverse gear change gear on the main shaft of the gear box (not shown) , which for the reverse gear function may be engaged with the main shaft. In a known way, other freely rotatable and with the main shaft engageable gear change gears on the main shaft for the respective gear steps, stand in

constant tooth engagement with fixed gears on the lay shaft 8 (see figure 3 ) .

As mentioned, the pistons 16a, b of the brake device 3 are operated through a suitable pressure fluid. In the example described, pressurized air from a pressure source, not shown, such as a compressor in the vehicle where the gear box is installed may be used. Such a source for pressurized air is usually present as standard in most vehicles referenced to here. The pressurized air is fed via not shown control components and piping connected to connections 6a, b in the housing of the brake device 3. The pressure of the pressurized air is controlled by a, here not shown, control valve or magnetic valve which in turn is controlled by a not shown electronic control unit. The control unit may also be an integrated part of the computer in the vehicle.

The control unit further receives, as mentioned and in a known way, signals from different sensors not shown here, e.g. a revolution sensor which detects the present speed of rotation of the reverse gear 2, a revolution sensor that detects the speed of rotation of the main shaft, a gear selector sensor which detects the chosen gear step from the driver etc. The control unit thereafter calculates a desired value for the speed of rotation of the reverse gear 2 to which its speed of rotation is to be braked at the gear change.

In figure 5 the brake device 3 is shown in more detail. The brake device 3 is with its different parts housed in a casted housing. The towards the gear box 1 facing assembly surface is, in this embodiment, designed to fit directly against the assembly surface on the gear box 1 that normally otherwise is covered by a maintenance cover and behind which the earlier mentioned reverse gear 2 is placed. An other suitable opening in the wall of the gear box 1 may naturally be arranged if a maintenance cover is missing. Two levers 10a, b are, at least

in some degree, turnably journalled at an shaft 17 or pin which in turn is fixed in the housing.

Pistons 16a, b are slidably and coaxially arranged in separate cylinders 18a, b in the housing and arranged to exert a mechanical pressure against the outer sides of the levers . The pistons 16a, b are on their outer, towards the levers 10a, b faced surface, somewhat convexely shaped and seal against the cylinder walls in the conventional way using seals or O-rings 19a, b. The levers 10a, b have such a length and are so placed that they extend into the gear box 1 and run along the respective side surfaces of the reverse gear 2 and at a such degree that they, directly or indirectly, e.g. via for this adapted brake linings placed at the outer ends of the levers 10a, b may produce enough friction between the reverse gear 2 and the respective lever 10a, b when they are activated. The friction may also be produced without particular brake linings, i.e. by metal-to-metal contact, which simplifies the construction but in spite of this offers sufficient friction. By using two levers 10a, b which when braking move in a direction towards each other and thereby press against the reverse gear 2 on either side, the side moments counterbalance each other whereby the risk of uneven load of the reverse gear 2 is minimized.

Figure 6 shows a cross-section through the gear box 1 where the placement of the reverse gear 2 in the gear box 1 is evident as also the placement of one lever 10 in relation to the reverse gear 2.

The invention has been described above referring to a preferred embodiment. Naturally, the invention is not limited to this but also other variations of the invention are possible within the scope of the claims.

It is thus possible to instead of two brake arms use only one arm which acts on one sole surface of e.g. the reverse gear.

Naturally, the brake device may be designed so that the direct braking effect is exerted on other parts in the gear box and also via brake linings. Further, instead of pneumatics or hydraulics, an electromechanical influence may be used on the lever or the levers. This may be a motor or a solenoid.

It is also conceivable that the levers are provided with teeth that engage with each other in the immediate vicinity of the pin, around which the levers are journalled. In this way both arms could be made to press against the gear box component from two sides with only one piston or one electromechanical device.