GB2056598A - Facilitating gear shift into reverse - Google Patents

Abstract

In a reverse speed shift device for a motor vehicle change-speed gearbox which actuates a brake device (16) during a part of the shift movement to brake a gear box shaft (17), a part of the shift device (4) actuates a switch (6) which causes an auxiliary force to act for a specific period upon a servo device (12) which actuates the brake device (16). Actuation of the switch (6) energises not only the servo device in the form of a solenoid (12) via a time- switch relay (11) but also a reversing lamp (7). Alternatively, the servo device may be pneumatic or hydraulic. <IMAGE>

Description

SPECIFICATION Reverse speed shift device for a motor vehicle change-speed gearbox The invention relates to a reverse speed shift device for a motor vehicle change-speed gearbox with a brake device actuated during a part of the shift movement by a part of the shift device to brake an after running gearbox shaft.

A reverse speed shift device of the type initially defined is known from DE-OS 23 36 250. In this reverse speed shift device, during the preselection movement in order to engage the reverse speed a spring arrangement is loaded through the selector sleeve of the gearbox input shaft so as to skew it, so as to brake the gearbox input shaft by the thus increased friction.

The known shift device exhibits the disadvantage that the components necessary for the normal shift actuation are utilized as a brake device, with the result that they must be of correspondingly complicated and costly construction from the outset.

It is generally customary in motor vehicle construction for a vehicle model to be offered with engines of different capacities, correspondingly adapted clutches and a substantially identical change-speed gearbox.

In the different engine-clutch-gearbox combinations it has been discovered that in many combinations scarcely any difficulties arise when an unsynchronised reverse speed is selected.

With certain engine-clutch-gearbox combinations, in which the clutch plate exhibited a high inertia, as a result of an increased after-running time of the connected gearbox shafts difficulties in the form of disturbing grating noises were always experienced when the driver attempted to engage the unsynchronised reverse speed within this after-running period.

Because the driver of a motor vehicle can only be expected to wait a certain time between disengaging a forward speed and engaging the reverse speed, it was necessary to find a solution which reduces this prolonged after-running time by simple means in this specific engine-clutch-gearbox combination.

It is the aim of the invention to produce a subsequently installable brake deviceforthe afterrunning gearbox shaft in a given motor vehicle change-speed gearbox without modifying the normal series and with the smallest possible outlay. At the same time the actuation of the subsequently installable brake device should not increase the normal shifting force.

This aim is achieved according to the invention in that the device components disclosed in Patent Claim 1 are added and the circuit measures disclosed embodied to a reverse speed shift device of the type initially defined.

Convenient embodiments of the solution according to the invention are explained more fully in Patent Claims 2 and 3.

Due to the fact that a part of the selection device actuates a switch which causes an auxiliary force to act for a specific period upon a servo device which actuates a brake device acting upon the gearbox shaft, the force necessary for braking the afterrunning gearbox shaft is not derived from the selection force at the selection lever, but from an auxiliary force, e.g., the electric current, the negative pressure of the internal-combustion engine or the pressure of a hydraulic pressurised medium.

In this manner the desired braking of the afterrunning gearbox shaft can be achieved without influencing the normal selection force at the selection device, whilst the control and use of an auxiliary force can be co-ordinated in such a way that even very brief and precise braking times can be attained.

The invention is explained more fully with reference to an exemplary embodiment illustrated in the accompanying drawing, wherein: Figure 1 shows a vertical section through the gearbox extension of a motor vehicle change-speed gearbox in the region of the manual shift device with the schematically indicated selection measure; Figure 2 shows a vertical section through a motor vehicle change-speed gearbox in the region of the brake device for braking the after-running gearbox shaft; and Figure 3 shows a horizontal partial section through the motor vehicle change-speed gearbox according to Figure 2 in the region of the brake device.

Figure 1 shows a conventional gearbox extension 1, which carries a conventional manual shift device 2. The lower end 4 of the manual selector lever, which co-operates with the selector shaft 3, cooperates in known manner with a lock 5 for the engagement of the reverse speed. When the lock 5 is overcome, in the present case by pressing the manual selector lever vertically downwards, the plane of the reverse speed can be preselected. In this case the end 4 of the manual selector lever actuates a switch 6 for a schematically illustrated reversing lamp 7.

The switch 6 for the reversing lamp 7 is connected through a line 8 to the plus pole of a voltage source.

A solenoid 12 is included in the cirucit 9 to the reversing lamp 7 through a line 10 and a time-switch relay 11. As is customary in motor vehicle contruction, the reversing lamp 7 and the solenoid 12 have their other terminal connected to earth.

As will be seen from Figures 2 and 3, the solenoid 12 is fixed by a screwthreaded bushing 13 in a bore 14 in the housing 15 of a motor vehicle changespeed gearbox. A brake device 16 for the gearbox shaft to be braked, in this case the layshaft gearwheel block 17, is arranged in its wide cylindrical region between the gearwheel of the constant and the gearwheel of the third speed.

The brake device 16 substantially comprises a brake band 18, one end 19 of which is anchored by a bolt arrangement 20 to the housing 15, and the other two loop-like ends 21 of which wrap a bolt 22 in the centre of which the armature 23 of the solenoid 12attacks.

As soon as the driver of the vehicle presses the selector lever downwards in order to actuate the reverse speed, in order to overcome the lock 5, he actuates the switch 6 through the lower end 4 of the selector lever by preselecting the plane of the reverse speed. By this means firstly the reversing lamp 7 is switched on and secondly the solenoid 12 is energised. The time relay 11 interposed in the line 10 leading to the solenoid 12 causes a switching off of the solenoid 12 after a period after which the revolving gearbox shaft 17 has been braked to zero.

The period to be controlled by the time relay 11 must of course be determined according to the individual case, but in the majority of cases a period between 0.5 and 1.5 seconds will be sufficient. The use of the auxiliary force makes it possible in this case for even very short periods for braking the after-running gearbox shaft to be maintained, inasmuch as the corresponding parameters of the brake device such as width of the brake band, angle of wrap of the brake band, friction lining on the brake band and actuating force of the servo device can be dimensioned appropriately.

The exemplary embodiment shown in Figures 1 to 3 represents only one possible construction. It is self-evident that the negative pressure of the internal-combustion engine orthe pressure of a hydraulic pressurised medium available in the motor vehicle may be used in equally favourable manner as auxiliary force for the servo device.

In the case ofthe pneumatic auxiliary force, it is possible in this case to use a simply acting membrane unit as a servo device, the loading of which with negative pressure is effected either through solenoid valves controlled by the switch 6 or else through pneumatic valves actuated directly by the lower end 4 of the selector lever, whilst by an appropriate arrangement of these pneumatic valves a time relay may be dispensed with if said pneumatic valves are arranged so that the membrane servo is loaded with negative pressure only during the preselection movement of the reverse speed, but is isolated from the negative pressure and connected to the atmosphere during the engagement of the reverse speed. A delayed release of the brake band can be achieved by an appropriate throttling of the ventilation.

In similar manner the brake device can be actuated by the hydraulic pressure of a pressurised medium.

The control of the pressurised medium supply which is necessaryforthis purpose can again be exercised electrohydraulically or purely hydraulically. The me asures required for this purpose are familiar to the expert and need not therefore be explained in detail.

Irrespectively of the embodiment of the brake device 16, the measures to be provided to the normal or standard gearbox are extremely minimal.

They are confined to the provision on the housing 15 of the gearbox of cast studs for the arrangement of the servo unit and of the bolt arrangement for the brake band and of a correspondingly suitable coun tersurfaceforthe brake band on the gearbox shaft 17 which is to be braked. In this case it may possibly become necessary to machine the zone between the gearwheel of the constant and the gearwheel for the third speed on the layshaft gearwheel block by fine turning or by grinding so as to reduce hammering in this region and to ensure a uniform action of the brake band.

All the other shift device components, such as are required for the normal actuation ofthe motor vehicle change-speed gearbox, remain totality unmodified. This gives rise to the further advantage that the device according to the invention for braking an after-running gearbox shaft does not influence the regular operation of the change-speed gearbox if it should happen to fail. With known devices, in which components of the shift device simultaneously acted as parts of the brake device, undesirable disturbances of gear selection could arise in the case of faults in the brake device.

The brake device according to the invention exhibits the further advantage that the individual parts of the brake device are known current compo- nents, the adaptation and design of which presents no difficulty to the expert. The rapid response time and the freely selective tightening force of the auxiliary force actuated servo device permit reliable solutions even for difficult individual applications.

Claims (3)

1. Reverse speed shift device for a motor vehicle change-speed gearbox with a brake device actuated during a part of the shift movement by a part of the shift device to brake an after-running gearbox shaft, characterised in that a part of the shaft device (4) actuates a switch (6) which causes an auxiliary force to actor a specific period upon a servo device (12) which actuates a brake device (16) influencing the after-running gearbox shaft (17).

2. Reverse speed shift device according to Claim 1, characterised in that the end (4) of the selector lever which co-operates with the selector shaft (3) in the preselection of the plane of the reverse speed actuates a conventional switch (6) for a reversing lamp (7) and in its circuit (9) there is included through a line (10) and a time switch relay (11) a solenoid (12), the armature (23) of which attacks one end (21) of a brake band (18) which wraps a region of the gearbox shaft (17) and the other end (19) of which is anchored to the housing (15).

3. Reverse speed shift device according to Claim 1, characterised in that the end (4) of the selector lever which co-operates with the selector shaft (3) during the preselection of the plane of the reverse speed actuates a valve, or through a switch a solenoid valve, which controls the loading of the servo device on the brake device (16) with an auxiliary force medium (negative pressure of the internal-combustion engine or pressure of a hydraulic pressurised medium).