Shifting force transmitting device and gear shift apparatus using same

D e s c r i p t i o n

The present invention relates to a resilient shifting force transmitting device for a gear shift apparatus, in particular for transmitting a shifting force between a gear shift lever operated by the driver and a gearbox in a motor vehicle, and to a gear shift apparatus in which such a device is used.

EP 1482213 Al discloses a shifting force transmitting device of this type, which is made resilient in order to prevent vibrations of the gearbox from being transmitted to the gear shift lever or least to attenuate such vibrations.

There is a problem with such resilient shifting force transmitting devices in that due to a possible deformation of the device, there is no strict one-to-one relation between the position of the gear shift lever, on the one hand, and of components of the gearbox which should be controlled by said lever, on the other hand. If the transmitting device is easily deformed, it is difficult for the driver to feel whether the gearbox has indeed reached a desired configuration. Further, since the range of displacement of the gear shift lever is usually limited, so is the deformation which can be applied, and accordingly, so is the maximum force it can transmit to the gearbox. I.e., if shifting in the gearbox is tight, it may be difficult to apply the shifting force necessary for reaching a desired configuration.

BESTATIGUNGSKOPIE

EP 1482213 Al seeks to solve this problem by providing a shifting force transmitting device having a spring rate which is variable according to the amount of deformation, namely which has a low spring rate at low deformation and a high spring rate at high deformation. In this way, since the amplitude of vibrations of the gearbox is small, they can only cause a small deformation of the transmitting device, and, hence, only a low force is transmitted to the gear shift lever. By a shifting movement of the gear shift lever, having a large amplitude, a reasonably high shifting force can be applied to the gearbox.

However, since the spring rate is low at small deformations, it is still difficult for the driver to control the shifting movements in the gearbox precisely. On the other hand, strong and rapidly fluctuating forces which are likely to occur in the shifting apparatus in a phase of the shifting process in which gearwheels of a newly selected gear are beginning to lock in the gearbox are strongly felt by the driver, giving him the impression that the gearbox is recalcitrant.

The object of the present invention is to provide a resilient shifting force transmitting device and a gear shift apparatus using such a transmitting device which allow the driver to keep precise control of a shifting movement in the gearbox while preventing him from feeling undesirable force fluctuations during the shifting process.

This object is achieved by a resilient shifting force transmitting device for a gear shift apparatus, the device having a spring rate which is variable according to the amount of deformation, which is characterized in that the device has a first, high spring rate at a first, low deformation and a second, low spring rate at a second, high deformation. The inventors found that the force a driver applies at the shift lever of a gear shift apparatus is variable according to the phase of the shifting process, and that it is highest during a synchronizing phase of the shifting process and the subsequent engagement phase in which

a synchronizer sleeve enters the engagement ring of a mating gear, which is also the phase in which the above-mentioned force fluctuations are likely to occur. By designing the force transmitting device to have a low spring rate in a force range corresponding to these phases of the shifting process, the driver can be prevented from feeling the fluctuations, whereas when the force applied by the driver is low, at the beginning and the end of the shifting process, the device provides a rather rigid coupling between the gear shift lever and the gearbox, enabling a precise control.

Generally speaking the second deformation is a fraction of a millimetre, preferably at least 0.1 mm.

The first spring rate should be at least twice at high as the second spring rate.

At a third deformation higher than the second one, the device may have a third spring rate which is higher than the second spring rate, in order to enable a high shifting force to be transmitted.

In that case, the spring rate must have a minimum somewhere between the first and the third deformations. Preferably, this minimum is in a deformation range of one to three millimetres .

According to a practical embodiment, the shifting force transmitting device comprises a leaf spring having two end portions which are displaceable with respect to each other under the effect of a shifting force, and a central portion which is laterally offset with respect to a straight line extending between the two end portions. Such a leaf spring, when operated under compression, has a highly nonlinear spring rate which decreases with increasing compression of the spring.

In order to prevent permanent deformation of such a leaf spring under an excessive shifting force, the device may further comprise an auxiliary spring element connected to a first one of the end portions of the leaf spring and an abutment connected to the other end portion of the leaf spring, the auxiliary spring coming into contact with the abutment when the leaf spring is deformed beyond a threshold. This auxiliary spring may e.g. be a solid body of resilient material.

Further, the shifting force transmitting device may comprise an outer casing, a central engaging portion for engaging a shift lever of the gearbox, and at least two of said leaf springs arranged between the engaging portion and the casing so as to transmit push and pull shifting forces between said casing and said engaging portion.

The object of the invention is also achieved by a gear shift apparatus comprising a gear shift lever and at least one shifting force transmitting device as defined above operably connected to said gear shift lever.

In this apparatus the gear shift lever and the shifting force transmitting device are preferably connected by a push-pull cable.

The gear shift lever is preferably designed such that if a lever force applied it is less than ION the transmitting device has said first deformation, and if a lever force of more than 2ON is applied it has said second deformation

Further features and advantages of the invention will become apparent from the subsequent description of embodiments referring to the appended drawings.

Fig. 1 is a perspective view of an embodiment of the shifting force transmitting device;

Fig. 2 is a cross section of the device in an equilibrium state; and

Fig. 3 is a cross section of the device in a stressed, deformed state; and

Fig. 4 is a force-deformation characteristic of the device.

Fig. 5 is a perspective view of a gear shift apparatus comprising two of the shifting force transmitting devices; and

Fig. 6 illustrates the force applied by a driver to the gear shift lever of the apparatus of Fig.

5 in a gear shifting process.

Fig. 1 is a perspective view of a device for resiliently transmitting operating forces between a driver-operated gear shift lever, on the one hand, and a controlled lever mounted on a gearbox in a motor vehicle, on the other hand. The device has an elongate outer casing 1 from which protrudes a push-pull rod 2. The push-pull rod 2 is connected to the gear shift lever via a cable guided in a flexible but incompressible tube, according to a design familiar to the man of the art. In the centre of the casing 1, there is receptacle 3 for engaging a spherical knob of the control lever of the gearbox. The receptacle 3 is displaceable in the longitudinal direction of the casing 1. To this effect, it is held between two spring assemblies 4, 5, each of which comprises two L-shaped rubber blocks 6, 7 and a leaf spring 13.

As is best seen in Fig. 2, in each spring assembly 4, 5, the rubber blocks 6, 7 have mutually orthogonal branches 8, 9 and 10, 11, respectively. In a relaxed configuration of the device, as shown in Fig. 2, branch 9 is in contact with a peripheral wall of casing 1, branch 11 is in contact with receptacle 3, and branches 8, 10 face each other, so that between

the two rubber blocks 6, 7, a T-shaped space 12 is formed. In a portion of this space 12 corresponding to the cross bar of the T, the slightly curved leaf spring 13 extends between the two rubber blocks 6, 7.

If a pushing force is applied to the casing 1 by push-pull rod 2, the casing 1 is displaced with respect to the receptacle 3, as shown in the cross section of Fig. 3. Since in the configuration of Fig. 2 the leaf springs 13 of the two assemblies 4, 5 are practically unstressed, the spring assembly 4 opposite to push-pull rod 2 does not expand noticeably, and a gap 14 forms between branch 11 and receptacle 3. On the other hand, the spring assembly 5 between receptacle 3 and push-pull rod 2 is compressed, whereby the curvature of its leaf spring 13 is increased. It is easily seen that in a configuration where the curvature of the leaf spring 13 is small, the curvature increases strongly when the assembly is compressed by a given amount, and that the increase of curvature becomes the smaller, the greater the curvature is. In other words, the derivative of the curvature of spring 13 with respect to the length of assembly 4, 5 is negative, and its amount decreases with decreasing length. This causes the spring assembly 4 to exhibit a strongly nonlinear spring rate: the spring rate is highest when the leaf spring 13 is in the unstressed configuration of Fig. 2, and it becomes the smaller the more the spring assembly 4 is compressed. Only when the facing branches 8, 10 of the rubber blocks 6, 7 come into contact and begin to be deformed, the spring rate of assembly 4 increases steeply again.

Spring assembly 4 exhibits the same behaviour in case of the push-pull rod 2 transmitting a pulling force. In this way, a spring force-displacement characteristic as shown in the graph of Fig. 4 is obtained. Zero displacement corresponds to the equilibrium position of Fig. 2. The ordinate is representative of the restoring force effective between the casing 1 and the receptacle 3. There is a range of approximately +/- 0.2 mm width around the equilibrium position in which the device is rather

rigid, exhibiting a spring rate of up to approximately 200 N/mm. When the displacement increases, the rigidity becomes less, and in the displacement range of approximately 0.5 to 2 mm it reaches a minimum of approximately 50 N/mm. At a displacement of 2 mm, corresponding to the rubber blocks 6, 7, of one of the spring assemblies 4, 5, coming into contact with each other, the rigidity increases strongly again, so that at a displacement of more than 2 mm, the spring rate is noticeably higher than around equilibrium position.

Fig. 5 is a perspective view of a gear shift apparatus according to the present invention. It comprises a base 15 for mounting on a transmission tunnel of a motor vehicle in which a gear shift lever 16 is mounted with two rotational degrees of freedom. Within the base, a spring-loaded detent mechanism is provided which defines a neutral position and several engaged positions corresponding to different gear ratios of a conventional gearbox, not shown, which is controlled by the apparatus. The possible paths of movement of the gear shift lever are conventionally defined by a mask in which a pattern of slots is formed, through which the gear shift lever 15 extends. The pattern comprises a neutral slot and several engagement slots extending orthogonally from the neutral slot, their ends corresponding to the above-mentioned engaged positions. The detent mechanism, being familiar to the man of the art, is not represented in detail in the Fig.

Two of the above-described force-transmitting devices 17 are connected to gear shift lever 16 by push-pull wires guided in incompressible tubes 18, 19. One of the devices 17 transmits a rotation of the lever 16 in the neutral slot, the other transmits a rotation along the engagement slots. The receptacles of the devices 17 are for engaging operating knobs of the gearbox. The gear shift lever 16 has a reduction rate of approx. 2:1 to 4:1, i.e. a displacement of the handle 20 at the free end of lever 16 of 1 cm corresponds to a displacement of 0.5 to 0.25 cm of the casing 1 of one of the devices 17.

Fig. 6 illustrates the development of the force a driver applies to the gear shift lever 16 in a gear shifting process. In a first phase labelled A in the Fig., the driver overcomes a resistance of the above-mentioned detent mechanism when turning the gear shift lever 16 away from an engaged position and into neutral position. When the lever 16 has reached the neutral slot, near 38.1 ms in Fig. 6, it can move in the neutral slot practically without resistance. When re-entering an engagement slot, between 38.1 and 38.2 ms, resistance of the detent mechanism makes itself felt again. The resistance of the detent mechanism does not exceed 25N applied to the handle 20, corresponding to a force of not more than 75 N at the force transmitting devices 17 if a reduction of 3:1 by the gear shift lever 16 is assumed. As can be seen in Fig. 4, the spring rate of the devices 17 is high at such a force, and the deformation of the devices is small, so that shifting movements driven in the gearbox via the transmitting devices 17 are closely coupled to the position of lever 16 and can be felt precisely by the driver.

In phase B of Fig. 6, synchronization of the gears occurs in the gearbox. Now the force at the handle 20 increases above 25 N, its peak depending on the speed at which the driver moves the handle 20. In the graph, an exemplary peak value of approx. 40 N is shown, typical values being in a range of 40 to 80 N. Taking account of the reduction rate of gear shift lever 16, this corresponds to a force of approx. 120 N applied to the transmitting device 17. I.e. in phase B the transmitting device reaches a deformation state in which it is rather soft.

When the gears have been synchronized in the gearbox, they are brought into engagement in phase C of Fig. 6. This involves a momentary interruption of traction forces, which may induce a certain loss of synchronization. The gears will then not engage smoothly, causing the shifting force transmitted to the gears by the transmission device 17 to vary wildly, as indicated by a dashed line in Fig. 6, which in a conventional, rigidly

coupled gear shifting apparatus would give the driver the unpleasant sensation of a poor shift. However, since the spring rate of the devices 17 is soft at such forces, the driver does not feel the strong oscillations, but rather a low-pass filtered force as illustrated by the solid curve in phase C. I.e. what the driver feels is a smooth shift.

As pointed out above, the shifting force can easily exceed 4ON if the driver shifts quickly. If the maximum force applied by the driver is e.g. 80 N, the force acting on the transmission device amounts to approx. 250N. In this range, as shown in Fig. 4, the spring rate is high again. Therefore, the deformation of the transmitting device - and, accordingly, the deviation between the shift lever position and the state of the gearbox - does not grow to an impractical extent under a high shifting force, and a high shifting force can be applied to the gearbox if necessary even when the shift lever reaches an abutment at the end of one of the engagement slots into which it was moved by the driver.

L i s t o f r e f e r e n c e s i g n s

casing 1 push-pull rod 2 receptacle 3 spring assembly 4, 5 rubber block 6, 7 branch 8, 9, 10, 11 space 12 leaf spring 13 gap 14