This application is a U.S. National-Stage entry under 35 U.S.C. §371 based on International Application No. PCT/EP2008/002001, filed Mar. 13, 2008, which was published under PCT Article 21(2) and which claims priority to European Application No. 07005326.9, filed Mar. 14, 2007, which are all hereby incorporated in their entirety by reference.
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 1 482 213 A1 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).
EP 1 482 213 A1 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.
At least one 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. In addition, other objects, desirable features, and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.
The at least one object, other objects, desirable features, and characteristics, are 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 millimeter, preferably at least about 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 millimeters.
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, for example, 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 the 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 at least one object, other objects, desirable features, and characteristics, are 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 about 10N the transmitting device has the first deformation, and if a lever force of more than about 20N is applied it has the second deformation
The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and.
The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description.
As is best seen in
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
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
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 approximately 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 approximately 0.5 to 0.25 cm of the casing 1 of one of the devices 17.
In phase B of
When the gears have been synchronized in the gearbox, they are brought into engagement in phase C of
As pointed out above, the shifting force can easily exceed 40N if the driver shifts quickly. If the maximum force applied by the driver is, for example, 80 N, the force acting on the transmission device amounts to approximately 250N. In this range, as shown in
While at least one exemplary embodiment has been presented in the summary and foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.
Number | Date | Country | Kind |
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07005326.9 | Mar 2007 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2008/002001 | 3/13/2008 | WO | 00 | 4/8/2010 |