GB2276698A

GB2276698A - Adjusting a damper characteristic

Info

Publication number: GB2276698A
Application number: GB9404555A
Authority: GB
Inventors: Stefan Otterbein; Udo Neumann
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1993-03-31
Filing date: 1994-03-09
Publication date: 1994-10-05
Also published as: GB9404555D0; DE4310458A1; JPH06320931A; DE4310458C2

Description

-1 2276698 Method of adjusting a damper characteristic and a damper

arranaement for effectina the method

Prior art

The invention relates to a method of adjusting the damper characteristic of a damper, in particular a shock absorber forming part of a chassis system, according to the preamble of claim 1 as well as to a damper arrangement for effecting the method.

Such a method of adjusting the damper characteristic of a shock absorber forming part of a chassis system is known from DE-A-41 12 005. In the known method of adjusting the damper characteristic of a damper, which is connected by one end to the vehicle body and by the other end directly or indirectly to at least one wheel unit, the relative movement of two damper parts which are movable relative to one another is detected and a corresponding electric signal is produced. From said signal, a dependent signal value is derived, in particular a signal which corresponds to the piston acceleration, and from the two signals a control signal is then derived using a logic operation, with the overall aim of the known method being to effect an adjustment of the damper characteristic during the operating phases in which the damper is exposed only to low damping forces. Said operating phases generally arise in the region of the reversal points of the damper piston, and a changeover of the damping characteristic during said operating phases is advantageous in terms of noise optimization since changeover of the damper in the presence of a higher differential pressure normally leads to damper 1 operating noises which may be at least extensively avoided by changing over in the region of the reversal points of the damper piston.

Although the known method or the system operating according to the known method leads as a rule to advantageous results, continuing investigations have shown that a further improvement of the known method or of the known damper system would be desirable, at any rate for certain applications.

The object of the present invention is therefore to improve such a method of the type indicated initial ly still further as regards the suppression of changeover noises and to indicate a reliably operating, inexpensive damper arrangement for effecting the method.

The set object is achieved by a system of the type described having the features of claim 1 and, as regards the damper arrangement, by a damper arrangement having the features of claim 3.

Advantages of the invention An important advantage of the method according to the invention is that a fluid flow, in particular a pressure oil flow, in a flow channel may be monitored very precisely and, on the other hand, relatively easily for the occurrence of zero crossings of the flow rate, with the advantage achieved first of all over the initially described known method or damper system being that only a single measured quantity has to be monitored and evaluated in order to generate changeover enabling signals. Furthermore, monitoring the flow rate of the damper fluid as opposed to monitoring relative movements of the damper parts offers the advantage that, before a changeover in the region of the reversal points of the piston movement, it is still possible to await the completion of specific pressure equalizing processes, which at the moment of 2 reversal of the direction of the damper piston still lead to a continued flow of the fluid in the previous direction until the flow rate has actually become zero, so that the changeover is not actually effected until the differential pressure possibly leading to changeover noises has actually become zero.

A particular advantage of the damper arrangement for effecting the method according to the invention is further that the devices for measuring the flow rate of the damper fluid may be realized using a single leaf spring which in its state of rest closes a monitored circuit, is deflected by the damper fluid flowing through a flow channel and so interrupts said circuit, with one single leaf spring being sufficient to control a changeover of the damper characteristic in the region of both reversal points of the damper piston. It is further possible to dispose a leaf spring at either end of a flow channel or at opposite-lying openings of two flow channels, with the two leaf springs preferably being connected in series in a common circuit which is interrupted by one or the other leaf spring so long as the flow rate differs from zero or is still higher than a preselected limit value. In said refinement, however, it is impossible to distinguish between the two reversal points.

With regard to the preferred refinement of the damper arrangement for effecting the method according to the invention, it should be noted that it is admittedly already known from DE-A-40 19 463 to detect piston movements with the aid of changeover contacts on the piston of a damper; in the known arrangement, however, the changeover contacts are used to make it possible to detect the occurrence of the inward stroke and the outward stroke of the piston and to control a valve as a function of the operating state at any one time and not to detect a flow in a flow channel and purposefully to initiate changeover processes in the region of the zero crossings of the flow rate of the damper fluid. Furthermore, 3 in the known system. the constructional design of the changeover contacts using a sliding part, which is seated on the piston and slidingly displaceable relative to the piston, is in terms of construction relatively expensive for certain applications.

Drawings Further details and advantages of the invention are described in greater detail hereinafter with reference to drawings.

The drawings show:

Fig.1 a diagrammatic block diagram illustrating the method according to the invention; Fig.2 a diagrammatic partial longitudinal section through a damper arrangement for effecting the method according to the invention; Fig.3a + b diagrammatic views of the time characteristic of the piston speed and of the current in a circuit for generating changeover enabling signals; Fig.4 a diagrammatic partial longitudinal section through a modified damper arrangement for effecting the method according to the invention; and Fig.5a + b diagrammatic views of the time characteristic of the piston speed and of the current in a circuit for generating changeover enabling signals.

Fig.1 shows in particular a chassis control system 10 which in a conventional manner includes a damper arrangement 12, e.g. a 4 1 k shock absorber having a damper housing and a piston, which is slidingly displaceable in the damper housing and is provided with a controllable valve device 14. According to the invention, the velocity of a damper fluid in a flow channel of the damper arrangement is detected with the aid of a flow meter 16. The output signal of the flow meter 16 is supplied to a zero crossing detector 18. which supplies an output signal when the flow rate becomes zero or - in more general terms - falls below a preselected limit value. The output signal of the zero crossing detector 18 is supplied to one input of a logic circuit 20 illustrated as an AND circuit.

The chassis control system 10 further comprises devices for changing over the damping characteristic of the chassis or of a damper of the chassis. Said devices include a changeover signal generator 22, by means of whose output signals according to prior art a changeover of the controllable valve device 14 of the damper arrangement 12 is frequently directly effected. According to the invention, however, the output of the changeover signal generator 22 is connected to a second input of the AND circuit 20 so that, upon the occurrence of a changeover signal of the changeover signal generator 22, a changeover of the controllable valve device 14 is effected only when the existence of the flow rate zero is signalled by the output of the zero crossing detector 18 simultaneously at the other input of the AND gate 20. The zero crossing detector 18 connected to the flow meter 16 therefore, in the event of a zero crossing of the flow rate, supplies a changeover enabling signal by means of which the AND condition is met at the input of the AND circuit 20, with the result that a changeover signal from the output of the changeover signal generator 22 may effect a changeover of the controllable valve device only when a pressure equalization has been effected via the monitored flow channel so that the changeover of the controllable valve device 14 may be carried out without changeover noises and with the minimum wear of the

C; valve device 14 and the other parts of the damper arrangement 12.

For practical implementation of the method according to the invention it is possible to use extensively conventional and commercially available electric circuits, flow meters and valve devices of the kind which - with the exception of the flow meter - are used, for example, in the known systems initially discussed. Also commercially available are numerous suitable flow measuring devices, whose different styles of construction are at least partially directly suitable for measuring the velocity of the fluid flow in the flow channel of a damper arrangement.

For implementing the method according to the invention, however, a damper arrangement is preferred, in which the elements of the flow meter are integrated in a simple, inexpensive and reliable manner into the damper arrangement.

In particular, the damper arrangement 12 according to Fig.2 of the drawings comprises a conventional shock absorber having a cylindrical housing or an outer tube 24 and a movable piston 26, which is slidingly displaceable therein and is locked in an axial direction by means of a nut 30 on a piston rod 28 in the region of a free end 28a thereof. which has a reduced external diameter. The piston 26 has two piston bores 32. the inner wall of each of which is coated with an insulating layer 34 which extends adjacent to the piston bores 32 and also over the end faces of the piston 26. In the region of each piston bore 32. the insulating layer 34 of electrically nonconductive material surrounds a tube 36 made of electrically conductive material such as, for example, copper. Each tube 36 defines in the piston 26 a through flow channel 37. which as a throttle bore connects a top working chamber 38 and a bottom working chamber 40 of the shock absorber to one another and, upon a movement of the piston 26 relative to the outer tube 24. has a throughflow in one or the other direction of 6 p P the damper fluid. in particular a damper oil. situated in the shock absorber. Each tube 36 terminates at the end faces of the piston 26 flush with the outside of the insulating layer 34 provided there or possibly juts slightly outwards beyond the adjacent regions of the insulating layer 34.

In the preferred embodiment according to Fig.2 being considered, there is provided on each of the end faces of the piston 26 a leaf spring 42 or 44, which is insulated from the piston material by the insulating layer 34. The top leaf spring 42 has a recess 42a in the region of the one - in Fig. 21 the left - flow channel 32, while th e bottom leaf spring 44 has a corresponding recess 44a in the region of the other flow channel. The leaf springs 42, 44 are so constructed and arranged that in their state of rest, namely when the flow rate of the damper fluid in the respective associated flow channel 37 is zero or approximately zero, they are in electrically conductive contact with the respective adjacent tube end. When however, as a result of a movement of the piston 26 relative to the outer tube 24, there is a flow of the damper fluid through the throttle channel or the tube 36 from the working chamber 38 into the working chamber 40 or vice versa, the radially outer end of the leaf spring 42 or 44 situated at the outlet end of the tube 36 is lifted off the associated end of the tube 36, thereby interrupting the electrically conductive connection between the tube 36 and the relevant leaf spring 42 or 44.

Since the two leaf springs 42. 44 in the embodiment are electrically conductively connected in series to one another by the conductive tube 36, then in the event of a flow of the damper fluid through the tube 36 the electrically conductive connection existing in the state of rest between two connection leads 46, 48, which in a conventional manner are led through a bore 28b of the piston rod 28 and connected to the radially inner ends of the leaf springs 42 and 44 respectively, is interrupted. An interruption of the 7 electrically conductive connection between the connection leads 46. 48 therefore signals the lifting of one or the.other leaf spring 42 or 44 off the associated end of the electrically conductive tube 36 and hence a flow rate differing from zero of the damper fluid in the relevant throttle or flow channel 37 defined by the tube 36. Conversely. the existence of an electrically conductive connection between the connection leads 46. 48 indicates that the two leaf springs 42, 44 are each conductively resting against the associated tube end, which means that the rate of flow of the damper fluid through the tube 36 is zero or, in the case of a specific preloading of the leaf springs 42. 44 towards the associated tube ends. has reached a preselected lower threshold value.

From the above description of the embodiment according to Fig.2 it is clear that with the aid of the described, simple leaf spring arrangement on the piston 26 of the shock absorber an indication is given not only as to whether there is a flow of the damper fluid through one of the flow channels 37 but also, at the same time, as to whether there is a zero crossing of the flow rate, so that the spring leaf arrangement shown in Fig.2 simultaneously forms the flow meter 16 and the zero crossing detector 18-of the chassis control system 10 according to Fig.1, in which case the "current" or "no current" signal which may be picked up at the connection leads 46, 48 may be supplied directly to the one input of the AND circuit 20, whose second input is connected to the output of the changeover signal generator 22. A prerequisite for operationof the damper arrangement according to Fig.2 in the manner described above is that the piston rod 28 is made of a non-conductive material or, as indicated in the drawing, is insulated from the leaf springs 42, 44 by insulating layers 341 and that the damper fluid used is non-conductive.

As Figs.3a and 3b reveal, in the case of the embodiment according to Fig. 2, given a time characteristic of the piston 8 Q V, speed v according to Fig.3a, short gate pulses T are produced approximately in the region of the top and bottom dead cpntre of the piston movement, as is illustrated in Fig.3b which shows the time characteristic of the current i in the circuit containing the leaf springs 42, 44. In the method according to the invention, the gate pulses T serve as changeover enabling signals and ensure - cf. the AND circuit in the arrangement according to Fig.1 - that changeover signals for an adjustment of the damper characteristic may only become effective when the damper is being acted upon by low damping forces which, ideally, are verging on zero, with the appropriate changeover points according to the invention being determined by special monitoring of the flow of the damper fluid in at least one flow channel.

From Fig.3b it is further apparent that, when using a damper arrangement according to Fig-2, irrespective of the direction in which a zero crossing of the piston speed v is passed through, the gate pulse T obtained is always positive so that with the damper arrangement according to Fig.2 it is not possible, when enabling a changeover process, to take into account whether the piston is at that moment situated in the region of its top dead centre or in the region of its bottom dead centre.

According to Fig.4 of the drawings. in a further refinement of the invention a damper arrangement is therefore proposed, which allows differing or distinguishable changeover enabling signals to be produced on attainment of the top dead centre of the piston and on attainment of the bottom dead centre of the piston, this being described in greater detail below with reference to the diagrammatic view of the time characteristic of the current in the damper arrangement according to Fig. 4 in conjunction with Fig.5 of the drawings.

In particular. the damper arrangement according to Fig.4 has only a single leaf spring 42 cooperating with one flow channel 9 37,, with the flow channel 37, as in the embodiment according to Fig.2, again being formed by an electrically conductive tube which is insulated from the piston 26. The piston 26 is moreover additionally provided with at least one further throttle opening or a channel 50 connecting the two working chambers 38, 40. The effect thereby achieved is that, upon an upward movement of the piston 26, a connection is maintained for the damper fluid between the top working chamber 38 and the bottom working chamber 40 when the leaf spring 42 closes the flow channel 37.

As the diagrams according to Figs.5a and 5b reveal, the leaf spring 42 is lifted by the flow of damper fluid in the flow channel 37 during the downward movement of the piston 26 off the conductive tube 36, thereby interrupting the circuit between the connection leads 46. 48 which. in the embodiment according to Fig.4. contains the leaf spring 42 and the conductive tube 36. When the fluid flow through the flow channel 37 then, approximately in the region of the bottom dead centre of the piston, becomes zero or reaches a lower limit value determined by the geometry of the arrangement and the elasticity of the leaf spring 42, the abovementioned circuit is then closed, with the current 1 in the region of a positive edge of the signal according to Fig.5b jumping from zero to a preselected value i,. The circuit between the connection leads 46. 48 remains closed during a subsequent upward movement of the piston 26,, since the leaf spring 42 is pressed by the increased pressure in the top working chamber 38 firmly against the top end of the tube 36. However. when the piston 26 then resumes a downward movement, the leaf spring 42 is lifted by the fluid flow in the flow channel 37 off the tube 36 and the circuit is interrupted, with the current in the region of a negative edge of the signal according to Fig.5b jumping from the preselected value i, to the value zero. In the embodiment according to Fig.4, it is therefore possible to distinguish between the attainment of the bottom dead centre of the piston movement and the n r attainment of the top dead centre of the piston movement since the current characteristic presents, in the first case, a positive edge or a jump from zero to i. and, in the second case, a negative edge, i.e. a jump from i. to zero. Said direction of current change in the monitored circuit may be easily determined by means of a suitable known circuit arrangement and may be utilized in such a way that certain changeover processes are permitted only upon attainment of the top dead centre and other changeover processes are permitted only upon attainment of the bottom dead centre. It goes without saying that the circuit outlined in Fig.1 has to be correspondingly extended in order to distinguish between said two possibilities.

Whereas in the above description, particularly in connection with the embodiment according to Fig.4, it was assumed that the leaf spring completely closes the flow channel 37 upon an upward movement of the piston 26, in a refinement of the invention it is further possible to make the leaf spring 42 so thin and narrow that it has only a minor influence upon the free cross-section of the flow channel 37 depending on whether it is deflected or rests against the tube 36. In such a case, it is of course then possible to dispense with a separate flow channel 50. Given a corresponding construction of the two leaf springs 42, 44 in-the embodiment according to Fig.2,, it is then further possible to dispose the two leaf springs at opposite ends of the same flow channel 37. On the other hand, it should be ensured in all embodiments that the forces effective in a peripheral direction of the piston 26 are distributed as uniformly as possible so that, bearing this in mind, even when using narrow leaf springs it may be advantageous and advisable to distribute a plurality of flow channels symmetrically along the periphery of the piston and to do so irrespective of whether leaf springs are provided at one or both ends of the flow channels in question, since by said means it is possible to counteract a tendency of the piston 26 to tilt.

11 Q

Claims

Claims

Method of adjusting the damper characteristic of a damper, in particular a shock absorber forming part of a chassis system, having two damper parts which are movable relative to one another and having at least one flow channel through which, at least upon a relative movement of the damper parts effected in a preselected direction, a flow of a damper fluid occurs, wherein upon occurrence of a changeover signal an adjustment of the damper characteristic is effected in dependence upon a changeover enabling signal signalling the presence of low damping forces, characterized in that the flow of damper fluid through the flow channel is detected and a changeover enabling signal is produced whenever the flow rate reaches a preselected lower limit value.
Method according to claim 1, characterized in that depending on the direction of the relative movement of the damper parts a respective one of two distinguishable changeover enabling signals is produced.
3. Damper arrangement for effecting the method according to claim 1 or 2, having a damper, which comprises two damper parts which are movable relative to one another, operates with a damper fluid and has a flow channel through which a fluid flow occurs upon a relative movement of the damper parts, characterized in that associated with the flow channel (37) is a flow meaduring device (16, 18), by means of which a changeover enabling signal may be 12 produced when the flow rate falls below the preselected limit value.
4. Damper arrangement according to claim 3, characterized in that the flow measuring device (16, 18) comprises at least one leaf spring (42, 44) made of electrically conductive material which is clamped at one end, may be acted upon and deflected in the region of the flow channel (37) by the fluid flow and is part of a control circuit (46, 42, 36, 44, 48) for producing changeover enabling signals which is operable by deflection of the leaf spring out of its position of rest.
Damper arrangement according to claim 4, having a passive shock absorber. which operates with a damper fluid and has a piston provided with two through throttle openings each forming a flow channel, characterized in that associated with one end of one flow channel (37) at one end face of the piston (26) is a first leaf spring (42) which may be deflected by a flow of the damper fluid, that associated with the opposite opening of the other flow channel (37) at the other end of the piston (26) is a second leaf spring (44) and that the two leaf springs (42, 44) are electrically connected in series via electrically conductive walls (36) of their associated flow channels (37) between connection leads (46, 48) of the control circuit.
6. Damper arrangement according to claim 4, having a passive shock absorber, which operates with a damper fluid and has a piston provided with a through throttle opening forming the flow channel, characterized in that disposed at either end of the flow channel (37) is a leaf spring (42r 44) which may be deflected by a flow of the damper fluid and that the leaf springs (42. 44) may be electrically conductively connected to one another by an 13 electrically conductive wall (36) of the flow channel (37).
Damper arrangement according to claim 5 or 6. characterized in that the conductive wall of each flow channel (37) is formed by a conductive tube (36) which 1 inserted into a piston bore and is insulated from the piston (26).
8. Either of the damper arrangements substantially as herein described with reference to the accompanying drawings.

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