Patent Application
20140060981
The present disclosure relates to a braking system for a vehicle.
A known vehicle braking system includes an operating element which controls a wheel braking unit. The wheel braking unit includes an actuator, a friction unit, and resilient member. The friction unit has an air clearance which must be overcome before it produces friction which brakes the wheel.
EP 2 146 109 A1 shows a disk braking system with a brake valve and a hydraulic retractor system, so as to maximize the air clearance in a normal operation mode and to make a manual braking effective in a safety mode. The retractor system includes a brake piston, a brake spring, and a retractor plunger. The retractor plunger is rigidly connected to the brake piston.
It is desired to have a braking system safety mode with a reduced air clearance, since the brake valve which controls the wheel braking system has available a reduced volume capacity in the safety mode. Thus, a better response behavior of the brake can be attained in the safety mode.
According to an aspect of the present disclosure, a braking system is provided with an improved control of the wheel braking system in the operation modes.
The vehicle braking system includes a wheel braking unit with an actuator, friction unit, and resilient member. An operating element controls the wheel braking unit, and the braking system is operated by a control parameter in a normal operation mode. When the control parameter falls short of a threshold value, the system operates in a safety mode. In the normal operation mode, the control parameter acts on the actuator so that the actuator establishes a first air clearance in the friction. In the safety mode, a resilient member establishes a second air clearance in the friction unit, which is smaller than the first air clearance, and wherein the control parameter can be overridden by a compensating element.
A friction unit may be, for example, a wheel shaft-rotating brake disk and a brake pad, fixed relative to a housing, which acts against the brake disk to bring about a friction contact. Alternatively, the friction unit may be a wheel shaft-rotating friction disk with friction pads and at least one contact element, which is fixed relative to the housing and acts against the friction disk. The contact element can be shaped as a round stop disk arranged concentrically, relative to the wheel shaft. Several resilient member are preferably arranged over the circumference, for example, three or four. The braking system can also be constructed as a drum brake, a shoe brake, or a cone brake.
An air clearance is an axial or radial gap, that is, axial or radial relative to the rotating axis of the braking system, between the elements of the friction unit, that is, between the brake disk and the brake pad or the friction disk and the contact element. The actuator exerts an adjustment effect on the friction unit to create an air clearance. A contrary effect, such as a restoring effect, is exerted by the resilient member on the friction unit.
With the braking system in the normal operation mode, a control of the wheel braking system or an action on the friction unit in the direction of a friction contact can be carried out, without the adjusting effect or the restoring effect of the actuator having to be overcome—that is, without this adjusting force having to be additionally applied. Rather, it is ensured that the control parameter, which triggers the restoring force, is overridden. This restoring force is the product of the pressure and piston areas with a hydraulic actuator, if the actuator is designed as a cylinder-piston unit, and with pressures of up to over 200 bar, can be significant with an agricultural utility vehicle. Furthermore, with the braking system in accordance with the invention, the advantage is to be found in the fact that with a reduced volume capacity of the operating elements in the safety mode as a result of the reduced air clearance, a safe braking can nevertheless take place with a rapid response.
Preferably, the compensating element for overriding the control parameter comprises spring elements. It is hereby advantageous if this arrangement is simply constructed and standard parts can be used.
In a first embodiment, the actuator can be connected via the spring elements to the friction unit to yield to tension and/or to pressure. In a second embodiment, the actuator can be connected via the spring elements to a housing of the wheel braking system to yield to tension and/or to pressure. The housing can be, for example, a brake caliper. With both designs, the simple structure with springs as standard parts is advantageous.
In another embodiment, the spring element can comprise a hydraulic storage unit. In this design, it is advantageous in that it makes minor demands on the need for space in the area of the brake, since the storage unit can be placed outside the housing of the wheel braking system.
The control parameter is preferably hydraulic oil pressure produced by an oil pump. Advantageously, oil pressure is available for the normal operation mode, independently of an operation of the braking system.
In another preferred design, a pressure storage unit, in which the hydraulic oil pressure can be stored, is provided. In this way, a pressure supply, independent of an oil pressure source, is advantageously guaranteed over a specific period of time. Alternatively, instead of hydraulics, pneumatics can also be provided.
In another preferred design, the operating elements comprise a hydraulic brake valve. In particular, it is preferred to have a check valve between the oil pump and the operating element, or between the oil pump and the hydraulic brake valve in a supply line.
In a first embodiment, the pressure storage device is located between the check valve and the brake valve, and the pressure storage unit is connected in series in a hydraulic connection line between the check valve and the brake valve.
Preferably, in the first embodiment, the control parameter for the actuator is measured or sensed between the pressure storage unit and the hydraulic brake valve. In the first embodiment, it is advantageous that after a failure of the oil pump, hydraulic pressure in the hydraulic line to the actuator continues to be present.
In a second embodiment, the pressure storage unit branches off between the check valve and the hydraulic braking valve. The pressure is sensed between the check valve and the oil pump. In the second embodiment, it is advantageous that after a failure of the oil pump, the actuator is no longer supplied with the hydraulic pressure via the hydraulic line, so that after the readings fall short of the threshold values of the control parameter, the braking system is in the safety mode, whereas the pressure storage unit still provides, as in the normal operation mode, for a certain number of brakings with oil pressure, which can be designated as an overlapping.
Preferably, the actuator is a hydraulic cylinder-piston unit. The actuator is connected to the operating element by a hydraulic line.
For all embodiments, it is preferable that branch line connects the hydraulic line to a hydraulic reservoir for relieving the hydraulic pressure during the change from the normal operation mode to the safety mode. This ensures that with a failure of the pressure supply, for example, by the oil pump, the hydraulic pressure in the hydraulic line is reduced, so that the braking system is in the safety mode. Furthermore, it is preferred that at least one throttle valve be located in the hydraulic line, wherein in particular, it is preferable that at least one throttle valve be located before the branch to the hydraulic reservoir and one throttle valve, after the branch to the hydraulic reservoir. This advantageously guarantees that an oil flow into the hydraulic reservoir is limited to a defined value. Furthermore, one can adjust the pressure decline over time with a lack of or failure of the pressure supply, by coordination with the throttle valve. In another preferred embodiment, two resistance-equivalent throttle valves or orifices connected in series can be provided. In this way, a clogging of the throttle valve after the branch can be avoided.
Preferably, the wheel braking unit has a second actuator—in particular, a cylinder-piston unit—which places the friction unit into a friction contact or frictional locking in the normal operation mode, and in the safety mode, after exerting control through the operating elements. The second actuator is preferably controlled by the control parameter.
For all embodiments, it is also preferable if the brake valve, the check valve, and the control parameter sensor for the actuator are designed so they can be integrated in the structure, preferably within a housing. The sensing of the pressure storage unit is also preferably integrated. This guarantees that the risk of a line buckling is reduced and different supply or signal statuses can be present for the brake valve and the first actuator and the second actuator.
a is a schematic diagram of the brake system of
b is a schematic diagram of the brake system of
Referring to
A branch line 34 connects the first hydraulic line 32 to a hydraulic oil reservoir 36. A first throttle valve 38 and a second throttle valve 40 are arranged parallel to one another, upstream from this branch 34. A third throttle valve 58 is located downstream from the branch line 34. The function of this arrangement is described further below.
The wheel braking unit 12 includes a first actuator 14 in the form of a first cylinder-piston unit, a second actuator 44 in the form of a second cylinder-piston unit, and a friction unit 16, which includes a friction disk 48 with friction linings and a stop disk 50. The friction disk 48 rotates around a rotation axis A and the stop disk 50 and the actuators 14, 44 are mounted so they cannot rotate. The stop disk 50 can move axially with respect to the axis A. Alternatively, the friction unit 16 may include a brake disk and a brake pad.
Furthermore, a resilient member 18 is provided in the form of a coiled helical compression spring, wherein in principle, other spring types may also be appropriate. The resilient member 18 is supported on one side (not shown) on a housing 66 of the wheel braking unit 12. The housing 66 may be an annular housing in a typical design, or alternatively, a brake caliper. On the other side, the resilient member 18 is coupled to the stop disk 50. The resilient member 18 is positioned between the housing 66 and the stop disk 50 and is biased to urge the stop disk 50 towards the friction disk 48. In this way, at least one placement of the stop disk 50 against the friction disk 48 is attained.
Furthermore, a compensating element 22, in the form of a compression spring, is located between the first actuator 14 and the stop disk 50. In this way, the first actuator 14 and the stop disk 50 are connected to one another, so they can move relative to one another or yield to tension. The function of the relative movement between the first actuator 14 and the stop disk 50 is described further below.
During a normal operational mode of the braking system 10, a combustion engine (not shown) of an agricultural utility vehicle drives the pump 26 which produces a hydraulic pressure in the braking system 10, which is stored in the pressure storage unit 24. With regard to the normal operation mode, a distinction between a braked status and an un-braked status must be made.
When an operator actuates the operating elements 20 via the brake pedal 42, the braked status of the normal operation mode is introduced. By actuating the brake pedal 42, the brake valve 30 is opened by a corresponding amount, so that a volume of pressurized hydraulic oil is communicated to the second actuator 44, through the second hydraulic line 46. In this way, the stop plate 50 is moved towards the friction disk 48 by the second actuator 44 in the normal operation mode, and friction contact occurs in the friction unit 16. Before the actuation, an air clearance or space separates the stop plate 50 from the friction plate 48, which must be overcome before the stop disk 50 engages the friction plate 48. The air clearance can be between 0.5 mm and 1.5 mm in the un-braked status of the normal operation mode, and is preferably approximately 1 mm.
In the embodiment of the first actuator 14 of
a and 2b show alternative embodiments of the first actuator 14. With the alternative of
With the three described embodiments of the first actuator, the compensating elements 22, 64, and 68 are respectively used to override an actuation of the brake by the second actuator 44. The function of the compensating elements 22, 64, 68 is decisive for the transition from the un-braked status to the braked status of the normal operation mode. As described above, the second actuator 44 moves the stop disk 50 against the friction disk 48 or towards the friction disk 48 upon actuation of the brake pedal 42. The individual compensating element 22, 64, 68 makes possible hereby a relative movement between the stop disk 50 and the first actuator 14, which, as described above, moves the stop disk 50 from the friction disk 48 because of the hydraulic pressure for the adjustment of the air clearance. In the braked status of the normal operation mode, therefore, the second actuator 44 and the parallel spring force of the resilient member 18 overcome the spring force of the individual compensating element 22, 64, 68, so that it is deflected, and the first actuator 14, in fact, experiences no or almost no movement. Since in this status the control parameter also acts on the first actuator 14, the control parameter is overridden by the individual compensating element 22, 64, 68.
The transition from the normal operation mode to the safety mode takes place if hydraulic oil pressure is no longer available or there is insufficient hydraulic oil pressure. This can be the case, for example, if the oil pump 26 has broken down or there is a leakage or a buckling or a compression of a hydraulic line. In such a case, the hydraulic pressure in the hydraulic line 32 is reduced to such an extent that oil flows into the hydraulic oil reservoir 36, via the branch 34, through the throttle valve 24. If the hydraulic pressure in the first actuator 14 falls short by a certain extent, so that the force of the actuation on the stop disk 50 falls short of the restoring force of the resilient member 18 on the stop disk 50, the stop disk 50 is acted on by the resilient member 18 against the friction disk 48, so that the air clearance is at least almost eliminated. Provision can also be made so that after the elimination of the air clearance, a certain braking effect is already attained. In this state, the braking system 10 is in the safety mode, in which in a known manner, the operator can produce a hydraulic pressure in the hydraulic line 46—with reduced volume capacity of the brake valve 30, by means of the brake pedal 42 and via the brake valve 30, in order to move the stop disk 50 against the friction disk 48 via the second actuator 44, and to produce a friction locking. Thus, when operating the braking system 10 in the safety mode, an air clearance, or at least only a minimal air clearance, need not be overcome, before a frictional engagement between the stop disk 50 and the friction disk 48, is developed.
The difference between the embodiment of
In the embodiment of
In the second embodiment of
The pedal feeling of the second embodiment is determined in that as a result of the failure of the pressure supply, the braking system 10 has fallen into the safety mode, that is, the first actuator 14 does not maintain an air clearance; the second actuator 44, however, is supplied with oil pressure from the pressure storage unit 24 for a certain number of brakings via an actuation of the brake valve 30 by means of the brake pedal 42. Thus, with a normal braking by means of the still existing oil pressure from the pressure storage unit 24, an air clearance need not be first overcome before the friction unit 16 is brought into a friction locking.
While the disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description is to be considered as exemplary and not restrictive in character, it being understood that illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected. It will be noted that alternative embodiments of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations that incorporate one or more of the features of the present disclosure and fall within the spirit and scope of the present invention as defined by the appended claims.
