VTP – Continuously Variable Transmission

Configuration Buzzword: variable twin planet (VTP).

 

General


Striving for the ideal

The motivation. In our search for the ideal configuration of mechanical components and variators, VDS has developed the modular transmission system VTP.

The principle. The VTP transmission system works with a hydrostatic-mechanical power split: in the pure hydrostatic power range and (depending on design) with up to three overlap ranges.

The core element is a dual planetary set at the output of the transmission. The reverse planetary set is active only at low speeds in pure hydrostatic operation; the overlap of mechanically and hydrostatically transferred power occurs in the second planetary set.

The benefits. The arrangement and translation ratios, even with small hydrostatic units, deliver high tow bar pull and large gear ratio spread with low mechanical effort.


VTP transmission schema H1F

VTP transmission schema 1RH1F

VTP transmission schema 1RH2F




Niche segments

Diversity even for small orders.
Due to modular structure, availability in different sizes, and combinations with different variators, VTP transmissions can also be provided for small lot sizes at reasonable cost.

We offer a lot for small lot sizes.



Figure: VTP modular setup

Applications

Go the safe route, ensure functionality. Buzzword: practice.


Award-winning

AEBI. As the first vehicle with a VTP transmission, the highland off-road transporter AEBI VT450 Vario was presented in 2012 by AEBI Schmidt Group at the Agrama Expo in Bern, Switzerland. The functionality of the innovative VTP drive system was proven even in critical driving situations.
The AEBI transporter earned the title “Tractor of the Year 2014” in the category special tractors.

Revealed off-road

Test off-road. VDS equipped its Land Rover Defender on a trial basis with the VTP450 continuously variable  transmission. Their off-road project demonstrated utmost functionality, mobility and safety in challenging driving situations.
This was a revelation for the test drivers: “I was impressed by the easy operation under extreme off-road conditions. Take your foot off the gas and the vehicle stops, whether uphill or downhill. Simultaneous clutch operation, braking and shifting are history.”


Full power

Landini/McCormick. At the EIMA 2014 expo in Bologna the tractor Power Mondial by Landini/McCormick was presented with a VTP transmission.

Application domains


Defender

Municipal vehicle

Agric tractor

Municipal vehicle - (direct mount)

Municipal vehicle (remote mount)

Agric tractor

Telehandler





Technical description

Infinitely variable introduction. Infinitely variable driving pleasure.


VTP in all variants.

Models. As hydrostatic variators, you can use compact units integrated in the housing in back-to-back configuration or separate hydropumps and hydromotors in a closed circuit. In all cases, the design involves hydropumps in a swash plate version in combination with constant or variable motors in swash plate or in bent-axis versions.

Notes. To achieve better transmission functionality and shifting quality, requirements must be met in terms of control characteristics, response behavior, etc. Compact units are on the market with displacement of 28 to 175 cc. Depending on their application and their resulting profiles, difference profiles of up to 480 bar are permissible.
For the use of hydropumps and hydromotors in modular composition, a broad range of standard hydrostatic units is available for various applications.

Functional description. At low speed or output speed, power transfer occurs via the variator only. Via the connection between ring gear H2 (Figure beside) with the housing in planetary set 2, power flows from the hydromotor via sun gear S2 and the planet carrier to the drive wheels. The transmission components in the mechanical power train have no load in this operating mode. Their rotational speed on the output side is defined by the kinematic coupling in planetary set 1 and on the input side by the coupling to the transmission input shaft. Planetary set 2 has high translation ration selected to achieve high tow bar pull for small hydrostatic units.

 
Shifting without a loss of pull. The rotational motion of sun gears S1 and S2 and of the planet carrier forces a rotational speed onto ring gear H1 which, with sufficient rotational speed at the sun gears, leads to synchronous rotational speed at clutch K1 on forward or at clutch KR on reverse.
When synchronous rotational speed is achieved, there is a shift from pure hydrostatic drive to the bordering power split range without interruption of the pull. Shifting occurs via overlapping closing of the corresponding clutch and subsequent opening of the ring gear brake. The clutches and brakes are multiple-disc models. It is also possible to use claw clutches, but this requires special control characteristics in the variator.

Power branch 1. After a shift, the mechanical drive power is transferred via ring gear H1, which is coupled to the transmission input shaft and rotates at constant speed. Continuous change of the rotational speed in the hydrostatic branch steplessly adapts the transmission translation ration. Immediately after a shift, in the power-split range. the sun gear rotates in planetary set 1 against the rotational direction of the ring gear and thus reduces the rotational speed of the planetary carrier. In this operational range the transmission works with reactive power, which means that the hydromotor works as a pump and via the hydrostatic circuit returns to the mechanical path. Changes in the tilt angle of the hydropump adapts the rotational speed of the hydromotor from maximum rotational speed against the rotational direction of the ring gear via tilt angle zero to maximum rotational speed in the same direction as ring gear H1. On tilt angle zero the transmission works at maximum efficiency because the complete drive power is transferred purely mechanically. The hydromotor delivers only the power dissipation to support the torque at sun gear S1.
Further adjustment of the swash plate increases the rotational speed of sun gear S1 in the same direction as ring gear H1 until maximum vehicle speed is reached in the first power-split range.

Power branch 2. Shifting from the first to the second power-split range occurs via load switching with compensation for the increment by the variator unit. Via overlapping shifting of clutches K1 and K2, this special shifting function forces upon ring gear H1 a continuous rotational speed increase, and during acceleration of the ring gear the overall translation ratio is kept constant by adapting the rotational speed of the sun gear or is adapted to the respective driving conditions. After shifting, the transmission translation ratio in the second overlap range is nearly the same as the translation ratio before shifting in the first overlap range. This procedure enables stepless shifting of the transmission translation ratio in two overlap ranges with high overall spread.
Die translation ratio in planetary set 1 is set significantly less than in planetary set 2. On the one hand, this achieves high transmission gear ratio spread in the power-split ranges; on the other hand, this keeps the pressure level in the hydrostatic circuit in ranges where the hydropump and the hydromotor work at good efficiency.

Rotational speed and efficiency. Figure (Rotational speed graph) shows the rotational speed relationship in a VTP transmission with an overlap range for reverse, a pure hydrostatic range for low vehicle speed, and two overlap ranges for forward. Figure (Transmission efficiency) shows the efficiency behavior in relation to vehicle speed at constant input rotational speed. The characteristic camel back is noticeable in the middle of the overlap ranges, where the complete drive power is transferred purely mechanically and the transmission has the best efficiency.

Rotational speed graph

transmission efficiency




Sizes. The VTP transmission system comes in two sizes. In all sizes the mechanical, hydraulic and electronic components required for achieving stepless transmission shifting are integrated in a basic module. Upstream and downstream input and drive modules enable adaptation of the intended variators and drive stages.

Transmission design. The specified figures reflect the nominal input torque in Nm.



VTP450 Module

   
Rated input speed 3600 rpm
Maximum input torque 450 Nm
Maximum output torque 1700 Nm
Rated input power 110 kW
T/M Ratios      H2F
                     1RH1F
-3,17 to 0,47
-1,75 to 1,79
Hydropump A4VG28, A4VG45, A4VG65 
Hydromotor A2FM28, A2FM45, A6VM55 
Engine Flange tbd 


VTP1750 - Technical Data

Transmission
configuration
H2F SI
hydrostatic drive,
2 powersplit gears
forward
1RH1F SI
1 powersplit gear rev.,
hydrostatic drive,
1 powersplit gear fwd
Rated input speed 2000 to 2300 rpm
Maximum input torque 1750 Nm / 1300 ft-lbs
Maximum output torque 8800 Nm / 6500 ft-lbs
Rated input power 300kW (408 HP)
Transmission Ratios -3,95 rev to
0,787 fwd
-1,42 rev to
1,42 fwd
Hydropump / Hydromotor A4VG110 / A6VM115
Engine Flange SAE 1
Option: PTOs 1 and 2 i = 0,694 / 950 Nm (700ft-lbs) / 300 kW


Figure: Twin planetary set

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